A recent report (from the parliamentary Air Quality Expert Group) says that ‘pollution from tyre wear and brake dust contribute to half of particle pollution from road transport’. What measures are Juratek, the brake supplier, taking to reduce the harmful particles in friction materials?
It is self-evident that the action of two surfaces rubbing together, like brake pads on brake discs, or tyres on the road, will cause wear to both surfaces. In the case of brakes, about half of this wear debris is liberated into the air, some of it is dispersed to the roadside and the rest sticks to the wheels of the car and vehicle body in close proximity to the car’s wheels – we have all experienced the ‘dirty wheel’ problem with our alloys.
As a result of this, over in the US, both California and Washington states have imposed regulations to reduce copper and other heavy metals from being present in braking products. The first level of the legislation began in 2014 in California and 2015 in Washington. All brake manufacturers and importers were required to self-certify that their brake pads contained no more than 0.1% by weight of asbestos, cadmium, chromium, lead, and/or mercury.
On 1st January 2021, the second phase of the legislation will go into effect. This phase will require brake manufacturers and importers to self-certify that their brake pads contain no more than 5% by weight of copper. By 2025, this must be less than 0.5%.
Of course, this law does not apply in Europe, however, the principles behind this law are to everyone’s benefit. Reducing harmful pollution is good for everyone.
Like others in industry, Juratek has been rightly concerned about the health hazards that might be posed by this brake wear debris and, for some years now, the company’s range of brake pads has been fully free from heavy metals and copper. This presented the product development team with a significant challenge – to ensure that the products still had industry leading standards of performance and freedom from noise and judder, whilst retaining reasonable pad and disc life. In summary, the aim was to ensure Juratek pads provide premium service performance, without costing the earth.
Of course, governments are looking to go further than just restricting the use of some of the more problematic ingredients of brake pads. It has been established that this wear debris, or particulate matter, which is a mixture of both pad and disc debris, ranges in particle size from >100μm to approx. 0.1μm, with some of it falling in the critical respirable range of 10μm to 1μm. (PM10 & PM2.5)
To reduce particle emissions further will require a much broader approach across a number of fronts. One potential solution is the application of a special hard coating to the surface of brake discs to reduce their wear rates, and, of course, carbon-ceramic discs also offer potential for reduced wear, albeit at a significantly higher cost. The automotive industry is also exploring partially enclosing brakes and fitting them with filters in order to capture the bulk of particulate emissions. Chances are the most likely final outcome will be a combination of all these measures.