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Comments on comminution.

The December 1992 issue of Mining Magazine carried a lead article on 'Cutting Comminution Costs' and invited comments. A selection of those received is presented here.

As mentioned in our December 1992 comment page, comminution consumes a large amount of power and is a costly process. As might be expected, everyone involved with comminution, be they the manufacturers of the often large and powerful machines, the project engineers who have to select equipment for a new plant, or the academics investigating how mineral particles break, all have their own ideas.

In the certain knowledge that there will be other points of view beyond those expressed here, we present a selection of comments on the subject of comminution.

A manufacturer's view

Writing of fine crushing and new cone crusher technology, P. Hedvall, A. Svensson and J.F. Steer of Allis Minerals Systems' Crushing and Screening Division make a number of points regarding the improvement of energy efficiency in comminution. They point out that large modern crushing plants for the production of aggregates in the quarrying industry often incorporate four, five or even six stages of crushing, in contrast to the normal maximum of three crushing stages found at metal mines.

Amongst the reasons for this, they suggest that in a mining operation a deterioration in the product from the crushing plant is often masked: a coarser product merely means more work is thrust onto the grinding section, whereas at a quarry, the product from the crushing section is the saleable end product on which the company's revenue depends. This, and the fact that the value per tonne of quarry products tends to be much less than that of metalliferous ore, has resulted in aggregate producers being much more interested in cost savings in the crushing plant than, in general, are mine operators.

One of the key factors in crusher design is the consideration of how the energy is transferred into the flow of material passing through the crusher chamber: it is not so much the setting that determines the fineness of the product, but the energy input per tonne of material which is important.

Consideration of Bond's formula for the energy required in comminution shows that, for a given size reduction ratio of, say, 3:1, fine crushing needs more energy than coarse crushing. It is for this reason that the normal mine crushing plant has more crushers in the tertiary stage than in the secondary stage. A corollary of this is that, when looking for energy savings in crushing, there is most to be gained by improving the efficiency of the fine crushing section.

There is, in general, a limit to the amount of energy which can actually be put into a tonne of ore inside a given crusher. In fine crushing applications, it is usually preferable to use a larger number of smaller crushes, which are better able to utilise power, than a smaller number of larger crushers. The most profitable avenue to explore when searching for higher performance is to make sure that each crusher operates at a level as close as possible to its maximum rating. This calls for steady and controlled conditions approximating to a choke feed, indicating the benefit of a surge bin ahead of the crusher, from which it can be fed smoothly and continuously.

The tonnage throughput depends on the volumetric characteristics of the crusher's crushing chamber and also on the bulk density of the material to be crushed. For a given ore the latter, in turn, depends on the material's size-range distribution. A wide-ranging ('long') size fraction (say 0-32mm) has a much higher bulk density than a closely-sized ('short') fraction (say 16-32mm), the smaller pieces tending to fill the voids between the larger particles. If the material includes a high proportion of fines, there is a tendency for it to pack in the crushing chamber and the deleterious effect on its crushability is considerable.

Much is to be gained by screening out the fines ahead of crushing. Screens are not just an unavoidable extra complication, they are an integral part of the comminution process. There are, however, in closed-circuits incorporating both screens and crushers, many examples of screens which were selected to deal with a crusher's supposed product curve and which were then found to be too small. If the crusher selection has been a little optimistic and the crusher does not give as fine a product as predicted, there is an increase in circulating material and a higher-than-expected load on the screen, making it appear to be the screen which is undersized.

Both crushers and screens give better performances when they are fed material at a uniform rate. It is thus beneficial in terms of energy efficiency to incorporate surge bins not only ahead of crushers but also ahead of screens.

The advent of microcomputers has made it possible to increase the performance of crushers using a system of automatic setting regulation. In Hydracone crushers the shaft is supported by what amounts to a hydraulic jack and monitoring the hydraulic pressure gives a direct read-out of the crushing force. Thus there are two parameters which can be monitored - motor power draw and hydraulic pressure. These can be used as the basis of control.

