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Repairing and Hard Sur ; by the Welding Process

8th September 1944
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Page 26, 8th September 1944 — Repairing and Hard Sur ; by the Welding Process
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The Application of Arc and Gas Welding in the Repair and Reclamation of Broken and Worn Commercial Vehicle Components

By P. L. Pocock,

A.IVI.Inst.W., Int.A.M.Inst.Prod.E., M.Inst.Met., M.I. and S.Inst. THE haulage of war Materials and other essential goods is a highly important branch of our war machine. Spare parts are in short supply and, due to shortage of labour or demands on the vehicles, regular overhauls are not always feasible. These factors make it a necessity that, wherever possible, all broken and worn parts should be repaired, and welding is the medium. Even to-day it is not used on the scale that it should be, and concerns which have to maintain fleets of motor vehicles should, in their own interests, consider installing welding equipment.

Selection of good, reliable and efficient apparatus is vital to successful welding practice, and intending purchasers will be well advised to buy only from reputable manufacturers who specialize in its production. All garages and workshops should have both oxyacetylene and arc-welding equipment, as repairs suitable to buth processes of welding are encountered in motoavehicles, and there are many instances when it is necessary to have a cutting blowpipe, for which the oxy-acetylene outfit is necessary.

The types of repair encountered can be classified under two headings—jointing, and building up and hard surfacing. Grouped under the first heading come such parts as cracked and broken cylinder blocks and heads, crankcases, axles and shafts, chassis frames, wings, etc., whilst, under the second heading, we may include exhaust valves, camshafts, crankshafts, brake drums, chain wheels, clutch fingers, gears, etc. Friction, abrasion and corrosion are the chief causes of wear in the moving parts of vehicles.

Increased Service Life

and Conservationby Welding'

To-day, due to the spares shortage, working parts have to last much longer than would be normally expected. Even were spares readily obtainable, components should not be thrown on to the scrap-heap if they can possibly be repaired. A proper repair can not only give longer life to the component, but it can even result in the obtaining of higher efficiency than follows the fitting of a new part.

Parts subject to wear can readily be salvaged by build,' ing up worn surfaces with material of varying degrees of hardness and'la ugliness, which process is here referred to as surfacing. In point of fact, much can be done in the manufacturing stages of working parts to prolong their life by from two to ten times that of parts untreated, and this is a conseivative estimate.

There are diflerent methods of repairing broken and cracked cylinder heads and blocks, and these are the oxyacetylene, carbon ate and metallic-arc methods of welding. Where the broken parts are free to move under the forces of expansion and contraction, metallic-arc welding. should he used, hut where the expansion and contraction would produce complicated stresses, either oxy-acetylene or carbon-arc welding should be employed, the casting being preheated prior to being welded.

In many cases, with the carbon-are process, the casting may be welded without preheating, a copper-alloy filling wire being used, This low-temperature process has many advantages. On cast iron, the alloy filler wire, which is produced by the Lincoln Electric Co., Ltd., seems to have a definite affinity tor cast iron, and such welds can be carried out with fused borax as a flux. This process is equally successful on malleable-iron castings.

In Fig. 1 is shown a cracked cylinder head before welding. The casting must first be prepared by thoroughly cleaning the metal around the weld area, and veeing out along the crack. It is not necessary to tin the metal edges, as in bronze welding; the respective angles of filler wire and carbon should be as indicated in Fig. 2. The arc should be played on the filly wire so as to disperse the flow of heat equally on each side of the vee. The fused borax flux is best applied by dipping the filler wire in the borax. A isin. carbon was used with a current of approximately 170 amps. A Lincoln SAE 200 ;lc. plant was employed for this job, using the negative pole for the carbon. However, should it be necessary to use an a.c.-type of plant, Repairs to chassis are made quite simple by arc welding, and the work can be carried out without the need for dismantling. With arc welding, the heat conducted by the base metal is very small, and therefore little or no distortion takes place in the parts being welded.

