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Hammer Mill Application Focus: Grinding Grains for Animal Feed

Posted by Cassie Brown

Mar 29, 2013 9:37:00 AM

Producers of animal feed all know a simple truth: when processing cereal grains for animal feed, finished particle size matters.  A lot.corn before and after hammer mill processing

Blendability, and digestibility – even the economics of feed production – are all affected by the finished particle size of the grains.  But this is not a one-size-fits-all situation.¹  The ideal finished particle size varies by the grain being processed, and depending on the species, the life stage of the animal.²  With all of this in mind, selecting the proper method of size reduction is a critical decision.


Roller Mill or Hammer Mill

Unlike the angular shaped particles produced in a roller mill, the pulverizing action of the hammer mill results in particles that are more rounded. These smoother surfaces make it easier for the grains to be blended with other components of the feed.²


So Many Hammer Mills

A hammer mill is essentially a steel box surrounding a rotor. Swinging hammers attached to the rotor, flail out when the rotor spins. A screen covers the discharge opening to regulate the finished particle size.

As material enters the hammer mill, it is pulverized by a combination of hammer blows, particle on particle contact, and impact with the walls of the hammer mill. The material remains in the grinding chamber until it is able to pass through the screen covering the discharge area.

But those are just the basics. There are myriad styles of hammer mills: industrial mills, full circle screen hammer mills, horizontal grinders, tub grinders, and more.  As for size, hammer mills can range in size from 6” to more than 60” rotor widths.  Choosing the right hammer mill for your purposes depends greatly upon the material you are processing, and your production goals.


The Full Circle Solution

The design of the full circle screen hammer mill makes it the ideal method of size reduction when processing cereal grains for animal feed.  Let’s take a closer look:


With swine operations reporting that up to 75% of their budget is allocated for feed production,³  the need for energy efficiency cannot be overstated.

As its name suggests, the full circle screen hammer mill differs from the traditional industrial hammer mill because it has nearly double the screen coverage of the rotor:

 screen coverage for full circle screen hammer mill                       screen coverage for industrial hammer mills                                     

    Full Circle Screen Hammer Mill                                 Industrial Hammer Mill


The greater screen coverage of the full circle mill means that there is more area for the material to evacuate the grinding chamber. As a result, a higher throughput rate can be achieved at a lower horsepower in comparison to industrial hammer mill models.  

Particle Size Flexibility

Precision and consistency of the finished particle size has a strong effect on the digestibility of the feed.  A finished particle size that is either too large or too small will have adverse effects on animal performance.²

The primary factor determining finished particle size is the measurement of the perforations in the screen covering the discharge area. The size of these perforations is equal to the maximum finished particle size of the material processed.

The ideal particle size range of 650 to 750 microns³ can easily and consistently be achieved through proper screen selection. In addition, screens can easily be changed to accommodate the processing goals of a variety of grains using the same hammer mill.

The secondary factor in determining finished particle size if the speed of the hammer mill. When the rotor spins, the hammers flail out and impact the material with great severity causing it to break down.  As a result, the higher the rotor speed, the greater the number of hammer mill blows, and thus a finer end product.  An optional component for the full circle screen hammer mill is a variable frequency drive electrical control. This control panel allows the operator to raise or lower the rotor speed as needed for different applications.



The pulverizing action of the hammer mill produces a finished particle that is easily blendable. The nearly 360 degree screen coverage of the full circle screen hammer mill allows for the greatest throughput to horsepower ratio of all hammer mill designs. A consistent and precise finished particle size can be achieved by screen selection. Finally, the ability to change screen size, and the option of a variable speed frequency drive control, enable processing a variety of grains using the same hammer mill.



¹ Steinhart, Terry L., Iowa State University (2012). Swine Feed Efficiency: Influence of Particle Size. Retrieved from  http://www.swinefeedefficiency.com

²Pork Production in Mississippi is Particle Size Important for Swine Diets?(2013). http://www.msucares.com/livestock/swine/particle.html

³Sayler, Julie. (2012). Small Particle Size Makes a Big Difference.http://swineperformance.vitaplus.com/2012/04/small-particle-size-makes-a-big-difference/  

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Topics: finished particle size, full circle screen hammer mills, variable frequency drive, size reduction equipment, corn, animal feed, cereal grains

Full Circle Screen Hammer Mills: Low Horsepower, High Throughput

Posted by Cassie Brown

Jul 20, 2012 12:59:00 PM

high production full circle screen hammer millSize reduction equipment comes in a wide variety of shapes and sizes: vertical or horizontal hammer mills, jaw crushers, roller mills and ram-fed grinders, just to name a few. For the most part, the size and shape of the mill/grinder/crusher plays a key role in the functionality of the machine, and for the applications it is best suited for. Nowhere is this truer than with the Full Circle Screen Hammer Mill.


A Peek Inside...

The full circle screen hammer mill gets its name from the 300 degree screen coverage of the rotor, while all other styles of hammer mills typically have closer to 180 degree coverage of the rotor. 

describe the image                    

 Full circle screen hammer mills                                 


Ideal Applications

To achieve the circular, nearly full coverage of the rotor requires that the screen be somewhat pliable, and therefore relatively thin. In addition, the full circle screen mills use thin, notched hammers that reduce material with a tearing/grinding action, as opposed to the pulverizing effect of the large, heavy hammers often used in the industrial hammer mills. As a result, the full circle mills are best suited for light, easy to grind materials that do not require initial grinding against a breaker plate. 

Some examples include:

 cuf application.wordle resized 600

 Size Reduction 101

When material enters the grinding chamber, it is repeatedly struck by hammers that flail out as the shaft spins.  A combination of these hammer blows, particle on particle impact, and impact with the walls of the grinding chamber all work together to break the material down. The material remains in the grinding chamber until it is reduced to a size that will pass through the screen. 

The larger the screen area, the greater the opportunity for the material to evacuate the mill. As a result...

 full circle mills.throughput

 Additional Considerations

Once you have decided that the full circle screen hammer mill is best for your material, determining the following criteria will ensure so that the mill is configured to meet your production goals:

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

With this information, the following can then be determined:

  • Hammer mill size - Rotor diameter and internal mill width.
  • Hammer size and style - Number of hammers, size, style and metallurgy.
  • Screens  - Style and thickness of screen, 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? Gravity, air assist, or full air evacuation?
  • 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.  


intro to size reduction ebook





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Topics: full circle screen hammer mills, particle on particle contact, biofuels, briquetting, bio-fuel applications, circular hammer mill, corn, animal feed, corn meal, corn flour, hammer mill design styles

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