The DHE philosophy

Dorbyl Heavy Engineering (DHE), a wholly-owned subsidiary of Dorbyl Ltd, the largest engineering group in South Africa, has, since 1949, designed and manufactured 640 grinding mills, most of which have been supplied to users in Africa. The largest mill supplied to date was a 5.80 m x 8.50 m (19 ft x 28 ft) ball mill with a 4,850 kW drive motor.

D.A. Reid, executive director of DHE's Products Division, comments that the selection of grinding mills for a specific application is based on ore characteristics (work index, grain size, grindability), the grinding mode (wet or dry), capacity, circuit configuration (open or closed circuit), feed size, desired product size and other special process requirements.

The need for crushing prior to grinding has in the past two decades largely been replaced by the advent of autogenous grinding mills. However, in applications where the ore competency demands crushing prior to grinding, the derivation of the transition point where crushing stops and grinding commences, is a matter of economics.

In Fig. 2, the total cost per tonne (capital plus operating) of crushing increases with decreasing product size, whereas the total cost per tonne of grinding decreases with decreasing feed size. Consequently, the total cost of comminution, Curve C, passes through a minimum. Hence the size at which the minimum occurs should be the transition size between crushing and grinding.

In applications where the ore competency is compatible with autogenous grinding, the run-of-mine ore is normally crushed to 100% passing 300 mm to facilitate easier handling of the material. The ore is then milled either in the autogenous or semi-autegenous mode, depending on the ore competency and the application.

Autogenous grinding mills had originally been devised to replace the multistage crusher plants as well as the rod mills which preceded ball mills, especially in base-metal comminution circuits. The aim was to produce, in a single process, a product which would be a suitable feed to ball mills. For various reasons, these mills took on the 'pancake' geometry (L:D ratio |is less than~ 1).

DHE has taken the application of autogenous mills one step further than just serving as fine crushers or coarse primary mills. DHE autogenous mills have been in operation as single-stage mills in various South African gold mines for the past 15 years. In this application these mills are yielding throughputs of 100 - 140 t/h and are producing a final product of 80% passing 74 microns from a typical feed of 80% passing 150 mm. The work index of the ore milled is approximately 19 kWh/t.

It is DHE philosophy to investigate the possibility of single-stage autogenous grinding for all mill enquiries received, since this comminution route holds big advantages to the end user in terms of reduced capital and operating costs.

Equipment selection: Application power is determined by using modified Bond and Rowland formulae. The actual mill size for the required application power is derived from proven power draw formulae using selected mill diameters, the mill charge fraction and the critical speed fraction.

Furthermore, ore type characterisation is done via the determination of ore breakage functions in pendulum tests. These breakage characteristics are used to estimate full scale performance of crushers, rod, ball and autogenous mills. For the latter a standard abrasion test is added.

J.K. Simmet Comminution Simulation software enables a vast number and variety of circuit designs to be simulated so that the optimal design for the task and expected range of variation of input and flow conditions may be arrived at, or at least approximated, before expensive experiments with real plant - or involving a pilot plant - are undertaken.

The final decision regarding the exact size and type of grinding circuit configuration required is made in close liaison with the customer.

The DHE open end mill: The features of the open end discharge autogenous mill include a true low level discharge via the open end, the benefits of which are a high hydraulic gradient plus centifugal force, which give a lower pulp level and hence less dwell time of particles in the mill, which minimises heavy mineral lock-up and over-grinding; the choking effect of pan lifters is eliminated, which makes the mill highly tolerant of rapid variations in feed particle size distribution; speed optimisation is possible without pan lifter limitation on slurry flow.

Another feature is a high critical speed, of up to 90%, which has the benefit of yielding a more activated charge plus high circulating loads for a fine grind, while achieving maximum power draft per unit mill diameter. In addition, the mill has a high charge level, which utilises the capacity of the mill fully and also helps achieve maximum power draft per unit mill volume. The length:diameter ratio is larger than 1, which means the mill shell and drive train are relatively less expensive than those of 'pancake' mills. The mill is supported on the shell by slipper bearings, which gives flexibility in the design of mill feed and discharge arrangements.

