CHAPTER XXXV. STANDARD TYPES OF CRUSHING AND PULVERIZING MACHINERY. IT has seemed advisable to devote a chapter to the description of various standard types of crushing and pulverizing machinery. In selecting the particular machines to be described in this chapter, the writer has attempted to include those, and only those, which are known to him as being in satisfactory operation at one or more American cementplants. It is possible that in endeavoring to exclude worthless types some meritorious machines may have been unintentionally neglected; but it is safe to say that over 95 per cent of the cement made in this country is crushed and pulverized by machines described in the following pages. In describing the various types of crushers and pulverizers, the drawings of the mills and the data relative to their construction and mechanical operation have been taken mostly from trade catalogues or from descriptions prepared by the manufacturers. The data on output, fineness and power 1equired were, however, in almost all cases obtained from managers of cement-mills, and are believed to be entirely reliable. Classification of Grinding Machinery. So many types and varieties of crushing and pulverizing machinery are now on the market that it is difficult, from a single description, to form much of an idea of the relation of any given one of these machines to any of the others. To aid in this, the machines described in the following pages have been grouped under eight classes, according to their general methods of action. This grouping is as follows: Class 1. JAW CRUSHERS; material crushed between two jaws which approach and recede..... BLAKE CRUSHER. Class 2. CONE GRINDERS; material crushed by the revolution of a toothed cone or spindle within a toothed cup......GATES CRUSHER, CRACKERS. Class 3. ROLLS; material crushed between two or more plain, fluted, or toothed cylinders revolving in opposite directions...... ROLLS. Class 4. MILLSTONES; material crushed between two flat or grooved discs, one of which revolves. MILLSTONES, BUHRS, STURTEVANT EMERY MILLS, CUMMINGS MILL. Class 5. EDGE-RUNNERS; material crushed in a pan, under a cylinder turning on a horizontal axis and gyrating about a vertical axis. EDGE-RUNNERS, DRY-PAN. Class 6. CENTRIFUGAL GRINDERS; material crushed between rollers and an annular die, against which the rollers are pressed by centrifugal force. HUNTINGDON MILL, GRIFFIN MILL, NAROD MILL, CLARK PULVERIZER. Class 7. BALL GRINDERS; material crushed by balls or pebbles rolling freely in a revolving horizontal cylinder. KOMINUTER, BALL MILL, TUBE MILL. Class 8. IMPACT PULVERIZERS; material crushed by a blow in space delivered by revolving hammers, bars, cups, or cages. WILLIAMS MILL, RAYMOND PULVERIZER, STURTEVANT DISINTE- Class 1. Jaw Crushers. In this familiar type of coarse crushing machines, of which the Blake crusher is both the oldest and best-known representative, the material is fed between two powerful jaws, and crushed by their near approach to each other. The principle upon which these machines work is well adapted for breaking stone, but is not serviceable for finer reduction. The Blake crusher in its various forms, and the Dodge and other devices of the movable-jaw type, are therefore machines suitable for first reduction only. For detailed descriptions of the Blake crusher, and of the modifications in which the same principle has appeared, reference should be made to the valuable paper cited below.* In mining and metallurgical practices jaw crushers are commonly used, but in the cement industry they have almost entirely given place to the gyratory crushers described in the next section. Class 2. Cone Grinders; Gyratory Crushers. Under this heading are grouped the crushing machines in which the material is crushed between a toothed or grooved cone or spindle and the grooved cup within which it revolves. The Gates crusher, the Mosser crusher, and the McEntee and other "crackers" are here *Blake, W. P. The Blake stone and ore-breaker: its invention, forms, and modifications, and its importance in engineering industries. Trans. Amer. Inst. Mining Engineers, 1903, pp. 988-1031. included. The "crackers" have been described quite fully on page 239, in dealing with the crushing practice in natural-cement plants, and the Mosser crusher is of essentially the same design as these crackers, though built for heavier work. The Gates crusher, shown in view in Fig. 87, and in section in Fig. SS, is probably the most extensively used machine of its type. In re gard to its power requirements, capacity, etc., its manufacturers state: "In estimating power to drive our breakers we have provided for running an elevator and screen also. But it must be borne in mind that no close estimate can be made to cover all sorts of rock and ore; and further, it should be observed that it requires much more power per ton to break rock to inch than is required to break it to an inch. The estimates given in Table 176 are intended to cover the ordinary macadam breaking. For fine breaking add liberally to the power. Long experience has demonstrated the reliability of the following general rule, applicable to breaking the hardest rock to 24-inch ring, viz.: The Gates breaker will not require over one horse-power per ton of rock broken per hour." The estimate (see Table 177) of the cost of crushing with a Gates crusher is based by Professor Richards on the results of a number of The names of the several parts designated by numbers in the above illustration may be found in the following table: 1. Bottom plate 2. Bottom shell 3. Top shell 4. Bearing-cap 5. Oil-cellar cap 6. Spider 7. Hopper 8. Eccentric 9. Bevel-wheel 10. Wearing-ring 11. Bevel-pinion 12. Band-wheel 13. Break-pin hub 18. Head 19. Concaves 22. Chilled wearing-plates 24. Octagon step 26. Upper ring nut 27. Lower ring nut 29. Lighter screw 30. Lighter screw, jam nut 31. Counter-shaft 33. Oiling-chain mill tests at ore-treatment plants. As the ore handled at these mills was, in general, harder than the raw materials used in Portland-cement manufacture, allowance should be made for this feature. In the group of crushing machines here considered the material is crushed between two or more cylinders which revolve in opposite directions. These cylinders may be plain-surfaced, longitudinally fluted, or toothed, according to the character of work they are expected to perform. As the fineness of the product is regulated chiefly by the Richards, R. H. Ore Dressing, vol. 1, p. 50. 1903. |