Stronger than steel

It is often thought that steel is stronger than aluminium. However, with the correct manufacturing approach, aluminium rims can be stronger, lighter and better for the transport industry than those made from steel.

Aluminium rims are formed by forging or casting the metal. During the forging process, the wheel is manufactured from a single block, which is heated up and pushed into a mould at a pressure of 800 000 t. Casting requires the aluminium to be melted and poured into a cast.

John Jewiss, MD of Arconic South Africa, which manufactures Alcoa aluminium rims, explains that cast aluminium rims are weaker due to impurities. Cast aluminium wheels are often used for cars to ensure that the wheel crumbles on high-speed impact with a sidewalk to avoid the car being flung into the air.

Forged aluminium rims are much stronger. Jewiss notes: “There is a fallacy that aluminium wheels are weaker than those made from steel. It depends on the manufacturing process and the grade of aluminium used. If the grains follow the shape of the wheel, the aluminium wheel will be stronger.”

He adds that it takes about 13,6 t of pressure to deform a steel wheel, whereas a forged aluminium rim can withstand up to 71,2 t of pressure.

Aluminium wheels are also much lighter. The weight of the wheels will vary depending on their size and the grade of the material used. However, Jewiss notes that the Alcoa nine-inch aluminium wheels, for example, weigh 22,3 kg. A steel counterpart would weight between 45 and 48 kg.

“It is quite a big saving. Just on a truck, that is a weight saving of about 240 kg. On a 26-wheel trailer rig, for example, a transporter can save up to half a tonne in weight,” Jewiss explains.

By decreasing the weight of the actual vehicle, transporters of high-value goods can increase the number of products transported, or could save on fuel consumption.

A lighter wheel can also translate into additional savings for transport operators through longer tyre life. Aluminium is better at dissipating heat than steel, which means aluminium wheels run cooler. This, in turn, increases the life of the tyres, brakes and suspension components.

Jewiss uses Van Tonder Transport, which runs Alcoa wheels from Arconic, as an example. Van Tonder claims to have 40 to 50-percent more tyre life since switching to aluminium.

Aluminium rims, which can cost up to R3 000 each, are more expensive than those made from steel. Steel rims cost up to R1 000. However, transport companies can quickly make back their money through cost saving on tyres in addition to the benefits of weight saving.

“Tyres are much more expensive than rims. Most transporters travel around 20 000 km a month. After every eight to ten months, in perfect conditions, transport operators will have to replace their tyres. If they can get twelve months instead of eight months, they would cover the costs of the rims in just two and a half years by saving on tyres,” Jewiss explains.

Investing in aluminium wheels also requires tender love and care. Jewiss advises companies to polish the wheels after they have been washed and advises against painting them.

“To prevent the aluminium wheels being stolen, many people paint them to look like steel. However, when the surface of the aluminium rim is painted, it loses its heat dissipation properties and the transport operator loses the benefits of less tyre wear,” he says.

“If a company has a good maintenance regime, aluminium wheels will last a lifetime. I have seen aluminium wheels on buses that are 18 years old and still going strong,” Jewiss concludes.