Selection of a type of coupling of a shaft with a hub

The following comparison of basic properties of individual types of coupling may be helpful for a simpler selection of the type of coupling of a shaft with a hub. When selecting the design of the coupling, it is necessary to take into account its utility, time demands and financial costs of the design, production, assembly and disassembly of the coupling.

Design of the coupling

Shaped couplings

Shaped couplings of shafts with hubs are designed only for transfers of torsional moments. The transfer of external loading is ensured with these couplings using matching profiles of the shaft and hub (splined shafts, polygonal couplings) or inserted elements (pins, keys, wedges). Shaped couplings are loaded for deformation, shear and possibly for bend. For dimensioning of the coupling, only a check for deformation is usually authoritative and sufficient. Unlike friction couplings, there does not appear any additional stress in the hub here due to prestressing of the coupling. However, a considerable notch effect of holes and splines on the shaft is a disadvantage of this design. Therefore, it is necessary to check these shafts for shape strength.

Commonly used shape couplings

  1. Couplings with longitudinal (joint) pin
  2. Couplings with cross pin
  3. Couplings with keys
  4. Couplings with straight-sided splines
  5. Couplings with involute splines
  6. Polygonal couplings

Power (friction) couplings

Power couplings of shafts with hubs allow transfer of axial forces in addition to torsional moments. External loading in these coupling is transferred using friction between the shaft and hub, which appears in the coupling during its assembly. In case of clamping couplings and couplings with clamping rings, the friction in the coupling is caused by normal forces caused by bolts, hoops, conical surfaces or tapered rings. In case of pressure (pressed on) couplings the friction is caused by normal internal forces caused by elastic deformations of the coupled parts. In the course of assembly of the coupled parts, there appears pressure that must not exceed the permitted value. Smooth and non-weakened section of the shaft and options of very fine adjustment of the mutual position (turning) of the coupled parts are advantages when compared with shaped couplings.

Commonly used power couplings

  1. Pressed on couplings
  2. Clamping couplings with cylindrical surfaces
  3. Clamping couplings with conical surfaces
  4. Couplings with clamping (distance) rings

Prestressed shaped couplings

These couplings use a combination of both above-mentioned principles for transferring external loading. A typical example can be found in conical clamping couplings, pressed on polygonal couplings and couplings with longitudinal and axial wedges. Prestressed shaped couplings are rarely used in practice.

Utility properties of the coupling

Type of coupling Use, operation, maintenance and repair of the coupling Production and assembly of the coupling
Pin couplings  
  • For transfer of small, shock-free and non-cyclical torsional moments
  • The ability of the coupling to be disassembled must be ensured using a suitable design
  • Holes for cross pins have very adverse notch effects.
 
  • Very simple production
  • During assembly it is necessary to prevent release
  • Suitable for piece and lot production as well
Couplings using keys and wedges  
  • Only for transfer of torsional moments
  • Suitable for fixed couplings, less suitable for sliding couplings
  • Unsuitable for cyclical torsional moments
  • Centrical bearing of the hub
  • Reliability against fatigue breaks affected adversely by notch effects of the groove
  • Easy disassembly of the coupling
 
  • Production of grooves requires the use of special tools
  • Easy assembly of the coupling
  • In case of fixed couplings, it is necessary to prevent axial shifts
  • Suitable for piece production, less suitable for lot production
Splined couplings  
  • Only for transfer of torsional moments
  • Suitable for high loading, cyclical and shock loading
  • Suitable for fixed and sliding couplings as well
  • Ensuring co-axiality and perpendicularity of the coupling is not easy
  • Reliability against fatigue breaks affected adversely by notch effects of splines
  • Easy disassembly of the coupling
 
  • Production requires special machine equipment
  • Easy assembly of the coupling
  • In case of fixed couplings, it is necessary to prevent axial shift
  • Suitable for lot production, unsuitable for piece production
Polygonal couplings  
  • Only for transfer of torsional moments
  • Suitable for high and cyclical loading at high speed of rotation
  • Suitable for fixed and sliding couplings as well
  • High reliability against fatigue breaks
  • Easy disassembly of the coupling
 
  • Production requires special grinding machines
  • Easy assembly of the coupling
  • In case of fixed couplings, it is necessary to prevent axial shift
Pressed on couplings  
  • For transfer of torsional moments and axial forces as well
  • Suitable for high loading, cyclical and shock loading
  • High accuracy of co-axiality and perpendicularity of the coupling
  • High reliability of the coupling
  • Very difficult (impossible) disassembly of the coupling
 
  • High demands for accuracy of production
  • Relatively difficult and dangerous assembly
  • Suitable for piece and lot production as well
Clamping couplings  
  • For transfer of torsional moments and axial forces
  • Easy adjustment of mutual position of the parts
  • Reliability of the coupling depends on the manner of preventing clamping parts from release
  • High reliability against fatigue breaks
  • Easy disassembly of the coupling
  • A danger of injury to the operator from external non-rotary shapes during operation
 
  • Easy production and assembly of the coupling
  • It is necessary to machine the divided parts together
  • Suitable for piece and lot production as well
Couplings using clamping rings  
  • For transfer of torsional moments and axial forces
  • Easy adjustment of mutual position of the parts
  • Reliability of the coupling depends on the manner of securing the coupling against release
  • High reliability against fatigue breaks
  • Easy disassembly of the coupling
 
  • Relatively demanding production of rings (better to purchase finished components)
  • Simple production of the surfaces being connected
  • Easy assembly of the coupling

Time demanding design, production, assembly and disassembly of the coupling

Type of coupling Production and assembly of the coupling Disassembly of the coupling
Pin couplings Very fast production and assembly of the coupling Depends on the constructional design of the coupling
Couplings using keys and wedges Relatively slow production without special equipment

Fast assembly of the coupling

Fast
Splined couplings Relatively fast production only with the use of suitable equipment

Fast assembly of the coupling

Fast
Polygonal couplings Relatively fast production only with the use of suitable equipment

Fast assembly of the coupling

Fast
Pressed on couplings Fast production and assembly of the coupling Unsuitable for fast repairs and disassembly
Clamping couplings Fast production and assembly of the coupling Fast
Couplings using clamping rings Fast production and assembly of the coupling Fast

Costs for production, operation, assembly and disassembly of the coupling

Type of coupling Production costs Costs for disassembly of the coupling
Pin connections Low Minimum
Couplings with keys and wedges Medium Minimum
Splined couplings High

(economical only in case of lot production)

Minimum
Polygonal couplings High

(economical only in case of lot production

Minimum
Pressed on couplings Medium Considerable

(sometimes even impossible)

Clamping couplings Relatively small Minimum
Couplings using clamping rings Medium

(can be reduced by purchasing finished rings)

Minimum

In case of fixed couplings, the operational costs are zero, costs for sliding couplings are only given by lubrication