A coupling is a device that connects two shafts or a shaft and a rotating component, rotating together during the transmission of motion and power, and does not normally disengage. Sometimes it also serves as a safety device to prevent the connected components from experiencing excessive loads, providing overload protection.

 

 

Coupling Classification

        Couplings can be divided into Rigid Couplings and Flexible Couplings two major categories.

        Rigid Couplings They do not have the ability to buffer and compensate for the relative displacement of the two axes. Strict alignment of the two shafts is required. However, this type of coupling has a simple structure, low manufacturing cost, convenient installation and maintenance, ensures high alignment of the two shafts, transmits a large torque, and is widely used.

        Flexible Couplings Can also be divided into Couplings without elastic elements flexible couplings and flexible couplings with elastic elements The former only has the ability to compensate for the relative displacement of the two axes, but cannot buffer or dampen vibrations. Common examples include slider couplings, toothed couplings, universal couplings, and chain couplings; the latter, due to the inclusion of elastic elements, in addition to compensating for the relative displacement of the two axes, also has buffering and damping effects, but the transmitted torque is generally less than that of flexible couplings without elastic elements due to limitations imposed by the strength of the elastic elements. Common examples include elastic bushing pin couplings, elastic pin couplings, cloverleaf couplings, tire couplings, serpentine spring couplings, and leaf spring couplings.

Rigid Couplings

1 Flange Couplings

        Two half couplings with flanges are connected to the two shafts respectively using ordinary keys, and then the two half couplings are connected together with bolts to transmit motion and torque. The structure is simple, the manufacturing cost is low, the installation and disassembly are convenient, and it can ensure that the two shafts have high alignment accuracy and transmit large torque, but it cannot absorb vibration and impact. It is often used for equal diameter connections, low-speed, light-load, stable, impact-free, and long transmission shaft connections.

2 Sleeve Couplings

      Sleeve couplings use a common sleeve and rigid connecting components such as keys, splines, or tapered pins to connect the two shafts. Sleeve couplings have a simple structure, are easy to manufacture, have low cost, and small radial dimensions, but are inconvenient to install and disassemble, requiring axial movement of the shaft. Suitable for low-speed, light-load, impact-free load, balanced operation, and connections of shafts with upper size limits. The maximum operating speed generally does not exceed 250r/min . Sleeve couplings do not have axial, radial, and angular compensation capabilities.

 

3 Clamp Couplings

        Clamp couplings use two axially split clamps, clamped together with bolts to connect the two shafts. Torque is transmitted by the frictional force between the surfaces of the two half couplings, using keys as auxiliary connections. Easy to install and disassemble, no axial movement of the shaft is required, but the axial alignment accuracy of the two shafts is low, the structure and shape are more complex, the balance accuracy is low, and the manufacturing cost is high. Often used for equal diameter connections, low-speed, light-load, stable, impact-free, and long transmission shaft connections.

Flexible Couplings

Couplings without elastic elements

1 Toothed Couplings

        Toothed couplings consist of parts such as an inner gear ring with the same number of teeth and a flange half coupling with outer teeth. The outer teeth are of two types: straight teeth and drum-shaped teeth. The so-called drum-shaped teeth are made spherical, with the center of the sphere on the gear axis. The tooth side clearance is larger than that of ordinary gears. Drum-shaped toothed couplings allow for larger angular displacements. ( Compared to straight-toothed couplings ) it can improve the contact conditions of the teeth, increase the torque transmission capacity, and extend the service life. When the toothed coupling is working, the two shafts produce relative displacement, and the tooth surfaces of the inner and outer teeth periodically slide axially relative to each other, inevitably resulting in tooth surface wear and power loss. Therefore, the toothed coupling needs to work in a well-lubricated and sealed state. Suitable for connecting two shafts that transmit large torque, have large relative displacement, and have low installation accuracy requirements. The inner and outer teeth mesh, compensating for large radial and angular deviations, used in heavy machinery (such as rolling mills).

