GB498204A - Improvements in or relating to forehearths for molten glass - Google Patents

Abstract

498,204. Glass manufacture. BRITISH HARTFORD - FAIRMONT SYNDICATE, Ltd. Oct. 20, 1937, No. 28616. Convention date, April 1. [Class 56] Relates to a forehearth for conveying molten glass from a tank furnace to a feeding or gathering device and in which the temperature of the middle portion of the flowing glass is controlled by means permitting radiation of the heat through the top wall of the cooling-section, of the forehearth. According to the invention, air is blown along the underside of the top wall of the cooling-section to increase the dissipation of heat through the top wall in order to obtain any desired temperature of the glass at the delivering end of the forehearth. The forehearth comprises a rear cooling- section 10, Fig. 1, and a forward heating or homogenizing section 11, and blocks 26, 27 may be used to separate the space above the glass in the section 10 from that in the section 11 and in the tank furnace 18, respectively. The sections 10, 11 are suitably heated,for example by burners disposed in tunnels 30, Figs. 1 and 3, and are supplied with a predetermined mixture of gas and air as described in Specification 28617/37. The roof or cover over the section 10 comprises blocks arranged to constitute a flat crown which is provided with vertical vents or exhaust ports 46. These vents extend into two exhaust manifolds 47, 48 which are provided with discharge outlets 52, 53, respectively, through which the products of combustion escape. These outlets are controlled by dampers 54 and 55 which can be opened to any desired degree by means of a lever 57 raised or lowered by a screwed rod 60. The cover is also provided with longitudinal intake manifolds 67, Fig. 3, each of which is supplied with air under pressure from a branch pipe 68 attached to a supply pipe 69. The volume of air blown through the pipe 69 is controlled by an adjustable damper 72 and also by a slide valve 73 which is connected to the lever 57, so that opening of the discharge outiets 52, 53 is accompanied by an increased flow of air into the manifolds 67, and vice versa. Each manifold 67 communicates through passages 75 with shallow horizontal cooling-ports 76 situated close to the underside of the crown of the section 10. Air from the ports 76 is blown across the crown to the vents 46 and cools the crown without changing combustion conditions in the tunnels 30 and without impinging on the glass. Adjustment of the valves 73 and of the levers 57, together with adjustment of the heating- devices in the tunnels 30, enables any desired temperature gradient to be obtained in the length of the glass flowing through the section 10. In a modification, additional cooling air from the pipes 68 is blown into annular slots at the upper ends of the flues 52, 53 to assist the escape of the cooling air from the ports 76 through the flues.