Basic knowledge of couplings(1)

Coupling

In course of work, mechanical part that makes two axes always connected is called coupling.

1. Function

Couplings are commonly used to couple two shafts and transfer motion and torque between them; It has the ability to absorb vibration and mitigate shocks; It can be used as a safety device to prevent the connected parts from being subjected to excessive loads and to protect against overload; When the shaft is coupled with the coupling, the two shafts can be separated only after the machine is stopped.

2. Classification

3. Classification requirements

Fixed coupling: Requires the centerline of the two axes being joined to be strictly centered.

Movable coupling: Allows a certain installation error for both axes.

Flexible coupling: Different materials of the elastic element can compensate the displacement between the two axes within a certain range, and also buffer the shock absorption.

4. Displacement compensation

Due to manufacturing and installation errors, post-loading deformation, bearing wear, unbalanced rotating parts, and temperature variations, the axes of the two shafts coupled by the coupling often have some degree of relative displacement and deflection.

The coupling has to take various measures on the structure to make the coupling have the ability to compensate for various offsets, otherwise it will cause additional loads in the shaft, coupling and bearing design, resulting in deterioration of working conditions.

The types of displacement between the two axes are: axial displacement, radial displacement, angling displacement and integrated displacement.

Fixed rigid coupling

1. Structural features

A. Simple structure, convenient maintenance and high torque transmission.

B. Lack of compensation for relative displacement between two axes.

C. Alignment of the two shafts is very high. If the two axes are relatively displaced, it will cause additional load and severe wear on the shaft, coupling and bearing, which will seriously affect normal operation of the shaft and bearing. In addition, shock and vibration absorption cannot be alleviated when the load is transmitted.

2. Application

Low speed, high torque, smooth load, short and rigid shaft connection.

3. Kinds

Flange coupling and sleeve coupling.

4. Flange coupling structure features

A. Composition: Two flanged half-couplings and a set of bolts.

B. Working principle: The two flanged half-coupling halves are connected by two shafts respectively, and then the two coupling halves are bolted together to transmit motion and torque.

C. Centering mode: 1. Centering by mutual fitting of two coupling halves with shoulders and grooves, the semi-couplings are connected by ordinary bolts; (The torque is transmitted by the friction force generated by the pre-tightening ordinary bolt on the contact surface of the flange; the centering of the bolt with the hinge hole is subjected to the pressing and shearing transmission torque by the screw.) 2. Both semi-couplings are formed with shoulders that cooperate with a split ring for centering.

D. Application: Low speed, high torque, smooth load, short and rigid shaft connection.

E. Simple structure, large transmission torque, reliable transmission force and good neutrality, convenient assembly and disassembly, and wide application; but no displacement compensation function.

5. Sleeve coupling structure features

A. Composition: The common sleeve is connected to the two shafts by a key connection or a pin.

B. Advantages: Simple structure, convenient manufacture, low cost and small radial size.

C. Disadvantage: It needs to move axially when assembling and disassembling.

D. Applications: When the diameter of the two shafts is small, the two shafts have high neutral precision and the work is stable, it is used for occasions with low transmission torque.