Allis-Chalmers

Equipment Sizing: Crusher or Grinding Mill

UNTIL THE THIRD THEORY OF COMMINUTION of “Work Index” method of determining crushing and grinding mill size was introduced, there was no way of accurately figuring the most applicable, most economical size of crushing and grinding mill.

Naturally, with little or no factual operating data correlated in useful form, it was easy enough, even for the most experienced, to arrive at an incorrect size of crusher or grinding mill, especially when a slightly smaller unit carried an advantage in initial investment.

The “Work Index” method, frequently referred to as the Bond* method, is based on extensive field operating data and equally extensive laboratory data covering wide varieties of materials, ranges of reduction sizes and types of equipment. The correlation of all this factual material enabled the establishment of a consistent common factor, known as the Work Index, for accurately determining crushing and grinding mill sizes.

The Work Index is actually the total work input in kwhr/short ton required to reduce from theoretically infinite particle size to 80% passing 100 microns, or to approximately 67% passing 200 mesh.

Knowing the Work Index, one has but to apply the proper given equation to determine the power input required. The calculated power input in turn enables you to ….Read more

Open or Closed Circuit Crushing

The factors governing the determination of capacity for any open circuit crushing stage are much the same as those we outlined in connection with the secondary stage. In a properly designed crushing plant, excepting those plants which by-pass a portion of the pit-run around the head end of the flow line and inject this fraction back into the system at one of the reduction stages; the open circuit tonnages decrease from stage to stage, because fractions of the flow which are finer than the setting of each stage are scalped off and bypassed around it. Sometimes finished-product fractions are taken off immediately after the primary, or secondary, stage and sent directly to the finished-material storage; this bleeding off of finished material may also be carried on at each scalping point in the flow line. These various possibilities in flow diversion, and re-entry, point clearly to the necessity for preparing a complete flowsheet of the proposed plant before attempting to calculate the required capacity of any crushing stage. Only by doing this can we hope to approximate the requirements for the different stages.Vibrating Screen
The facts on which we base our flowsheet must ….Read more

Crushing Plant: Surge Bins VS Stockpiles

I need to further comment on the influence of surge storage upon plant operation. The provision of adequate surge storage at the right places in the flow line is of sufficient importance to warrant a little further consideration.stockpile

It is desirable, in the crushing plant, as it is in any production process, to achieve a smooth and uninterrupted flow through the plant so that the reduction crushers and sizing screens will be operating at all times under uniform load conditions, and at full capacity. It is not always possible to feed the plant in this manner; a smooth flow of feed to the primary crusher is the exception, rather than the rule; therefore, if we are to smooth out the flow in the plant itself we must have elasticity in our flow line, and the logical way to obtain it is to provide surge storage ahead of each crushing stage. We can, of course, get around this by providing enough crushing capacity to absorb the peaks, but this method is expensive p. also it throws a variable load on-the screens; and screens do not perform at maximum efficiency under such ….Read more

Single VS Multi-Stage Crushing

There are no set rules for determining whether the secondary stage should consist of one single crusher, or of two or more machines operating in parallel. The decision must be made upon the merits of each problem. If the required receiving opening necessitates the selection of a crusher whose capacity equals or exceeds that of the primary crusher there is no object in going to a two-stage arrangement. Frequently this will be the case where a primary jaw crusher is to be followed by a gyratory machine. On the other hand, if the primary is a large gyratory, and the full output of this crusher is to gauge the. output of the plant, it will be necessary to install a, battery of two or more gyratories for the secondary reduction. The number and size of these will depend upon the size of the primary, its setting, the type of secondary to be used, and its setting. It is desirable that the multiple set-up be selected in even numbers, rather than odd; that is, either two or four units, rather than three. The difficulties in achieving an equitable distribution of feed into three units has been amply demonstrated ….Read more

Secondary Crushing Equipment

The term “secondary crushing” has become well established and familiar through long usage; it applies to the crushing stage, either single or multiple, which follows immediately after the primary crusher, taking all or a portion of the product of the primary crushing stage as its feed. The term should not be used, as it sometimes is, to designate a particular type or size of crusher because any type and size might conceivably be used for secondary crushing. A very large number of secondary crushers in our present-day plants were originally primary crushers in those same plants. “Secondary” and “second-stage” are synonymous, and are equally good and descriptive definitions.secondary_and_tertiary_crushing_circuits

The term “tertiary” has been used rather extensively in recent years to cover not only third-stage crushers, but in a more general sense to delineate any and all crushers in the reduction and fine-reduction classes; a use which certainly takes liberties with the intent of the word. It is a legitimate term as applied strictly to a third stage of reduction, just as “quaternary” may be used to designate a fourth stage. Our own preference is to ….Read more

