Coupling is a device which connects two or two axes with rotating parts and rotates together in the process of transferring motion and power without detuning under normal circumstances. 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.
Coupled assembly requirements
Coupling is generally rigid and flexible. Rigid coupling requires high coaxiality and rotation accuracy on both sides of the connecting shaft, and the axial direction should not interfere with each other. Check the fittings size before assembly, try to use stamping instead of tapping to assemble unilateral parts, and then connect them together. For flexible coupling, larger errors (including eccentricity, angle and axial position) are allowed, but they must be within the compensation capacity of the selected coupling.
How to find it
Coupled timing mainly measures coaxiality (radial displacement or radial clearance) and parallelism (angular displacement or axial clearance). According to the different measuring tools, there are four methods.
1. The coaxiality (radial displacement) of the coupling is measured by a ruler, and the parallelism (angular displacement) of the coupling is measured by a planar gauge and a wedge gauge. This method is simple and widely used, but its accuracy is not high. As shown in the figure:
2. Measure coaxiality and parallelism of coupling directly with micrometer, plug ruler and center card. Adjustment method: usually add or subtract the foot of the motor (motor) gasket in the vertical direction or move the motor position in the horizontal direction to achieve.
Assembly Method of Shaft Coupling
The assembly of the shaft coupling is one of the key points in the installation of the coupling. Most of the coupling and shaft are interference fit. The connection mode is divided into key connection and keyless connection. The shaft hole of coupling is divided into two forms: cylindrical shaft hole and conical shaft hole. Assembly methods include static pressing method, dynamic pressing method, temperature difference assembly method and hydraulic assembly method.
This method uses fixture, jack, manual or motor press according to the force required for assembly. Static pressure method is generally used for conical shaft holes. Because of the limitation of hydrostatic method, it is difficult to exert a greater force when the disturbance is large. At the same time, in the stamping process, the slightly convex summit of the mating surface between the coupling and the shaft is cut off, and the mating surface will be damaged. Therefore, this method is seldom used.
This method refers to the use of impact tools or machinery to complete the assembly process. It is generally used in conjunction between coupling and shaft where there is little transition or interference. On the assembly site, this method is usually hammered. In this method, wood blocks or other soft materials are cushioned on the hub end as a buffer component, and the coupling is knocked in by the impact force of the hammer. This method is not suitable for local damage caused by coupling of brittle materials such as cast iron, hardened steel and cast alloy. This method also destroys the mating surface and is often used for assembling low-speed small couplings.
Temperature difference assembly
Wheel coupling can be easily mounted on the axle by expanding the coupling by heating or contracting the axle end by cooling. Compared with static pressing method and dynamic pressing method, this method has many advantages, and is very suitable for brittle material wheels using temperature difference assembly method.
Temperature difference assembly method mostly uses heating method, but cooling method seldom uses. There are many heating methods, some put the hub into oil with high flash point for oil bath heating or welding torch baking, some use oven heating, assembly site mainly uses oil bath heating and welding torch baking. The highest temperature reached by oil bath heating depends on the nature of oil, generally below 200 C. When the hub is heated by other methods, the temperature of the coupling can be higher than 200 C, but from the point of view of metallography and heat treatment, the temperature of the coupling can not be arbitrarily increased, and the recrystallization temperature of steel is 430 C. If the heating temperature exceeds 430 C, the internal structure of the steel will change, so the upper limit of the heating temperature must be less than 430 C. For safety, the upper limit of heating temperature should be below 400 C. For the actual heating temperature of the coupling, it can be calculated according to the interference value between the coupling and the shaft and the matching requirement of the coupling after heating.
Inspection after assembly
After the coupling is installed on the shaft, the verticality and coaxiality of the coupling and the shaft should be carefully checked. Generally, two micrometers are set at the end face and the outer circle of the coupling. When the shaft is rotated, the full runout (including end runout and radial runout) of the coupling is observed to determine the accuracy and coaxiality of the coupling and the shaft. Different speeds and coupling types require different full runout values. After the coupling is installed on the shaft, the deviation value of the full run-out must be within the tolerance range of the design requirements, which is one of the main quality requirements of the coupling assembly.
There are many reasons why all the jump values of the coupling do not meet the requirements. For field assembly, the coupling is not coaxial due to improper key assembly. Correct installation of keys should make the two sides of keys and keyway walls closely adhere to each other. Generally, when assembling, the key should be checked by coloring method. It can not match the file or spade very well, so that it meets the requirements. There is a gap at the top of the key, about 0.1-0.2 mm.
High-speed rotating machinery requires high coaxiality between coupling and shaft. Single-key connection can not achieve high coaxiality. Double bond or spline connection can improve coaxiality.
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