The Role And Selection of Different Types of Couplings

Couplings are commonly used components in mechanical transmission. They are mainly used to connect two shafts or shafts between different components and other rotating parts, make them rotate together and transmit torque, and sometimes can also be used as a safety device. The difference is that in the process of mechanical operation, the coupling realized by the coupling cannot be disconnected, while the coupling realized by the clutch can be disconnected or connected at any time by the operating mechanism or the automatic control device.

different types of couplings

1. Flange Coupling

Flange coupling (also known as flange coupling) is to use bolts to connect two flanged disc half couplings. The two half couplings are respectively connected to the two shafts by keys to realize the connection of the two shafts and the transfer Moments and movements. Flange coupling is simple in structure, easy to manufacture, low in cost, reliable in operation, convenient in assembly and disassembly and maintenance, and large in transmission torque, which can ensure high alignment accuracy of the two shafts, and is generally used for stable load. High-speed or high-accuracy transmission requires high shafting transmission. Flange coupling does not have the performance of radial, axial and angular compensation. If the accuracy of the alignment of the two shafts cannot be guaranteed during use, the service life of the coupling, transmission accuracy and transmission efficiency will be reduced, and cause Vibration and noise.

2. Slider Coupling

The structure of the slider coupling is similar to the cross slider coupling. The difference is that the intermediate cross slider is square. The intermediate slider is used to slide in the corresponding radial groove on the end surface of the half coupling on both sides to achieve two Half coupling coupling. The slider coupling has a loud noise, low efficiency, and fast wear. Generally, it is not used as much as possible, and it is only used in occasions where the speed is very low. 

3. Chain Coupling

The chain coupling utilizes a common chain and is simultaneously meshed with two parallel sprockets with the same number of teeth. The main difference between different types of chain couplings is the use of different chains. The common two-row roller chain couplings, single Row roller chain coupling, toothed chain coupling, nylon chain coupling, etc. The performance of the double-row roller chain coupling is better than other structural couplings. It has a simple structure and is easy to assemble and disassemble. It does not need to move the two coupled shafts during disassembly. It has a compact size, light weight, and a certain compensation capacity. It has the advantages of low installation accuracy, reliable operation, long life and low cost. The main models are: GL type (without cover), GLF type (with cover).

4. Tooth Coupling

A toothed coupling is composed of an inner ring gear with the same number of teeth and a flange half coupling with external teeth. The external teeth are divided into two kinds of straight teeth and drum teeth. The so-called drum teeth are made by making the external teeth into a spherical surface. The center of the spherical surface is on the gear axis, and the tooth side clearance is larger than that of the general gear. Large angular displacement (relative to straight tooth coupling) can improve the contact conditions of the teeth, improve the ability to transmit torque, and extend the service life. When the toothed coupling works, the relative angular displacement of the two shafts occurs, and the tooth surfaces of the internal and external teeth periodically slide relative to each other in the axial direction, which will inevitably form tooth surface wear and power consumption. Therefore, the toothed coupling requires good lubrication and Sealed state. The toothed coupling has a small radial size and a large load carrying capacity. It is often used for low-speed and heavy-duty working conditions. The high-precision and dynamically balanced toothed coupling can be used for high-speed transmission. Because the angular compensation of the drum-shaped gear coupling is greater than that of the straight gear coupling, it is widely used.

5. Universal coupling

Universal couplings have a variety of structural forms, and common ones include cross shaft universal couplings and ball cage universal couplings. The common feature of the universal coupling is that the angular compensation is large, and the angle between the two axes of the universal coupling of different structural forms is different, generally between 5 and 45 degrees. It is mainly divided into: SWC type universal coupling, SWP type universal coupling, SWZ type universal coupling, WSD type universal Coupling, WS type universal coupling, WSH type sliding bearing universal coupling.

6.diaphragm coupling

Diaphragm coupling is made up of several sets of diaphragms (stainless steel) connected with two coupling halves by bolts. Each set of diaphragms is formed by stacking several pieces. The diaphragms are divided into connecting rods and different shapes. Slice. The diaphragm coupling relies on the elastic deformation of the diaphragm to compensate for the relative displacement of the two shafts. It is a high-performance flexible coupling with metal elastic elements. It does not require lubrication. It has a compact structure, high strength, and long service life. No rotation gap, not affected by temperature and oil pollution, with acid, alkali and corrosion resistance characteristics, suitable for high-temperature, high-speed, corrosive medium working environment shaft drive, widely used in various mechanical devices shaft drive, Such as water pumps, fans, compressors, hydraulic machinery, petroleum machinery, printing machinery, textile machinery, chemical machinery, mining machinery, metallurgical machinery, aviation (helicopters), high-speed power transmission systems for ships, steam turbines, piston power mechanical transmission systems, crawlers The high-speed, high-power mechanical transmission system of the type vehicle and the generator set is applied to the high-speed transmission shaft system after dynamic balancing. Compared with the gear coupling, the diaphragm coupling has no relative sliding, no lubrication, sealing, noise, and basically no maintenance. It is more convenient to manufacture and can partially replace the gear coupling.

