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• BETTER AND CHEAPER BODYWORK

14th March 1958, Page 113
14th March 1958
Page 113
Page 114
Page 113, 14th March 1958 — • BETTER AND CHEAPER BODYWORK
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Advances in Welding and the Possibilities of Other Techniques Brighten the Future for the Use of Aluminium for Bulk Vehicles

By P. A. C. Brockington,

THE economy of using aluminium bodywork for bulk transport

. . vehicles is easily calculable by operators, because the outfits normally make regular journeys and carry loads of unvarying weight. Operating costs per ton of payload can therefore be more readily worked out for such vehicles than is the case with less specialized types. The signs .are, too, that the cost of running bulk-transport outfits with aluminium bodywork will drop.

. On the international scene, Russia is competing keenly as a supplier of raw material and this may lead to a price war. From the technical aspect, research is being conducted into more advanced methods of construction, including the production in quantity of various subassemblies which could be commonly applied to different kinds of vehicle.

At present, aluminium is not a suitable medium for the carriage of some loads, but certain processes are being evolved to remove this obstacle. Valuable experi.ence gained by the aircraft industry—at great cost—may further be applied for the production of vehicle bodywork at loWer cost.

Paving the Way

Those operators who are embarking upon bulk transport are paving the way for progress by the vehicle builders, which may be stimulated when the European free trade area is established and international traffic in hulk materials increases.

There is no doubt that the improved practicability of welding light-alloy structures has enabled development to be accelerated. A reduction of nearly 70 per cent, in the price of argon gas over the . past 10 years, has enabled argon shielded-arc welding processes to become commercially attractive.

Their outstanding advantage is that no corrosive flux is required. Removal of the flux added to the expense of construction, and in any event was impossible with lapped joints. Tanks intended for foodstuffs or contaminable chemicals had to be butt-welded. After successful application in the shipping and aircraft industries, these processes are now employed for vehicle bodies with a corresponding reduction in expense. In the Argonarc process, developed by the British Oxygen Co., Ltd., a non-consumable tungsten electrode is shrouded in inert argon gas, and filler wire is added separately, if required, to the gas zone.

Argonaut welding, evolved by the same concern, and the Lynx and Sigma processes, developed by Quasi-Arc Ltd., are of the consumable-electrode type,, the electrode being normally of similar composition to the base metal. Operation is fully automatic over a wide range of wire speeds by matching the electrodemelting and wire-feed rates.

Cleanliness Essential

Cleanliness is essential to good welding, especially as an oxide film reduces weldability. This has meant that welding should take place immediately after preparation, but there is now a treatment which enables a aleaped surface to be left for 24 hours before welding, This could ease production problems,

The Northern Aluminium Co., Ltd., think that welding is better than riveting for the making'. oi pressurized tanks. Aluminium-magnesium alloy normally used for such vessels, its optimism strength is provided when in an annealed condition: The recent introduction by the company of two-section welded plate in widths of up lo II ft. simplifies the production of large -structures like tanks.'

Riveting, however, is considered preferable for other alloys which are weaker in the annealed or soluticin-heated condition than aluminium-magnesium. They may be employed for most standard structures, but ,if' welded together an excess of material would be required to compensate for impaired strength. This factor may, however, be considered in the design stage so that its disadvantage may be mitigated.

The Quasi-Arc concern and the Syntilla Manufacturing Co., Ltd., Dunstable, bodybuilders, emphasize that structures should be specially designed for welding. Syntilla have employed the Sigma process for some years, and state that reduced strength of metal in the weld zone is compensated for, in all but the lighte`st fabrications, by the ease with which extra strength can be provided where necessary.

Production of advanced types of welded structures demands accurate jigs and the availability of presses to fold heavy plate. Accurate preforming reduces the amount of welding required. and it is further claimed that Sigmawelded tipper bodiei are some 23 per cent, lighter than riveted structures.

T.I. Aluminium, Ltd., also underline the desirability of matching design to the Characteristics of welding. In theory, they say, riveting makes for a more flexible structure, but lapped joints are sources of stress whereas. welding avoids " notch " effects. Riveted lapped joints, however; prevent the spreading of fatigue cracks. T.I. technicians state that the heat-affected zone extends 2 in. each side of an acetylene weld, but only 1 in. if the Argonarc or consumable-electrode process is employed, the small area of argon-shielded welding being a measure of its _advantage in regard to strength.

Greater Penetration The greatest practical advantage of the consumable-ele.Ctrode process is its speed, a normal rate of 1 . ft. 6 in. 'a minute comparing with 3 in. a minute for Argonarc welding. The consumable-electrode method has greater penetration, but this is a disadvantage when thin plates are being welded. Argonarc welding is thus to be preferred for plates of up to in. thick.

When the question of stress .distribution in connection with frame members subject to deflection has to be considered, Northern Aluminium recommend using a small number of heavy members in preference to a larger number of light members braced with angle plates and similar components. Flange bulging of top-hat section is often caused by employing rivets that are too large. Bolted structures are easily repaired if damaged, and this is . often thought to compensate for their greater weight compared with riveted assemblies. Unless bolts are accurately turned and their holes reamered to provide a precise fit, state the concern, the metal will tend to fret at the bolt holes, and flange movement near the bolts may cause excessive wear.

T.1. technicians mention the value of light-alloy extruded sections for tank fabrication. The cross-section of an extruded stiffening ring can be of any shape to suit the designer, and special choice does not unduly complicate the structure or add much to cost. This latitude is not possible in steel-tank manufacture.

