advanced vibrating screen for sale

black beauty screed hd vibrating screed | concrete tool supply

Black Beauty HD Vibrating Screed with 1.5 HP Honda GX-35 4-cycle engine.Superior performance in low slump concrete. The Black Beauty with 1.5 HP Honda 4-cycle gas engine will screed 2 to 9 slump and will not sink or ride over the concrete. Screed can be utilized effectively with up to a 16 Equilateral Screed Bar.

Adjustable T-bar provides maximum control to maintain a perfectly level bar. Fully enclosed eccentric weight will not allow concrete to penetrate bearing housing.Heavy duty transmission boasts a large clutch drum and structural superiority.Suspension design improves vibration control to the operator and drive system.[PRICE INCLUDES SHIPPING within the Continental United States!!]For international shipping quotes contact: [email protected]

industrial separating screens & replacement screens | custom advanced

Custom Advanced specializes in industrial replacement screens and separating screens for many applications. We can service companies in need of Rotex-style, SWECO-style or Great Western-Style separator screens. Whether you have a circular, rectangular or box style screen, Custom Advanced can take your measurements and requirements to make the replacement screen and all needed accessories. Custom Advanced is also capable of replacing entire screening units.

Circular Separators (SWECO-Style) Items to fit equipment manufactured by Sweco, & Midwestern Industries just name a few. Rectangular Separators (ROTEX-Style) We offer a full line of replacement parts and accessories to handle your Rotex or Sprout rectangular gyratory separator needs. Box Separators (Great Western-Style) We offer screens & accessories to fit equipment manufactured by Great Western, Buehler & more. Additional Screen Types We supply a complete line of cylindrical/rotary screens and industrial hook screens. We can also create custom screens for your specific applications. Woven Wire Cloth We stock a wide variety of wire mesh. We know downtime is always an issue and we make it a point to provide quick turnaround. Test Sieves It is our goal to assist you with your application needs and to better serve our customers we now offer a full line test sieves. Refurbished Screens & Separators If you don't want to pay list price for a new screener, contact Custom Advanced to inquire about our refurbished screens. Replacement Parts & Motors We are a stocking distributor for a variety of replacement screening accessories and screener parts

vibro screen, ultrasonic vibrating screen, vibrating filter manufacturers, suppliers - navector

Navector has been a trusted manufacturer & supplier in advanced screening machines & solutions since 2005 founded in Shanghai,including full technical, mechanical and laboratory support for advanced screening work through a large scale precision separating plant. Navectors screens and sifters are built to the highest standards of quality and precision which can process grading, classifying, filtering,or dewatering works.

vibrating screen,vibrating screen machine,sand screening machine - hxjq mining machine manufacturer

The vibrating screen is a kind of sieving equipment of international advanced level, developed by our company on the basis of carrying on the advantages of traditional screens and absorbing the outstanding technology from abroad. It is widely used for grading and screening materials in the following fields: minerals, quarry, building materials, water conservancy and hydro power, transportation, chemical industry, smelting and so on.

Sand screening machineis chiefly used in the stone production line or gravel production line for separating the large stone and small one. In the artificial sand production process, it is able to be used for separating the qualified sand and unqualified one. According to the different size of sieve pore, the product granularity can be adjusted.

The body of Vibrating Screen machineconsists of base frame and supporting structure. The base frame is welded using heavy channels and angles and special care has been taken during design. Screen supporting structure and Screen are made from wear resistant special Coil Steels.

Sand screening machine is single-axis circular-movement inertial vibrating screen, whose working depends on inertial motor and inertial strength produced by eccentric plate. Because of the vibration of screen box, the materials are threw out, so that materials of certain size go through the screen mesh, and the screening aim is realized.

Since the magnetic exciter is installed on the gravity center of screen box, the two long elliptical axises form a shape like a Chinese character, and the upper of long elliptical axis at inlet end is in the same direction with the outlet, which favors the spread of materials which are at the screen box. However, the upper of long elliptical axis at outlet end is opposite to the direction of the outlet, which can reduce the movement speed of materials, and help the difficult-screened materials go through the screen mesh. What's more, the effective area of sand screening machine is increased because of the elliptical screen surface; as a result, the processing capacity is promoted.

large vibrating screen design & maintenance

Large vibrating screens represent a unique challenge for Manufacturers, Plant Designers, and Plant Operators. The inherent mode of operation for vibrating screens is self-destructive. More often than Manufacturers admit, Designers plan for, or Operators staff for, a vibrating screen succeeds and self-destructs. This is a problem. It can magnify with larger vibrating screens.

