THE PART OF PLASTICS THE POST-WAR VEHICLE
Page 26
Page 27
Page 28
If you've noticed an error in this article please click here to report it so we can fix it.
The view is expressed that designers and builders of commercial motors have not yet appreciated the structural value of plastics to the same extent as aircraft engineers and, for this reason, only limited use has at present been made of them Relative fields of application of different types of plastic, of both the thermo-setting and thermo-softening varieties, are broadly defined with practical examples, and general post-war possibilities for their expanded utilization in this sphere are outlined
DURING recent weeks a number of articles has appeared in " The Commercial Motor' voicing the opinion that the motor manufacturer should more closely collaborate with the operator and maintenance engineer, so as to produce
vehicles more suited to the requirements of the latter two. The majority of the authors
. stressed mainly the importance of standardization and accessibility. The importance of lubrication was scarcely mentioned. This was remarkable, because I think most maintenance engineers wonld agree that the life pf any vehicle is, to a large extent, dependent uponthe efficient lubrication of its chassis. Chassis lubrication, broadly speaking, is.standardized, and perhaps because of this, very few beneficial changes have been made to it during the past 15 years (so it is doubtful if standardization is good for the vehicle).
When changes are Made in this most important sphere I hope to see them result not in the form of some new " super grease gun" but in the elimination of the necessity to lubricate. It is peculiar to find, with individual makes-of vehicle, isolated examples of lubrication being unnecessary at the following points :—Chassis AI—propeller shaft universal joints ; chassis It—spring-shackle pins ; chassis C—clutch thrust mechanism ; chassis 1)-.-. water pump ; chassis E—steering-linkage joints; chassis F—brake linkage. I believe also that an American concern is developing hub races embodying this advantage. All these examples are known to give good service dyer very long periods, and it is difficult to understand why manufacturers have not made fuller use of them, as, if combined in any one chassis, they would practically eliminate chassis lubrication (excepting main units), and I feel that this point would be greatly appreciated by all
maintenance engineers.
Most of the desirable features mentioned have been achieved by the use of plastics, but in my opinion vehicle engineers have not developed their use to the same extent as have industrial and aircraft engineers. This may be due to the fact that most vehicle engineers acquire their early training in a stronghold of metal tradition, and are concerned, in practice and in thought, with metals as almost the only possible materials of construction. Any non-metallic substance that did obtain a foothold in this stronghold did so in the face of rather strong opposition, but this was achieved in industrial and aircraft engineering as a result of prolonged tests under extremely severe conditions and because it was eminently suited to the job. .
. The motoring public, too, was apt to be prejudiced against the use of plastics: I have even heard it said that their use confirmed that the Manufacturer was trye.24
ing to put over an inferior product under the cloak of artistic attraction. This opinion is unfortunate, and it would be well to consider some of the various uses to which plastics have been put with great success, and to which development would suit them for a wide range of specialized uses in motor-vehicle construction
GEARS.—A wide range of gears has been developed for industrial engineering, ' ranging from the type used in electric clocks to those of 5-ft. diameter and 10-in. thicknew for heavy machinery (they have also been used successfully for engine timing gears). The main advantages ' of plastic gears which make them superior to the metallic type are:—(l) Capacity for absorbing shock and intermittent stresses which can break down metal gears; (2) silence in action; (3) high strength to weight ratio; (4) little lubricant needed; (5) they will not score metals; (6) they resist the action of most acids and will not rust in humid atmospheres.
BEARINGS.--The qualities required for a bearing are similar to those of a gear, and some outstanding examples have been developed. Heavy rolling machines in steel-rolling mills have been fitted with plastic bearings, and one published report states (in addition to the advantages given for gears) :,—(1) Low coefficient of friction—using water as a " lubricant," the coefficient of friction was one-quarter to one-third that of an oil-lubricated white-metal bearing under running conditions of 400 ft. per min. and 500 lb. per sq. in. of projected siirface; (2) no tendency to score shaft; (3) plastic bearings last three to four times as long as bronze bearings. Amongst the host of other uses are for off-pump gears, pump vanes, thrust washers and ball-bearing races.
