Patent GB-744893-A (GB)
Title: Improvements in or relating to the manufacture of electrical capacitors
IPC: H01G13/06
Filed: 1951-05-02
Abstract: 744,893. Capacitors. DUBILIER, W. April 30, 1952 [May 2, 1951], No. 10317/51. Class 37. [Also in Group XXII] An electrical capacitor is made by passing a strip of metallized paper 12, Fig. 1, successively over the peripheries of a plurality of electric branding wheels 10a, 10b, each of which acts electrically to burn away or evaporate a portion of the metal coating along a zig-zag or sinuous line of progressively increasing pitch, the individual wheels being caused to act sequentially on different parts of the length of the strip, and then winding the strip on to a mandrel. Successive portions of the metal coating on opposite sides of the line lie in radial alignment in the finished capacitor. The peripheries of the wheels 10a, 10b are provided with raised portions 26a, 26b, shown developed into a plane in Fig. 2 and which correspond with the line to be burned in the metal coating. The strip may be driven by passing it between frictional rollers or by driving a take-up roller 14 by an electric motor and its movement may be assisted by the branding wheels which are coupled together by a chain, gearing, or the like to ensure that they rotate in synchronism. Rollers 21a, 21b, 21c and 21d hold the strip in close contact with rollers 15a, 15b, 15c and 15d which are connected to earth on the frame of the machine while the wheels 10a, 10b are mounted in insulating material and connected to a hightension source 16, such as a D.C. generator or rectified power supply, through a resistance 17 and a capacitor 18. In order that the patterns corresponding to the wheels 10a, 10b will be produced in succession on the strip, masks 23a, 23b are provided each of which passes over a guide roller in the form of an endless loop having a length equal to twice the periphery of the wheel and a slot equal to its half length so that each wheel operates only on alternate revolutions. Alternatively, a single mask may be used for both wheels. Each mask may be made as shown in Fig. 8 with two perforated bands meshing with pegs on the branding wheel and connected by a strip 58 of stiff material to which is attached the masking material 60, such as paper or plastic. Three branding wheels may be employed with masks each equal in length to three times the periphery of a single wheel. If more than three wheels are employed the masks can be restricted to double the periphery of a single wheel by choosing an even number of wheels and providing synchronous, rotary switch means to connect the wheels to the electric supply at appropriate intervals of time. Alternatively, the masks may be omitted and the branding wheels 20a, 20b and 20c, Fig. 7, connected in turn to the high-tension source by a rotary arm 35 which co-operates with three conducting sectors 42, 43, 44 each connected to one of the branding wheels. The arm is rotated by reduction gearing from the branding wheels so that each wheel is operative for one complete revolution in every three. To prevent shortcircuits between the electrodes due to lack of synchronism in the operation of the branding wheels, each wheel may have a portion A, Fig. 2, to burn away the end of each pattern or, alternatively, this may be done by a roller 50, Fig. 7, which is operated by a second synchronous switch 45 to burn away a strip (not shown) thus severing some of the electrodes so that the capacitance between them is lost. Specification 744,969 is referred to.