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CLUTCH FRICTION MATERIALS: The friction material acts as a coating on the surface of the clutch disc. Because they are rough in nature, they offer a higher coefficient of friction—a higher coefficient of friction results in greater frictional force and better motion transfer.
There are two types:
(a) Woven friction material
(b) Molded friction material
(a) Fabric friction material
This material is made by spinning strands of asbestos fibers, sometimes into brass strands, weaving this strand into a cloth and then impregnating it with a binding material. This type of friction material can be divided into laminated variety and “solid” woven variety. In the laminated variety, the fabric layers are placed one on top of the other and held together by the binding material, sometimes aided by stitching.
In the “solid” type, the fabric is woven with the necessary thickness, and this woven structure has a much greater mechanized resistance. Both types usually incorporate brass wire.
(b) Molded friction material
The type of moulded or composite lining is composed of asbestos fibers in their natural state, mixed with a binding material and then moulded in moulds under pressure and at high temperature. A metal wire is included in the frame to provide better usability qualities.
Basically, bonding materials are chemical compounds. There is a wide variety of different fastening materials. They can be broadly classified as follows:
(a) Asphalt-based compounds
(b) Vegetable gums
(d) Synthetic resins.
1. Asphalt-based compounds
Natural oils and gums are added to asphalt-based compounds. Its coefficient of friction ranges from 0.3 to 0.4 up to a temperature of 250 degrees Celsius. The coefficient tends to increase with increasing temperature.
Excess bonding material also helps to achieve a higher coefficient of friction, but as excess material can be removed at high temperatures, it is difficult to maintain a high coefficient of friction. The wear properties of friction materials impregnated with this bonding material are good, especially when the product is moulded.
2. Vegetable gums
The coefficient of friction for this type of bonding material is slightly higher, i.e. between 0.35 and 0.45. This coefficient of friction is maintained up to a temperature of 250 degrees Celsius. This bonding material has better wear properties than asphalt-based compounds.
Rubber as a bonding material has a coefficient of friction of 0.6. It can be inflexible or rigid form. Although Rubber has a high coefficient of friction, the material tends to disintegrate under pressure.
4. Synthetic resins
These can be further classified as alcohol soluble and oil soluble. The coefficient of friction for alcohol-soluble synthetic resins ranges from 0.4 to 0.5 up to a temperature of 230 degrees Celsius. At higher temperatures, the coefficient of friction tends to decrease. The material is unaffected by the lubricating oil and can withstand high pressures.
Oil-soluble synthetic resins have a coefficient of friction of 0.35-0.38 that can be maintained even at high temperatures. They are often used with asphalt-based rubber and plant compounds and provide excellent wear qualities.
Cotton is occasionally used in place of or blended with asbestos, and these fabrics can be made to provide a coefficient of friction of 0.6 But this high coefficient of friction cannot be maintained beyond a temperature of 150 degrees Celsius. Sometimes cork is also used, but it must be kept in oil. Cork has a coefficient of friction of 0.3 and can withstand pressures of up to 140 kN / m2
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