Excellent electrodes for this type of work are those of the deep penetration Mis variety, such as Fieetweld 5. This electrode gives very dense welds and uniformly deep penetration through the whole of the joint. It is usual to use reversed polarity with this type of elec trade, i.e., electrode, positive, and earth clamp, negative. Fleetweld 5 is obtainable in the sizes shown in Table I, and the amperages to be used with different sizes of electrode are also given.

For this type of repair, both downhand and vertical welding mast be employed. With downhand welding the angle of electrode manipulation is as shown in Fig. 3. In general, the length of arc should be held approximately in. from the work surface, and a steady rate of travel be maintained throughout the whole of the deposition, Vertical %hiding is more difficult to master than downhand but, with practice, it soon becomes easy to the operator. The vertical-upward is the best method, and this should be carried out as shown in Fig. 4.

Broken axias and other shafts should be set up in a rolled jig and should be bevelled prior to welding, which should be carried out, using a head shield, the jig being rotated by the hand so that welding is continuous around the shaft.

The repair of .aluminium parts by arc welding presents no difficulty whatsoever. Fig. 5 shows a damaged aluminium crankcase. A piece of scrap aluminium was first shaped to fit the hole, which was veed out along the joint. It was then thoroughly wire-brushed so as to ensure that the work was perfectly clean. Tacking was carried out by increasing the normal amperage by approximately 50 per cent. A short arc and rotary motion were employed, as shown in Fig. 6.

Table 2 gives the correct current values. The maximum current value should be used wherever possible and normal polarity employed the electrode being held perpendicular to the work sue lace.

The joint was welded in the direction of the arrows as shown in Fig 5. Afterwards, the slagcovering was lightly tapped off, the mid vigorously wire-brushed and finally cleaned by rinsing in a 5 per cent, nitric acid solution followed by hot-water rinse.

Techniques and Materials' for Repairs and Salvage The processes by which worn parts can be repaired and salvaged are gas and arc welding, and the method employed is by building up with one of several materials—MIS, wear-resistant alloy steels and Stellite for either electric arc or gas welding, and 31 per cent, nickel' steel with gas welding, or, irs some cases, ferro-silicon cast-iron rods and other special types of welding rod ,and electrode. The methods which can be employed to prolong the life of these parts in the manufacturing stages are the deposition of wear-resistant alloys by electric arc or gas welding, or the shorter process of surface hardening. Stellite, together with some types of W.R.A.S., cannot be machined aud finishing operations can be carried met

only by grin ling. The coinposition of W.R.A,S. is generally chnemium and manganese, carbon up to 16 per cent., and small percentages of other alloying elements; this type of material gives a hardness' range of from 300 to 500 Brinell, and may be quenched to give a greater degree lei hardness. Straight carbon steels, i.e., 1 per cent. carbon, are also used for this purpose. Other types of lowand high-alloy steels are available, each being produced for a specific purpose.

Alloys suitable for use on parts subject to shock and impact would, perhaps, not be so suitable for components which are subject to friction and abrasion. Some of these alloys can be machined, Whilst others can be finished only by grinding. This is an important factor in selecting hardsurfacing material for any particular job.

Stellite is one of the cobalt-tungsten-chromium alloys and its resistance to corrosion and friction is very high. It gives a hardness range of between 400 and 650 Brinell. It is obtainable in three grades—I, 12 and 6. No. 1 is the hardest, but should not be used if the part has to withstand impact forces. Nos, 12 and 6 are relatively tough and should be employed for parts which are subject to severe shock. Both Stellite and wear-resisting alloy steels are obtainable for gas and arc welding. Arc welding offers advantages when large areas have to be covered, and the process is obviously quicker and cheaper.

Components or parts which can be repaired by hard. surfacinginclude such items as camshafts, brake drums, chain wheels, clutch fingers. crankshafts, starter rings, valves and valve inse:ts, gears, etc. Hard-surfacing, however, cannot be carried out by all of the three methods.

There are many factors to be taken into account in the use of any particular process. To give an example: Stellite and some types of wear-resisting alloys cannot be

deposited on to steel which is high in manganele, brasses and bronze, except in the case of the last mentioned, when a piece of Stellite can be brazed on to make a wearing pad. Ferro-silicon should be applied only to cast-iron parts, and 31 per cent. nickel is invariably employed when it is not possible to use Stellite or W.R.A.S.

