Definition and Function

A coupling is a mechanical device used to connect two shafts, allowing them to rotate together and transmit torque. Its main function is to effectively transmit the power of power sources (such as motors, engines, etc.) to working components (such as pumps, compressors, machine tools, etc.), while also compensating for axial, radial, and angular deviations between two shafts to a certain extent, reducing the transmission of vibration and impact, and ensuring the smooth operation of the shaft system.

Main types and structural characteristics

Rigid coupling

Structure: The rigid coupling mainly consists of two half couplings and connecting bolts. Two half couplings are tightly matched with the ends of two shafts, usually fixed to the shafts and half couplings through key connections, and then connected together with bolts. It has no elastic components, and its structure is simple and compact.

Features: Capable of transmitting large torque, suitable for situations with extremely high concentricity requirements and minimal relative displacement between working axes. However, due to the lack of buffering and compensation functions, high installation accuracy is required, otherwise it is easy to cause problems such as vibration and wear of the shaft and equipment.

Elastic coupling

Structure: usually includes an active half coupling, a driven half coupling, and elastic elements. Elastic components can be made of materials such as rubber, polyurethane, metal springs, etc. For example, the elastic elements of rubber elastic couplings are rubber blocks or rubber rings, which are distributed between the half couplings and connected to them through vulcanization and other processes.

Characteristics: While transmitting torque, the elastic deformation of the elastic element is used to compensate for the displacement deviation between the shafts, and it can effectively buffer and absorb vibration and impact. Suitable for situations with certain axial displacement and vibration, such as frequent start-up of some power equipment and significant load changes. However, the fatigue life of the elastic element will limit the service life of the coupling.

Hydraulic coupling

Structure: It mainly consists of a pump impeller, a turbine, and a working chamber filled with liquid (usually oil). The pump wheel is connected to the driving shaft, and the turbine wheel is connected to the driven shaft. During operation, the pump impeller rotates under the drive of the drive shaft, allowing the liquid in the chamber to obtain energy, which in turn drives the turbine to rotate, thereby achieving power transmission.

Features: It has good shock absorption, overload protection, and stepless speed regulation functions. It can adapt to large load changes and protect equipment through liquid slippage during overload. But there is a risk of liquid leakage and the efficiency is relatively low.

Toothed coupling

Structure: Composed of two half couplings with external teeth and two outer sleeves with internal teeth. The external teeth and internal teeth mesh with each other, transmitting torque through the contact between the internal and external teeth. To ensure good lubrication and sealing, toothed couplings are usually equipped with oil grooves and sealing devices.

Characteristics: It can transmit large torque and compensate for certain axial and radial displacement, but its structure is complex, the cost is high, and it requires high lubrication and maintenance.

working principle

Rigid coupling: When the driving shaft rotates, torque is transmitted to the half coupling through a key connection. The two half couplings are tightly connected by bolts, allowing the driven shaft to rotate synchronously and achieve torque transmission. Due to the absence of elastic elements, it requires the axes of the two shafts to be completely aligned, otherwise additional stress will be generated.

Elastic coupling: The driving shaft drives the driving half coupling to rotate, and the elastic element undergoes elastic deformation under the action of the driving half coupling. This deformation causes the driven half coupling to follow the rotation, thereby transmitting torque to the driven shaft. Elastic components play a crucial role in compensating for inter axis displacement and buffering vibration.

Hydraulic coupling: The active shaft drives the pump wheel to rotate, and the pump wheel agitates the liquid in the working chamber, allowing the liquid to gain kinetic energy. The liquid impacts the turbine, driving it to rotate and transmitting power to the driven shaft. During this process, the liquid plays a role in energy transfer and buffering.

Tooth type coupling: The driving shaft drives the outer half of the coupling to rotate, and the outer teeth mesh with the inner teeth. The torque is transmitted to the outer sleeve through the contact force between the teeth, and then transmitted to the driven shaft by the outer sleeve. The meshing of internal and external teeth can adapt to a certain axial displacement, and through appropriate lubrication, friction and wear between teeth can be reduced.

advantage

Realizing shaft connection and power transmission: Couplings can connect the shafts of different devices, effectively transmitting power from one device to another, ensuring the coordinated operation of the entire mechanical system.

Compensating for inter axis deviation: Except for rigid couplings, most couplings have a certain compensation function, which can adapt to the axial, radial, and angular displacement of the shaft during installation and operation, reducing equipment damage and failure caused by poor shaft alignment.

Buffer and shock absorption: Elastic couplings and hydraulic couplings can buffer and absorb vibrations and impacts from power sources, protect connected equipment, and improve the service life and reliability of equipment.

Disadvantages and countermeasures

Wear and tear issue: Regardless of the type of coupling, wear and tear may occur during long-term use. For example, the tooth surface of a toothed coupling is prone to wear, while the elastic components of an elastic coupling may experience fatigue wear. The response measures include regular inspections of wear and tear, and timely replacement of severely worn components; In the design phase, select appropriate materials and structures to improve the wear resistance of components.

High requirements for lubrication and sealing (some couplings): For example, gear couplings and hydraulic couplings require good lubrication to ensure normal operation while preventing liquid leakage. It is necessary to regularly inspect the lubrication system and sealing device to ensure the quality and quantity of lubricating oil, and replace damaged seals in a timely manner.

Application scenarios

Industrial field: In various industrial production lines, such as machinery manufacturing, chemical industry, power, mining and other industries, couplings are used to connect motors with pumps, compressors, crushers, conveyor belts and other equipment, ensuring stable power transmission and normal operation of equipment.

In the field of transportation, couplings also play an important role in the power systems of vehicles such as automobiles, ships, and railway locomotives. For example, the main engine of a ship is connected to the propulsion shaft system through a coupling to transmit power and adapt to the vibration and displacement of the shaft system.