In this paper, the brake noise is an important indicator of the brake linings, and also a difficult problem in quality control. And reduce noise, prevent dual damage. At present, it has become our friction material industry of a very prominent problem, the current domestic semi metal products widespread this problem. Sometimes, the beginning without the use of noise, but to a certain number of kilometers, such as 1-2 million kilometers there is noise, some equipped with domestic brake disc has a noise, and equipped with imported disc without noise, some opposite.
For braking noise, it can be considered as a resonance of the brake system, and the friction vibration can be considered as the source of the noise. The cause of braking noise is varied, and it has become a complex system engineering. In the development process of the friction material, we do not only consider the influence of the inherent characteristics of the material itself, but also take into account the relevant characteristics of the dual parts of the material. Generally when braking friction due to vibration frequency changes caused by brake noise. The friction vibration and friction materials are related to the friction vibration and friction materials in 200-500HZ, the surface treatment, the compression elasticity, the tensile strength, the porosity, the friction coefficient, the friction coefficient, and the friction coefficient.
This paper focuses on the relevant factors of the structure, formulation design and process of the noise and braking materials, and makes a simple discussion to make the product as little as possible in the actual production process to meet the needs of customers.
The related factors of the product's comprehensive friction performance and the noise of the products:
1. A good friction products not is the friction coefficient, the higher the better, for cars with disc brake tablets. According to the author's many years of actual production experience shows that, the friction coefficient of the products control below 0.4, the optimum range should be between the mu =0.35~0.38, general semi metal disc products in this range when used rarely occur brake noise, and when the friction coefficient of the products is higher than 0.4 occurrence possibility of noise to 1 or 2 times larger. In general, the product of the friction coefficient is stable, whether the brake process is stable and whether there is a close relationship between the noise. In particular, the product in the use of the process of increasing the pressure of the contact surface, the sudden rise in temperature of the surface of the contact surface, the "adhesion" and "separation" caused by the change of friction characteristics, the pressure increases, the wear intensifies, the dual position of each other to change, the emergence of vibration noise. Therefore, the stability of instantaneous friction coefficient, the constant transmission torque is the prerequisite to ensure that the brake noise is not generated. This requires that the friction coefficient of the brake product is comparable to that of the speed, and the comparability of the temperature and pressure is stable. The change rate of instantaneous friction coefficient in the product braking process is less.
The ratio of dynamic friction coefficient, static friction coefficient, and instantaneous minimum / maximum ratio of 1 is the best. This kind of brake product is usually installed in the car, and it is seldom to produce noise.
2 the overall hardness of the product can not be too large. The product itself resin content, surface treatment, increasing the number of friction, the amount of the amount of material (density) are related to the hardness, appropriate adjustment of these ratios, optimizing the structure will be satisfied with the results. Here should be noted that: we advocate the product hardness moderate. Can not say that the overall elasticity, the lower the better, for example: multi rubber product itself is very good elasticity is very low, but the actual brake when the noise is too large, which as the former said, material elasticity is too large, torque transmission is not smooth, the anti will cause more noise, but the rubber modified to reduce the product brake noise is effective, this is not hard brittle.
3. The friction increasing agent ultra refinement can make the noise is reduced to a minimum, friction products tend to add inherent big friction coefficient of the material, such as feldspar powder, chromium powder, white corundum, 3 oxidation 2 aluminium substances. These substances themselves Mohs hardness high (usually more than 5-8) of these materials is often used as a friction increasing agent added to the product, but the practice has proved that the friction increasing agent of ultra refinement in preventing products generated noise factors is essential. For example: work in process (WIP) by adding the same amount of 200 to increase friction agent will produce noise, switching to 325 mesh would have no noise, if the same friction increasing agent ultra refined to more than 1500 mesh, dosage and 3% percent and brake noise does not occur. This is a more practical application of the super refinement of the friction increasing agent.
4 products with long curing time of product is easier to produce noise than curing time, this is mainly because the curing time of its structure has changed, the overall hardness has increased.
5 the amount of feed can also cause noise, which may be related to the density and natural frequency of the product.
