Roller mill is a form of compression mill that uses a single, double or triple cylindrical heavy wheel mounted horizontally and rotated about their long axis either in opposing pairs or against flat plates, to crush or grind various materials. One of the rollers is run by a motor and the others are rotated by friction as the material is drawn through the gap between the rollers.
Roller mills use the process of stress (which is applied by the rotating wheels) and attrition in milling of solids in suspensions, pastes or ointments and some solid materials. The rollers rotate at different speeds and the material is sheared as it passes through the gap.
To obtain the desired particles size, the following should be controlled;
- The gap between the rollers
- The speed differential between the rolls
- Feed rate
The design of a roller mill differs depending upon its application and they are usually named according to the work they perform e.g;
- Crackers – A mill used to crack grain or other types of friable materials.
- Flakers – Mills used to flake grains or other materials
- Grinders (Rollers mill grinders) – Roller mills that are used to grind in a feed mill.
- Crimpers – Roller mills that crimp grains
- Crimper – Crackers a roller mill that cracks and at the same time crimp grains.
- Crumbler – A roller mill specially designed for breaking up pellets into smaller particles.
Two variants of roller mill are recognized and they are;
- Multiple or corrugated rollers
- Ribbed or saw-toothed rollers.
Pharmaceutical uses of Roller Mill
- It is used in the preparation of ointment; paste, creams and other semi-solid preparations.
- Roller mills are used for crushing seeds prior to extraction.
Advantages of Roller Mills
- Produce more uniform, less fines and oversized particles when it comes to product quality.
- Generates less heat (0-30C) unlike hammer mill that generates up to 100C
- Less moisture loss
- Better work environment due to low machine noises level
- It is energy efficient/energy saving
- Reducing working hazard due to dust generation from the milling material.
Disadvantages of Roller Mills
- Not effective on fibre or two-dimensional products. Works best on easy to grind materials like corn, cereal grains etc.
- Additional operator inputs are required since the rolls need to be adjusted to suit grind requirements.
- Michael E. Aulton, and Kevin Taylor (2013). Aulton’s Pharmaceutics: The Design and Manufacture of Medicines fourth edition. Elsevier Ltd, NY.
- Sud Sushant and Kamath Archana (2013). Methods of Size Reduction and Factors Affecting Size Reduction in Pharmaceutics. International Research Journal of Pharmacy. 4(8): 57-64.