LANDSKRONA, Sweden — Haldex published the following post on its website with the goal of informing users how to get the best results from their commercial vehicle’s brakes.
From frozen pizza to flat-pack furniture, not all products are at their best straight out of the box.
Another example is disc brake pads. “Friction material contains a lot of different substances, and a big part of it is organic materials. You need to heat these materials up to achieve the correct friction level. Until after bedding in, the friction may be lower. It’s like baking a cake,” states Fredrik Rennstam, Haldex application engineer and technical support manager.
This bedding-in process involves pressure but primarily temperature – exceeding 250degC for an extended period – to stabilize the materials. Doing so will result in a 20-25% improvement in braking performance, according to Jonas Benson, homologation and vehicle testing manager. (Having said that, overheating brakes can dramatically shorten their life far out of proportion of the increase in temperature).
In most cases, a few weeks of normal operation of a loaded vehicle will generate enough heat to stabilize the friction material. But to help operators get through the first 20 to 50 braking cycles, Haldex coats its pads with a grippy rubber-like coating, called Greencoat, to increase friction levels. By the time it has worn off, the pads should be bedded in.
In case of doubt, the best way to find out the state of the pads is to drive the vehicle onto a roller brake tester and record the output brake torque for each wheel end. Of course, these tests usually take place at partial, rather than full load, because of the risk posed to a tester of a potential rupture of a fully compressed air suspension bellows. Still, with partial loading resulting in a minimum pressure of about 2-2.5 bar, it is possible to take two torque readings (up to wheel slip), and then extend those figures by linear extrapolation up to the maximum pressure. The R13 statutory requirements are 5m/s^2 for motor-driven vehicles and 4.5m/s^2 for semi-trailers. There may also be value in comparing the results of one wheel-end to another, as significant differences between brakes may indicate a problem.
Operators should always present a warmed-up vehicle to an RBT test, as it is most likely to perform at its best. Humidity can accumulate on brake surfaces and corrosion can form on brake discs of vehicles parked up overnight or over the weekend; those factors might affect friction levels, and so performance, during the test. It is another example of the close interaction between the wearing parts of a braking system. “We always talk about a friction couple; brake pads are only half the story,” observes Rennstam.
In any case, brakes that have not been bedded in well may never reach their theoretical performance. As Benson says, “If the pad has gone to sleep so, it’s extremely hard to wake it up again, unfortunately.” Instead, he advises prevention.
To view the entire post, click HERE.