GB1508820A - Electrical melting apparatus for glass - Google Patents

Abstract

1508820 Resistance heating element OWENSCORNING FIBERGLAS CORP 27 Aug 1975 35379/75 Heading H5H In electrical melting apparatus e.g. glass melting apparatus having a plurality of elongate parallel resistance heating elements 120 extending across the interior of a melting receptacle 122 provided with a discharge outlet 124 at its bottom, each elongate element 120 which has a width W (Fig. 5) greater than its thickness t (Fig. 6) is oriented with its width dimension W vertical and is provided with short end connector portions 146 connected by electrically parallel vertically spaced longer central portions 148. This parallel arrangement ensures that should the upper central potion 148 become cooler than the lower central portion 148, the resistance of the upper central portion 148 will decrease so that more current will flow along Path I than Path II and the temperature of the upper central portion 148 will increase. Similar compensation will occur if the lower central portion 148 becomes cooler than the upper central portion. As shown each element 120 is made of platinum or a platinum alloy containing rhodium. The elements 120 are made tubular and are reinforced in the elliptical central region 144 by tubular refractory cores 158 of good heat conductivity material e.g. aluminium oxide and in the connector portions 146 by solid refractory heat conducting aluminium oxide. The aluminium oxide cores assist in equalizing the heat distribution and consequently heat generation. The end connectors 146 are curved tubes, as shown, with additional metal strips 152, 154 secured to the top and bottom of the portions 146a and 146b of the connectors 146. The improved conductive path provided by strips 152, 154 assists in the uniform division of current to the upper and lower paths I and II. The end connectors 146 of the elements 120 are clamped between water-cooled bus bars 160, 162 extending lengthwise of the melting receptacle 120. The bus bars 160, 162 are connected to stepdown transformers. A control circuit senses voltage variations caused by changes in resistance of the heating element and modifies the supply current to restore the temperature to the elements 120. An alternative form of element (Figs. 10 and 11, not shown) comprises a straight tube to which is attached a parallel tube by two inclined portions. The ends of the straight tube form the connectors. Instead of the elements 120 being arranged with dimension W vertical as in Fig. 3, they may be slightly inclined, the inclinations being in opposite directions relative to the central longitudinal plane of the receptacle. The angle of inclination to the vertical decreases from the central plane. The molten glass emerging through the outlet 124 in filaments 20 is further heated to control its viscosity by the platinum walls 272, 274, 270 lining the outlet 124 which are supplied from a transformer via terminals 286.