Patent GB-841658-A (GB)
Title: Electric glass working
IPC: C03B29/00
Filed: 1958-04-14
Abstract: 841,658. Arc heating apparatus. CORNING GLASS WORKS. April 14, 1958 [April 24, 1957], No. 11838/58. Class 39(3). [Also in Group XXIII] An electric glass working apparatus, e.g. for cutting or welding glass, comprises two or more arc runner electrodes arranged in a common plane in spaced relation alongside a workpiece to be heated and a magnet so arranged with respect to said electrodes that its magnetic lines of force have a component at right angles to the plane thereof. As shown, a platform 13 projects from a vertical column 12 on a base 11 and supports a hollow core magnet 15 which is surrounded by a tube 17 of highly refractory dielectric material having an inwardly extended flange 18 supporting arc runner electrodes 19 and 20 and an arc return conductor 21. A workpiece 25 is suspended within the magnet 15 from a chuck 26 attached to the lower end of a vertical shaft 27 supported from a side arm 28 projecting from the column 12. Electric power is applied to the magnet 15 and the electrodes 19 and 20 at a voltage high enough to cause an arc discharge across the gap 22, the shorter of two gaps 22 and 23 between the electrodes. The magnetic field bends the arc into a curve a, b c : the part a then moves under the influence of the field to the left along electrode 19, the part c moves to the right along electrode 20, and the part b remains anchored to the surface. The arc thus stretches and wraps itself tightly round the workpiece which is thereby heated. As the arc arrives at the electrode ends it bows outwardly towards the return conductor 21 as shown at d across the gap 23, and then splits into two parts e and f which carry current in the opposite directions indicated and continue such travel until they join one another at the gap 22, whereupon the heating cycle is repeated. When sufficiently heated the glass becomes conductive and by maintenance of a suitable potential the short arcs e and f may serve almost entirely as electrically conducting brushes carrying heating current into and out of the hot conducting glass. Uniform heating may be assured by rotation of the workpiece or by periodically reversing the direction of current flow to the electrodes or the polarity of the magnet. In a modification, Fig. 4, eight arc runner electrodes are provided, suitably supported brushes 42 and 43 being rotated about the electrodes to connect power successively to adjacent pairs thereof to heat segments of a path about the workpiece. Relays under the control of a distributer switch may be provided to connect selected electrodes to the power supply in sequence, Fig. 5 (not shown). Modifications suitable for heating large workpieces are described, Figs. 6 and 7 (not shown). The electrodes may be hollow and connected to a vacuum line, Fig. 8 (not shown). The arc may be started and maintained by superimposing high frequency pilot waves on the electrodes periodically, Fig. 9 (not shown). Fig. 10 shows an embodiment wherein a rectangular workpiece 100 is surrounded with arc runner electrodes 101 and 102 provided with magnetically operable arc travel stopping gates 105 to 108. Each gate passes through a bushing 103 in the arc return conductor 109 and is normally held in a retracted position by a spring 110 but can be closed bytheenergisation of an associated magnet coil 111. The gates may be operated at will to stop the arc travel or be disabled to permit resumption of the arc travel, and thus provide means for an "arc travel and dwell" type of operation. Suitable circuits for providing constant current power supplies, Figs. 11 to 13 (not shown), are also described. Specification 645,521 is referred to.