A coupling is a device that connects two shafts or two shafts with rotating parts. In the process of transmitting motion and power, they rotate together and do not separate under normal conditions. Sometimes it is also used as a safety device to prevent the connecting parts from bearing excessive load and play the role of overload protection.

The connection mode can be divided into rigid connection and flexible connection. For the rigid coupling, the coaxiality and rotation accuracy of both sides of the coupling are required to be high, without axial interference. Before assembly, check the fit size properly, try to press fit instead of percussion fit single-sided parts, and then connect. Large error (including shaft offset) is allowed for flexible coupling. Make sure that the center, angle and axial position of the coupling are within the compensation capacity of the selected coupling.

When the coupling is aligned, it is mainly to measure coaxiality (radial displacement or radial clearance) and parallelism (angular displacement or axial clearance). There are four methods that can be used according to the different tools used in the measurement.

The coaxiality (radial displacement) of the coupling is measured with a square, and the parallelism (angular displacement) of the coupling is measured with a planer and a wedge respectively. The method is simple, applicable to a wide range, but with low accuracy. It is commonly used in low and medium speed operation equipment. According to the chart:

Use dial indicator, feeler gauge and center card to measure coaxiality and parallelism of coupling directly. Adjustment method: usually in the vertical direction, under the support of the main engine (motor), or in the horizontal direction, by moving the position of the main engine.

The assembly of connector is one of the key points of connector installation. The fit between the connector and the shaft is mainly interference fit. Connectivity is divided into critical and non critical connectivity. The shaft hole of connecting shaft can be divided into two forms: cylindrical shaft hole and conical shaft hole. Installation methods include static installation, dynamic installation, temperature difference installation, hydraulic installation, etc.

According to the pressure required for assembly, use fixture, Jack, manual or mobile press. Taper hole is usually formed by static pressure. Due to the limitation of the static indentation method, it is difficult to exert large force in the case of large interference. In the process of pressure, because of the asymmetry of the small bulge on the mating surface of the coupling and the shaft, the fracture of the mating surface of the coupling and the shaft is caused. So this method has not been widely used.

The method involves the use of impactors or machines to complete the assembly process. It is often used in the transition fit or small interference of coupling and shaft. Assembly ground is usually knocked by hand hammer. The method is to place wood blocks or other soft materials as cushion blocks on the end face of the wheel hub and knock the coupling with the impact force of a hammer. This method can lead to local damage of brittle materials such as cast iron, quenched steel and cast alloy, so it is not suitable for use. This method can also destroy the mating surface, so it is often used in the assembly of low-speed small coupling.

Heating expansion or cooling contraction can make the coupling easy to install on the shaft. Compared with static and dynamic methods, this method has many advantages. The temperature difference assembly method is very suitable for the hub made of brittle materials.

The main assembly method is heating method, and the auxiliary is cooling method. There are many kinds of heating methods, some are to put the wheel hub in the flash point oil for oil bath heating or furnace baking, some are to use the oven heating, assembly site mostly use oil bath heating or furnace baking. The temperature that an oil bath can be heated to depends on the nature of the oil, usually below 200C. When the hub is heated in other ways, the temperature of the coupling can be higher than 200C. However, considering metallography and heat treatment, the heating coupling temperature can not be increased at will. The upper limit of recrystallization temperature of steel is below 430 ℃. If the heating temperature exceeds this temperature, the internal structure of steel will change. Therefore, the upper limit of heating temperature must be less than 430 ℃. In order to ensure that the maximum heating temperature is lower than 400 ℃, the actual heating temperature of coupling can be determined according to the coupling and shaft The interference value between the two parts and the calculation of the requirements when the coupling heating device is installed on the rear axle.

After the connector is assembled on the shaft, the verticality and coaxiality of the connector should be carefully checked. Generally, the distance between the connecting end and the outer ring is 2%. When rotating the shaft, observe the overall runout of the coupling (including end face runout and radial runout), and determine the vertical direction and axis direction of the coupling. Different speeds and different types of couplings have different requirements for overall runout. In the assembly of coupling shafting, the overall runout deviation must be within the tolerance range required by the design, which is one of the main requirements for the quality of coupling.

High speed rotating machinery requires coaxiality of coupling and shafting. Single key connection cannot achieve high coaxiality. Through double key connection or spline connection, the coaxiality between the connector and the axis can be improved.