ball mill supervisor

service

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Be Aware:Many service and repair procedures should be done only by authorized personnel. The service technicians at your Haas Factory Outlet (HFO) have the training, experience, and are certified to do these tasks safely and correctly. You should not do machine repair or service procedures unless you are qualified and knowledgeable about the processes.

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gsilver provides update on mill commissioning - company to present at emerging growth conference

Guanajuato Silver Company Ltd. is pleased to announce that it has been invited to present at the Emerging Growth Conference at 12:00pm ET on June 23, 2021. GSilver invites individual and institutional investors as well as advisors and analysts to attend its real-time, interactive presentation at the Emerging Growth ConferencePersons wishing to attend the online presentation are invited to register by Clicking Here.

Guanajuato Silver Company Ltd. (the Company or GSilver) (TSXV:GSVR)(OTCQX:GSVRF) is pleased to announce that it has been invited to present at the Emerging Growth Conference at 12:00pm ET on June 23, 2021. GSilver invites individual and institutional investors as well as advisors and analysts to attend its real-time, interactive presentation at the Emerging Growth Conference

Persons wishing to attend the online presentation are invited to register by Clicking Here. Attendees not able to join the event live on the day of the conference, will have the opportunity to view an archived webcast, made available subsequently on www.EmergingGrowth.com.

In anticipation of the upcoming conference, GSilver is providing an update on its progress to re-establish operations at its recently acquired El Cubo mine and mill located approximately 11 kilometers east of Guanajuato city, in central Mexico. The Company continues to target commercial production beginning in Q4 2021.

Approximately 90% of planned staffing at the manager and superintendent level has been obtained, including mill and mine management positions, procurement and accounting staff, and heads of geology at both the El Cubo mine and the El Pinguico project. To date, approximately 85 positions have been filled at the combined operation.

Hernan Dorado, COO, stated: We are very pleased with the pace with which we are filling the vital operating positions at this early stage of our ramp-up process. Our ability to readily hire quality people, often graduates of the University of Guanajuato, speaks to the depth of mining experience within the greater Guanajuato community.

Plant maintenance crews have begun their work on schedule. Crews have dismantled and cleaned the ball mills and have completed a preliminary mechanical inspection. Mill number 3 is in excellent condition, with mills numbers 1 and 2 needing some additional maintenance work anticipated in the Companys due diligence process during the acquisition. Critical parts for all mills have arrived and are now in stock for installation or replacement. Global Physical Asset Management Inc. of Mesa, Arizona has been engaged to inspect the ball mills and make recommendations for additional refurbishment.

Two crushers have been ordered by the Company in anticipation of restarting the plant. A used secondary crusher a Symons 4.25ft Standard in excellent condition was sourced within Mexico and has now arrived on site. A new tertiary crusher also a Symons 4.25ft Standard has been sourced in the USA, ordered, and is scheduled to arrive in Guanajuato within two weeks time.

At El Cubo, GSilver crews and scoop trams are rehabilitating haulage tunnels from the main Dolores access portal to the 11-1875 and 7-2175 stopes, the two main areas that will be targeted first by GSilver when mining recommences.

As discussed in the Companys PEA (see news release dated February 16, 2021), GSilver plans to use contract miners in the early stages of its operations at El Cubo. During the week of June 14, representatives of eight different mine contractor groups visited El Cubo. GSilver anticipates receiving bids from all of these groups before the end of June, allowing ample time for the Company to make a measured decision as to which mine contractor to engage for the re-start of operations.

GSilver personnel continue to study whether combining material from the two deposits, or treating material from the deposits separately, would generate higher metallurgical recoveries. Metallurgical testing of material from El Cubo and El Pinguico is ongoing.

Hernan Dorado Smith, a director of GSilver and a qualified person as defined by National Instrument 43-101, Standards of Disclosure for Mineral Projects, has approved the scientific and technical information contained in this news release.

GSilver is an exploration and development company engaged in reactivating past producing silver and gold mines near the city of Guanajuato, Mexico. The Companys El Cubo and El Pinguico projects are significant past producers of both silver and gold located in close proximity to Guanajuato city, and to each other. The Company is currently focused on refurbishing the El Cubo mill and recommencing production from the combined El Cubo / El Pinguico operation, as well as delineating additional silver and gold resources through underground and surface drilling on its projects located in this 480-year-old mining camp.

The Emerging Growth conference is an effective way for public companies to present and communicate their new products, services and other major announcements to the investment community from the convenience of their offices.

The Conference focus and coverage includes companies in a wide range of growth sectors, with strong management teams, innovative products & services, focused strategy, and the overall potential for long term growth. Its audience includes potentially tens of thousands of individual and institutional investors, as well as investment advisors and analysts. All sessions will be conducted through video webcasts.

For further information regarding Guanajuato Silver Company Ltd. please contact:James Anderson, Director, +1 (778) 989-5346Email: [email protected] to watch our progress at: www.GSilver.com

This new release does not constitute an offer to sell or a solicitation of an offer to buy any securities of the Company in the United States. The Companys securities have not been and will not be registered under the United States Securities Act of 1933, as amended (the U.S. Securities Act), or any state securities laws and may not be offered or sold within the United States or to or for the account or benefit of a U.S. person (as defined in Regulation S under the U.S. Securities Act) unless registered under the U.S. Securities Act and applicable state securities laws or an exemption from such registration is available.

Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release.

This news release contains certain forward-looking statements and information, which relate to future events or future performance including, but not limited to, the timing and ability of the Company to successfully refurbish the El Cubo mill, procure equipment, hire personnel and supply and process sufficient mineralized material and resources from El Cubo and El Pinguico through the mill to successfully begin commercial production of silver and gold in Q4 2021 at the projected amounts, grades, costs and revenues and the success related to any future exploration and/or development programs.

Such forward-looking statements and information reflect managements current beliefs and are based on information currently available to and assumptions made by the Company; which assumptions, while considered reasonable by the Company, are inherently subject to significant operational, business, economic and regulatory uncertainties and contingencies. These assumptions include: our mineral resource estimates at El Cubo and El Pinguico and the assumptions upon which they are based, including geotechnical and metallurgical characteristics of rock conforming to sampled results and metallurgical performance; tonnage of mineralized material to be mined and processed; resource grades and recoveries; assumptions and discount rates being appropriately applied to production estimates; success of the Companys combined El Cubo / El Pinguico operation; prices for silver and gold remaining as estimated; currency exchange rates remaining as estimated; availability of funds for the Companys projects; capital, decommissioning and reclamation estimates; prices for energy inputs, labour, materials, supplies and services (including transportation); no labour-related disruptions; no unplanned delays or interruptions in scheduled construction and production; all necessary permits, licenses and regulatory approvals are received in a timely manner; and the ability to comply with environmental, health and safety laws. The foregoing list of assumptions is not exhaustive.

