This report reviews the principle of and problems encountered in the process of commercialization of the low temperature grinding system “CRYOMILL” which has been developed by the authors. The principle of the system “CRYOMILL” is to cool materials having low temperature brittleness such as thermoplastic etc. by liquid nitrogen injection down to the temperature below its glass transition point and to grind the material by high-speed revolving mill. During grinding process it is necessary to control heat generation which is inherent to the material and the key point in commercialization is to utilize cold energy effectively throughout the total system.
This article gives a short survey of the process of low temperature grinding. A special emphasis is given on the clean high recycle process (CHR process), which has been developed by our company in order to treat small-size motors and wires.
In Germany the project group of AEG, BBC and Siemens had succeeded in magnetically suspended test run with superconducting magnets for the first time in March 1976 on a circular test track in Erlangen. The test vehicle was propelled by an on-board linear induction motor. A clearance of 100mm between the track surface and the bottom of cryostats was achieved at 120km/h. Furthermore, a rotating drum test-rig for linear synchronous motor (LSM) is in preparation for conversion of the circular track to LSM system, because in future practical system the trains will be propelled by LSM. Outline of the plan for practical system is described also.
Mechanical and physical properties of candidated structural materials for cryogenic service are described, and commented on an appropriate selection of materials. On selecting materials, many factors are taken into consideration according as the systems that are compatible with the intended usage. This article, therefore covers the criteria on allowable stress for materials, the evaluation method on fracture toughness of ductile materials, the weld strength of Austenite stainless steel (SUS 304, SUS 316) and the stress induced magnetization on these materials. The joint efficiencies of Aluminium alloy 5083 welded by filler metal 5183 are also included. As for thermal properties, average thermal conductivities of several kinds of Fiber Reinforced Plastics (FRP) utilized for support system are described and suggested on a combinated use of carbon FRP and glass FRP for high strengh structure with low heat input.