appliion area of mobile impact crushers

mobile crushers - metso outotec

Mobile crushers are often referred to as mobile crushing plants. They are track-mounted crushing machines which, thanks to their mobility, can maximise productivity and reduce operating costs while increasing safety and reducing environmental impact.

The concept of mobile and semi-mobile crushers has been around for a long time, but for years many machines were very heavy and moving them required thoughtful planning. As result, the crushers that were supposed to be mobile were seldom relocated and tended stay put in permanent facilities.

Nowadays, the weight of mobile crushers has decreased considerably, and crushing as well as mobility properties improved notably. Mobility is not substitute for effective crushing anymore, and tracked mobile crushers meet the same basic criteria as stationary plants.

Mobile cone crushers are traditionally used as secondary, tertiary, and quaternary crushers. However, if the grain size of the processed material is small enough by nature, then they can also operate at the first stage of the crushing process.

Mobile HSI crushers have a horizontal impact crushing unit and they are used as primary, secondary, or tertiary crushers. Mobile VSI crushers, in turn, are equipped with vertical shaft impact crushing unit, and they are extremely efficient in the last stage of the crushing process, producing precisely shaped cubical end products.

Metso Outotecs mobile crushing equipment consists of two different product families, Lokotrack mobile crushers and Nordtrack mobile crushers. Both families can be utilized in aggregates production in quarries and construction sites, recycling applications, as well as in mining operations.

Nordtrack, on the other hand, is ideal if you work in short-term contracting jobs or are just starting your own operations. The family consists of two mobile jaw crusher models and one mobile impact crusher.

p&q university lesson 7- crushing & secondary breaking : pit & quarry

In the quarry, crushing is handled in four potential stages: primary, secondary, tertiary and quaternary. The reduction of aggregate is spread over these stages to better control the product size and quality, while minimizing waste.

The primary stage was once viewed merely as a means to further reduce stone following the blast or excavation prior to secondary crushing. Today, primary crushing is viewed as more important within the balance of production and proper sizing needs. The size and type of the primary crusher should be coordinated with the type of stone, drilling and blasting patterns, and the size of the loading machine. Most operations will use a gyratory, jaw or impact crusher for primary crushing.

In the secondary and subsequent stages, the stone is further reduced and refined for proper size and shape, mostly based on specifications to produce concrete and asphalt. Between stages, screens with two or three decks separate the material that already is the proper size. Most secondary crushers are cone crushers or horizontal-shaft impact crushers. Tertiary and quaternary crushers are usually cone crushers, although some applications can call for vertical-shaft impact crushers in these stages.

A gyratory crusher uses a mantle that gyrates, or rotates, within a concave bowl. As the mantle makes contact with the bowl during gyration, it creates compressive force, which fractures the rock. The gyratory crusher is mainly used in rock that is abrasive and/or has high compressive strength. Gyratory crushers often are built into a cavity in the ground to aid in the loading process, as large haul trucks can access the hopper directly.

Jaw crushers are also compression crushers that allow stone into an opening at the top of the crusher, between two jaws. One jaw is stationary while the other is moveable. The gap between the jaws becomes narrower farther down into the crusher. As the moveable jaw pushes against the stone in the chamber, the stone is fractured and reduced, moving down the chamber to the opening at the bottom.

The reduction ratio for a jaw crusher is typically 6-to-1, although it can be as high as 8-to-1. Jaw crushers can process shot rock and gravel. They can work with a range of stone from softer rock, such as limestone, to harder granite or basalt.

As the name implies, the horizontal-shaft impact (HSI) crusher has a shaft that runs horizontally through the crushing chamber, with a rotor that turns hammers or blow bars. It uses the high-speed impacting force of the turning blow bars hitting and throwing the stone to break the rock. It also uses the secondary force of the stone hitting the aprons (liners) in the chamber, as well as stone hitting stone.

With impact crushing, the stone breaks along its natural cleavage lines, resulting in a more cubical product, which is desirable for many of todays specifications. HSI crushers can be primary or secondary crushers. In the primary stage, HSIs are better suited for softer rock, such as limestone, and less abrasive stone. In the secondary stage, the HSI can process more abrasive and harder stone.

Cone crushers are similar to gyratory crushers in that they have a mantle that rotates within a bowl, but the chamber is not as steep. They are compression crushers that generally provide reduction ratios of 6-to-1 to 4-to-1. Cone crushers are used in secondary, tertiary and quaternary stages.

With proper choke-feed, cone-speed and reduction-ratio settings, cone crushers will efficiently produce material that is high quality and cubical in nature. In secondary stages, a standard-head cone is usually specified. A short-head cone is typically used in tertiary and quaternary stages. Cone crushers can crush stone of medium to very hard compressive strength as well as abrasive stone.

The vertical shaft impact crusher (or VSI) has a rotating shaft that runs vertically through the crushing chamber. In a standard configuration, the VSIs shaft is outfitted with wear-resistant shoes that catch and throw the feed stone against anvils that line the outside of the crushing chamber. The force of the impact, from the stone striking the shoes and anvils, fractures it along its natural fault lines.

VSIs also can be configured to use the rotor as a means of throwing the rock against other rock lining the outside of the chamber through centrifugal force. Known as autogenous crushing, the action of stone striking stone fractures the material. In shoe-and-anvil configurations, VSIs are suitable for medium to very hard stone that is not very abrasive. Autogenous VSIs are suitable for stone of any hardness and abrasion factor.

Roll crushers are a compression-type reduction crusher with a long history of success in a broad range of applications. The crushing chamber is formed by massive drums, revolving toward one another. The gap between the drums is adjustable, and the outer surface of the drum is composed of heavy manganese steel castings known as roll shells that are available with either a smooth or corrugated crushing surface.

Double roll crushers offer up to a 3-to-1 reduction ratio in some applications depending on the characteristics of the material. Triple roll crushers offer up to a 6-to-1 reduction. As a compressive crusher, the roll crusher is well suited for extremely hard and abrasive materials. Automatic welders are available to maintain the roll shell surface and minimize labor expense and wear costs.

These are rugged, dependable crushers, but not as productive as cone crushers with respect to volume. However, roll crushers provide very close product distribution and are excellent for chip stone, particularly when avoiding fines.

Hammermills are similar to impact crushers in the upper chamber where the hammer impacts the in-feed of material. The difference is that the rotor of a hammermill carries a number of swing type or pivoting hammers. Hammermills also incorporate a grate circle in the lower chamber of the crusher. Grates are available in a variety of configurations. The product must pass through the grate circle as it exits the machine, insuring controlled product sizing.

Hammermills crush or pulverize materials that have low abrasion. The rotor speed, hammer type and grate configuration can be converted for different applications. They can be used in a variety of applications, including primary and secondary reduction of aggregates, as well as numerous industrial applications.

Virgin or natural stone processing uses a multi-stage crushing and screening process for producing defined aggregate sizes from large lumps of rock. Such classified final fractions are used as aggregates for concrete, asphalt base, binder and surface course layers in road construction, as well as in building construction. The rock is quarried by means of drilling and blasting. There are then two options for processing the bulk material after it has been reduced to feeding size of the crushing plant: mobile or stationary plants.

When stone is processed in mobile primary crushing plants, excavators or wheel loaders feed the rock into the crusher that is set up at the quarry face, gravel pit or in a recycling yard or demolition site. The crushed material is then either sent to the secondary/tertiary processing stage via stacking conveyors or transported by trucks. Some mobile crushers have an independent secondary screen mounted on the unit, effectively replacing a standalone screen.

The higher the compressive strength of rock, the higher also is its quality, which plays an important role particularly in road construction. A materials compressive strength is delineated into hard, medium-hard or soft rock, which also determines the crushing techniques used for processing to obtain the desired particle sizes.

The materials quality is influenced significantly by particle shape. The more cubic-shaped the individual aggregate particles are, the better the resulting particle interlock. Final grains of pronounced cubic shape are achieved by using several crushing stages. A cubicity showing an edge ratio of better than 1-to-3 is typical of high-quality final aggregate.

As the earths natural resources are becoming ever more scarce, recycling is becoming ever more important. In the building industry, recycling and reuse of demolition concrete or reclaimed asphalt pavement help to reduce the requirements for primary raw materials. Mobile impact and jaw plants are uniquely positioned to produce high-quality reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) for reuse in pavements, road bases, fill and foundations.

Use of RAP and RCA is growing dramatically as road agencies accept them more and more in their specs. But because RAP and RCA come from a variety of sources, to be specified for use by most departments of transportation they must be processed or fractionated and characterized into an engineered, value-added product. RCA or RAP are very commonly crushed and screened to usable sizes often by impact crushers and stored in blended stockpiles that can be characterized by lab testing for use in engineered applications.

Impact crushers are increasingly used for crushing recycling material. Impact crushers are capable of producing mineral aggregate mixes in one single crushing stage in a closed-cycle operation, making them particularly cost-effective. Different crusher units can alternatively be combined to process recycling material. A highly efficient method of processing recycling material combines crushing, screening and separation of metals. To produce an end product of even higher quality, the additional steps of washing to remove light materials such as plastics or paper by air classification and via electromagnetic metal separator are incorporated into the recycling process.

Mobile impact crushers with integrated secondary screens or without integrated screen used in conjunction with an independent mobile screen are ideal for producing large volumes of processed, fractionated RAP or RCA on a relatively small footprint in the plant. Mobile impactors are especially suited for RAP because they break up chunks of asphalt pavement or agglomerations of RAP, rather than downsize the aggregate gradation. Compression-type crushers such as jaws and cones can clog due to packing (caking) of RAP when the RAP is warm or wet.

Contaminants such as soil are part of processing demolition concrete. Mobile impact and jaw crushers when possessing integrated, independent prescreens removing dirt and fines before they ever enter the crushing circuit reduce equipment wear, save fuel, and with some customers, create a salable fill byproduct. A lined, heavy-duty vibrating feeder below the crusher can eliminate belt wear from rebar or dowel or tie bar damage. If present beneath the crusher, this deflector plate can keep tramp metal from degrading the conveyor belt. That way, the feeder below the crusher not the belt absorbs impact of rebar dropping through the crusher.

