Patent GB-892182-A (GB)
Title: Improvements in or relating to an electric furnace for melting glass and like materials
IPC: C03B5/44
Filed: 1959-05-08
Abstract: 892,182. Glass-melting furnaces. VERRERIES POCHET ET DU COURVAL. May 8, 1959 [May 13, 1958], No. 15821/59. Class 51 (2). [Also in Group XT] A high-temperature glass &c. melting furnace comprises a chassis A, an upper section B of bi-trapezoidal shape formed of bricks 13 resiliently held by spring-pressed thrust members 16 mounted on frame girder 5 with a roof of bricks 22, a middle section C of truncated conical or pyramidal shape defined by water-cooled tubes 23, 24, a hearth D on a lower removable frame 12, and electrodes E<SP>1</SP>- E<SP>7</SP> made of graphite, tungsten or molybdenum. The hearth D comprises side bricks 37 resiliently held by spring-pressed thrust members 40 mounted on frame 12, and refractory sole plates 41 carried by water-cooled copper plates 42 and formed with pouring-tubes 46. The bricks 13, 22, 37 and 41 are made of mullite prepared by electrically melting a mixture of bauxite and kaolin. The tubes 23, 24 are respectively connected by end portions 25, 26 and 27, 28 and by fabric-reinforced rubber pipes 30, 31, 32 and 33 to a supply header 34 and a discharge header 35. During operation of the furnace, a solidified coating of glass &c. forms on the tubes 23, 24. If necessary, a very thin coating 36 of material relatively impervious to infra-red rays, e.g. a glass or alumina with a binder of kaolin, is first formed on the tubes. Main electrodes E<SP>1</SP>, E<SP>2</SP> are horizontally and fixedly mounted in water-cooled carriers in end bricks 13, and main electrodes E<SP>3</SP>, E<SP>4</SP> are similarly mounted in the hearth D. A vertical starting electrode E<SP>5</SP> comprises a rod 58 in a watercooled carrier 60 suspended from arms 63 fixed to insulating plates 64, 66 disposed on rods or tubes 67 slidable vertically in sleeves 68 carried by the chassis A. Auxiliary electrodes E<SP>6</SP> and E<SP>7</SP> are each mounted on rods 71 slidably engaging insulating plates 73, 74 fixed to a metal cradle 75 pivotally mounted at 76 to brackets 77 on the chassis. In a modification, Figs. 9 and 10 (not shown), the furnace is substantially triangular in plan view with upper and lower electrodes at each corner. The furnace is started up by charging with raw materials through a shoot 47, melting a small pool in the middle by a propane-oxygen burner, and inserting therein electrodes E<SP>6</SP>, E<SP>7</SP>. These are gradually moved apart as melting takes place, until they strike electrodes E<SP>1</SP>, E<SP>2</SP> which are then switched in, electrodes E<SP>6</SP> and E<SP>7</SP> then being withdrawn. Before melting is complete, electrode E<SP>5</SP> is inserted and roof bricks 22 are positioned leaving a charging opening, electrodes E<SP>3</SP>, E<SP>4</SP> and E<SP>5</SP> being kept at the same voltage. Electrode E<SP>6</SP> is finally withdrawn, after which electrodes E<SP>1</SP> and E<SP>3</SP> melt the incoming material and electrodes E<SP>3</SP> and E<SP>4</SP> refine it. In order to tap the furnace, one or two pouring-tubes are heated by a propane-oxygen lance to soften the glass which drips on to tungsten rods 78 establishing a current flow with electrodes E<SP>3</SP> and E<SP>4</SP> to maintain fluidity of the issuing glass.