Patent GB-800033-A (GB)
Title: Improvements in and relating to apparatus for cutting electrically conductive materials
Inventor: RUDORFF DAGOBERT WILLIAM ALFRE
IPC: B23H1/02
Filed: 1955-02-18
Abstract: 800,033. Cutting by spark discharges. SPARCATRON, Ltd. May 17, 1956 [Feb. 18, 1955; March 1, 1955: March 29, 1955], Nos. 4918/55, 6021/55 and 9145/55. Class 83 (4). An electric spark erosion apparatus has an inductance 2 and a saturable core reactor 3a connected in series across an alternatting current supply 1, the inducance 2 being connected in the discharge circuit including the electrode 4 and workpiece 5. A capacitor 10 may be included in the discharge circuit and a direct current supply may be connected across this capacitor, Fig. 14 (not shown); alternatively the capacitor may be in shunt with the inductance, Fig. 4 (not shown), or a network of inductors and capacitors may be provided therein, Figs. 9, 10 (not shown). The reactor 3a has a biasing winding 6 connected through a variable resistor 7 and choke 8 with a direct current source 9. The biasing winding 6 may be omitted, Fig. 1 (not shown), and the biasing voltage applied directly across the reactor 3a, Fig. 12 (not shown), with a blocking condenser provided on each side of the reactor. A capacitor or a rectifier may be included in series with the reactor and inductor, Figs. 5, 6 (not shown). A cored inductance may be used or an auto-transformer or a transformer may be used instead of the inductance 2, Figs. 7, 8 (not shown). In another embodiment, Fig. 11, the alternating current is supplied to the centre tap of an inductor 2a and parallel circuits each containing a saturable reactor 3a are provided. In another embodiment, Fig. 13 (not shown), the reactor 3a has two biasing windings through which the current flows in opposite directions for cancelling out the inductive effect or the biasing circuit of the current in the main circuit ; one of the biasing windings may be supplied with direct current obtained from a full-wave rectifier in series with the main winding of the reactor, Fig. 18 (not shown), or from a full-wave rectifier connected across the primary of a transformer used as the inductor 2, Fig. 19 (not shown). In a further embodiment, Fig. 15, a timed pilot sparking circuit supplies current through a transformer 25 whose primary is in series with an alternating current source 22 and in shunt with a rotary spark gap 26 ; an auxiliary spark gap 27 is provided. The rotary spark gap may be rotated in synchronism with the frequency of the alternating source 1, Fig. 16 (not shown). In another embodiment, Fig. 17 (not shown), three-phase supply is used. In a further embodiment shown in the Figure accompanying the third Provisional Specification the alternating current supply at a transformer 44, used as a cored inductor, is derived from a direct current source 43 by means of a Colpitts oscillator circuit including a triode 41 whose tank circuit includes the primary 44a of the transformer. Variable condensers 45, 46 are used for varying the frequency. Alternatively a Hartley oscillator may be used. Means may be provided for varying the values of the inductances and capacitors of the components used in the various embodiments.