Attrition Mills 3h3a6v

Attrition mills: Roller mills GRINDERS

WORKING PRINCIPLE OF ATTRITION MILLS • Attrition mills use the hammermill principle to a certain extent; i.e., shattering by/impact. However, they also impart a shearing and cutting action. Grinding is done between two discs equipped with replaceable wearing surfaces. One or both of these discs is rotated; if both, they rotate in opposite directions. When one disc is rotated, and the other stationary, the assembly is used for shredding and deferring. Often materials which have been coarsely ground by other mills, are ed through an attrition mill for blending or smoothing out an ingredient or mixture containing liquids which may have clumps. The discs of an attrition mill are generally in a vertical position so that materials not capable of reduction can by gravity out of the grinding area.

ROLLER MILLS • Principal: Material is crushed by the application of stress. Stress is applied by rotating heavy wheels,mullers or rollers • Variants: Multiple smooth rollers or corrugated, ribbed, or saw-toothed rollers can provide cutting action

MECHANISME • Two parallel rolls rotate towards one another at high speeds, say 400 – 3000rpm. Material is gravity fed between the parallel rolls and as it enters the ‘nip’ of the rollers, it experiences both crushing and shearing forces that grind the particle into smaller pieces. Roll surfaces can be either corrugated or smooth on the surface, depending on the need, and typically a speed differential between the rolls, ranging from 1:1 to 3:1, is necessary.

• Most roller mills are compromised of multiple grinding sections vertically stacked on top of one another and material falls by gravity from one pair of rollers to the next • The number of section determined by the material properties and the amount of reduction required to achieve the desired grind size. • corrugations, speed ratio between the rolls, and the gap between the grinding rolls are all precisely engineered for each product. The objective is to reduce the material in size to a narrow particle size distribution and with few unwanted fines

EXAMPLE OF OTHER SIZE REDUCER USING ATRITION PRINCIPLE

Colloid mill: Colloid mill works on the principle of shearing. The colloid mill is useful for milling, dispersing, homogenizing and breaking down of agglomerates in the manufacture of food pastes, emulsions, coatings, ointments, creams, pulps, grease etc. The main function of the colloid mill is to ensure a breakdown of agglomerates or in the case of emulsions to produce droplets of fine size around 1 micron.

The material to be ground is added so that it is slightly more than fills the voids between the pellets. The shell is rotated at a speed which will cause the pellets to cascade, thus reducing particle sizes by impact. It has been proposed that in the plastics industry the term ball mill be reserved for metallic grinding media, and the term pebble mill for non-metallic grinding media.