Drum-shaped gear coupling has large bearing capacity; large angular displacement; long service life; under the same conditions, the torque transmitted by the straight-tooth coupling is increased by 15 to 30%; the structure is reasonable and the performance is reliable. The side is drum-shaped, so that the contact condition of the axis is improved at a certain angle, thereby reducing the contact stress, eliminating the load concentration of the tooth end of the straight tooth coupling, that is, eliminating edge compression, improving work performance. The compensation performance is good. The tooth shape of the external gear sleeve is drum-shaped, which increases the relative deviation allowed of the two connected shafts. The allowable inclination angle can be up to 6 degrees, generally 1.5°~2.5°. Commonly used for low-speed and heavy-duty shafting transmission; dynamically balanced tooth coupling can be used for high-speed transmission: such as gas turbine shafting transmission. Disadvantages: complex manufacturing; needs lubrication.

The load-bearing capacity and life of the drum-shaped gear coupling depend on the contact strength, and the radius of curvature of the tooth surface and the tooth mesh angle directly affect the contact strength. The relationship between the tooth mesh angle and the radius of curvature and the contact strength-a contact stress F-the gear bear Circumferential force E-material elastic modulus-tooth surface curvature radius-displacement circle radius-meshing angle-tooth internal and external tooth meshing height Tooth surface curvature radius and tooth meshing angle directly affect the contact stress, the meshing angle is small and the radius of curvature is large, the contact radius is large Low stress. The meshing angles of drum-shaped gear couplings abroad are 20°, 21.5°, 28°, and 30°. We choose a 20° meshing angle to help reduce contact stress.

Selection for Coupling 

The choice of the coupling mainly needs to consider the level of the transmission shaft speed, the size of the load, the installation accuracy of the two connected parts, the stability of the rotation, etc. With reference to the characteristics of various types of couplings, choose a suitable coupling type, basically as follows:

1. The size and nature of the torque to be transmitted and the requirements for the buffer and vibration reduction function

Due to the difference in structure and materials, the coupling capacity of the coupling used in the transmission system of each mechanical product is different. The torque during frequent start, reverse rotation and braking is several times the torque during normal and smooth operation. It is overloaded and will shorten the service life of the elastic element of the coupling. The coupling only allows short-term overload, generally short When overloading, it should not exceed 2~3 times of the nominal torque. For example: For transmission under high power and heavy load, a toothed coupling can be used. The toothed coupling transmits a large torque, but it must be lubricated and sealed to work continuously. It is necessary to check the sealing situation frequently and note Lubricating grease; for the transmission with severe impact load or the requirement to eliminate the torsional vibration of the shaft system, a coupling with high elasticity can be selected.

2. The working speed of the coupling and the bow|centrifugal force

The allowable speed of various types of couplings is determined by calculation based on the allowable linear speed and maximum outer edge size of different materials of the coupling. The allowable speed range of couplings of various varieties and specifications is different. You can increase the allowable speed range of the coupling by changing the material of the coupling product. For high-speed transmission shafts, the centrifugal force on the outer edge of the coupling should be considered, and a coupling with a higher balance accuracy can be selected. For example: precision diaphragm coupling, high-precision drum gear coupling, etc.

3. The magnitude and direction of the relative displacement of the two axes

Due to manufacturing errors, assembly errors, installation errors, deformation of the main and driven shafts due to manufacturing errors, assembly errors, installation errors, deformation of the base, temperature changes, relative movement between various components, etc. And the relative displacement produced. The displacement direction, axial, radial, angular (a) and displacement amount produced by the shafting transmission under different working conditions are different. In practical applications, after installation and adjustment, it is difficult to maintain strict and accurate alignment of the two shafts, and a flexible coupling that compensates for the relative displacement of the two shafts should be selected. For example: if there is axial movement, and the shaft system that needs to control the axial displacement rotates, the elastic diaphragm coupling should be used. When the radial displacement is large, the slider coupling can be used. Universal couplings can be used for the connection with large angular displacement or intersecting two shafts.

4. Reliability and working environment of the coupling

Various types of couplings are used with different types of host products. The working environment around them is relatively complicated. The conditions of temperature, humidity, water, dust, various acid and alkali media, and radiation all have an impact on their long-term continuous operation. Couplings that are usually made of metal components and do not require lubrication are more reliable;

Couplings that require lubrication are susceptible to lubrication performance and may pollute the environment. Couplings containing non-metallic components such as rubber are sensitive to temperature, corrosive media, and strong light, and are prone to aging.

5. Coupling manufacturing, installation, maintenance and cost.

The structural types, materials and manufacturing accuracy of various types of couplings are different, and their costs and manufacturing costs are very different. When purchasing, you can choose a coupling that is easy to assemble and disassemble, simple to maintain, and low in cost on the premise of meeting the requirements for use and performance.

When selecting a coupling, the user should select the specifications and specifications suitable for their own use from the standard coupling according to the actual conditions and requirements, and the above factors.