Vibrating screen structures are subjected to nearly 250 million fatigue cycles in an operating year. The design and construction of these structures are critical in achieving reliable screen performance. Regardless of screen size, the maxims for design continue to be:

A screen design meeting these criteria yields the lowest cost per ton performance. Large screen technology is evolving more scientifically than did the development of small screen technology. As vibrating screen designs increase beyond six foot widths, reliable designs result from sophisticated engineering methods and manufacturing techniques. In addition, large screen technology amplifies the direct relationship of production cost and reliability.

Static Stresses: At rest, motionless, a vibrating screen structure is subjected to the force of gravity, at a minimum. A vibrating screen must first support its own weight. Other motionless stresses are present in the structure as a result of cutting, bending, welding, burning, drilling, assembly, tolerancing, and manufacturing variances. Quite simply, these stresses exist whether or not the screen is operating.

The second step in FEA can be considered the construction of structural loads. These include the imposition of static, dynamic, material, and fatigue conditions on the mathematical model, which approximates the load conditions. An example would be to describe a structural misalignment and the forces input co bolt up this structure through the misalignment.

Reliable vibrating screen designs are dependent upon the proper marriage of a firms manufacturing capabilities and the requirements of the design. It is not reasonable to expect that closely toleranced airframes will be successfully produced in a metal-bending job shop. As design safety factors narrow on larger screens, manufacturing techniques evolve which minimize production variables. Design tolerancing is necessarily compatible with manufacturing accuracy.

Residual metal working stress is the left-over stress in metal when melted or formed into a shape. It is a result of a materials resistance to change shape. Stress concentration sites are more commonly termed notches or stress risers. These areas are not stresses, but sharp geometric transitions or reversals in a structure. Stress loads focus their effect on a structure at these sites. Experience has proven that the methods and procedures of structural assembly can result in preloading screen bodies with excessive static stresses. The scope of this discussion is limited to the discussion of welding, forming, and bolting as they relate to conditions described above.

The side plate of a vibrating screen literally bristles with fasteners. Multi-shift production facilities, as well as maintenance crews, quickly realize the merits of this system. Unlike conventional threaded fasteners, swaged bolts exhibit a distinctly different physical appearance when installed versus loosely installed. The guess-work and wasted efforts to repeatedly insure all bolts are properly torqued are eliminated. A second-shift assembler need not consult with his first-shift counter-part regarding loose or torqued bolts . Sound maintenance practice precludes the reuse of major structural fasteners. A huck-type fastener is destroyed during removal. Normal threaded fasteners depend on proper installation torques to achieve the optimum clamping force. Registered torque wrench values may not be indicative of the true values due to the effects of thread lubrication and frictional force of the fastener face on the bolting surface. Swaged fasteners are installed strictly in tension at an optimum preset tensile load. The positive clamping values are reliably consistent. Installation error is minimal. Replaceable, non-structural components may be installed with conventional fasteners.

Anticipated operating and maintenance costs over the productive life of a processing plant design significantly influence the go or no-go decision to build the plant. Large vibrating screens can both add to and reduce the magnitude of these costs. Plant designers must examine the serviceability of these large units. This includes the complexity of installation, start-up, routine maintenance, major repairs, and operating instrumentation. In assessing these costs, the likely condition exists somewhere between the extreme of a screen leaping momentarily out of position long enough to repair itself and swarms of mechanics covering the unit like bees on honey over several production-robbing shifts.

As larger vibrating screens are used, their size will exceed cost-effective shipping limits fully assembled. Screen manufacturers will join the ranks of other major equipment suppliers in on-site assembly and testing of these units. The incremental costs associated with these efforts must be considered in evaluating the plant construction and start-up costs.

The use of larger vibrating screens results in the dependence of a larger percentage of total plant production on each unit. It is imperative that plant operators maximize the production availability of large screens. This effort is enhanced by carefully planned operating and maintenance procedures. Since volumes have been published on efficient and successful preventative maintenance programs, this discussion will not deal with that topic. There are several suggestions that can be made to help potential big screen users better position themselves to react to the service requirements of these units.

As trite as it sounds, talk to potential screen suppliers specifically about the service requirements of their screens. Determine how recently a manufacturer has entered the wide screen market. Was this entry preceded by years of research and testing? There are generally two major shortfalls in a hastily planned new product introduction. Invariably, replacement parts availability is a problem. Second is the frustrating response to a frantic maintenance question, The only guy who knows that unit is on an island in Indonesia. Solidly planned programs will have organizational depth.

The labor pains, which have normally accompanied the birth of new vibrating screen designs, have been no less severe with the gradual introduction of large, high-capacity screens. More difficulty would have been encountered without the aid of advanced engineering and manufacturing techniques.

