As one of the oldest and most frequently used machines for uniformly reducing the particle size of bulk materials, the hammer mill is a robust and reliable piece of equipment. It offers material handling companies a way to break down and crush various feed materials, including chemicals, cosmetics, grains, minerals, spices, and wood flour. Comprised of a series of hammers attached to a pivoting shaft, the principle behind hammer mill operation is relatively simple.
This simplicity enables designers for material handling systems to customize a hammer mill to serve various applications. Agriculture, chemical, food processing, mining, paper, and other industries depend on hammer mills to break down raw products to the necessary particle size range. Hammer mills can reduce material from midsized, granulated particles to fine powders. Regardless of the application, industry, or material, hammer mills are integral to the materials handling processes that promote quality production.
How Hammer Mills Support Quality in Bulk Material Processing
Quality in the bulk materials sector relies on the integrity of the machines used to process the product. For bulk material handling companies looking to use hammer mills in their application, it’s essential to source a reputable hammer mill within their system. Like any other machinery, hammer mills have evolved as the requirements for reduction machinery have changed. Today’s hammer mills are designed with capacity and efficiency requirements in mind, though their basic purpose hasn’t changed.
Today’s hammer mills still achieve the uniform particle size similar to what their ancestors once attained, though often with much larger throughputs, while utilizing energy more efficiently. Uniformity in particle size is crucial to food processing and other industrial applications. Screening technology improvements have enhanced the quality of end products and made hammer mills more productive. As an example, hammer mills are used to crush seed, allowing mfg to achieve greater oil extraction..
Understanding the Benefits of Hammer Mills in Production
Hammer mills also work well when mixing two solid powders made up of fibrous elements, while they’re also used to prepare and suspend powders within liquids for chemical and food processing industries, along with the pharmaceutical sector. Additionally, hammer mills are often used to scrap vehicles for recycling, with crushed metals and alloys melted and then used in new production.
Other production advantages hammer mills provide include:
- Coming in a wide array of sizes and capacities.
- Less utility cost.
- Enabling continuous operation for 24/7 production.
- Grinding or crushing takes less time, so saves on labor costs.
- Installing hammer mills is relatively trouble-free.
- Needing less maintenance.
- Offering a high capacity-to-reduction ratio for primary, secondary or even tertiary milling stages.
- Reducing material size particularly well for more brittle materials.
Choosing the Best Hammer Mill for the Application
Hammer mills fit into a category of reduction machinery that includes ball mills, jaw crushers, roll mills and shredders. Additionally, hammer mills come in a variety of styles for various applications. Yet even among these varieties, their functions remain essentially equivalent to these other types.
In brief, hammer mill operations involve:
- A feeder that introduces material into the grinding chamber.
- Moving hammers and internal components that make contact with the material to reduce particle size.
- Screens or grates that only allow material through openings when it reaches a specific size.
There are five key types of hammer mills, with each type appropriate for certain applications.
Gravity Discharge Hammer Mills
These are the simplest types of hammer mills, featuring a steel chamber within which swinging hammers are attached to a shaft. This rotating shaft moves at high speeds, causing the hammers to impact the material while also making contact with a breaker plate inside the chamber, which augments the grinding action. Its simplicity makes these industrial hammer mills easy to adapt, with various sizes and designs available.
Hammer mills designed for gravity discharge process a range of materials, including:
- aggregates
- brass
- ceramics
- coal
- coke
- dry chemicals
- glass
- metals
- porcelain
- resin
- feeds, grains & rework applications
These hammer mills work well for grinding abrasive materials, as they have replaceable steel plates that line the interior, protecting internal components from wear.
Full-Screen Hammer Mills
Using the same type of thin hammers as pneumatic hammer mills and the same basic mechanism for grinding, the full-screen variety offers screen coverage of almost 300 degrees. This gives the material a larger surface area through which right-sized particles can exit after being sufficiently ground. As such, these hammer mills allow greater throughput per amount of horsepower than other types.
Materials full-screen hammer mills handle include:
- corn
- grain
- grasses
- planer shavings
- sawdust
- spices
These hammer mills require thinner, more pliable screens to achieve optimal coverage, which makes it well-suited for lighter, easily ground materials that don’t rely on a breaker plate as a primary means for grinding.
Pneumatic Discharge Hammer Mills
There are two differences between pneumatic hammer mills using skinnier hammers and a ribbed lining plate shaped like a washboard within the grinding chamber. This plate works along with hammers and particles colliding with each other to reduce material. The most notable dissimilarity involves using moving air to force material out of the hammer mill. Separate or attached to the hammer mill’s shaft, a fan pulls material through the grinding chamber and conveys it to a storage container.
