Size reduction by compression can be carried out on a small scale using a mortar and a pestle. End-runner mill and Edge-runner mill (also known as Chilean mill or Roller stone mill) are the mechanized forms of mortar and pestle-type compression comminution. This milling equipment consists of two heavy wheels made of either stone or metal, connected by a shaft. The wheels rotate at its axis in a shallow circular pan. The material to be milled is fed into the centre of the pan and is worked outwards by the action of the wheels. Scrapers are employed in scraping the material constantly from the bottom of the wheel vessel after which it is feed to the wheel were it gets crushed to powders.
The principles of size reduction applied by these mills are crushing due to heavy weight of the stones or metal and shearing force which is as a result of movement of these stones or metal. In the End-runner mill, a weighted pestle is turned by the friction of material passing beneath it as the mortar rotates under powder. The Edge-runner mill has the paste equivalent mounted horizontally and rotating against a bed of powders.
Pharmaceutical uses of End-runner mill and Edge-runner mill
- It is used in the size reduction of non-sticky materials
Advantages of End-runner mill and Edge-runner mill
- It produces fine particles
- Requires less attention during the milling operation
Disadvantages of End-runner mill and Edge-runner mill
- It is not suitable for milling sticky materials
- Machine noise leading to noise pollution
- 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.
This article titled “Edge-Runner Mills and End-Runner Mills” discusses Edge-Runner and End-Runner Mills, explaining its operating principles, uses, advantages and disadvantages.