All About Cryogenic Stress Relief
Cryogenics is the study of very low temperatures and how materials react at those temperatures. The field of cryogenics studies effects at temperatures below 180 C. This is a logical dividing line since the normal boiling points of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen, and air) lie below -180 C while the Freon refrigerants have boiling points above -180 C.
History
The field of cryogenics took a huge leap forward, when early in 1945 scientists discovered that metals frozen to low temperatures showed more resistance to long term wear. Based on the theory of cryogenic hardening and stress relief, the industry was founded by Ed Busch in 1966. Ed founded a company in Detroit called CryoTech.
Cryogenic Processing Stress Relief
Cryogenic stress relief is a great way to relieve stress from parts before, during, and after machining. It is a very thorough stress relief process, provided the warm up process is very slow and deliberate. By being in too much of a hurry and shortening the process, you end up re-introducing residual stress back in to the parts.
This process works well for standard machined metal parts, castings, forging, plastic, or composite materials. It is non-destructive to the carbon content of steel and leaves the surface clean and free of oxides, with no discoloration, as effected by heat stress relief. It essentially deadens the stress in machined or welded components and makes a world of difference in aluminum parts requiring intricate machining steps.
Aluminum and non-ferrous metals using cryogenic stress relief gain better machineability after processing, which is a real aid in tight tolerance work. They get stronger and tougher from the densification of the molecular structure, but the best part is that they are as close to being stress dead as possible.
Molecular Structure
The big question in practice about cryogenic stress relief is what can be done to relieve the stresses before machining? Through advances made in cryogenics, it has been discovered, researched, and proven that when parts are treated in a cryogenic chamber at temperatures of -300 F at a controlled time/temperature cycle, all internal stresses are relieved, thanks to the alignment of the molecular structure that had been distorted during the process. Now, when these cryogenic stress-relieved parts are machined, there will be no distortion on the machined surface. Any distortion that occurs would be caused by improper machining, dull cutting tools, or insufficient material removed by the first cut.
Cryogenics is an exiting and bold new science that has much future promise.
