To perform excellent welding work, and to elevate the reliability of welds, it is essential to perform with selected operating conditions when the fundamental conditions such as the shape of materials to be welded, chemical composition, welding position, etc. have been decided, the working condition is to be set on the basis of the welding condition which serves as the standard.
Therefore, attempt was made to find such standard welding condition. Besides, in any of plastics for welding, the effect of air utilized as the welding gas is not a little under the high temperature at the time of welding, hence investigation was conducted so as to find a welding gas which will not adversely affect the welds.
The standard welding condition for hot jet welding method should provide for such item as the thickness of plate, pressure of welding gas, quantity of the welding gas, temperature of the welding gas, welding speed, welding rod to be used, shape of the groove, number of layers, motion of filler rod tip, etc. That is, by prescribing the standard working condition, the substantial standard will be given for the designing of welds, so that it is useful to promote the efficiency of the welding work and mechanical properties of welds. Furthermore, study was made on the problems of welding gas in connection with polyvinylchloride, low-and high-pressure polyethylenes which are in general use as plastics for weldidg.
Namely, in relation to the effect of the welding gas on the tensile strength of the weld produced in accordance with the standard welding conditions of respective plastics, and about the process of decomposition of respective plastics by high temperature welding gas, experiments and discussion were made.
As indicated on the basis of the thickness of plate, the standard welding condition for polyvinylchloride will be as tabulated in Table 1. In actual welding, it is desirable to set the working condition, referring to the standard welding condition in relation to the fundamental conditions of welding such as the welding material, type of welding process, object of welding, welding position, etc. On the other hand, there exists the welding gas most suitable for respective plastics, and by use of such gases, the strength of welds will be increased significantly. Particularly, inert gas with admixture of hydrogen is effective.
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