You might think that here isn’t much to be said about truck bodies that we haven’t said before. However, this month, we’ve seen something entirely new – a bottom-discharging grain truck. It has a unique design which the maker says increases load and productivity.
For a long time, tipper truck bodies have remained virtually the same the whole world over since the first serious examples were developed for use on the Hoover Dam back in the 1920s. Now, though new materials and specifications are being introduced to cope with the weight, punishment and abrasion hauling rocks, sand and gravel can inflict. Both roadgoing and non-road trucks suffer from the same problems – wear, damage and carry back. All of which add up to a loss of productivity and profit.
Gorica, a firm that builds bodies has recently completed an order for a slightly less usual raw product though – grain. It might not be the most abrasive of substances, but it does require a very specific design as Gorica’s Paul Austin Price explains: The chutes open from the bottom to discharge, and feed from the top. It’s all quite straightforward, but much more efficient than using conventional tipper bodies. In fifteen minutes they can discharge fifty-two tonnes” he says.
By contrast, the old tipper bodies could only carry about 40 tonnes and moving the grain took longer.
“The old way just caused chaos, but by doing it this way, the trucks are in and out very quickly” said Brian Barriskill, logistics manager of Al Ghurair Foods He added: “We can get along with less trucks with this system, because a lot of what we do is routine shifting, so that is the reason why we went along these lines.”
The bodies are pulled mostly by Renault trucks, though the firm operated a mixture of Scainia, Volvo and also Tata trucks. “We like to mix and match brands, because some of the trucks are more suitable for different operations” Barriskill said. He added that it is a good time to buy a truck head at the moment. “The market is very different to what it was 18 months ago. Then, you were lucky to get a truck, now there is no problem to get just what you need.”
He added: “Last year, we went to see some used trucks that had been converted to left hand drive. It was very much a case of if we didn’t buy them there and then, they would have been gone the following day.”
“For the tipper trucks we did use all Scania, now they are used for more specialised long distance work.”
“The Tatas we have found quite good, which we normally use for work up to Ras Al Khamiah and the like. They are made by Daewoo and built in South Korea.”
However, it is the Renault fleet that has proved the most useful for hauling the new top-loading, bottom-discharging bodies. In fact the bodies are part of a larger, more intergrated systemwhich involves being fed by an overhead silo, a bit like what has been used at gravel quarries for many years. Once the grain has reached its destination, the bottom discharge chute means that the product can be fed directly onto a conveyor and straight to a mill.
Although flammable, grain is not explosive like flour can be, so there was no need to make these bodies blast proof or anything like that. However, they did need to be sufficiently strong to take round-the-clock working, and the design had to be such that the grain could flow out. “Inside the walls are angled, so that all the product is removed,” head truck operator Ahamed Syed explained. There is an electronically controlled fabric roof on the bodies so that contaminants won’t enter the food stock while driving.
EJECTOR
Elsewhere in the PMV world, new designs for truck bodies are constantly being dreamed up. “During the spring we visited some of the major manufacturers of dumpers and presented our new design concept. We received many favorable reactions,” says Per-Olof Stark, from steel making operation SSAB Plate.
Making bodies that tip out of harder material is one way of holding back wear, but Caterpillar has come up with an entirely different concept: Simply make the ejector system differently, so that the load is pushed out, rather than lifting the back.
A good example of this is the 730 Ejector articulated truck, which incorporates the self-cleaning ejector mechanism that allows material to be spread and dumped on the move without lifting the body.
Because the body is not raised, the ejector truck can work efficiently on sites. As such, the truck can work on sites where stability issues or overhead obstacles limit the the use of conventional dump trucks. The ejector body also offers clean load ejection to eliminate production-robbing carry-back, where material is not fully ejected from the truck.
The load ejection concept delivers many benefits. Material can be spread while the truck is moving to cut cycle time, decrease power train loads and reduce the amount of support equipment needed for spreading and dozing. The ejector also prevents material from adhering to the inside of the truck body after the dump, so payload can be maximized, improving productivity, reducing fuel consumption and lowering cost per tonne. Ejecting a load without raising the body increases stability, so the truck can work on inclines, side slopes and in very soft underfoot. The truck is also useful in tunneling and underground applications and on sites where overhead obstacles, such as conveyors, power lines or bridges, interfere with dumping.
The reinforced ejector body is made from high-yield, heat-treated steel. Its top rails incorporate the same steel used on the Cat 769D off-highway truck. The ejector mechanism includes a high-strength blade and technology similar to that proven on Cat wheel tractor-scrapers. The ejector body is designed to work with small rocks though (up to 150mm diameter), so such a thing would not be suitable for applications like offshore projects, where moving bigger rocks is required.
ALUMINUM
There are other projects in the pipeline, too. One technical research paper suggests a design concept where even the largest non-road mining truck body could be made from aluminum. This might sound ridiculous, as we all know that this material is just too soft for such use, but the academic study provides results of a field service history with developments in various designs. The study, found on mining website onemine.org argues that aluminum truck bodies are not the novelty they might seem. Mention is made of current US usage and predictions given as to future development of aluminum bodies in the mining industry. The paper notes that way back in 1932 an aluminum unit proved very satisfactory in service on the Hoover Dam project but at that time the only high strength aluminum alloys available were not weldable and with the high cost of construction, a sound economic case for an aluminum body could not be made. After World War II great advances in aluminum welding techniques, using the inert gas shield, combined with the development of high strength alloys with good welded properties and welding characteristics changed the whole picture. Welded aluminum bodies were rapidly developed and by 1958 attention was again focused on the use of aluminum for off-highway truck bodies.
The paper goes on to explain how a Canadian firm, Alcan, embarked on an extensive development program to prove the durability and economics of aluminum truck bodies for the mining and construction industries. The first step was to design a prototype aluminum body which took particular advantage of the fact that the ‘modulus’ of aluminum is only one third that of steel. This means that within the elastic range, aluminum moves three times as much as steel which makes it more flexible and capable of absorbing much greater impact shocks.
The study suggests this design will be the best. Time will tell if this analysis is correct.