Pure Design

Pure Design

We see many specialised vehicles on our roads that have been built for a specific purpose. DANIELLE DU TOIT looks at such vehicles and ponders the body-building challenges they present. A large portion of the transport/freight infrastructure in South Africa is road-based and therefore truck-trailer reliant. We rarely look at such vehicles that pass us on the road and wonder how they were built, who built them, or for what purpose were they built…

Abnormal loads
The National Road Traffic Regulations (NRTR) prescribe certain limitations on vehicle dimensions, and when a vehicle or load can’t be dismantled without disproportionate effort, expense or risk of damage to units that can travel or be transported legally, it’s classified as an “abnormal load”. Vehicles are deemed abnormal as a result of their atypical length, width, height, overhang, load projections and wheelbase regulated by the National Road Traffic Act (NRTA). They’re grouped into an abnormal load classification that’s dependent on width, length and mass. In South Africa the legal gross vehicle mass (GVM) is 56 000 kg. That means the vehicle and trailer, once loaded, shouldn’t weigh more than that.

Mighty mover... a typical abnormal load rig delivering an earth-mover.Among the abnormal load vehicles we’re used to seeing on our roads are car carriers. They fall under abnormal load vehicles due to their length and height. The GVM will vary according to the vehicles being transported: sedans and hatchbacks weigh less than sports utility vehicles (SUVs) and light duty vehicles (LDVs), and will take up less space.

Another influencing factor regarding GVM and the number of cars on board is the build of the car carrier. Standards are different for each manufacturer. Some carriers will carry three cars while others may carry nine.  A challenge is engineering a load/offload operation that’s easy to use and in the shortest timeframe possible. “Ease of operation and load/offload time is a huge factor,” says Jovan Enslin Jnr, of Pretoria-based Homez Trailers and Bodies.

“Time is money in the transport industry.” The car-carrying vehicles at Homez Trailers and Bodies are manufactured using a product called Domex, which is high tensile steel. Tensile steel strength is the maximum amount of pressure that can be applied to a material before it begins to stretch. The unit used to measure the amount of pressure is MPa – megapascal. Normal steel has a tensile strength of about 355 MPa, whereas Domex has a tensile strength of around 700 MPa. “By using high strength steel you can reduce material thickness without sacrificing on strength and gain on payload,” says Enslin.

One of the most important safety features is brakes. On a car carrier, the tyres and rims are smaller than those used on other trailers, so the brake drums, liners and boosters are all smaller. By law all bulk carrying vehicles should be fitted with anti-lock braking systems or, as it’s more commonly known, ABS, which allows the wheels to continue turning while braking, thus helping to prevent skidding. ABS also maintains “steerability” and generally reduces braking distances, prevents jack-knifing and reduces tyre wear.

When large-scale mining equipment or giant transformers have to be moved, a lowbed trailer is usually called in. These are built specifically to carry large, heavy loads – much larger than the allowed GVM, and are categorised as abnormal load vehicles. They’re able to transport large loads due to their special design and engineering. Often they’re semi-trailers and thus without a front axle. As with most trailers, special care is spent on building the lightest but strongest possible trailer. Many will be built using Domex but the neck may be manufactured utilising a different product to ensure extra strength and durability.

Due to their size and nature, all components fitted have to be application specific. The size of the brake boosters is increased and the brake linings are made of a special material to withstand a higher brake force and to reduce friction and heat. “The suspension systems on these lowbeds are heavier duty to allow for the weight it needs to carry,” says Chris van de Wetering of Afrit, which builds a 53 ton tridem axle lowbed. “We fit axles with a higher load capacity per axle: 13 tonne capacity as opposed to a nine tonne.”

A side tipper is not classified as an abnormal load vehicle.Side tippers, although quite large, don’t fall under “abnormal load” vehicles: they’re classified as bulk trailers. These vehicles usually fall within the 22 meter permissible length and don’t require any special permits specified by NRTA. They usually transport maize, corn, sunflower seed and coal. They come in many sizes, depending on application and customer preference, but usually the payload capacity is between 34 000 kg and 37 000 kg. The materials used to build this vehicle have to be of high quality and durability, so high tensile steel is also used to keep strength up but weight down.

The advantages in using side tipping trailers are that they have a low centre of gravity and are therefore more stable on the road. Equal load distribution also means the vehicle is steadier. They’re also able to transport and unload large rocks and high impact materials – and they allow for more trips each day as opposed to conventional back-end tippers, as they’re manufactured in such a way operators are able to run a tandem truck trailer system. Side tippers should preferably use air suspension systems to provide stability during the tipping process. Air suspension also allows for a softer ride, thus putting much less strain on the load being transported.