 

2 Universal Couplings

        Universal couplings utilize their structural characteristics to allow continuous rotation of the two connected shafts even when they are not on the same axis and have an angle between their axes, reliably transmitting torque and motion. The biggest advantage of universal couplings is that they have a large angular compensation capacity, compact structure, and high transmission efficiency. The angle between the axes of different types of universal couplings varies, generally between 5°-45° 之间。

3 Slider Couplings

      Torque is transmitted through the intermediate slider to compensate for radial deviations, but it is prone to wear at high speeds. The coupling has a simple structure, small radial dimensions, and is more complex to manufacture. It is suitable for connecting two shafts with small relative radial displacement, low speed, no violent impact, and high rigidity.

 

 

flexible couplings with elastic elements

1 Cloverleaf Couplings

        Cloverleaf couplings, also known as claw couplings, consist of two metal claw discs and an elastic body. A cloverleaf-shaped elastic element is placed between the protrusions of the two half couplings to connect them. It has the characteristics of compensating for the relative displacement of the two shafts, damping, buffering, small radial dimensions, simple structure, no lubrication required, high load-bearing capacity, and convenient maintenance.

 

2 Diaphragm Couplings

        Several sets of diaphragms (stainless steel thin plates) are connected to the two half couplings with bolts in an interleaved manner. Each set of diaphragms consists of several stacked plates. Diaphragms are divided into connecting rod type and different shapes of integral type. Diaphragm couplings rely on the elastic deformation of the diaphragms to compensate for the relative displacement of the two connected shafts. It is a high-performance flexible coupling with strong metal elements.

 

3 Tire Couplings

        The tire coupling is connected to the flanges of the two halves of the coupling by bolts. The torque is transmitted by the friction force generated between the tire and the flange end faces by tightening the bolts. The tire ring undergoes torsional shear deformation during operation, so the tire coupling has high elasticity and a large capacity to compensate for the relative displacement of the two shafts. It also has good damping, and its structure is simple, requiring no lubrication, and assembly, disassembly, and maintenance are relatively convenient. Its disadvantages are that its load-carrying capacity is not high and its external dimensions are large. When the torque is large, additional axial loads will be generated, so it is not suitable for occasions with large loads and high speeds, and the assembly of the tire ring is relatively difficult.

 

4 Bellows Coupling

        It uses a thin-walled tube (bellows) with a corrugated outer shape directly welded or bonded to the two halves of the coupling to transmit motion. This type of coupling has a simple structure, small external dimensions, convenient processing and installation, and high transmission accuracy. It is mainly used in small-power precision machinery and control mechanisms that require a compact structure and high transmission accuracy.

 

Selection Introduction

1 Type Selection

1) Two-shaft alignment conditions

- Strict alignment --- Fixed coupling

- Cannot guarantee strict alignment or displacement will occur during operation --- Movable coupling elastic coupling

- When zero backlash is required, select diaphragm type or groove type

- When high torque transmission is required, select diaphragm type, cross type, or star type

- Servo motors are often equipped with diaphragm type, while stepper motors often select groove type

- Cross type is often used in cylinders or film winding electric fields, and the precision performance is slightly inferior (requirements are not high)

2) Load conditions

Stable load or small changes ---Rigid coupling

Frequent starting and braking or large load changes ---Elastic coupling

3) Speed conditions

Operating speed < allowable speed of coupling

Low speed ---Rigid coupling

High speed ---Elastic coupling

4) Environmental conditions

Low environmental temperature (< -20℃) or high (>45℃) couplings with rubber or nylon as elastic elements should not be selected; consider installation dimensions

2 Size Selection

- Select according to the diameter of the shaft to be connected, speed, and calculated torque

3 Coupling Selection Process

- Based on the load conditions, first roughly select a type

- Coupling torque calculation ( T 電 ≥ T 聯)

- Determination of eccentricity and allowable space dimensions (eccentricity: angular deviation, axial deviation, radial deviation)

- Select the specific model according to the torque, eccentricity, and allowable space dimensions

- Finally determine the size of the shaft holes at both ends (the size of the shaft holes at both ends can be different)