At recent brake friction conferences, one subject that is discussed with increasing frequency is pad compressibility. Brake pads can compress when in use due to pressure and temperature conditions. This compressibility can impact braking performance. Today’s disc brake pads typically have a specification detailing an allowable range of compressibility at a predetermined set of conditions.

Disc brake pads are comprised of many raw materials including resin, fibers, fillers, lubricants, etc. For the engineer wishing to adjust the compressibility of the brake pad, they would consider changing the grade of one or more of the raw materials used in the formulation. Many of these materials, however, do not impact compressibility. Fortunately, cashew particles can play a big role in impacting pad compressibility.

This case study takes a look at four distinct cashew particle products in Palmer’s portfolio and compares their performance using an industry standard test. First, let’s discuss the particles tested.

The four products were chosen in an effort to span the performance range of cashew particles. The first product is 3400, a brown friction particle. Brown friction particles are the original cashew products. They have been around for decades. Almost exclusively used in the aftermarket, this is the most commonly found friction particle in the world. These commodity products are typically available at low prices and offer low performance.

The next product chosen is 6000. This is a black friction dust. The technology to create black cashew particles is much newer than that of brown particles, but it has still been around for some time. Black friction particles offer better thermal performance than brown particles and are becoming more popular in the market as formulators deal with increasing brake temperatures. Although it has higher technology compared with 3400, 6000 represents the lower range within the black cashew particle products.

The third product is 6010. This is also a black particle, but the formula is adjusted to provide higher heat resistance. 6010 is used in both the aftermarket and OE and is considered to be mid-range relative to other black cashew particles from Palmer.

The final product is 6250. Again, this is a black particle with significant adjustment to improve performance… particularly for thermal properties. 6250 would be used exclusively for OE applications.  For the purpose of this paper, 6250 represents the high end of the Palmer portfolio.

A few things need mention regarding sample preparation. First, in order to limit the number of variables in the test and maximize the impact of the cashew particles, sample pucks for testing were comprised only of cashew particle and phenolic resin. Specifically, the pucks were 80% cashew particle and 20% phenolic resin (by weight). Additionally, all materials were screened to the same particle size. It is well known that particle size has a significant impact on compressibility. We eliminated that impact by using only a targeted particle size.

Pucks with surface area of 1 in2 were produced in a positive mold at controlled temperature and pressure and postbaked.

The sample pucks were tested in conjunction with ISO 6310… an industry standard for evaluating compressibility. The pucks were run at various temperatures. The data shared below was for pucks tested at 400°C.

ISO 6310: Compressibility at Elevated Temperatures

The data shows that there is a trend toward lower compressibility when moving through the Palmer portfolio towards higher technology cashew particles. This trend has also been confirmed at lower temperatures.

Palmer has assisted customers whose goal was to alter overall pad compressibility with this type of data. Our knowledge of our portfolio related to compressibility can help customers to find solutions to problems more directly and without a trial and error approach.