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To anneal glass, it is necessary to heat it to its annealing temperature, at which its viscosity, η, drops to 10 13 Poise (10 13 dyne-second/cm 2). [2] For most kinds of glass, this annealing temperature is in the range of 454–482 °C (849–900 °F) [ citation needed ] , and is the so-called stress -relief point or annealing point of the glass.
To prevent such material weaknesses, objects made from molten glass are annealed by gradual cooling in a lehr oven, from the annealing point, a temperature just below the solidification temperature of the glass. [1] In the process of annealing glass, the temperature is first equalised by holding or "soaking" the glass at the annealing point for ...
Soda–lime glass (for containers) [2] Borosilicate (low expansion, similar to Pyrex, Duran) Glass wool (for thermal insulation) Special optical glass (similar to Lead crystal) Fused silica Germania glass Germanium selenide glass Chemical composition, wt% 74 SiO 2, 13 Na 2 O, 10.5 CaO, 1.3 Al 2 O 3, 0.3 K 2 O, 0.2 SO 3, 0.2 MgO, 0.01 TiO 2, 0. ...
Deformation point (Glass deforms under its own weight on the μm-scale within a few hours.) 11–12.3 12–13.3 Glass transition temperature, T g: 12 13 Annealing point (Stress is relieved within several minutes.) 13.5 14.5 Strain point (Stress is relieved within several hours.)
The glass transition of a liquid to a solid-like state may occur with either cooling or compression. [10] The transition comprises a smooth increase in the viscosity of a material by as much as 17 orders of magnitude within a temperature range of 500 K without any pronounced change in material structure. [11]
Guitar slide made of borosilicate glass. Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10 −6 K −1 at 20 °C), making them more resistant to thermal shock than any other common glass.
Annealing is most often used to soften a metal for cold working, to improve machinability, or to enhance properties like electrical conductivity. In ferrous alloys, annealing is usually accomplished by heating the metal beyond the upper critical temperature and then cooling very slowly, resulting in the formation of pearlite. In both pure ...
The temperature range for process annealing ranges from 260 °C (500 °F) to 760 °C (1400 °F), depending on the alloy in question. This process is mainly suited for low-carbon steel. The material is heated up to a temperature just below the lower critical temperature of steel.