The development of vibrating screens over the last century has seen many variations to suit the exacting requirements of industry. Indeed, as each year passes, industry has presented the challenge to screen manufacturers of supplying larger machines than those used in the past and the question is often posed what is the maximum limit?

Innovations introduced such as bouncing ball decks, heated decks, tri-sloped and bi-sloped decks and pool washing features have all sought to achieve improved anti-blinding results and improved capacity for a given screening efficiency. Although the benefits achieved by the inclusion of these features were shown in some cases to be beneficial, the application of good throw in conjunction with the required G force in the operation of the screen has proven in screen performance today, to provide maximum screening efficiency and capacity. The importance of good throw is often overlooked and should be the first consideration when wishing to maximize screen capacity.

For a straight line motion screen the throw is the distance between the extremities of motion. For a circular motion screen, the throw is measured across the diameter of motion but if the screen has an oval motion, throw is measured by taking the mean of the major and minor axes.

The throw which is specified for a particular application is determined on a screen body eccentric weight basis and normally does not take into allowance the load of material which will be handled by the vibrating screen.

Therefore it is imperative that the live weight of the vibrating screen is sufficient to maintain, within reason, the throw which has been originally specified so as to effectively handle the loads being fed to the screen.

The above comments relate essentially to a dry screening application but in wet applications where metalliferous pulp is received on the screen, the benefits of a large throw in terms of increased screen capacity have been demonstrated in commercial practice. The ideal machine for receiving pulp for wet screening or desliming, dewatering etc. is a horizontal screen. Among other reasons, the horizontal screen provides the benefit of long retention time for handling the pulp. Also the straight line motion provided with good throw imparts a positive breaking of surface tension present between the pulp and the screen deck within the apertures.

The inclusion of large vibrating screens in the design of new plants by planning engineers and metallurgists responsible for such work, particularly where large associated equipment is available, is inevitable and is in fact a progression of size we have witnessed over the years.

We should remind ourselves that size progression could not proceed without the accumulation of experience in screen body design, in application knowledge, improved quality of manufacture and refinements of mechanism design with regard to achieving improved bearing life which allows the use of a good G force.

As referenced previously G force and throw are interrelated and therefore with the good G forces available today in the modern vibrating screens, the way is clear to taking full opportunity of increasing throw to handle the high tonnages which can be expected and are currently experienced on large vibrating screens.

Where abrasion of the screen deck surface is severe as in most metalliferous mining applications, and the separation sizes are in the order of mm to 50 mm aperture sizes, polyurethane screen panels are now in common use because of their excellent resistance to wear. The trend in the use of polyurethane panels in the metalliferous mining industry is quite definite and in fact in the major mining operations in Australia at least, the use of polyurethane screening panels is firmly established.

With reference to metalliferous tailings the need for dewatering presents a new dimension. The amount of tailings produced is very much greater since some 98-99% of mined ore is rejected in tailings form compared with varying amount of 3 to 5% rejected in a coal washing operation. Furthermore with dewatering of metalliferous tailings, using equipment as mostly used in coal washing would present maintenance problems because of the more abrasive nature of the tailings and therefore for that reason it is customary to discharge all metalliferous tailings slurry to a dam.

The screen-cyclone system relies on the blinding tendency of the screen deck apertures for its success, using either stainless steel wedgewire or polyurethane deck panels in conjunction with the use of cross dams spaced every 120 cm along the deck surface. When considering the screen-cyclone system it is important to appreciate that the screen function is not one of separation at a given aperture size but bleeding of water through the restricted deck apertures caused by the semi blinding condition. That is, if the deck apertures were to remain completely free of blinding, which is not the case, practically all of the tailings would pass through the apertures in the first pass and would not allow the system to function.

The underflow from the primary cyclones should be deposited on the horizontal section of the screen deck at the feed end where the maximum of water should be removed with the assistance of an additional section of wedgewire located on a 45 inclined back plate to remove free water that has accumulated on top of the bed of slurry most solids having stratified to the deck surface. The underflow should be evenly distributed across the width of the screen at minimum velocity, so as to allow the full benefit of stratification provided by the screen.

The actual results from the initial test run taken on the pilot plant installed at Philex Mining Corporation, Philippines in March, 1980 are as follows using a gravitated flow of tailing slurry from the concentrator.

The problems involved in installing, maintaining, and operating large vibrating screens have been summarized and discussed, based on a survey of current use of such screens in selected North American mineral processing applications. Practical, effective solutions for the more serious common problems are described, along with some recommendations on design practice for specifying, selecting, and installing large screens.

