Tippers: The power of gravity

The first dump body style carts were used in the mining industry and were typically pulled by horses along a railway track. After 1900, a four-wheeled horse-drawn flatbed wagon with a rectangular body lifted with a hand hoist in the front was employed, according to Donald F. Wood, a professor of transportation at San Francisco State University.

The invention of the first motorised tipping truck followed soon after the advent of the car. A simple offshoot of a standard passenger vehicle, it was used to carry coal, the most common consumer good at the time.

In the beginning, people simply relied on the principle of gravity for dumping. The dump body pivoted off centre and, when level, would be locked in place. Releasing the lock would activate the body to dump to the rear. The dump body, when empty, remained locked in a non-dumping position. When loaded, the dump body’s centre of gravity would automatically shift, activating it to dump. Wood has found that some of the first rigid dump trucks designed on this principle appeared as early as 1904 when the Mann gravity dump was built in England.

Wood’s records also show that one of the first hydraulic dump bodies was the Robertson Steam Wagon with a hydraulic hoist that received power from the truck’s engine or an independent steam engine. It was built in 1905.

Meanwhile, the first known Canadian dump truck was invented in Saint John, New Brunswick, in 1920 by Robert Mawhinney. To create the dumping mechanism, a mast was mounted between the cab of the vehicle and the dump box. A cable was threaded over a sheave at the top of the mast and connected to a winch at the base and to the lower front end of the dump box. The dump box was then pivoted at the rear end of the truck frame. A simple crank handle was used to operate the winch, which raised the front end of the dump box, dumped the load, and lowered the box.

Wood, however, has found evidence that the concept has been around in the US since 1911, when the Anthony Company used a dump body based on a mechanical hoist connected to a power take-off (PTO). He also refers to a 1911 Sampson that had a vertical hydraulics hoist, also powered by the truck engine.

Historians agree that tipping trucks have become a common sight around the world since the second decade of the past century, some of them electrically hoisted.

In ‘Yellow Steel’, William Haycraft unveils that Ohio-based company Euclid pioneered the development of tipping equipment in North America. George Armington Jr., a hydraulics designer by trade, came up with idea to create a heavy-duty off-highway truck and a bottom dump wagon. In 1934 the company introduced a 10/11-tonne dump model called the Trak Truk – the first rear-dump truck that was designed for heavy-duty off road service.

According to Heinz-Herbert Cohrs, who wrote ‘500 years of Earthmoving’, some of the heaviest tippers that existed in the 1950s were so-called Tournarockers, articulated steering vehicles manufactured by Texan company Letourneau. Reportedly, they were highly efficient because of a tight turning circles and the fact that the driving wheels managed to maintain contact with the ground when dumping.

Today, virtually all tippers operate hydraulically and come in a variety of configurations, each designed to accomplish a specific task in the construction material supply chain.

While chassis design, tyre size and load and local axle load still predicate the size of a tipping body, it is the choice of building materials that has changed constantly. In the past half century, the industry has seen bodies made from timber, mild steel, aluminium, fibre-reinforced plastic (FRP) and, recently, high tensile steel, which is able to challenge most existing materials in regard to weight and durability. Especially the usage of high-tensile steel has given the industry a push, as it can cater to a variety of cargo, from sand or gravel to coarse bulk cargo or spoil.

Covering a thickness range form 0.7 mm to 130 mm and beyond, high-tensile steel is a wear-resistant material with very consistent features that makes it easy to process. Lately, ultra-thin steel has taken the centre stage, as lightweight vehicles that provide maximum payload are sought-after around the globe. One application where the new, material can come in handy is transportation screws, which can now be made down to less than a millimetre. Other examples include truck beds that can now be made lighter by using a thinner sheet with the same lifetime.

On the design front, the industry has come up with a range of creative solutions to transport and discharge aggregate in the most efficient way. The classic semi-trailer combination is typically being cleared via the rear, which is why it is traditionally referred to as an end dump design. The tipping trailer is typically powered by an electric or pneumatic motor, or a hydraulic line from the PTO (power take-off) mounted on the truck. The key advantage of the design is rapid unloading, however, it can become unstable when raised in the dumping position, limiting usability where the dumping location is uneven or off level.

In addition to that classic design, the bottom dump trailer – often called belly dump – is based on a clam shell type dump gate at the bottom of the tray. The key advantage of a bottom dump trailer is its ability to lay material in a linear heap. In addition to that configuration, they can also be of the 'cross spread' type with the gates opening front to rear instead of left and right. In the US, bottom dump trucks were already dominating earthmoving sites by the 1950s, according to Cohrs.

The side dump design, meanwhile, can boast hydraulic rams, which tilt the dump body onto its side, spilling the material to either the left or right side of the trailer. Most manufactures use twin slave hydraulic cylinder rams that tilt the tub bed to dispose of the material. Experienced operators can place the material on site, and on spot, eliminating the need for additional machinery to spread a stockpile of material.

In contrast to the classic understanding of tipping equipment, Munich-based truck maker F.X. Meiller GmbH & Co KG has recently presented a sleek all-wheel drive tipper capable of dumping on all four directions.

Chinese transportation designer Haishan Deng created a series of concept drawings depicting what Meiller’s new “super tipper” in action that won him a 2007 Red Dot Award for product design from Germany’s Design Zentrum Nordrhein Westfalen, an institution formed in 1955 to promote industrial design aesthetics. Inspired by the movement of quadruped animals, Deng designed the super tipper with independent suspension arms that absorb uneven terrain better than conventional dump trucks.

Whilst Deng’s concept may indicate a preference for the rigid alternative, both dump truck and tipping trailer are facing a bright future in the construction and mining industry. With a history going back to the time before internal combustion engines even existed, the modern tipper has come a long way and will keep undergoing design changes in the future. Despite that on-going change, however, the design concepts has remained true to the original idea of unloading cargo as efficient as possible.

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