Size Reduction 101: How a Hammer Mill Works
If you were looking for the latest magic bullet for trimming your waistline (and aren't we all?) unfortunately, Google has lead you astray.
Material size reduction is our topic of discussion today. There are many terms that fall under this umbrella: crush, grind, pulverize, shred, de-lump, de-fiberize, just to name a few. Likewise, there is a whole host of machinery styles that accomplish these goals: hammer mills, grinders, shredders, lumpbreakers, impactors, jaw crushers and more.
The core process is the common denominator:
But how does it work?
The simplest way to describe the concept of size reduction is to look at the industrial hammer mill model:
Hammer mills operate on the basic principle that most materials will crush, shatter or pulverize upon impact. This is accomplished by a simple four step process:
- Material is fed into the mill, typically by gravity.
- Inside the grinding chamber, the material is repeatedly struck by flailing ganged hammers which are attached to a shaft that rotates at a specified speed. The material is crushed by a combination of hammer blows, collision with the walls of the grinding chamber and particle on particle impacts.
- Perforated metal screens or bar grates cover the discharge opening of the mill retain the coarse material for further processing while allowing properly sized material to pass through.
- Hard, heavy material such as stone, glass or metal can exit the mill via gravity. Lighter or low density materials such as wood and paper require pneumatic suction for effective discharge.
One size does not fit all
Well, that would be too easy, wouldn't it? Finished particle size is determined by a combination of the following: screen (or bar grate) size, shaft speed and hammer configuration.
For example, a fast shaft speed, small screen and large number of hammers typically produces a fine end product. Conversely, a larger screen, fewer hammers and slower shaft speed will result in a coarse product. Disclaimer alert: It is important to know that this is a very simplistic explanation of a very complex engineering process. Each of these factors is determined based on careful consideration of the the material being processed and the user's production goals.
Each of the key components: screen size, shaft speed and hammer configuration can be changed individually or in combination to achieve the precise finished particle size at the desired production rate.
For a summary of the information contained in this blog post, click below to download our "How Does a Hammer Mill Work?" Factsheet:
