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Cryogenic grinding, also referred to as freeze grinding, is the act of cooling or chilling a material and then reducing it into a small particle size. For example, thermoplastics are difficult to grind to small particle sizes at ambient temperatures because they soften, adhere in lumpy masses and clog screens. When chilled by dry ice, liquid carbon dioxide or liquid nitrogen, the thermoplastics can be finely ground to powders suitable for electrostatic spraying and other powder processes.[1] Cryogenic grinding of plant and animal tissue is a technique used by microbiologists. Samples that require extraction of nucleic acids must be kept at -80 ºC or lower during the entire extraction process.[1] For samples that are soft or flexible at room temperature, cryogenic grinding may be the only viable technique for processing sample
read this
http://cda-adc.ca/jcda/vol-72/issue-9/795.pdf
http://en.wikipediawiki/Cryogenic_grinding
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please read
http://studentbank.in/report-cryogenic-grinding--5420 for Cryogenic Grinding technical information and seminar report
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Submitted by
SUHAIB THALEKKARA MARUTHURU
[attachment=7774]
OBJECTiVES
INTRODUCTION
PROBLEMS IN CONVENTIONAL GRINDING
WORKING
ADVANTAGES OF CRYO GRINDING
EXPERIMENTAL STUDIES
APPLICATION
CRYOGENICS
The term “ Cryogenics” originated from the Greek word which means creation or production by means of cold. Cryogenics is the study of very low temperatures or the production of the same.. Liquid nitrogen is the most commonly used element in cryogenics and is legally purchasable around the world.
APPLICATIONS OF CRYOGENICS
In Gas Industry
As the source of gas
As Rocket propellant
In Biology
In Food Industry
In Electronics
In Medicines
In Grinding
GRINDING
The process is carried out with a grinding wheel made up of grits for removing materials from work piece surface.
Grinding can be classified into two types
Grinding for material removal
Grinding for powdering
PROBLEMs IN CONVENTIONAL GRINDING PROCESS
High heat generation
Introduction of tensile residual stress
Less tool life
Clogging and Gumming of the mill
Oxidation
Loss of Etheric oil in Spice grinding
CRYOGENIC GRINDING …..also known as Freeze Grinding
Cryogenic grinding involves cooling a material below its embrittlement temperature with cryogenic fluid. Typically Liquid Nitrogen or in certain applications, liquid Carbon Dioxide is used.
This process has several benefits
Ability to process soft or elastic material
Increased productivity
Low Power Consumption
Smaller size particle
Minimal loss of volatile component
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The report(s) of cryogenic grinding is available in this thread:
http://studentbank.in/report-cryogenic-g...2#pid33432
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Submitted by
Karthik .S.N
CRYOGENIC GRINDING
ABSTRACT
The term "Cryogenics" originates from Greek word which means creation or production by means of cold. As prices for energy and raw materials rise and concern for the environment makes safe waste disposal difficult and Costly, resource recovery becomes a vital matter for today's business. Cryogenic grinding technology can efficiently grind most tough materials and can also facilitate Cryogenic recycling of tough composite materials and multi component scrap. The heart of this technology is the CRYO-GRIND SYSTEM. It employs a cryogenic process to embrittle and grind materials to achieve consistent particle size for a wide range of products. The cryogenic process also has a unique capability for recycling difficult to separate composite materials.
Cryogenic grinding is a method of powdering herbs at sub-zero temperatures ranging from 0 to minus 70°F. The herbs are frozen with liquid nitrogen as they are being ground. This process does not damage or alter the chemical composition of the plant in any way. Normal grinding processes which do not use a cooling system can reach up to 200°F. These high temperatures can reduce volatile components and heat-sensitive constituents in herbs. The cryogenic grinding process starts with air-dried herbs, rather than freeze-dried herbs.
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.
Physical properties of liquid nitrogen is produced by the separation of air into its components in an air separation plant and is distributed in vacuum insulated transport vessels to the end user where it is stored in a vacuum insulated storage vessel till it is used. At atmospheric pressure liquid nitrogen is at a temperature of -320 deg F and possesses a latent energy content of 94 BTU/LB resulting in a total cooling energy content of 179.6 BTU/LB. Nitrogen is anon-flammable, non toxic and inert gas which makes up 78.09% of the air we breathe.
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