Potential savings: DHE has to date installed seventeen single-stage opened discharge autogenous mills in South Africa, the mill sizes ranging from 4.85 m x 9.15 m (16 ft x 30 ft) to 4.85 m x 12.19 m (16 ft x 40 ft). In one particular installation, as an example of what can be achieved, two mills were installed to replace an old comminution circuit, comprising three-stage crushing followed by ball and pebble mills. The customer has since reported a saving in comminution operating costs of 25%.

A project engineer's view

Derek Barratt, Senior Consultant, Grinding Systems, with Fluor Daniel Wright(*), considers first the selection of machines for a new conventional plant.

The decline in the use of 'conventional' secondary/tertiary crushing and rod/ball milling in favour of autogenous/semi-autogenous and secondary grinding, when designing new plant, has resulted in several attempts to reduce capital and operating costs for crushing. For instance, the advent of larger cone crushers (e.g. Nordberg's MP 1000 series), higher speed crushing, higher energy crushing (Allis Mineral Systems), Water Flush|TM~ crushing (Nordberg) and high pressure rolls crushing (Krupp/Polysius) all claim to reduce operating costs on a cost-per-tonne basis.

Examination of these innovations/options in the context of designing an overall comminution circuit requires a closer look at:

* unit capacity, t/h

* feed sizing and limitations

* product sizing as feed to grinding

* plant layout considerations

* unit operating availability

* specific power consumption, kWh/t (per unit and overall)

* operating work index, Wi (per unit and overall)

* maintenance costs in terms of replacement wear parts and labour.

The capital cost of a new plant is obviously influenced by:

* the number of units required

* the number of stages of crushing required to feed single-stage ball milling

* the use of large diameter ball mills (5m dia. and larger)

* the assumption that rod mills would no longer be used because of the higher operating cost compared to fine crushing and the trend towards larger diameter ball mills

* the requirements for material handling (screens, feeders, conveyors, transfer points, etc.)

* the requirements for intermediate product storage/surge capacity (feeder bins, fine ore bins, etc.)

* the effect of all the above on space requirements, site and plant layout.

It has to be recognised that the commercial use of many of these crushing options is in its infancy and has hitherto been applied to smaller scale plants, less than 3,000 t/d per unit, exceptions being the larger cone crushers in the aggregate sector and on a test basis for copper ores. Eventually, wider acceptance of 1,000 hp cone crushers and larger banana type screens could lead to a capital cost advantage compared to the autogenous/semi-autogenous alternative for plants of 25,000 t/d capacity and higher.

New autogenous/semi-autogenous plant: The number of new plants which have been designed over the last 25 years and particularly over the last 13 years, to feature autogenous or semi-autogenous mills, is legion. Selection of equipment for this comminution route is based on examination of all the factors listed for 'conventional' plant in terms of the development of capital and operating costs, with greater emphasis placed on:

* physical properties of the rock/ore types

* pilot plant testing

* development of critical size (for which crushing is definitely cheaper than grinding)

* power efficiency

* flowsheet configuration

Unit sizes of equipment in these circuits range from:

* 500 hp to 17,000 hp for primary mills

* 500 hp to 7,500 hp for secondary (ball) mills

* 11,000 hp for gearless drives (ring motors)

* 5 m to 11 m diameter for primary mills

* 2.5 m to 6 m diameter for secondary (ball) mills

The maximum power rating for a single pinion drive is currently 7,500 hp. This has been installed on both primary and secondary mills (e.g. Korri Kollo, Bolivia) and is a standard for 6 m dia. ball mills (e.g. Kennecott at Copperton and Phelp Dodge's La Candelaria).

These current maxima for unit equipment sizes and unit power ratings are expected to be exceeded by the end of this century. Selection of drive type is being influenced by the increasing popularity of variable speed drives, whether they are ring motors, DC motors or load commutated inverted synchronous motors.

The prime justification for selecting the autogenous or semi-autogenous route is rounded in its lower total incremental capital cost, as illustrated in Fig. 4, in spite of its higher cost of basic equipment when both are compared to the equivalent costs for 'conventional' plant. Total incremental cost includes civil, structural, mechanical, electrical and controls installation. Grinding and classification cost includes basic equipment purchase and installation, with building structure and ancillaries excluded. Any reduction in operating cost, when converted to a net present value, is project specific and minor by comparison, usually as a result of trading-off slightly higher power and media costs against reduced operating and maintenance labour plus maintenance supplies.

Modifications/expansions: Modifications and expansions to existing 'conventional' plants are usually assessed on the basis of:

* significant improvements in operating cost

* significant increases in throughput and product revenue

* modest increases in throughput and product revenue resulting from improvement in process control

All three of these criteria are interdependent and can be applied in two specific scenarios:

* reduction in the operating cost for grinding by elimination of rod milling, if applicable, and production of a finer feed to ball milling. This can be achieved by finer dry crushing or installation of Water Flush|TM~ crushing. Conversion of rod mills to ball mills is another option to be considered (as, for example, at Amax's Sleeper mine).

* replacement of secondary/tertiary crushing with autogenous or semi-autogenous primary grinding, secondary grinding using existing ball mills, conversion of rod mills (if applicable) to ball mills, addition of new ball mills (if required) and installation of pebble crushers (if required). Many plant expansions have followed this route, including Codelco's El Teniente copper/molybdenum plant, Mt. Isa's copper plant, Placer Pacific's Marcopper and Western Mining's Leinster nickel.

A recently completed expansion project is Inco's Mills Rationalisation scheme, in which the addition of one Allis Mineral Systems' 32 ft diameter by 13.5 ft long (9.76 m x 4.12 m) semi-autogenous (SAG) mill with a 11,000 hp (8,200 kW) twin DC drive to the Clarabelle concentrator permitted the mothballing of the Frood Stobi concentrator.

Conclusions: The types of equipment which are available to the process engineer in the design of comminution circuits have changed little in concept during this century. Whereas it is cheaper to crush than to grind in terms of operating cost, economies of scale have rendered autogenous or semi-autogenous grinding more attractive in terms of reduced capital cost per t/d milled.

Newer concepts, such as pressure rolls, Water Flush|TM~ crushing and tower mills are each limited by their respective feed size to specific applications and cannot be described as being suitable for large-tonnage projects.

Until a breakthrough is made in developing a means of commercially reducing the overall specific power consumption (kWh/t, as calculated by the Bond equation) the best industry can do is to minimise capital and operating costs by the correct application of existing technology.

An academic view

Dr. B.A. Wills and Professor K. Atkinson of the Camborne School of Mines, Cornwall, U.K. point out in a paper soon to be published in Minerals Engineering that comminution is one of the most intensively researched areas of the minerals industry. Much effort has been spent in attempting to reduce the high operating costs, but relatively little in developing practical methods to promote enhanced liberation of the minerals from each other. They point out the need to research more deeply into the mechanisms of the breakage processes in current comminution machines, particularly into the promotion of intergranular fracture. In order to do this, control of crack propagation and the nature and role of grain boundaries are, they suggest, areas deserving most attention.

The paper explores some aspects of the Griffiths theory of brittle behaviour, as well as elastic and plastic behaviour, and presents ideas on the role of mineral grain boundaries in crack propagation. In their discussion, the authors point out that the energy efficiency of creating new surface in the comminution of quartz from 1,000 |mu~m to 100 |mu~m is about 0.5%. This shows that massive amounts of energy are put into rocks during comminution, well above the amounts needed to break the particles. This excess energy causes cracks to propagate in an unstable fashion.