Tankers are also specialised vehicles seen on our roads. These large trailers can be built to transport almost anything, from milk, water, petroleum and diesel to highly flammable and dangerous goods (DGs) such as liquefied petroleum gas (LPG) and sulphuric acid. The differences between tankers are vast. Tankers used to transport food grade products are built from stainless steel for hygiene reasons and compartmentalised. Many also make use of a cladding for insulating purposes. Tankers used to transport petrol, diesel, solvents and water are built using aluminium, primarily because of its light weight and pliability of the material. They’re also compartmentalised, primarily because of safety considerations and the ability to distribute to more than one customer if needed.

Tankers transporting LPG (such as butane and methane) are built using much thicker, stronger steel due to the pressure being exerted on it by the contents. The shape of a tanker also distinguishes it – for example, food grade and petroleum or LPG. LPG tankers are cylindrical due to the strength that shape gives under extreme pressures as opposed to elliptical, which is less strong.

Though there are many ways in which tankers can be built, all must meet certain criteria and design codes. Tank Clinic, a manufacture and repair centre for tankers (with branches in Johannesburg, KwaZulu-Natal and Cape Town), X-Rays all its welds to check for any weaknesses, conducts a water pressure test and gets approval by an authorised inspection authority.

When transporting dry products, such as lime, cement, ash and sand, the operator will need a different type of tanker, and that’s where the “spitzer” – or pneumatic tanker – comes in: it’s a specialised transporter also built with aluminium for reduced weight. They can be specially designed to be emptied in two ways: the first being bottom dumping, which is self-explanatory. There are strategically placed inlets and usually one or two outlets under the vehicle that are opened and the product allowed to empty. The inlets provide air flow so as to not introduce a vacuum. The second method is via a pneumatic blower. This involves moving or pushing the product using a compressor attached to the vehicle and utilising energy produced by the vehicle’s engine. This is called a power take off (PTO) pump and it converts rotary power to hydraulic power. A PTO pump is used in most hydraulic applications, including side tippers, back-end and front-end loaders and skips units.

Walking floors
“A walking floor trailer is the most amazing machine.” That comes from John Rivvet Carnac, an industry expert. “They don’t tip and therefore won’t fall over.” Walking floor trailers are used to transport various products and require direct top loading which maximises payload. However, the main benefit of a walking floor is that it can unload itself. The floor is hydraulically driven via a conveyance system that pushes the load out through the back. All walking floors work on the same friction-versus-area principle, generally using 24 slats. Every third slat moves forward under the load; the second group of every third slat moves forward under the load; and the final group of every third slat moves forward under the load, the last stage being when all the slats move back towards their starting position – effectively pushing the load out toward the discharge end of the vehicle. Walking floors lessen the need for manpower, and save time and therefore money. Depending on the application requirements they’re manufactured using aluminium or Domex. A Domex walking floor is more suited to heavy duty work, such as offloading scrap metal, logs or concrete.

Aluminium is more suited for gravel, sand and animal feed, with the maximum load designed to move 36 tons. A walking floor almost completely eliminates the need to sweep the floor after offloading and, with regular maintenance plus the installation of an oil cooler, more than one offload can be done every hour.

So far the vehicles dealt with have been large, dwarfing humans and regular cars. However, there’s rarely a limit to what man can build. An American company called Letourneau manufactures mining equipment and has built a machine capable of moving 73 tons. The L-2350 Generation 2 is the world’s largest front loader. It has a 7,31 meter lift height and a 3,5 meter reach. Each of its rubber wheels is driven by its own independent motor. It also weighs a staggering 267 tons. Width and length respectively are 6,76 meters and 20,3 meters.

Another monster is the Caterpillar 797F off-highway end-tipper, a two-axle vehicle developed for use in mining applications. The 797F is so large it has to be assembled on site and needs approximately 14 semi-trailers to transport the cab, tyres and dump body. It can’t be driven on normal roads due to its exceptional size and requires disassembly for transportation to a new site. It can haul up to 363 tons. The vehicle weighs 624 tons and has 10 disc brakes for its front wheels and 16 for the rear. Its fuel tank holds 3 785 litres. By comparison, a Volkswagen 2007 Golf Chico has a 49 litre capacity tank. The 797F stands 15,7 meters high – about the same height as a three-storey building. There are two operating in South Africa, both with Anglo Coal in Richards Bay.

There’s a vehicle for almost any application. And if not, there will be a manufacturer capable of building one to your specific needs. This article has just touched the surface of specialised vehicles and what they can achieve. A whole magazine could be dedicated to reporting on such transporters, their achievements and milestones but, as with many success stories, there are as many failures and just as much could be written about those. And after a year the vehicles featured in this issue might well be obsolete due the advances in technology and constant innovation. Maybe in a year we’ll look back and see how manufacturers are struggling to keep up with the times.

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