High-speed Systems The British Aluminium Co., Ltd., officially endorse the Argonaut and Sigma processes for the building.' of of heavy vehicles. The high speed of these systems is held to be valuable for long runsof butt-and-fillet welding, and they can both be employed more conveniently than the Argonarc method by companies in outof-the-way districts.

They are also said to be cheaper than Argonarc or metal-arc welding for most joints in metal in. thick or more. Weld quality is high, and the same strength is conferred as by Argonarc welding. Equipment may be mounted on a trolley and traversed automatically if manual methods are inappropriate.

To indicate the commercial advantage of using light-alloy tanks, the .cOncern state that a 4,400-gal. alutninium tank would run at the same gross weight as a 4,000-gal. tank in steel. In a year's operation the aluminium tank might-earn £303 more than the other, 'although iti cost would 'be about 45 per cent. greater.

Eliggest payloads can be carried in chassisless semi-trailer tanks, the construction of which has become more practicable not only with improved welding techniques, but also because of the development of high-strength aluminiummagnesium alloys.

Longitudinal Stiffeners

Problems associated with the buckling of plates at the top of a chassisless tank, caused by compressive stresses, may be solved by the proper use of longitudinal stiffeners correctly spaced.

Ease of replacement of sections without sacrifice of sealingproperties is a feature of the bolted containers and van bodies made by G. E. Neville and Son, Ltd., Mansfield, and should appeal to users of ordinary and insulated containers for bulk transport Standard 1-ft. rolled sections can be assembled to form components of suitable lengths, according to platform dimensions, and can be dismantled for transit, or temporary storage, thus affording operational flexibility.

An important part of Neville design. is that torsional stresses are resisted by Vregisters in the flanges of the sections; so that the bolts, which are cadmiumplated, are relieved of shearing stresses 'Thii should avoid tendencies towards:frel ting around the bolts and prolong life. Nuts are self-locking.

A continuous V-register is formed on the inside of each flange, and there is,a groove for the sealing strip on the outside. Seepage of water is prevented by the application of a sealing solution. A standard Neville container is being tried by Anglo-Continental Container Services, Ltd.

An interesting departure from -normal practice has been made by Park Royal Vehicles, Ltd., in the fabrication of a batch of 63 6-ton insulated containers for British Road Services, the design of which was evolved in conjunction with the T.1. company. Planking of a special extruded tongued-and-grooved section is _ used vertically for the sides and transversely at the ends, and the sections are cemented with Araldite, a cold-setting resin produced by Acro Research, Ltd. The side planking is riveted to extruded angle sections which form the main undcrframe.

The Aluminium Development Association believe that the adhesion provided by cementing is convarable to that obtained by welding, soldering, brazing or riveting. In aeroplane construction, cementing is employed to bond stringers to the skin and wings, aircraft exemplifying this practice include the Britannia, Canberra and Dove.

Another important aircraft application of possible commercial-vehicle interest is bonding aluminium sheet to both . sides of an aluminium-foil honeycomb. This is performed with Redux, a hot-setting cement produced by Aero Research, who think that honeycomb construction could be successfully applied. to the production of vehicle bodies.

Fewer Man-hours

Redux has been employed by Aero Research for the construction of side and tail boards of lorries in the Northern Aluminium fleet, and the process has enabled the man-hours for completing a set of drop sides and tailboard to be reduced from eight to two and a half. Cementing provides a neat appearance, and its low peeling stress is not a serious

disadvantage in practice as a small number-of suitably placed rivets can obviate " separation.

Developed in the research laboratories of the General Electric Co., Ltd., in 1946, cold-pressure welding is a process of joining two pieces of metal solely, by the application of preSsure, and it is particularly suitable for welding light-alloy materials and copper.

It is employed by the company in the construction of a number of components used in the electrical industries, and will, . it is considered, play an increasingly important part in the hermetic or vacuum scaling of containers for food, drugs and so on, in addition to the fabrication of , larger structures. 'The fact that it can be recommended for building boat and bridge assemblies as well as vehicle structures indicates its potential.

No Heat Required Roll welding is used for forming parts. from sheet, plate or strip, ring welding for perimeter joints, and plain welding" for joining two overlapping parts in a series of spots or a continuous seam. • Strength of the joints is generally corn. parable to those made by conventional means, and it is notable that no heat,' flux or Chemical is required.

Presses of the standard type, with which a typicalindustrial workshop isnormally equipped, can be employed for cold welding, arid tools are made to average standards, tt is not normally necessary to construct the tools of hardened material, and dies .for coin, rnercially pure aluminium can be made of mild steel or unhardened chromemanganese tool steel... Die wear is slight.

In the opinion of a bodybuilder specializing in aluminium structures, local thinning of the metal and distortion could be caused by cold-pressure welding, and the high pressures required could create difficulties in the production of long seams. Local stitching is, however, simple. Pressure welding of studs could offer a number of advantages.

Pressure Welding

A development of pressure welding, known as roll bonding, has been applied experimentally by Northern Aluminium to the fabrication of, double-skinned components, and may represent a process that could be used commercially for various parts of vehicle body structures.

Two light-alloy plates are cut to smaller dimensions than those of the finished component. They are also of heavier gauge than in final form.

A " foreshortened " pattern is then painted on the inside of one of the plates and a blanking material is applied over the area marked by the pattern. The two plates are placed together and rolled to a thinner gauge. Simultaneously the edges around the pattern are welded by the high pressure exerted by the rolls. . The free internal section is then inflated, expansion being controlled by platens or a die. If commercially developed, the, process could simplify making double-skinned sides, hold-over plates and flooring.

Tags

People: Redux
Locations: Neville, Canberra, Britannia, Dove

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