In order to properly assess the information gathered through the survey questionnaire, the results pertaining to each group of applications will be presented and discussed separately in the following section. The small number of installations actually surveyed makes any rigorous statistical interpretation of the data difficult, therefore the information is presented in a generalized fashion. Notwithstanding the small sample of operations as compared to the total number of such large screen installations around the world, the results are felt to fairly represent typical operating, maintenance and installation problems and practices in the sectors of the mineral processing industry the survey covered.

The results reported in this section refer to inclined vibrating screens used in conventional crushing and screening plants. Four operations replied to the survey questionnaire, all four are medium sized producers, primarily of copper concentrate, some with significant by-product production of Mo or Ag. Daily throughputs range from 5,300 tons to 38,000 tons.

The major problem areas reported by the users of these screens were bearing failure and replacement and side plate cracking. The minor problems reported were loose bolts, seals and routine wear items such as cloth and liner changes. Reported availability of the screens ranged from 92-96%. At one operation, the crushing and screening plant is oversized and operates only one shift per day, therefore downtime for maintenance is readily available and actual availability was not reported.

The maintenance of large vibrating screens in conventional crushing applications would normally consist of the regular replacement of wear parts, such as liners and screen cloths, as well as regular lubrication of the bearings and other moving parts as recommended by the manufacturer of the particular screens in use.

The operations with large horizontal vibrating screen installations replying to the survey questionnaire were Syncrude Canada Ltd., Climax Molybdenun (Henderson Operations), Quintana Minerals and Fording Coal Ltd. As previously noted, the screen applications at these operations are all basically very similar, involving wet screening of relatively large tonnages of slurry feed.

The major problem areas with these screen installations once again include bearing failure and side plate cracking in three out of the four installations. The fourth installation, Henderson, reported major problems with the mounting springs and feed lip both of which have presently been rectified to the point where only minimal unscheduled downtime occurs.

The major problems associated with the horizontal screens were with bearings and side plate cracking, and were evident soon after commissioning. Major efforts were undertaken at all the operations to correct the serious problems.

Large vibrating screens are normally selected for applications where multiple screens would be more costly to purchase and install. There have been a considerable number of large screen installations in a variety of mineral processing applications, therefore a considerable amount of operating data with respect to the screen components and performance has been gathered. From the plant designers viewpoint the design of a screen installation should consider the following areas:

The design of a large vibrating screen installation requires close attention to not only the screen itself, but also to the ancillary structures, maintenance procedures and personnel comfort and protection.

Large vibrating screens represent a considerable investment in equipment alone. In addition the loss due to interrupted production should one of these units go out of service can be economically much more severe. As plant tonnages have risen and larger equipment has been utilized in single trains or a small number of multiple trains, the risk of having a single large screen down for any length of time has become too great to ignore.

trommel screeners for sale | komplet

provides plants and machines for crushing and screening for recycling rubble and other construction material directly in site. We are leader in the world for the construction of treatment systems and waste recycling equipment.

circular vibrating screen | vibrating screen for sale - agico cement

Circular vibrating screen is a multi-layer vibrating screen for circular motion. The circular vibrating screen adopts a cylindrical eccentric shaft exciter and an eccentric block to adjust the amplitude. The material sieve has a long flowing line and many screening specifications. It has features of reliable structure, strong excitation force, high screening efficiency, low vibration noise, strong durability, and maintenance, convenient and safe to use. The circular vibrating screen is widely used in product classification of mining, building materials, transportation, energy, chemical, and other industries.

It is mainly composed of a screen box, vibrator, suspension (or support) device, and motor. The motor drives the main shaft of the exciter to rotate through a triangle belt. Due to the centrifugal inertial force of the unbalanced weight on the exciter, the screen box is vibrated. By varying the eccentricity of the exciter, different amplitudes can be obtained.

As a kind of vibrating screening machine, circular vibrating screen is mainly used to generate radial centrifugal inertia force (exciting force) by unbalanced heavy wheel rotation of the vibrator, which drives the screen box and makes the screen vibrate. The trajectory of the screen frame is ellipse. The material on the sieve is thrown up by the force of the upward movement of the sieve, and after a certain distance, it falls back to the sieve surface. And repeat the cycle again, the screening is completed during the movement from the feeding end to the discharging end. The amplitude of the vibrating screen can be adjusted by changing the weight and position of the counterweight.

linear vibrating screen | vibrating screen machine - agico cement

Linear vibrating screen is a new type of vibrating screen machine, widely used in mining, coal, smelting, building materials, refractory materials, light industry, chemical industry, and other industries. The linear vibrating screen can also screen and classify powdery and granular materials, and is widely used in plastics, abrasives, medicine, grain carbon, fertilizer and other industries.

The linear vibrating screen uses the principle of self-synchronized vibration, using a vibration motor as the vibration source, a rubber spring as a shock absorber and a highly wear-resistant material as a sieve plate, and eccentric compression sealing and other advanced technologies. It has advantages of long life, low noise, and high screening efficiency. Apply for sieving ore, natural ore, coke and other powdery materials.

Motor pedestal: Install the vibration motor, the connecting screws must be tightened before use, especially three days before the new sieve machine is tried out. It must be tightened repeatedly to avoid accidents caused by loosening.

Bracket: It consists of four pillars and two-channel steels, supporting the screen box. The pillars must be perpendicular to the ground during installation, and the channel steels under the two pillars should be parallel to each other.

The linear vibrating screen uses vibration motor excitation as the vibration source, so that the material is thrown on the screen and moves forward linearly. The material enters the feed port of the screening machine evenly from the feeder, and several The oversize and undersize products of specifications produced through the multi-layer screen are discharged from their respective outlets. It is more suitable for assembly line operations.

The linear vibrating screen uses the counter weights installed at the upper and lower ends of the motor shaft to convert the rotary motion into horizontal, vertical, and inclined three-dimensional motion, and then transmits this motion to the screen surface. The change of the phase angle of the upper and lower counter weights can change the direction of material travel.

The linear vibrating screen is driven by dual vibration motors. When the two vibration motors are synchronized and counter-rotated, the excitation force generated by the eccentric block cancels each other in the direction parallel to the motor axis, and stacks in the direction perpendicular to the motor axis. As a result, the trajectory of the screen machine is a straight line. The two motor shafts have an inclination angle with respect to the screen surface. Under the combined action of the exciting force and the gravity of the material, the material is thrown up and jumped forward in a linear motion on the screen surface, so as to achieve the purpose of screening and grading the material. It can be used for automatic operation in the assembly line. It has the characteristics of low energy consumption, high efficiency, simple structure, easy maintenance, and no dust spillage in the fully enclosed structure. The sieve mesh number is up to 400 meshes, and 7 kinds of materials with different particle sizes can be sieved.

best vibro sifter machine | sieving machine | eversun,sieving machine

With 30 years of experience and professional expertise, EVERSUN vibro sifter machine is proundly created for handling fine materials. It can efficiently screen foreign matters, filter impurities, and grade materials to ensure high quality products. Compared to conventional vibrating screeners, EVERSUN vibro sifter machine are more efficient and more accurate. Each machine can achieve six levels of sieving with more precision.

EVERSUN vibro sifter machine allow users to adjust the phase angle of the upper and lower ends on the motor, which can change the vibration trace of the material on the screen surface. Through that way, the throughput and accuracy can be kept into one perfect balance .

EVERSUN vibro sifter machine are available in a variety of models to suit all industries and are suitable for all production lines. EVERSUN group can also provide customized machines and solutions for all clients based on their requirements.

Our Unique ServiceFor all our vibro sifter machines, our factory will provide: 1. Detailed pre-sale sieving suggestion. 2. Customization service. 3. Online technical support. 4. Video inspection of machine before delivery 5. Video installation of machine 6. Reliable after sale service. 7. 18 months quality guarantee and life time technical assistance. 8. We can send engineeres to clients company for assistance. 9. All the assistance needed from clients.

Vibro Sifter or Sifter Machine to Screen Impurities and Foreign Material from Main Product Looking for the latest models of high-grade and durable Vibro Sifter or need a new range of Sifter machine that can easily handle the fine materials or separate them from the main particles or powder form? You will get the latest models of sifter machines offered by the name of Eversun Vibro Sifter Machines . We have advanced machines that are easy to use and can efficiently screen foreign materials and provide you something more like filter impurities and grade materials to ensure high quality products. They are the most vital, more efficient and more accurate machines that are capable enough to achieve six levels of sieving with more precision. They are commonly required for pharmaceutical industry, food processing, chemical and different other industry verticals. Easy to Use and Advanced Sifter Machines One of the plus points of using such machines is that you can adjust the phase angle mainly for both upper and lower ends on the motor. Adjusting the phase helps in change the vibration trace of the material on the screen surface. You can keep accuracy in perfect balance. Depending on your requirement, you can choose the right models of machines. We also offer you customized machines that are specifically designed as per your requirement and type of industry that you want to serve in better way. Choose an Exclusive Range of Vibro Sifter Depending on your choice and requirement and type of industry, which you need for sieving solutions, you can choose the right range of Vibro Sifter or sifter machine that is easily available and delivered directly to your doorstep as per your requirement. Eversun Machinery has been offering you a broad range of high-grade and durable machines that are offered with a user guide and maintenance support. We ensure your selected sifter machine will be delivered on time and in secure way right to your doorstep. Vibro sifter and sifter machines offered by us are second to none and c

screens for woody biomass | biomass handling

Because of the wide variation in material characteristics, selecting the appropriate screen for woody biomass is not as straight forward as it is for other materials. This article is intended to provide general screen selection information based on the authors experience as to what types of screens work best with different forms of woody biomass.