In aircraft the uses of plastics are too numerous to mention, outstanding examples being the American " Clark 4'6," the entire fuselage of which comprises two large mouldings, 5/32 in. thick, of Duramold (hard
■-■7,■,2 mood veneer impregnated with phenolic resin). Our own Mosquito is constructed mainly froM resin-inapreg certain special types of plastic, we show here 6e, London. The plastic slots on the stairAirs and show no appreciable deterioration.
flared plywood. Then there is the almost universal use of " Perspex," one of the I.C.I. products, -which has excellent light-transmitting properties, substantially better than even the finest-quality optical glass.
Another example is to be seen at Harrods. In 1939 a series of escalators was installed; instead of the usual beechwood slats, some 20,000 moulded-plastic slats were used, these being fitted to laminated-Bakelite sheets. The moulded slats have a serrated edge to prevent slipping, and the company's chief engineer, whom I recently contacted, expressed every satisfaction concerning their use.
The above examples, in my opinion, warrant development by the vehicle manufacturer, and may give the maintenance engineer some hope of the elimination of the ghastly (to him) effects that result when metal comes into contact with metal, as he appreciates, probably better than anyone else, the t■eavenly ideal of their separation by a film of lubricant, which is seldom realized • in earthly practice. I do not think that the manufacturer need have any fears of the maintenance engineer being prejudiced against the future Use of developed plastics (after all, he has had to accept, and finally test by prolonged operation, all ideas emanating from the factory). To offer him bearings that will not score his crankshafts, etc., made from a substance once chiefly associated with the "fancy goods" and "luxury trades," will probably remind him that diamonds were once in the same class, until utilized industrially, and now give him the best possible finish to many bearings and other parts.
Accessibility (or the lack of its; has always been an important point to the maintenance engineer ; this subject has been mainly considered in the manual sense and not much thought given to "visual accessibility." Most fuel-filter bowls have to be dismantled to ascertain their contents ; few are transparent, but the use of the latter, type is greatly appreciated and often saves time 'and labour in unnecessary dismantling.
BATTERY CASES.—These are still made of a bituminous compound and necessitate peering into from three to 1.2 small holes to ascertain the acid level. Transparent cases would eliminate this difficulty, and, rather more important, would allow for the actual and immediate examination of the battery plates themselves. Radio accumulators have had such cases for years.
IGNITION DISTRIBUTORS.—The cases of these, although invariably made from plastics, are equally invariably opaque. American manufacturers are developing a transparent distributor cap moulded from polystyrene; the exceptionally high dielectric properties of this
material are well suited to this purpose, whilst it allows a dear view of the Contact points, the amount of arcing between them, and the possible " tracking " .between segments, so that they immediately become apparent under running conditions.
Some 20 years ago the Stromberg carburetter fitted to F.W.D. lorries had a transparent float chamber; its resurrection would be welcome as it would enable the contents or possible defects to iT.)e immediately observed. The quantitieS Of oil in the engine, gearbox and rear axle should also be subjects of .eay observation, and not acts of contortionism on the part of the mechanic. Engine oil pumps being nove'very reliable, it is doubtftil if oil-pressure gauges are necessary; some operators have, in fact, removed them owing to the danger of broken pipes; thus a. visual indicator for the quantity of oil is, I consider, even more important.
Most of the .ab(ave come within the scope of the rather loosely applied term, imported from the -U.S.A., "preventive maintenance." The frequency with which some maintenance operations have to be carried out makes one think that the definition should be, " the xreventian of the sins of the designer becoming apparent."