. Stellite is adaptable for the repair and salvage of clutch fingers, tappet rods and valves, valve inserts, valve spindle ends, cams, etc.

W.R.A.S. can be applied to crankshafts, camshafts, spindles, etc. One important point must be remembered when depositing Stelae and some of the above-mentioned alloys, that

finishing operations can be carried out only by grinding, and unless the workshop be fitted out for this, consideration muss be given to the use of 3i per cent a:ckel and types of W.R.A.S. which are machinable. Siliconmanganese, high-carbon steel or ferrosilicon are all machinable, and some can be readily hardened by quenching. Ferro-silicon can be used on cams, valves and camshafts, and al per cent. nickel for brake drums, camshafts, chain wheels. starter rings, gears, shafts, etc

When using Stellite or W.R.A.S., it is always best to attempt to complete the whole of the deposit in one run; if when using the gas-welding process the deposit is of a depth which cannot be achieved by the leftward technique, the rightward method, sr arc welding. must be used.

The advantage of applying this alloy by electric-arc welding in that hard-surfacing can be carried out without the need for preheating, which may not always be possible. and, moreover, may not be beneficial to the base metal. Where the base material has been case-hardened, this portion should be ground away before hard-surfacing material is deposited.

Successfully to deposit these alloys by gas welding, the following precautions should be taken and the method, as described, adopted. The parts to be hard-faced must be absolutely clean and free from dirt, rust, grease, etc. The preparation ot metal edges is subject to the conditions under . which the part works. To give an example, if the part be liable to shock loads, the preparation differs from that required for parts where there is little or no shock. Fig. 7A, for example, shows the correct preparation for parts not subject to any great shock. Should the part be subject to severe impact, it would be prepared as shown in Fig. 7B. Preparation for longitudinal seams is shown in Fig, 7C In all cases edges should be rounded .off.

In preheating (which does not apply to small parts 'which can be brought to dull red heat during welding operations), the part should be heated to a temperature of approximately 500 degrees C. Mediums:zed parts can be preheated with the blowpipe, using a neutral flame; thick sections will need a muffle or a furnace.

An excess of acetylene must be used as this is one of the • fundamental principles of the low-temperature process. The excess acetylene combines with a thin, top layer of the base metal, increasing the carbon content of the layer. which naturally fuses at a lower temperature than the bulk of the base metal, giving the material a sweaty appearance. The excess of acetylene should ha 2i times the length of the inner white cone of the flame; adjustment is best carried out with welding goggles on.

The welding flame should be directed to the beginning point of the seam, the inner white cone being held.approxis niately in. away from the work surface, and the blowpipe maintained at an angle of from 40 to 60 degrees, according to the thickness of the deposit required, and that of the base material. The nozzle size used should be twice

as large as that normally employed on steel of the same thickness. After the base material has started to sweat for an area of approximately in. around the inner white cone, the hard-facing rod should be applied gently with a soft action, the end being kept in contact with the work

and in the envelope of the flame. • The deposit is built up to the required depth, as the base metal becomes in a sweaty condition and the weld proceeds. care being taken to float oil any scale and so

prevent the formation of blow-holes. Fig. 8 is sell. explanatory of the welding operation for both the leftward and " rightward methods. When the deposited seam is com pleted, the flame should be withdrawn slowly with a circular motion. The component should then be covered with insulating material, such as ashes or something similar, and allowed to cool slowly to prevent the formation nI

cracks in the deposit. If the base metal or deposit tends to. crack, it should be reheated in the furnace or muffle and then allowed to cool.

Deposition by arc we:ding is carried Out with almost the same technique as used in the ordinary arc-welding process, with the following exceptions. The electrode is held nearly vertical and slightly higher current values are used. The arc is held at approximately i• in. to in. from the work surfase, and a wide, weaving movement of approximately 1 in. must be imparted to the electrode to prevent excessive penetration; should this &cur exces sive inter-alloying of the hard-facing and base material takes place and reduces the hardness and efficiency of the deposit. A smooth flowing arc should be maintained to prevent formation of blow-holes and, for the same reason, care should be taken to prevent any sticking of the electrode.