Readers are cautioned that such forward-looking statements and information are neither promises nor guarantees, and are subject to risks and uncertainties that may cause future results to differ materially from those expected including, but not limited to, market conditions, availability of financing, currency rate fluctuations, actual results of development and production activities, actual resource grades and recoveries of silver and gold, unanticipated geological or structural formations and characteristics, environmental risks, future prices of gold, silver and other metals, operating risks, accidents, labor issues, equipment or personnel delays, delays in obtaining governmental or regulatory approvals and permits, inadequate insurance, and other risks in the mining industry. There are no assurances that GSilver will be able to successfully re-start the El Cubo mill to process mineralized materials to produce silver and gold in the amounts, grades, recoveries, costs and timetable anticipated. In addition, GSilvers decision to begin processing mineralized material from its above and underground stockpiles at El Pinguico and estimated resources at El Cubo through the El Cubo mill is not based on a feasibility study of mineral reserves demonstrating economic and technical viability and therefore is subject to increased uncertainty and risk of failure, both economically and technically. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability, are considered too speculative geologically to have the economic considerations applied to them, and may be materially affected by environmental, permitting, legal, title, socio-political, marketing, and other relevant issues. There are no assurances that the results of the Companys recently announced preliminary economic assessment and projected production of silver and gold will be realized. There is also uncertainty about the spread of COVID-19 and variants of concern and the impact they will have on the Companys operations, supply chains, ability to access El Pinguico and/or El Cubo or procure equipment, contractors and other personnel on a timely basis or at all and economic activity in general. All the forward-looking statements made in this news release are qualified by these cautionary statements and those in our continuous disclosure filings available on SEDAR at www.sedar.com. These forward-looking statements are made as of the date hereof and the Company does not assume any obligation to update or revise them to reflect new events or circumstances save as required by law.

Guanajuato Silver Company Ltd.PH: +1(778) 989-5346 E: [email protected] W: GSilver.com CA: Suite 578 999 Canada Place, Vancouver B.C. V6C 3E1MX: Carretera Guanajuato Silao km 5.5, Int 4, Col. Marfil CP36250, Guanajuato, Gto., Mexico

Request an Investor Kit: Guanajuato Silver Co Include me in the Accredited Investor email list Some investment opportunities are limited to accredited investors. Whether you are an accredited investor or not depends on where you live and other criteria. For full details go to https://investingnews.com/accredited-investor-definition/ or search for "accredited investor" in the search bar above. By completing this form, you are giving consent to receive communication from Guanajuato Silver Co using the contact information you provide. And remember you can unsubscribe at any time.

ball mills

In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment.In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed and used, but the ball mill has become standard due to its simplicity and low operating cost.

A ball millefficiently operated performs a wide variety of services. In small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the Steel-Head Ball or Rod Mill will take up to 2 feed and grind it to the desired fineness. In larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2 to as fine as 8 mesh.

Many grinding circuits necessitate regrinding of concentrates or middling products to extremely fine sizes to liberate the closely associated minerals from each other. In these cases, the feed to the ball mill may be from 10 to 100 mesh or even finer.

Where the finished product does not have to be uniform, a ball mill may be operated in open circuit, but where the finished product must be uniform it is essential that the grinding mill be used in closed circuit with a screen, if a coarse product is desired, and with a classifier if a fine product is required. In most cases it is desirable to operate the grinding mill in closed circuit with a screen or classifier as higher efficiency and capacity are obtained. Often a mill using steel rods as the grinding medium is recommended, where the product must have the minimum amount of fines (rods give a more nearly uniform product).

Often a problem requires some study to determine the economic fineness to which a product can or should be ground. In this case the 911Equipment Company offers its complete testing service so that accurate grinding mill size may be determined.

Until recently many operators have believed that one particular type of grinding mill had greater efficiency and resulting capacity than some other type. However, it is now commonly agreed and accepted that the work done by any ballmill depends directly upon the power input; the maximum power input into any ball or rod mill depends upon weight of grinding charge, mill speed, and liner design.

The apparent difference in capacities between grinding mills (listed as being the same size) is due to the fact that there is no uniform method of designating the size of a mill, for example: a 5 x 5 Ball Mill has a working diameter of 5 inside the liners and has 20 per cent more capacity than all other ball mills designated as 5 x 5 where the shell is 5 inside diameter and the working diameter is only 48 with the liners in place.

Ball-Rod Mills, based on 4 liners and capacity varying as 2.6 power of mill diameter, on the 5 size give 20 per cent increased capacity; on the 4 size, 25 per cent; and on the 3 size, 28 per cent. This fact should be carefully kept in mind when determining the capacity of a Steel- Head Ball-Rod Mill, as this unit can carry a greater ball or rod charge and has potentially higher capacity in a given size when the full ball or rod charge is carried.

A mill shorter in length may be used if the grinding problem indicates a definite power input. This allows the alternative of greater capacity at a later date or a considerable saving in first cost with a shorter mill, if reserve capacity is not desired. The capacities of Ball-Rod Mills are considerably higher than many other types because the diameters are measured inside the liners.

The correct grinding mill depends so much upon the particular ore being treated and the product desired, that a mill must have maximum flexibility in length, type of grinding medium, type of discharge, and speed.With the Ball-Rod Mill it is possible to build this unit in exact accordance with your requirements, as illustrated.

To best serve your needs, the Trunnion can be furnished with small (standard), medium, or large diameter opening for each type of discharge. The sketch shows diagrammatic arrangements of the four different types of discharge for each size of trunnion opening, and peripheral discharge is described later.

Ball-Rod Mills of the grate discharge type are made by adding the improved type of grates to a standard Ball-Rod Mill. These grates are bolted to the discharge head in much the same manner as the standard headliners.

The grates are of alloy steel and are cast integral with the lifter bars which are essential to the efficient operation of this type of ball or rod mill. These lifter bars have a similar action to a pump:i. e., in lifting the product so as to discharge quickly through the mill trunnion.

These Discharge Grates also incorporate as an integral part, a liner between the lifters and steel head of the ball mill to prevent wear of the mill head. By combining these parts into a single casting, repairs and maintenance are greatly simplified. The center of the grate discharge end of this mill is open to permit adding of balls or for adding water to the mill through the discharge end.

Instead of being constructed of bars cast into a frame, Grates are cast entire and have cored holes which widen toward the outside of the mill similar to the taper in grizzly bars. The grate type discharge is illustrated.

The peripheral discharge type of Ball-Rod Mill is a modification of the grate type, and is recommended where a free gravity discharge is desired. It is particularly applicable when production of too many fine particles is detrimental and a quick pass through the mill is desired, and for dry grinding.

The drawings show the arrangement of the peripheral discharge. The discharge consists of openings in the shell into which bushings with holes of the desired size are inserted. On the outside of the mill, flanges are used to attach a stationary discharge hopper to prevent pulp splash or too much dust.

The mill may be operated either as a peripheral discharge or a combination or peripheral and trunnion discharge unit, depending on the desired operating conditions. If at any time the peripheral discharge is undesirable, plugs inserted into the bushings will convert the mill to a trunnion discharge type mill.

Unless otherwise specified, a hard iron liner is furnished. This liner is made of the best grade white iron and is most serviceable for the smaller size mills where large balls are not used. Hard iron liners have a much lower first cost.

Electric steel, although more expensive than hard iron, has advantage of minimum breakage and allows final wear to thinner section. Steel liners are recommended when the mills are for export or where the source of liner replacement is at a considerable distance.

Molychrome steel has longer wearing qualities and greater strength than hard iron. Breakage is not so apt to occur during shipment, and any size ball can be charged into a mill equipped with molychrome liners.

Manganese liners for Ball-Rod Mills are the world famous AMSCO Brand, and are the best obtainable. The first cost is the highest, but in most cases the cost per ton of ore ground is the lowest. These liners contain 12 to 14% manganese.

The feed and discharge trunnions are provided with cast iron or white iron throat liners. As these parts are not subjected to impact and must only withstand abrasion, alloys are not commonly used but can be supplied.

Gears for Ball-Rod Mills drives are furnished as standard on the discharge end of the mill where they are out of the way of the classifier return, scoop feeder, or original feed. Due to convertible type construction the mills can be furnished with gears on the feed end. Gear drives are available in two alternative combinations, which are:

All pinions are properly bored, key-seated, and pressed onto the steel countershaft, which is oversize and properly keyseated for the pinion and drive pulleys or sheaves. The countershaft operates on high grade, heavy duty, nickel babbitt bearings.

