End-runner mill similar to edge runner mill is a mechanized form of mortar and pestle type size reduction equipment. A heavy-weight pestle rotates due to the friction of material present between mortar and pestle upon rotation of mortar driven by a motor at the base.
Principle of End Runner Mill:
The
principle of size reduction applied in these mills is crushing due to the heavyweight
of the stones or metal pestle and shearing force as a result of the 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
to be processed.
Construction of End Runner Mill:
End-runner
mills are the mechanized forms of mortar and pestle-type compression
comminution. This milling equipment consists of a pestle made of either stone
or metal, connected by a shaft, Fig.1. The pastel rotates at its axis in a
shallow steel or porcelain mortar. The pestle is mostly dumb-bell shaped. The
mortar is fixed to a flanged plate at the bottom. It also consists of scrappers
at the center and alongside the circular pan. The pestle is mounted
horizontally and rotating against a bed of powders.
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| Fig.1: End Runner Mill (a) Schematic (b) Mill Used in Practice |
Working of End Runner Mill:
The
material to be milled is fed into the center of the circular mechanical mortar
(pan) and is worked outwards by the action of the wheels and the mill is
operated. The pestle rotates against a bed of powders. Mortar revolves at high
speed and causes the pestle to revolve. Scrapers are employed in scraping the
material constantly from the bottom of the wheel and are fed back to the wheel
where it gets crushed further. Finally, the pestle is raised from the mortar
manually or automatically to facilitate emptying and cleaning.
Uses of End Runner Mill:
- It is used to reduce fibrous crude drugs to a fine size.
- It is used for grinding semisolid preparations such as ointments and pastes to a fine size.
- It is used for the uniform distribution of the contents in the viscous dispersion medium.
- It can be used for both wet and dry grinding of crude drugs.
Advantages of End Runner Mill:
- It has a simple design and thus cleaning and maintenance are easy.
- It utilizes less electrical power.
- It produces fine and sometimes very fine particles.
- Requires less attention during the milling operation.
- It has no problem of choking or clogging as it has no sieves for size separation.
Disadvantages of End Runner Mill:
- It runs only on the batch operation.
- It is not suitable for milling sticky materials.
- Unsuitable for drugs that are hard and unbroken or in slightly broken condition.
- Machine noise causes a lot of noise pollution.
- It requires scrapper adjustment intermittently.
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