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Page 51
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LEAF companies like TPI and Dawn
press, using hot press techniques, have proved immensely tough as well as scruff and gouge resistant.
OF LIFE
I Air suspension is now becom.7, such a common fitment on avy trucks at least, that leaf rings tend to be thought of as 1-fashioned, even crude.
onoleaf and parabolic minimum sually two or three) leaf steel rings as alternatives to the traional multi-leaf cart springs, are longer a novelty. They cut unlen weight, but need more mping to compensate for the sence of inter-leaf friction. But composite, glass-reinforced istic (GRP) materials are set to ing leaf springs a new lease of All Leyland Daf 200-Series adds have had G101 composite rings since 1985. And earlier s year they were also adopted Iveco for the rear suspension up-to-3.5-tonne Daily (which has front lependent wishbone suspension). At the Frankfurt Motor Show this year was evident that GRP springs are here stay as a means of reducing weight. e tare weight of a 17-tonne GVW fourweler can be reduced by over 100kg if mposite springs are substituted for steel rabolics, and the saving can be over Okg against multi-leaf springs. Mercedes-Benz is fitting out a pilot Leh of 1500 vans — 2.8-tonne GVW 8D/210 models — with GRP springs er the next few months. The 208D van Frankfurt had British-made GKN rings on the front; those at the rear re supplied by BASF.
is Mercedes' intention, provided the exriment works, to dual-source both front I rear springs from the two suppliers. avier GKN composite springs
fitted to a 7.5-tonne Mercedes 12 fire-appliance chassis which I be monitored in service before ing cleared for pilot production. Meanwhile MAN is exrimenting on heavy chassis — )se with 11.5-tonne rear and iren-tonne front axles — with 113 auxiliary or helper leaves. e company's development enleers say it will take time to ablish confidence in the durabil
of non-metallic springs among avy-truck users. Only then will rings with composite main yes be considered for producn. BASF is the current ourite with MAN, though ings from GKN and Hoesch icar are also under evaluation. In the United States General )tors' Inland Division has had ne success wtih GRP springs in isenger cars. Heavier GM units semi-trailer bogies have been ler test in the UK for three or ir years with Rubery Owen Rockwell, in running gear supplied to Montracon, among others.
It is frustrating, for those seeking to promote the wider acceptance of composite springs, that epoxy resin-based GRP laminates are seen by heavy-vehicle operators as a cheap substitute for steel in low-volume cab-shell manufacture.
In this application, such as Foden and Dennis cabs, ambient temperature curing is used, and though the finished mouldings are as strong as pressed-steel they tend to shatter rather than dent.
ERF gave the image of GRP laminates a boost in the mid-seventies. The first B-series cab and all subsequent C, CF and E cabs use mouldings produced under high temperatures and pressures. The strength of hot-pressed GRP laminates became apparent during the sixties and seventies. GRP-faced body panels with a plywood or insulating foam core made by press, using hot press techniques, have proved immensely tough as well as scruff and gouge resistant.
Use of epoxy-based glass-fibre laminates on vehicles springs is a whole new ball game. But the use of temperature and pressure in the moulding process has been the key to success in spring manufacture, with GKN leading the way.
At GKN Composites' production plant at Telford, in which D=1.5 million was invested in 1983 (and where pressed-steel Leyland Ergomatic cabs were made), security is as tight as at Michelin's factories. The manufacturing recipe which enhances the durability of the finished springs in hostile environments is top secret.
Sales director Chris Morley is confident that GKN remains ahead of its foreign competitors in composite spring development. The production contracts to supply Leyland Daf Vans, Iveco and now Mercedes speak for themselves.
Spring research and development by GKN Technology at its technical centre in Wolverhampton is now self-funding. The next challenge for Morley is to break into the heavier truck market. This is where GKN, like MAN, acknowledges that durability must be demonstrated if confidence is to be established.
COMPROMISE
An ingenious compromise has been reached by GKN with those truck manufacturers whose reservations prevent them switching in one jump from steel to GRP for spring specifications. The hybrid leaf spring devised by GKN, working closely with steel spring maker Tinsley Bridge Industries, has two leaves.
One is steel with traditional eye-ends; the other is composite GRP and takes the main bending loads. The two leaves are clamped together at both ends, where the composite leaf is enclosed in endcaps moulded from a new lowfriction non-epoxy GRP material called Wearlite.
Fore-and-aft axle location is taken care of by the eye-end bearings of steel saddle end fittings employed where a hanger or shackle pin attachment has to be made, as in the now familiar Leyland-Daf van applications.
It remains a rule for GKN that laminate strength must not be jeopardised by driling or cutting the springs' longitudinal glass fibre: hence the mould-in-location dimples in conjunction with clampheld end fittings. Attachment to the axle in the middle of the spring is via two dimple-located