Rotors are used to drive swinging or fixed-hammer mills, the latter of which is driven by large plates with support pins embedded all around the plates’ circumference. A hammer mill is a device that uses impact to break up large chunks of material into smaller pieces. The rotor is supported by a rigid metal casing that typically includes screens and sometimes corrugated liners to aid in the grinding process.
Characteristics of a Good Hammer Mill
Here are some of the characteristics of a good wood hammer mill:
- Dispenser Material is fed into the grinding chamber by rotary feeders or augers. Metered feeding evenly distributes product across the hammer mill rotor’s width, increasing efficiency and reducing hammer wear. In many types, a high-grade magnet removes tramp metal that could damage the mill.
- A hammer mill has a feed device and starts/off controls.
- Materials are ground or crushed with hammers or knives. 1,800-3,600 rpm is typical. Several designs let hammers and knives rotate for even wear. They can be made in different styles or shapes depending on the material to be ground.
- Rotor attaches hammers or knives via a rotating shaft and electric motor. Concentric weight balance around the shaft or support plate reduces vibrations. Altering the number and pattern of hammers on the rotor also changes the grinding intensity.
- In some applications, a system with a motor directly attached to the rotor or driven by belts for more precise speed control.
- Mill screens classify particles, keeping the larger ones in a while and letting smaller ones go out of the grinding machine.
Design Variations of Hammer Mills
Hammer mill design hinges on whether the hammers swing. “Lump breaker” refers to a hammer mill with fixed hammers. Configuration, coatings, number of hammers, pitch, and spacing affect hammer mill design. This ensures that the hammers perform well for their intended use.
Below is a brief explanation of how each type of hammer mill works:
Full Circle Screen Hammer Mills
360-degree rotating display screens are available. Particle evacuation is improved, and spices, grasses, and other light materials can be reduced as a result.
Gravity Discharge Industrial Hammer Mills
Heavy-duty, HD swinging hammers mounted on a shaft reduce particle size and discharge milled material into a bin or mechanical conveyor below via gravity in gravity discharge hammermills. Ceramics, dried chemicals, and glass are all examples of materials that can benefit from coarser reductions in these mills.
Horizontal In-feed Hammer Mills
Material is fed into the grinding chamber using a chute located on one side of the machine rather than the top. Using this type of hammermill design is ideal for grinding heavy particles that are aggressively reduced in size.
Lump Breakers
Different types of hammer mills, such as lump breakers, operate differently. Fixed hammer configurations are smaller than swinging hammer configurations. This equipment’s primary function is to condition materials into free-flowing granular or powder form through the use of hammers that mesh with one another or fixed combs attached to the machine. These can be used for various materials, including sugar, cement, and dried chemicals.
Pneumatic Discharge Hammer Mills
This design resembles gravity discharge mills but has more precise tolerances and a greater number of hammers. Vacuum-driven hammermills can remove ground material from the mill with greater efficiency and produce finer products such as grains, wood, biomass, and paper.
Final Thoughts
Hammermills can be used to reduce material to various particle sizes, depending on their intended use. Electric motors come in a wide range of horsepower ratings, power, and size.
