IIW History 1948-1958

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B. Specification of Resistance Welding Equipment. This subject was without doubt one of those which it was necessary to tackle quickly , particularly as regards the definition of the power of a welding machine. Manufacturers in different countries had adopted different definitions : some of them are based on the maximum short circuit power, others on the maximum power under ·welding conditions, others again on the equivalent thermal power, but for different conventional services of which the duty cycles varied from 20 to roo% . Users who had a clearly defined problem to solve and who consulted several manufacturers therefore received offers of machines, the power indicated for which did not appear to have any relationship one with another, nor was it possible to make any comparison between the various machines offered. It was therefore absolutely necessary to t ackle this problem in a fundamental way and to enunciate simple rules which could be followed by everybody. In 1950 Commission III took up the question and put forward suggestions for characterizing apparatus from the electrical point of view by two values : the so called nominal power, being the maximum power absorbed at the highest setting, the electrodes being short-circuited and the machine adjusted to have the minimum secondary impedence, the conventional power being the apparent power that the machine can absorb for a so% duty cycle (the duration of the cycle being one minute) without exceeding the temperature rises permitted by the regulations of the International E lectrotechnical Commission. The fi rst of these values enabled the user to know the upper limit of the power to be provided for the connection of the machine, which was indispensable to him in order to provide for its installation. The second value enabled him to estimate the size of the transformer for the machine and the possibilities for its use. Furthermore, and also with a view to informing the user, the Commission put forward proposals regarding the characteristics which should be shown on the name plates of the machines. It was this material which, transmitted to the ISO via Commission VII (Standardisation), served as a basis for the work of Sub-Committee I SO/TC 44/SC 6 (vVelding - Resistance Welding Equipment). This work, carried out in very close liaison with Commission III of the IIVV, culminated in December, 1957 in the presentation, at the plenary meeting of ISO/TC 44, of the document I SO/TC 44 (Secretariat ro9) 161 F : Draft I SO proposals for rati n g of resistance weld-£ng eq·m:pment . This document was approved in principle by the plenary meeting of the Committee. In the near future it will constitute an I SO recommendation giving the definition of the power of machines, the temperature rise limits permitted, the methods of testing and measurement and the indications to be included on the nameplates. In this draft will be found the two ideas proposed by Com– mission III of the II\V, which have become l), the maximimi short cfrcit1:t power, and 2), the conventional power at a ditty cy cle of 50% and these have been defined by an indication of the conditions under which they should be determined. In parallel with this fundamental wo rk, Commission III has under prepar– ation documents concerning acceptance tests for resistance welding mach-ines. As a first st ep, spot welding machines have been studied from this point of view and the Swedish delegation, which had undertaken the work, prepared a first draft, the revision of which, temporarily held up until the position of ISO/TC 44/SC 6 with regard to machine specifications was settled , can now be actively resumed.