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The Industrial Hammer Mill: A Versatile Workhorse

Posted by Cassie Brown

Mar 7, 2012 8:56:00 AM

One Design,  Many Applications

The basic design of the industrial hammer mill is really quite simple:

  • A steel chamber containing a shaft to which rectangular steel hammers are affixed.
  • Replaceable plates lining the mill's interior to reduce wear caused from grinding abrasive materials.
  • Steel screens or bar grates cover the mill's discharge opening.
Material is fed in through the top of the mill. Once in the grinding chamber, it is reduced by a combination of repeated hammer blows, particle on particle impact, and contact with the walls of the mill. The material will remain in the grinding chamber until it is reduced to a size that is able to pass through the screen covering the mill's discharge opening.
The simplicity of this design makes it a very versatile hammer mill, one that can be adapted to suit a wide variety of materials, such as:

 industrial hammer mill applicationsr

 Similar, Yet Different

The same hammer mill for fishmeal and coal?  Well, yes and no. The basic framework of the mill is the same. However, the configuration of the variable components is how they differ. That determination is based on the following criteria:

  • Material being processed -  Material characteristics such as: friability, flowability, moisture content, and infeed size
  • Desired finished particle size  - Gravel, granules, powder?
  • Desired production rate - 10 lbs/hr, 10 tph, etc.

With this information, the following can then be determined:

  • Hammer mill size - Rotor diameters between 6" and 44", and internal mill widths of 6" to 72".
  • Hammer size and style - Number of hammers, size, style and metallurgy.
  • Screens or bar grates - Style and thickness of screen or bar grates, and size of openings.
  • Choice of proper RPM
It's Optional
Finally, once the the mill is configured, the last determination is whether or not any optional peripheral equipment is needed. For this, the following questions must be answered:
  • How will the material be fed into the mill? By hand, auger, or belt conveyor?
  • How will the material be taken from the mill? Heavy materials such as stone or metal may evacuate via gravity, while light or low density materials will require pneumatic suction.
  • Is dust a concern?

Answers to these questions will help to determine the best types of optional equipment such as belt conveyors, augers, rotary feeders, and dust collection, as well as the most efficient design of the infeed and discharge chutes.  

And that's about it...If you would like more information, please click below to download our free eBook!

industrial hammer mill ebook



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Topics: finished particle size, hammer mill, hammer configuration, bar grates, moisture content, hammers, internal liner plates, size reduction equipment

How Do You Grind Pallets for Recycling?

Posted by Cassie Brown

Feb 14, 2012 10:30:00 AM

Pallets, Pallets Everywhere...

We all have them. Whether you buy, sell, ship or wherehouse, just about any business that handles merchandise in large quantities has pallets. They are the ideal tool for storing and moving myriad materials. But what happens when the pallets become broken, or are just no longer needed? All too often they become a costly waste handling problem. However, if we explore the possibility of recycling, this waste handling problem becomes a saleable product.

The following illustration shows some of the possiblities:

pallet recycling end products

Questions to Ask

Whenever comparing different methods of size reduction, certain general criteria must be considered:
  • Required throughput
  • Required finished particle size
  • Size and uniformity of in-feed material
  • Method of feeding and collecting

To achieve the majority of pallet grinding goals, a two-phase process is necessary to make the most valuable output product.

Phase One: Breaking Them Down

Given their dimensions and overall bulk, the ideal method for reducing both whole pallets and pallet scrap is the slow speed ram-fed grinder.

  • The open "deck" design of the ram fed grinder allows for easy infeed of whole or partial pallets whether by hand, or stacked on a fork truck.
  • The hydraulic ram forces the pallets into the grinding rotor which features four-way reversible tool-steel cutting teeth which are hard enough to cut through nails or other ferrous metals.
  • The pallet material is continuously ground until it is able to pass the screen covering the grinder's discharge area.

Screen size can vary, and screens may be changed to correspond with production goals. However, it is not recommended that a screen smaller than 1" be used in this application.  The smaller the screen, the longer the mill will need to work to produce the required size. Therefore, when processing a bulky product such as pallets or pallet scrap, use of a screen smaller than 1" will dramatically reduce the throughput of the ram fed grinder.

Phase Two: The Finish Grind

So, let's consider how we get to the finish line. For this phase, a finish grinding hammer mill is the best solution. Each of the items shown on the list of suggested end products require a specific finished particle size. The role of a finish grinding hammer mill is to produce the required finished size, anywhere from mulch to sawdust.

  • The pre-ground pallets are fed into the grinding chamber of the hammer mill where a combination of hammer blows, particle on particle contact, and impact with the internal breaker plate work in unison to further reduce the material.
  • The material remains in the grinding chamber until it is able to pass through the screen covering the mill discharge.
  • Screens are available in a variety of sizes, and can be interchanged to correspond with the operator's production goals.
  • If the finish grinding hammer mill is outfitted with an integral fan, the process is taken to the next level. The pneumatic suction pulls the material through the hammer mill, then conveys the finished material to storage.

Exponential Throughput!

Here's where it gets cool. Add the finish grinding hammer mill to the ram fed grinder and not only do you go from whole pallets to the exact desired finished particle size, but the throughput rate is increased as much as 400% over that of the ram fed grinder alone. Here's why:

  • Since the finish grinding hammer mill is producing the finished particle size, the ram fed grinder doesn't need to be concerned with it.  As a result, a larger screen (2" to 3") can be used on the ram fed grinder, thus providing less resistance and allowing material to flow through the system at a much higher rate while still liberating all metals from the wood.

Critical Middle Step

While the ram fed grinder and the finish grinding hammer mill are the stars of the show, it can't be overstated that the ideal set-up will also include two rotary magnet hump tunnels between the ram fed grinder and the finish grinding hammer mill. Anyone who handles pallets is aware that they contain metal fasteners, typically nails, which hold them together. All metals must be removed if the end product is to be saleable. And, while they are not hazardous to the initial grind, it is critical that all metals be removed prior to infeed into the finish grinding hammer mill to avoid a potentially explosive environment.

Putting it All Together

When you combine all of the essential elements, the system looks like this:

pallet grinding system


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Topics: finished particle size, hammer mill, miscellaneous wood scrap, pallet grinding system, pallet scrap, ram fed grinder, finish grinding hammer mill, pallets, tool-steel cutting teeth, rotary magnet hump tunnels, hump tunnel magnets, biofuels, briquetting, hammers

Size Reduction 101: How a Hammer Mill Works

Posted by Cassie Brown

Feb 14, 2012 8:57:00 AM

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:

larger to smaller


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 mill diagram


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:

  1. Material is fed into the mill, typically by gravity.
  2. 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.
  3. 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.
  4. 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.

smartphones ground.ps resized 600


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.

intro to size reduction ebook

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Topics: finished particle size, bar grates, material size reduction, hammers, grinders, industrial hammer mill, hammer mills, lumpbreakers, shredders, jaw crushers, impactors

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