As well as propagating cracks at high rates, the high imparted forces may also produce cracking at the rock surface due to relaxation of the high compressive stresses at the points of loading, such as between successive nips in compression crushers. Products from compression crushing fall into two distinct size ranges: coarse particles resulting from induced tensile failure and fines from compressive failure near the points of loading. Products from impact crushing, however, are often very similar in size and shape.

Stress relaxation is a little researched but potentially very important effect in comminution. In recent years the high-compression roller mill, developed in Germany, has found application in the cement and limestone industries. There is some evidence to show that mineral liberation can be improved using these devices: it is interesting to note that when the pressure is released many micro-cracks are observable, which substantially reduce the work index of the rock. In some cases, these cracks have been observed at the grain boundaries and this is already being exploited in many kimberlite processing plants to enhance liberation of the diamonds without breaking the valuable larger stones.

The comminution method most closely simulating the gentle mechanical action which produces liberated grains in alluvial deposits is autogenous grinding. Several tests have shown that ores ground autogenously float faster and with better selectivity than if ground conventionally. By this argument, the energy efficiency of autogenous grinding should be higher than that of steel-media grinding. However, much depends on the type of rock and there are reports of unit energy costs for autogenous grinding being higher than conventional by between 25% and 100%. It may be that much of the energy in autogenous grinding is wasted in doing nothing.

Some recent studies have examined the benefit of thermally-assisted liberation, in which rock is heated to 600|degrees~C then quenched in water before comminution. Differential expansion and contraction of the different mineral grains lowered the resistance to grinding. However, testwork to assess liberation improvements after conventional steel grinding proved inconclusive.

The authors conclude that areas worthy of investigation are:

* the nature and role of grain boundaries in crack propagation;

* the importance of strain rate on crack propagation, and the comparison of the nature of crack propagation in steel and autogenous grinding;

* the role of impact and compressive crushing on crack nucleation and the importance of stress relief;

* the potential for heat treatment as a prelude to grinding.

Technical innovations

Barmac Duopactor: The Barmac Duopactor rock-on-rock crusher, manufactured by Tidco Croft Ltd, a division of Allis Mineral Systems, is essentially a tertiary or quaternary crusher which may be adjusted to yield generous quantities of fines.

The Duopactor uses a field-proven rock-lined rotor which acts as a high velocity dry stone pump, hurling a continuous rock stream into a stone-lined crushing chamber. Material fed into the top of the machine is accelerated by the rotor to exit velocities of up to 100 m/sec. The rotor continuously discharges into the crushing chamber. This process replenishes the rock lining, while at the same time maintaining a rock-on-rock chain reaction of crushing and grinding. A second stream of material, in a controlled quantity, can be cascaded into the crushing chamber turbulence, causing a supercharging of the particle population within the chamber, improving the energy transfer. This, in combination with the other variables of rotor diameter and speed plus crushing chamber profile, enhances power efficiency, reduces wear and provides an efficient means of controlling the grinding and crushing action, to either maximise or minimise fines.

Attrition energies generated within the crushing chamber are many times greater than the energy levels typical of conventional impact crushers and grinding mills, which provides significant power savings when producing fine products. The adoption of autogenous rock-on-rock design principles throughout the machine reduces wear costs to a minimum.

Tidco Barmac Duopactors have long been used in the quarrying industry, particularly for the production of agricultural lime from 50 mm limestone feed. Applications in the metalliferous mining industry are gathering pace. One recent example, previously mentioned in Mining Magazine (December 1991, pp 367-370) is at RTZ's Renco mine, Zimbabwe, where Barmac VSI machines were installed. Nominally tertiary crushers, the location of the Barmacs between mill feed silo and ball mill implies that they are operating as a primary milling stage.

