Design and Function of Freewheels

Freewheels are machine elements with ­particular characteristics:

  • In one direction of rotation there is no contact between the inner and outer ring; the freewheel is in freewheeling operation.
  • In the other direction of rotation there is ­contact between the inner and outer ring; in this direction it is possible to transmit high torque.

For example the outer ring of the freewheel shown in the figure beside can freewheel clockwise while the inner ring is stationary. If, however, the outer ring is turned in the opposite direction, there is contact between the inner and outer ring and the inner ring is driven (driving operation).

Freewheels are used as:

  • Backstops
  • Overrunning Clutches
  • Indexing Freewheels

Freewheels can fulfill these functions complete­ly automatically in the most diverse machines. No mechanical or hydraulic operating equipment is required, as for example with external actuated clutches or brakes.

 

Freewheels consist of an inner and an outer ring between which clamping elements are arranged. Clamping elements can be sprags or rollers. We differentiate as follows:

  • Freewheels with bearing support and
  • Freewheels without bearing support.

For a freewheel to function, the concentric alignment of the inner and outer ring is required. In the case of freewheels without bearing support, concentric alignment like this must be provided by the customer.

RINGSPANN freewheels are an indispensable design element in the machine building industry as well as in the aerospace industry. Many designs are only economical if freewheels are used. The freewheel as an automatic driving element is preferred to conventional solutions because it offers the following significant
advantages:

  • operating safety,
  • efficiency and
  • a higher degree of automation.

With more than 50 years experience in the development, production and sales of freewheels, RINGSPANN offers the most comprehensive range of freewheels. A global network of subsidiaries and sales agencies ensures the best possible personal on-site service. Assembly and production facilities in various countries provide fast, reliable delivery.

 

Applications of Freewheels

Backstop

Freewheels are used as backstops if reverse rotation of the operating direction is to be prevented. In many machines and installations, for technical safety or functional reasons, it is necessary to ensure that you are working in just one specified direction of rotation. This is why there are legal stipulations requiring a mechanical safety device for the operation of, e.g. conveyor systems.

The normal operating mode of a backstop is freewheeling operation; the locking (torque transmission) is performed at zero speed. The immediate engagement of the clamping elements ensures the required high operating safety.

 

In general, backstops are used where the inner ring freewheels and the stationary held outer ring prevents reverse rotation.

 

The more complicated designed backstops where the outer ring freewheels and the stationary held inner ring prevents reverse rotation are rarely used today.

Overrunning Clutch

The overrunning clutch engages machines or machine parts and automatically interrupts their contact as soon as the driven part of the overrunning clutch is turned faster than the driving part. In many cases, this can replace a more expensive externally actuated clutch.

With overrunning clutches the engagement takes place in the driving operation (torque transmission), while in freewheeling operation the torque transmission between the inner and outer ring is interrupted. In ­driving operation the speeds of the inner and outer ring are equal, while in free­wheeling operation they are different.

 

The figure shows an overrunning clutch where in driving ­operation the power flow is transferred from the inner ring to the outer ring and in freewheeling operation the outer ring overruns the inner ring at a higher speed.

 

The figure shows an overrunning clutch where in driving ­operation the power flow is transferred from the outer ring to the inner ring and in freewheeling operation the inner ring overruns the outer ring at a higher speed.

Indexing Freewheel

The indexing freewheel transmits a back and forth motion into a stepped rotation (indexed feed). The RINGSPANN indexing freewheel works precisely and quietly and enables an infinitly adjustable setting of the feed.

 

The figure shows an indexing freewheel where the outer ring makes the back and forth motion and the inner ring carries out the indexed feed.

 

The figure shows an indexing freewheel where the inner ring makes the back and forth motion and the outer ring carries out the indexed feed.

Areas of Application for Freewheels

Areas of application for Backstops

Gear units

Electric motors

Gear motors


The backstop prevents reverse rotation in a drive of a conveyor ­installation if the power fails or the motor is turned off.

 

Inclined conveyors

Elevators

Bucket elevators


The backstop prevents reverse rotation of the conveyor load if the power fails or the motor is turned off.

 

Gebläse

Ventilatoren



The backstop prevents reverse rotation under the back pressure of the conveyed medium if the motor is turned off.

Pumps

Compressors


The backstop prevents reverse rotation under the back pressure of the ­conveyed medium if the motor is turned off.


Areas of application for Overrunning Clutches

Textile machines

Printing machines


During normal operation of textile or printing machines, the ­overrunning clutch separates the barring drive which is used for set up from the main drive.

 

Fans

Ventilators


If fans or ventilators are turned off, the overrunning clutch ­prevents the flywheel mass from rotating the drive.

 

Pumps

Generators


In multimotor drives the overrunning clutch disengages the inactive or lower speed drive.

Roller conveyor


The overrunning clutch ensures that the conveyed material can be pushed or pulled faster over the rollers than the speed of the drive.


Areas of application for Indexing Freewheels

Textile machines

Printing machines


The indexing freewheel generates an indexed feed in textile and printing machines.

 

Packaging machines

Filling plants


The indexing freewheel is used in packaging machines and filling plants for an indexed feed.

 

High voltage switches



In high voltage switches for tensioning a spring, the indexing freewheel is used in the place of a reduction gear.

Seed spreader


The indexing freewheel replaces a reduction gear in seed spreader.

Categories of Freewheels

Complete Freewheels

  • With bearing support between inner and outer ring
  • Completely enclosed
  • With own lubrication
  • Connection to the outer ring and the ­customer part by:
    - bolting to the face,
    - mounting flange,
    - keyway connection on the outer ring,
    - lever arm or
    - shaft coupling.
 
 

Housing Freewheels

  • With bearing support between inner and outer ring
  • Completely enclosed by its own housing
  • With own lubrication
  • With bearing supported input and output shafts
  • Stationary arrangement
 

Basic Freewheels

  • With bearing support between inner and outer ring
  • For assembly with connecting parts
  • Lubrication – if necessary – to be provided by the customer
 

Integrated Freewheels

  • Without bearing support. Concentric ­alignment of inner and outer ring must be provided by the customer
  • Integrating the outer ring on the customer part by bolting to the face
  • Lubrication – if necessary – to be provided by the customer
 

Internal Freewheels

  • Series both with and without bearing ­support. In the case of series without ­bearing support, concentric alignment of the inner and outer ring must be provided by the customer
  • Installing the outer ring in the customer´s housing with press fit or keyway connection. This makes compact, space-saving ­solutions possible
  • Lubrication – if necessary – to be provided by the customer
 

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