IIW History 1948-1958

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3. The necessity.. because of the development of rectifier transformer welding set s, of asking the I EC (International E lectro-Technical Commission) that a method of international specific ation for elements of dry-cell rectifiers should be drafted. A long investigation was necessitatecl _by the absence, in the various specifi– cations, of a universal basis of judgement making it possible to define and eva– luate the suitability for welding of generators. T est s carried out in France and S\veden, using practically non-inductive circuits, gave rise to the idea of an in– Lrinsic striking voltage for a given type of electrode. Based on this idea, a method was proposed in document II-36-54 to evaluate the suitability for welding of generators, working on the basis of comparisons and using reference electrodes. F urthermore, on the initiative of the Italian Institute of \i\Telding, Professor A. CARRER directed an experimental investigation, the purpose of which was to compare the judgement given by several well-qualified welders on the behaviour during welding, using basic electrodes, of various generators or welding circuits ; measurements were carried out, principally by means of oscillograms, on voltage, current and power. Several reports have been prepared (r) and an analysis of the result s obtained bas revealed a close correlation between the subjective evaluation of the welders and the value of a coefficient r proposed by Professor CARRER and defined as follows : vV W = average power in the arc when stable conditions ha\ e been established; w = the lowest average power in the arc during any r/ roo second period measured during the r / ro second following the break of the short circuit caused by the transfer of a globule of the metal in the arc. r is approximately one, where the suitability for welding is good. In addition, other criteria were t aken into account : - the open circuit voltage, the straight line minima dy namic characteristics defined by Ch. J ENNINGS (z), the internal resistance R defined by LAXGKAU, the number of volt-milliseconds developed by the generator after break– ing the arc or index V ro, the product of R. V ro. The application of the statistical method of correlation (the SPE. .\.RMAN coefficient) has shown : that there is no close relationship between the suitability for welding and the no-load volt age of generators; that there is a close relationship between the judgement of the welders and the value of the product R. V ro, which increases in accordance with the suitability of the generators as judged by the welders. These investigations, in connexion with which experimental work is still being carried out and various developments are taking place, should make it possible, account being taken of the methods of practical application, finally to propose the most suitable criterion. - In t he meantime, the vl'Ork of Sub-Committee 4 (Arc v\ elding Equipment) 1' =

{r) See in particular documents II-1-56; II-B-1-57; II-B-2-57; II-B-7-57; II-B-23-57. (2) See Welding J ou.ma.I, February 1951, « Dynamic charact eristics of D.C. vVelding :Jiachines ».