Briefly about brake pad formulation, that is, the friction material?
There are many different kinds of formula systems on the market, but everything is the same, just like what martial arts novels say, fist out of Shaolin, sword back to Huashan, kung fu is nothing but “fast, accurate, straight and hard”, Mr. Bruce Lee in these four aspects to the extreme.
I’m going to go back to the topic. (The following is purely professional knowledge, may bring discomfort, please read with caution).
To summarize the friction material is a polymer ternary composite material, is a physical and chemical complex.
It is made of polymer binder (resin and rubber), reinforcing fibers (what the market said that the formula refers to this) and friction performance adjuster three major components and other matching agent composition, by a series of production and processing of products made.
Friction material is characterized by a good coefficient of friction and wear resistance, while having a certain degree of heat resistance and mechanical strength to meet the performance requirements of the vehicle or machinery transmission and braking.
A. Classification of friction materials
1. According to the work function can be divided into two categories of transmission and braking friction materials.
uch as the transmission role of the clutch plate, the clutch assembly through the clutch friction surface plate fit and separation of the power generated by the engine to the drive wheels, so that the vehicle began to walk.
Braking role of brake pads (divided into disc and drum brake pads), the brake pads through the vehicle braking mechanism will be tightly attached to the brake disc (drum), so that the walking vehicle to slow down or stop.
2. According to the shape of the product, it can be divided into brake pads (disc pads, drum pads), brake belts, brake tiles, clutch pads, and anisotropic friction pads.
Disc type pads are flat and drum type pads are curved. Brake tiles (train tiles, oil rigs) are curved products, but are much thicker than ordinary curved brake pads, in the range of 25-30mm.
Brake belts are commonly used on agricultural and construction machinery, and are soft friction materials. Clutch discs are generally circular shaped products.
The heterogeneous friction plate is mostly used in various engineering machinery, such as friction presses, electric hoists, etc.
3. According to the product material: mainly according to the classification of reinforcing fiber, can be divided into asbestos friction materials, metal friction materials, carbon ceramic friction materials.
Second, the composition of the friction material
Friction materials belong to polymer ternary composites, which include three parts: polymer compounds as binder; inorganic or organic fibers as reinforcing components; fillers as friction performance modifiers or matching agents.
1. Organic binder
Friction materials used in organic binders for phenolic resins and synthetic rubber, and phenolic resins are the main.
Their characteristics and role is when in a certain heating temperature when the first softened and then into the viscous flow state, the flow and uniform distribution in the material to form the material matrix, and finally through the resin curing effect of rubber vulcanization, the fibers and fillers bonded together, the formation of dense texture has considerable strength and can meet the friction material performance requirements of friction sheet products.
The quality of the resin requirements are.
(1) good heat resistance, a good thermal decomposition temperature and low heat loss.
(2) powder resin fineness to be high, conducive to the uniformity of the dispersion of the mixture, can reduce the amount of resin in the formulation.
(3) Low free powder content.
(4) Suitable curing speed and flow distance
2. Fiber reinforced materials
Fiber reinforced materials constitute the base material of the friction material, which gives friction products sufficient mechanical strength, so that it can withstand the friction in the production process of grinding and riveting processing of the load force and the use of the process due to braking and transmission and impact, shear, pressure.
China’s relevant standards and automobile manufacturers according to the actual conditions of use of the friction plate, the corresponding mechanical strength requirements of the friction plate. Such as: impact strength, flexural strength, compressive strength, shear strength, etc..
In order to meet these strong performance requirements, the need to choose the right fiber species to increase, to meet the strength performance.
Friction materials require the following fiber components for their use.
(1) Good reinforcement effect.
(2) Good heat resistance. In the friction working temperature will not occur fusion, carbonization and thermal decomposition phenomenon.
(3) has a basic coefficient of friction.
(4) The hardness should not be too high, so as not to produce brake noise and damage to the brake disc or drum.
(5) Good process operability.
Filler in the friction material components, mainly composed of friction performance modifiers and matching agents. The purpose of using fillers, mainly in the following areas.
(1) to adjust and improve the friction properties of products, physical properties and mechanical strength.
(2) control the coefficient of thermal expansion, thermal conductivity, shrinkage, and increase the stability of the product size.
(3) Improve the braking noise of the products.
(4) Improve the manufacturing process performance and processing performance of the products.
(5) Improve the appearance quality and density of products.
(6) Reduce the production cost.
Third, the technical requirements of friction materials
1. Suitable and stable friction coefficient.
Friction coefficient is the evaluation of any kind of friction material is one of the most important performance indicators, related to the friction pad to perform the transmission and braking function of good or bad.
It is not a constant, but by the temperature, pressure, friction speed or surface state and the surrounding media factors such as the impact of a number of changes.
The ideal friction coefficient should have the ideal cold friction coefficient and can control the temperature recession.
Due to the heat generated by friction, increasing the working temperature, resulting in a change in the coefficient of friction of the friction material.
2. Good wear resistance.
Friction material wear resistance is a reflection of its service life, but also to measure the durability of friction materials is an important technical and economic indicators.
The better the wear resistance, that its service life is longer.
However, the wear of friction materials in the working process is mainly caused by the shear force generated by the friction contact surface.
Operating temperature is an important factor affecting the amount of wear.
When the surface temperature of the material reaches the thermal decomposition temperature range of organic binder, organic binder such as rubber, resin decomposition, carbonization and weight loss phenomenon.
With the increase in temperature, this phenomenon intensifies, the bonding effect decreases, the wear volume increases sharply, called “thermal wear
3. Have good mechanical strength and physical properties.
Friction material products in the assembly before use, there is a need for drilling, riveting assembly and other mechanical processing, in order to make the brake pad assembly or clutch assembly. In the friction process, the friction material in addition to withstand very high temperature at the same time, but also to withstand the greater pressure and shear force.
Therefore, the friction material must have sufficient mechanical strength to ensure that the processing or use of the process does not appear broken and broken.
4. Low brake noise.
Brake noise is related to the comfort of the vehicle driving, and the surrounding environment, especially the urban environment caused by noise pollution.
For cars and city buses, braking noise is an important performance requirement. In terms of car disc pads, noiseless or low-noise brake pads with good friction performance become the first product.
With the development of the automobile industry, people are now paying more and more attention to brake noise, and the relevant departments have put forward the standard regulations. Generally, the noise generated by the car braking should not exceed 85 dB.
5. Less wear on the couple surface.
Friction material products transmission or braking function, are to be realized through the friction with the couple that the friction disk (drum) in the friction.
In this friction process, the pair of friction couples will wear each other, which is a normal phenomenon.
But as a consumable material friction material products, in addition to their own should be as small as possible wear, wear on the couple should also be small, that is, should make the couple’s life relatively long.
This is to fully demonstrate the characteristics of good friction performance.
At the same time in the process of friction should not be the couple that the friction disc or brake drum surface grinding into heavy abrasions, scratches, grooves and other transitional wear conditions.