Patent GB-622645-A (GB)
Title: Improvements in methods of making spark gaps, apparatus therefor, and product thereof
IPC: H01T21/00
Filed: 1946-02-18
Abstract: 622,645. Spark-gaps. MALLORY & CO., Inc., P. R. Feb. 18, 1946, No. 5053. Convention date, March 10, 1945. [Class 39 (i)] [Also in Group XXVII] The invention relates to a method' of making spark gaps, to spark gaps produced by the method and to a machine for carrying out the method. The spark gaps are of the kind including a pair of metal end plates on which contacts are mounted and which are separated by a spacer tube of fusible dielectric material, and the method comprises fusing the ends of the tube to the end plates while the contacts are in parallel and concentric contacting relation and separating the contacts from each other a predetermined distance while the tube is at a temperature at which it is plastic and maintaining the parallelism and concentricity of the contacts. Fig. 5 shows the spark gap. It comprises two contact assemblies made up of end plates 10 welded to contact-carrying plates 16 to which contacts 20 are either welded or brazed. The two assemblies are held together by an insulating tube 22 such as a glass tube which is fixed to the plates 10 by fusing the insulating material to the plate. There are holds 21a in each plate 16. Holes 14 in the end plates 10 are covered by glass tubes 15, 60, having their ends sealed. A machine for fusing the assemblies to the tube 22 comprises a vertical frame carrying a head on which is mounted a chuck for holding one contact assembly and a horizontal platform on which is a second chuck for holding the other contact assembly. The head can be moved up and down in a slot in the frame and fixed in any desired position. Fig. 2 shows the two chucks 40, 46 with the assemblies fixed to them. The lower chuck includes a permanent magnet 45 which holds it to the platform 43 which is of magnetic material. The chucks each have three resilient jaws formed by slits 41, 47 and the jaws resiliently engage the assemblies. The upper chuck can be adjusted by a screw 37 in addition to the adjustment provided by the movable head. A glass tube 62 is sealed to the lower contact assembly and this tube serves for the supply of hydrogen during fusing. An indicator 59 is provided to indicate the distance apart of the contacts. When it is desired to carry out the fusing the upper chuck 40 is lowered by lowering the head until the contacts are approximately ¥ inch apart. By means of the screw 37 the chuck 40 is lowered until the contacts are <1>/32 inch apart. The lower chuck is adjusted so that the contacts are concentric. In this position the chuck 40 is compressed to allow the upper contact assembly to drop on to the lower and is then released. The upper contact is then moved away approximately 1 inch and the space tube 22 placed in position and the chuck 40 brought down until the upper contact just touches the top of the tube. The heat for sealing is provided by a heater coil and high-frequency heater. The hydrogen is turned on and the coil is positioned slightly below the lower contact. When the sealing temperature is reached the upper contact is moved downwards by means of the screw 37 to push the tube against the plate 10 to produce a seal. The hydrogen will have been ignited. The heater coil is then moved to a position slightly above the upper contact. As before when the sealing temperature is reached the upper contact assembly is forced down by the screw 37 to form a seal and then with the heat still on the upper contact is brought down until it touches the lower contact. The reading on the dial is noted, the heater is turned off and by rotating the screw the upper contact is moved away until the desired spacing between the contacts has been obtained as indicated by the dial. After the spark gap has cooled the upper glass tube 60 is sealed by a torch and the hydrogen turned off. The spark gap is then removed from the machine and the interior may be filled wth an inert gas before the tube 62 is cut off and its end sealed. The permanent magnet 45 is held to the chuck 46 by a ring of material of the alloy known under the Registered Trade Mark "Cerro Bend." The end plates 10 are either of chrome iron or of the alloy known under the Registered Trade Mark, " Kovar." U.S.A. Specification 2,354,786 is referred to.