As previously explained, apart from Stellite are!, W.R.A.S., many parts of motor vehicles are btfilt up with 3i per cent. nickel-steel alloy rods and, in the case of castiron valve seats, by ferro-silicon. With the last-named type of hard filler-rod material, should the part be of a suitable dimension, it can be quenched in water froth bright red heat to give a very hard deposit. The method of applying either ai per cent. nickel or ferro-silicon is normally the same as used in ordinary welding practice, using a neutral flame in each case. With ferrosilicon a cast-iron flux is used..

To obtain maximtrm evenness of deposit on all circular parts such as valve-seat inserts, it is best to use a rotating jig. This can be made quite easily, and 'a simple form is illustrated in Fig. 9. The va:ve insert should be prepared and then placed on the jig. Being of small section, it can be preheated to approximately 500 degrees C. with a blowpipe, and when this temperature has been attained, welding operations can be commenced. As the weld proceeds the valve insert is turned around by the foot with the aid of the protruding spokes.

The finished part, after cooling, is ready for final grinding operations.

Worn cams can be effectively built-up by welding, using ferro-silicon filling material; if the cams be badly worn, it is best to preheat them, and jig should be used. Welding should be carried out as when welding cast iron, the

cams being built up to the required depth. Camshafts can also be built-up with 31per cent. nickel or W.R.A.S. They may also be built-up • by arc welding without preheating. Naturally, this method is quicker and less costly. Such electrodes as Fleetweld 5 arid 7 may be used for the application. After building-up, the camshaft cart be quenched to give a fairly bard deposit, or a run of Wearweld may be deposited. Broken shafts can also be

repaired with Fleetweld 5. After tacking the pieces together and before welding, the shaft should be trued-up in a lathe.

Worn crankshaft journals may be built-up with Si per cent nickel or Fleeivreld 7. To facilitate welding operations a jig is a distinct advantage. We will assume we are building-up the crankshaft by the arc-welding process, so preheating is not necessary and the crankshaft can be put straight into the jig. The size of the electrode selected will depend on the area to be built-up. It is advantageous to complete the seams in one run if possible. If it be necessary to deposit a second layer, care must be taken to ensure that all slag is removed and the metal is quite clean before the second layer is deposited. Fig. 10 shows the correct mithod of laying down runs and successive layers of weld metal. Brake drums are another example where the arc-weldingprocess can be used successfully, and should arc-welding facilities not be available, Si per cent, nickel ro.ds can be used with the oxy-acetylene process.

Starter-ring gears can he built-up with Si per cent. nickel. The worn parts should be prepared by filing or grinding to ensure they are quite clean and metal run on, taking care not to build-up unduly in excess of the original dimensions, as this will only necessitate extra finishing operations. The weld metal should not be allowed to get too fluid, as this makes it difficult to build-up to the desired shape.

The metal should be sufficiently molten to permit of adequate fusion of filler rod and base metal. Should the metal become too fluid, it will, through the force of gravity, tend to run over the edges of the teeth and make the repair unsightly and increase the work required in finishing. Camshafts and gear wheel* are but two examples of the many parts which can be effectively hardened by the Shorter process, which is, in a way, a process allied to welding. It has the efficiency and certainty about its results that is obtainable only by machine precision work. The principle ot the process is simple, and it has done away with the old ineffective hand method of blowpipe hardening, which, unfortunately, is still practised in many workshops. Briefly, the Shorter process is a method of hardening steel and east iron by localized heating with the oxy-acetylene blowpipe followed by rapid water quenching. The heating and quenching are carried out by specially constructed machines, so it will be readily understood that the processes are closely controlled, the machine being a precision instrument working to very fine limits. There is no comparison nettseen this type of machine-hardening and that carried out by hand. The depth and area of the hardened layer is uniform throughout the job, which is almost impossible of attainment with the hand method.

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