Assembly method of pump-coupling

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Methods of coupling assembly In coupling assembly, it is essential to master key aspects such as the installation of the coupling on the shafts, aligning the two shafts connected by the coupling, checking the components, and assembling the coupling in accordance with the requirements specified in the drawings. 　　I. Methods of alignment When aligning couplings, the key parameters to measure are coaxiality (radial displacement or radial clearance) and parallelism (angular displacement or axial clearance). There are four methods depending on the tools used for measurement. A straightedge is used to measure the coaxiality (radial displacement) of the coupling, while a straight gauge and a wedge gap gauge are employed to measure its parallelism (angular displacement). This method is simple and widely used, but it does not offer high precision; it is generally applied to equipment operating at low or medium speeds where higher precision is not required. (2) Directly use a dial indicator, feeler gauge, and centering gauge to measure the coaxiality and parallelism of the coupling. The method of adjustment: It is usually achieved by adding or removing shims under the feet of the drive motor in the vertical direction, or by moving the position of the drive motor in the horizontal direction. 　　II. Method of installing the coupling on the shaft The installation of the coupling on the shaft is one of the key aspects in coupling installation. The fit between the coupling and the shaft is usually an interference fit. Connections can be either keyed or keyless, and the shaft hole of the coupling comes in two forms: cylindrical and conical. Assembly methods include static pressing, dynamic pressing, thermal differential assembly, and hydraulic assembly. 　　(1) Static pressing method: This method involves using clamps, jacks, or manual or mechanical presses, depending on the amount of force required for assembly, and it is generally used for conical shaft holes. Due to the limitations imposed by pressure machinery on the static pressing method, it is difficult to apply a large force when the interference is high. At the same time, during the pressing process, the tiny uneven protrusions on the mating surface between the coupling and the shaft are cut off, causing damage to that mating surface. Therefore, this method is not widely used. 　　(2) Dynamic pressing method: This method involves using impact tools or machinery to carry out the assembly process, and it is generally applied in situations where the fit between the coupling and the shaft is a transitional fit or has a moderate degree of interference. At the assembly site, a hammer is usually used for this purpose; a wooden block or some other soft material is placed on the end face of the hub as a cushion, and the coupling is driven in using the impact force of the hammer. This method poses a risk of localized damage to couplings made from brittle materials such as cast iron, quenched steel, and cast alloys, and therefore should not be used. This method also damages the mating surfaces, so it is often used for the assembly of low-speed and small couplings. 　　　(3) Temperature difference assembly method: The coupling is heated to cause it to expand, or the shaft end is cooled to cause it to contract, thereby allowing the coupling to be easily installed on the shaft. This method has more advantages over the static pressing and dynamic pressing methods; for hubs made of brittle materials, the temperature difference assembly method is highly suitable. The temperature difference assembly method mostly uses heating, while cooling is used less frequently. There are various methods of heating; some involve submerging the hub in oil with a high flash point for oil bath heating or using a welding torch for heating, while ovens are also used for this purpose. At the assembly site, oil bath heating and welding torch heating are the most commonly used methods. The highest temperature that can be achieved with oil bath heating depends on the properties of the oil, and is generally below 200°C. When heating the hub using other methods, it is possible to raise the temperature of the coupling above 200°C, but from a metallurgical and heat treatment perspective, the heating temperature of the coupling cannot be increased arbitrarily, as the recrystallization temperature of steel is 430°C. If the heating temperature exceeds 430°C, it will cause changes in the internal structure of the steel; therefore, the upper limit for the heating temperature must be below 430°C. For safety reasons, the upper limit for the set heating temperature should be below 400°C. As for the actual heating temperature required for the coupling, it can be calculated based on the interference fit between the coupling and the shaft, as well as the requirements for fitting the coupling onto the shaft after it has been heated. 　　(4) Inspection after assembly: After the coupling is assembled on the shaft, its perpendicularity and coaxiality with the shaft should be carefully checked. Generally, two dial indicators are placed on the end face and outer circle of the coupling. As the shaft is rotated by turning the drum, the values of the overall runout of the coupling (including end face runout and radial runout) are observed in order to determine the perpendicularity and coaxiality between the coupling and the shaft. Couplings of different speeds and types have varying requirements regarding total runout. After the coupling is installed on the shaft, it is necessary to ensure that the deviation in its total runout falls within the tolerance limits specified in the design requirements; this is one of the main quality criteria for coupling installation. There are many reasons why the total runout value of the coupling does not meet the requirements; firstly, it may be due to errors resulting from machining. For on-site assembly, improper fitting of the keys causes the coupling and the shaft to be out of alignment. The proper installation of the key should ensure that its two sides fit tightly against the walls of the keyway; generally, a coloring method is used for inspection during assembly, and if the fit is not satisfactory, a file or chisel can be used to make it meet the requirements. There is generally a gap at the top of the key, around 0.1-0.2 mm. 　　High-speed rotating machinery requires high coaxiality between the coupling and the shaft; a single key connection cannot achieve high coaxiality, while a double key connection or a spline connection can improve the coaxiality between them. 　　III. Installation of the coupling Before installing the coupling, clean all the components thoroughly. For the cleaned components, wipe off any oil that remains on them. For couplings that are to be put into use in a short time, after drying them, some turbine oil or engine oil can be applied to their surfaces to prevent rust. For couplings that are to be in use over an extended period, they should be coated with rust preventive oil for maintenance. For couplings used in high-speed rotating machinery, dynamic balance tests are generally carried out at the manufacturing plant; once these tests are successful, markings indicating the relative positions of the various components are made. It is very important to assemble according to the markings provided by the manufacturer during assembly. If the components are assembled arbitrarily without following the markings, it is very likely that vibration of the unit will occur due to poor dynamic balance of the couplings. Furthermore, the coupling bolts on the flanges of this type of coupling are load-bearing, allowing the coupling bolts on each coupling to have roughly the same weight. In gear couplings used in large centrifugal compressors, the difference in weight between the coupling bolts is generally less than 0.05g. Therefore, the bolts between different couplings cannot be interchanged arbitrarily; if one of the coupling bolts needs to be replaced, its weight must be the same as that of the original bolt. Furthermore, when tightening the coupling bolts, they should be tightened symmetrically and gradually, so that the clamping force on each bolt is roughly the same; this prevents the coupling from becoming skewed after assembly due to uneven stress on the bolts. If possible, a torque wrench should be used. For rigid removable couplings, after assembly, it should be checked whether the rigid removable parts of the coupling can move slightly and whether there is any sticking. After assembly, all types of couplings should be rotated to check whether they turn smoothly. In short, proper installation of the coupling can improve the performance of the equipment, reduce its vibration, and extend the service life of the coupling.