Chinese engineer Zu Chongzhi is credited with inventing water-powered hammermills in the 5th century AD. These ancient hammermill designs used the power of strongly flowing rivers to turn a water wheel to the mill. The same principle was later applied to water mills throughout Europe during the Middle Ages. The 16th-century German scientist Georgius Agricola – known by many as the Father of Mineralogy – utilized hammermills for mining operations during the Renaissance. The modern hammermill design is thought to have been developed in the early 19th-century, with the industrial revolution bringing the use of steam-powered hammermills. They became widely used by a number of industries in the 20th-century.
Since the beginning of the 21st-century, manufacturers have concentrated on building hammermills to deliver greater efficiency and reliability through cutting-edge design and use of modern materials.
What to Look for in Hammermill Design
Hammermills include a rotor with rigid hammers connected directly to a shaft or swinging hammers connected to large plates fashioned with support pins around their circumference. A hammermill typically consists of four or more hammers used to grind the material into smaller particles through impact. The rotor is supported inside a rigid metal casing that typically includes screens and sometimes corrugated liners to aid in the grinding process and to control particle size.
Common Hammermill Features Include:
- Feeding Device through which material enters the grinding chamber, typically a multi-pocket rotary feeder or auger.
- Metered feeding provides even distribution of product across the full width of hammermill rotor to provide greater efficiency and more even wear of the hammers.
- Many types include a high-grade magnet for removing tramp metal that can accelerate wear or damage the mill.
- Controls that start/ stop the mill and provide adjustment of the feeding device.
- Hammers or Knives to grind or crush by impacting materials at high speeds.
- Rotations per minute (rpm) typically vary from 1,800 to 3,600 rpm.
- Many designs allow the hammers or knives to rotate clockwise or counterclockwise for more even wear.
- They come in varying styles or shapes for use in grinding specific materials.
- A Rotor consists of a rotating shaft coupled to an electric motor on which the hammers or knives are positioned. Hammers are uniformly positioned around the circumference of the shaft or support plates to ensure concentric weight balance that reduces vibration when operating. Hammers can also vary in quantity and vary in pattern on the rotor to provide different levels of grinding intensity.
- Drive System with the motor directly coupled to the rotor or driven through belts for more precise speed control in specific applications.
- Mill Screens arranged in close tolerance to the hammers are used for classifying the particles, retaining larger particles while allowing smaller ones to exit the grinding process.
Different Hammermill Designs
A key element in hammermill design regards whether the hammers are fixed or swinging. Most modern hammermills use a swinging hammer design, with those with fixed hammers sometimes referred to as lump breakers. Hammermill design can differ based on configuration, coatings, length, number, pitch, and spacing of the hammers, which are often customized to provide optimal results for a specific application.
The following hammermill designs describe how they function:
- Full circle screen hammermills feature screens that encompass 300 degrees of the rotor. This improves particle evacuation and suits reduction of spices, grasses, and other lightweight materials.
- Gravity discharge industrial hammermills also referred to as gravity discharge or bottom discharge hammermills, feature heavy-duty, HD, swinging hammers mounted on a shaft to reduce particle size, discharging milled material via gravity into a bin or mechanical conveyor below. These mills are often used for coarser reductions on materials like ceramics, dried chemicals, or glass.
- Horizontal in-feed hammermills, which include grinders used for trim scrap or wooden pallets, feed material into the grinding chamber from the side rather than from the top. This hammermill design works well for heavy grinding of particles that aggressively reduce material.
- Lump breakers function differently from other hammermills. They feature smaller fixed hammer configurations than swinging hammers. Their purpose is to condition material into free-flowing granular or powder form using hammers that mesh with one another or fixed combs attached inside the unit. These are used for materials like cement, dried chemicals, and sugar.
- Pneumatic discharge hammermills operate similar to gravity discharge mills, though they feature more precise tolerances and often a greater quantity of hammers. This hammermill design utilizes an external source of vacuum to pull ground product from the mill, increasing efficiency and enabling finer outputs for products like grains, biomass, wood, and paper.
Hammermills serve as primary, secondary, or tertiary reduction equipment, grinding material into specific particle ranges depending on the application. Their power and size also vary, with some electric motors capable of achieving extremely high horsepower.
Sourcing the Best Prater Hammermill Design
Prater Industries has been manufacturing hammermills since its inception in 1925, with the company’s original hammermill design used in animal feed processing. Prater has worked to constantly improve the designs of its hammermills for nearly a century, customizing them to work with specific materials and for an expanding number of applications. The development of Prater’s innovative hammermill designs has multiplied the company’s capabilities for fabricating an array of reduction equipment, which is now used by a wide assortment of industries.
Prater hammermills are often customized for specific applications, particle size ranges, and output, while also designed to produce uniform particle sizes consistently over time. The company’s hammermill design also reduces downtime by allowing easy access to the grinding chamber for maintenance and cleaning. Additionally, hammers are often specially coated to extend their lifecycle and increase throughput.
Full Screen Hammermill Design
Known also as its G-series hammermill design, Prater’s Full Screen Hammermills are easy to maintain and made to operate 24/7.
Benefits of Prater’s Full Screen Hammermill design include:
- Capable of continuous operation
- Easy maintenance and screen changes
- Even wear of hammers
- Increases throughput without increased requirements for power
- Tip speeds for hammers range from 14-21 thousand feet per minute
- Uniform granular grinding
Mega Mill Hammermill Design
Prater’s Mega Hammermill helps bridge the gap between the company’s G-series hammermills and its fine grinders.
Benefits of Prater’s Mega Mill Hammermill design include:
- Cantilevered grinding rotor makes for smooth and quiet operations
- Capable of continuous operation
- Demands less power
- Lessens downtime and maintenance
- Provides uniform grinding while minimizing heat build-up
- Results in higher quality finished product
- Runs more efficiently with lower airflow
Learn more about the Prater Hammermill and Mega Mill Hammermill by checking out our videos on YouTube.