Any type of drive can be furnished for Ball-Rod Mills in accordance with your requirements. Belt drives are available with pulleys either plain or equipped with friction clutch. Various V- Rope combinations can also be supplied.

The most economical drive to use up to 50 H. P., is a high starting torque motor connected to the pinion shaft by means of a flat or V-Rope drive. For larger size motors the wound rotor (slip ring) is recommended due to its low current requirement in starting up the ball mill.

Should you be operating your own power plant or have D. C. current, please specify so that there will be no confusion as to motor characteristics. If switches are to be supplied, exact voltage to be used should be given.

Even though many ores require fine grinding for maximum recovery, most ores liberate a large percentage of the minerals during the first pass through the grinding unit. Thus, if the free minerals can be immediately removed from the ball mill classifier circuit, there is little chance for overgrinding.

This is actually what has happened wherever Mineral Jigs or Unit Flotation Cells have been installed in the ball mill classifier circuit. With the installation of one or both of these machines between the ball mill and classifier, as high as 70 per cent of the free gold and sulphide minerals can be immediately removed, thus reducing grinding costs and improving over-all recovery. The advantage of this method lies in the fact that heavy and usually valuable minerals, which otherwise would be ground finer because of their faster settling in the classifier and consequent return to the grinding mill, are removed from the circuit as soon as freed. This applies particularly to gold and lead ores.

Ball-Rod Mills have heavy rolled steel plate shells which are arc welded inside and outside to the steel heads or to rolled steel flanges, depending upon the type of mill. The double welding not only gives increased structural strength, but eliminates any possibility of leakage.

Where a single or double flanged shell is used, the faces are accurately machined and drilled to template to insure perfect fit and alignment with the holes in the head. These flanges are machined with male and female joints which take the shearing stresses off the bolts.

The Ball-Rod Mill Heads are oversize in section, heavily ribbed and are cast from electric furnace steel which has a strength of approximately four times that of cast iron. The head and trunnion bearings are designed to support a mill with length double its diameter. This extra strength, besides eliminating the possibility of head breakage or other structural failure (either while in transit or while in service), imparts to Ball-Rod Mills a flexibility heretofore lacking in grinding mills. Also, for instance, if you have a 5 x 5 mill, you can add another 5 shell length and thus get double the original capacity; or any length required up to a maximum of 12 total length.

On Type A mills the steel heads are double welded to the rolled steel shell. On type B and other flanged type mills the heads are machined with male and female joints to match the shell flanges, thus taking the shearing stresses from the heavy machine bolts which connect the shell flanges to the heads.

The manhole cover is protected from wear by heavy liners. An extended lip is provided for loosening the door with a crow-bar, and lifting handles are also provided. The manhole door is furnished with suitable gaskets to prevent leakage.

The mill trunnions are carried on heavy babbitt bearings which provide ample surface to insure low bearing pressure. If at any time the normal length is doubled to obtain increased capacity, these large trunnion bearings will easily support the additional load. Trunnion bearings are of the rigid type, as the perfect alignment of the trunnion surface on Ball-Rod Mills eliminates any need for the more expensive self-aligning type of bearing.

The cap on the upper half of the trunnion bearing is provided with a shroud which extends over the drip flange of the trunnion and effectively prevents the entrance of dirt or grit. The bearing has a large space for wool waste and lubricant and this is easily accessible through a large opening which is covered to prevent dirt from getting into the bearing.Ball and socket bearings can be furnished.

Scoop Feeders for Ball-Rod Mills are made in various radius sizes. Standard scoops are made of cast iron and for the 3 size a 13 or 19 feeder is supplied, for the 4 size a 30 or 36, for the 5 a 36 or 42, and for the 6 a 42 or 48 feeder. Welded steel scoop feeders can, however, be supplied in any radius.

The correct size of feeder depends upon the size of the classifier, and the smallest feeder should be used which will permit gravity flow for closed circuit grinding between classifier and the ball or rod mill. All feeders are built with a removable wearing lip which can be easily replaced and are designed to give minimum scoop wear.

A combination drum and scoop feeder can be supplied if necessary. This feeder is made of heavy steel plate and strongly welded. These drum-scoop feeders are available in the same sizes as the cast iron feeders but can be built in any radius. Scoop liners can be furnished.

The trunnions on Ball-Rod Mills are flanged and carefully machined so that scoops are held in place by large machine bolts and not cap screws or stud bolts. The feed trunnion flange is machined with a shoulder for insuring a proper fit for the feed scoop, and the weight of the scoop is carried on this shoulder so that all strain is removed from the bolts which hold the scoop.

High carbon steel rods are recommended, hot rolled, hot sawed or sheared, to a length of 2 less than actual length of mill taken inside the liners. The initial rod charge is generally a mixture ranging from 1.5 to 3 in diameter. During operation, rod make-up is generally the maximum size. The weights per lineal foot of rods of various diameters are approximately: 1.5 to 6 lbs.; 2-10.7 lbs.; 2.5-16.7 lbs.; and 3-24 lbs.

Forged from the best high carbon manganese steel, they are of the finest quality which can be produced and give long, satisfactory service. Data on ball charges for Ball-Rod Mills are listed in Table 5. Further information regarding grinding balls is included in Table 6.

Rod Mills has a very define and narrow discharge product size range. Feeding a Rod Mill finer rocks will greatly impact its tonnage while not significantly affect its discharge product sizes. The 3.5 diameter rod of a mill, can only grind so fine.

Crushers are well understood by most. Rod and Ball Mills not so much however as their size reduction actions are hidden in the tube (mill). As for Rod Mills, the image above best expresses what is going on inside. As rocks is feed into the mill, they are crushed (pinched) by the weight of its 3.5 x 16 rods at one end while the smaller particles migrate towards the discharge end and get slightly abraded (as in a Ball Mill) on the way there.

We haveSmall Ball Mills for sale coming in at very good prices. These ball mills are relatively small, bearing mounted on a steel frame. All ball mills are sold with motor, gears, steel liners and optional grinding media charge/load.

Ball Mills or Rod Mills in a complete range of sizes up to 10 diameter x20 long, offer features of operation and convertibility to meet your exactneeds. They may be used for pulverizing and either wet or dry grindingsystems. Mills are available in both light-duty and heavy-duty constructionto meet your specific requirements.

All Mills feature electric cast steel heads and heavy rolled steelplate shells. Self-aligning main trunnion bearings on large mills are sealedand internally flood-lubricated. Replaceable mill trunnions. Pinion shaftbearings are self-aligning, roller bearing type, enclosed in dust-tightcarrier. Adjustable, single-unit soleplate under trunnion and drive pinionsfor perfect, permanent gear alignment.

Ball Mills can be supplied with either ceramic or rubber linings for wet or dry grinding, for continuous or batch type operation, in sizes from 15 x 21 to 8 x 12. High density ceramic linings of uniform hardness male possible thinner linings and greater and more effective grinding volume. Mills are shipped with liners installed.

Complete laboratory testing service, mill and air classifier engineering and proven equipment make possible a single source for your complete dry-grinding mill installation. Units available with air swept design and centrifugal classifiers or with elevators and mechanical type air classifiers. All sizes and capacities of units. Laboratory-size air classifier also available.

