RADIATIVE HEAT-TRANSFER IN GLASS MANUFACTURE - ONE-DIMENSIONAL AND 2-DIMENSIONAL PROBLEMS

The one-dimensional radiation-conduction model, originally developed b y Gardon, has been used to calculate: firstly, the rate of reheat of g lass surfaces after forming in metal moulds, and secondly, the rate of temperature changes in glass in a forehearth following a step change in roof temperature. The extent of reheat at short times (< 2 s) is no t greatly dependent on the absorption properties of the glass but is m uch more so when the reheat time is long e.g. in hand working and in f orming large articles. The forehearth temperature changes calculated b y the ''correct'' radiation-conduction method are more rapid than thos e calculated by the ''effective conductivity'' method. A two-dimension al radiation-conduction model has been developed and used to calculate the rates of temperature change in glass in a forehearth. These calcu lations also show that the ''effective conductivity'' method is inadeq uate, especially when applied to time-dependent problems.