These mobile jaw and impact crushers may feature a diesel and electric-drive option. In this configuration, the crusher is directly diesel-driven, with the conveyor troughs, belts and prescreen electric-driven via power from the diesel generator. This concept not only reduces diesel fuel consumption, but also results in significantly reduced exhaust emissions and noise levels. This permits extremely efficient operation with low fuel consumption, allowing optimal loading of the crusher.

Jaw crushers operate according to the principle of pressure crushing. The raw feed is crushed in the wedge-shaped pit created between the fixed crusher jaw, and the crusher jaw articulated on an eccentric shaft. The feed material is crushed by the elliptic course of movement and transported downwards. This occurs until the material is smaller than the set crushing size.

Jaw crushers can be used in a wide range of applications. In the weight class up to 77 tons (70 metric tons), they can be used for both virgin stone and recycled concrete and asphalt aggregates processing as a classic primary crusher for natural stone with an active double-deck grizzly, or as a recycling crusher with vibrating discharge chute and the crusher outlet and magnetic separator.

Output for mobile jaw crushers ranges from 100 to 1,500 tph depending on the model size and consistency of the feed material. While larger mobile crushers produce more aggregate faster, transport weights and dimensions may limit how easily the crusher can be shipped long distances. Mobile jaw crushers can have either a vibratory feeder with integrated grizzly, or a vibrating feeder with an independent, double-deck, heavy-duty prescreen. Either way, wear in the system is reduced because medium and smaller gradations bypass the crusher, with an increase in end-product quality because a side-discharge conveyor removes fines. A bypass flap may provide easy diversion of the material flow, eliminating the need for a blind deck.

Jaw crusher units with extra-long, articulated crusher jaws prevent coarse material from blocking while moving all mounting elements of the crusher jaw from the wear area. A more even material flow may be affected if the transfer from the prescreen or the feeder trough is designed so material simply tilts into the crushing jaw.

Mobile jaw and impact crushers alike can be controlled by one operator using a handheld remote. The remote also can be used to move or relocate the crusher within a plant. In other words, the crusher can be run by one worker in the cab of an excavator or loader as he feeds material into the crusher. If he sees something deleterious going into the hopper, he can stop the crusher.

Impact crushing is totally different from pressure crushing. In impact crushing, feed material is picked up by a fast moving rotor, greatly accelerated and smashed against an impact plate (impact toggle). From there, it falls back within range of the rotor. The crushed material is broken again and again until it can pass through the gap between the rotor and impact toggle.

A correctly configured mobile jaw or impact crusher will enhance material flow through the plant and optimize productivity. New-design mobile jaw and impact crushers incorporate a highly efficient flow concept, which eliminates all restriction to the flow of the material throughout the entire plant. With this continuous-feed system, each step the material goes through in the plant is wider than the width of the one before it, eliminating choke or wear points.

For example, a grizzly feeder can be wider than the hopper, and the crusher inlet wider than the feeder. The discharge chute under the crusher is 4 inches wider than the inner width of the crusher, and the subsequent discharge belt is another 4 inches wider than the discharge chute. This configuration permits rapid flow of crushed material through the crusher. Also, performance can be significantly increased if the conveying frequencies of the feeder trough and the prescreen are adapted independently to the level of the crusher, permitting a more equal loading of the crushing area. This flow concept keeps a choke feed to the crusher, eliminating stops/starts of the feed system, which improves production, material shape and wear.

Users are focused on cost, the environment, availability, versatility and, above all, the quality of the end product. Simple crushing is a relatively easy process. But crushing material so that the particle size, distribution and cleanliness meet the high standards for concrete and asphalt requires effective primary screening, intelligent control for optimal loading, an adjustable crusher with high drive output, and a screening unit with oversize return feed.

This starts with continuous flow of material to the crusher through a variable-speed control feeder. Having hopper walls that hydraulically fold integrated into the chassis makes for quick erection of hopper sides on mobile units. If available, a fully independent prescreen for either jaw or impact models offers the ability to effectively prescreen material prior to crushing this allows for product to be sized prior to crushing, as opposed to using a conventional vibrating grizzly. This has the added value of increasing production, reducing wear costs and decreasing fuel consumption.

This independent double-deck vibrating screen affects primary screening of fines and contaminated material via a top-deck interchangeable punched sheet or grizzly, bottom-deck wire mesh or rubber blank. Discharged material might be conveyed either to the left or to the right for ease of positioning. The independent double-deck vibrating prescreen improves flow of material to the crusher, reducing blockages and feed surges.

Modern electrical systems will include effective guards against dust and moisture through double-protective housings, vibration isolation and an overpressure system in which higher air pressure in the electrical box keeps dust out. Simple and logical control of all functions via touch panel, simple error diagnostics by text indicator and remote maintenance system all are things to look for. For crushing demolition concrete, look for a high-performance electro- or permanent magnet with maximum discharge capacity, and hydraulic lifting and lowering function by means of radio remote control.

For impact crushers, a fully hydraulic crusher gap setting with automatic zero-point calculation can speed daily set-up. Featured only on certain mobile impact crushers, a fully hydraulic adjustment capability of the crushing gap permits greater plant uptime, while improving quality of end product.

Not only can the crushing gap be completely adjusted via the touch panel electronic control unit, but the zero point can be calculated while the rotor is running. This ability to accurately set the crusher aprons from the control panel with automatic detection of zero-point and target-value setting saves time, and improves the overall efficiency and handling of the crusher. On these mobile impact crushers, the zero point is the distance between the ledges of the rotor and the impact plates of the lower impact toggle, plus a defined safety distance. The desired crushing gap is approached from this zero point.

While the upper impact toggle is adjusted via simple hydraulic cylinders, the lower impact toggle has a hydraulic crushing gap adjustment device, which is secured electronically and mechanically against collision with the rotor. The crushing gap is set via the touch screen and approached hydraulically. Prior to setting of the crushing gap, the zero point is determined automatically.

For automatic zero-point determination with the rotor running, the impact toggle moves slowly onto the rotor ledges until it makes contact, which is detected by a sensor. The impact toggle then retracts to the defined safe distance. During this procedure, a stop ring slides on the piston rod. When the zero point is reached, the locking chamber is locked hydraulically and the stop ring is thus fixed in position. The stop ring now serves as a mechanical detent for the piston rod. During the stop ring check, which is carried out for every crusher restart, the saved zero point is compared to the actual value via the electronic limit switch. If the value deviates, a zero-point determination is carried out once again.

These impact crushers may feature a new inlet geometry that allows even better penetration of the material into the range of the rotor. Also, the wear behavior of the new C-form impact ledges has been improved to such an extent that the edges remain sharper longer, leading to improved material shape.

The machines come equipped with an efficient direct drive that improves performance. A latest-generation diesel engine transmits its power almost loss-free directly to the crushers flywheel, via a fluid coupling and V-belts. This drive concept enables versatility, as the rotor speed can be adjusted in four stages to suit different processing applications.

Secondary impact crushers and cone crushers are used to further process primary-crushed aggregate, and can be operated with or without attached screening units. These crushers can be used as either secondary or tertiary crushers depending on the application. When interlinked to other mobile units such as a primary or screen, complicated technical processing can be achieved.

Mobile cone crushers have been on the market for many years. These machines can be specially designed for secondary and tertiary crushing in hard-stone applications. They are extraordinarily efficient, diverse in application and very economical to use. To meet the diverse requirements in processing technology, mobile cone crushing plants are available in different sizes and configurations. Whether its a solo cone crusher, one used in addition to a triple-deck screen for closed-loop operation, or various-size cone crushers with a double-deck screen and oversize return conveyor, a suitable plant will be available for almost every task.

Mobile cone crushers may be available with or without integrated screen units. With the latter, an extremely efficient triple-deck screen unit may be used, which allows for closed-loop operation and produces three final products. Here the screen areas must be large so material quantities can be screened efficiently and ensure that the cone crusher always has the correct fill level, which is particularly important for the quality of the end product.

Mobile, tracked crushers and screen plants are advancing into output ranges that were recently only possible using stationary plants. Previously, only stationary plants were used for complicated aggregate processing applications. But thanks to the advancements made in machine technology, it is becoming increasingly possible to employ mobile technology for traditional stationary applications.

Mobile crushers are used in quarries, in mining, on jobsites, and in the recycling industry. These plants are mounted on crawler tracks and can process rock and recycling material, producing mineral aggregate and recycled building materials respectively for the construction industry. A major advantage of mobile crushers is their flexibility to move from one location to the next. They are suitable for transport, but can also cover short distances within the boundaries of their operating site, whether in a quarry or on the jobsite. When operating in quarries, they usually follow the quarry face, processing the stone directly on site.

For transport over long distances to a new location or different quarry, mobile crushers are loaded on low trailers. No more than 20 minutes to an hour is needed for setting the plant up for operation. Their flexibility enables the mobile crushers to process even small quantities of material with economic efficiency.

Mobile plants allow the combination of prescreening that prepares the rock for the crushing process and grading, which precisely separates defined aggregate particle sizes into different end products to be integrated with the crushing unit into one single machine. In the first stage, the material is screened using an active prescreen. After prescreening, it is transferred to the crusher, from where it is either stockpiled via a discharge conveyor or forwarded to a final screen or a secondary crushing stage. Depending on the specified end product, particles are then either graded by screening units or transported to additional crushing stages by secondary or tertiary impact crushers or cone crushers. Further downstream screening units are used for grading the final aggregate fractions.

The process of prescreening, crushing and grading is a common operation in mobile materials processing and can be varied in a number of ways. Mobile crushers with up to three crushing stages are increasingly used in modern quarries. Different mobile crushing and screening plants can be combined for managing more complex crushing and screening jobs that would previously have required a stationary crushing and screening plant.

Interlinked mobile plants incorporate crushers and screens that work in conjunction with each other, and are coordinated in terms of performance and function. Mining permits are under time constraints and mobile plants provide faster setup times. They provide better resale value and reusability, as mobile plants can also be used individually. They also reduce operating costs in terms of fewer haul trucks and less personnel.

