Clutch systems are used in a variety of industries such as agriculture, transit, automotive, construction and more.
Hydraulic, mechanical, pneumatic and electric clutches all utilize the clutch disc. Also known as a clutch plate, this device plays an integral role in shifting gears of a vehicle or piece of heavy machinery. Similar to brake blocks and pads, clutch discs incur a great deal of friction. For this reason, a stainless steel plate is commonly used for added durability. In order to maximize effectiveness, the plate is often coated with friction materials. While the use of asbestos is limited due to related health hazards, carbon-composites, semi-metallic and non-metallic substances are all used in the production of clutch discs.
Ceramics, mineral fibers, cellulose, aramid fibers, chopped glass, steel and copper fibers are all employed in varying degrees to create composites suited to specific clutch systems. Heavy duty applications such as trucks and performance cars, for example, use ceramic clutch discs because of their increased coefficient of friction, heat resistance, durability and extreme strength. While general composites are known, manufacturers are often secretive of their specific friction material compositions in order to beat out competitors.
In general, the compression of a clutch pedal causes several springs connected to a pressure plate to compress as well. This compression pulls the plate, and connected clutch disc, away from the flywheel which is bolted to the engines crankshaft. The disconnection stops the rotation of the clutch disc which intern disconnects the central hub of the disc from the input shaft. The driver may then shift gears. After shifting, the pedal is released and the clutch disc reengages the flywheel. The clutch system works to ensure consistent clutch engagement and disengagement. This process, however, creates a great deal of friction on the clutch disc.
Friction can wear the coating of the disc resulting in its slipping against the flywheel causing the transmission to lose step. This loss of grip indicates that a replacement clutch disc is needed. Important considerations when selecting the proper disc include torque rating, power, rotational speed and maximum pressure allowances. Additionally, it is important to consider the type of clutch system in place. Hydraulic clutches for example, would be classified as a wet clutch while a mechanical clutch is dry. Wet clutches may utilize multiple clutch discs to improve friction despite the presence of fluids.