Structural Analysis and Design of Industrial Cardan Shaft

The industrial cardan shaft assembly is mainly composed of the cardan shaft and its spline welded at both ends and universal joint forks. The cardan drive shaft is generally provided with a sliding spline composed of a sliding fork and a spline to change the transmission length.

The length and angle of the industrial transmission shaft change in a certain range when it is working. The design shall ensure that the spline sleeve and shaft have sufficient length when the shaft length is at the maximum value. While the length is at the minimum value, the spline sleeve does not stick with the shaft. The angle of the industrial propeller shaft directly affects the service life of the universal joint, the service life of the universal transmission efficiency and the unevenness of rotation of the cross shaft.

When the length is fixed, the choice of sectional dimension of the transmission shaft should ensure that the cardan shaft has enough strength and high enough critical speed. The so-called critical speed refers to the speed when the working speed of the transmission shaft is close to its bending natural vibration frequency, namely the resonance phenomenon occurs, so that the amplitude increases sharply and causes the transmission shaft to break. The critical speed Nk of the transmission shaft is:

Nk=1.2×108(√Dc2+dc2)/Lc2

Where, Lc is the length of transmission shaft, that is the distance between the center of two universal joints; Dc and dc are the inner and outer diameters (mm) of the shaft tube of the transmission shaft.

When designing the transmission shaft, the safety factor K=nk/nmax=1.2~2.0 is taken. K=1.2 is used for accurate dynamic balance, high-precision expansion spline and universal joint clearance comparison, and nmax is the maximum speed of the transmission shaft (r/min).

When the length of the transmission shaft exceeds 1.5m, in order to improve the nk and the overall layout, the transmission shaft is usually broken into two or three, the universal joint uses three or four,KL,and the intermediate support is added on the middle transmission shaft.

In addition to meeting the requirement of critical speed, the sectional dimension of the shaft tube should also ensure sufficient torsion strength. The torque stress of the shaft should be satisfied:

τc= 16DcTs/π（Dc4-dc4）≤[τc]

In the formula, τc is allowable torsion shear stress, which is 300Mpa; The rest of the signs are the same.

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