In a laboratory, most materials required for sampling are, in practice, nonhomogeneous mixtures. The best method of obtaining a small representative sample of the nonuniform whole is to take a quantity of the material large enough to be compositionally representative and reduce it to a fine homogeneous powder. For this purpose, a laboratory mill/grinder is usually used. The first consideration when purchasing a laboratory mill or grinder is to decide whether it will be used for wet or dry milling. Find all the latest mill and grinder models on LabWrench.com.

Dry Milling

The purchaser should next consider how finely the material needs to be ground.

A. Mid-Range Grinding (Final Fineness: ~0.01-0.1 mm)

Typically used for chemical products and pharmaceutical products, as well as minerals and ores. The purchaser should next consider the properties of the material to be ground.

Rotor Beater Mill

This type of mill is ideal for free-flowing, soft to hard materials.

Size reduction is achieved by hammering, impact and shear effects. The feed material passes from the hopper into the center of the grinding chamber where it is crushed between the rotor, sieve and grinding inserts. Rotor beater mills offer the highest degree of operating safety.

Disc Mill

This type of mill is ideal for hard materials.

A disc mill can be used to grind, cut, shear, shred, fiberize, pulverize, granulate, crack, rub, curl, fluff, twist, hull, blend or refine. Substances are crushed between opposing discs or plates, which may be grooved, serrated or spiked.

Mortar Mill

This type of mill is ideal for medium-hard-brittle to soft-brittle grinding materials.

Grinding occurs in a mortar and a grinding jar made from the same material.

B. Coarse Grinding (Final Fineness: ~0.3-20 mm)

Typically used for glass, ceramics, minerals, ores and stones as well as some chemical products and pharmaceutical products. The purchaser should next consider the properties of the material to be ground.

Jaw Crusher

This device is ideal for hard materials.

A jaw crusher consists of a set of vertical jaws, one of which is moved back and forth against the other. The jaws are farther apart at the top than at the bottom, forming a tapered chute so that the material is crushed into progressively smaller fragments as it travels downward, until it is small enough to fall through the opening at the bottom.

Cutting Mill

This type of mill is ideal for soft to medium-hard and fibrous materials. It is often used for preliminary size reduction.

A rotor equipped with special cutting plates inside the mill revolves at high speed.

Fine Grinding (Final Fineness: <0.005 mm)

Typically used for chemical products and pharmaceutical products. The purchaser should next consider the properties of the material to be ground.

A. Mixer Mill

This type of mill is ideal for ambient and cryogenic grinding of biological samples, plant material, plastics, pharmaceuticals and chemicals.

Mixer mills grind samples by imparting motion to the container in which grinding elements have been placed. As the container is rolled, swung, vibrated or shaken, the inertia of the grinding elements causes them to move independently into each other and against the container wall, grinding the sample. In cryogenic grinding, the use of dry ice or liquid nitrogen embrittles the sample to aid in grinding

B. Rotor Beater Mill

This type of mill is ideal for free-flowing, soft to hard materials.

Size reduction is achieved by hammering, impact and shear effects. The feed material passes from the hopper into the center of the grinding chamber where it is crushed between the rotor, sieve and grinding inserts. Rotor beater mills offer the highest degree of operating safety.

C. Laboratory Jet Mill

This type of mill is ideal for hard, brittle or abrasive materials.

The process material is driven at near sonic velocity around the perimeter of the chamber by multiple jets of air or steam. No grinding media are involved. Size reduction is the result of the high-velocity collisions between particles of the process material itself.

D. Planetary Ball Mill

This type of mill is effective for most material types.

A planetary ball mill consists of at least one grinding jar arranged eccentrically on a wheel that spins in the opposite direction to the grinding jar(s). This releases high dynamic energies resulting in a fine grinding of the sample.

Wet Milling

Wet milling is used for homogenization of suspended solids, emulsions and dispersions. Typical applications include cosmetics, soaps and some pharmaceutical products. The purchaser should consider what capacity grinder is required.

A. <600 liters

For small capacity applications, a bead mill should be considered.

Bead Mill

These are typically used for laboratory samples that are very difficult to disrupt with standard mechanical homogenizers.

The combination of the rotational effect and the grinding beads produces a faster, more effective lysing process for biological samples. Bead mills also allow for closed-vessel and multiple-sample processing with no risk of cross-contamination. This equipment is beneficial to laboratories that process multiple small-volume samples.

Planetary Ball Mill

This type of mill provides rapid and fine grinding of soft to very hard materials, emulsions and pastes.

A planetary ball mill consists of at least one grinding jar arranged eccentrically on a wheel that spins in the opposite direction to the grinding jar(s). This releases high dynamic energies that result in a fine grinding of the sample.

B. >600 Liters

For small capacity applications, a rotor-stator homogenizer should be considered. Industrial-scale mills are also available for larger-scale applications.