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Successful search for strong, lightweight transport

SSAB Tunnpl : 26 November, 2003  (New Product)
Advanced thinking in high strength steels is one of the distinguishing features of the Superior Trailer Works of Fontana, California. The company is highly proficient in putting to effective use the properties of high strength steels for their interchangeable bodies. Up to 100 percent higher strength, 20 percent lower weight and 100 percent better wear resistance are some of the benefits achieved.
The result is that the company's customers can carry more payload and achieve better operating economy in a highly competitive market. The successes of the Supe-rior Trailer Works are evident, and the company has achieved a very strong leadership on the Californian market. The company has now been nominated for the 2003 Swedish Steel Prize.

The Superior Trailer Works produces bodies for trucks and trailers, principally for construction site transport. The company's bodies now dominate among the many trucks operating in plant and con-struction site work in southern California. As a rough estimate, 90 percent of all new rigs come from the Superior Trailer Works.

'No one in the business can compete with us on lightweight bodies,' declares Jay Pocock who owns and operates the Superior Trailer Works together with his father. 'We have always focused on the customer benefits of our products, which is what has led to our success.'

Easier to unload
One of the company's main products is the interchangeable body which is used for transport to sites that are difficult to access all the way with a tractor and trailer. An interchangeable body enables the driver to first unload the tractor and then drive back and winch the trailer body onto the tractor for the next unloading operation. This makes it easier to unload the rig without having to tow the trailer right up to the work site.

Interchangeable bodies are produced according to two main principles - box construction and semi-tubular construction. Each of these has its advantages and disadvantages.

'Entirely box-shaped construction requires a great deal of material to hold it together,' explains Jay Pocock, who is also responsible for the company's product development. 'The body is heavy, and the parts of the body outside the subframe are also liable to deformation by a heavy load.'

Innovative design
The semi-tubular design also needs heavy reinforcements to withstand the load and is made of thicker steel. This body type also has a smaller volume and is 20 percent heavier.

The new body produced by the Superior Trailer Works, which has now been nominated for the Swedish Steel Prize, has the larger volume of the box, but is made of thinner steel thanks to the in-novative and well thought-out design that stabilises the structure. An example of the way Jay Po-cock has thought through the application is reflected in the design of the body walls.

He has chosen a bent wall profile, with reinforcing folds at the areas where the sheet steel is sub-jected to high loads. The sides and the front and rear gates can thus be made of very thin ultra-high strength, cold-reduced steel with tensile strengths of 1000 and 1200 MPa. The sheet thicknesses are 1.5 and 1.2 millimetres. The floor is made of the same material and is 1.9 millimetres thick. Profiles that form enclosed boxes are welded to the top and bottom edges of the structure. These are also made of ultra-high strength steel. When the front and long sides are joined together, the result is a very sturdy cage that rests on the trailer and subframe made of extra-high strength, hot-rolled steel.

Remarkable weight reduction
'The body has exactly the flexibility necessary to withstand the difficult conditions on our roads,' considers Jay Pocock.

A perfectly rigid body is out of the question and Jay Pocock regards the body as he would a sail. The mast and boom must be rigid, but the sail must be able to move a little to be truly efficient.

'The good formability has made it possible to design the optimum body,' continues Jay Pocock. 'This has enabled us to save a great deal of weight.'

The material used has cut the weight by around 20 percent and increased the strength of the body by up to 100 percent. The weight saving is remarkable, since the company had already been using high strength steel.

Lower weight results in better economy for the customers, and this is the best sales argument the Superior Trailer Works can offer. All payment for freight to a plant project is made on a per tonne basis.

Jay Pocock reaches for his calculator and a piece of paper: 'Every body we supply saves 540 kilos compared to a conventional body. So the total for a rig is more than 1 tonne. At average prices, this yields 7000 dollars annually in increased earnings for every rig. Our bodies are never the cheapest, but the additional cost is soon recovered. After that, it's pure profit for the customer.'

Twice as good at withstanding wear
A positive benefit is the wear resistance of the new body, 100 percent better than in the past.

'I had not expected that high strength steel would have such good properties in this respect,' ex-plains Jay Pocock. 'It's hardly noticeable that the trucks carry gravel, soil and asphalt. There are virtually no scratches on the sheet steel, and the load obviously slides more easily on the surface.'

Environmental requirements also influence the development of the lightweight bodies for which the Superior Trailer Works has become known. The increasingly strict checks made by the authorities encourage low weight. Automatic weight checks are already made on some of the major highways in the US, and more of them are on the way. In California, the authorities have long been working on measures designed to reduce traffic, partly due to the heavy wear on the roads. Strict rules govern the design of vehicles in terms of length, number of axles and axle load.

New projects around the corner
The Superior Trailer Works concentrates on painting and assembly. All preparatory work, plasma cutting, bending and other forming of the sheet steel are done by subcontractors.

'We concentrate on what we are best at, which also includes product development, marketing, sales and service,' says Jay Pocock. 'The remainder is entrusted to our partners.'

So it's a matter of finding reliable partners close by who can handle sheet steel working and who have the competence and equipment to manage high strength steel.

This means that they must stay abreast of developments, since the Superior Trailer Works will not be content with merely staying where they are now. A new project that is just around the corner is a trailer body that has been plasma cut and formed from just one piece of sheet steel. The method will save a great deal of welding and assembly.
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