The very first version of a tipping truck used to haul and dump material would have been nothing more than a simple two-wheeled cart drawn by a horse. The loaded front body was hooked, and when unlatched, would dump. The concept was simple and efficient, so it was readily adapted when the motorised vehicle entered the engineering stage in 1888.
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.
According to Donald F. Wood, a professor of transportation at San Francisco State University, 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 and laid the foundation for front and side-tipping equipment as we know it today.
Nowadays, virtually all tippers operate hydraulically and come in a variety of configurations, each designed to accomplish a specific task in the bulk material supply chain. They are not only used in the mining and construction industry, but also cart bulk freight like grain and fertiliser, sand, gravel, pellets and even pet food. They are typically powered by an electric or pneumatic motor, or a hydraulic line from the PTO (power take-off) mounted on the truck.
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. In the mining and construction segment, the side tipper has come to dominate the industry. It 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.
As opposed the traditional end dump design*, the side tipper is almost immune to tipping over while dumping. It is, however, highly likely that it will tip over if dumping is stopped prematurely. Also, when dumping loose materials or cobble-sized stone, the side dump model can become stuck if the dumped load is fouling the path of the wheels. Depending on the application, the problem is tackled by experimenting with a varying dump angle. Some manufacturers reach a dump angle of 50° – ensuring less material will get stuck in the tub, thus preventing tipping over or cracking during the unloading process.
Regardless of the tipping angle, the body must be strong, yet flexible enough to allow for bending and twisting without cracking. While chassis design, tyre size and load often restrain the size of the tub, the choice of building materials has changed constantly to meet that challenge.
In the past half century, the industry has seen bodies made from timber, mild steel, aluminium, and even glass fibre-reinforced plastic – but it is the recent advent of high-tensile steel has given the industry a notable push. The material is able to challenge most alternatives in regard to weight and durability. Tough and malleable at the same time, it can cater to a variety of cargo, from sand or gravel to coarse bulk cargo or spoil – a key advantage in the side tipper market, which is focusing on the mining and resources segment first and foremost.
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 to help cut fuel consumption and reduce adverse environmental impacts.
Design-wise, some companies have experimented with a bowl-shaped body to free the tub of body runners, stiffeners and cross members and thereby reduce tare weight and heat distortion. Based on a cradle-like chassis, the bowl shape is meant to provide full load support over the length of tub and retain contaminated liquid in the bowl base, which could be useful in the mining industry, for instance. One company specialising in the bowl design is Australian trailer expert, Azmeb.
Also in Australia, local transport company, Kalari, has introduced a 'side tipper tanker' to allow both wet and dry material to be carried at the same time. The innovative vehicle is used, for example, when transferring water and slurry (in the tankers) and dry tailings (in the side tippers) from a customer's separation plant to an outback mine. According to Kalari, the development of these vehicles reduced the number of trucks required to service the client and led Kalari to win an Australian Freight Industry Environmental Award.
South Africa’s SA Truck Bodies can also offer a dual bin design, with to tubs sharing the same chassis. The company is currently producing two differently shaped bodies, a V-type bin and a so-called Volume model, which can offer more payload, but is not as bulbous as the Azmeb design, for instance.
By its own account, the side tipping design at large – regardless of body shape, layout or construction material – is the brainchild of US company, Side Dump Industries. “At SDI, we believe in the power and profitability side dump trailers provide to so many industries. In fact, we developed the side dump technology used worldwide today,” the Nebraska-based company states openly. “Most of our competition still manufacture their trailers based on our early design.”
Employing deep frame rails, SDI trailers are designed so they can carry the load over the suspensions of both trailer and truck, thereby reducing the overall stress on the frame. For the same reason, the company is also using bolted cross-member and hucked pivot connections, allowing the frame to flex with no cracking.
On the equipment side, the hydraulic hoist can make or break the whole project. The quality of steel and welding are extremely important to the integrity of the cylinders, as they are put under a lot of stress from constant extending and retracting.
Around the globe, side tipping equipment is mostly built in a classic semi-trailer configuration, but high performance solutions are now gaining ground as well. In Australia and Argentina, the B-double design has proven a viable alternative, for instance – at least up to a certain payload. Experience has shown that the pressure of carrying too much weight over the length of a B-double can cause serious harm to chassis, axles, suspension system and brakes, especially in off-road applications.
That’s why the old truck and dog combination still has a solid fan base as well. In Australia, it can reach a size of 25m and boast up to six axles on the dog trailer, making for a payload of 43 tonnes and more.
Around the globe, and irrespective of the industry, it is the low centre of gravity that is responsible for the side tipper’s on-going success. Plus, it has a second safety advantage over the end dump variant, as it gives the driver a perfect view of the load whilst unloading. The ability to stock pile material in a row has made it an indispensable tool in the construction and mining industry, allowing for equal load distribution and ensuring a safe work environment.