The benefits of the bright brown metal copper have been rediscovered over the past year: during the COVID-19 pandemic, it has helped reduce the risk of cross-infection in hospitals and care homes, thanks to the metal’s antimicrobial properties.

However, it performs in the same way whether formed into a push plate on a door, or as roadside dust that blows into a stream. Since copper is harmful to fish, wildlife and invertebrates, the US states of California and Washington have decided to limit its use in vehicle brakes starting in 2021 to a maximum of 5% by weight, reducing to 0.5% in 2025.

Haldex is one of the first brake suppliers to provide friction materials that, at less than 0.5%, exceed the current requirements. It is now shipping the material for disc brakes to the independent aftermarket and US OEMs, and plans to supply the same material in Europe in two years’ time after the completion of customer testing. Because European legislation hasn’t caught up with US laws in this area, the low-copper friction material will launch in Europe ahead of any legal requirements. Haldex is truly leading the industry to make friction material more eco-friendly.

Accomplishing this goal has not been easy. As copper commonly accounted for about 10% of brake friction material by weight, finding a suitable replacement is of crucial importance. Copper’s primary function within the brake friction material is the same reason why it is used in domestic wiring; its superior conductivity helps draw heat away from the disc, and reduce brake fade. (It also works as a lubricant).

This latest change in composition is just the latest change in a long-evolving product. Over the years, a number of materials have been removed, mainly for health concerns, like lead, cadmium and asbestos.

“It is challenging to find raw materials with suitable properties,” points out Jonas Benson, manager of homologation and vehicle testing. “It is one of the most complex manufactured goods, including many different compounds and industrial byproducts.”

In addition, commercial vehicle brake pads need to be more robust than those of passenger cars because the additional vehicle weight. Amounting to more than 40 tonnes, that translates into inertia, which, when the brakes are applied, generates intense heat. Explains Benson: “Our testing is worst-case, which is a bad driver down the German Alps. The callipers can exceed 900°C – and the pads are even hotter – but they can’t fall apart. When you apply the pedal really hard, there’s a clamping force of over 20 tonnes.”

To make the perfect brake pad requires not only the right ingredients, but also process parameters of mixing, time, temperature and pressure, states Haldex global category manager Carl-Magnus Eriksson.

While the copper-free pad’s exact recipe remains a closely-guarded secret, Haldex asserts that the performance of the new semi-metallic friction material at their core will be just as good as that of previous premium pads, and, importantly, cost no more. They will also be the same size and replaced in the same way.

The development shows that Haldex continues to invest in product development to keep ahead of the market. Partly, this is to match the OEs’ preferences and expectations for global supply of low-copper friction material. But such work benefits not only Haldex’s customers, but also the environment and society at large. This is a case where the brake supplier, which is a supporter of the UN’s ’17 goals’ for sustainable development, is turning its environmental responsibilities into action.

And it won’t stop here. There is increasing concern in Europe about the health risks posed by dust particles smaller than 2.5 micron to humans, particularly in urban areas. Such particles are generated by vehicle brakes (among other sources). Haldex will continue to develop friction materials to meet evolving standards.

Testing times

Although Haldex is not a manufacturer of friction material, it might as well be, given the amount of work it puts into validation tests. It takes a minimum of three years for a new material from a supplier to reach sales-ready status, called internally ‘state of production’. This work is carried out by Haldex’s friction material team.

Haldex vehicle testing manager Jonas Benson outlines the Haldex testing procedure. As the company cannot possibly test all of the materials being developed, it chooses a few of the most promising that are available globally. That selection is partly based on the results of some ISO standard tests carried out by the friction material manufacturer. He states: “If we find it interesting commercially, and if the supplier has produced it before, and we have references, then we will start a process of dyno testing with simulating the loads of a fully-laden commercial vehicle under different operational conditions including legislation testing.”

First, it verifies the results of the suppliers’ tests, which takes two days. Then it moves on to disc crack testing, using test procedures developed by Daimler. “To deal with thermal stress, you need a good casting for the [brake] rotor. But you also need a gentle pad,” he observes. That is a 10-day test.

Also carried out is a test to the UNECE R13 brake standard, a legal requirement for brakes and one part of type approval. That takes a day. Finally are two ISO standardised tests, a two-day global specification performance test and an eight-day global specification wear test.

Once the pads pass all of the internal tests, they are offered to selected customers for two years of pre-sales field testing, in this case involving some 30 vehicles. “It’s important that the pads are run in different operations, whether construction – low mileage but aggressive or line-haul, which in flat countries you don’t brake often and traffic is low. Aggressive driving will wear the pads, as thermal stress is higher. On the other hand, if you drive them on the highway but never brake, the friction level still needs to be high, so you can have a problem with that,” adds Benson. As vibration has an impact on the pads, they are tested in different regions with different speed limits and quality of roads.

Following Haldex tests, the material is released to other parties for testing, including not only customers but also axle manufacturers, who will run them for a year. Their focus is on technical inspections; edge crumbling, corrosion at the sides, environmental issues and lifetime.

Although a long time in coming, friction material tested in this way is well worth the wait, as it has been thoroughly evaluated before reaching the open market. Customers may find that reassuring.