Edge Runner Mill
Principle
It consists of either one or two rollers made of heavy steel or granite mounted on a horizontal shaft, which are turned around a vertical shaft attached to a steel or granite foundation. The stones are generally between 0.5 and 2.5 m in diameter, weighing as much as 6 Tonnes for the larger sizes. Runners are kept on course by scrapers which keep the material to be ground in front of them. Reduced pressure is caused in part by crushing: by stones crushing each other, but primarily by friction between runners and bed stones. Edge runner mills have gradually been replaced by more sophisticated machines, but they remain valuable in the reduction of roots and barks to powder, especially for extremely tough and fibrous materials.Construction
In Figure you can see how an edge runner mill is constructed. A number of tons may be required to move the rollers. On a stone or granite bed, the rollers move. A roller revolves around its axis and is powered by a central shaft. The bed is equipped with rollers that are mounted on a horizontal shaft.
Working
On the bed is placed the material to be ground. It is kept in the wheel's path by scraping it with a scrapper. Stones revolve around their axes while also traveling around a shallow bed of stones. For a wheel to get smaller, the outer part must also travel a greater distance than the inner part. This grinding process takes place over time. Powder is sieved for the appropriate particle size after it is collected. Batch processing is used.Uses
Grinding tough materials into fine powder is what it is used for. These mills still produce plant-based products, but they produce more sophisticated chemicals and drugs.Merits
- The machine does not require attention while operating.
- Particles produced by it are fine
Demerits
- In comparison to other mills commonly used, it occupies more space.
- There is a possibility of contamination with roller material.
- Milling takes a lot of time.
- Non-sticky materials cannot be milled this way.
- It consumes a significant amount of energy.
End Runner Mill
Principle
This type of mill has an eccentric pestle mounted in a ceramic, granite, or metal mortar, which is rotated by an electric motor. Since the pestle rotates freely within the mortar due to friction, the material being crushed is simultaneously impacting and being sheared by the rotating pestle. Spring-loaded scrapers return materials to the grinding area continuously, and at the end of the process, the pestle can be rotated with ease so that it can be cleaned and emptied. This type of mill is also effective with fibrous materials such as bark, leaves, fruits, and woods because of its moderately fine powder.During this process, the heavy weights of the stones or metal pestles crush and shear each other together in movement, reducing particle size. By rotating the mortar under the powder to be processed, the friction between a weighted pestle and the material passing beneath it turns the pestle.
Construction
The figure shows an end runner mill in construction. An end runner mill can be thought of as an intermediate mill. The mortar consists of a steel plate flanged to a steel mortar. The horizontal shaft bearing the pulley is attached to a beveled cog fitting below the flanged plate. A high rotational speed is thus possible with the plate with mortar. The pestle is designed as a dumb-bell so that it can balance and grind effectively when its weight is applied. Its flat bottom ensures efficient grinding. There is a hinged arm attached to the pestle. The pestle can be raised from the mortar as a result of this arrangement, making it easier to empty and clean. This pestle has a longer, narrower central portion compared to the arm sleeve. Consequently, Pestle can move up and down over the material in the mortar.
Working
Mortar is used to grind the material. After scraping the material into the pestle, it is placed into the mortar. This causes the mortar to spin rapidly. There is a pestle inside the mortar. The pestle is rotated by a rotating mortar. This process involves both shearing and crushing in order to reduce the size of the materials. A sieve is used to collect the material and turn it into powder.Demerits
- Batch processing is the only way to use it.
- Sticky materials cannot be processed using it.
- Aims to avoid drugs that are hard and undamaged, or even slightly damaged.
- A lot of noise is generated by the machine.
- Machine scrappers need adjusting intermittently.
Merits
- It is easy to clean and maintain because it is designed simply.
- Electricity consumption is low.
- Particles produced are usually fine, and sometimes even very fine.
- There is less supervision needed during the milling process.
- There are no sieves for separating sizes on it, so it cannot clog or choke.
Uses
- A fibrous crude drug is reduced to a fine powder by the process.
- Finely ground semisolid preparations like pastes and ointments are grinded using this machine.
- Throughout viscous dispersion media, it is used to distribute contents uniformly.
- Dry and wet grinding of crude drugs can be accomplished using it.
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