With a so-equipped mobile crusher, the feed operator can shut the machine down or change the size of the material, all using the remote control, or use it to walk the crusher from one part of the site to the other, or onto a flat bed trailer for relocation to a different quarry or recycling yard. This reduces personnel and hauling costs compared to a stationary plant. With the mobile jaw or impact primary crusher, the only additional personnel needed would be a skid-steer operator to remove scrap steel, and someone to move the stockpiles.

Thanks to better technology, mobile plants can achieve final aggregate fractions, which previously only were possible with stationary plants. Production availability is on par with stationary plants. Theyre applicable in all quarries, but can be used for small deposits if the owner has several quarries or various operation sites. For example, an operator of several stone quarries can use the plants in changing market situations at different excavation sites. In addition, they also can be used as individual machines. A further factor is that mobile plants, in general, require simpler and shorter licensing procedures.

The high cost of labor keeps going up. A stationary crusher might be able to produce multiple times the amount of product, but also would require about seven or eight workers. Aggregate producers can benefit when producing material with the minimized crew used for mobile jaw and impact crushers.

Using correct maintenance practices, mobile crushers will remain dependable throughout their working life. Crushing and processing material can result in excessive wear on certain components, excessive vibration throughout the plant, and excessive dust in the working environment. Some applications are more aggressive than others. A hard rock application is going to require more maintenance on top of standard maintenance, as there will be more vibration, more dust and more wear than from a softer aggregate.

Due to the nature of its purpose, from the moment a mobile crusher starts, the machine is wearing itself out and breaking itself down. Without routine, regular maintenance and repair, a mobile crusher will not be reliable nor provide the material customers demand.

The first area of wear on any machine is the feed system. Whether its a feeder with an integrated grizzly, or a feeder with an independent prescreen, how the machine is fed contributes to wear. When setting up and maintaining a machine, the machine must be level. A machine that is unlevel left to right will experience increased wear on all components, including the feeder, the screens, the crushing chambers and the conveyor belts. In addition, it reduces production and screening efficiency, as the whole area of the machine is not being effectively used. Also, having the machine sit high at the discharge end will have the effect of feeding the material uphill in the feeder and reducing its efficiency, thus reducing production.

Another area for consideration is the equipment used to feed the machine. The operator using a loader to feed the crusher will have no control over the feed size, as he cannot see whats in the bucket. Whereas with an excavator, the operator can see whats inside and has more control over the feed into the hopper. That is, the operator is not feeding so much material all at once and is controlling the size of the feed. This reduces wear in the feed hoppers impact zones and eliminates material blockages due to feed size being too large to enter the chamber.

Dust is a problem in its own right, especially for the power plant of the mobile crusher. In a very dusty application, it is easy to plug the radiator and have engine-overheating problems. High dust levels cause increased maintenance intervals on air filters, and if not controlled properly, can enter the diesel tank and cause problems with the fuel system. Also, dust that gets inside the crusher increases wear. But if systems are put in place to remove the dust, it should keep it from going into the machine in the first place.

Dust also is a hazard on walkways and a problem for conveyors. If maintained, side-skirting and sealing the conveyors keeps dust from spilling out, building up underneath the conveyor, or building up in rollers, pulleys, bearings, and causing wear on shafts. Its important to maintain the sealing rubbers on the conveyor belts to avoid those issues. Routine maintenance calls for removing accumulated dust from inside and under the machine.

Dust also is a problem for circuit boards and programmable controllers. Dust causes electrical switches to malfunction because it stops the contacts from correctly seating. Electrical systems under positive air pressure dont permit dust to penetrate the control system. In control panels with a correctly maintained positive pressure system, filters remove dust from air that is being pumped into the cabinets. If the filters are plugged, the system will not pull as much air through, allowing dust, moisture and heat to build in the cabinet.

There are also impact aprons against which the rock is thrown, which also see high wear. There are side plates or wear sheets on the sides of the machine. The highest wear area is around the impact crusher itself, around the circumference of the rotor. If not maintained, the wear items will wear through and compromise the structure of the crusher box.

Conduct a daily visual check of the machine. The jaw is simple; just stand up on the walkway and take a look down inside. A crushers jaw plate can be flipped so there are two sides of wear on them. Once half the jaw is worn out, flip it; once that side is worn, change it.

The impact crusher will have an inspection hatch to see inside. Check to see how much material is left on the blow bars and how much is left on the wear sheets on the side of the crusher box. If half the bar is worn out after one week, change the blow bars in another week.The frequency of changes depends entirely on the application and the rock that is being crushed.

They have to be user serviceable, user friendly, and able to be changed in a short time. The best way to change these parts is a service truck with a crane; some use excavators but thats not recommended by any means.

After initial blasting, breakers are used to break down aggregate that typically is not only too large to be hauled in dump trucks, but also too large for crushers that size rock to meet asphalt, drainage system, concrete and landscaping specifications. Breakers can be mounted to a mobile carrier, such as an excavator, or to stationary boom systems that can be attached to a crusher. The total number of hydraulic breakers can vary from site to site depending on production levels, the type of aggregate materials and the entire scope of the operation.

Without hydraulic breakers, workers rely on alternative practices that can quickly affect production rates. For instance, blasting mandates shutting down operations and moving workers to a safe location. And when you consider how many times oversize aggregate might need to be reduced, this can lead to a significant amount of downtime and substantially lower production rates.

Aggregate operations can use hydraulic breakers to attack oversize without having to clear the quarry. But with an ever-growing variety of manufacturers, sizes and models to choose from, narrowing the decision to one hydraulic breaker can be overwhelming with all of the stats and speculation. Thats why its important to know what factors to consider before investing in a new hydraulic breaker.

In most cases, heavy equipment dealers are very knowledgeable about quarry equipment, including breakers, so they are a good resource for finding the best model for a carrier, usually an excavator or stationary boom system. More than likely, they will have specifications and information about various breaker sizes to help gauge what model is best. But being familiar with what to look for in a breaker can streamline the selection process.

The best places to look for breaker information are in the manufacturers brochure, website, owners manual or catalogue. First, carefully review the carrier weight ranges. A breaker that is too big for the carrier can create unsafe working conditions and cause excessive wear to the carrier. An oversized breaker also transmits energy in two directions, toward the aggregate and through the equipment. This produces wasted energy and can damage the carrier. But using a breaker thats too small puts excessive force on the tool steel, which transmits percussive energy from the breaker to the material. Using breakers that are too small also can damage mounting adapters and internal components, which considerably decreases their life.

Once you find a breaker that meets the carriers capacity, check its output power, which is typically measured in foot-pounds. Foot-pound classes are generalizations and are not based on any physical test. Often the breakers output will be documented in one of two ways: as the manufacturers calculated foot-pound class or as an Association of Equipment Manufacturers measured foot-pound rating. Foot-pound class ratings can be deceiving since they are loosely based on the breakers service weight and not the result of any physical test. The AEM rating, on the other hand, measures the force a breaker exerts in a single blow through repeatable and certified testing methods. The AEM rating, which was developed by the Mounted Breaker Manufacturers Bureau, makes it easier to compare breaker models by reviewing true figures collected during an actual test procedure.

For instance, three breaker manufacturers might claim their breakers belong in a 1,000-lb. breaker class. But AEM testing standards could reveal all three actually have less foot-pound impact. You can tell if a breaker has been AEM tested if a manufacturer provides a disclosure statement or if the breaker is labeled with an AEM Tool Energy seal. If you cannot find this information, contact the manufacturer. In addition to output energy specifications, manufacturers often supply estimates for production rates on different types of aggregate material. Make sure to get the right measurements to make the best decision.

In addition to weight and output power, look at the breakers mounting package. Two things are crucial for mounting a breaker to a carrier: a hydraulic installation kit and mounting components. Breakers need hydraulic plumbing with unidirectional flow to move oil from the carrier to the breaker and back again. A one-way flow hydraulic kit is sufficient to power the breaker as long as the components are sized to properly handle the required flows and pressures. But, consider a bidirectional flow hydraulic kit if you plan to use the same carrier with other attachments that require two-way flow. Check with the dealer or breaker manufacturer to determine which hydraulic package best fits current and future needs.

Hydraulic flow and pressure specifications also need to be considered when pairing a breaker to a hydraulic system. If the carrier cannot provide enough flow at the right pressure, the breaker wont perform with maximum output, which lowers productivity and can damage the breaker. Additionally, a breaker receiving too much flow can wear quickly, which reduces its service life. For the best results, follow the hydraulic breaker specifications found in owners manuals, catalogs and brochures. Youll find out if a breaker has additional systems that might require additional servicing. For instance, some breakers feature nitrogen gas-assist systems that work with the hydraulic oil to accelerate the breakers piston. The nitrogen systems specifications need to be followed for consistent breaker power output.

Brackets or pin and bushing kits are commonly required to attach the breaker to the carrier. Typically they are bolted to the top of a breaker and are configured to match a specific carrier. Some manufacturers make universal mounting brackets that can accommodate two or three different sizes of carriers. With the adjustable pins, bushings or other components inside these universal brackets, the breaker can fit a range of carriers. However, varying distances between pin centers can complicate hookups to quick coupling systems. In addition, loose components, such as spacers, can become lost when the breaker is not in use and detached from the carrier.

Some carriers are equipped with quick-coupling systems, which require a breakers mounting interface to be configured like the carriers original attachment. Some manufacturers produce top-mount brackets that pair extremely well with couplers. This allows an operator to use the original bucket pins from the carrier to attach the breaker, and eliminates the need for new pins. This pairing also ensures a fast pickup with the quick coupler.

Its also a good idea to check which breaker tools are available through the dealer and manufacturer. The most common for aggregate mining are chisels and blunts. There are two kinds of chisels commonly used in aggregate mines: crosscut and inline. Both chisels resemble a flat head screwdriver, but the crosscut chisels are used when carrier operators want to direct force in a left-to-right concentration; whereas, inline chisels direct force fore and aft. With chisel tools, operators can concentrate a breakers energy to develop cracks, break open seams or define scribe lines.

If a chisel cant access or develop a crack or seam, a blunt can be used. Blunts have a flattened head that spreads the energy equally in all directions. This creates a shattering effect that promotes cracks and seam separation. Ask your dealer if the tools you are considering are suited for the application. Using non-original equipment manufacturer tool steel can damage the percussive piston in the breaker, seize into the wear bushings, or cause excessive wear.