6 steel fiber quality will also affect the brake noise, the general high carbon content of steel fiber or the heat treatment temperature is too high steel fiber will cause the brake noise. So in our choice of fibers, fillers, and increase or decrease friction modifier should try to choose itself inherent Mohs hardness of low or moderate application of material. For example: good heat resistance and high strength of aramid (Kevlar), itself not only to wear and does not damage the duality, by adding a small amount of aramid fiber can reduce the braking noise, but ceramic fiber although high temperature friction coefficient stability, but ceramic fiber itself a Mohs hardness of high (more than 6) often WIP in the use of ceramic fiber will increase the noise. In order to reduce the noise of the occurrence probability we often advocated using the Mohs hardness is low or moderate materials for enhanced stuffing. Such as barium sulfate, diatomite, ice powder, pyroxene mineral powder, copper powder, aluminum powder, iron powder, graphite, mica, vermiculite powder and rubber, Ding Qingfen etc. strive to overall hardness of the products is not high, to reduce the brake noise (see reduce noise formula structure reference table)Two. Improving the production process of the friction products is an important part to reduce the noise:
1. The disc brake pads in the production process of steel back (bottom) parallel warpage degree, perpendicularity and brake pad manufacturing precision tolerances will affect the use effect. Production practice shows that exceed the standard products of parallelism and verticality, braking will produce vibration and noise. In the production process of the press, tooling, mold, etc. their own production accuracy will directly affect the accuracy of product manufacturing. For example: multi layer molding products on the more than a single mold press of the parallel degree error or even directly affect the use of the product to produce brake noise.
Product 2. The appearance of the structure and the size, morphology and sometimes make the products of the brake noise, long-term product use process we found some disc does not change in the formula and the structure of the material premise, only in size or appearance to be improved in, such as brake pad symmetrical chamfers on two sides, products in the middle row crumbs slot will cause noise probability to a minimum (from the original 10% down to 1%) for example in the 1990s we produce red Audi 100) car brake disc encountered this problem, but also through open chamfer and flutes, to solve the problem of braking noise. The mechanism is chamfered and grooved the inherent vibration frequency of the braking system changed (equal or more reasonable) become more coordinated. Therefore, noise is reduced.
Three. Note that the quality of the accessories of the brake products, the impact of the material on the noise:
The good or bad of the anti vibration pad will directly affect the level of braking noise. Strictly speaking, a composite material made of anti shock pad (case of the United States 3M company's high temperature shock pad) its effect is better. Also should pay attention to the police line (especially alarm circlip) installation location is correct or not, whether the steel plate coated with heat shock proof paint, will affect the product size of the noise.
Four. The related factors of braking noise:
As mentioned earlier, the occurrence of brake noise is not only because of the brake pad material structure, natural frequency and the brake system and vehicle (system of dynamic balance) stiffness, strength and installation accuracy (brake branch pump clearance and travel) many factors related, especially friction pairs (disc and drum) matching, are very important brake materials and Pangu matching, often need 1:1 test selection on the rack with inertial Luntai and put the problem such as various kinds of factors into consideration and the structure of materials and formula for reasonable optimization screening to ideal solution braking noise.
Brake noise is a system and a variety of factors closely related to the major issues, to be a good solution to this problem, we need to continue to work hard to further the structure of the brake system (including stiffness, strength, material, surface morphology), the more thorough and more thorough penetration. And only on the half metallic structure of the friction brake piece, to make it into a noise free, comprehensive performance index is perfect, it is also very difficult subject, on the current production and use of our country compared with foreign advanced countries, the remaining large gap
1 is China's current friction material variety is also relatively simple, quality level (due to the market price constraints) is still very low.
2 is a multifunctional composite application of the friction material is still very little.
3 the ultra fine penetration rate of China's increasing friction is still very poor, and the application is not widespread.
4 friction material noise problem of professional research team is also very little, scientific and technological achievements, technology talent can not meet the needs of the actual market.
5 the application and theoretical guidance of the friction material is still there, and there is a certain blindness in product production and foreign technology. Seen in the above reasons, the author believes that the noise and the use effect of the semi metallic disc brake pads in China is much more than the advanced enterprises in foreign countries, but we have the confidence to make tomorrow and the future!
Remarks
The article was published in Luoyang, Henan on August 2009 3-7
(the Ninth National Symposium on friction, friction, wear resistance, abrasion resistance and Technology)
