Different applications, quantity of throughput and final end products often designate the method employed to grind materials (Figure 3). Crushers are commonly shearing or compression disruptors and are used to create larger particles in the 50-100 mm range. These particles are often just a primary step in some processing schemes. Most crushers are able to either process a large continuous stream of materials or larger batches. Grinders often produce smaller particles in smaller scales. There are many types of grinders based on the method of grinding and the force used to grind materials.
Figure 3. Types of crushing and grinding machinery for laboratory use.
Different applications, quantity of throughput and size of final products often designate the method employed to grind materials from large scale crushers to finer impact mills. Table 2 gives the relative reduction of particle size from original material and the equipment needed.
Table 2. Particle size reduction comparison table.
| Particle Size |
Reduction from Original |
Type of Equipment |
| Large |
2-5 x |
Crusher |
| Medium |
5-10 x |
Crusher |
| Fine |
10-50 x |
Crusher or Mill |
| Microfine |
50-100 x |
Mill |
| Superfine |
100-1000 x |
Mill |
Mills are the most common laboratory grinders used to create fine, microfine or superfine particles needed for analytical testing and processing. Some common laboratory mills include (Figure 4):
- Ring and Puck Mills use multiple grinding surfaces usually as opposing plates that move in opposite directions with a disc or puck moving and grinding materials on a plane (see SPEX SamplePrep’s Shatterbox and technical notes for more information).
- Impact Mills have a moving impactor that pulverizes a sample through repetitive motions (see SPEX SamplePrep’s Freezer/Mill and technical notes for more information).
- Ball Mills or Ball-Medium Mills grind through impact of a grinding media such as balls, rods, etc. (see SPEX SamplePrep’s Mixers and Mills and technical notes for more information).
- Vibratory or Shaker Mills use high speed vibrations and grinding media to combine multiple grinding forces to reduce materials to fine powders. These mills can include grinding forces and media like balls, beads and grinding media.
- Combination Mills use multiple techniques and forces such as combination of ball media with vibratory and shaking motions (see SPEX SamplePrep’s line of Geno/Grinder products and technical notes for more information).
Shatterbox Freezer/Mill Mixer/Mill Geno/Grinder
Figure 4. Examples of Ring/Puck Mill, Impact Mill, Ball Mill, and Combination Mill from SPEX SamplePrep.
Often successful grinding is more that picking a grinder but also understanding the chemical and physical characteristics of your sample. In our next post we will take a look at material state and how it effects grinding.”