Regular breaker maintenance is necessary, yet its one of the biggest challenges for aggregate operations. It not only extends the life of the breaker, but also can keep minor inconveniences from turning into expensive problems. Some manufacturers recommend operators inspect breakers daily to check grease levels and make sure there are no worn or damaged parts or hydraulic leaks.

Breakers need to be lubricated with adequate amounts of grease to keep the tool bushing area clear and reduce friction, but follow the manufacturers recommendations. For example, adding grease before properly positioning the breaker can lead to seal damage or even catastrophic failure. And too little grease could cause the bushings to overheat, seize and damage tools. Also, manufacturers advise using high-moly grease that withstands working temperatures greater than 500 degrees. Some breakers have automatic lube systems that manage grease levels, but those systems still need inspections to ensure there is adequate grease in their vessels. Shiny marks on the tool are a good indication the breaker is not properly lubricated.

Little has changed in basic crusher design over past decades, other than that of improvements in speed and chamber design. Rebuilding and keeping the same crusher in operation year after year has long been the typical approach. However, recent developments have brought about the advent of new hydraulic systems in modern crusher designs innovations stimulated by the need for greater productivity as well as a safer working environment. Importantly, the hydraulic systems in modern crusher designs are engineered to deliver greater plant uptime and eliminate the safety risks associated with manual intervention.

Indeed the crushing arena is a hazardous environment. Large material and debris can jam inside the crusher, damaging components and causing costly downtime. Importantly, manually digging out the crusher before repairs or restarts puts workers in extremely dangerous positions.

The Mine Safety and Health Administration has reported numerous injuries and fatalities incurred when climbing in or under the jaw to manually clear, repair or adjust the typical older-style jaw crusher. Consider that fatalities and injuries can occur even when the machine is locked out and tagged out. Recent examples include a foreman injured while attempting to dislodge a piece of steel caught in the primary jaw crusher. Another incident involved a fatality when a maintenance man was removing the toggle plate seat from the pitman on a jaw crusher. The worker was standing on a temporary platform when the bolts holding the toggle seat were removed, causing the pitman to move and strike him.

The hydraulic systems on modern crusher designs eliminate the need for workers to place themselves in or under the crusher. An overview of hydraulic system technology points to these three key elements:

A hydraulic chamber-clearing system that automatically opens the crusher to a safe position, allowing materials to pass. A hydraulic overload relief that protects parts and components against overload damage. A hydraulic adjustment that eliminates the maintenance downtime associated with manual crusher adjustments, and maintains safe, consistent crusher output without the need for worker intervention.

Whether a crusher is jammed by large material, tramp iron or uncrushable debris; or is stalled by a power failure the chamber must be cleared before restarting. Manual clearing is a lengthy and risky task, especially since material can be wedged inside the crusher with tremendous pressure, and dislodging poses much danger to workers placed in harms way inside the crusher.

Unlike that of the older-style jaw, the modern jaw will clear itself automatically with hydraulics that open the crusher to a safe position, and allow materials to pass again, without the need for manual intervention. If a feeder or deflector plate is installed under the crusher, uncrushable material will transfer smoothly onto the conveyor without slicing the belt.

To prevent crusher damage, downtime and difficult maintenance procedures, the hydraulic overload relief system opens the crusher when internal forces become too high, protecting the unit against costly component failure. After relief, the system automatically returns the crusher to the previous setting for continued crushing.

The modern crusher is engineered with oversized hydraulic cylinders and a traveling toggle beam to achieve reliable overload protection and simple crusher adjustment. All closed-side setting adjustments are made with push-button controls, with no shims being needed at any time (to shim is the act of inserting a timber or other materials under equipment). This is a key development as many accidents and injuries have occurred during shim adjustment, a process which has no less than 15 steps as described in the primary crusher shim adjustment training program offered by MSHA.

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choosing a mobile impact crusher for recycling what you need to know

RPN connected with product experts and Canadian distributors representing eight of the leading global manufacturers of mobile impact crushers to gain a little more insight into the benefits, features and evolution of this integral tool of today's C&D, concrete and asphalt recycling industries.

Mobile impact crushers, also known as the tracked impact crusher or recycling impactor, are recognizable mainly due to the fact that these crushers are mounted on a tracked undercarriage. Overall range of capacity for mobile impact crushers is roughly about 100 to 500 tons per hour.

Today's mobile impact crushers are especially ideal for smaller-scale recycling operations, for on-site recycling of demolition waste, and for tight-space urban and roadside applications. These units feature a diesel or electric drive system, are transportable by trailer, and can be simply driven off at the location of material that needs to be processed, and go to work very quickly.

With their capability to produce accurately-sized end-product with a cubical end product shape, mobile impact crushers work well as closed circuit stand-alone plants, or they can add significant productivity to any operation, working in tandem with a jaw crusher or screen plant.

Tracked impact crushing plants have evolved greatly over the last several decades, as their designs have been continuously updated and as the crushing market has changed. Major trends include the introduction of electric drive and hybrid systems as opposed to diesel-hydraulic drive systems, and decreases in size, weight, fuel consumption, cost-per-ton, and sound and dust generation.

Today's mobile impact crushers are ideal for use in a wide range of applications, including as a mobile recovered concrete crusher, or for asphalt and mixed C&D waste. They are available compliant to Tier 4 Final emissions standards, and can be equipped with or without a built-in screen, as well as many options specifically geared towards creating recycled materials. Todays mobile impact crushers are safer, more mobile, easier to maintain and operate, and are available with sophisticated machine automation and monitoring.

"The growth in recycling of concrete and asphalt recycling industries has led to higher demand for smaller, more mobile crushers," says John O'Neill, McCloskey International's VP of sales. "Over the last 10 years we have improved our control panel systems to provide operators with more knowledge and information about what is going on inside their machines at all times. The units are also easier and faster to set up."

According to Daryl Todd of B.C.-based Frontline Machinery, the Canadian dealer for Belgium-based crushing and screening plant manufacturer Keestrack, "Wesee a strong movement towards turning concrete and asphalt rubble materials into higher quality recycled materials such as construction sand, washed recycled drain rock, road mulch, RAP (reclaimed asphalt pavement) and a host of other quality products with a much higher value.

"The impact crusher's ability to handle steel-reinforced concrete, along with custom options, such as plastics and wood-waste removal systems, washing systems and more, has enabled recyclers to create much higher quality end products, and crush and process materials previously deemed only waste, or too difficult to process."

"The reason is the quality of the material and very cubical shape produced. The impact crusher is a first- and second-stage crusher in one unit, so you can crush a 600-mm product down to a final product for resale as recycling aggregate.

"Our machines are excellent in recycling asphalt, as we can slow down the rotor speed to crush the asphalt, but not the aggregate inside the asphalt, so the material can be reused in asphalt mixing plants, a huge savings on cost."

According to Norbert Dieplinger, Austria-based SBM Mineral Processing's international business development manager, "Specs are getting tighter so crushers must be much more accurate than in the past. For example, a few years back you could just crush aggregate down to 0- to 3-inch material and use it for road base. Now, engineers are allowing the use of more and more recycled asphalt into their mix, instead of all-natural aggregate and crushed concrete, and not just as road base material. With impact crushers, the shape is exactly what you need, you can get down to smaller sizes and they can process building debris with rebar."

Alexander Taubinger, Rubble Master's managing director and VP sales, says "Cost of ownership and costs per ton are key figures for our customer base." Rubble Master machines feature a diesel-electric drive that burns less fuel, and low maintenance costs are due to the company's latest design and product development.

"Back in the day, it was all about tons per hour. Machines were built overly strong and heavy with large, inefficient power solutions. This is second or third priority these days, since contractors have to meet other job requirements when it comes to most recycling applications."

He adds that with respect to end markets, Rubble Master has always been focused on the final product size and quality. "Lots of contractors still only think about reducing the size of material. It's all about reusable and resalable product size and quality these days."

The changing value of recovered metal, especially over the last decade, is a consideration for all recyclers and contractors managing recycled materials. For users of mobile impact crushers in the processing of concrete and C&D rubble, even with the fluctuating price of recovered steel seen over the last several years, efficient metal separation remains a key component.

"Unfortunately, with the way things have turned as of late, scrap iron is not worth a lot. But I can tell you that having systems in place to remove it is paramount," says Tim Harms, crushing and screening product manager, Kolberg Pioneer (a KPI-JCI & ASTEC Screens company.)

"If you have any metal contamination in your end product, you'll be in trouble trying to resell that product. So it's very important to get it removed. Ten years ago, scrap was of higher value and that was part of the equation. Now it's just the fact that you need to get it out so that you can resell the product. Impact crushers are very good at liberating scrap iron from concrete."

Stephen Whyte, product manager, mobile product development, KPI-JCI & Astec Mobile Screens, adds that the growth of the contractor/rental market has also been key in driving the growth of all tracked crushing and screening plants.

"Guys today can load a tracked impact crusher, go do a job for a week, load it off on the weekend, and they can be set, ready to go on the next site the following week," says Whyte. "It's the contractor/rental market that's really driven the mobile impact crusher market."

He adds that for impact crushing in general, mobile, tracked units are the least path of resistance to get into the business. "You've got the highest reduction ratio. You've probably got the lowest capital investment. And you can get the most bang for your buck'. Almost always you will see entry-level tracked impactors as the first choice for contractors getting into the C&D materials recycling business, no matter the brand."

The stand-out feature of the mobile crusher or tracked impactor for recycling applications, is its mobility, combined with high productivity per hour. Units are fully self-contained on their tracked undercarriage and can easily be driven off a trailer by one operator and quickly put to work, with excellent capability for moving directly to materials. Some models are even capable of tracking (moving about on their tracks) while crushing.

"The ability to move within the job site and job to job is important to the contractor, or other end user, thus driving the demand for portable crushers," says Jody Beasley, national sales director at Screen Machine. "One of the biggest expenses in material processing is physically handling the material. Every time material is moved, labour and expenses are involved. Tracked impact crushers bring the machine to the job site, right to the pile, and allow for very efficient material processing.

