Cold is good for the ground material and the grinder: cold grinding allows particularly fine and high-quality powders to be produced. This technology also helps to separate recyclable materials by type.
Heat in high-performance mills
Countless manufacturing processes require raw materials in powder form. As a rule, the finer the material is ground, the higher the quality of the end product. For paint additives, for example, grain sizes between 100 and 400 micrometers are required. However, heat is generated during grinding, especially in modern high-performance mills that operate at high speeds. However, not all materials can withstand the resulting temperatures, or the desired grain size cannot be achieved with heat.
There are also materials that cannot be ground under normal conditions. Thermoplastics, elastomers and some waxes are too tough, too elastic or too soft for this. Other materials can melt or stick together during grinding - which is not good for the grinders either. Other products, such as spices, drastically lose quality above a certain temperature. All of this can be avoided by cooling the material to be ground.
Cryogenic gas where it is needed
In cold grinding, the ground material is cooled and embrittled with liquid nitrogen or carbon dioxide. The liquid gas is added on the way from the storage tank to the grinder: a so-called paddle screw cooler simultaneously ensures material transport and a low temperature. The cold ground material enters the grinder together with the gas. Both provide cooling during the grinding process.
You can also cool the grinder itself instead of the product. In this case, cryogenic gas is sprayed directly into the grinder, where it lowers the temperature to the desired level. In both cases, the supply and dosing can be precisely controlled. The right amount of cold is delivered exactly where it is needed.
Both techniques make it possible to grind particularly finely. Thanks to the cold, the quality of the raw material remains unaffected. Last but not least, the mill throughput is also significantly increased: the cold, brittle ground material is easier to process. As melting and sticking is prevented, the mills can run at optimum speed.
Pure separation
The same principle also helps with recycling, where shredding is also a crucial production step. Cryogenic technology facilitates the separation of materials here. This usually involves breaking down composite materials such as fiber-reinforced thermoplastics, galvanized plastic parts or packaging with product residues. Conventional grinding methods reach their limits here.
Only with cryogenic grinding technology can the raw materials be separated into pure components. The different material properties are exploited in the process: each material reacts differently in terms of linear expansion and brittleness.
A very welcome side effect of cold grinding is the inerting of the mill. The gases displace the oxygen from the process and create a chemically inert atmosphere that prevents fires and explosions. Inerting also prevents chemical reactions, in particular the oxidation of the ground material. This is a particularly important aspect for foodstuffs.
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