First, asbestos brake pads (due to cancer risk has been replaced by NAO type)
Asbestos brake pads from the very beginning when it has been used as asbestos brake pads reinforcing material, since asbestos fibers have high strength and high temperature properties, and therefore meet the brakes and clutch disc and pad requirements. In the composition ratio of the asbestos in brake pads, asbestos accounts for 40-60%, but people have now found that most of the potential hazards of asbestos, asbestos has been shown to be carcinogenic medical profession.
In addition to health hazards, the asbestos brake pads, there are still another important issue. Because asbestos is insulated, the heat capacity is particularly poor, usually repeated use brakes will heat film piled up in the brake, brake pad gets hot, it is necessary to change the braking performance, to produce the same friction and braking force will need more brakes times, a phenomenon known as "brake shrink" if brakes reaches a certain temperature, will lead to brake failure.
Second, non-asbestos organic brake material type (NAO)
Type non-asbestos organic brake materials mainly used glass fiber, aromatic polyester fiber Cool Cool or other fibers (carbon, ceramic, etc.) as a reinforcing material, its performance depends on the type of fiber and other additives mixture.
Non-asbestos organic brake material is mainly used as a substitute for asbestos developed for brake drum or a brake shoe, but recently they are also beginning to be used as an attempt to substitute a front disc brake. In terms of performance, NAO brake pads closer to asbestos brakes, rather than semi-metallic brake pads. Unlike semi-metallic brake pads that have good thermal conductivity and good temperature controllability.
The new NAO raw materials and asbestos brake pads compared to any different? Typical asbestos-based friction material containing five to seven kinds of base mixture, which includes reinforcing fibers of asbestos, add a variety of materials and adhesives, such as linseed oils, resins, benzene intoxicated wake resin. In comparison, NAO friction material contains about 17 different profiles stick polymeric material, because removing the asbestos can not be equated simply replace an alternative, but a large number of mixture needed to ensure the braking performance, so as to be flat or braking effect over asbestos friction block.
NAO brake pads material has undergone several changes, now NAO material in many respects has effectively exceeds the performance of asbestos brake pads, which are mainly in the anti-friction properties and noise and so on.
Third, the "semi-metal" type brake pads mixture
"Semi-metal" mixture brake pads (Semi-met) is mainly used as a coarse steel wool fiber reinforcement and important mixture. (Fine fibers and particles) can easily type the asbestos and non-asbestos organic brake pads (NAO) to distinguish from the appearance, in addition they also have a certain magnetism.
"Semi-metal" mixture brake pads (Semi-met) The main advantage lies in its ability to temperature and high temperature brake with asbestos-type heat transfer performance difference between the brake disc, brake drum cooling capacity difference compared they help brake discs and brake drum when the heat dissipation from the surface out, heat is transferred to the brake caliper and its components. Of course, if the heat will cause problems not handled properly, the rear brake fluid heating temperature will rise, if the temperature reaches a certain level, it will lead to atrophy of the brake and brake fluid boiling. This heat while the caliper piston seal and return spring also has some influence, will accelerate the aging of components, which is also when the brake caliper assembly to re-repair and replacement reason metal parts.
Fourth, the special fiber types
21 century and the new developed high-tech products, green products. High temperature, good thermal performance decline, stable friction coefficient, does not lead to rust brakes, brake disc wear small, self-resistant, long life, easy running, brake smoothly. But its raw material cost is expensive. Complex production process, higher product costs. From a comprehensive cost perspective, special fiber brakes is much lower, it will be a big future trends in materials brakes, the main representative brand AOV.
Of course, standard specification should be finalized first, because the only way to test any new friction material formulations. These specifications should include friction properties, fatigue resistance, temperature adaptability, wear resistance and noise. The better the friction block friction material at different temperatures and pressures to maintain the better friction properties, in other words, at low or high temperatures, its performance should be little change. Friction material, the better, the more unlikely after repeated brake brake atrophy, which makes the "brake pedal feel" good. Preferred materials will also reduce wear and reduce noise.
Brakes in North America with a substantially semi-metallic formulations, Japan and Europe are using less metal formula, brakes domestic variety, in recent years through consolidation within the industry, most stable product quality, basically meet the domestic market demand.