Materials pneumatic discharge hammer mills handle include:
- biomass
- bone meal
- carpeting
- green wood
- hogged wood scrap
- meat
- paper
- wood chips
Pneumatic discharge hammer mills sometimes feature notched hammers for shredding and tearing. While helping material exit the grinding chamber, especially for products with lower density, the suction created by the fan often increases throughput considerably over more basic hammer mills. However, the former is used primarily for finer grinding and classifying particles, whereas the latter hammer mills result in quicker material processing and coarser particles.
Horizontal In-Feed Hammer Mills
Featuring the ability to feed the machine from the side, these hammer mills work well for larger scrap, especially that which is longer or linear. Horizontal in-feed hammer mills also process material without pre-grinding. This design is used for pallet and trim scrap grinding machines and features robust screens at the discharge point to classify particle size.
Materials horizontal in-feed hammer mills handle include:
- scrapped pallets
- trim scrap
- truss plant scrap
- two-by-fours
- whole pallets
Generally, feeding rollers control the speed at which the product goes into the grinding chamber.
Lump Breakers
Also known as lump crushers or flake breakers, lump breakers differ from other hammer mills in their function and design. Unlike other hammer mills that feature swinging hammers on a rotating shaft that moves at high speeds, lump breakers utilize stationary hammers on a shaft that moves considerably slower. The hammers remain rigid while the shaft rotates, with the hammers passing between combs attached along the grinding chamber’s walls. The size of finished particles depends on how the combs and hammers are spaced, with rotations per minute and size of the hammer also controlling particle size.
Materials lump breakers handle include:
- agglomerated powders
- cement
- dry chemicals
- sugar
With their configuration, lump breakers can handle a certain amount of pressure on the belt directly under the hopper. Known as a “head load,” this property makes the machine well-suited for larger material, along with processes encouraging material flowability, like deagglomeration and removing lumps.
Tips on Maintaining Hammer Mills
Like any other industrial equipment, maintaining hammer mills is more cost-efficient than repairing those that haven’t been regularly serviced. Hammer mills must deal with considerable wear and tear, so they must receive routine maintenance to prevent components from failing, which can lead to unplanned downtime and costly repairs. It’s important to have a preventative maintenance plan that involves systematic inspections to ensure a long equipment lifespan. Additionally, having replacement parts on hand also reduces the length of work stoppages.
It's generally a good idea to keep the following parts stocked:
- Hammers: These are either two-way or four-way reversible, with cutting edges becoming rounded over time, affecting the hammer mill’s overall efficiency; the number of rotations the hammer can withstand depends on the hammer type, though whenever cutting edges become rounded, they should be promptly replaced.
- Hammer rods: These interact directly with the hammers, so should be inspected when hammers are rotated or replaced; in the case of hammer rods, when they become grooved they affect the hammer mill’s performance and should then be replaced.
- Screens: In models of hammer mills that feature screens, they need to be regularly inspected to prevent off-sized particles in the final product; when perforations in screens become elongated, it’s time to replace them.
- Bar grates: For those hammer mills that feature bar grates, they too must be inspected regularly to keep off-sized particles from passing through; when the edges of bar grates become overly rounded, they must be replaced.
- Wear plates: Used to prevent damage from the processing of harder or more abrasive materials, wear plates extend the life of hammer mills; wear plate thickness should be checked to ascertain whether they need to be replaced, with excess space between bolts an early sign of thinning plates and an indication they should be replaced.
- Bearings: To ensure continuing reliability, a hammer mill’s bearings should be lubricated, though not overly lubricated, while bearing inspections should occur every 6 to 12 months; this allows for cleaning old grease from the equipment while also ensuring they’re not over-lubricated, with any replacement bearings requiring monitoring for the first 12 hours after being half-filled with new lubricant.
Proper lubrication also helps reduce the premature wear of any of a hammer mill’s moving parts. This will also keep components from having to be replaced too often. Airflow is also a factor, so it should be checked along with lubricants so that excessive material buildup within the hammer mill doesn’t occur.
The Importance of a High-Quality Hammer Mill
For any production requiring particle reduction equipment, hammer mills are essential for meeting quality needs. As reliable and efficient machinery capable of processing a wide range of materials, hammer mills are integral to many industries. The ability to customize hammer mills to meet specific applications makes them invaluable as part of any material processing system.
Whether it’s a gravity discharge hammer mill for abrasive materials, a full-screen hammer mill processing grain, a pneumatic discharge hammer mill for biomass, a horizontal in-feed hammer mill to break down pallets or a lump breaker to make agglomerated powders flow better, hammer mills need to be of the highest quality. When considering whether hammer mills should be part of a material handling system, manufacturers should weigh opinions and glean knowledge from potential partners who design and make them to ensure getting the right machine.
