| Cryogenics is the study of how materials react at | | | | clean and free of oxides. Unlike heat stress relief, there |
| very low temperatures - usually bellow -180 C. This | | | | is no discoloration. The process essentially deadens |
| figure was chosen as a dividing line since the boiling | | | | the stress in welded or machined components, and |
| points of 'permanent gases' such as helium, hydrogen, | | | | can make a big difference to the durability of parts |
| neon, nitrogen and oxygen, are all below -180 C, while | | | | requiring intricate machine processing. |
| the boiling points of the Freon refrigerants are above | | | | Aluminum can benefit from cryogenic stress relief, as |
| -180 C. | | | | can non-ferrous metals. They become stronger and |
| The History of Cryogenic Stress Relief | | | | tougher as a result of the densification of their |
| One of the most important breakthroughs in the field | | | | molecular structure, making them as close to |
| of cryogenics occurred in 1945, when scientists | | | | stress-dead as possible. |
| discovered that materials frozen to very low | | | | Changes in Molecular Structure |
| temperatures showed more resistance to long term | | | | One of the main practical questions is what can be |
| wear. This discovery lead to the founding of the | | | | done to relieve the stresses before machining? |
| CryoTech company, who specialized in cryogenic | | | | Advances in cryogenics have revealed that when |
| processing by Ed Bush, in 1966. | | | | parts are treated to temperatures of around -300 F, at |
| Cryogenic Processing and Stress Relief | | | | a controlled time / temperature cycle, all internal |
| Cryogenic stress relief is very effective in relieving | | | | stresses are revealed. This is because of the |
| stress from parts before, during, and after machining. | | | | alignment of the molecular structure that was distorted |
| This stress relief process is very thorough, assuming | | | | during the process. When parts that have been |
| that the warm up process is very slow and deliberate. | | | | through cryogenic stress relief are machined, there will |
| If you rush the process, you end up re-introducing | | | | be no distortion on the machined surface. If there is |
| residual stress back in to the parts. | | | | any distortion, it will be due to improper machining, or |
| Metal parts, castings, forging, plastica, and composite | | | | dull tools. |
| materials all respond well to cryogenic processing. It is | | | | Cryogenics is still a relatively new science, and it is one |
| a non-destructive process, which does not affect the | | | | that has a bright and promising future. |
| carbon content of steel, and leaves any surfaces | | | | |