How Do Pneumatic Discharge Hammer Mills Work?

Posted by Cassie Brown

Nov 5, 2012 8:37:00 AM

Size Reduction 101

Hammer mills of all shapes and sizes process material with the same basic pulverizing action. Rectangular steel hammers are attached to a shaft inside of a steel grinding chamber. As the shaft spins, the hammers flail out bringing them into contact with the material being processed. A combination of hammer blows, particle on particle impact, and contact with the mill’s interior work in unison to reduce the material until it is able to pass through the screen covering the mill’s discharge opening.

 

Evacuation Options

Once the material is reduced to the desired finished particle size and passed throught the screen, there are two options for how it exits the mill. The method is determined by the material's characteristics. If the material is:

 gravity vs pneumatic resized 600

 

How Does Pneumatic Discharge Work?

It's all about the fan. Air swept mills are used primarily when grinding light, relatively non-abrasive materials to a mid range to fine particle size because lighter particles require suction to overcome the rotor airflow. The fan pulls the material from the mill in-feed through the grinding chamber. In addition, it pulls the finished product through the suction pipe, into the fan itself, and then blows the material out of the discharge pipe either to storage or next stage grinding.


pneumatic 13.diagram resized 600

Why Choose Pneumatic?

There are three key benefits:

  1. A properly designed pneumatic discharge system can increase production 300-400% over gravity dischage mills when grinding light materials to a fine particle size.
  2. Without air, dusty material will take the path of least resistance, typically out the feed chute. In a pneumatic system, dust is controlled and contained because all material is pulled in a common direction.
  3. The fan also aids in material transport to storage or next stage processing.
Bonus advantage:
The ability of the fan to pull the material through the screen allows for processing of materials with slightly higher moisture content than can be effectively processed via gravity discharge.

For a summary of this blog post, click below to download our factsheet:

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Topics: particle size, particle on particle contact, hammer mill design styles, gravity discharge industrial hammer mill, pneumatic discharge hammer mills, air assist, low density materials, abrasive materials

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.  

For a summary of this blog post, plus product brochures on our line of full circle screen hammer mills, download our new 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

Hammer Mills: 5 Key Styles You Need to Know About

Posted by Cassie Brown

Apr 12, 2012 3:50:00 PM

 

You Need a Hammer Mill for That…

So, you have a material that you would like to make smaller for a given purpose. Sounds simple, right?  Well, in most cases it is. However, there are a number of considerations that must be made to get you to the finish line in the most efficient and  most economical way.  

But First a Little Background

Hammer mills are just one type of machinery among the much larger category of size reduction equipment that also includes:  shredders, jaw crushers, ram fed grinders, roll mills, ball mills, and more. Looking a bit closer, even within hammer mills, there are several styles to choose from. Among those styles, the functionality of a hammer mill remains basically the same:
  • Material is fed into a grinding chamber
  • Contact with moving hammers, and interior mill components reduce the material’s size
  • Material remains in the hammer mill’s grinding chamber until it is able to pass through a screen or grate with certain size openings.
The following is a comparison of five key styles of hammer mills:

 

Gravity Discharge Industrial Hammer Mills

Industrial hammer mills have the simplest and most recognizable funtionality. A rectangularindustrial hammer mill steel chamber houses a shaft to which swinging hammers are attached. As the shaft rotates at high speed, the hammers flail out impact the material. In addition to the hammers, size reduction occurs through particle on particle contact and through contact with the breaker plate inside the grinding chamber. Because of their simplicity, the industrial hammer mill is easily adaptable to different sizes and milllab scale hammer mill  designs.
Important to know: Replaceable steel liner plates protect the mill's interior from wear caused by grinding abrasive materials.
Ideal Applications: glass, coal, coke, dry chemicals, metals, resin, porcelain, aggregates, brass, ceramics.
 

 

 

Pneumatic Discharge Hammer Mills

The grinding mechanism of this group is quite simliar to the gravity discharge hammerhigh production industrial grindermills. However, the pneumatic mills typically use a thinner hammer and the interior wall of the grinding chamber features a ribbed liner plate. This plate has a washboard effect on the material, and works in unison with the hammers and particle on particle impact to reduce the material. finish grinding hammer mill with integral fanThe biggest difference of course is the group's the use of air assitance to evacuate material from the mill. Whether attached to the main mill shaft, or as a separate optional component in a high production model, the fan pulls the the material through the mill, and conveys it to storage.
Important to know:  Specially designed notched hammers are ideal for tearing and shredding. In addition to assisting the evacuation of  light or low density materials, the pneumatic suction can increase throughput up to 400% over gravity discharge hammer mills. 
Ideal Applications:  hogged wood scrap, wood chips, green wood, biomass, paper, carpet, meat and bone meal 

 

Full Circle Screen Hammer Mills         

This next group also features the same grinding mechanism as the first two, and the same thin hammers as the pneumatic hammer mills. The amount of screen coverage is what sets the full circle screen hammer mills apart.  
describe the image The nearly 300 degree coverage of the rotor translates to a greater surface area for the processed material to evacuate the grinding chamber. As a result, compared to the industrial mills, you get greater throughput per horsepower with full circle screen hammer mills.
diagram of circ-u-flow screen coverageImportant to know: To achieve the circular, nearly full coverage of the rotor requires that the screen be somewhat pliable and therefore relatively thin. Because of this, the full circle screen mill is best suited for light, easy to grind materials to that do not require initial grinding against a breakerplate.
Ideal Applications: corn, grain, spices, grasses, planer shavings, sawdust

 

Horizontal Infeed Hammer Mills

The unique quality of the horizontal infeed mills is that material is fed into the side of the hammer mill, instead of the top. This design makes them ideal for long, linear or trim scrap grinderotherwise large, geometric materials to be processed with out a pre-grind. This group includes trim scrap grinders and pallet grinders. As with the prior styles, the horizontal mills use heavy duty screens covering the discharge area to determine finished particle size.
Important to know:  the style and design of the hammers aggressively moves the material into the mill. Feed rolls are ideal to properly control the rate that material enters the grinding chamber.
Ideal Applications: trim scrap, truss palnt scrap, 2x4s, whole pallets, pallet scrap

  

Lumpbreakers

The Lumpbreaker is quite different from the prior categories in both designsingle rotor lumpbreaker and functionality. Instead of swinging hammers attached to a shaft rotating at high speed, the lumpbreaker has stationary hammers attached to a slower moving shaft. As the shaft rotates, the hammers remain rigid, and pass between combs attached to the wall of the grinding chamber. Lumpbreakers do not use screens for sizing. Instead, the configuration of spacing between the hammers and combs, along with hammer size and RPM allows some control over the finished particle size.
Important to know: The open infeed, fixed hammers and slow shaft rotation give the lumpbreaker the ability to accept a certain amount of a headload, making it suitable for large blocky materials, de-agglomerating, de-lumping, and returning materials to a flowable consistency.
Ideal Applications: sugar, cement, dry chemicals, agglomerated powders

Broad Categories

For the purpose of this post we broadly examined five of the more common styles of hammer mills. It is important to note that each of these categories could be further broken down to highlight the scope of its variables.

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Topics: full circle screen hammer mills, particle on particle contact, size reduction equipment, industrial hammer mill, hammer mills, hammer mill design styles, gravity discharge industrial hammer mill, liner plates, pneumatic discharge hammer mills, ribbed liner plates, air assist, low density materials, abrasive materials, horizontal infeed hammer mills, trim scrap grinder, pallet grinders, feed rolls, stationary hammers, hammers and combs, deagglomeration, delumping

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