Slip Clutch Design Guide

In This Article:

How it Worksphoto of polyclutch mechanical slip clutches

Additional Resources


Construction

A Polyclutch® consists of two parts: a cartridge and a housing (see below).

Slip Clutch Operation

The cartridge is set screwed or keyed to the input shaft. The cartridge includes the clutch pack: outer plates, friction pads, inner plates

  • Plates are brass with a proprietary finish
  • Inner plates are keyed to the cartridge hub
  • Outer plates are keyed to the cartridge housing
  • Friction pads are a proprietary plastic-based composite (no asbestos)

The housing is either set screwed or keyed to the output shaft, or (as shown), attached to the output gear or pulley, with a bronze bearing to allow relative motion between the input shaft and the output gear/pulley.

Torque is controlled by changing the pressure applied to the clutch pack. In an adjustable style clutch, the torque level is controlled by compressing the springs with the adjusting nut. In a fixed style clutch, a collar is attached to the hub in a fixed position, and the torque level is set by pushing and locking the spring collar to a calibrated position.

All slip clutch torques are calibrated to +/- 20% but can be held to closer tolerances.

Backlash of 6° is standard for Slipper models and 2° for the Slip-Ease models. Slipper models can be held to 2° if required.

Our proprietary burn-in process insures that all clutches will perform consistently right out of the box, with no break-in period required.

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Installation

Shaft-through versions: Insert input shaft into cartridge and tighten set screws. Insert housing around input shaft, with torque pins engaging holes in outer plates. Input shaft will keep the cartridge and housing aligned.

Shaft to Shaft versions: Insert input shaft into cartridge and tighten set screws. Insert output shaft into housing and tighten set screws. Input and output shafts must be properly journaled with centerlines within +/- .010 T.I.R.

Do not lubricate the clutch. Friction materials are designed to run without additional lubrication. Lubrication will cause a change in torque and erratic behavior. The inherent axial loaded design will keep dirt and dust out of the friction surfaces.

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Capacity

The clutch capacity is based on continuous operation at 50 RPM for over 25 million cycles. Torque, RPM, duty cycle and life are interdependent. A reduction of any of these will allow an increase in any other. (Running at 25 RPM will allow twice the torque, or running for only 10% of the cycle will allow higher RPM, etc.)

The limit is based on heat buildup measured in watts per:

Watts = Torque (inch pounds) x RPM x Duty Cycle* x 0.011.

*(% of the time the clutch is slipping, expressed as a decimal. For example, 0.5 = 50% of the time the clutch is slipping)

Please consult our factory for high torque, high RPM and rapid cycling applications.

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Design Limitations

  • Max. 1.25" shaft size on a through-shaft
  • Min. 1/8" (3mm) bore size
  • Max. 750 lb-in torque limitation
  • Not to be used as a universal joint or a spring coupler
  • Does not de-couple at overload
  • Cannot be exposed to radiation
  • Contact a Polyclutch application specialist if slip clutch would be directly exposed to weather or wash down

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Design Advantages

  • Smooth, reliable breakaway and continuous slip
  • Proprietary burn-in process = no-stiction: static friction lower than dynamic friction
  • No-break in period: Precise torque with consistent repeatability from day 1
  • No sudden shock on sensitive paper/film/wire/thread, etc.
  • Long life of 20 to 30 million revolutions in slip condition
  • Torque range from 0.5 lb-in to 750 lb-in
  • Fixed, adjustable and custom designs
  • Clutches are bi-directional
  • No lubrication needed
  • Lower cost alternative to servo motors
  • More compact/smaller and less expensive than magnetic clutches
  • No reset required, no clicker (compare to ball detent)
  • Offers mechanical safety in mechanically controlled systems
  • American engineered and made in the USA

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Design Engineering Applications

Overload Protection: Protect machinery and operator. Clutch will slip when mechanism is jammed. Motion will continue when impediment is removed.
 
Torque Control: Screw bottle caps, screws, controls, etc., to correct torque setting. Combine with one way clutch to slip at rated torque in one direction and freewheel or positive drive in other direction.
  • Repeatable accurate torque for capping machines, automatic screw driving, valve control, etc.
 
Tension Control: Maintain constant tension while winding or unwinding wire, paper, film, thread, etc. Slip clutch automatically compensates for changes in speed and diameter. Pneumatic clutch can change tension during operation.
 
Force Control: Push product against gate with constant force. Remove gate and move to next position. No damage to product or conveyor – clutch does all the slipping. Also used for overload protection when jammed and for indexing the conveyor.
 
Position Retention and Brake: Hold lid, cover, door, screen, etc., at any position. Fingertip control. Combine with one way clutch for free movement in one direction 
  • Ideal for friction hinges when smooth movement of lids, doors, screens, covers, etc., is required
 
Indexing: Hold index wheel with solenoid operated pin. Motor runs continuously with clutch slipping. Pin pulls back to index to next station. Can be single or partial revolution. Can index tables, conveyors, vending machines, controls, etc.
 
Soft Starts/Cushioned Stops: Inertia makes clutch slip when starting and/or stopping. Results in less shock throughout the system. Ideal for slip at the end of stroke.
 

Field Application Examples

View several slip clutch field applications.

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CAD Drawings

2D or 3D CAD drawings for each model, standard bore sizes, to drop into your existing design project.  (Contact us directly for custom models)

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Slip Clutch Line Overview

A guide for selecting a Polyclutch: overview of all slip clutch product series. Maximum torque capacities and maximum input shaft sizes for each line.

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Literature

Download the Slip Clutch Catalog/Design Guide PDF


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