CRYOGENIC GRINDING OF THERMOPLASTICS AND ELASTOMERS
In cold grinding, the materials to be ground are cooled and embrittled with cryogenic liquid nitrogen or carbon dioxide. This method achieves particularly high grain fineness while maintaining product quality. In addition, the mill throughput is significantly increased. In particular, cooling the grinding process with cryogenic gases in the case of heat-sensitive substances prevents a rise in temperature which results from the conversion of the electrical energy of the mill motors. This prevents melting and sticking of the ground material.
In order to grind tough and elastic materials with a high throughput into fine powder, an efficient cryogenic cold grinding system is required. The feed material must firstly be cooled with a suitable refrigerant such as e.g. liquid nitrogen to a defined temperature usually below the glass transition or softening temperature to cool. On the other hand, the duration of the grinding process should be kept as short as possible, because the material to be ground, which is heated again by the energy input of the grinding tools, should not be deformed but be grinded.
- Liquid nitrogen tank
- Blasting medium
The objectives of the cryogenic milling of thermoplastics and elastomers are:
- a high throughput to obtain low production costs
- usually a large proportion of fine or finest material, as this increases the product value
- a low specific energy requirement to save electricity costs
- the avoidance of thermal damages
- to prevent the risk of dust explosions and fires during grinding
The Messer Group operates a highly specialized test facility, which offers the opportunity to profit from process developments, to estimate production costs or to produce sample batches. Qualified sample grinding is carried out using liquid nitrogen.
All grinding parameters, such as throughput, electricity and nitrogen requirements as well as the particle size distribution are measured, evaluated and made available to the customer. The results obtained can be transferred to large-scale productions.
In addition to pure grinding sample production, an estimate of the production costs under production conditions and a comparison to other grinding processes can be made. Even existing mills at the customer’s site can be optimized. Granulate coolers, nitrogen control valves and temperature control can be provided for carrying out tests on these plants on site.