The Benefits of Automatic Carbon-Arc Welding

Kitmondo 06 May 2014

This article first appeared in Practical Engineering 1940 Vol1 No19. The information contained within the article is therefore correct as of 1940. The publication attempts to provide an historical perspective into Engineering methods of the time.

Automatic carbon-arc welding is reported to have many advantages in the construction of aluminium tank cars. The automatic process permits faster construction and a considerably better quality weld, together with marked freedom from distortion. This development was brought about by a desire to improve quality - not to lower costs, which are practically unchanged due to the increased flux cost cancelling the labour saving.

Easier Setting-Up

Since no bevelling of plate edges is required, the full thickness of metal is utilised in the welding by simply butting the square edges together, greatly simplifying the set-up of the work. The welding time per tank is noticeably shorter than with previous methods, since the automatic weld is made in two passes instead of the three formerly used. The fact that automatic welding permits welds of complete overlapping penetration accounts for the greatly improved quality of the weld.

Freedom from distortion, which has been a factor in previous methods of fabricating aluminium, is permitted with the automatic carbon-arc method because of the faster welding this process makes possible. Very little straightening is required on round tanks welded by this process, whereas, with the previous method, considerable straightening was necessary. This advantage not only simplifies production of the shell itself, but because the shell is so uniformly round, the heads are readily fitted to the ends of the shell.

The use of automatic carbon-arc welding in the construction of aluminium tank cars has been used in the tractor-type 32ft. "Electronic Tornado" automatic carbon-arc welder manufactured by the Lincoln Electric Company, Ltd., Welwyn Garden City, Herts, welding an inner longitudinal seam in an aluminium tank.

Materials used in constructing tank cars of aluminium include a bottom plate fin, two sides, or top plates 1/2in. thick; and two heads 5/8in. thick. The tanks are 78in. outside diameter and 32ft. overall length. Square-edge tight-butt welds are used throughout in construction. The difference in thicknesses of the butting edges is taken care of by maintaining uniform outside diameters and making up the difference by an off-set on the inside of the tank.

Two Passes Only

Three longitudinal welds are required in constructing the shells. Two passes, one inside and one outside, are required for each longitudinal seam. The first longitudinal pass is made on the inside with the seam properly backed up with a water-cooled copper chill bar, giving complete penetration with one pass. The second pass, made on the outside, is applied to obtain overlapping penetration and for the sake of appearance. It is made without any backing up.

In welding the heads to the shell, the head is fitted and the tank rotated under the carbon arc which welds the outer seam, with the inside properly backed up with copper chill bars. Filler metal for the weld is supplied by aluminium wire fed into the arc. The second pass on the head weld is done manually after grooving with a chipping tool.

These aluminium tanks have, for the most part, been utilised for glacial acetic acid service. This is the basic material for the manufacture of rayon and non-inflammable film. Two of the aluminium tanks have also been put into service for carrying peroxide. These were constructed of a 99.5 per cent aluminium alloy. The balance of the tanks, for acetic acid service, were constructed of a 97.5 per cent aluminium alloy.