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TOPPLING FEARS

14th December 1985
Page 47
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Page 47, 14th December 1985 — TOPPLING FEARS
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Which of the following most accurately describes the problem?

Can tipping semi-trailers be as safe as rigids? Jack Semple looks at the latest tests and developments to persuade operators that they can

EARLY this year a tipper fell on the cab of an ICI artic (pictured above) at a depot in Derby surrounded by houses, Had the tipper body punctured the barrel instead of the cab, the mix of ferrous sulphate and nitric acid which would have resulted would have given off a highly poisonous gas.

The driver miraculously escaped serious injury by getting as low as possible in the cab when he saw the tipper falling.

Stability of tipping trailers has been a concern of operators and manufacturers since the law was changed to allow 38tonners on to Britain's roads, thereby increasing the attractiveness of attics against 30-tonne rigids. Incidents like the one at Derby also explain the interest of the Health and Safety Executive. which has grown since tipping trailers became more prominent during the miners strike. Traditionally, tipping trailers have been regarded as 10 times more likely to roll over than rigids. Improvements in design have probably reduced the likeldiood of rollovers among some of the newest trailers, but risks are still perceived as high.

Leading tipping trailers manufacturers have put a lot of money and effort into improvements of standard tippers. This month Crane Fruehauf; which claims to have done more than all y maker, challenged any chassis cab manufacturer to take on its CF 38-tonne tipper with a 30-tonne rigid on a tilt test.

CF is under no illusions that rigids could be made inure stable than artics. but claims that its 38-tonner would beat any 30-tonner at present in production. The company continues to use stability as a strong selling point — although it adds that no operator is willing to put a value on safety.

The company's 38-tonner, launched at Tipcon in 1984, has been replaced with a modified and strengthened version of the older bath-tub design. The strong alloy extrusion which formed the bottom rail of the original (of which 250 units were sold) was found to be too rigid. This set up a resonance in service which caused cracking in the side post welding. The modifications have not adversely affected stability, and the increased flexibility may even have improved this aspect, CF says.

No tests of tippers arc required as the law stands at present beyond the general duty under the Health and Safety at Work Act that the equipment should work safely itinstructions are followed. Nevertheless CF and other companies continue to test tippers and search for more information about how they behave in operation.

Unfortunately, while most people agree on the need for improvements, there is a marked disagreement about the best way to test trailers. CF's method is to use a tilt bed. The tipper is loaded, raised, and then slowly tipped laterally. CF claims that its trailer can remain upright with 9.5 degrees of sideways tip following recent tests when the trailer was loaded with sand.

In addition to looking for signs that the tipper is going to topple, test engineers fix straining gauges to the chassis and body to detect signs of failure elsewhere. This method of testing best mirrors the strains to which tippers are subjected in operation, CF says.

BUT Dr Bob Keen of Bristol i'olytechnic disagrees. Ile has been researching tipper stability or five years,. recently for the I ISE. "Drivers do not try and tip off the side of a cliff," he maintains.

Keen uses different test equipment and techniques. Instead of a tilt bed, he uses load cells, axle-load gauges, strain gauges and moveable 1.6-tonne concrete weights. His trailer, from Craven Tasker with tipping gear from Drum Engineering, never tips at more than three degrees from vertical — the worst slope on which a "prudent" driver would tip, says Keen.

Two important differences from CF's tilt bed tests, apart from the degree of tilt, are that the trailer can be loaded unevenly, and that the trailer is raised while it is at an angle of sideways tilt.

One of Keen's most important claims is that a tipping trailer is most likely to fall over when it is raised to between 15 and 20 degrees from horizontal, rather than the fully tipped position of about 45 degrees. Exact details were still being calculated this week from test results.

Load distribution is one of the most important factors in rollovers, and explains why tippers can topple even when they are on level hard standing. The Derby incident, for example, was almost certainly caused by the load sticking unevenly.

Wind, another factor in stability during tipping, was found to be less important than many operators believe. . Some form of formal testing for trailers or design would be the natural extension of all the test work being done on tippers at present, says Keen, although the details could prove difficult in practice.

"We hope to be able to produce a computer programme for bodybuilders to use," says Keen. In the meantime, the HSE will shortly be bringing forward guidance notes on tippers.

Keen is impressed with the Craven Tasker tipper he used in his experiments. He stresses that his major concern is not about the large manufacturers but with smaller firms whose design and standards of assembly may not be up to scratch. "You only have to be a couple of mm out at the rear to be way out of line at the front. Sometimes you can see by eye that a tipper is not straight. "Buy from a reputable manufacturer with a history of testing his vehicles," is Keen's advice.

Truck manufacturers could do more to ensure the quality of rigid tippers, he adds.

Drivers have been surveyed during the research at Bristol. "I've been impressed by the level-headed approach of most drivers," says Keen. But there is need for more information for them, he believes. And a few can be irresponsible, for example going off for a cup of tea after starting to tip.

ALTOGETHER different solutions have been developed by various manufacturers to give trailers more stability during tipping. George Neville, for example, is promoting additional side landing legs to help keep the tipper level.

More radical options include doing away with the tipper mechanism altogether. Walking floors are gaining popularity among operators who have had major problems with rollovers and who arc prepared to pay substantially more for their trailers initially.

The American concept of tipping the whole trailer on a platform to discharge is already being used by Carlsberg and British Sugar, and Keen predicts that more specialised operations will use this method in future.

Despite concern about their stability, tipping trailers seem almost certain to become increasingly popular as the main vehicle for moving large volumes of' material around the country. There is no "maximum size", dictated either by law or design limits. One tipper has been built to 71m3 (96yd3) and is probably the biggest in Britain so far.

The test, as always, is what sort of material will it be unloading? Stability has been enchanccd by sonic makers by improved design of the chassis, bodymounting and suspension (CF strongly recommends air rather than steel springs).

Operators' experiences seems to confirm that some tipping trailers are substantially more stable than others, although the new generation of designs have still to prove themselves in lengthy service.

But no matter how good tipper designs arc, prudent operators and drivers will be aware that all tippers have the potential to topple.

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Locations: Derby, Bristol

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