Selection of coupling

The selection of the coupling mainly considers the speed of the required transmission shaft, the size of the load, the installation accuracy of the connected two parts, the stability of rotation, the price, etc., and selects a suitable coupling type with reference to the characteristics of various couplings.
The following points can be considered in the specific selection:
1. Due to manufacturing, installation, load deformation and temperature change, it is difficult to maintain the strict and accurate alignment of the two shafts after installation and adjustment. There is the necessary displacement and deflection angle CI in X and Y directions. When the radial displacement is large, the slider coupling can be selected, and the universal coupling can be selected for the connection of large angular displacement or intersecting two shafts. When the two shafts produce large additional relative displacement during operation, the flexible coupling shall be selected.
2. The working speed of the coupling and the centrifugal force caused by it. For high-speed transmission shafts, couplings with high balancing accuracy, such as diaphragm couplings, should be selected, rather than slider couplings with eccentricity.
3. Magnitude and nature of torque to be transmitted and requirements for vibration damping function. For example, for high-power heavy-duty transmission, gear coupling can be selected. For transmission with severe impact load or requiring elimination of torsional vibration of shaft system, tire coupling can be selected.
Most couplings have been standardized or normalized. The designer's task is to choose, not design. The basic steps of selecting coupling are as follows:
Select the type of coupling
According to the size of the transmitted load, the speed of the shaft, the installation accuracy of the connected two parts, and referring to the characteristics of various couplings, select a suitable coupling type.
The following points can be considered in the specific selection:
1) The magnitude and nature of the torque required to be transmitted, as well as the requirements for the buffer and damping function. For example, for high-power heavy-duty transmission, gear coupling can be selected; For the transmission with severe impact load or requiring to eliminate the torsional vibration of shaft system, the coupling with high elasticity such as tire coupling can be selected.
2) The working speed of the coupling and the centrifugal force caused by it. For high-speed transmission shafts, couplings with high balancing accuracy, such as diaphragm couplings, should be selected, rather than slider couplings with eccentricity.
3) The magnitude and direction of the relative displacement of the two axes. When it is difficult to maintain the strict and accurate alignment of the two shafts after installation and adjustment, or the two shafts will produce large additional relative displacement during operation, the flexible coupling shall be selected. For example, when the radial displacement is large, the slider coupling can be selected, and the universal coupling can be selected for the connection of large angular displacement or intersecting two shafts.
4) Reliability and working environment of coupling. Generally, the coupling made of metal elements without lubrication is more reliable; The performance of couplings requiring lubrication is easily affected by the degree of lubrication perfection and may pollute the environment. Couplings containing rubber and other non-metallic components are sensitive to temperature, corrosive medium and strong light, and are easy to age.
5) Manufacturing, installation, maintenance and cost of coupling. On the premise of meeting the convenience performance, the coupling with convenient assembly and disassembly, simple maintenance and low cost shall be selected. For example, the rigid coupling is not only simple in structure, but also easy to assemble and disassemble. It can be used for transmission shafts with low speed and high rigidity. General non-metallic elastic element couplings (such as elastic sleeve pin coupling, elastic pin coupling, quincunx elastic coupling, etc.) are widely applicable to general medium and small power transmission due to their good comprehensive ability.
Selection and calculation of universal coupling
Calculated torque of universal coupling:
Tc=TKnKhK Ka≤Tn(N·m)
Under alternating load: TC ≤ TF (n · m)
Where TN - nominal torque of universal coupling, n · m, (it is the theoretical calculation value under given conditions, i.e. coupling speed, n ≈ 10R / min. bearing life ln = 5000h, axis angle = 3 °, and the value when the load is stable);
TF -- fatigue torque of universal coupling, n · M
T -- Theoretical torque of universal coupling, n · M
T=9550
PW -- driving power, kw
N -- rotating speed of universal coupling, R / min
Kn -- speed correction coefficient of universal coupling,
KH -- correction coefficient of bearing life of universal coupling
K -- correction coefficient of angle of two axes of universal coupling
Ka -- load correction coefficient. When the load is uniform and the work is stable, Ka = 1.0; In case of uneven load and medium impact, Ka = 1.1 ~ 1.3; Ka = 1.3 ~ 1.5 for large impact load and frequent forward and reverse rotation, and Ka > 1.5 for large impact load and frequent forward and reverse rotation.
For the universal coupling with high speed, large folding angle or its length exceeding the provisions, in addition to the above calculation, its rotation flexibility must also be checked. The rotation flexibility is expressed in N, generally: n > 18000.
Where - axis angle of universal coupling, (°); N -- rotational speed of universal coupling, R / min