A special purpose batch mill designed especially for grinding and mixing involving acids and corrosive materials. No corners mean easy cleaning and choice of rubber or ceramic linings make it corrosion resistant. Shape of mill and ball segregation gives preferential grinding action for grinding and mixing of pigments and catalysts. Made in 2, 3 and 4 diameter grinding drums.

Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/161 5/8) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.

Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of effective classification.If finer grinding is wanted two or three stage grinding is advisable as for instant primary rod mill with 75100 mm (34) rods, secondary ball mill with 2540 mm(11) balls and possibly tertiary ball mill with 20 mm () balls or cylpebs.To obtain a close size distribution in the fine range the specific surface of the grinding media should be as high as possible. Thus as small balls as possible should be used in each stage.

The principal field of rod mill usage is the preparation of products in the 5 mm0.4 mm (4 mesh to 35 mesh) range. It may sometimes be recommended also for finer grinding. Within these limits a rod mill is usually superior to and more efficient than a ball mill. The basic principle for rod grinding is reduction by line contact between rods extending the full length of the mill, resulting in selective grinding carried out on the largest particle sizes. This results in a minimum production of extreme fines or slimes and more effective grinding work as compared with a ball mill. One stage rod mill grinding is therefore suitable for preparation of feed to gravimetric ore dressing methods, certain flotation processes with slime problems and magnetic cobbing. Rod mills are frequently used as primary mills to produce suitable feed to the second grinding stage. Rod mills have usually a length/diameter ratio of at least 1.4.

Tube mills are in principle to be considered as ball mills, the basic difference being that the length/diameter ratio is greater (35). They are commonly used for surface cleaning or scrubbing action and fine grinding in open circuit.

In some cases it is suitable to use screened fractions of the material as grinding media. Such mills are usually called pebble mills, but the working principle is the same as for ball mills. As the power input is approximately directly proportional to the volume weight of the grinding media, the power input for pebble mills is correspondingly smaller than for a ball mill.

A dry process requires usually dry grinding. If the feed is wet and sticky, it is often necessary to lower the moisture content below 1 %. Grinding in front of wet processes can be done wet or dry. In dry grinding the energy consumption is higher, but the wear of linings and charge is less than for wet grinding, especially when treating highly abrasive and corrosive material. When comparing the economy of wet and dry grinding, the different costs for the entire process must be considered.

An increase in the mill speed will give a directly proportional increase in mill power but there seems to be a square proportional increase in the wear. Rod mills generally operate within the range of 6075 % of critical speed in order to avoid excessive wear and tangled rods. Ball and pebble mills are usually operated at 7085 % of critical speed. For dry grinding the speed is usually somewhat lower.

The mill lining can be made of rubber or different types of steel (manganese or Ni-hard) with liner types according to the customers requirements. For special applications we can also supply porcelain, basalt and other linings.

The mill power is approximately directly proportional to the charge volume within the normal range. When calculating a mill 40 % charge volume is generally used. In pebble and ball mills quite often charge volumes close to 50 % are used. In a pebble mill the pebble consumption ranges from 315 % and the charge has to be controlled automatically to maintain uniform power consumption.

In all cases the net energy consumption per ton (kWh/ton) must be known either from previous experience or laboratory tests before mill size can be determined. The required mill net power P kW ( = ton/hX kWh/ton) is obtained from

Trunnions of S.G. iron or steel castings with machined flange and bearing seat incl. device for dismantling the bearings. For smaller mills the heads and trunnions are sometimes made in grey cast iron.

The mills can be used either for dry or wet, rod or ball grinding. By using a separate attachment the discharge end can be changed so that the mills can be used for peripheral instead of overflow discharge.

operations and maintenance training for ball mills

Learn how to optimise your ball mill systems in this 5-day training seminar focused on best practices for operations and maintenance (preventive and reactive) to achieve energy savings, reduced maintenance costs and overall improved productivity of the ball mill systems. Ball mills are used for many applications in cement production: raw meal grinding, coal and petcoke grinding as well as finish cement grinding. Each of these systems have their similarities and differences. This ball mill seminar is designed to train your personnel on the overall technology, operation and maintenance of your ball mill cement grinding system. The seminar focuses on the latest best practices for the operation and maintenance of ball mill systems to allow for optimal cement production, energy savings, reduced maintenance costs as well as the continuous improvement of the overall equipment operation. The course offers classroom instruction from our FLSmidth ball mill specialists and case studies based on real situations at different ball mill installations. Working sessions are scheduled to allow for a thorough study of the design and function of the main equipment, including but not limited to the latest methods for optimisation and possibilities for upgrades and modernisation of the current systems and operations. Maintenance training is focused on routine preventive maintenance to minimize downtime in ball mill systems, as well as developing preventive maintenance programmes and troubleshooting techniques to quickly identify and fix problems. Beyond what you will learn about your ball mill systems, this seminar provides excellent networking opportunities with our specialists as well as your counterparts from the cement industry.

Learn how to optimise your ball mill systems in this 5-day training seminar focused on best practices for operations and maintenance (preventive and reactive) to achieve energy savings, reduced maintenance costs and overall improved productivity of the ball mill systems.

Ball mills are used for many applications in cement production: raw meal grinding, coal and petcoke grinding as well as finish cement grinding. Each of these systems have their similarities and differences. This ball mill seminar is designed to train your personnel on the overall technology, operation and maintenance of your ball mill cement grinding system.

The seminar focuses on the latest best practices for the operation and maintenance of ball mill systems to allow for optimal cement production, energy savings, reduced maintenance costs as well as the continuous improvement of the overall equipment operation.

The course offers classroom instruction from our FLSmidth ball mill specialists and case studies based on real situations at different ball mill installations. Working sessions are scheduled to allow for a thorough study of the design and function of the main equipment, including but not limited to the latest methods for optimisation and possibilities for upgrades and modernisation of the current systems and operations.

Maintenance training is focused on routine preventive maintenance to minimize downtime in ball mill systems, as well as developing preventive maintenance programmes and troubleshooting techniques to quickly identify and fix problems.

FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.

operating and troubleshooting a grinding circuit

In the operation of a grinding circuit you are managing several pieces of equipment as a single unit. If you make a change in the ore in the fine ore bin, that change will be reflected through the entire grinding process and beyond into the rest of the concentration system. The first thing that an operator will have to learn is to be able to tell when the rod mill is, or isnt, grinding fine enough. With a little practice the operator will be able to simply look at the discharge of a rod mill and determine how well it is working. The variables that are being looked at are color and consistency of the slurry. If the rock is staying in suspension or is it classifying as it slides over the discharge trunnion? The amount of rejects that are being discharged. And the manner in which the slurry is beading on the side of the discharge trunnion as it is flowing across it. These will give an indication of any change in the density or the ore. To verify any change that you think that you see in the discharge, simply take a density. If it has changed then so has your circuit. Once you have finished weighing the density sample, pour it out over your gloved hand, you will be able to feel and see the difference in the grind.

Lets pretend that you have taken all of your densities, checked the grind and the number of rejects that are coming out of the mill. Prom this information you have decided that the circuit could use some more tonnage. So you go to your control panel and increase the through put, oh, ten tons per hour. What happens to your circuit? First the extra ore enters the rod mill the density begins to climb and the grind gets coarser. You start to get a few rejects. Then the heavier density with the courser grind is pumped to the cyclone. Both the overflow and the underflow from the cyclone become heavier. Remember you now have a higher amount of ore that will have to be ground further. This causes the density of the ball mill to climb. Which in turn is discharged back to the cyclone. If now, you go back through the circuit, and check your variables you will notice that the rod mill density has increased. The grind has gotten worse. The cyclone over flow density and the ball mill density has gotten heavier.

