How Does a Hammer Mill Work?

There are many terms that fall under the umbrella of size reduction: crush, grind, shred, de-lump, de-fiberize, just to name a few. Likewise, there is a whole host of machinery styles that accomplish these goals: grinders, shredders, lump breakers, impactors, jaw crushers and more. The core process is the common denominator: a large material is processed into a smaller material.

The simplest way to describe the concept of size reduction is to look at the industrial hammer mill model. Hammer mills operate on the concept that most materials will crush, shatter or pulverize upon impact. This is accomplished by a four step process:

1. Material is fed into the mill in one of many ways, including: hand fed, auger or belt conveyor

2. Inside the grinding chamber the material is repeatedly struck by flailing ganged hammers which are attached to a shaft that rotates at a very high speed. The material is crushed by a combination of hammer blows, collision with the walls of the grinding chamber, and particle on particle impacts.

3. Perforated metal screens or steel bar grates cover the discharge opening of the mill. The material remains in the grinding chamber and continues to be reduced until it is able to pass through the openings in the screen or bar grate. The result is a consistent, specific finished particle size.

4. Hard, heavy materials such as stone glass or metal can easily exit the mill via gravity. Lighter. Lower density materials such as wood or paper require pneumatic suction for effective discharge.

It is important to note that this is not a one-size-fits-all situation. Once the appropriate type of hammer mill is selected, the finished particle size is then achieved by a combination of screen (or bar grate) size, shaft speed, and hammer configuration.

Very generally speaking, a fast shaft speed, small screen and large number of hammers will produce a fine product. Conversely, a slower shaft speed, larger screen and fewer hammers will result in a coarser product. However, each of these three components must be determined based on careful consideration of the material's characteristics, and the processor's production goals.

Any of the three: screen size, shaft speed or hammer configuration may be changed individually, of in combination to achieve the precise finished particle size at the desired production rate.

Cassie Brown

Schutte-Buffalo Hammermill, LLC.


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