Gyratory VS Jaw Crushers: Advantages & Disadvantages

No discussion of primary crusher selection would be complete without a comparison of the two leading types: the standard gyratory crusher and the Blake jaw crusher. Although their fields of application overlap to a considerable degree (at least in the realm of primary crushing) there is no real conflict between these two machines; one supplements the other and, between them they very effectively cover an imposingly large proportion of the entire field of primary crushing applications. This does not mean that other types, such as the sledging rolls, for example, are not better suited for certain applications; but there are very few primary crushing jobs to which the gyratory or jaw crushers, or both of them cannot be applied with at least a fair degree of satisfaction.Advantages and Disadvantages of Gyratory and Jaw Crushers

Either of the two types can be built to handle the hardest and toughest rock or ore that can be economically mined or quarried. The jaw crusher, because of its box-frame construction, and simple toggle mechanism, is especially well adapted to extra heavy design for the crushing of extremely tough materials: in this respect it holds some advantage over ….Read more

Crushing Equipment Selection

In open pit quarry operations the loading of the blasted rock for transportation to the primary crusher house involves either power-shovels. Any size of primary crusher may be used for hand-loaded rock; it all depends upon how much secondary shooting, and hand sledging, the operator feels he can afford. So called “one-man” stone or stone of a size that can be lifted into small cars or carts by the average laborer can be handled through a 10 or 13″ gyratory crusher, or a jaw crusher of equivalent receiving opening. Usually, for hand-loading operations, capacity and product size govern the choice of the primary crusher. The unit labor cost of feeding hand-loaded stone is higher for small crushers than it is for larger machines but, if the labor market is such as to permit hand-loading in the quarry, a little additional labor at the crusher will not add materially to the cost of production.open_pit_mining

In the American quarry, gravel pit, and open-cut mine, the power shovel, supplemented to a lesser extent by other types of excavating equipment, has, within the last forty years, practically eliminated hand loading. Today, ….Read more

Crushing Plant Capacity

The suggested reserve capacity for quarry operations applies as well to open-pit mining operations employing power shovels for loading the ore. Usually the original crusher is expected to produce the required daily tonnage in such plants in one or two shifts, so a time-reserve does exist which can be utilized to make up for delays. But this can only be accomplished by overtime operation of pit, transportation, and primary crusher-house, which under existing labour conditions is costly. From the standpoint of economical operation, reserve capacity in the primary crusher is just as important here as it is in the commercial crushing plant.Primary_Crushing_Plant_Capacity

Underground mining operations are, in many cases, provided with a substantial surge capacity between the mine and the primary crushing plant. Furthermore, in medium and large operations of this character, the primary crusher is almost invariably large enough (to meet the required output) so that the mined ore causes little or no trouble due to bridging or blocking. For such operations the reserve may safely be cut to a somewhat narrower margin than we have suggested for the preceding classes of operation. From 10 ….Read more

Primary Crushing

The term “primary crusher,” by definition, might embrace any type and size of crushing machine. The term implies that at least two stages of crushing are involved, but in many cases the machine which performs the function of initial crusher is the only crusher in the plant. The factors influencing the selection of a crusher for this service are much the same, regardless of how many crushing stages there are in the flowsheet; therefore, the term “primary crusher,” by common usage, is applied to the crusher which takes up the job of reduction where the blasting operations leave off.
Selecting the right type and size of primary crusher is a problem of prime importance in the designing of a crushing plant of any nature and size. Usually this machine is the largest and most expensive single item of equipment in the plant; a mistake in the choice can only be remedied fully by replacement; and, because the entire primary crusher-house arrangement is generally “tailored”.to fit the crusher, such .replacement is almost always a costly procedure. While personal favouritism toward some particular type of crusher may safely be allowed to swing a close decision, it should never blind the engineer or operator ….Read more

Crushing Products Size and Shape -What to Expect

I have made a number of general remarks regarding the character of product delivered by crushers of various types, and under different conditions of operation. Generalities are of value only if we have some standard to which comparisons may be referred; therefore, we should like to present more specific information on the kind of product to be expected from crushing equipment under “average” operating conditions. Much of the data on which sizing/design curves and tables are based comes from operations involving those two very important types: gyratory and jaw crushers; therefore these curves and tables are more nearly representative of the work of these types than of rolls or hammermills. They may be used for these latter types however if due allowance is made for peculiarities of each type, as pointed out in the descriptions of the different machines.

Crushed_StoneThe preparation of a set of product gradation curves involves a considerable amount of work in the collection of the necessary test data, and a certain degree of discrimination in sorting such data and weeding out erroneous results. There are several reasons why no set of product gradation curves can be regarded as ….Read more

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