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Several installation techniques of coupling

2019-12-9 16: 32: 52 Views


      The assembly of the coupling on the shaft is one of the keys to the installation of the coupling.Couplings and shafts are mostly fitted with interference fits. The connection is divided into keyed and keyless connections. The shaft hole of the coupling is divided into two forms: cylindrical shaft and tapered shaft hole.The assembly methods include static pressure method, dynamic press-in method, temperature difference assembly method and hydraulic assembly method.
      Static pressure method: This method uses clamps, jacks, manual or motorized presses according to the size of the required press-in force during assembly. The static press-in method is generally used for tapered shaft holes.Because the static press-in method is restricted by the pressure machine, it is difficult to apply a large force when the interference is large.At the same time, the uneven small peaks on the mating surface between the coupling and the shaft will be cut off during the press-in process, causing the mating surface to be damaged.Therefore, this method is generally not widely used.
      Power press-in method: This method refers to the use of impact tools or machinery to complete the assembly process. It is generally used in situations where the coupling and shaft fit is transitional or small.The assembly site usually uses a hand hammer to beat it. The method is to padded wooden blocks or other soft materials on the end surface of the wheel hub as a buffer, and rely on the impact force of the hand hammer to knock the coupling in.This method has the risk of local damage to couplings made of brittle materials such as cast iron, quenched steel, and cast alloys, and should not be used.This method will also damage the mating surface, so it is often used for the assembly of low-speed and small couplings.
      Temperature difference assembly method: The coupling is heated to expand by heating or the shaft end is cold and contracted by cooling, so that the wheel coupling can be easily installed on the shaft.This method has more advantages than the static press-in method and the dynamic press-in method. For the wheel hub made of brittle materials, the temperature difference assembly is very suitable.The temperature difference assembly method mostly uses heating method, and the cooling method uses relatively few methods.There are many heating methods. Some put the wheel hub in high flash point oil for oil bath heating or welding torch baking, and some use an oven to heat it. The assembly site uses oil bath heating and welding torch baking.The maximum temperature that the oil bath can reach depends on the nature of the oil, and it is generally below 200 degrees.When other methods are used to heat the hub, the temperature of the coupling can be higher than 200 degrees. However, from the perspective of metallography and heat treatment, the heating temperature of the coupling cannot be increased arbitrarily. The recrystallization temperature of steel is 430 degrees. Temperatures above 430 degrees will cause changes in the internal structure of the steel. Therefore, the upper limit of the heating temperature must be less than 430 degrees. For the sake of safety, the upper limit of the heating temperature should be below 400 degrees.As for the actual heating temperature of 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 on the shaft.
      Inspection after assembly: After the coupling is assembled on the shaft, the verticality and coaxiality of the coupling and the shaft should be carefully checked.Generally, two dial indicators are set on the end face and outer circle of the coupling. When the shaft is rotated by the turning car, observe the value of the total runout (including end runout and radial runout) of the coupling to determine the coupling and the shaft. The verticality and concentricity of the situation.Different speeds and different forms of couplings have different requirements for full runout. After the coupling is assembled on the shaft, the deviation value of the full runout of the coupling must be within the tolerance range required by the design. This is a 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 of all, the error may be caused by processing.For on-site assembly, the coupling and the shaft are out of axis due to improper assembly of the key.The correct installation of the key should make the two sides of the key closely fit the wall of the keyway. Generally, the coloring method is used for inspection during assembly. If the fit is not good, use a file or a spatula to repair it to meet the requirements.
      High-speed rotating machinery requires high coaxiality between the coupling and the shaft, and high coaxiality cannot be obtained with a single key connection, and the coaxiality between the two can be improved by using a double key coupling or a spline connection.

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