"It's all about tons per hour. Our machines have been designed to produce maximum tonnage and one significant way they do that more efficiently is through our patented Crusher Relief System. The Screen Machine Crusher Relief System allows the operator to raise the crusher lid up to six inches while the machine is in operation. This is a huge help in preventing jams inside the crusher and ultimately delivers thousands of additional tons of product over the life of the machine."

According to Stephen Whyte, KPI-JCI and Astec Mobile Screens, "Mobile impact crushers are higher capacity than they were when they first came on. When the first tracked machines came in, they were seen as crushers that were highly portable but would do less weight than the typical portable [trailer-mounted] machine. Whereas now, some of the tracked machines we manufacture can reach those same capacities, and compete with the portable setups.

"Another great feature with our impact crushers is that they allow operators to crush and track at the same time," he continues. "This is why you'll see a lot of these units being used along the highway. One operator can basically load the machine and operate the tracked crusher at the same time."

"This is very important," adds Kolberg-Pioneer's Tim Harms. "You can be crushing and don't have to disengage the crusher to track the machine. You can continue to crush while the machine is being moved around on its tracks, which is a big advantage with respect to time savings. Time is of a huge value. If you lose 10 percent of your time, just because you've got to wait for the crusher to stop so you can move it, those are dollars."

Traditionally, mobile impact crushers have used a diesel-hydraulic engine for the track-drive and power to the crusher. The advent of electric-drive and hybrid systems is one of the main advancements that has occurred over the last decade, and its development is seen by many as one of the most significant trends going forward, especially considering the importance of fuel efficiency, rising transport and operational costs and the global focus on reducing emissions.

"Lowest cost per ton produced is crucial in the customer's business," says Metso Minerals' product manager, Jouni Hulttinen, who adds that main focus areas in their Lokotrack line development have been ease of transport, maintenance and service, as well as safety and energy efficiency.

"Energy efficiency has been a very focused development area," says Hulttinen. "We have reduced fuel consumption up to 20 percent with our tracked impactors." He says one good example is the Lokotrack LT1213(S) (S' designates a built-in screen component) which uses a stand-by function' where the machine switches to idling mode if there is no load on the engine. "Just five minutes on stand-by, per hour, can save 10 litres of fuel per day."

According to Norbert Dieplinger, the drive systems in crushers manufactured by SBM are available as diesel-electric or can be run 100-percent electric. "Not only does electric power reduce the carbon footprint, it can save contractors up to 30 percent on fuel costs when you compare them to the diesel-hydraulic drive systems that were common in the past and are still used by lots of manufacturers," he says.

"This permits high fuel efficiency and allows optimal loading of the crusher," explains Joe Schappert, Kleemann's senior technical sales manager. "Outstanding performance is made possible in part by the extremely efficient direct drive, with which these machines are equipped. A latest-generation diesel engine transmits its power almost loss-free directly to the flywheel of the crusher, via a robust fluid coupling and V-belts. This drive concept enables enormous versatility, as the rotor speed can be adjusted in four stages to suit different processing applications."

A first question to ask when considering a purchase, according to McCloskey's John O'Neill, is: what do you want the machine to do? He says it is necessary for a solid sense of reality to be a big part of the buying decision. "Too many times the customer is upset because they expect peak performance to be the norm, when they need to be looking at all aspects of their operation and how it can support the crusher and the desired end goals or products."

"What kind of support equipment is available and can it support the tonnage capacity of the crusher?" he asks. He adds that other important questions include: Who are the customers? What is the application you intend to use it for? What spec are you working with? How large are the piles to be crushed?"

"If the impact crusher needs a part or maintenance items, can you be confident that the manufacturer will get those parts to you as quickly as possible?" asks Screen Machine's Jody Beasley. "Our machines are manufactured in Ohio, and all parts orders are fulfilled here. We pride ourselves on the fact that more than 97 percent of in-stock parts orders ship the same day."

"All impactors are not created equal, and the differences are significant," says Daryl Todd, Frontline Machinery. "We strongly suggest taking a close look when comparing various models. Start off with the technical specifications, including engine horsepower, the weight of rotor and blow bars, as well as ease of transport, machine weight and dimensions."

Todd says there are many questions to ask, including: Is the rotor direct-drive from the engine, electric drive or hydraulic drive? What is the hopper capacity and feeding height? And what are the after-screen options - single-, double- or triple-deck? Does the machine have the ability to track while in full production? What type / quality are the key components such as hydraulics and electronics? And what is the type and quality of steel used in the frame, crusher housing and rotor? He adds that any mobile impact crusher should also have a user-friendly design, with ease of changing blow bars, and ease of access for maintenance and servicing.

Keestrack's Michael Brookshaw says one of the main questions to ask when considering an impact crusher is: can you transport the unit with your own transport means? "The material that you need to crush in your area is important," he says.

"Look at the costs per ton involved on the purchasing and running of the unit. What are the amounts of material that need to be crushed? Are they large deposits of 30,000 tons or smaller deposits of 500 to 1,000 tons? You should also consider the feed size and capacity that you will need. Would electric drive provide an advantage on the environmental side of the business?"

He adds that the technical aspects of the unit are also very important. Electric drive, pre-screen before the crusher, crusher overload system, pan feeder under the crusher, weight, as well as service and operator friendliness of the unit are all areas that need to be considered. Joe Schappert from Kleemann says that buyers considering a purchase should make sure they choose the correct size for the application and consider how product will flow through the crusher.

"The Kleemann Continuous Feed System (CFS) manages a more equal loading of the crushing area, in which the conveying frequencies of the feeder trough and the pre-screen are adapted independently of each other to the level of the crusher, thus significantly boosting performance.

"Our new impact crushers are differentiated by their size and productivity," continues Schappert. "Our model MR 110 Zsi EVO 2 has a crusher inlet opening of 43.3 inches (1,100 mm), and the MR 130 Zi EVO 2 has a crusher inlet opening of 51 inches (1,300 mm). These provide feed capacities of up to 350 or 450 tph, respectively.

"Consider diesel-electric drives," he adds. "Our latest EVO 2 Mobirex mobile impact crushers utilize direct-drive crushers and electric drives for the vibrating conveyors, belts and the pre-screen. This permits high fuel efficiency and allows optimal loading of the crusher."

Looking ahead, Daryl Todd of Frontline Machinery says there will be more hybrid technology, electric/diesel hybrids, meaning reduced fuel consumption, as well as improved noise reduction. He says that we'll also see advances in contaminant removal systems and washing systems integrated into closed-circuit impact crushers.

GPS systems are another area where Todd expects advances to continue. "GPS systems provide remote monitoring and control, tying in with onboard belt scales," he says. "This allows managers to have total insight into remote operations."

Michael Brookshaw of Keestrack says their telematic system allows customers, distributors and the manufacturer to monitor their machines, inform from distance and advise on capacity, running of the unit and fault finding.

"There has also been much development in the area of wear parts, which are more durable than ever," says Brookshaw. "Our electric-hybrid and full-hybrid system, which we call Keebrid, are excellent in the areas of durability, lower emissions, running costs and all environmental issues."

For McCloskey's John O'Neill, the trend of using one machine to do multiple parts of an operation will continue to decline. "The crusher should crush and the screeners should screen," he says. "Trying to squeeze it all onto one platform is hard and often results in compromises, which if not acceptable to the customer, can be disastrous on the job site."

Rubble Master's Taubinger expects to see improvements in efficiency in all regards. "We expect a very heavy focus on emissions such as dust and noise, as well as more fuel efficiency, safety and ease of operation."

"Advanced diagnostic tools can enable the operator to monitor processes in real time with the ability to adjust settings on a touch screen on the crusher, or even from inside an excavator cab. This leads to further increases in safety and efficiency with a reduction in maintenance, operating costs and downtime.

"Diesel-electric power is the future because of all the advantages it provides with respect to decreased fuel costs and decreased carbon footprint," adds Dieplinger, who also points out that this will make a big difference in years to come, especially considering new carbon taxes being implemented globally.

According to Metso's Jouni Hulttinen, base construction for bikeways, road base and industrial areas are growing end markets for material made from recycled C&D, concrete and asphalt. He says mobile impact crushers, and all types of crushers for recyclable materials, will increasingly move more towards application in the production of high-quality end products.

"Use of the end material has gone from the most basic application to higher-spec building materials," says Hulttinen. "The future trend will go more towards substituting aggregates, new concrete made from recycled concrete, and recycled asphalt added to make new asphalt." RPN

impact crusher - an overview | sciencedirect topics

The impact crusher (typically PE series) is widely used and of high production efficiency and good safety performance. The finished product is of cube shape and the tension force and crack is avoided. Compared with hammer crusher, the impact crusher is able to fully utilize the high-speed impact energy of entire rotor. However, due to the crushing board that is easy to wear, it is also limited in the hard material crushing. The impact crusher is commonly used for the crushing of limestone, coal, calcium carbide, quartz, dolomite, iron pyrites, gypsum, and chemical raw materials of medium hardness. Effect of process conditions on the production capacity of crushed materials is listed in Table8.10.

Depending on the size of the debris, it may either be ready to enter the recycling process or need to be broken down to obtain a product with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimise the degree of contamination of the final product.

The three types of crushers most commonly used for crushing CDW materials are the jaw crusher, the impact crusher and the gyratory crusher (Figure 4.4). A jaw crusher consists of two plates, with one oscillating back and forth against the other at a fixed angle (Figure 4.4(a)) and it is the most widely used in primary crushing stages (Behera etal., 2014). The jaw crusher can withstand large and hard-to-break pieces of reinforced concrete, which would probably cause the other crushing machines to break down. Therefore, the material is initially reduced in jaw crushers before going through any other crushing operation. The particle size reduction depends on the maximum and minimum size of the gap at the plates (Hansen, 2004).

An impact crusher breaks the CDW materials by striking them with a high-speed rotating impact, which imparts a shearing force on the debris (Figure 4.4(b)). Upon reaching the rotor, the debris is caught by steel teeth or hard blades attached to the rotor. These hurl the materials against the breaker plate, smashing them into smaller particle sizes. Impact crushers provide better grain-size distribution of RA for road construction purposes, and they are less sensitive to material that cannot be crushed, such as steel reinforcement.

