- Annealing (glass)
Annealing is a process of slowly cooling
glassto relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a Lehr. [E. F. Collins (1921) Electrically heated glass annealing lehr. Journal of the American Ceramic Society 4 (5), 335–349. ] Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock. Annealing glass is critical to its durability. If glass is not annealed, it will retain many of the thermal stresses caused by quenching and significantly decrease the overall strength of the glass.
The glass is heated until the
temperaturereaches a stress-relief point, that is, the annealing temperature (also called annealing point) at a viscosity, η, of 1013 Poise= 1012 Pa·s, at which the glass is still too hard to deform, but is soft enough for the stresses to relax. The piece is then allowed to heat-soak until its temperature is even throughout. The time necessary for this step varies depending on the type of glass and its maximum thickness. The glass is then slowly cooled at a predetermined rate until its temperature is below the strain point (η = 1014.5 Poise). Following this, the temperature can safely be dropped to room temperatureat a rate limited by the heat capacity, thickness, thermal conductivity, and thermal expansion coefficientof the glass. After the annealing process the material can be cut to size, drilled or polished.
At the "annealing point" (η = 1013 Poise) stresses relax within several minutes, while at the "strain point" (η = 1014.5 Poise) stresses relax within several hours. [Werner Vogel: "Glass Chemistry"; Springer-Verlag Berlin and Heidelberg GmbH & Co. K; 2nd revised edition (November 1994), ISBN 3540575723] Stresses that are still present below the strain point are permanent.
Fabrication and testing (optical components)
* [http://etsyglass.com/blog/index.php/2007/04/22/annealing-for-fused-glass-and-other-fusing-fun/ Annealing for Fused Glass]
* [http://etsyglass.com/blog/index.php/2007/04/20/lampwork-and-annealing/ Lampwork and Annealing]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Annealing — may refer to: *Annealing (metallurgy), a heat treatment that alters the microstructure of a material causing changes in properties such as strength and hardness *Annealing (glass), heating a piece of glass to remove stress *Annealing (biology),… … Wikipedia
Annealing (metallurgy) — Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization … Wikipedia
Annealing temperature — may refer to: *Annealing (glass) *Polymerase chain reaction … Wikipedia
Glass production — Glass is common in everyday life, from glass windows to glass containers. The manufacture of glass for everyday purposes may involve complexity and automation. This article deals with the mass production of glass. Glass container productionGlass… … Wikipedia
Glass tiles — are pieces of glass formed into consistent shapes. Glass was used in mosaics as early as 2500 BC, but it took until the 3rd Century BC before innovative artisans in Greece, Persia and India created glass tiles.Whereas clay tiles are dated as… … Wikipedia
Annealing — An*neal ing, n. 1. The process used to render glass, iron, etc., less brittle, performed by allowing them to cool very gradually from a high heat. [1913 Webster] 2. The burning of metallic colors into glass, earthenware, etc. [1913 Webster] … The Collaborative International Dictionary of English
Glass transition — The liquid glass transition (or glass transition for short) is the reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle state into a molten or rubber like state … Wikipedia
annealing — Treatment of a metal, alloy, or other material by heating to a predetermined temperature, holding for a certain time, and then cooling to room temperature, done to improve ductility and reduce brittleness. Process annealing is carried out… … Universalium
Glass — This article is about the material. For other uses, see Glass (disambiguation). Moldavite, a natural glass formed by meteorite impact, from Besednice, Bohemia … Wikipedia
Glass electrode — A glass electrode is a type of ion selective electrode made of a doped glass membrane that is sensitive to a specific ion. It is an important part of the instrumentation for chemical analysis and physico chemical studies. In modern practice,… … Wikipedia