You think that the rod mill grind could be better, after all, the density is above the recommended range that your supervisor wants it run at. So you add a little water. The water decreases the retention time. It also improves the grinding action of the rods. The higher density was cushioning the rods. The movement in the core area of the rod load had been restricted due to the excess tonnage. Increasing the water improved the rate of fine material discharge. Maintaining the correct density will insure that the rate of discharge is correct. The lighter density may produce less coarse and marginally less fines but it will produce more of the middle sizes.

This size is called MIDDLINGS, which will have a large percentage of ore fine enough to be sent to the next stage of concentration. The water has caused both the amount of fines and the amount of coarse produced to drop. The amount of the middling sizes increased. The cyclone overflow would allow a lot of this middling size to escape the grinding circuit. This would decrease the amount of material that the ball mill would have to grind. Which in turn would lower the amount of ground ore returned to the cyclone for reclassification. This again would lower the resulting ball mill load even further.

Although the cyclone overflow density may not change for a short period of time due to the extra water and the extra ore in the over flow more or less balancing each other out. It will as the decreased density of the underflow changes the grind of the ball mill. The density of the cyclone overflow will still be too high, but it has dropped a little from what it was. At this point, as the finished product, this is the MOST IMPORTANT DENSITY. To bring the density back to the operating perimeters, you add water going to the cyclone feed pump box. This will compensate for the higher density. Again there will be a reaction to the water in the underflow of the cyclone, but it will be a minor one, and a simple check of the overflow after a period of time will determine if any more adjustments are necessary. The other worry that the operator will have is the capacity of his circuit.

The maximum tonnage that can be processed will depend upon the capacity of the smallest piece of equipment that must handle the volume. This is another characteristic of each individual grinding circuit. It may be the rod mill that cant take the load, or perhaps the cyclone or pump box. Whatever it is, you may he guaranteed that one piece of equipment will reach its limit before any of the others. That will be the one that you will watch the most. The reaction of our fictitious circuit is, by no means, meant to be taken as a standard reaction to the different variables. How the ore will behave in the mill will depend upon the grinding characteristics of each individual ore body.

The purpose of this exercise was to illustrate the DYNAMICS OF A CIRCUIT. How a change in one portion of the mill will affect the rest of the circuit. It was also to show that it is possible for an operator to get into trouble if he doesnt allow enough time for a change to completely go through the circuit before making another change. Checking the results of a change to soon can also lead to trouble. An example of this would be in the rod mill. If the operator had checked the rod mill load prior to the time it took for the extra volume of ore to fill up the mill, he could possibly feel that the resulting density was still within the perimeters set down by the supervisor. When in fact they hadnt finished climbing yet. The results could be an overloaded grinding circuit, and a very poor grind.

When a circuit becomes overloaded it is because the amount of ore that is going out of the overflow is less than the total volume of the ore coming into the circuit. What is known as a CIRCULATING LOAD builds up. This is the ore that is going to the classifier, back to the ball mill, back to the classifier, back to the mill again. The work index and the size of the cyclone feed will determine the ratio of ore that is returned to the ball mill for further grinding. A ball mill operates more with the grinding surface action of the balls than the impact form of grinding that the rod mill uses. Taking this into account you can see that if the rod mill doesnt reduce the ore to a size that the ball mill can reduce quickly, the circuit load will climb until its volume is greater than can be handled.

To maintain the maximum amount of through put that the grinding mills can handle it is necessary to keep what is termed as the MEDIA RUNNING LOAD to its maximum. This is the amount of grinding rods or balls that are in the mills. As the mills tumble and turn the grinding media wears away until the mill charge is too low to maintain the grind. The solution to this problem is to add more media. In the case of the rod mill the circuit will have to be shut down to accomplish this, the ball mill, however may have its media added while it is running. The standard method used to put the balls into the mill is to drop them into the feed end along with the feed. The rod mill will have a set of rollers put into the discharge end of the mill. The rods are then rolled in on top of these rollers to be dropped off onto the existing rod load. To know when to charge the mills you have to consult the RUNNING LOAD of the mill. This is simply the amperage load that the motor is working against. Every electric motor has a maximum amperage point, after which it kicks out. The running load is the percentage of the maximum amperage load that the electric motor can safely handle.

The grinding circuit is the most expensive circuit in the concentrator plant to run. To make the most profit from this equipment, it is necessary that it is run at the maximum amount of tonnage that the mills will handle. While maintaining the efficiency level that is set by management. There are times when it may seem that if you drop the tonnage five tons per hour you would save yourself a lot of work. The increased effectiveness would out-weight the lost tonnage. Most operators reason that the ore will not go away and it will still be here to be processed tomorrow. Unfortunately all of the mines finances will be set up on set of perimeters that have to be met. The farther that you can exceed them the bigger the safety margin you can have for emergency shut downs and unexpected expenses. That extra five tons per hour may be the gravy money. How the operator does his job goes a long way in the operation of a successful mine. There has been more than one mine that has been shut down by poor operating practices. It is the operators job to get every ton that he can out of his equipment. Keep down time to minimum. And to recover as much of the mineral as he or she can.

Before we get to a few of the safety aspects of grinding, I would like to REVIEW some areas of concern for the operator when CIRCUIT CHECKS are being done. Lets start at the feeders. Here the operator must watch for ore stoppages. Foreign objects in the feed that could damage belts, or block transfer chutes. With these chutes come lost and worn liners and ore blockages. The conveyors have to be watched for belt wander and mechanical damage and weightometer be kept clean.

With the mill themselves, the trunnion bearing oil ring has to be watched. Leaking liner bolts and other wear caused by the abrasion of the ore has to be reported or fixed. Bull gears and some types of bearings have to be lubricated. Running loads monitored, as well as the other standard readings that are required. And last but not least maintaining good housekeeping standards.

mill manager resume samples | qwikresume

A Mill Manager is responsible for overseeing the production, quality, safety, and costs of the mill that produces feed for animals. While the job duties tend to vary based on the type of mill, the following are certain core duties listed on the Mill Manager Resume keeping inventory of feed ingredients; ordering as needed, handling customer questions and complaints; ensuring all employees are trained on safety and continue to stay updated; scheduling feed production, and testing the feed quality. Other duties include handling complaints, setting quality assurance standards, and maintaining filling equipment and other equipment needed to perform duties.

Those seeking this job role must be able to portray on the resume the following skills and abilities staying updated on new technology and ways to make process improvements; proven managerial experience, knowledge of business and management principles; familiarity with industry-standard equipment and technical expertise, and knowledge of quality and productivity. A bachelors degree in animal science, poultry science, or feed mill management is recommended.

Summary : Continue learning from new experiences. With over 30 years of milling & management experience across North America, I am committed to safe production, achieving my goals through leading by example and developing the strength of my teams.

Summary : Abilities and skills and attitude to do the work that you need done. I know and understand that this job has long hours and long days and that is not a problem. I can operate, perform routine maintenance, and inspect and take care of equipment. If you give me the opportunity, you have my word that I will be a dedicated, safe, productive, and efficient employee.

Summary : As a Mill Manager, responsible for Improving equipment uptime, capability and reliability through the passionate facilitation of TPM initiatives and the AWC SEE (Strategic Equipment Excellence) program as well as all five phases of Six-Sigma improvement or the Defining, Measuring, Analyzing, Improving, and Controlling of equipment related problems.

Objective : Mill Manager with 3 years of experience in 5. Planning and coordinating department's activities to support SQDC targets, and meet and/or exceed client and/or customer's expectations, Leading and/or facilitate Kaizen events and actively participate on assigned teams and/or projects.

