Coupling assembly method

- Sep 26, 2019-

Static indentation

This method is based on the size of the pressing force required for assembly, using a clamp, a jack, a manual or a motorized press, and the static press-in method is generally used for a tapered shaft hole. Since the static press-in method is limited by the pressure machine, it is difficult to apply a large force when the interference is large. At the same time, during the pressing process, the uneven peaks on the mating surface between the coupling and the shaft are cut off, so that the mating surface is damaged. Therefore, this method is generally not widely used.

Dynamic indentation

This method refers to the use of impact tools or machinery to complete the assembly process, generally used in the case of the coupling between the coupling and the shaft is a transition fit or a small interference. The assembly site usually hits with a hammer by placing a wooden block or other soft material on the end face of the hub as a cushioning member. The impact of the hammer is used to knock the coupling into it. This method poses a risk of local damage to couplings made of brittle materials such as cast iron, hardened steel, and cast alloys, and should not be used. This method also damages the mating surface and is often used in the assembly of low speed and small couplings.

Temperature difference assembly method

The coupling is heated or the cooling is contracted by cooling, so that the wheel coupling can be easily attached to the shaft. This method has many advantages over the static press-in method and the dynamic press-in method. For the hub made of brittle material, the temperature difference assembly method is very suitable.

Most of the temperature difference assembly methods use a heating method, and the cooling method is used less. There are various methods of heating. Some of them are placed in a high flash point oil for oil bath heating or torch baking, and some are heated by an oven. The assembly site is often heated by oil bath and torch. The maximum temperature that can be achieved by oil bath heating depends on the nature of the oil and is generally below 200 °C. When the hub is heated by other methods, the temperature of the coupling can be higher than 200 ° C. However, from the viewpoint of metallurgy and heat treatment, the heating temperature of the coupling cannot be arbitrarily increased, and the recrystallization temperature of the steel is 430 ° C. If the heating temperature exceeds 430 ° C, it will cause a change in the internal structure of the steel, so the upper limit of the heating temperature must be less than 430 ° C. For insurance purposes, the upper limit of the heating temperature should be below 400 °C. As for the actual heating temperature required for the coupling, it can be calculated according to the interference value of the coupling and the shaft and the requirements when the coupling is heated and assembled on the shaft.

Post-assembly inspection

After the coupling is assembled on the shaft, the perpendicularity and concentricity of the coupling to the shaft should be carefully checked. Generally, two dial gauges are arranged on the end face and the outer circle of the coupling. When the cranking rotates the shaft, observe the values of the full runout of the coupling (including the end face runout and the radial runout), and determine the coupling and the shaft. The case of perpendicularity and concentricity. Couplings with different speeds and different types have different requirements for full runout. After the coupling is assembled on the shaft, the deviation of the full runout of the coupling must be within the tolerance range of the design. This is the coupling. One of the main quality requirements for assembly.

There are many reasons why the total runout value of the coupling does not meet the requirements. First, there may be errors caused by machining. For field assembly, the coupling is not the same as the shaft due to improper assembly of the keys. The correct installation of the key should make the two sides of the key closely fit the wall of the keyway. Generally, it is checked by coloring during assembly. If the fit is not good, it can be repaired with a file or a blade to meet the requirements. The top of the key generally has a gap of about 0.1-0.2 mm.

The high-speed rotating machine has high requirements on the coaxiality of the coupling and the shaft, and high coaxiality cannot be obtained by single-key connection, and the coaxiality of the two can be improved by the double-key connection or the spline connection.