Couplings belong to the category of general mechanical parts and are used to connect the active and driven shafts in different institutions to rotate together so that they rotate together. Often synthesised from two halves, respectively, with a key or a tight fit and other couplings, fastened at the end of the two shafts, and then by some means the two halves of the coupling together. Couplings can be both compensation between the two shafts due to manufacturing and installation inaccuracies, deformation or thermal expansion and other reasons for the occurrence of the offset (including axial offset, radial offset, angular offset or a combination of offset); as well as mitigation of shock, and vibration absorption.
Couplings can be divided into two main categories, one is a rigid coupling, the other is a flexible coupling. Rigid coupling does not have the ability to cushion and compensate for the relative displacement of the two axes, requiring the two axes to be strictly centred, but this type of coupling structure is simple, easy to install, dismantle and maintain, to ensure that the two axes have a high degree of alignment, the transfer of torque is larger, widely used. Flexible coupling has no elasticity and elasticity of two types, no elasticity with the ability to compensate for the relative displacement of the two axes, but can not cushion shock absorption; elasticity of this type of elastic element, in addition to the ability to compensate for the relative displacement of the two axes, but also has the role of buffer and shock absorption. Therefore, the selection of the coupling needs to have a lot of attention.
The selection of couplings is mainly based on factors such as the speed of the shaft to be transferred, the size of the load, the mounting accuracy of the two parts to be coupled, the smoothness of rotation, and the price. Referring to the characteristics of various types of couplings, choose a suitable type of coupling. Most of the couplings have been standardised or specification, the designer's task is to select rather than design, the basic steps for selecting couplings are:
1. The size and nature of the torque to be transmitted, as well as the requirements of the buffer damping function. For example, for high-power heavy-duty transmission, can choose the tooth type coupling; for serious shock load or require the elimination of torsional vibration of the shaft system transmission, can choose the tyre-type coupling and other couplings with high elasticity.
2. The working speed of the coupling and the size of the centrifugal force caused by the high-speed transmission shaft, should be used to balance the high accuracy of the coupling, such as diaphragm coupling, etc., and should not be selected there is an eccentric slider coupling, etc..
3. The size and direction of the relative displacement of the two shafts when the installation and adjustment, it is difficult to maintain strict and accurate alignment of the two shafts or work in the process of the two shafts will produce a large additional relative displacement, should be used in flexible couplings. For example, when the radial displacement is large, the slider coupling can be selected, large angular displacement or intersection of the two shafts can be selected universal coupling.
4. The reliability of the coupling and the working environment is usually made of metal components, do not need to lubricate the coupling is more reliable, need to lubricate the coupling of its performance is susceptible to lubrication of the perfect degree of influence, and may contaminate the environment; containing non-metallic components such as rubber couplings, temperature, corrosive mediums and light, etc. is more sensitive, and prone to aging.
5. Due to manufacturing, installation, load deformation and temperature changes and other reasons, when the installation and adjustment is difficult to maintain strict and accurate alignment of the two axes, there is a certain degree of displacement in the X, Y direction and skew angle CI, when the radial displacement is larger, the slider coupling can be selected; angular displacement of the larger or intersecting the two axes of the coupling, you can choose universal coupling and so on. When the work process produces a large additional relative displacement, should be selected with flexible coupling.
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