How Arc Welding San Cheapen Repairs
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Ukeep fleet-maintenance men right up-to-date with the ses of electric welding on chassis, body and engine repairs, I have secured first-hand knowledge of the methods practised by a number of maintenance engineers. The average shop, in my experience, has a 24-hour service facility for fleets of buses, trailers, lorries, tractors, etc. All equipment is regularly inspected.
The most suitable form of welding machine is a 200-amp. or 300-amp. motor-generator electric-arc welder, which can be seen in the accompanying illustrations. The number of money-saving uses found for such a machine is really quite
surprising. Almost all the maintenance engineers I have met have told me that immediately after securing an electric-arc welding plant they discovered that, in addition to the serious breaks they repaired, the possession ot such equipment resulted in their paying more attention to the less serious jobs which they had formerly neglected. The following instances will give some idea of how they put this versatile piece. of equipment to good use.
Starting on the more frequent jobs—cracked cylinderblocks or heads, these are usually repaired without dismantling the engine—at least, in all but extremely bad cases. Cylinder block and head welding work is generally one of three types:—Srnall exterior cracks, which can be easily welded; large cracks which require some preparation work; or unusual cases; such as when the block is broken and one piece,' or several pieces, are knocked out.
Repairs of these types need the following special equipment:—The electric-arc welding set, a supply of electrodes for welding cast iron, a diamond-point chisel, a wire brush, and some means for readily moving the casting into various positions. In addition, a protective head shield, preferable to goggles, and a pair of welder's gloves are needed.
The Importance of Cleanliness.
For repairing exterior cracks of the first-named kind, the job is properly prepared and all foreign matter is cleaned off the parts to be welded. The presence of any oil or dirt will interfere with the best results. To secure a tight job, a small sealing bead of weld metal is deposited. One company reported that for only 2s. (Is. 6d. for labour and 6d. for operating the welding machine) it was able to mend a leaking crack in a cylinder block of a large engine.
For larger cracks, one method that has proved helpful 13 to V out the crack, either partly to expose the clean metal or to make a V that reaches to the full depth of the crack, and then to apply the sealing bead.
When the work is properly prepared, cast-iron shieldedarc electrodes are used. It has been found that an electrode with a steel base gives a solid weld on cast iron, of greater tensile strength than the cast iron itself, This type of electrode gives a good bond or union with the cast iron, and, due to the low current which can be used on it, the hardening effect usually present along the line of fusion is materially reduced, making a machineable weld. The low current used is a feature of the electrode coating.
Before starting to weld, the electrode is made positive and the work negative (readily accomplished with a modern machine which has a polarity-reversing switch). Approximately 80 amps. and 23 volts at the arc are used. The proper setting is obtained by using a low current and a high open-circuit-voltage setting. The machines shown in the pictures are of the dual-control type, which deliver direct current at the arc, and enable independent control of the current and voltage to be obtained. This type of control enables the most accurate arc characteristics to be obtained • for this work.
Not more than a 3-in, bead should be laid down at one
• tirn.e. Immediately after each bead is applied, it is peened lightly and the first head is allowed to
cool somewhat before the next bead is applied. Great care is taken to see that the work is always clean, whilst it is not allowed to get too hot.
Where a single piece is broken out of the casting, it is helpful to tack-weld an electrode on to the broken piece. This will provide an easy, way of holding the piece in position while welding it_ In severe cases of cylinder-head damage, such as when a piece has been broken out, it is necessary that the broken piece or pieces be carefully fitted together. Here, again, it is essential to have the parts absolutely clean. If several pieces can be fitted together their edges are chamfered, they are tack welded together, and then welded into one solid piece. The edges of the cylinder-block fracture are also chamfered where the reassembled part is to be applied. Where several of the broken pieces are lost, it is generally advisable to weld-in a single iron plate instead of trying to patch the broken parts together.
When welding a good grade of casting, no difficulty should be encountered if the work be clean and if proper equipment be used. In this connection it should alwaxs be remembered that no electric-welding equipment, no matter how efficient, will compensate for dirt and oil on the work. One method of being certain that all oil is driven out of the casting is frequently to heat ahead of the weld. This, however, is not practicable in all cases.
When a break runs into a machined face, as in the case of a gasket joint, the broken pieces are set so that they extend a little above the original surface. This allows for grinding the part down, to make a good gasket fit.
Sealing Pin-holes.
In order to avoid the chance of pin-holes, which result from failure or inability to clean the work properly, it is sometimes advisable to apply sulphur to the weld so soon as the arc is stopped, and to melt enough to seal any pinholes which might be present. This application of sulphur is necessary only when the condition of the base metal prevents absolutely tight welds. Good sound welds can be made on clean cast iron.
Due to the severe service to which fleet equipment is often subjected, operating under heavy loads in all kinds of weather and over all sorts of roads, sometimes it will be necessary to repair a broken frame. As a case in point, one of the main side members of a large trailer broke just in front of the rear axle. The frame was broken completely across from top to bottom, appearing as if it would require
a long and complicated procedure to repair. it. With electric welding, however, the job lost most of its terrors; as a matter ot fact the frame was not even detached from the body. The work consisted simply of cutting a piece of steel plate, approximately in. thick to conform to the frame, and extending it about 18 ins, each side of the break. This steel plate was electrically welded to the frame, completely around the four edges of the plate. The job required only a few hours.
Frequent repairs are necessary to trailer and lorry bodies, due to the wear and tear of service, collisions, etc. A trailer was brought into one shop with parts of the body indicated with chalk marks, where repairs were needed. These consisted of a hole punched in the side, a loose endplate and several places where the side plating had pulled from the framing. In the case of the hole, a small piece of steel was placed over the opening on the inside and electrically welded from the outside. The end-plate, rusted and worn loose, was made tight by welding. At one point (a lower corner of the body, just ahead of the wheel recess) the mudguard was pulled loose. It was fixed by prising it bath into position and arc-welding it in place.
Speedy Repair of Small Parts.
Small parts of lorries, such as brake shoes, spring shackles. etc., are readily repaired by arc welding.
Repairs such as these cost only a few pence, are permanent and save the cost of a replacement. Moreover, they save the time of waiting while a new .part arrives. Arc welding machines are made in a variety of types and sizes. The motor-generator set shown in the accompanying pictures is of popular make and has a 200-amp. output at a maximum arc-voltage of 40. Smaller machines arc, of course, available. A 150-amp. model, requiring less than 2i sq. ft. of floor space, was recently introduced by a leading manufacturer. It was developed especially for vehicle repair work and can be used on any a.c. power line. It is handy, readily movable around the shop, and small enough
to be hauled to outside emergency jobs. '
Savings available with welding equipment in fleet Maintenance are large, sufficient, in many cases, to pay for the welding equipment in a few months.
In conclusion, if is. riot the purpose of this article to picture electric-welding equipment as the cure-all for every fleet-owner's ills, although if any single piece of equipment could be considered a panacea for curing high maintenance costs, then a welding machine must be it. R.B.