Generally, jaw and impact crushers exhibit a large reduction factor, defined as the ratio of the particle size of the input to that of the output material. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike and thus generates a higher amount of fine material (OMahony, 1990).

Gyratory crushers work on the same principle as cone crushers (Figure 4.4(c)). These have a gyratory motion driven by an eccentric wheel. These machines will not accept materials with a large particle size and therefore only jaw or impact crushers should be considered as primary crushers. Gyratory and cone crushers are likely to become jammed by fragments that are too large or too heavy. It is recommended that wood and steel be removed as much as possible before dumping CDW into these crushers. Gyratory and cone crushers have advantages such as relatively low energy consumption, a reasonable amount of control over the particle size of the material and production of low amounts of fine particles (Hansen, 2004).

For better control of the aggregate particle size distribution, it is recommended that the CDW should be processed in at least two crushing stages. First, the demolition methodologies used on-site should be able to reduce individual pieces of debris to a size that the primary crusher in the recycling plant can take. This size depends on the opening feed of the primary crusher, which is normally bigger for large stationary plants than for mobile plants. Therefore, the recycling of CDW materials requires careful planning and communication between all parties involved.

A large proportion of the product from the primary crusher can result in small granules with a particle size distribution that may not satisfy the requirements laid down by the customer after having gone through the other crushing stages. Therefore, it should be possible to adjust the opening feed size of the primary crusher, implying that the secondary crusher should have a relatively large capacity. This will allow maximisation of coarse RA production (e.g., the feed size of the primary crusher should be set to reduce material to the largest size that will fit the secondary crusher).

The choice of using multiple crushing stages mainly depends on the desired quality of the final product and the ratio of the amounts of coarse and fine fractions (Yanagi etal., 1998; Nagataki and Iida, 2001; Nagataki etal., 2004; Dosho etal., 1998; Gokce etal., 2011). When recycling concrete, a greater number of crushing processes produces a more spherical material with lower adhered mortar content (Pedro etal., 2015), thus providing a superior quality of material to work with (Lotfi etal., 2017). However, the use of several crushing stages has some negative consequences as well; in addition to costing more, the final product may contain a greater proportion of finer fractions, which may not always be a suitable material.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Fig. 15.9), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 15.9. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements. (A) Single-toggle jaw crusher, (B) disc or gyrosphere crusher, (C) gyratory crusher and (D) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (Section 15.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Figure 16.8), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 16.8. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements (redrawn, adapted and modified from Ref. 39). (a) Single-toggle jaw crusher, (b) disc or gyrosphere crusher, (c) gyratory crusher, and (d) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (section 16.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

The main sources of RA are either from construction and ready mixed concrete sites, demolition sites or from roads. The demolition sites produce a heterogeneous material, whereas ready mixed concrete or prefabricated concrete plants produce a more homogeneous material. RAs are mainly produced in fixed crushing plant around big cities where CDWs are available. However, for roads and to reduce transportation cost, mobile crushing installations are used.

The materiel for RA manufacturing does not differ from that of producing NA in quarries. However, it should be more robust to resist wear, and it handles large blocks of up to 1m. The main difference is that RAs need the elimination of contaminants such as wood, joint sealants, plastics, and steel which should be removed with blast of air for light materials and electro-magnets for steel. The materials are first separated from other undesired materials then treated by washing and air to take out contamination. The quality and grading of aggregates depend on the choice of the crusher type.

Jaw crusher: The material is crushed between a fixed jaw and a mobile jaw. The feed is subjected to repeated pressure as it passes downwards and is progressively reduced in size until it is small enough to pass out of the crushing chamber. This crusher produces less fines but the aggregates have a more elongated form.

Hammer (impact) crusher: The feed is fragmented by kinetic energy introduced by a rotating mass (the rotor) which projects the material against a fixed surface causing it to shatter causing further particle size reduction. This crusher produces more rounded shape.

The type of crusher and number of processing stages have considerable influence on the shape and size of RA. In general, for the same size, RAs tend to be coarser, more porous and rougher than NAs, due to the adhered mortar content (Dhir etal., 1999). After the primary crushing, which is normally performed using jaw crushers (Fong etal., 2004), it is preferable to adopt a secondary crushing stage (with cone crushers or impact crushers) (CCANZ, 2011) to further reduce the size of the CDW, producing more regularly shaped particles (Barbudo etal., 2012; Ferreira etal., 2011; Fonseca etal., 2011; Pedro etal., 2014, 2015; Gonzlez-Fonteboa and Martnez-Abella, 2008; Maultzsch and Mellmann, 1998; Dhir and Paine, 2007; Chidiroglou etal., 2008).

CDW that is subjected to a jaw crushing stage tends to result only in flatter RA (Ferreira etal., 2011; Fonseca etal., 2011; Hendriks, 1998; Tsoumani etal., 2015). It is possible to produce good-quality coarse RA within the specified size range by adjusting the crusher aperture (Hansen, 1992). In addition, the number of processing stages needs to be well thought out to ensure that the yield of coarse RA is not affected and that the quantity of fine RA is kept to the minimum (Angulo etal., 2004). This is because the finer fraction typically exhibits lower quality, as it accumulates a higher amount of pulverised old mortar (Etxeberria etal., 2007b; Meller and Winkler, 1998). Fine RA resulting from impact crushers tends to exhibit greater angularity and higher fineness modulus compared with standard natural sands (Lamond etal., 2002; Hansen, 1992; Buyle-Bodin and Hadjieva-Zaharieva, 2002).

One of the commonly known issues related to the use of RCA is its ability to generate a considerable amount of fines when the material is used (Thomas etal., 2016). As the RCA particles are moved around, they impact against one another, leading to the breakage of the friable adhered mortar, which may give rise to some technical problems such as an increase in the water demand of concrete mixes when used as an NA replacement (Thomas etal., 2013a,b; Poon etal., 2007).

The coarse fraction of RMA tends to show a higher shape index owing to the shape of the original construction material (e.g., perforated ceramic bricks) (De Brito etal., 2005). This can pose a problem in future applications as RMA may not compact as efficiently as RCA or NA (Khalaf and DeVenny, 2005). Its shape index may be reduced if the material is successively broken down to a lower particle size (De Brito etal., 2005).

Impact crushers (e.g., hammer mills and impact mills) employ sharp blows applied at high speed to free-falling rocks where comminution is by impact rather than compression. The moving parts are beaters, which transfer some of their kinetic energy to the ore particles upon contact. Internal stresses created in the particles are often large enough to cause them to shatter. These forces are increased by causing the particles to impact upon an anvil or breaker plate.

There is an important difference between the states of materials crushed by pressure and by impact. There are internal stresses in material broken by pressure that can later cause cracking. Impact causes immediate fracture with no residual stresses. This stress-free condition is particularly valuable in stone used for brick-making, building, and roadmaking, in which binding agents (e.g., tar) are subsequently added. Impact crushers, therefore, have a wider use in the quarrying industry than in the metal-mining industry. They may give trouble-free crushing on ores that tend to be plastic and pack when the crushing forces are applied slowly, as is the case in jaw and gyratory crushers. These types of ore tend to be brittle when the crushing force is applied instantaneously by impact crushers (Lewis et al., 1976).

Impact crushers are also favored in the quarry industry because of the improved product shape. Cone crushers tend to produce more elongated particles because of their ability to pass through the chamber unbroken. In an impact crusher, all particles are subjected to impact and the elongated particles, having a lower strength due to their thinner cross section, would be broken (Ramos et al., 1994; Kojovic and Bearman, 1997).

Figure 6.23(a) shows the cross section of a typical hammer mill. The hammers (Figure 6.23(b)) are made from manganese steel or nodular cast iron containing chromium carbide, which is extremely abrasion resistant. The breaker plates are made of the same material.

The hammers are pivoted so as to move out of the path of oversize material (or tramp metal) entering the crushing chamber. Pivoted (swing) hammers exert less force than they would if rigidly attached, so they tend to be used on smaller impact crushers or for crushing soft material. The exit from the mill is perforated, so that material that is not broken to the required size is retained and swept up again by the rotor for further impacting. There may also be an exit chute for oversize material which is swept past the screen bars. Certain design configurations include a central discharge chute (an opening in the screen) and others exclude the screen, depending on the application.

The hammer mill is designed to give the particles velocities of the order of that of the hammers. Fracture is either due to impact with the hammers or to the subsequent impact with the casing or grid. Since the particles are given high velocities, much of the size reduction is by attrition (i.e., particle on particle breakage), and this leads to little control on product size and a much higher proportion of fines than with compressive crushers.

The hammers can weigh over 100kg and can work on feed up to 20cm. The speed of the rotor varies between 500 and 3,000rpm. Due to the high rate of wear on these machines (wear can be taken up by moving the hammers on the pins) they are limited in use to relatively non-abrasive materials. They have extensive use in limestone quarrying and in the crushing of coal. A great advantage in quarrying is the fact that they produce a relatively cubic product.

A model of the swing hammer mill has been developed for coal applications (Shi et al., 2003). The model is able to predict the product size distribution and power draw for given hammer mill configurations (breaker gap, under-screen orientation, screen aperture) and operating conditions (feed rate, feed size distribution, and breakage characteristics).

For coarser crushing, the fixed hammer impact mill is often used (Figure 6.24). In these machines the material falls tangentially onto a rotor, running at 250500rpm, receiving a glancing impulse, which sends it spinning toward the impact plates. The velocity imparted is deliberately restricted to a fraction of the velocity of the rotor to avoid high stress and probable failure of the rotor bearings.

The fractured pieces that can pass between the clearances of the rotor and breaker plate enter a second chamber created by another breaker plate, where the clearance is smaller, and then into a third smaller chamber. The grinding path is designed to reduce flakiness and to produce cubic particles. The impact plates are reversible to even out wear, and can easily be removed and replaced.

The impact mill gives better control of product size than does the hammer mill, since there is less attrition. The product shape is more easily controlled and energy is saved by the removal of particles once they have reached the size required.

