Adjusting spring
A feather key is a machine element from mechanical engineering and is used to implement a shaft-hub connection . The connection is positive and is used to transmit torque (e.g. drive shaft - gear ).
construction
The feather key is a solid, elongated metal part with a rectangular cross-section , is inserted into a correspondingly milled feather key groove in the shaft and protrudes from it.
The associated hub is provided with a continuous and broached groove and is pushed axially over the feather key for assembly. The feather key acts as a driver by means of a form fit on its flanks and transfers the torque of the shaft to the component to be driven (in the case of a drive shaft) or the torque of the driving component to the shaft to be driven (in the case of an output shaft). The wheel must be secured against shifting on the shaft in the axial direction. Common forms of axial fixation on the shaft shoulder are locking rings or locknuts .
Dimensioning
The size of the feather key results
- for the cross-section from the shaft diameter (for example, the key cross-section (W × H) 12 × 8 mm is provided for a shaft diameter of 40 mm) and
- for the length from the torque to be transmitted (calculation of the surface pressure between hub and key and between key and shaft; the latter can often be omitted because the shaft material is usually stronger than that of the hub).
calculation
The calculation is only based on surface pressure, as the standard dimensions for the feather key are selected so that the permissible shear stress is not exceeded if the permissible surface pressure is maintained.
standard
|
DIN 6885 |
|---|---|
| Area | Security elements |
| title | Driver connections without tightening, keys, grooves, part 1: tall form; Part 3: low shape, dimensions and application |
| Latest edition | 1968-08 / 1956-02 |
| ISO |
Keys are standardized according to their shape and dimensions in DIN 6885. This standard specifies u. a. also states that a fit with the tolerance field P9, N9 or JS9 according to the standard shaft fit system according to DIN 7155 is used to tolerate the groove width . The feather key thus corresponds to a standard shaft with tolerance zone position h (upper dimension = 0). DIN 6892 specifies the design and calculation bases for feather key connections.
Design variants
There are round-faced feather keys, straight-faced feather keys as well as round-faced feather keys with retaining and jacking screws.
The usable length of a round-ended feather key is its total length minus its width, as the roundings on both sides in the hub do not carry. In the case of straight keys, the total length is to be used as the load-bearing length.
A similar type of shaft-hub connection is the woodruff key , formerly also known as a Woodruff wedge . Here a semicircular groove is milled in the shaft with a side milling cutter and a semicircular disk is inserted as a wedge. The hub is designed exactly as when using a feather key. The disadvantage of this variant is that the shaft is weakened more by the necessary, deeper groove, which is why this version is used less frequently.
Advantages / disadvantages and alternatives
- Advantages of a feather key connection:
- inexpensive
- easy to assemble / disassemble
- low manufacturing costs
- good recyclability
- Disadvantages of a feather key connection:
- Notch effect on the shaft
- the keyway weakens the load-bearing cross-section of the shaft and hub
- additional protection against axial displacement is necessary
- conditionally suitable when changing load direction
- not suitable for shock loads
- transmittable torque relatively low
- creates imbalance (remedy possible with several symmetrically arranged keys)
- Alternatives to the key connection:
Web links
swell
- ^ Gustav Niemann, Hans Winter, Bernd-Robert Höhn: Machine elements . 4th edition. 1: Construction and calculation of connections, bearings, shafts. Springer, Berlin, Heidelberg, New York 2005, ISBN 3-540-25125-1 , pp. 778 .