Steering towards SAF

The quest for a more reliable self-steering axle on its Bruce Rock Engineering-built Ultra-Quad road train combinations saw Western Australian based David Campbell Transport turn to SAF-Holland for a solution.

When it comes to harsh operating environments, they don’t come much tougher than the Pilbara region in northern Western Australia.

Here the iron ore is extracted from the ground at an astonishing rate, with the raw material transported in quad road trains to Port Hedland where it’s loaded onto ships bound for export markets across the globe.

Everything about the rugged side-tippers used to transport the ore must be ultra heavy-duty to ensure outstanding durability over long distances in harsh conditions, and the axles are certainly no exception.

When David Campbell Transport (DCT) started having ongoing issues with another brand of self-tracking axle it was using, SAF-Holland was quick to step into the breach and offer an alternative that, provided it proves successful in trials, will see the company rolling out the solution across its entire super-quad side-tipper fleet.

“We’ve had a lot of issues with disc calliper and bearing failures over the last four years with another brand of axle we’ve been using so we’ve decided to trial SAF self-steering axles to see how they stand up in our application,” says David Campbell, CEO of DCT.

The Ultra-Quad combinations produced by Bruce Rock Engineering (BRE) feature a tri-axle group on the lead trailer and quad axles including a rear self-steering SAF Intra axle on the subsequent three trailers to ensure an acceptable swept path on turns.

David says safety is a high priority in the DCT operation, which is why disc brakes are featured on around 90 per cent of the trailer fleet and on 100 per cent of new trailers purchased over the last four years.

“Safety is so important when you have combinations with a gross combination mass (GCM) of 210 tonnes and a payload capacity of 150 tonnes, as is the case with the Performance-Based Standards (PBS) Ultra-Quads we run,” David says.

“When you have disc brakes you know they are always going to work effectively – if they are set up properly there’s no way they can wind themselves out of adjustment like drums.”

David says there is also a marginal tare weight advantage with discs over drums but he reiterates that by far the biggest consideration in running disc brakes is safety.

The SAF Intra self-steering axle has a weight capacity of nine tonnes and an additional weight of 136kg in comparison with the corresponding fixed axle.

According to SAF, advantages of the steering axle include less tyre wear, lower fuel consumption, a high level of driving comfort, optimal manoeuvrability due to precise tracking and a higher resale value of the trailer.

The unit also features a stabilisation damper providing weight optimised steering stabilisation to improve handling on both straight and winding roads.

The stabilisation damper is suspended on the axle body on one side and on the steering tie rod on the other. It is either pressed (shortened) or pulled (lengthened) depending on the direction of the steering knuckles’ movement. The unique design of this SAF stabilisation damper means that its internal spiral spring is always compressed during both movements.

As the side force decreases, the spring force proportionally increases, forcing the steering knuckles back into the straight-ahead position. The spiral spring, supported by the damper properties, is also the reason for a sturdy and flutter-free straight drive.

To make reversing possible with a self-steering axle, it has to be set rigid. With SAF self-steering axles this is achieved with an electro-pneumatic locking mechanism that can be easily controlled by the trailer EBS unit.

Depending on the track, spring centres and type of wheels installed, SAF self-steering axles can achieve a steering angle of up to 20 degrees. The units installed in David Campbell’s fleet have 14 degrees of steering angle.

All SAF axles feature long-term corrosion protection by way of a cathodic dip coating process on particularly exposed parts such as axles, hubs, hub caps, wheel studs and nuts.

David Campbell’s trucks are on the road night and day, covering around 700km in each 12-hour shift, which adds up to around 400,000km annually.

This sort of high utilisation, according to David, shows up issues in equipment that other lower kilometre operators may not experience.

“With our high mileages we generally see problems before others,” he says – adding that he has high hopes for a long and trouble-free run from the SAF Intradisc self-steer axles on the trailers.

“We’re intrigued to see how they perform in this application and if they excel we’ll be specifying SAF axles on all of our new trailers,” David says.

With over 500 trailers and 90 prime movers, the business operates from various depots across WA in applications as diverse as mining, heavy haulage, grain, refrigerated, livestock carrying and compost.

Speaking about PBS, David says he is very happy with how the system operates and the advantages it provides.

“In my opinion, for us PBS actually does deliver a better performance standard for multi-combinations,” says David.

“The way our Ultra-Quad combinations handle is incredible.”

Playing an important role in this are the SAF Intradisc rear steer axles which enable the quad-axle trailers in the Ultra-Quad combinations to track exceptionally well both on the straight highway stretches and around corners.

Fast Fact
This is the first time that SAF self-steer axles have been used in combination with YORK mechanical suspension. According to SAF-Holland Australia Product Manager, Nemanja Miletic, the two brands blend seamlessly.

“The engineering team of SAF-Holland Australia made quite a few modifications in order to make the combination feasible,” he says. “This is another great example of an Australian transport industry necessity leading to a new invention – history in the making.”