Large impact crushers will reduce 1.5m top size ROM ore to 20cm, at capacities of around 1500th1, although units with capacities of 3000th1 have been manufactured. Since they depend on high velocities for crushing, wear is greater than for jaw or gyratory crushers. Hence impact crushers are not recommended for use on ores containing over 15% silica (Lewis et al., 1976). However, they are a good choice for primary crushing when high reduction ratios are required (the ratio can be as high as 40:1) and the ore is relatively non-abrasive.

Developed in New Zealand in the late 1960s, over the years it has been marketed by several companies (Tidco, Svedala, Allis Engineering, and now Metso) under various names (e.g., duopactor). The crusher is finding application in the concrete industry (Rodriguez, 1990). The mill combines impact crushing, high-intensity grinding, and multi-particle pulverizing, and as such, is best suited in the tertiary crushing or primary grinding stage, producing products in the 0.0612mm size range. It can handle feeds of up to 650th1 at a top size of over 50mm. Figure 6.22 shows a Barmac in a circuit; Figure 6.25 is a cross-section and illustration of the crushing action.

The basic comminution principle employed involves acceleration of particles within a special ore-lined rotor revolving at high speed. A portion of the feed enters the rotor, while the remainder cascades to the crushing chamber. Breakage commences when rock enters the rotor, and is thrown centrifugally, achieving exit velocities up to 90ms1. The rotor continuously discharges into a highly turbulent particle cloud contained within the crushing chamber, where reduction occurs primarily by rock-on-rock impact, attrition, and abrasion.

This crusher developed by Jaques (now Terex Mineral Processing Solutions) has several internal chamber configurations available depending on the abrasiveness of the ore. Examples include the Rock on Rock, Rock on Anvil and Shoe and Anvil configurations (Figure 6.26). These units typically operate with 5 to 6 steel impellers or hammers, with a ring of thin anvils. Rock is hit or accelerated to impact on the anvils, after which the broken fragments freefall into the discharge chute and onto a product conveyor belt. This impact size reduction process was modeled by Kojovic (1996) and Djordjevic et al. (2003) using rotor dimensions and speed, and rock breakage characteristics measured in the laboratory. The model was also extended to the Barmac crushers (Napier-Munn et al., 1996).

Figure 9.1 shows common aluminum oxide-based grains. Also called corundum, alumina ore was mined as early as 2000 BC in the Greek island of Naxos. Its structure is based on -Al2O3 and various admixtures. Traces of chromium give alumina a red hue, iron makes it black, and titanium makes it blue. Its triagonal system reduces susceptibility to cleavage. Precious grades of Al2O3 are used as gemstones, and include sapphire, ruby, topaz, amethyst, and emerald.

Charles Jacobs (1900), a principal developer, fused bauxite at 2200C (4000F) before the turn of the 20th century. The resulting dense mass was crushed into abrasive particles. Presently, alumina is obtained by smelting aluminum alloys containing Al2O3 in electric furnaces at around 1260C (2300F), a temperature at which impurities separate from the solution and aluminum oxide crystallizes out. Depending upon the particular process and chemical composition there are a variety of forms of aluminum oxide. The poor thermal conductivity of alumina (33.5W/mK) is a significant factor that affects grinding performance. Alumina is available in a large range of grades because it allows substitution of other oxides in solid solution, and defect content can be readily controlled.

For grinding, lapping, and polishing bearing balls, roller races, and optical glasses, the main abrasive employed is alumina. Its abrasive characteristics are established during the furnacing and crushing operations, so very little of what is accomplished later significantly affects the features of the grains.

Aluminum oxide is tougher than SiC. There are four types of gradations for toughness. The toughest grain is not always the longest wearing. A grain that is simply too tough for an application will become dull and will rub the workpiece, increasing the friction, creating heat and vibrations. On the other hand, a grain that is too friable will wear away rapidly, shortening the life of the abrasive tool. Friability is a term used to describe the tendency for grain fractures to occur under load. There is a range of grain toughness suitable for each application. The white friable aluminum oxide is almost always bonded by vitrification. It is the main abrasive used in tool rooms because of its versatility for a wide range of materials. In general, the larger the crystals, the more friable the grain. The slower the cooling process, the larger are the crystals. To obtain very fine crystals, the charge is cooled as quickly as possible, and the abrasive grain is fused in small pigs of up to 2ton. Coarse crystalline abrasive grains are obtained from 5 to 6ton pigs allowed to cool in the furnace shell.

The raw material, bauxite, containing 8590% alumina, 25% TiO2, up to 10% iron oxide (Fe2O3), silica, and basic oxides, is fused in an electric-arc furnace at 2600C (4700F). The bed of crushed and calcined bauxite, mixed with coke and iron to remove impurities, is poured into the bottom of the furnace where a carbon starter rod is laid down. A couple of large vertical carbon rods are then brought down to touch and a heavy current applied. The starter rod is rapidly consumed, by which time the heat melts the bauxite, which then becomes an electrolyte. Bauxite is added over several hours to build up the volume of melt. Current is controlled by adjusting the height of the electrodes, which are eventually consumed in the process.

After cooling, the alumina is broken up and passed through a series of hammer, beater, crush, roller, and/or ball mills to reduce it to the required grain size and shape, producing either blocky or thin splintered grains. After milling, the product is sieved to the appropriate sizes down to about 40 m (#400). The result is brown alumina containing typically 3% TiO2. Increased TiO2 content increases toughness while reducing hardness. Brown alumina has a Knoop hardness of 2090 and a medium friability.

Electrofused alumina is also made using low-soda Bayer process alumina that is more than 99% pure. The resulting alumina grain is one of the hardest, but also the most friable, of the alumina family providing a cool cutting action. This abrasive in a vitrified bond is, therefore, suitable for precision grinding.

White aluminum oxide is one of the most popular grades for micron-size abrasive. To produce micron sizes, alumina is ball-milled or vibro-milled after crushing and then traditionally separated into different sizes using an elutriation process. This consists of passing abrasive slurry and water through a series of vertical columns. The width of the columns is adjusted to produce a progressively slower vertical flow velocity from column to column. Heavier abrasive settles out in the faster flowing columns while lighter particles are carried over to the next. The process is effective down to about 5 m and is also used for micron sizing of SiC. Air classification has also been employed.

White 99% pure aluminum oxide, called mono-corundum, is obtained by sulfidation of bauxite, which outputs different sizes of isometric corundum grains without the need for crushing. The crystals are hard, sharp, and have better cleavage than other forms of aluminum oxides, which qualifies it for grinding hardened steels and other tough and ductile materials. Fine-grained aluminum oxide with a good self-sharpening effect is used for finishing hardened and high-speed steels, and for internal grinding.

Not surprisingly, since electrofusion technology has been available for the last one hundred years, many variations in the process exist both in terms of starting compositions and processing routes. For example:

Red-brown or gray regular alumina. Contains 9193% Al2O3 and has poor cleavage. This abrasive is used in resinoid and vitrified bonds and coated abrasives for rough grinding when the risk of rapid wheel wear is low.

Chrome addition. Semi-fine aloxite, pink with 0.5% chromium oxide (Cr2O3), and red with 15% Cr2O3, lies between common aloxite, having less than 95% Al2O3 and more than 2% TiO2, and fine aloxite, which has more than 95% Al2O3 and less than 2% TiO2. The pink grain is slightly harder than white alumina, while the addition of a small amount of TiO2 increases its toughness. The resultant product is a medium-sized grain available in elongated, or blocky but sharp, shapes. Ruby alumina has a higher chrome oxide content of 3% and is more friable than pink alumina. The grains are blocky, sharp edged, and cool cutting, making them popular for tool room and dry grinding of steels, e.g., ice skate sharpening. Vanadium oxide has also been used as an additive giving a distinctive green hue.

Zirconia addition. Aluminazirconia is obtained during the production process by adding 1040% ZrO2 to the alumina. There are at least three different aluminazirconia compositions used in grinding wheels: 75% Al2O3 and 25% ZrO2, 60% Al2O3 and 40% ZrO2, and finally, 65% Al2O3, 30% ZrO2, and 5% TiO2. The manufacture usually includes rapid solidification to produce a fine grain and tough structure. The resulting abrasives are fine grain, tough, highly ductile, and give excellent life in medium to heavy stock removal applications and grinding with high pressures, such as billet grinding in foundries.

Titania addition. Titaniaaloxite, containing 95% Al2O3 and approximately 3% Ti2O3, has better cutting ability and improved ductility than high-grade bauxite common alumina. It is recommended when large and variable mechanical loads are involved.

Single crystal white alumina. The grain growth is carefully controlled in a sulfide matrix and is separated by acid leaching without crushing. The grain shape is nodular which aids bond retention, avoiding the need for crushing and reducing mechanical defects from processing.

Post-fusion processing methods. This type of particle reduction method can greatly affect grain shape. Impact crushers such as hammer mills create a blocky shape while roll crushers cause splintering. It is possible, using electrostatic forces to separate sharp shapes from blocky grains, to provide grades of the same composition but with very different cutting actions.

The performance of the abrasive can also be altered by heat treatment, particularly for brown alumina. The grit is heated to 11001300 C (20152375 F), depending on the grit size, in order to anneal cracks and flaws created by the crushing process. This can enhance toughness by 2540%.

Finally, several coating processes exist to improve bonding of the grains in the grinding wheel. Red Fe2O3 is applied at high temperatures to increase the surface area for better bonding in resin cut-off wheels. Silane is applied for some resin bond wheel applications to repel coolant infiltration between the bond and abrasive grit, and thus protect the resin bond.

A limitation of electrofusion is that the resulting abrasive crystal structure is very large; an abrasive grain may consist of only one to three crystals. Consequently, when grain fracture occurs, the resulting particle loss may be a large proportion of the whole grain. This results in inefficient grit use. One way to avoid this is to dramatically reduce the crystal size.

The earliest grades of microcrystalline grits were produced as early as 1963 (Ueltz, 1963) by compacting a fine-grain bauxite slurry, granulating to the desired grit size, and sintering at 1500C (2735F). The grain shape and aspect ratio could be controlled by extruding the slurry.

