Producers of animal feed all know a simple truth: when processing cereal grains for animal feed, finished particle size matters. A lot.
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:
Throughput
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:
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.
Summary
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.
References
¹ Steinhart, Terry L., Iowa State University (2012). Swine Feed Efficiency: Influence of Particle Size. Retrieved from http://www.swinefeedefficiency.com
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:
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.
Why Choose Pneumatic?
There are three key benefits:
- A properly designed pneumatic discharge system can increase production 300-400% over gravity dischage mills when grinding light materials to a fine particle size.
- 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.
- 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.
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Size 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.
Full circle screen hammer mills Industrial 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:
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...
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:
Challenging the Industry Standard
In earlier posts we discussed how the simplicity of hammer mill technology lends itself well to many applications. On occasion though we encounter an application where the hammer mill is not only effective, it far exceeds the industry standard. E-scrap processing is one of those areas.
Traditionally, whether the goal is data destruction, recycling of materials - or both, e-scrap has been processed in large industrial shredders. Shredders process the e-scrap by using a shearing action that cuts the material as it passes through claw-like knives. While this is method is effective, drawbacks include frequent maintenance to replace the shredder knives, and the costly price point of the standard industrial shredder.
Hammer Mill 101
Hammer mills process material with a 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 interior, work in unison to reduce the material until it is able to pass through the screen or heavy bar grate covering the mill's discharge opening.
A Better Mousetrap
Now let's look at that process as it relates to e-scrap processing, to see how it is more efficient and effective:
1. Flexibility - The simplicity of the hammer mill design offers great flexibility, making it suitable for processing a wide variety of e-scrap materials down to the exact desired finished particle size. Mill size, hammer style and configuration, and screen size are determined based on the processor's production goals. In fact, multiple types of e-scrap media can be processed in the same hammer mill, without reconfiguration.
2. Complete Data Destruction - As it is pulverized, the e-scrap material is continuously scraped and scoured by the turbulent action within the mill. As a result, all retrievable data is destroyed.
3. Liberation of Metals and Other Materials - The second benefit of the pulverizing process is that the hammering action breaks the e-scrap apart, liberating the metals and various other materials. Once broken apart, all pieces remain in the grinding chamber and continue to be pulverized until they are able to pass through the screen covering the mill's discharge opening.
4. Low Cost, High Production - Hammer mills are available in a range of sizes, and are highly customizable based on the material(s) being processed and the user's production goals. A mid-sized hammer mill configured for computer hard drives can process up to 2500 units per hour. A shredder with the same throughput capacity would cost roughly four times that of the hammer mill.
5. Minimal Maintenance - The knives of the shredder dull quickly, and in many cases must be changed monthly. In comparison, one set of 4-way reversible hammers will, on average, last up to one year.
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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 rectangular
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 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 hammer
mills. 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.
The 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.
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.
Important 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
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otherwise 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 design
and funtionality. 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.
Want to learn more? Click on the link below to download our How Does a Hammer Mill Work? factsheet:
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:
r
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!
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:
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:
Size reduction solutions to two of the biggest challenges when converting waste wood to biofuelsThroughout our 80+ year history, wood processing has been one of our cornerstone industries. Among our largest customers are forest products companies, lumber yards, makers and recyclers of pallets, furniture manufacturers, truss plants and more. Each with unique products, but all with one common issue: wood waste. The level of waste varies depending on the industry. An interesting example is forest products companies. When processing logs for lumber, up to 40% of the tree is deemed scrap in terms of its lumber value.
Traditionally, these by-products were considered waste, and at best, used as onsite boiler fuel or sold at a minimal profit to local buyers for such uses as landscape mulch and animal bedding. Enter biofuels. Amid growing environmental concerns and the desire to reduce dependence on fossil fuel, the emphasis on biofuel creation continues to increase. As a result, wood has emerged as an ideal feed stock. Now the wood waste once seen as a disposal problem is now a valuable product.
But here is the hitch - each of the potential biofuel end products have specific material characteristics that are critical to their effieciency. As a result, there are a number of challenges inherent in using a non-uniform scrap material as biofuel feed stock. In two specific cases, hammer mills are instrumental in taking wood waste from the sawmill floor to the biofuel market.
To illustrate this point, let’s use the example of converting wood waste to pellets and briquettes.