Ive said this many times before and I will repeat it once again. Biomass is not an easy material to handle. It appears in a myriad of species, forms and sizes; it knits together, doesnt flow well, consolidates and packs easily. It can have a wide range of moisture contents, basic and bulk densities and calorific values. It will freeze; is very dusty, catches fire easily and is self-combustible. It can contain all manner of contaminants. On the other hand, wood pellets are uniform in size and moisture content, are very free flowing, but are quite fragile and easily degrade and require special handling.

All of the particular material characteristics of the specific woody biomass being processed must be taken into consideration when choosing an appropriate screen. Also, one must consider the conditions under which the screen will be operating; the quantity of material to be processed, the location, temperature, moisture, and operating hours will all have an impact on the screen effectiveness and must be considered when selecting a screen. Additionally, the intent of the screening function must be considered. What is the purpose of the screen; is it to scalp off gross oversized material, remove fines, screen for thickness, or separate into several classifications for other process considerations?

There are a lot of screen types available and most of them have been tried at one time or another on woody biomass. One type of screen may work well in one circumstance or location but not be effective in another. There are some basic types that have proven to work well if properly applied.

The disc type of screen consists of a set of rotating, parallel shafts mounted in a steel frame and on which are mounted profiled, steel discs. The discs on one shaft interface with the discs on the next shaft. The spacing between the shafts, called the slot length (SL), and the space between interlaced discs, called the interface opening (IFO) can be selected to provide the desired screen open area through which material can pass. Material is fed onto the end of the screen, and is carried along the tops of the rotating discs. The profiled discs jostle the material; particles smaller than the screen opening fall through between the discs and shafts and particles larger than the screen openings are carried over the end of the disc screen. The width, length, number of shaft assemblies and the disc spacings are selected based on the quantity of material to be handled and on the target size of the material being accepted or rejected. Disc screens can have multiple screen opening sizes along the length, in order to do multiple classifications. The disc profiles can be different depending upon the material being handled. Discs should be fabricated from an abrasion resistant steel. Shaft rotational speeds are quite low, 30-40 rpm.

Disc screens are often equipped with an automatic, anti-jam system. Should load sensors or speed switches sense that the screen is jammed or is slowing down, the drive will stop, reverse for a few seconds, then re-start in the forward direction. If still jammed, this sequence will be repeated 2-4 times and if still jammed, then the drive will shut down, and a person will have to inspect the machine and un-jam it, if required.

Most disc screens are used as `scalping screens, where the prime function is to remove gross over-sized pieces of material. They are usually the very first screen in a conveying / screening system. Another function for disc screens is to be used as an `unloading screen before a `hog or grinder, the intent being to remove particles smaller than the hogged material target size, thereby bypassing and unloading the hog.

If used for handling wastewood or `hog fuel, disc screens can be exposed to a considerable amount of contaminants including: sand, grit, dirt, rocks, snow, ice, metal and frozen lumps. So, they must be of heavy duty construction with abrasion resistant steel discs.

A unique style of disc screen is the star screen, which utilizes polyurethane, star shaped discs on shafts that rotate at a much higher speed than a conventional steel disc screen and are intended to break apart and separate light, stringy materials.

There are a lot of disc screen manufacturers; some have great disc screens but unfortunately many manufacturers have not mastered the subtleties of disc screen design. The best disc screens are manufactured by: Jeffrey-Rader, Acrowood, and West Salem Machinery, among others.

The gyratory screen consists of a box frame with one or more screen plates mounted one above the other. The inclined box frame is suspended from articulated shaft hangers that permit the screen frame to oscillate in a horizontal plane when the counterweighted drive is running.

Material is fed onto the upper end of the sloped screen; the oscillating motion causes the material to slide down the sloped surface of the screen plates, with the under-sized material falling through the screen holes and the over-sized material being retained on top and discharging over the end of the screen.

