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..