Crushing & Grinding | Types of Fine Grinders | Roller Mill's

The roller mill is at present used exclusively for the grinding of grain in the manufacture of flour. It is, however, also suitable for grinding any moderately tough material that must be reduced to a very fine powder. Since this mill has a shearing action rather than crushing by direct pressure or having a rubbing action, it may be used where material is to be reduced to a moderately fine size but with the minimum of fines. See the picture above and below.

vertical Roller Mill

Construction & Working Process:

 It contains two pairs of rolls, and the rolls in each pair rotate toward each other. The rolls are corrugated, and one roll of each pair turns faster than the other one. This results in a shearing action instead of the direct pressure that is brought about in the ordinary crushing rolls. The drive side of the mill, half in elevation and half in section. Shaft pulleys are attached to the fast roll of either pair. The driving belt takes a turn around these pulleys and around the idler pulley. This pulley drives an idler shaft which passes through to the opposite side of the roll stand. From the other end of his idler shaft, belts go to the slow roll of each pair. Above the rolls proper is an oscillating feeder that delivers the material to be crushed equally to both pairs of rolls.

 
One roll of each pair runs in fixed bearings. The other roll of each pair runs in bearings that are mounted on adjustable bell cranks. These bell cranks are pivoted at the bottom and are adjustable by a hand-wheel and screw at the top. In this way, the distance between the rolls, and therefore the amount of reduction accomplished in each pass, may be regulated.

Crushing & Grinding | Intermediate Crushers | Hammer Mill and Single-Roll Crusher

The general name covers a wide variety of crushing and shredding devices that operates rather by impact than by positive pressure.

One type of such device is shown in above picture.In this machine a number of discs are assembled on a central shaft.Between these discs are hinged hammers, in the form of plain rectangular steel bars, which may be from 1/8 to 1/2 in. in thick. On one side of the casing are breaker plates of white cast iron or manganese steel, and around the bottom is a cage containing hundred screen bars. The shaft is rotated at a high speed, and centrifugal force causes the hammers to swing out radially. Brittle or friable material like coal, pitch, limestone or similar substances is beaten around inside the mill and by impact against the breaker plates or against the screen bars is crushed until it falls through the screen. By using hammers of different weights and screen bars of different cross sections, the machine can be adapted to materials ranging from brittle materials like coal on the one hand to fibrous materials like tanbark on the other hand.

The construction is such that hammers can be easily replaced when they have worn. You have see the picture of hammer mill, part of the screen cage is hinged so it can be lowered to remove from the mill any hard material that cannot be pulverized. For brittle materials like coal or limestone the cross section of the screen bars is usually rectangular as shown in above pictures. There are many types of these mills, differing in the details of construction and in the shape of the hammer bars, but the action of all the mills of this type is essentially the same.

There are a number of modifications of this type in which the beaters are smaller and only a single ring of them is used. In such cases both the screen bars and the sides of the housing act as attrition surfaces. Such mills are used for grinding resin, pitch, drugs, cork, and similar soft or fibrous materials.

Single-Roll Crusher:

Another type of machine that falls in this class because it depends mainly on impact, but which is not ordinarily classed as a hammer mill is the single-roll crusher. Such a mill is shown in the picture below.

 

The single-roll is usually provided with corrugations or teeth of different sizes and rotate at a relatively high speed. Its action is similar to the hammer mill in that it crushing effect is produced by the teeth driving the material to be crushed against the breaker plate, thus crushing it by impact rather than by positive pressure. These machines are made in a variety of designs and are quite generally used for crushing coal..

 

 

 

Crushing and Grinding | Classification of Crushing and Grinding Machinery or Equipments

The general terms used to describe the operations that subdivide solids mechanically are seldom used with any very definite significance. The terms crushing and grinding are usually associated in this phrase to signify subdividing to greater or less extent, neither of the terms is used alone with any precise meaning, although, in general, grinding means subdividing to a finer product than crushing.

Crushing & Grinding Equipments

In spite of the wide use of crushing machinery in hard-rock practice in the mining industry, little is really known of the basic theory that underlies processes for the mechanical subdivision of solids. As in certain other fields, this lack of theory and total reliance on empirical observation have led to an especially wide variety of types of equipment. By a process of a natural selection rather than analysis, certain devices have become preeminent for hard-rock crushing, and as a result, the mining industry in recent years has practically standardized on certain types of machines for specific ranges of crushing.

In the fields in which the chemical engineer is interested outside hard-rock practice, there is absolutely no standardization. Consequently we shall be largely a description of types of crushing machinery with an indication of the uses to which such apparatus is suited, although such usage arises more often from tradition and custom than from rational comparisons.

Classification of Crushing and Grinding Machinery:

Because of wide variety of devices used, it is extremely difficult to make a rigid classification of crushing machinery. The only classification in which definite limitations of the groups can be established is the division into coarse crushers, intermediate crushers, and fine grinders. Coarse crushers are defined as those types of machinery that can be developed to take, as feed, lumps as large as may be desired. Fine grinders are defined as those machines that can be made to give a product that will pass a 200-mesh screen. Intermediate crushers are those machines that ordinary do not take indefinitely large feed, nor will they make a product that will pass a 200-mesh screen.

The different devices may be classified under these heads as follows:

1.Coarse Crushers

(a) Jaw Crusher
(i) Blake Jaw Crushers
(ii) Dodge Jaw Crusher
(b) Gyratory Crusher

2.Intermediate Crushers

(a) Rolls
(b) Disc Crushers
(c) Edge Runners
(d) Disintegrators (cage)
(e) Hammer Mill

3.Fine Grinders

(a) Centrifugal
(i) Raymond
(b) Buhrstones
(c) Roller Mills
(d) Ball Mills and Tube Mills
(e) Ultra-fine Grinders

Machines in the coarse crusher class are ordinary employed where the feed is from 1 1/2 to 2 in. in diameter and larger. The largest devices of this class that have been made will take rocks up to 60 in. in diameter. No type of crusher except those listed in this class can be built in sizes that will take these very large pieces of feed.