A lehr is a temperature-controlled kiln for annealing objects made of glass. Kilns are thermally insulated chambers or Ovens in which controlled temperature regimes are produced Annealing is a process of slowly cooling Glass to relieve internal stresses after it was formed Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many The name derives from the German verb lehr meaning to learn and is cognate with the English lere also meaning to learn or acquire knowledge of (something)[1]
Rapid cooling of molten glass generates an uneven temperature distribution in the body of the glass which results in mechanical stress sufficient to cause cracking before the object has reached ambient temperature, or to result in susceptibility to cracking in later use, often resulting from thermal shock. Stress is a measure of the average amount of Force exerted per unit Area. Thermal shock is the name given to cracking as a result of rapid temperature change To prevent this, objects manufactured from molten glass are annealed by cooling very gradually in a lehr from a temperature just below the solidification point of the glass.
In glass manufacture, a lehr is typically a long kiln with a temperature gradient from end to end, through which newly-made glass objects such as glasses or vases are transported on a conveyor belt. In Vector calculus, the gradient of a Scalar field is a Vector field which points in the direction of the greatest rate of increase of the scalar A belt conveyor consists of two or more Pulleys with a continuous loop of material - the conveyor belt - that rotates about them However, the same effect can be obtained in a small kiln by controlling the cooling rate with an electronic temperature controller.
References
- ^ Shorter Oxford English Dictionary, Oxford University Press
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