MITcalc - 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

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

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