Technical and Industrial
Page 48
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Alloy Wheels For Heavy Vehicles
DUNLOP light-alloy forged wheels fitted to the new 4,000-gal. six-wheeled Thompson tanker (described on page 52) in place of 10 steel wheels provide an overall saving of approximately 350 lb., which is equivalent to 46 gal. of petrol of average specific gravity. The tanker is equipped with independent front-wheel suspension and the low weight of the wheels should be at least marginally beneficial with regard to the operational characteristics of the springs.
The wheels are of the three-piece type of 20-in, diameter and incorporate a cadmium-plated steel flange and selflocking ring weighing 8-5 lb. and 10-5 lb. respectively. With a rim width of 7 in. a front wheel has a total weight of 64-5 lb. whereas an equivalent steel wheel weighs 100 lb. The rim width of a rear wheel is 6-5 in. and the weight of the wheel is 63 lb., the weight of a comparable steel wheel being 98 lb. Tyre equipment comprises Dunlop RB6 rigid-breaker 10.00-20 covers at the front and 8-25-20 covers at the rear.
A fatigue life at least comparable with
that of a conventional steel wheel is claimed, so long as due care is given to tyre fitting and handling to avoid abrasion (and consequent corrosion) of the steel and aluminium sections. The wheels are of L77 alloy.
It is notable that forged wheels are preferred to the cast type (as fitted to racing cars) for commercial-vehicle applications because their use eliminates the need for X-raying the sections for blow holes and thus reduces the amount of scrap material.
The wheels are now produced by machining from forged billets, the total machining time being about 10 hr. A press forge would, however, be employed if increased demand justified production in quantity and this would reduce machining time to about 10 mm. If tubeless tyres became generally acceptable to commercial vehicle operators, a wheel with a single-piece rim may be developed with a welded-in disc, which would considerably reduce the price differential between steel and aluminium wheels.
P.A.C.B.