Correlating Needs of Builder, • Driver and Maintenance Engineer _
The manufacturer, like the maintenance engineer, undoubtedly has his problems, and only a profound understanding of each other's difficulties, and the pooling of their energies, will overcome these problems. M.,any Maintenanceengineers commenced their careers with the ;manufacturers, and their acquired knowledge of operational problems consequently fits them to be of exceptional, value, as having perhaps. a more complete understanding. of a motor vehicle, thus their ability to advise the manufacturer should, be apparent. . Most engineers will agree that the v.ehicle. itself causes some ,reaction On the driver. If ea .vehicle be smart in appearance, comfortable and easy to control, it invariably receives more considerate treatment than one not so endowed. Some steps, haye been takeo during very recent years to give.some measpre of comfort to ye.hicie cabs, and I think that it would be well to. pursue this subject, hoping that the dividends received .from considerate handling of the yehkleewill favourably balance any additional initiaI:cost.. I feel sure that plastics will play a great part in future cab-interior construction. The usual sheet metal dOes not " weather "too well, and its high thermalconductivity causes climatic changes. to be reflected almost as accurately ,as. by. a thermometer. A cab so made can be unpleasantly hot in the summer and equally unpleasantly cold in , the .winter. Plastics have done Much to renimve these objections in aircraft, factory. and industrial engineering, and it should not.be difficult to develop them for cab and body construction. The costmay be rather more, but this will ProbablY be balanced by the eliminatibn of the need for repainting eVery second or third year, as in most cases the " depth " of colouring in plaatiCs is equal to its thickness and not merely a protective skin.
Why cab interiors should be painted black or some equality depressing colour is difficUlt to understand ; most factories and offices have undergone substantial improve.: ment in their interior surroundings, with beneficial results to production and the well-being of employees. The improvement of " atmosphere " in drivers' cabs would probably give equally good results. If Perspex will give better visibility, and its ease. of:shaping allow us to dispense with dangerous sight-obseuring windscreen pillars, then, for the benefit of all, 3et us develop and fit such screens.
Plastics in the form ofsynthetic tyres-haVes _recently
come before the public eye, and many have been the 'complaints concerning them. It is unfortunate that the early work of the two British chemists, 'Mathews and Strange, who patented, in 1910, a process of polymerizing isoprene, butadiene, and other substances to form synthetic rubber, was not encouraged. During the same • period sitailar experiments were being made in Germany, whose scientists persisted in their efforts and reached complete success ; to-day Buna synthetic rubbers are world famous.
For many applications synthetic rubber has advantae,r4s over natural rubber, chiefly because it is little affected by the action of oil and petrol, and, is able to withstand some degree of heat. I personally feel that when tyres are fully developed from synthetic rubber they will emerge superior to those of natural rubber, and in considerably less time than that taken to develop the latter, which have approximately half a, century of research and experience behind them..
The most ardent enthusiast of plastics realizes their lirnitations, and that it would be foolish to imagine with them lies 'the solution to all vehicle problems, or that synthetics are cheap; on the other hand, they may be expensive. The urgent thing to realize is, that prime • cost is not the prime, consideration ; the auitability of the material for definite purposes should first be examined, and certain advantages may he discovered wherein true low cost mayhe found. .Generally, the advantage of plastics lies .first in the fact that they possess outstanding advantages for many purposes, consequently I feel that operators and maintenance engineers should encourage the manufacturer to develop their use in motor vehicles, with a view to the production of even better machines.
. Research to Develop Improved StruCtUral. Plastics
Arising out of this view are the cognate problems involved in the production of better plastics. By this is .meant the creation. and manufactnre of specially developed resins possessing properties meeting the ,specific needs of the commercial-motor industry.
Engineers are accustomed •bytradition to assess the value of structural materials in terms of the mechanical properties they associate with, and expect from, metals. .Naturally enough,. organic substances, which constitute the oVerWhelnairig majority of plastics, can never present
,." mechanical picture " identical viith that of metals. There is little hope, for example, that any, plastic can be produced equivalent in tensile strength to high-tensile nickel-chrome-molybdenum steels. It is .SOrnetirries forgotten,, however; that there -is .equally little possibility Of the metallurgist developing an alloy with the extensibility or impact strength of rubber.. Rather,. it would seem, the goal must,be to evolve a material capable of fulfilling the practical 'demands of service, which, in the case of the commercial motor, May be very severe: . Two aspects of this problem have already been tackled and, indeed, largely solved. The post-war development of protein4ike plastics, such as nylon, is already assured, if for no other reason than because of the vastly superior ;tensile strength_which may he attained in this particular group. The problem • of heat resistance is being approached by the ;highly complicated channels of organic synthesis, involving the replacement of carbon in the resin molecules by silicon. Where this move will end cannot readily be foreseen. The bugbear of low impact strength so often associated with many types of thermosoftening and therrno-setting plastic appears td have been overcome by the development of special Long-fibre fillers, iii Conjunction with phenolic, moulding pOWders.