Bad Soden, Germany,

Powder “produced from thin air”: Cold grinding with gases

Industrial gas specialist Messer at Powtech 2010 Hall 7, Booth 418

Industrial gas specialist Messer will provide information about cryogenic grinding of composite materials, plastics and foodstuffs at Powtech 2010 in Nuremberg, Hall 7, Booth 418.

The application areas of the materials could hardly vary more, but the grinding method is always the same: cryogenic procedures from Messer use ultra-cold gases such as nitrogen and carbon dioxide to grind or recover a wide range of materials. These include thermoplastics, elastomers, waxes and paint additives, and also spices which lose aroma and flavour because of the high temperatures that prevail when they are ground. At Powtech 2010 in Nuremberg from April 27 to 29, Messer’s exhibits will include samples of ground materials from the fields of rubber and elastomers, foodstuffs and spices, thermoplastics, and the separation of composite materials. The largest privately managed producer of industrial gases in the world is an international provider of cryogenic gas applications for powder production and has its own cold grinding and recycling facility in Krefeld, Germany, where experiments are conducted in grinding customer products.

Cryogenic grinding and separation of composite materials

In cold grinding, the materials to be ground are cooled and made brittle using ultra-cold liquid nitrogen or carbon dioxide; this permits particularly fine particles to be produced. This also allows composite materials to be separated into their individual component materials in an economic and environmentally-friendly manner. Messer supplies the gases as well as the hardware required for this purpose. In Messer’s cold grinding and recycling facility sample batches are produced, grinding parameters are ascertained and production costs are estimated.

The entire plant set-up serves as a reference because it corresponds to a production plant, which means that the results obtained here can be scaled up directly for industrial production.

Separation of composite materials of plasticised PVC

The Messer Group recently ground garden hoses made of plasticised PVC, which is regarded as difficult to recycle. The cooling process with cryogenic gases makes the plasticised PVC brittle and crushes it into fine powder. However, it does not affect the polyester fibres in the hose the same way, owing to their great tensile strength and dimensional stability. In the pre-crushing phase the garden hoses are granulated without being cooled. This produces plasticised PVC granulate measuring up to five millimetres and at this stage the polyester fibres already begin to separate from the PVC. The PVC is ground down to the finest particle size in a cryogenic pinned mill. The polyester fibres remain largely uncrushed. At the end of the process, the material must be sieved to separate the polyester fibres from the PVC powder. The polyester fibres adhere to each other in lumps, and the PVC powder falls through the sieve deck with its mesh width of 500 micrometers. The high-quality powder can be reused.