Challenge No 1:
Particle size and uniformity These are critical factors in the preparation of wood to biofuel feedstock. On average, most biofuels require a consistent feedstock particle size of -1/8”. Typical waste wood as is much larger and non-uniform.
Hammer Mill Solution:The first and most obvious consideration is size reduction. Can hogged wood scrap, bark, pallets, furniture scrap, etc be ground to a size that is appropriate for biofuel production? The answer is of course, yes. The solution lies in selecting the correct wood grinder for your production goals.
To determine this, the following must be considered:
- Size and type of in-feed material
- Desired finished particle size
Answering these questions will determine not only what wood grinder is most suitable for your application, but also whether your goals require a one or two stage grinding process.
For example, if your waste material is hogged wood scrap and your goal is a -1/8” for pelletizing, a finish grinding industrial hammer mill would be most appropriate. From there, your production goals determine the size and style of the recommended mill.
Conversely, if your waste material is pallets and your goal -1/8” for pelletizing, you will require a two step process. A slow speed ram fed grinder is ideal for the initial grinding of the whole pallets. However, this type of mill is not suitable for the fine grinding required for the optimal finished particle size for pelletizing. A secondary grind in a finish grinding industrial hammer mill will be necessary. Typically, the material will be pneumatically drawn from the ram fed grinder, across magnets to remove all nails, and then though the finish grinder. The upside of this is that this pneumatic component can substantially increase the throughput rate and convey the finished product to storage.
Screen selection for the hammer mill is the second component in determining finished particle size. Referring again to our original three considerations, the desired end particle size will dictate the size of the openings on the perforated screen covering the discharge of the hammer mill. For example:
Finished particle size of 1/8” will require a screen size of 1/4" or smaller.
The material will remain in the grinding chamber of the hammer mill until it is reduced to a size that will pass through the screen.
Challenge No 2: Material moisture content
The majority of biofuel applications require a moisture content of ≤10%. However, it is not uncommon for waste wood, such as bark or green wood chips, to have ≥50% moisture content. Not only is the moisture content too high for fuel efficiency, it is also too high for a wood grinder to reduce the wood to a uniform particle size suitable for pelletizing.
Hammer Mill Solution
Under these circumstances, the solution is often a three phase process where hammer mills play a pivotal role. The following is an example of how one of our customers addressed this challenge. Their goal was to convert wood waste with an average 40 to 50% moisture content to suitable feed stock for pelletizing and briquetting.
An industrial wood grinder was used to pre-grind the green wood down to a uniform ½” particle size recommended for optimal drying in the rotary drier. The drier would reduce the moisture content down to the required ≤10%. Finally, the material is fed into a second industrial wood grinder where it is ground to its finished particle size, ideal for the customer’s pellet and briquette production.
For more information, click below to download our "Processing Green Wood for Biofuels" Factsheet:
Whether it is space constraints or small production, a laboratory scale hammer mill is often the right choice for size reduction. Often used for testing and batch sampling, common installations include: colleges and universities, government testing facilities, and pilot plants.
Below are answers to the top five questions we receive about our laboratory scale hammer mills:
1. Can my material be processed in a lab scale hammer mill?The laboratory scale hammer mill has the same full range of capabilities as larger industrial hammer mills. Applications include: chemicals, glass, food waste, biomass, lathe turnings, metal powders and much more. Material infeed size and production goals are the ultimate determining factors on whether or not a lab scale hammer mill is suitable for your operation.
2. How durable is the lab scale hammer mill?The lab scale mills are constructed based on customer specification. The options include carbon steel and 304 or 316 stainless steel. Stainless steel models feature all stainless steel contact surfaces. Replaceable internal liner plates are also an option, The liner plates protect the grinding chamber from wear that results from processing abrasive materials.
3. Can a lab scale hammer mill produce multiple particle sizes?Yes. In an earlier post we discussed the
factors determining particle size. In short: the screen size, shaft speed and hammer configuration selected give you the ability to steer the particle size in any direction you require. This principle holds true with the lab scale hammer mill as well.
Hammer configuration is determined by the material and processing goals, and is generally not changed once mill construction is complete. However, shaft speed and screen size are quite flexible. Screens can be purchased in multiple sizes and are easily interchanged. The smaller the opendings in the screen, the finer the product that is produced. An optional Variable Frequency Drive (VFD) control allows the operator the ability to control the rotor speed. Faster rotor speed results in harder and more frequent blows, where as a slower speed allows for a tighter particle size distribution.
