Indexing, Backstopping, and Overrunning Clutches: A Short Guide

Mechanical clutches play a vital role in meeting industrial needs on a large scale. 

Clutches work in power transmission systems where you need to apply torque in one direction of rotation. The use of clutches today protects against backlash and rollover. Professionals divide mechanical clutches into three basic applications. They are indexing, backstop (holdback), and overrunning clutches. 

Keep reading for a short overview of these three mechanical clutches

Indexing Clutches

An indexing clutch turns a shaft one step at a time. The back and forth motion become only one direction of movement. First, the indexing clutch drives in the forward stroke. Then, it spins freely on the return stroke. This accomplishes indexed material feed or a variable speed.

Indexing clutches are typical in manufacturing using material feeders. The clutch can start and stop at set intervals.

Typical applications of indexing clutches include:

  • Assembling machines
  • Indexing tables
  • Metal stamping
  • Packing machines
  • Press working
  • Printing machines

Backstopping Clutches

The freewheel only allows rotation in one direction using a backstopping clutch. As a result, it constantly overruns during operation. The backstop clutch prevents the rotation from moving in the reverse direction. The backstop clutch bearing will automatically engage with a fixed frame when the torque is reversed. 

Backstops can transmit nominal torque mounted on solid shafts. However, if mounted on hollow shafts, the transmittable torque decreases.

Backstop clutches service as a safety measure to protect equipment from damage and ensure worker security. 

Applications that rely on a clutch backstop include:

  • Bucket elevators
  • Fans
  • Gear reducers
  • Incline conveyors
  • Pump systems 

You can also think of a backstopping clutch in a vehicle like a brake. The clutch stops the vehicle from rolling backward. 

Overrunning Clutches 

With an overrunning clutch, most of the time, the clutch spins freely. Overrunning clutches are familiar with two-speed drive applications. The freewheel disengages automatically when the driven member rotates faster than the driving member. 

When the secondary motor drives the machines, the clutch overruns, it switches the speed from low to high. 

Standard applications that use overrunning clutches are:

  • Conveyor belts
  • Creep and starter drives
  • Disengaged centrifugal masses
  • Dual motor or engine drives

Additionally, there are four main types of overrunning clutches. They are ramp & roller, sprag, wedge, and wrap spring. The distinguishing factor between each overrunning clutch is the design and use. 

Clutches for Your Applications

Indexing, backstopping, and overrunning clutches are essential for applications to function correctly. Knowing which clutch suits an application best is even more vital.

Contact us at Kor-Pak Corporation to speak with our professionals about the clutches you need for your applications. Our experts have the industry knowledge to assist you.

Posted in Industrial Brakes and Clutches.