From grains to stones and from wood to ore, humans have been using tools to break down the size of various materials since the Early Stone Age. Primitive size reduction equipment used by our prehistoric ancestors were little more than stones used to pulverize plants for food or medicine and shaped to cut material like skins for clothing or shelter. These tools became more complex over time, becoming mills that ground grain and hammers for shaping ore. Modern equipment for reducing material size has become even more complex and mechanized.
Today, mechanized size reduction equipment cuts, mills, pulverizes, slices, and otherwise reduces the material into smaller portions in production facilities worldwide. The key to reducing material is energy, an important element in all particle size reduction processes. Equipment that can apply this energy to the material is the basis of many modern industries, so understanding the fundamentals of size reduction is necessary for those tasked with their operation and oversight.
Particle Size Reduction in Industry
Material processing to reduce particle size is used in the manufacturing many goods. Manufacturing processes in numerous industries utilize some form of particle size reduction. Equipment for breaking down raw material is indispensable for producing a myriad of products in multiple industries and for various reasons. Size reduction manipulates their properties, allowing end products made from them to be more efficiently produced, along with making them safer and better for end users.
The pharmaceutical industry uses size-reduction equipment to grind medicines into powder form for capsules. The agricultural industry utilizes milling machines to reduce grain, while the food and beverage industry process raw agricultural material with industrial reduction machinery to produce packaged foods and fruit juice. In the construction industry, stone crushers and other size-reduction equipment pulverize, loosen, and otherwise reduce minerals in the production of cement or other building materials.
Other materials and applications that require size reduction during production include:
- Breaking down hazardous waste
- Crushing junked vehicles
- Plastics recycling
- Recycling scrap metal
- Shredding electronic scrap
- Other industrial applications include breaking down coal for power generation or grinding herbs and spices to be packaged for the consumer market.
How Energy Relates to Particle Size Reduction
As raw materials often come in a size that’s too large to be used, size reduction is necessary to prepare many products for sale to end users. Energy is required to grind or cut material for solids, whereas for liquids, energy is used to atomize or emulsify it. Reducing particle size involves using various methods to break apart this raw material, with different types of size reduction equipment used depending on the application. Three laws apply to this process that explains the physics behind the equipment that’s used for size reduction applications.
The three laws that apply to size reduction equipment are:
- Kick’s Law notes that however much energy is required to reduce an amount of material into a specific proportion of its original size, the energy needed will be the same regardless of the original size of its particles.
- Rittinger’s Law shows that for solids, the surface area of particles within the material is directly proportional to the energy required to reduce their particle size.
- Bond’s Law says that the square root of the surface-to-volume ratio of a material is proportional to the amount of energy transfer necessary for a very large feed to form particles.
With knowledge about these laws and materials, it can then be deduced as to which type of particle size equipment will work best for a specific application and material. Before reducing a material, manufacturers often just plug in the size these particles need to be to determine what implements will work best. Once the best methods for applying energy to a material are decided upon, it’s easier to determine what type of particle size reduction equipment will work best for the application.
Particle Size Reduction Equipment
Particle size reduction equipment differs from industry to industry, but all refer to machines that grind, crush or otherwise reduce material size during processing. While there are innumerable variations on the machinery used in size reduction, equipment can be largely segmented into three categories, grouped according to the primary manner in which they reduce material.
Particle size reduction equipment falls into these general categories:
- Attrition: These include attrition and gap mills, which reduce particle size through rubbing action commonly known as autogenous grinding that’s caused by friction between particles or by grinding material against a surface.
- Compression or crushing: Often used for mining and in mineral processing applications, it includes size reduction equipment primarily used for crushing or grinding, such as ball mills, cone mills, flake crushers, jaw crushers, and roller mills.
- Impact: Essentially, these are impact mills like air classifier mills, fine grinders, hammer mills, jet mills, and pin mills, which use sharp, instantaneous blows from a moving implement striking the material.
- Shearing or cutting: This type of size reduction equipment uses a cutting or cleaving action, examples of granulators, and shredders.