One of the most significant developments since the invention of the Higgins furnace was the release in 1986, by the Norton Company, of seeded gel (SG) abrasive (Leitheiser and Sowman, 1982; Cottringer et al., 1986). This abrasive was a natural outcome of the wave of technology sweeping the ceramics industry at that time to develop high strength engineering ceramics using chemical precipitation methods. This class of abrasives is often termed ceramic. SG is produced by a chemical process. In a precursor of boehmite, MgO is first precipitated to create 50-m-sized aluminamagnesia spinel seed crystals. The resulting gel is dried, granulated to size, and sintered at 1200C (2200F). The resulting grains are composed of a single-phase -alumina structure with a crystalline size of about 0.2m. Defects from crushing are avoided; the resulting abrasive is unusually tough but self-sharpening because fracture now occurs at the micron level.

With all the latest technologies, it took significant time and application knowledge to understand how to apply SG. The abrasive was so tough that it had to be blended with regular fused abrasives at levels as low as 5% to avoid excessive grinding forces. Typical blends are now five SGs (50%), three SGs (30%), and one SG (10%). These blended abrasive grades can increase wheel life by up to a factor of 10 over regular fused abrasives, although manufacturing costs are higher.

In 1981, prior to the introduction of SG, the 3M Co. introduced a solgel abrasive material called Cubitron for use in coated abrasive fiber discs (Bange and Orf, 1998). This was a submicron chemically precipitated and sintered material but, unlike SG, had a multiphase composite structure that did not use seed grains to control crystalline size. The value of the material for grinding wheel applications was not recognized until after the introduction of SG. In the manufacture of Cubitron, alumina is co-precipitated with various modifiers such as magnesia, yttria, lanthana, and neodymia to control microstructural strength and surface morphology upon subsequent sintering. For example, one of the most popular materials, Cubitron 321, has a microstructure containing submicron platelet inclusions which act as reinforcements somewhat similar to a whisker-reinforced ceramic (Bange and Orf, 1998).

Direct comparison of the performance of SG and Cubitron is difficult because the grain is merely one component of the grinding wheel. SG is harder (21GPa) than Cubitron (19GPa). Experimental evidence suggests that wheels made from SG have longer life, but Cubitron is freer cutting. Cubitron is the preferred grain in some applications from a cost/performance viewpoint. Advanced grain types are prone to challenge from a well-engineered, i.e., shape selected, fused grain that is the product of a lower cost, mature technology. However, it is important to realize that the wheel cost is often insignificant compared to other grinding process costs in the total cost per part.

The SG grain shape can be controlled by extrusion. Norton has taken this concept to an extreme and in 1999 introduced TG2 (extruded SG) grain in a product called ALTOS. The TG2 grains have the appearance of rods with very long aspect ratios. The resulting packing characteristics of these shapes in a grinding wheel create a high strength, lightweight structure with porosity levels as high as 70% or even greater. The grains touch each other at only a few points, where a bond also concentrates in the same way as a spot weld. The product offers potential for higher stock removal rates and higher wheelspeeds due to the strength and density of the resulting wheel body (Klocke and Muckli, 2000).

Recycling of concrete involves several steps to generate usable RCA. Screening and sorting of demolished concrete from C&D debris is the first step of recycling process. Demolished concrete goes through different crushing processes to acquire desirable grading of recycled aggregate. Impact crusher, jaw crusher, cone crusher or sometimes manual crushing by hammer are preferred during primary and secondary crushing stage of parent concrete to produce RA. Based on the available literature step by step flowchart for recycling of aggregate is represented in Fig. 1. Some researchers have also developed methods like autogenous cleaning process [46], pre-soaking treatment in water [47], chemical treatment, thermal treatment [48], microwave heating method [49] and mechanical grinding method for removing adhered mortar to obtain high quality of RA. Depending upon the amount of attached mortar, recycled aggregate has been classified into different categories as shown in Fig. 2.

Upon arrival at the recycling plant, CDW may either enter directly into the processing operation or need to be broken down to obtain materials with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimize the degree of contamination.

The three types of crushers most used for crushing CDW are jaw, impact, and gyratory crushers (Fig.8). A jaw crusher consists of two plates fixed at an angle (Fig.8a); one plate remains stationary while the other oscillates back and forth relative to it, crushing the material passing between them. This crusher can withstand large pieces of reinforced concrete, which would probably cause other types of crushers to break down. Therefore, the material is initially reduced in jaw crushers before going through other types. The particle size reduction depends on the maximum and minimum size of the gap at the plates. Jaw crushers were found to produce RA with the most suitable grain-size distribution for concrete production (Molin etal., 2004).

An impact crusher breaks CDW by striking them with a high speed rotating impact, which imparts a shearing force on the debris (Fig.8b). Materials fall onto the rotor and are caught by teeth or hard steel blades fastened to the rotor, which hurl them against the breaker plate, smashing them to smaller-sized particles. Impact crushers provide better grain-size distribution of RA for road construction purposes and are less sensitive to material that cannot be crushed (i.e. steel reinforcement).

Gyratory crushers, which work on the same principle as cone crushers (Fig.8c), exhibit a gyratory motion driven by an eccentric wheel and will not accept materials with large particle sizes as they are likely to become jammed. However, gyratory and cone crushers have advantages such as relatively low energy consumption, reasonable amount of control over particle size and production of low amount of fine particles.

Generally, jaw and impact crushers have a large reduction factor, defined as the relationship between the input's particle size and that of the output. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike, and thus may generate twice the amount of fines for the same maximum size of particle (O'Mahony, 1990).

In order to produce RA with predictable grading curve, it is better to process debris in two crushing stages, at least. It may be possible to consider a tertiary crushing stage and further, which would undoubtedly produce better quality coarse RA (i.e. less adhered mortar and with a rounder shape). However, concrete produced with RA subjected to a tertiary crushing stage may show only slightly better performance than that made with RA from a secondary crushing stage (Gokce etal., 2011; Nagataki etal., 2004). Furthermore, more crushing stages would yield products with decreasing particle sizes, which contradicts the mainstream use of RA (i.e. coarser RA fractions are preferred, regardless of the application). These factors should be taken into account when producing RA as, from an economical and environmental point of view, it means that relatively good quality materials can be produced with lower energy consumption and with a higher proportion of coarse aggregates, if the number of crushing stages is prudently reduced.

mobile impact crushers | rubble master

Mobile impact crushers are used to recycle concrete and asphalt and process natural rock. They are easy to move on and between job-sites, which allows operators to crush on smaller job-sites. Best of all they often come with an on-board screen attachment to produce spec products eliminating the need for additional screening equipment on-site.

Machine configuration can be adjusted to produce a multitude of finished products. The aggregate quality is far superior than with other type crushers because of its gradation and cuboid material shape.

RUBBLE MASTER has been the market leader for mobile Compact Crushers in the USA and Canada for 20 years. RUBBLE MASTER mobile crushers deliver the best performance in their class without sacrificing mobility. Manoeuvrability, transportability, easy & safe to operate thats our main focus!

RUBBLE MASTER mobile impact crushers use a proven and powerful diesel-electric drivetrain. Contrary to many traditional crusher manufacturers RUBBLE MASTER has been using this highly efficient drivetrain since our beginning in 1991 because of its many benefits over the lifetime of a machine.

worldwide impact mobile crushers industry to 2026 - featuring terex, komatsu and eagle crusher among others

DUBLIN, July 05, 2021--(BUSINESS WIRE)--The "Impact Mobile Crushers Global Market Insights 2021, Analysis and Forecast to 2026, by Manufacturers, Regions, Technology, Application, Product Type" report has been added to ResearchAndMarkets.com's offering.

This report describes the global market size of Impact Mobile Crushers from 2016 to 2020 and its CAGR from 2016 to 2020, and also forecasts its market size to the end of 2026 and its CAGR from 2021 to 2026.

ResearchAndMarkets.comLaura Wood, Senior Press [email protected] For E.S.T Office Hours Call 1-917-300-0470For U.S./CAN Toll Free Call 1-800-526-8630For GMT Office Hours Call +353-1-416-8900

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Amazon has poached a long-serving senior Tesco executive to run its bricks-and-mortar retail operation, in the latest escalation of its attack on the high street. The departure of Tony Hoggett was announced on Friday by chief executive Ken Murphy. Mr Hoggett joined Tesco in 1990, became group chief operating officer in 2018 and was promoted to a newly-created role of chief strategy and innovation officer in April. At Amazon he will be senior vice president of physical stores, reporting to Dave C

Oil futures end sharply higher Friday, extending a bounce from the previous session triggered by a sharp fall in U.S. crude and gasoline inventories, but fail to erase a weekly loss as a spat over OPEC production levels remains unresolved.

(Bloomberg) -- The surging, post-pandemic U.S. economy is driving an unexpected boom in coal, the latest sign that demand for the dirtiest fossil fuel remains resilient.American coal production this year will swell 15% to meet stronger demand for electricity at home and abroad, according to the U.S. Energy Departments July outlook. That would be the most since at least 1990 and nearly double the 8% increase projected in May, when the economic rebound was still in earlier stages of recovery.The

(Bloomberg) -- Africas biggest tomato processing plant is barely managing to operate profitably, six years after the factory began production because it cant get adequate berries to crush.The 1,200-ton a day plant, owned by Sani Dangote, the immediate younger brother to Aliko Dangote, Africas richest man, is producing at 20% of capacity because farmers dont have enough resources to boost acreage. The factory was meant to reverse Nigerias dependence on imports of tomato paste from China and

Philip Morris International (PM) has agreed to acquire Vectura Group, an innovative inhaled drug delivery solutions provider, in an all-cash deal of approximately $1.2 billion. The deal is expected to close in the second half of 2021, subject to shareholders vote and regulatory approvals. Based in New York, Philip Morris manufactures and sells cigarettes, tobacco, nicotine-containing products, smoke-free products and associated electronic devices and accessories in over 180 countries. The trans

Blue Apron (NYSE: APRN) benefited from the increase in people eating at home during the pandemic, as services that delivered food to your door became almost a necessity and less of a luxury. The meal-kit delivery specialist saw its customer count rise, its orders per customer increase, and the average revenue per customer it generated jump. Now, meal-kit sales growth is set to dramatically decelerate.