ALUMINIUM AN D ITS ALLOYS.
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TSome Practical Notes on 0 ALUMINIUM and its alloys the designers of motor vehicles owe a debt of gratitude, for, without these materials, the modern motor vehicle would, weight for weight, be considerably less efficient. . _ • Aluminium is used in almost every branch of engineering work, but in no branch have its effects been so valuable as in the case of its employment in the construction' of all types iif commercial-motor vehicles. It must be remembered that a, motor vehicle is built to carry loads, whether they be human or otherwise, and the lighter it can be built, consistent with strength, the more weight it can carry in proportion to its engine power. Its own weight is non-paying 1 o a d, and if this load be high, petrol consumption, tyre wear, and general m a;nt e 'lance charges are all increased By the suitable employment of aluminium and its alloys wherever possible throughout the chassis, a saving of weight of 25 per cent. may be obtained; this figure, of . course, includes` he use of aluminium for the cylinders, where the bores -are fitted with cast-iron or steel liners. An engine of this de scription was described on page 404 of our issue dated December 9th, 1919. This type of engine, however, kris not met with much favour for use with commercial motor vehicles, although we believe that it has a considerable future, owing to the ease with which aluminium can be cast without developing blow-holes. Aluminium pistons have been employed with a good deal of success and for some ,considerable time on private cars, and some 60,000 Ricaxdo pistons are said to be employed ; they are now being tried on commercial vehicles. The difficulty with these pistons is that, owing to the high expansion of aluminium under the effect of heat, a large-clearance must be allowed between them and the cylinders, with the result that there maybe a certain amount of piston slap until the engine is thoroughly warmed up.
An important point in connection with the use of aluminium for cylinders is that the thermal conductivity rapidly increases with the temperature. This property is also of considerable benefit when aluminium alloy is used for Jcrankcases, as the lubricating oil is cooled far more rapidly than would be the case if cast-iron were emp/oyed... The same feature assists in keeping the aluminium Pistons at a lower temperature than those constructed in other materials.
Aluminium is being successfully employed for practically all those parts of lorries which are not subu44 jected to excessive wear and stresses. The majority of gearbox casings are cast in this material or its alloys, as are also the top and bottom tanks and side brackets of the majority of radiators. For clutch eones, it has the particular advantage of lightness which is so necessary in this component, for, the lighter the cone can be made, the easier it is to change gear. This quality of lightness is also particularly useful when aluminium is employed for the .casings of universal joints.
The machining of the metal is not difficult, if care be taken. Owing to its comparative softness, the tools are liable to dig in and tear the metal, but this can be avoided by taking a fine cut, and in the case of turning, to see that the tool is properly positioned.
When turning or. boring aluminium, the tool should be pointed, and with a large top clearance; it should be set just below the centre of the lathe for turning, and just above for boring,' and the speed should be as high as the nature of the work in hand w ill permit. If plenty of paraffin is employed, . a highly polished finish will result.
Whilst drilling, screw cutting or tapping it is ad vabIe use a lubricant, such as paraffin oil.
It, will be fonnd that the alloys of aluminium are more easily machined than the pure metal, being harder and not so liable to drag.
When grinding aluminium a piece of paraffin wax should first be held against the grinding wheel in order to fill its pores the material will not then adhere to the wheel.
It is very difficult to file aluminium with an ordinary cross-cut file, as the file becomes clogged very rapidly and it is difficult to clean • if, however, a -single cut file is used it may easily be cleaned with a wire brush. Files of the " Dreadnought " type are also much used in this connection.
Aluminium panels are employed to a great extent for the construction of chars-a-banes bodies, whilst thick sheet aluminium, or aluminium castings, are often employed for dashboards. A method of construeting bodies from flanged panels cast to shape has lately been introduced., offering much promise of success. For .pressed panel work the most suitable thickness of sheet to employ for hammering is either 16 or 18 S.W.O., which are supplied by the makers in sheets of from 8 ft. by 4 ft. to 12 ft. by 4 ft., or as -large as 12 ft. by 6 ft., if required for special purposes.
Aluminium hardens up fairly quickly while being worked, but, unless the panel has to be curved considerably, the metal dcies not require annealing ; when however, this is required, the annealing tem.peratUre varies from 750 degrees F. to 900 degrees F., depending upon the thickness of the sheet. It should be heated until fine hard wood sawdust just glows upon it.
The polishing of aluminium is very similar to that of brass -and may be, donewith any good polishing compound other than rouge, and used on a calico mop running at high speed. When a good surface has been obtained, it may be finished off on a soft mop with lime. A beautiful satin finish can be given to aluminium by scratch-brushing with a fine steel brush running at a high speed. No lubricant is required, and if any splashes of oil are thrown from the machinery, they should be removed by applying Sheffield lime to the brush. Aluminium can also be given a fine white frosted appearance by immersing articles of this material in a hot, weak solution of potash in order to remove grease and dirt. The bath used for washing is a 6 to 10 per eent, solution of powdered caustic soda, kept just under the boiling point when in use and contained in an enamelled iron bath. From time to time more soda, should be added to keep it at the requisite strength. After this treatment, the articles should be washed in cold water, and then dipped in nitric acid until all trace of blackness has disappeared and they become quite white ; fintly, they should again be washed in cold water, clipped into hot water, and dried in boiwood sawdust. This finish is particularly suitable for ornamental stampings and for preparing the metal for painting. In painting body panels hieh cannot be removed from the body; any old paint should be removed by a solvent, as the burning off may cause buckling and distortion. All grease must then be removed by the application of benzine, and a matt surface obtained by the use of emery cloth. Paint applied to such a surface will adhere quite satisfactorily, but it is better to give a primary coat of gold size, avoiding paints with a white lead base. The paint should be applied at a temperature of about 70 degrees F:, and in a dry atmosphere. In the majority of cases, two coats of paint and two or three of coach varnish will be found sufficient. Cast dashboards and panels merely given a couple of coats of varnish took extremely well. We are indebted to the British Aluminium Co., Ltd., of 109, Queen Victoria Street, London, E.C., for many of the practical hints contained in this article.