1, the binder material research The main role of the adhesive is the brake pads of the various components are closely bonded together to maintain the brake pads in the high temperature mechanical structure of the structural integrity. Brake film is the most commonly used binder is phenolic resin, it has excellent heat resistance and mechanical properties, electrical insulation and forming processing performance is good, and easy to obtain raw materials, cheap, process and production equipment is simple. But the use of pure phenolic resin will cause the brakes hardness is too high, brittle, heat limit temperature is only about 250 ℃. When more than 300 ℃, the thermal decomposition is quite serious, will lead to a significant decline in the performance of brake pads. Therefore, the phenolic resin must be toughened and heat modified. Foreign use of the modified resin mainly COPNA resin (decomposition temperature of about 400 ~ 500 ℃), silicone modified phenolic resin, boric acid modified phenolic resin, cyanide modified phenolic resin (resistant to high temperature above 350 ℃), epoxy Modified phenolic
Resin (normal use at 400 ℃), thermoplastic polyimide resin (heat resistance and wear resistance are very good), suspension resin. Suspension resin is the name of phenolic resin suspension polymerization process, it is a foreign research and development in the 1970s a new phenolic resin, also known as Phenolic Thermosphere (referred to as PTS), decomposition temperature reached 490 ℃, with the tree
Grease made of adhesive brake pads with a stable coefficient of friction, high temperature friction performance, low noise, heat recession and other advantages. The study found that the use of modified phenolic resin brake pads of the friction performance (including the friction before the recession coefficient, after the friction coefficient of friction, wear rate, damage to the other, etc.) than the use of traditional phenolic resin brake pads better ; Resin, brake pads between the strength and wear performance is not necessarily linked. The use of boric acid modified phenolic resin prepared by the brake pads, 400 ℃, still maintain a high coefficient of friction (above 0.4).
2, friction performance regulator
Friction performance modifier is a class of substances added to the friction material to improve the friction coefficient and wear rate, mainly divided into two categories of lubricants and abrasives. The main purpose of the lubricant is to reduce the friction coefficient during braking. Commonly used lubricants include graphite and various types of metal sulfides. Metal sulfides are considered to be better lubricants than graphite because the low bond strength of phenolic resin binders and graphite can not meet the requirements of modern automotive industry efficient braking, will accelerate the friction material wear, and metal sulfide does not exist this problem. However, some compounds such as lead and antimony sulfide are toxic, so safer metal sulfides such as tin, copper, molybdenum sulfide may become the ideal lubricant. The abrasive can increase the friction coefficient of the friction material, but at the same time increases the wear of the coupling. They remove the iron oxides on the dual materials and the adverse effects on the surface, but the high levels of abrasives increase the friction of the friction coefficient. The abrasive is mainly a hard particle of metal oxide, quartz powder and silicate compound. Its Mohs hardness is generally 7 to 8; commonly used abrasive zirconium oxide, zirconium silicate, alumina, silicon carbide, silica and chromium oxide. (Sb2S3) and zirconium silicate ZrSiO4) on the car brake, the friction coefficient is increased, The friction coefficient of the friction coefficient has a great influence on the friction properties of the friction material. Increasing the content of the lubricant can improve the stability of the friction coefficient, and increase the abrasive content to increase the friction coefficient Volatility, so it is important to coordinate the amount of lubricant and abrasive in the brake friction material.
3, the application of reinforced fibers in the brake pads in the 20th century 70s friction material began to no asbestos development, there have been a variety of asbestos fiber substitutes, mainly ceramic fiber, aramid fiber, carbon fiber, steel fiber, copper fiber , Aluminum fibers, glass fibers, mineral fibers, cellulosic fibers, potassium titanate whiskers and sepiolite fibers. With the deepening of research, the performance of single fiber reinforced friction material is not comprehensive, there are a variety of defects, and several fibers mixed together, the performance can be complementary, play a mixed effect, the performance of the friction material prepared, so mixed fiber reinforced friction Material has become a hot spot in recent years. Studies have shown that potassium titanate whiskers and aramid fiber adhesion together, can improve the friction surface film heat resistance and strength, but when the friction material contains only two kinds of fibers in a component, this favorable Synergistic effect is greatly reduced. Glass fiber, aluminum fiber brakes can not provide the ideal coefficient of friction and wear rate, and the use of aramid fiber instead of glass fiber, with potassium titanate as a friction performance regulator, can improve the performance of brake pads; Potassium brakes, the friction coefficient of the brazing material containing potassium phthalate is stable, and the thermal deterioration resistance and abrasion resistance are improved. It is reported that the friction coefficient of copper fiber and steel fiber brakes decreases with the increase of sliding speed, and the friction coefficient of aluminum fiber brake pads is not changed. Adding copper fiber can make friction material have high and stable friction coefficient and Very low wear rate. Some studies have compared the effects of aramid fiber, Cyon fiber PAN fiber (polyacrylonitrile fiber), carbon fiber on friction coefficient and wear resistance of friction material. The results show that the aramid fiber can overcome the thermal sensitivity of the resin, improve the stability of the friction coefficient, reduce the wear rate; Cypriot fiber can significantly improve the friction coefficient, but the maximum wear; carbon fiber reinforced friction material has the best heat resistance Decay performance; polyacrylonitrile fiber on the braking load and sliding speed of the least sensitive to the friction coefficient and the impact of the impact is not large. Compared with the resin, filler, friction performance modifier, reinforced fiber is more concerned by the brake film researchers. The influence of various reinforcing fibers on the friction performance of automobile brake pads has been studied at home and abroad. However, there are few studies on the field of ceramic fiber reinforced brake pads, which are confined to potassium titanate whiskers and silicon aluminum oxide, The future need to open up other types of ceramic fiber in the brake on the application.