Patent GB-568930-A (GB)
Title: Improvements in or relating to methods of and apparatus for perforating sheet material
IPC: B26F1/28
Filed: 1943-07-23
Abstract: 568,930. Spark-gap electric discharge apparatus. WILSEY, I. H.. July 23, 1943, No. 12026. [Class 39 (i)] [Also in Group VIII] Sheet material, such as paper, leather, &c., is perforated by passing electrical arc discharges simultaneously through the material at a number of points distributed over an area of the sheet extending both longitudinally and transversely of the sheet while the sheet is moved continuously in a direction longitudinally thereof. The invention is especially applicable for perforations with a large number of very small apertures paper which is to be used for making bags for packing flour. As shown, the machine comprises three sets of superposed insulated rollers 11, 12, 13, Fig. 5, 11a, 12a, 13a; and 11b, 12b, 13b, the outer sets being indicated diagrammatically in Fig. 15. The rollers 11 are plain metal rollers mounted on Insulating sleeves, and the rollers 12, 13 are arranged with variable gaps g<1>, g<2>, Fig. 5, between them and the centre roll 11, and, as shown in Fig. 6, are constructed with zig-zag conducting strips 47 insulatedly mounted and extending around the rollers 12. 13 and being supplied with current from conductors connected to spring-contacts 67a, 68a. As shown in Figs. 1 and 15, there are nine sets of zig-zag conductors 47 ... 47h ; 48 ... 48h; 49 ... 49h on the rollers 12, 12a. 12b, and nine sets 50 ... 50h; 51 ... 51h; 52 ... 52h on the rollers 13, 13a, 13b, and as a web of material passes up over the top driven roller 11 and through the rollers 12 ... 13, a series of sparks is passed across the gaps g<1>, g<2> at the rate of two discharges for each conductor 47, 48, &c. for each complete electrical cycle, so that the number of discharges per second may be as high as 270,000 per sec. with a rated output of 2500 cycles at 110 volts. 'As shown in Fig. 1, the conductors 47, 48, 49 are offset laterally with respect to one another and a pattern of perforations is produced. The electric supply arrangement is such that the sparking can be effected from selective sets of conductors. As shown in Fig. 15, the sparks are produced only from the three sets of conductors indicated in thick lines, viz. 47f, 47g, 47h, and so on. In a modification, all the conductors on the middle set of conductors on rollers 12a, 13a are cut out for operations on webs of narrow width. The electric supply system is shown in Fig. 19 and comprises an electric generator 81 driven by an electric motor 84, the armature 85 of which coacts with a separately excited field 86 in series with a rheostat 87 which governs the motor speed and hence the voltage of the generator 81. This generator is connected to the conductors 67a, 68a by means of nine step-up transformers 90 which are provided with variable condensers 109 in parallel with the primary coils 91 so as to enable the capacitive reaction of the condenser to be varied and thus allow the phase relation of the voltage and current to be changed at will. The circuit of the generator 81 is controlled by a switch 103 operated by a relay 102 which is energized by the closing of a hand-switch 100 and a switch 101 which is controlled by an adjustable centrifugal switch so'as to prevent energizing of the sparking circuits until the roller 12 is driven at a certain speed, and thus prevent charring of the material. To indicate the state of the electric circuits, a voltmeter 107 is provided, and also a neon-lamp 110 acts as a current indicator. In a modified form of transformer, two similar transformers are arranged in parallel, and the currents may be supplied' from both transformers, or only from one. Specification 558,834 is referred to.