Summary : Mill Manager professional with twenty-five years experience. Self-motivated, results-oriented initiator. Demonstrated ability to make decisions, set priorities, and resolve problems to achieve both immediate and long-term goals. Hard worker with start to finish follow-up skills; dependable and loyal. Excellent communicator with exposure in working with a variety of professionals and clients.

Headline : Responsible for Ensuring assigned departments perform tasks as outlined in Job Instruction Breakdowns, Quality Specifications, and Standard Operating Practices, Participating in identifying crewing needs; employee selection, hiring, and training process.

Objective : Maintenance experience in manufacturing facilities Experience in both Union and non Union environments Participated in labor negotiations as part of management team Trained in Lean Manufacturing, 5S, Kaizen, Pull Systems, Management By Sight Demonstrates ability to work independently, provide leadership and work well with people at all levels of the organization.

Summary : Responsible for Providing communication on departmental expectations, motivate team members, and identify opportunity for improvements, Providing team leadership consistent with company vision, mission, CITE principles.

ball mills - an overview | sciencedirect topics

A ball mill is a type of grinder used to grind and blend bulk material into QDs/nanosize using different sized balls. The working principle is simple; impact and attrition size reduction take place as the ball drops from near the top of a rotating hollow cylindrical shell. The nanostructure size can be varied by varying the number and size of balls, the material used for the balls, the material used for the surface of the cylinder, the rotation speed, and the choice of material to be milled. Ball mills are commonly used for crushing and grinding the materials into an extremely fine form. The ball mill contains a hollow cylindrical shell that rotates about its axis. This cylinder is filled with balls that are made of stainless steel or rubber to the material contained in it. Ball mills are classified as attritor, horizontal, planetary, high energy, or shaker.

Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles, as well as collision energy. These forces are derived from the rotational motion of the balls and movement of particles within the mill and contact zones of colliding balls.

By rotation of the mill body, due to friction between mill wall and balls, the latter rise in the direction of rotation till a helix angle does not exceed the angle of repose, whereupon, the balls roll down. Increasing of rotation rate leads to growth of the centrifugal force and the helix angle increases, correspondingly, till the component of weight strength of balls become larger than the centrifugal force. From this moment the balls are beginning to fall down, describing during falling certain parabolic curves (Figure 2.7). With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls are attached to the wall due to centrifugation:

where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 6580% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.

The degree of filling the mill with balls also influences productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 3035% of its volume.

The mill productivity also depends on many other factors: physical-chemical properties of feed material, filling of the mill by balls and their sizes, armor surface shape, speed of rotation, milling fineness and timely moving off of ground product.

where b.ap is the apparent density of the balls; l is the degree of filling of the mill by balls; n is revolutions per minute; 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.

A feature of ball mills is their high specific energy consumption; a mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, i.e. during grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.

Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction, and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles as well as collision energy. These forces are derived from the rotational motion of the balls and the movement of particles within the mill and contact zones of colliding balls.

By the rotation of the mill body, due to friction between the mill wall and balls, the latter rise in the direction of rotation until a helix angle does not exceed the angle of repose, whereupon the balls roll down. Increasing the rotation rate leads to the growth of the centrifugal force and the helix angle increases, correspondingly, until the component of the weight strength of balls becomes larger than the centrifugal force. From this moment, the balls are beginning to fall down, describing certain parabolic curves during the fall (Fig. 2.10).

With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls remain attached to the wall with the aid of centrifugal force is:

where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 65%80% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.

where db.max is the maximum size of the feed (mm), is the compression strength (MPa), E is the modulus of elasticity (MPa), b is the density of material of balls (kg/m3), and D is the inner diameter of the mill body (m).

The degree of filling the mill with balls also influences the productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 30%35% of its volume.

The productivity of ball mills depends on the drum diameter and the relation of drum diameter and length. The optimum ratio between length L and diameter D, L:D, is usually accepted in the range 1.561.64. The mill productivity also depends on many other factors, including the physical-chemical properties of the feed material, the filling of the mill by balls and their sizes, the armor surface shape, the speed of rotation, the milling fineness, and the timely moving off of the ground product.

where D is the drum diameter, L is the drum length, b.ap is the apparent density of the balls, is the degree of filling of the mill by balls, n is the revolutions per minute, and 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.

A feature of ball mills is their high specific energy consumption. A mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, that is, during the grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.

Milling time in tumbler mills is longer to accomplish the same level of blending achieved in the attrition or vibratory mill, but the overall productivity is substantially greater. Tumbler mills usually are used to pulverize or flake metals, using a grinding aid or lubricant to prevent cold welding agglomeration and to minimize oxidation [23].

Cylindrical Ball Mills differ usually in steel drum design (Fig. 2.11), which is lined inside by armor slabs that have dissimilar sizes and form a rough inside surface. Due to such juts, the impact force of falling balls is strengthened. The initial material is fed into the mill by a screw feeder located in a hollow trunnion; the ground product is discharged through the opposite hollow trunnion.

Cylindrical screen ball mills have a drum with spiral curved plates with longitudinal slits between them. The ground product passes into these slits and then through a cylindrical sieve and is discharged via the unloading funnel of the mill body.

Conical Ball Mills differ in mill body construction, which is composed of two cones and a short cylindrical part located between them (Fig. 2.12). Such a ball mill body is expedient because efficiency is appreciably increased. Peripheral velocity along the conical drum scales down in the direction from the cylindrical part to the discharge outlet; the helix angle of balls is decreased and, consequently, so is their kinetic energy. The size of the disintegrated particles also decreases as the discharge outlet is approached and the energy used decreases. In a conical mill, most big balls take up a position in the deeper, cylindrical part of the body; thus, the size of the balls scales down in the direction of the discharge outlet.

For emptying, the conical mill is installed with a slope from bearing to one. In wet grinding, emptying is realized by the decantation principle, that is, by means of unloading through one of two trunnions.

With dry grinding, these mills often work in a closed cycle. A scheme of the conical ball mill supplied with an air separator is shown in Fig. 2.13. Air is fed to the mill by means of a fan. Carried off by air currents, the product arrives at the air separator, from which the coarse particles are returned by gravity via a tube into the mill. The finished product is trapped in a cyclone while the air is returned in the fan.

The ball mill is a tumbling mill that uses steel balls as the grinding media. The length of the cylindrical shell is usually 11.5 times the shell diameter (Figure 8.11). The feed can be dry, with less than 3% moisture to minimize ball coating, or slurry containing 2040% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, AG mills, or SAG mills.

Ball mills are filled up to 40% with steel balls (with 3080mm diameter), which effectively grind the ore. The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture.

When hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. As mentioned earlier, pebble mills are widely used in the North American taconite iron ore operations. Since the weight of pebbles per unit volume is 3555% of that of steel balls, and as the power input is directly proportional to the volume weight of the grinding medium, the power input and capacity of pebble mills are correspondingly lower. Thus, in a given grinding circuit, for a certain feed rate, a pebble mill would be much larger than a ball mill, with correspondingly a higher capital cost. However, the increase in capital cost is justified economically by a reduction in operating cost attributed to the elimination of steel grinding media.

In general, ball mills can be operated either wet or dry and are capable of producing products in the order of 100m. This represents reduction ratios of as great as 100. Very large tonnages can be ground with these ball mills because they are very effective material handling devices. Ball mills are rated by power rather than capacity. Today, the largest ball mill in operation is 8.53m diameter and 13.41m long with a corresponding motor power of 22MW (Toromocho, private communications).

