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Tipping safety: a matter of degree

24th October 2002
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Which of the following most accurately describes the problem?

Like wet weekends, the topic of tipper stability comes around regularly. And a recent contract to supply 44-tonne trailers to Lafarge Aggregates subject to the IRTE Tipper Stability Standard has only re-focused attention on this subject. Brian Weatherley reports on GT Fruehauf's take on the matter._

• Back in the eighties at an RHA TipCon tipper stability seminar. Crane Fruehauf's tipper product manager Angus Spooner surprised a group of hard-bitten tippermen by declaring that an artic tipper was more stable than an eight-legger. Not an easy sell, given the audience.

Fast forward to 2002. "I'd probably say the same now," says Spooner defiantly. That confidence isn't a matter of pure bravado. In the late 70s and early 80s, worried by the number of artic tipper roll-overs and the growing interest of the HSE into them, Crane Fruehauf conducted its own series of stability tests. Spooner picks up the story again.

With no ruling or guiding legislation in force. we set out to create the safest practical tipping semi-trailer. This culminated in a tipper chassis design which would provide the maximum resistance to rollover without any external aids and with an attractive unladen weight."

Torsional rigidity

The process ultimately created Fruehauf's trademark chassis with its four large box section cross members, which offer tremendous torsional rigidity. The proof of the pudding was that during its tests Fruehauf demonstrated it could tilt to 9.5 .

"One of the results of our work on stability." recalls Spooner, "was the issue in 1992 by the IRTE of its own Guide to the specification of more stable tipping trailers." The IRTE's guiding

document defines two standard! Class A which says that a vehii should achieve 7 of sideways tilt wl the body fully raised; and Class B whi demands 5 . The standard h remained unchanged for the past years and was recently used by t aggregates giant Lafarge as the sta dard for awarding a major order 1 over 20 44-tonne tipping trailers.

The three contenders for the orde —CT Fruehauf, Stas and Wilcox—we all required to demonstrate they col meet the IRTE Class A standard. T trials were conducted at the Dine tilt table at Chertsey, and adjudicat by Lafarge with the manufacturers close attendance. "We all got througl although in varying degrees of paid admits Spooner wryly, "The key iss was 7," says Spooner. "And they c always try and go a bit further. We eight—but it wouldn't settle down we backed off to 7.61" (United Trai also recently confirmed its Class compliance—see CM1-8 August).

For the record, the Fruehauf tip' had a "modest" 30-tonne payload board, While insisting that the stabil standard is "at the heart of what are pursuing—Fruehauf's claim that our models meet the Class A stand2 is as true today as it was in 198 Spooner cautions: "It's just an empi cal standard that allows you to mak comparison. No one in their right m would actually do this—would they?"

It's a good question. Commen Motor has long held the opinion that I

TE standard should be viewed as a ,fety margin, not a maximum target aim for when tipping on uneven ound. Indeed it's a view the IRTE holds ;elf.

The tests themselves have created eir own mini-controversy over wither they should be conducted with e trailer suspension inflated or with e air dumped, allowing it to settle on e bump stops. GT Fruehauf is "antiimping". "It doesn't represent noral practice, and it's probably riot Imething many tyre or axle manycturers are likely to back up," Heves Spooner. (See industry news.)

ro-dumping

as, however conducted its test with e trailer air dumped following spelc recommendations from SAF in ,rmany, its axle supplier. One pronging argument is that it prevents iy sudden rush of air across the axles the load discharges, and the SUSnsion equalises, thereby avoiding ansmitting any rapid rebound or otion into the raised body.

However Spooner insists: "Loads nt come out that quick—or shouldn't the driver is careful! We specifically In't dump the air and say that with e suspension fully pumped up you get 1round load of some 32 tonnes evenly read across the bogie and sufficient ame stiffness. Dump the air when you and you could get up to 28 tonnes on e rearmost axle—we don't think at's desirable.

"As far as possible tests ought to replicate what you'd do in real life."

"If you were tipping into a road paver you'd never dump the air; we tell people specifically not to do it."

Lafarge ultimately placed an order for 28 trailers with Wilcox whose 101m long monocoque body is mounted on a Wilcox-designed and Tirsan manufactured high-tensile steel chassis with SAF running gear.

Despite losing out Spooner remains sanguine. "At Fruehauf we say well done' to United, Wilcox and Stas for designing their trailers to meet the II1TE Class A standard. We've been pursuing the practicalities of improving stability and safety since the 1970s—and we're pleased that others are taking the issue and the standard seriously." Following on from the Lafarge trials, there are moves within the IRTE to revisit the current tipper stability standard, Meanwhile, perhaps more important than achieving the "ultimate" stability test result is the fact that GT Fruehauf maintains market leadership in tipping trailers. "We're still very busy," says Spooner. "In fact I wish we could make more!"


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