At the February 1993 TMS Annual Meeting in Denver, Colorado, E. W. Lithgow (General Superintendent, Mines) presented a paper on 'Nickel Laterites of Central Dominican Republic: Mineralogy and Ore Dressing', in which he described the operations of Falconbridge Dominicana. Following recent plant modifications two single feed Barmac Duopactors, Model 9600 Mk.2, driven by 250 hp motors, are in operation. Feeding rates to the Barmacs at Falcondo are normally in the range of 130 t/h, with rotor velocities of slightly over 900 rev/min. The intensity of crushing can be controlled by either increasing or decreasing the rotor speed, as required. The Barmac can selectively treat lower grade and relatively harder ores without producing excessive amounts of fines, as the previous cone crusher/hammermill combination used to do from this type of feed. The quality of ore briquettes has improved as a result of the Barmac's crushing action, and the improved briquettes have in turn resulted in reduced nickel losses in the furnace slag and trouble-free furnace operation.

MMD rolls: One example of significant development in mineral size reduction is the manner in which MMD has extended the technology of roll crushing. Having established that the ratio of compressive to tensile strength of most of the world's minerals is about 10, MMD exploits this difference by breaking in tension or shear rather than by crushing, which it claims is an indiscriminate action giving no control over discharge size and producing excessive fines.

To achieve its unique breaking action, MMD uses large teeth on small rolls, which break rock by a snapping and chopping action as the mineral passes through. The spaces between the large teeth are such that undersize material can pass through without absorbing power, much in the manner of a scalping screen. MMD machines are thus able to handle large capacities in much smaller dimensions than are required by orthodox roll crushers, which need large diameter drums to provide an acceptable entrance throat to the nip point. Since all the material has to pass through this point, the speed of rotation of orthodox rolls is higher than is necessary with the MMD machine. This is a disadvantage from the wear aspect and also presents problems in dealing with tramp metal ff severe damage is to be avoided. An advantage of the MMD machine is that its low speed enables it to stall without damage. Recovery from stall is then easily achieved by reversal of one roll.

Tower Mill: The Tow-er mill, developed by the Japanese company Kubota Tower Mill Corp., is said to require about half the energy consumption of conventional ball mills.

The Tower mill can be described as a type of stirred ball mill designed for large-volume grinding. Its vertical shell does not rotate, thus giving an immediate cut in energy usage. Its internal classification system reduces over-grinding and, as grinding is by abrasion rather than percussion, it can produce ultrafine particles. Other plusses claimed are a lower noise level, low cost, simple foundations and a short installation period, plus greater operational safety. Periodic maintenance of the mill includes addition of new grinding media, replacement of tip and flight liners and replacement of protective bars and grids.

Recent installations which have been described in Mining Magazine are those of several 450 kW Tower mills in the regrind circuits at Red Dog Zn-Pb mine in Alaska (MM December 1990, pp 418-425) and a KW-500 Tower mill at MIM's zinc/lead concentrator at Mount Isa (MM, July 1992, pp 24-32), following MIM's successful experience with a Tower mill at its nearby Hilton mine.

VertiMill|TM~: Mineral Processing Systems, Inc. (MPSI), now part of Allis Mineral Systems, manufactures the VertiMill vertical stirred grinding mill, described as a highly efficient system for wet grinding. The VertiMill|TM~ was developed as an energy-saving alternative to the tumbling mill in fine grinding operations. The finer the product, the greater the power savings which can be realised compared with a tumbling mill. The VertiMill|TM~ can reportedly improve the efficiency of a grinding circuit by controlling the system to produce an overflow material of a specific product size. This precise method of overflow control reduces both operating costs and the generation of extreme fines. For applications requiring an ultrafine product, the circuit is revised and controlled to allow maximum generation of fines. This versatility is said to make the VertiMill|TM~ ideal for a very wide range of grinding applications.

When compared with a tumbling mill, the VertiMill|TM~ offers the advantages of lower installation costs, lower operating costs, higher energy efficiency, less floor space, simpler foundations, less noise, fewer moving parts, less overgrinding and greater safety. The mill can grind any material of 6 mm top size or less that can be ground in a tumbling mill. It is particularly suitable where products of 200 mesh or finer are required.