Gyratory screens can have multiple screen plate `decks where material falls through one screen onto a second screen with smaller openings. A typical sawmill wood chip screen would have a top screen with 45mm round holes (RH), possibly a middle 13-16 mm RH screen, and a bottom 3-5 mm screen. `Gross overs passing over the end of the top screen would be directed to a re-chipper. The middle screen is usually intended to simply unload the bottom screen to permit more effective fines screening. `Accepts retained on the middle and bottom screens would be diverted to the accept chip stream. `Fines rejected through the bottom screen plate would be directed to the fines stream and used either for fuel or in a secondary process such as panelboard manufacturing.

Gyratory screens have a large capacity per unit area as compared to other types of screens and generally use less power. The oscillation frequency at approximately 200 300 rpm is much lower, the stroke at 1.5 2 is much greater and the screen slope at 5 10 is much lower than that of vibrating screens. Support structures need to be `tuned to accommodate the horizontal frequency, particularly when supporting multiple screens. The gyratory action is much easier to accommodate from a structural perspective than the high speed vibrations common to vibratory screens.

Because of the sliding motion of the material as it moves down the surface of the screen plates, gyratory screens handle the material quite gently as compared to other styles of screens. However, because of their gentleness, gyratory screens are susceptible to `blinding when handling snow-laden wood chips or chips with high pitch content. To compensate, gyratory screens can be equipped with `ball-decks under the screen plate. The bouncing balls will bang against the underside of the screen plate and knock the blinding material off the screen. However, the balls will wear away, so the downstream process must be capable of rejecting or handling the small particles of ball material.

Gyratory screens are used in many industries, but are the most common screen in sawmills, planermills, panelboard plants, and pulp and paper mills. They are particularly good for handling chips, sawdust, shavings, wood strands or wood pellets.

The vibrating screen consists of an inclined box frame fitted with one or more woven wire mesh screens mounted one above the other. The screen frame is usually supported on coil springs and is driven by a counterweighted electric motor, producing vertical oscillations. The vibration frequency at 800 1000 rpm is significantly higher, the stroke much shorter at 1/4 3/8 and the decline angle at 15 20 is much steeper than that of gyratory screens. Support structures need to be `tuned to accommodate the vertical vibrations.

Oscillating in the vertical plane, vibrating screens accelerate the material particles until they become airborne and then fall further down the inclined screen mesh. Material smaller than the screen mesh passes through the screen, with larger material being retained on top of the screen and discharging over the end of the screen. Vibrating screens are useful where aggressive screening action is required, such as to loosen small frozen lumps of sawdust.

Flip-Flow screens consist of multiple, perforated, flexible, polyurethane screen panels that are mounted on two steel frames that move contrary to each other. As they move, the screen panels are alternately stretched and relaxed. As they are stretched, they impart very high, vertical `g-forces to the material on the screen, launching it into the air. The screen declination varies depending upon the material being handled, but is approximately 20 for wood chips. As with other screens, Flip-Flow screens can have multiple screen decks for different size classifications.

Material is fed onto the upper end of the sloped screen and the alternating stretching and relaxing of the screen panels causes the airborne material to bounce down the screen. Particles smaller than the screen openings fall through the screen panels, while larger particles are retained on the top of the screen panels pass over the end of the screen.

Due to the high `g-forces imparted to the particles, Flip-flow screens are very good at processing cohesive materials that are frozen or stuck together. And, as the polyurethane panels are stretched and relaxed, the openings are also stretched and relaxed, resulting in a screen that never blinds.

Flip-flow screens require much more power to drive than other machines of comparable capacity. They are very heavy duty and are costly. It is paramount that large sharp objects be kept out of the feed to the Flip-Flow screen in order to avoid damaging the polyurethane panels. Although the screen is mounted on isolation pads, the large mass and high vibration forces quite often necessitate separate support structures that go completely down to grade, so as to not impart unsuitable vibrations to the surrounding equipment or building.

Flip-Flow screens work especially well as secondary / tertiary chip screens in pulp and paper mills in extreme northern climates that have a lot of snow. The best Flip-Flow screen is the Liwell screen manufactured by Hein, Lehmann.

fastened. The screen drum lies on its side at a slight angle (2 8) and has fixed steel tires that rotate on trunnion wheels. Material is fed into the upper end of the drum and as the drum rotates, the material tends to ride up the side of the drum until it falls back to the bottom. Agitated particles smaller than the screen mesh opening fall through the screen, while larger particles are carried along the bottom internal surface of the screen drum and eventually are discharged out the end of the drum. Trommel screens can be equipped with multiple sizes of screens to produce various size classifications. Depending upon the application, trommel screens can be equipped with internal `lifters or spirals to help move the material along the drum bottom.