Modern ball mills consist of two chambers separated by a diaphragm. In the first chamber the steel-alloy balls (also described as charge balls or media) are about 90mm diameter. The mill liners are designed to lift the media as the mill rotates, so the comminution process in the first chamber is dominated by crushing. In the second chamber the ball diameters are of smaller diameter, between 60 and 15mm. In this chamber the lining is typically a classifying lining which sorts the media so that ball size reduces towards the discharge end of the mill. Here, comminution takes place in the rolling point-contact zone between each charge ball. An example of a two chamber ball mill is illustrated in Fig. 2.22.15

Much of the energy consumed by a ball mill generates heat. Water is injected into the second chamber of the mill to provide evaporative cooling. Air flow through the mill is one medium for cement transport but also removes water vapour and makes some contribution to cooling.

Grinding is an energy intensive process and grinding more finely than necessary wastes energy. Cement consists of clinker, gypsum and other components mostly more easily ground than clinker. To minimise over-grinding modern ball mills are fitted with dynamic separators (otherwise described as classifiers or more simply as separators). The working principle is that cement is removed from the mill before over-grinding has taken place. The cement is then separated into a fine fraction, which meets finished product requirements, and a coarse fraction which is returned to mill inlet. Recirculation factor, that is, the ratio of mill throughput to fresh feed is up to three. Beyond this, efficiency gains are minimal.

For more than 50years vertical mills have been the mill of choice for grinding raw materials into raw meal. More recently they have become widely used for cement production. They have lower specific energy consumption than ball mills and the separator, as in raw mills, is integral with the mill body.

In the Loesche mill, Fig. 2.23,16 two pairs of rollers are used. In each pair the first, smaller diameter, roller stabilises the bed prior to grinding which takes place under the larger roller. Manufacturers use different technologies for bed stabilisation.

Comminution in ball mills and vertical mills differs fundamentally. In a ball mill, size reduction takes place by impact and attrition. In a vertical mill the bed of material is subject to such a high pressure that individual particles within the bed are fractured, even though the particles are very much smaller than the bed thickness.

Early issues with vertical mills, such as narrower PSD and modified cement hydration characteristics compared with ball mills, have been resolved. One modification has been to install a hot gas generator so the gas temperature is high enough to partially dehydrate the gypsum.

For many decades the two-compartment ball mill in closed circuit with a high-efficiency separator has been the mill of choice. In the last decade vertical mills have taken an increasing share of the cement milling market, not least because the specific power consumption of vertical mills is about 30% less than that of ball mills and for finely ground cement less still. The vertical mill has a proven track record in grinding blastfurnace slag, where it has the additional advantage of being a much more effective drier of wet feedstock than a ball mill.

The vertical mill is more complex but its installation is more compact. The relative installed capital costs tend to be site specific. Historically the installed cost has tended to be slightly higher for the vertical mill.

Special graph paper is used with lglg(1/R(x)) on the abscissa and lg(x) on the ordinate axes. The higher the value of n, the narrower the particle size distribution. The position parameter is the particle size with the highest mass density distribution, the peak of the mass density distribution curve.

Vertical mills tend to produce cement with a higher value of n. Values of n normally lie between 0.8 and 1.2, dependent particularly on cement fineness. The position parameter is, of course, lower for more finely ground cements.

Separator efficiency is defined as specific power consumption reduction of the mill open-to-closed-circuit with the actual separator, compared with specific power consumption reduction of the mill open-to-closed-circuit with an ideal separator.

As shown in Fig. 2.24, circulating factor is defined as mill mass flow, that is, fresh feed plus separator returns. The maximum power reduction arising from use of an ideal separator increases non-linearly with circulation factor and is dependent on Rf, normally based on residues in the interval 3245m. The value of the comminution index, W, is also a function of Rf. The finer the cement, the lower Rf and the greater the maximum power reduction. At C = 2 most of maximum power reduction is achieved, but beyond C = 3 there is very little further reduction.

Separator particle separation performance is assessed using the Tromp curve, a graph of percentage separator feed to rejects against particle size range. An example is shown in Fig. 2.25. Data required is the PSD of separator feed material and of rejects and finished product streams. The bypass and slope provide a measure of separator performance.

The particle size is plotted on a logarithmic scale on the ordinate axis. The percentage is plotted on the abscissa either on a linear (as shown here) or on a Gaussian scale. The advantage of using the Gaussian scale is that the two parts of the graph can be approximated by two straight lines.

The measurement of PSD of a sample of cement is carried out using laser-based methodologies. It requires a skilled operator to achieve consistent results. Agglomeration will vary dependent on whether grinding aid is used. Different laser analysis methods may not give the same results, so for comparative purposes the same method must be used.

The ball mill is a cylindrical drum (or cylindrical conical) turning around its horizontal axis. It is partially filled with grinding bodies: cast iron or steel balls, or even flint (silica) or porcelain bearings. Spaces between balls or bearings are occupied by the load to be milled.

Following drum rotation, balls or bearings rise by rolling along the cylindrical wall and descending again in a cascade or cataract from a certain height. The output is then milled between two grinding bodies.

Ball mills could operate dry or even process a water suspension (almost always for ores). Dry, it is fed through a chute or a screw through the units opening. In a wet path, a system of scoops that turn with the mill is used and it plunges into a stationary tank.

Mechanochemical synthesis involves high-energy milling techniques and is generally carried out under controlled atmospheres. Nanocomposite powders of oxide, nonoxide, and mixed oxide/nonoxide materials can be prepared using this method. The major drawbacks of this synthesis method are: (1) discrete nanoparticles in the finest size range cannot be prepared; and (2) contamination of the product by the milling media.

More or less any ceramic composite powder can be synthesized by mechanical mixing of the constituent phases. The main factors that determine the properties of the resultant nanocomposite products are the type of raw materials, purity, the particle size, size distribution, and degree of agglomeration. Maintaining purity of the powders is essential for avoiding the formation of a secondary phase during sintering. Wet ball or attrition milling techniques can be used for the synthesis of homogeneous powder mixture. Al2O3/SiC composites are widely prepared by this conventional powder mixing route by using ball milling [70]. However, the disadvantage in the milling step is that it may induce certain pollution derived from the milling media.

In this mechanical method of production of nanomaterials, which works on the principle of impact, the size reduction is achieved through the impact caused when the balls drop from the top of the chamber containing the source material.

A ball mill consists of a hollow cylindrical chamber (Fig. 6.2) which rotates about a horizontal axis, and the chamber is partially filled with small balls made of steel, tungsten carbide, zirconia, agate, alumina, or silicon nitride having diameter generally 10mm. The inner surface area of the chamber is lined with an abrasion-resistant material like manganese, steel, or rubber. The magnet, placed outside the chamber, provides the pulling force to the grinding material, and by changing the magnetic force, the milling energy can be varied as desired. The ball milling process is carried out for approximately 100150h to obtain uniform-sized fine powder. In high-energy ball milling, vacuum or a specific gaseous atmosphere is maintained inside the chamber. High-energy mills are classified into attrition ball mills, planetary ball mills, vibrating ball mills, and low-energy tumbling mills. In high-energy ball milling, formation of ceramic nano-reinforcement by in situ reaction is possible.

It is an inexpensive and easy process which enables industrial scale productivity. As grinding is done in a closed chamber, dust, or contamination from the surroundings is avoided. This technique can be used to prepare dry as well as wet nanopowders. Composition of the grinding material can be varied as desired. Even though this method has several advantages, there are some disadvantages. The major disadvantage is that the shape of the produced nanoparticles is not regular. Moreover, energy consumption is relatively high, which reduces the production efficiency. This technique is suitable for the fabrication of several nanocomposites, which include Co- and Cu-based nanomaterials, Ni-NiO nanocomposites, and nanocomposites of Ti,C [71].

