annealing

annealing , process in which glass, metals, and other materials are treated to render them less brittle and more workable. Annealing consists of heating the material and then cooling it very slowly and uniformly; the time and temperatures required in the process are set according to the properties desired. Annealing increases ductility and lessens the possibility of a failure by relieving internal strains. The process, also called hot working, was known to the ancients.

annealing In optical manufacture, the process of allowing glass or ceramic to cool slowly at a controlled rate, to avoid stress patterns within the material. A large mirror blank, for example, is cast from molten material. If cooling is too rapid, temperature variations will arise and some areas will solidify more rapidly than others, creating internal stresses that can cause the mirror blank to shatter when it is being ground to shape. Annealing of a large telescope mirror can take several months.

annealing Slow heating and cooling of a metal, alloy or glass to relieve internal stresses and make up dislocations or vacancies introduced during mechanical shaping, such as rolling or extruding (ejection). Annealing increases the material's workability and durability. Tempering, on the other hand, is a process that involves rapid cooling.