TABULAR DATA OMITTED

Water Flush|TM~: One of the more significant innovations in comminution in recent years has come from Nordberg, in the form of Water Flush|TM~ (WF) technology. The WF cone crusher is capable of producing larger tonnages of finer products than conventional cone crushers. This capability has been proved in a number of U.S. mine installations.

WF technology is specifically designed to maximise particle reduction in a single pass through the cone crusher. Improved material transport capabilities provide for quicker removal of generated fines, thereby preventing these fines from forming pads in the crusher cavity.

Special design innovations to the WF cone crusher include modified eccentric speeds and throws to maximise fines output. Labyrinth-type seals protect the crusher lubrication system from water contamination. Internal drive components have been upgraded to allow higher operating horsepower. The load-carrying bearings are designed at tighter tolerances so that a smaller effective crusher setting can be maintained. Another major component modification is the stationary shaft around which the eccentric crushing action is generated. This shaft design is capable of withstanding the high cyclic stresses associated with smaller crusher settings and the modified speeds and throws.

The patented WF apparatus evenly distributes water around the crushing cavity and ensures a constant flow of fluid. The evenly distributed flow prevents an uneven accumulation of fines during the crushing process.

According to Nordberg engineers, the crushing action within a WF cone crusher allows an open-circuit crushing performance unmatched by other conical crushers. A unique liner design allows an increased number of sizing strokes to occur. These multiple impacts ensure a greater percentage of the crusher discharge is in a size range below the crusher's closed-side setting.

The first Water Flush|TM~ installation was in Brazil. Since then, eight such units have been delivered to U.S. mines. Four WF500s (500 hp) are in operation at Phelps Dodge's Chino mine to deal with oversize copper ore prior to fine grinding; two WF400s at Amax Gold's Sleeper mine were commissioned in October 1990 for primary 'grinding' of gold ore; one WF500 was recently commissioned at Amax Gold's Haydon Hill mine, and soon afterwards a WF300 was started up by Hibbing Taconite to deal with trommel oversize iron ore. Cyprus Minerals will soon install five WF800s at its Bagdad copper mine.

Operating experience with the Haydon Hill installation is covered in a separate article in this issue.

* Writing from: Fluor Engineers (Pty) Ltd, P.O. Box 784850, Sandton 2146, Republic of South Africa. Tel: +27 (0)11881 1798. Fax: +27 (0)11 881 1781.

Reward!

A reward is offered for information leading to the location of and positive identification of existing Allis Mineral Systems mills.

During the past 100 years, over 8,000 grinding mills have been supplied by Allis Mineral Systems and its predecessor companies: Allis Chalmers, Boliden Allis, Denver Equipment Company, Dominion Engineering, Hardinge, Kennedy Van Saun, Koppers, Marcy and Sala. Many of these mills are still in use.

Allis Mineral Systems' Customer Service Department still provides parts and service for numerous mills over 70 years old. Records and drawings are available for most of these mills except for a few that were manufactured under licence. By locating as many mills as possible, the company will be able to extend its range of customer services beyond its regular customers. Its objective is to establish lines of communication with every Allis Mineral Systems mill user and make available O.E.M. parts and field services to keep these machines in operation.

The following information is requested:

* Mill brand * Owner company * Full address * Serial number * Person responsible for maintenance * Telephone number * Size (if known) * Fax number

Please mail the above information, marked for the attention of the Customer Service Wanted Program, to:

Allis Mineral Systems, P.O. Box 15312, York, PA 17405-7312, U.S.A.

The first person to turn in the above information on any one machine will receive a reward. Complete name and address information is required from the person claiming the reward. Only one reward per person. Allis Mineral Systems or associated company employees or agents are not eligible for a reward.
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Title Annotation:crushing machinery designs in mining
Author:Brewis, Tony
Publication:Mining Magazine
Date:May 1, 1993
Words:5347
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