Patent GB-835202-A (GB)
Title: Improvements relating to methods of and furnaces for melting and refining glass electrically
Inventor: GELL PHILIP ANTHONY MAUNSELL
IPC: C03B5/027
Filed: 1955-02-22
Abstract: 835,202. Electric glass furnaces. ELEMELT Ltd. April 12, 1956 [Feb. 22, 1955], No. 5241/55. Class 39(3) [Also in Group XXXV] In a furnace in which glass is melted or refined by passing A.C. therethrough and comprising a furnace chamber 10 connected to a further chamber 11 by a duct 12 through which the molten glass and an auxiliary A.C. are passed, the auxiliary A.C. is regulated to provide the required difference in temperature between the glass in the furnace chamber 10 in the region of the opening into the duct 12 and the glass in the further chamber 11. This regulation is effected by measuring or detecting the magnitudes of the respective total currents in the glass in the furnace chamber at opposite sides 12<SP>1</SP>, 12<SP>2</SP> of the opening, and by partly or wholly correcting any inequality by varying an electrical quantity e.g. the voltage in either or both the main and auxiliary A.C. supply. 207 The main A.C. passes horizontally through the glass in the furnace chamber between opposed electrodes 13, 14 and the outlet duct is arranged transversely to the direction of current flow. The chamber 11 or the duct 12 contains one or more auxiliary electrodes 15. The phase angle between the voltage applied to the auxiliary electrode with respect to either of the main electrodes may be varied to ensure equal magnitudes of current at the sides 12<SP>1</SP>, 12<SP>2</SP> of the duct opening to prevent glass from cooling in the duct on one side and thereby rendering this glass less conductive and flow in the duct uneven. Current is fed to the main electrodes 13, 14 from a single phase transformer T1 through leads 21, 22 carrying current transformers CT1, CT2 the outputs of which are connected to a differential ammeter A1. The auxiliary electrodes 15 are connected to one pole 23 of a further transformer T2, the other pole 24 of which is connected to a slider 25 of an impedance e.g. inductance L1 connected across the leads 21, 22 in parallel with the main electrodes 13, 14. The transformer T2 is energized from a further phase of an A.C. supply, the voltage of which is in quadrature with that supplied to the transformer T1. The central tapping point of the inductance L1 is the electrical centre between the electrodes 13, 14, and when the ammeter A1 indicates asymmetrical heating, the slider 25 is adjusted along tapping points 27 of the inductance L1 to correct this either manually or automatically. The latter is effected by apparatus shown in Fig. 4, in which the current transformers CT1, CT2 are connected to a comparison circuit 55 containing two transformers having the same step up ratio connected respectively to the transformers CT1, CT2 and having their secondary windings connected to rectifying circuits connected to feed the rectified voltages in opposition across a resistor. Opposite ends of this resistor are connected by lines 56, 57 to a relay 58 having an armature movable in opposite directions from a central or unoperated condition according as to whether the line 56 is positive or negative with respect to the line 57. The relay 58 has three contacts to which lines 59, 60, 61 are connected. Lines 59, 61 are connected to a reversible regulator motor 62 connected by a line 63 to one of the mains terminals 64. The other terminal 64 is connected to the line 60. The motor is connected mechanically at 65 to the slider 25, which is thus moved to restore current in lines 21, 22 towards equality. In order to prevent hunting, a time delay switch may be connected in series with lines 56, 57 so that it is opened when the slider moves between successive contacts 27. Instead of correcting inequalities in the magnitudes of current flowing to the main electrodes a phase shifting network for varying the phase applied to the auxiliary electrode may be used. The tapped inductance L1 may thus be omitted, and the terminal 26 of the transformer T2 may be supplied through a phase shifting transformer. When borosilicate glass is heated, the auxiliary current is controlled to provide a glass in the second chamber of a viscosity of 10<SP>3</SP> poises. Specifications 835,201 and 853,205 are referred to.