Milling Methods Unveiled: Your North Star to the Right Technique

In every industry, particle size and distribution play a crucial role that drives innovation from enhanced properties to increased functionalities to ease of manufacturing. The design and geometry of milling equipment is the beating heart of particle size reduction. With such a dramatic effect as this, where do you even begin to make a decision on what equipment to use?

You should always start by letting the raw material speak to you in order to understand the type of force needed to reduce its size. But even then, there is a broad range of methods to narrow down. From coarse crushing to wet media milling, let’s get a better idea of which technique might be right for you.

Coarse crushing offers simple, heavy-duty action that includes jaw crushing and impact crushing. Jaw crushing compresses the material until it fractures. From stone to glass, this method can reduce the particle size down to 0.5mm or larger. Jaw crushing is ideal for not only final size reduction but can also provide a coarse starting point for further refinement of the particles. Impact crushers are another great option as these apply similar forces with high-speed collisions between the material and the grinding chamber giving more uniform particle distribution. Limestone and other minerals are perfect matches with this technique. Both of these techniques can even be used in conjunction with one another: jaw crushing as the primary step and impact milling as the secondary to allow for versatility and precise particle size control.

Roller mills and hammer mills offer mid-gauge particle size ranges down to 100 microns. Roller mills crush material between a pair of rotating rollers. This allows for uniform particles with minimal fines generation. Hammer mills are rapid and efficient for particle size reduction with their swinging hammers that pulverize material against a screen. A wide variety of materials, including fibrous and tougher materials, can be processed with this technique. Due to the rapid blows, this technique generates higher temperatures which can be counteracted with technologies such as cryo-milling for heat-sensitive materials.

Universal mills are considered the Swiss army knife of milling. This technique can achieve particle size distributions from tens of microns to 2,000 microns. Interchangeable screens and rotors allow for a diverse range of materials to be processed and is commonly used for food and pharmaceutical applications.

Fine and ultra-fine techniques include jet milling and wet and dry media milling. Jet mills and fluidized bed jet mills use a high-tech method that reduces material by particle-on-particle collisions with compressed air, gas, or steam. These particles can be reduced down to smaller than 5 microns. Such small particles can open up new worlds for pharmaceutical, cosmetic, and mineral applications due to the high surface area exposed. The result can be increased efficacy of active ingredients, precise color and sheen in pigments, and reduce material requirements in agricultural chemicals.

Media milling uses collision and shear forces to grind down particles, wet or dry. Ball mills operate under dry conditions while bead mills operate in a liquid slurry. These methods can reach particle sizes down to the nanometer range with narrow distributions. Particle size distributions this small are critical to the pharmaceutical and materials science industries from advancing medicines to increasing performance of batteries.

Understanding your starting point and desired outcome is crucial when determining which method to choose from as each piece of equipment is engineered to achieve specific particle size outcomes. These milling techniques are the backbone of material processing so let this knowledge be your north start and they will shape your raw material into something that could unlock new possibilities.

Willow Slusser is business development manager, Custom Processing Services (Reading, PA). With a degree in Biochemistry and Chemical Biotechnology from East Stroudsburg University, Slusser began her career as a chemist. She worked on extraction techniques before transitioning into technical sales, where her hands-on work with cutting-edge equipment crafted a deep connection with both process and client. Slusser now works in a business development role, leveraging her technical expertise to drive growth.