The process of toughening of borosilicate tempered sight glass

The process of toughening of borosilicate tempered sight glass
Tempered sight glass is the sight glass heated to the softening temperature (then in viscous flow state), we call this temperature range of tempering temperature range (620 C and 640 C), heat preservation time, and then quenched and the simple description of formation process of temperature change in tempered sight glass heating and quench process and should be force.

A. starts the heating phase:
Enter the sight glass tempering furnace heated by room temperature, because the sight glass is a poor conductor of heat, so the inner outer layer of high temperature, low temperature, the outer layer starts to expand, so the inner unexpanded, the outer surface of the inner expansion was inhibited the temporary compressive stress to tensile stress, the center layer, due to the compression of sight glass the degree is high, so although the rapid heating, the sight glass is not broken.
Note: from here we can know that sight glass enters the furnace. Due to the temperature difference between the inside and outside of the sight glass, the stress inside and outside the sight glass is caused. Therefore, the thick sight glass should be heated slowly, and the temperature will be a little lower. Otherwise, the sight glass will burst in the furnace due to the temperature difference between inside and outside.
B. continued heating phase:
Sight glass continues to be heated, the internal and external temperature difference between the inner and outer layers of the sight glass and other inner and outer layers reach the equivalent stress in the sight glass plate when the temperature is tempered.
C. begins the sudden cold stage (1.5 to 2 seconds before the start of the blow)
The sight glass sheet is blown into the wind gate by the tempering furnace. The surface layer temperature drops below the center temperature, the surface starts to shrink, and the central layer does not shrink, so the shrinkage of the surface layer is restrained by the central layer, so that the surface layer is subjected to temporary tensile stress, and the central layer forms compressive stress.
D. continues the sudden cold stage:
The sight glass inner layer further quenched sight glass surface hardened (the temperature has dropped to below 500 DEG C), then began to stop shrinking, inner cooling, shrinkage, surface layer and hardening of the inner layer inhibited the contraction, which results in the surface layer of compressive stress, and the formation of Zhang Yingli in the inner layer.
E. continues to cool (within 12 seconds)
The sight glass inner layer temperature is further reduced, the inner sight glass at this time reduced to 500 DEG, systolic acceleration, at this stage the outer layer of compressive stress, tensile stress of inner layer has been formed, but also the center layer is soft, not completely out of the viscous flow state, so it is not super final stress state.
F. steel completion (within 20 seconds)
At this stage, the inner and outer layers of sight glass are completely tempered, the temperature difference between the inner and outer layers is reduced, and the super terminal stress of tempered sight glass is formed, that is, the external surface is compressive stress, and the inner layer is Zhang Yingli.
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