26-01-2012, 12:51 PM
CRYOGENIC GRINDING
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INTRODUCTION
The science and technology of deep refrigeration processing occurring at temperatures lower than about 150 k. is the field of cryogenics. The name cryogenics is evolved from Greek word ‘kryos’ meaning icy cold. Phenomena that occurs at cryogenic temperatures include liquefaction and solidification of ambient gases; loss of ductility and embrittlement of some structural materials such as carbon steel; increase in thermal conductivity to a maximum value, followed by further decrease in temperature. Cryogenics is the low temperature (150 K) refrigeration.
APPLICATION OF CRYOGENICS
The major areas in which cryogenics find its applications are : -
1. Gas Industry – in air separation. The volume of production of nitrogen and Oxygen by cryogenic separation of air is the important of the separation of air, refrigeration and separation. In the separation column, the difference in the boiling points of the constituents of air is used to separate them out.
2. As the source of gas. For example, the breathing oxygen needed for the pilots of the fighter aircraft is supplied by vaporizing liquid oxygen on board. In this way is a weight reduction of 65% and space reduction of 85%.
CRYOGENIC GRINDING PROCESS
Since almost all materials embrittle when exposed to cold temperatures, cryogenic size reduction utilizes the cold energy available from liquid nitrogen to cool, embrittle and inert materials prior to and or during the grinding process. All materials which due to their specific properties at ambient temperatures are elastic, have low melting points, contain volatile or oily substances, have low combustion temperatures and are sensitive to oxygen, are ideal candidates for cryogenic size reduction.
ADVANTAGES OF CRYOGENIC GRINDING
• Smaller particles
• More uniform particle size distribution
• Efficient process
• Process cooling/temperature control
• Inertness
• Trial Facilities
• Can grind smaller rubber particles down to below 200 micron
• Regular particle size
APPLICATIONS OF CRYOGENIC GRINDING
CryoGrinding of steel
The large amount of thermal energy generated during machining and grinding at high speed and feed rate raises the temperature at the cutting zones excessively. This elevated temperature level under large cutting stresses accelerates plastic deformation and wear of cutting edges leading to increased cutting forces and premature tool failure.
