Fluid Energy Mill /Jet Mill/ Ultrafine Grinder

Principle

Material reduced in the size by attrition & impact. The feed stock is suspended within a high velocity air stream. Milling takes place because of high velocity collision b/w the suspended particles

Construction

It consists of a loop of pipe which has a diameter of 20 to 200 mm, depending on the overall height of the loop, may be up to about 2 m

There is a feed inlet and a series of nozzles for the inlet of air or an inert gas

It also has an outlet with a classifier which allows the air to escape but prevents to pass until they become sufficiently fine

Working

Solids are introduced into the stream and, as a result of the high degree of turbulence, impacts and attritional forces occur between the particles

A classifier is incorporated in the system, so that particles are retained until sufficiently fine

The feed to the mill needs to be pre-treated to reduce the particle size to 100 mesh, enabling the process to yield a product as small as 5 μm or less

Advantages

The particle size of the product is smaller than that produced by any other method of size reduction

Expansion of gases at the nozzles leads to cooling, counteracting the usual frictional heat which can affect heat-sensitive materials

Since the size reduction is by inter-particulate attrition there is little or no abrasion of the mill and so virtually no contamination of the product

For special cases with very sensitive materials it is possible to use inert gases

Having a classifier as an integral part of the system permits close control of particle size and of particle size distribution

The method is used where especially fine powders are required, as antibiotics, sulphonamides and vitamins

Disadvantage

Energy consuming

High head space

Avoid coarse materials into the chamber.

The fed device may be clogged with the clump materials Special feeding devices should be provided for the feeding of the materials

Use of compressed air results in generation of static electricity

Material recovered in the collection bags is difficult or impossible to remove by the normal blow back procedures