2024/08/28 by Hierl, Gerd, Wartenberg, Erwin W.
#660
paper · doi:10.34657/14179
The coefficient of heat transfer, h, is the process parameter of greatest influence on the degree of temper, when glass type and thickness are given. High values of h are achieved by quenching with liquids. However, maximum h can only be sustained temporarily since h depends on the temperature of the solid surface, Ts. Α numerical difference approximation was developed that permits computation of temperature fields and resulting temper stresses for quenching with temperature-dependent heat transfer coefficient. Calculations using systematical variations of h = f(Ts) show that temper stresses do not only depend on maximum height but also on maximum position. Therefore, the h-T characteristic of any quenching liquid chosen may not be optimal. The polyliquid process provides a simple method for adjusting h = f(Ts) by applying mixtures of a high-boiling carrier with low-boiling liquids. The effect of concentration and kind of the latter is demonstrated for 2 polyliquid model systems. Calculated temper stresses based on measured values of h=f(Ts) agree satisfactorily with measured temper stresses. Thus, measurement of h=f(Ts) is a suitable means for investigating the influence of polyliquid parameters on toughening performance. This is considerably less laborious than preparing, quenching, and testing a meaningful number of glass samples. Experimental control of an optimization carried out accordingly is demonstrated for maximum bending strength. Use of a polyliquid instead of a pure carrier enables a marked surplus in strength, particularly in case of severe surface abrasion.