The brake pads are one of the components of the braking system, which also includes the brake callipers and discs to name but a few. Each wheel has one disc, a calliper and 2 brake pads. The brake disc is attached to and spins with the road wheel of the car. The calliper, which is positioned around the disc, houses the pads, with one pad sitting either side of the disc itself. Hydraulic fluid causes the pads to be forced against the disc by pistons inside the calliper when the brake pedal is applied. It is the friction caused by the pads coming into contact with the spinning disc that slows the vehicle down. The speed and weight of a vehicle cause the brake pads to undergo extreme levels of stress and heat, hence why they get so hot! The heat caused by this friction is a major concern for vehicle manufacturers. If the brakes become too hot ‘brake fade’ can occur. This excessive heat results in a loss of braking power, which as you can imagine, is not good. The hydraulic fluid can also boil with excessive brake temperatures that can also lead to a loss of braking power. ใบเจียร
So what are the brake pads made from? Originally the part of the pad that comes into contact with the disc was made from asbestos. Asbestos was an ideal material because of its ability to absorb and dissipate heat. The problem however was that when asbestos breaks down it causes a toxic dust that is dangerous to humans if inhaled. A lot of this dust is created when braking so a new material was needed.
More recently non-organic material such as rubber, glass and Kevlar were used. The advantage with these was that the dust released was not toxic and so they were easier and safer to change and dispose of. The main disadvantage however was that they were softer than organic pads so wore down faster and needed changing more frequently. For these reasons non-organic pads are better used on smaller, lighter vehicles which do not need as much friction to stop as say larger trucks and Lorries. This lower level of friction means that the pads simply last longer.
Performance vehicles such as sports cars and F1 cars use ceramic brake pads due to their ability to withstand immense amounts of pressure, dissipate heat and wear well. The problem with ceramic brakes is that they are so expensive!
Today, most brake pads are considered ‘semi-metallic’ because they contain fragments of copper, iron, graphite, brass and steel which again are bonded together using a strong resin. The reason why these pads are so popular is simple; they are low cost and wear extremely well. However, there are a couple of downsides to semi-metallic brake pads as well… First of all they are heavy due to being made from metal. This can have a negative effect on fuel economy (albeit only slight). They also work best when warm so are less effective when cold. This needs to be borne in mind by the driver, especially on really cold days as it can affect the stopping distance of the brakes. Another drawback of semi-metallic brake pads is that they often cause an unavoidable grinding noise as the metal fragments within the pads come into contain with the metal disc. Some aftermarket discs are sold as quieter than factory discs. The benefits of these pads outweigh the negative elements though so they are still the most popular brakes of the day. Many brake pads manufactured today have special built in shims that are designed to cause a grinding noise when the brake pads are wearing thin. This alerts the driver that the pads require changing. If the pads are not changed when this occurs the hard steel backing of the pad can come into direct contact with the disc and will eventually cause damage to the discs themselves. This can destroy the disc that will then need replacing along with the pads.