As the amount of screen actually in contact with the material is quite low, trommel screens tend to be quite large compared to other screens of similar capacity. Long slivers tend to jam in the screen openings, resulting in the need for frequent cleaning. Trommel screens will handle a lot of abuse and are generally low cost, vibration free, and produce low noise.

Grizzly screens consist of declined parallel bars. Material is fed onto the upper end of the screen and material narrower than the bar spacing falls through the bars with the larger material sliding down the bars and off the lower end of the screen. In order for the large particles to flow down the screen, static grizzly screens are quite steep, >20. Vibrating grizzly screens can have a lower slope resulting in a longer retention time and a more efficient screen.

A passive form of grizzly screen utilizes screen plates with tapered, angular slots mounted in the bottom of chain conveyors. As the chain flights move material over the slots, material smaller than the slots will fall through. Such a screen is used for rough screening out small particles such as fines, sand and grit.

Finger screens are long, narrow vibratory screens with segmented, tapered finger plates with spaces between the fingers through which material may pass. Material is fed into the back end of the screen and the vibrating fingers move the material along the screen. Material smaller than the openings passes through the screen while large material is retained on top and eventually passes over the end of the screen. The tapered shape of the fingers prevents material from blinding over the openings.

Thickness screens are specialty wood chip screens for Kraft pulp mills, where limiting the thickness of wood chips being fed to the digesters helps the penetration of pulping chemicals and digesting efficiency with consequent improvements in throughput capacity. There are (3) types of thickness screens.

Disc screens used to be utilized as thickness screens, however, due to the wiping action between closely spaced discs, the discs wore quickly and soon lost their sizing accuracy. Most disc thickness screens were replaced by roll screens or bar screens in the 1990s. Sizing accuracy greatly improved and maintenance costs dropped dramatically.

Bar thickness screens are manufactured by Jeffrey-Rader and consist of multiple banks of parallel bars mounted in a steel frame. The bars and frame are declined at approximately 3.5. Alternate bars are interlaced and closely spaced one with the other, with the top of one bar higher than the other. Crank shafts raise and lower each set of bars, the intent being to `tip the wood chips on edge, so that the thinner chips can fall through the gap between the bars. Material is fed into the upper end of the machine and the oscillating bars cause the material to lift and bounce down the sloped bars. Thicker chips are retained on top of the bars and pass over the end of the screen. The bar screens do not pull the chips between the bars and therefore do not wear much; consequently, they retain their sizing accuracy for a long time.

Although the bar screen is fairly complex with a lot of moving parts, it is quite robust. It is equipped with vibration sensors that will shut the machine down to prevent the machine from destroying itself if it were allowed to run with the various components out of balance. The bar screens have a lot of oscillating mass and the supporting structures must be designed to accommodate this.

Roll thickness screens manufactured by Acrowood are much less complex than the bar screens, consisting of multiple rolls mounted in a steel frame. The rolls have a grooved, diamond shaped surface and are spaced to give the appropriate clearance between the roll tips on adjacent rolls, providing a gap through which the thinner chips can pass. The thicker chips are retained on top of the rolls and pass over the end of the screen. The roll screens have a low screen open area compared to the bar screen, which results in a large screen footprint.

Acrowood utilizes similar roll technology in their `pins and fines screens. The Acrowood roll screen is very accurate when new; however it is susceptible to unacceptable wear if there are a lot of rocks or grit in the material being fed to the screen. The roll screen handles chips gently and consequently has had problems with blinding if operating in heavy snow conditions.

The Acrowood roll screen has a low-profile and can be stacked one upon the other, resulting in a low building compared to other screen systems. Also, the roll screen doesnt impart dynamic forces into the supporting structure. But, these advantages are sometimes offset by the necessity for a larger building to accommodate the large screen footprint.

Paul Janz has more than 30 years experience in engineering design, project management, equipment manufacturing and maintenance, servicing the forest products and energy industries. His material handling experience includes: biomass handling and processing including forest residuals, logs, lumber, chips, woodwaste, wood pellets, wood strands, straw and poultry litter, sludge and biosolids; municipal solid waste (MSW); and coal and ash handling.

He has a keen interest in technologies which recover and utilize waste materials and convert them into products such as wood pellets. Pauls specialties are fibre flow analysis and mass balances, process optimization and designing novel solutions to complex processing and material handling problems.

I am interested in a trammel for screening sander fines out of sawdust in a wood working facility I am doing work for. There are several types of machines, such as saws, planers, panel saws and several sanders. This unit would be outside in the elements. Capacity required would be approximately 800 Cubic foot per hour, at 12# per cubic foot. Curious if you have something to offer. Please Advise Thank You