Friction Clutches and Friction Brakes

Friction Clutches and Brakes

Friction clutches and brakes utilize friction discs to transfer the energy from one rotating member to a second rotating member. The friction between the discs of the two bodies allows the clutch or brake to transmit torque. The friction discs are flat smooth surfaces that are alternately attached to the rotating and the non-rotating elements. The sequence and type of friction surface, as well as the load presented to the clutch/brake will determine the size and number of friction surfaces that are utilized to transmit the torque.

Once the torque capacity of the disc friction surfaces is exceeded then the clutch will slip. These friction clutches and brakes will also slip during engagement and disengagement, while the friction discs are being gradually squeezed together by whatever actuation method is used. This allows a smooth transfer of torque from one device to another, allowing gradual starts (for friction clutches) and controlled stops (for friction brakes).

Friction discs may be made from various materials. Coated and uncoated metals, various alloys, bonded composite friction materials, and combinations of these may be appropriate depending on the application. Carlyle Johnson offers a wide variety of surface types for friction clutches and brakes, as well as a large selection of friction surface quantities in every size and type of clutch. An in-depth description of the engagement methods of our clutches is available on our actuation comparison page.

Single vs. Multiple Disc Designs
Friction Clutch and Friction Brake Units

Type Torque Load Cost Tip Velocity*
Single Disc Low Capacity Lower 775 ft/sec
Multiple Disc High Capacity Higher 200 ft/sec

* At 5,000 RPM

Carlyle Johnson offers both single disc and multiple disc friction clutches and brakes. In many applications where low cost and only a small torque handling capability is required, a single friction surface will suffice. Multiple disc friction clutches and brakes offer the advantage of handling high torque loads in a compact size device.

A multiple disc clutch with seven sets of discs provides fourteen friction surfaces. The total area of these fourteen surfaces would require a very large single disc clutch or brake, to provide equal torque capability. The reason is found in elementary trigonometry. A fourteen-surface device with a diameter of 9.50" has the same area as a single surface device of 35.5"! In most high-torque applications, the space does not exist to house a single disc device of such great size.

Similarly, at high rotational speeds, the tip velocity of a large single disc device could become a safety hazard. A 35.5" device rotating at 5,000 RPM has a velocity at its outer edge of almost 775 feet per second. How fast is that? Well, it is fast enough to be measured as a "Mach number" - in this case Mach .69. By comparison, a 9.5" multiple disc device rotating at the same speed has a velocity of about 200 feet per second.

A large single disc design necessitates engineering considerations and complications in bearing design, inertia loads, component size, shielding, etc. These factors can make multiple disc friction clutches and brakes a preferred power transmission solution where high torques are present. Single disc clutches and brakes tend to be larger but less costly than multiple disc clutches and brakes, because they contain fewer parts and are simpler to design, fabricate, and assemble.

Multiple disc friction clutches and brakes are usually much more compact although at a cost penalty due to their increased complexity.

Overview - Friction Clutch
& Brake Units

Advantages of Friction engagement

  • Soft engagement of devices to be coupled
  • Engagement speed is not limited

Advantages of Single Disc Friction
Clutches & Brakes

  • Best option for low-torque applications
  • Cost-effective

Advantages of Multiple Disc Friction
Clutches & Brakes

  • Handles high torque loads
  • Safer at high rotational speeds
  • Compact

CJM Friction Clutch & Brake Models

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