Mechanical Lock-Up

Mechanical Lock-Up Clutches

Direct mechanical connection between input and output members is the most basic clutching method. Mechanical clutches are used in applications where exact, no-slip engagement and cycling is required.

Actuation of mechanical units can be manual or remote. Self-actuating types may use centrifugal force, wrapping, or a wedging action to engage input and output. Rotational speed, speed differential, and direction of rotation may trigger engagement. Other engagement types include pneumatic and hydraulic pressure to push a mechanism together or electromagnetism to pull surfaces together.

Types of Mechanical Lock-Up Clutches

Jaw Clutches

Square-jaw clutches have square teeth that lock into matching grooves in facing members. They provide instant, positive engagement in either direction of rotation. Because they cannot slip, safe engagement is only possible when shafts are stationary or moving at the same speed in the same direction. Running engagement is only possible up to about 10 rpm. Spiral-jaw have ramped surfaces on one side of the teeth allowing engagement speeds up to 150 rpm. They can only drive in one direction.

Multiple Tooth Clutches

Provide mechanical lock-up while allowing electromagnetic, hydraulic, or pneumatic engagement. Engagement is between many tapered, gear-like teeth. They offer much higher torque-carrying capacity than friction types of the same size and require a low or zero speed engagement.

Wrap-Spring Clutches

Link members with a coiled spring. Rotation in the direction of drive tightens the spring and transmits torque where rotation in the opposite direction will not transmit torque. They can drive in one direction and freewheel in the other. If one member is anchored, a wrap-spring unit serves as a backstop or brake. Examples: copiers, packaging, collators, and die cutting systems.

Sprag Clutches (Cam Clutch, Freewheels, Overrunning, Backstop, One-Way)

Sprags wedge between the cylindrical inner and outer races, transmitting torque when rotated. No outside control is needed. They drive in one direction and when rotation reverses, or if the output rotates faster than the input, they will slip or overrun.

Ramp and Roller Clutches

A roller moves along the ramp and wedges between input and output in one direction. In the other direction, the roller moves back on the ramp into an open space, disconnecting input and output.

Both sprag and ramp-roller designs can be used as a braking mechanism. If the outer race is stationary, the unit will freewheel in one direction and lock in the other, this is called backstopping. Both designs are used in overrunning applications where input and output are at two different speeds (back-up drives, creep drives).

Centrifugal Clutches

Consist of an input hub with friction-material shoes held in place. As the unit rotates, centrifugal force pushes the shoes against the outer member or drum. Greater speed causes greater torque transmission. Torque rise is gradual rather than immediate. They are used on high inertia loads such as bulk conveyors, mixers, or pumps where it is best to allow the motor to accelerate unloaded and introduce the load gradually.

Key Manufacturers of Mechanical Lock-Up Clutches We Offer

  • Formsprag Clutch (Altra)
  • Nexen
  • R+W America
  • Stieber Clutch (Altra)
  • UST Tsubaki
  • Warner Electric (Altra)


Content on this page was created using excerpts from the Power Transmission Handbook (5th Edition), which is written and sold by the Power Transmission Distributor’s Association (PTDA). The Power Transmission Handbook is just under 400 pages and is a valuable resource for anyone involved or interested in the power transmission industry.

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