4. Is the lab scale hammer mill scalable?
Absolutely. The lab scale hammer mill is, quite simply a miniature version of larger production models. Thus, the lab scale hammer mill production results can be extrapolated to that of its larger counterparts.
5. What can I expect in terms of set-up and maintenance?
The lab scale hammer mill is fully assembled upon delivery. The operator simply needs to connect the mill's motor or control panel to the main building power source. The top of the hammer mill hinges open to allow easy access for cleaning, screen changes and hammer rotation. As with larger hammer mills, optional dust collection systems can be integrated if needed.
For a one page summary of this post, click below to download our Laboratory Scale Hammer Mills - Top 5 FAQs Factsheet:
When asked what I do for a living, it is not uncommon for the conversation to go something like this:
Me: I work for Schutte-Buffalo Hammermill, we manufacture –
New Friend: Paper! You’re that paper company, right?
Me: Well, no. Actually, we manufacture size reduction machinery, such as hammer mills.
New Friend: (puzzled look)
At this point I usually find it helpful to give a real-life example…
Me: You know that cinnamon you sprinkled on your toast this morning?
New Friend: Yes…
Me : It was made in a hammer mill! The dried, curled cinnamon bark “sticks” are ground in a hammer mill to make the fine powder that you are familiar with.
New Friend: Cool!
Why a hammer mill?
Hammer mills can be used to process a seemingly infinite list of materials. For spices it is the best tool for the job because of the operational flexibility, and the ability to control finished particle size. With the exception of high oil content spices such as nutmeg and mace (unless cryogenically frozen), the hammer mill is ideal for processing a wide variety of spices and dried herbs, such as : red pepper, white pepper, black pepper, coriander, cumin, cinnamon, oregano, thyme, cloves, and turmeric just to name a few…
One mill, many spices
The simplicity of the hammer mill makes it very adaptable to the varying characteristics of different spices. It is this versatility that makes the hammer mill the ideal choice for those processing more than one variety. Because the processing mechanism results in crushing by impact instead of compression, spices are ground to the exact desired particle size without significant heat increase that could cause loss of flavor or aroma.
Sizing
The importance of exact finished particle size cannot be overstated when grinding spices. The key component to a hammer mill processing the exact particle size is the perforated screen covering the mill’s discharge opening. Screen selection allows the processor to determine the largest allowable finished particle size. Material remains in the mill’s grinding chamber and continues to be pulverized until it is able to pass through the screen. Screens of varying sizes can be used interchangeably in the same mill. A 1/8” perforated screen will produce a coarser tea cut finished size. Whereas a 1/32” screen will produce a fine powder. The second component of particle size determination is the rotor speed. As the rotor spins, the hammers impact the material in the grinding chamber with great severity.
Generally speaking:
High rotor speed = increased number of severe hammer blows = finer particle size
Slower rotor speed = decreased number of softer hammer blows = coarser particle size
In addition, very hard materials such as cloves, ginger and turmeric will require a higher rotor speed to produce the same finished particle size as softer materials like white and black pepper. An optional variable frequency drive electrical control allows the operator to easily speed up or slow the rotor speed as needed for different applications.
Hammer mills in many styles and sizes
Finally, what size and style of hammer mill is best? This is determined by infeed material characteristics and desired throughput rate. For softer, easier to process materials, a hammer mill with a nearly full circle screen is most suitable. The 300 degree screen coverage allows for the greatest throughput at the lowest horsepower.
Fibrous herbs, and roots such as kava, cassava, yam, carrot and ginseng are best ground in a more traditional industrial hammer mill. This style of hammer mill contains an internal ribbed breaker plate which is the first point of contact when material enters the grinding chamber. Given its ribbed construction, the breaker plate has a wash-board effect, breaking, down the material, thus making the pulverizing action of the hammers more efficient while reducing wear on the screens.
Both the circular screen and industrial hammer mill models range in size from pilot scale to high production models. The size of the mill and the recommended horsepower of the motor is dependent on the processor’s throughput goals.
For more information, please download our How Does a Hammer Mill Work? factsheet: