Wedge (technology)

Historical splines

A nose wedge on the pin and segment gear of a foundry furnace

Wood connection - longitudinal connection of the German wedge

Wood connection - longitudinal connection of the French wedge

The wedge is a machine element and serves as a shaft-hub connection . The wedge looks like a feather key , but is beveled at an angle of 34 '(corresponds to a tangent of 1: 100) and is driven into the corresponding groove with a hammer . In contrast to the feather key, in which the force is transmitted between the shaft and the hub by means of a form fit, in the case of a wedge connection this takes place by means of a force fit on its inclined surfaces in the radial direction. A special shape is the nose wedge , which is reinforced at one end so that it can be easily loosened with a wedge puller. Another design is the hollow wedge , which does not require a groove in the shaft.

This group of machine elements also includes the insert wedge , in which the associated hub is driven onto the wedge inserted into the shaft.

The disadvantage of these wedges lies in the fact that correct concentricity of the shaft and hub cannot be achieved. In the axial direction, the hub can only be fixed in an exact position on the shaft with a continuous groove. For this reason, the spline connection is only used for connections that do not require high accuracy, for example with slow running shafts. The maximum speed with wedge connections is around 1200 / min, whereby a strong imbalance of the system can already be felt. The advantage is that no further axial securing of the hub on the shaft is required.

C45K is usually used as the material for wedges ; production is in accordance with DIN 6880.

Areas of application

Wedge connections are mainly used in the following areas:

• Agricultural machinery
• Construction machinery
• Conveyor system construction

The advantage of wedge connections is that they are extremely insensitive to dirt.

Due to their installation, wedges cause a very unfavorable load profile, since there are only two contact surfaces between the shaft and the hub: the first at the point where the wedge is used and the second at the point exactly opposite the shaft. If two wedges are used, they are offset by 120 °, resulting in three contact points between the shaft and the hub. This makes the connection more suitable for alternating and shock loads.

Design of the wedge connection

The design of a wedge connection is based on the permissible surface pressure on the flanks, since an exact calculation is not possible due to the unknown actually acting driving forces. This preload is therefore neglected in the further calculation, and empirical values ​​are used for the permissible surface pressure values. The actual effective surface pressure is calculated as follows: Surface pressure on the flanks in . In which ${\displaystyle p={F_{u} \over {t_{2}l_{t}i}}}$ ${\displaystyle N \over {mm^{2}}}$

• ${\displaystyle F_{u}}$is the circumferential force on the shaft, which results from the torque to be transmitted ,
• ${\displaystyle {t_{2}}}$ the hub groove depth is
• ${\displaystyle l_{t}}$ the load-bearing wedge length is and
• ${\displaystyle i}$is the number of circumferential wedges.