Variations on particle size reduction equipment are used in industrial settings, many of which are developed to handle very specific applications and materials. To ensure the process is done most efficiently, it’s important to understand what machinery and which techniques will best achieve the desired particle size reduction. Equipment used for reducing material works primarily to separate out a key element, improve chemical activity, enhance bioavailability or offer better material handling characteristics.
Typically, hammer mills consist of a rotor assembly with swinging hammers within a cylinder-shaped housing, which contains a cutting plate (also called a deflector liner). The impact energy of the hammers causes particles to strike this cutting plate at speed, causing them to break into smaller pieces. The plate slows the velocity of the particles, deflecting them back toward the hammers for further reduction. Towards the bottom of the housing is a screen, which is used to control particle size as material leaves the mill, with the screen’s hole sizes determining the particle size of the end product by using retention time to adjust the cut.
Size Reduction Equipment: Hammer Mills by Prater
Prater Industries makes two types of hammer mills, our Full-Screen Hammer Mill and Mega Mill Hammer Mill. The full-screen model features wider rotors to accommodate different hammer arrangements and is rated for continuous operation with increased throughput, though without additional power requirements.
Materials processed with Prater’s Full-Screen Hammer Mill include:
- Grains and pulses
- Livestock feed
- Pet food
The Mega Mill fulfills a need for size reduction equipment between standard hammer mills and fine grinders. With a maximum horsepower ratio to screen, it uniformly grinds with very little heat buildup. The machine’s can additionally be configured with various hammer types and shapes that make them versatile for multiple applications.
Prater’s Mega Mill Hammer Mill works well for applications such as:
- Animal feed
Using impact and attrition, fine grinders reduce materials until they are ground to a grain size level. Solid materials are broken down through mechanical forces, breaking up particles by overcoming internal bonding forces. Grinding not only reduces particle size but also changes the shape and nature of the particles.
Size Reduction Equipment: Fine Grinders by Prater
Designed to grind dry material that flows freely, our Fine Grinders are capable of very tight particle distributions, with sizes of particles as fine as 37 microns. It’s well-suited for resins, sugars, and other heat-sensitive materials.
Prater’s M Series Fine Grinders work well for processing products like:
- Activated carbon
- Iron oxide
Our 10-Bar Fine Grinder is a single pass mill designed for use in environments where explosions are a risk. Able to withstand explosive pressure up to 145 pounds per square inch, it’s well-suited for heat-sensitive products that need tight particle size distributions, such as for grinding sugar.
Air Classifying Mills
Air classifying mills utilize two mechanisms that stress materials to achieve size reduction. The milling portion first mechanically reduces particle size through direct impact with blades against the material. Meanwhile, attrition breaks down material as particles collide with each other within eddies of air that result when the blades pass close to the cutting plate. This roughly results in particle size reduction of 80 percent via impact from the blades and 20 percent via attrition from collisions due to moving air.
Air also conveys material through the mill, while bladeson an independently controlled rotating disk classifies the product, separating product into fine and coarse particles. Fines are then conveyed by air out of the mill, with coarser material returning to the grinding chamber for further size reduction. This recirculation continues until particles reach a certain size.
Size Reduction Equipment: Air Classifying Mills by Prater
Prater’s air classifying mill produces a finer grind with narrower particle size distribution than typical designs, with ranges from a mean size between 5-7 microns and 149 microns. Its capabilities allow the mill to process a variety of challenging materials in three stages.
Our air classifying mill’s capabilities include processing of:
- Boric acid
- Powder coating
- Wood flour
Why Choose Prater Industries for Size Reduction Processing
Prater Industries is a leading industrial equipment and systems manufacturer, providing solutions to factories in numerous industries. These include feed production, grain milling, food processing and baking, pet food, rubber, chemical, plastics, and agricultural sectors. The company’s production equipment requires as little maintenance as possible, though it’s also designed to ease cleaning, repair, and replacement of components when necessary. Learn more by contacting the team today.