The pin mill also categorized as a disc mill is a kind of milling equipment that can break up cellular materials selectively without damaging the starch granules. It consists of two horizontal steel plates with vertical projections arranged in concentric circles on opposing faces and becomes more closely spaced towards the periphery.
Pin mill uses a series of pin breakers attached to discs instead of hammer in the rotating grinding head to achieve high energy impact between the mill and the particles. It is traditionally employed to disintegrate starch- protein bond that exist in the material and produce fine flour.
Pin mill work by similar principle as hammer mills (impacts and shearing) but with typically faster tip speed rotor-stator configuration of intermeshing pins which impact the particles as solids are directed through the intermesh pins. The mill product leaves by centrifugal forces to the periphery and is then collected or further processed. This method of milling is most likely to produce materials in the micronized regime (as less than 40 micrometres) and with uniform product size. Cooling of the rotating disks is a useful way of removing heat from the mill.
The particle size produced by pin mill is determined by the following factors
a. Distribution of the pins
b. Physical properties of the fed material
c. Rotor tip speed
d. Material’s (solid’s) feed rate
e. Gas flow rate through the mills
The process can be optimized by
a. Increasing the rotor tip speed to the maximum.
b. Minimizing both solid feed rate and airflow rate.
1. It achieves smaller particle size than hammer mill at relatively reasonable energy consumption.
2. Recent advances have improved heat removal from the mill using cryogenic conditions.
3. Pin mill occupies little floor space.
4. It has a wide range of applications; can be used in milling dry, moist or slurry materials.
1. High wear due to friction
2. The machine is difficult to clean after use.
3. Tendency of forming wide particle size distribution due to narrow range of size reduction.
4. Low capacity due to its size
5. Mill fouling
6. Heat generation due to friction.