Planetary ball mill was used to synthesize iron nanoparticles. The synthesized nanoparticles were subjected to the characterization studies by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques using a SIEMENS-D5000 diffractometer and Hitachi S-4800. For the synthesis of iron nanoparticles, commercial iron powder having particles size of 10m was used. The iron powder was subjected to planetary ball milling for various period of time. The optimum time period for the synthesis of nanoparticles was observed to be 10h because after that time period, chances of contamination inclined and the particles size became almost constant so the powder was ball milled for 10h to synthesize nanoparticles [11]. Fig. 12 shows the SEM image of the iron nanoparticles.

The vibratory ball mill is another kind of high-energy ball mill that is used mainly for preparing amorphous alloys. The vials capacities in the vibratory mills are smaller (about 10 ml in volume) compared to the previous types of mills. In this mill, the charge of the powder and milling tools are agitated in three perpendicular directions (Fig. 1.6) at very high speed, as high as 1200 rpm.

Another type of the vibratory ball mill, which is used at the van der Waals-Zeeman Laboratory, consists of a stainless steel vial with a hardened steel bottom, and a single hardened steel ball of 6 cm in diameter (Fig. 1.7).

The mill is evacuated during milling to a pressure of 106 Torr, in order to avoid reactions with a gas atmosphere.[44] Subsequently, this mill is suitable for mechanical alloying of some special systems that are highly reactive with the surrounding atmosphere, such as rare earth elements.

In spite of the traditional approaches used for gas-solid reaction at relatively high temperature, Calka etal.[58] and El-Eskandarany etal.[59] proposed a solid-state approach, the so-called reactive ball milling (RBM), used for preparations different families of meal nitrides and hydrides at ambient temperature. This mechanically induced gas-solid reaction can be successfully achieved, using either high- or low-energy ball-milling methods, as shown in Fig.9.5. However, high-energy ball mill is an efficient process for synthesizing nanocrystalline MgH2 powders using RBM technique, it may be difficult to scale up for matching the mass production required by industrial sector. Therefore, from a practical point of view, high-capacity low-energy milling, which can be easily scaled-up to produce large amount of MgH2 fine powders, may be more suitable for industrial mass production.

In both approaches but with different scale of time and milling efficiency, the starting Mg metal powders milled under hydrogen gas atmosphere are practicing to dramatic lattice imperfections such as twinning and dislocations. These defects are caused by plastics deformation coupled with shear and impact forces generated by the ball-milling media.[60] The powders are, therefore, disintegrated into smaller particles with large surface area, where very clean or fresh oxygen-free active surfaces of the powders are created. Moreover, these defects, which are intensively located at the grain boundaries, lead to separate micro-scaled Mg grains into finer grains capable to getter hydrogen by the first atomically clean surfaces to form MgH2 nanopowders.

Fig.9.5 illustrates common lab scale procedure for preparing MgH2 powders, starting from pure Mg powders, using RBM via (1) high-energy and (2) low-energy ball milling. The starting material can be Mg-rods, in which they are processed via sever plastic deformation,[61] using for example cold-rolling approach,[62] as illustrated in Fig.9.5. The heavily deformed Mg-rods obtained after certain cold rolling passes can be snipped into small chips and then ball-milled under hydrogen gas to produce MgH2 powders.[8]

Planetary ball mills are the most popular mills used in scientific research for synthesizing MgH2 nanopowders. In this type of mill, the ball-milling media have considerably high energy, because milling stock and balls come off the inner wall of the vial and the effective centrifugal force reaches up to 20 times gravitational acceleration. The centrifugal forces caused by the rotation of the supporting disc and autonomous turning of the vial act on the milling charge (balls and powders). Since the turning directions of the supporting disc and the vial are opposite, the centrifugal forces alternately are synchronized and opposite. Therefore, the milling media and the charged powders alternatively roll on the inner wall of the vial, and are lifted and thrown off across the bowl at high speed.

In the typical experimental procedure, a certain amount of the Mg (usually in the range between 3 and 10g based on the vials volume) is balanced inside an inert gas atmosphere (argon or helium) in a glove box and sealed together with certain number of balls (e.g., 2050 hardened steel balls) into a hardened steel vial (Fig.9.5A and B), using, for example, a gas-temperature-monitoring system (GST). With the GST system, it becomes possible to monitor the progress of the gas-solid reaction taking place during the RBM process, as shown in Fig.9.5C and D. The temperature and pressure changes in the system during milling can be also used to realize the completion of the reaction and the expected end product during the different stages of milling (Fig.9.5D). The ball-to-powder weight ratio is usually selected to be in the range between 10:1 and 50:1. The vial is then evacuated to the level of 103bar before introducing H2 gas to fill the vial with a pressure of 550bar (Fig.9.5B). The milling process is started by mounting the vial on a high-energy ball mill operated at ambient temperature (Fig.9.5C).

Tumbling mill is cylindrical shell (Fig.9.6AC) that rotates about a horizontal axis (Fig.9.6D). Hydrogen gas is pressurized into the vial (Fig.9.6C) together with Mg powders and ball-milling media, using ball-to-powder weight ratio in the range between 30:1 and 100:1. Mg powder particles meet the abrasive and impacting force (Fig.9.6E), which reduce the particle size and create fresh-powder surfaces (Fig.9.6F) ready to react with hydrogen milling atmosphere.

Figure 9.6. Photographs taken from KISR-EBRC/NAM Lab, Kuwait, show (A) the vial and milling media (balls) and (B) the setup performed to charge the vial with 50bar of hydrogen gas. The photograph in (C) presents the complete setup of GST (supplied by Evico-magnetic, Germany) system prior to start the RBM experiment for preparing of MgH2 powders, using Planetary Ball Mill P400 (provided by Retsch, Germany). GST system allows us to monitor the progress of RBM process, as indexed by temperature and pressure versus milling time (D).

The useful kinetic energy in tumbling mill can be applied to the Mg powder particles (Fig.9.7E) by the following means: (1) collision between the balls and the powders; (2) pressure loading of powders pinned between milling media or between the milling media and the liner; (3) impact of the falling milling media; (4) shear and abrasion caused by dragging of particles between moving milling media; and (5) shock-wave transmitted through crop load by falling milling media. One advantage of this type of mill is that large amount of the powders (100500g or more based on the mill capacity) can be fabricated for each milling run. Thus, it is suitable for pilot and/or industrial scale of MgH2 production. In addition, low-energy ball mill produces homogeneous and uniform powders when compared with the high-energy ball mill. Furthermore, such tumbling mills are cheaper than high-energy mills and operated simply with low-maintenance requirements. However, this kind of low-energy mill requires long-term milling time (more than 300h) to complete the gas-solid reaction and to obtain nanocrystalline MgH2 powders.

Figure 9.7. Photos taken from KISR-EBRC/NAM Lab, Kuwait, display setup of a lab-scale roller mill (1000m in volume) showing (A) the milling tools including the balls (milling media and vial), (B) charging Mg powders in the vial inside inert gas atmosphere glove box, (C) evacuation setup and pressurizing hydrogen gas in the vial, and (D) ball milling processed, using a roller mill. Schematic presentations show the ball positions and movement inside the vial of a tumbler mall mill at a dynamic mode is shown in (E), where a typical ball-powder-ball collusion for a low energy tumbling ball mill is presented in (F).

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