Electric Welding and Welding Appliances by Herbert Carpmael

Author:Herbert Carpmael
Language: eng
Format: epub, pdf
Publisher: Constable & company ltd.
Published: 1920-03-25T05:00:00+00:00

The switchgear and resistances for the welding circuit are fitted in the front portion of the body on the off side. The oablee from this gear run down through the floor to terminals on either side of the body. From these terminals the cables can be taken to where the are is required. The welding leads are supplied in convenient lengths, which can be thimbled together as required, and junction boxes are provided for the insulation and protection of temporary connections.

The plant is designed to weld mild steel plates from J in. to 2 in. thick and upwards, and for all descriptions of steel and iron forgings and castings. The output of the dynamo is from 18 to 20 kilowatts. When the car has been taken to the place where the repairs are to be carried out, the controller-lever on the steering column is put into the neutral position, and the main switch on the welding switchboard is closed. The

Fio. 48.—Tilling-StevenB Arc Welding Lorry—Interior.

motor is then entirely out of the circuit, and the engine and dynamo are set ready for generating current for welding.

Another firm which has specialised in the manufacture of machines for supplying-current for arc welding is that of Crompton and Co., Limited, of Chelmsford, and it has turned out some large machines for this particular class of work. It makes machines of various types, from those designed to keep one single arc going to those intended to supply current to several separate welders working in parallel, each with his own steadying resistance. Such generators as the latter are simply compoimd wound, so as to give a level characteristic and to ensure stability. They do not differ essentially from ordinary compound-wound dynamos, and do not therefore call for special comment or for more detailed reference. Single welder machines, however, may sometimes be compound wound so as to give a faUing characteristic, that is to say, be oyer compounded so that increase in current tends to reduce the voltage, or they may have three windings, one of them energised from a separate exciter. Then, again, the machines may be motor-driven, the motor being either for alternating or direct current. All the Crompton machines intended for arc welding purposes are, so

we nnderBtand, demgoed to withstaod overloads of 25 per cent, for two hours, 50 per ceat. for short periods aod 100 per cent, momeatarily. To make a provisioD of this kind is distinctly wise, because the dnty of a welding generator is witbont doabt extremely udDOdfl, since the load is s very varying quantity. la the case of a small generator, supplying only one welder, the variation may well amount, momentarily, to overloads of twice the normal, the load rising instantaneoDEtly from zero value.

Two machines have been chosen to illustrate the special ptodocts of the Crompton firm. Th^ are ahown in Figs. 61 and 52. The former shows a petrol-driven self-ocHitained welding set, the engine, petrol tank, oil tank, radiator, generator and switchboard being mounted on one bed-plate, so as to be readily portable.

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