During long-term operation of the water pump, it is common to experience wear on the bearing housing of the pump bearing frame, wear on the bearing position, cracking and rupture of the pump body, cavitation and erosion wear of the water pump. After the above problems occur, the traditional solution for enterprises is to repair them by welding or brushing and plating, but both have certain drawbacks: the thermal stress generated by high temperature welding cannot be completely eliminated, which can easily cause material damage and lead to bending or fracture of components; However, electric brush plating is limited by the thickness of the coating and is prone to peeling off. Both methods use metal to repair the metal and cannot change the "hard to hard" fit relationship. Under the combined action of various forces, it will still cause further wear. Contemporary Western countries often use polymer composite materials as a repair method for the above problems, which have strong adhesion, excellent compressive strength and other comprehensive properties. The application of polymer materials for repair can be done without disassembly or machining. There is no influence of welding thermal stress, and the repair thickness is not limited. At the same time, the metal material of the product does not have the flexibility, which can absorb the impact and vibration of the equipment, avoid the possibility of further wear, and greatly extend the service life of equipment components, saving a lot of downtime for enterprises and creating huge economic value.
Static balance of impeller
When the water pump rotor works at high speed, if its mass is uneven, a large centrifugal force will be generated during rotation, causing vibration or damage to the water pump. The balance of the rotor is achieved through the mass balance of its various components, including the shaft, impeller, shaft sleeve, balance disc, etc. Therefore, static balance verification should be carried out on newly installed impellers. The specific method is:
(1) Install the impeller on the fake shaft and place it on the static balance test bench that has been adjusted horizontally. There are two tracks on the test bench, and the false axis can roll freely on them.
(2) Mark the side of the impeller that is heavier. If the quality of the impeller is unbalanced, the heavier side always automatically turns downwards. Add heavy blocks (using surface glue or clamps to add or remove iron plates) to the symmetrical position of the heavier part (i.e. the lighter side) until the impeller can stop at any position.
(3) Weigh the weight of the weighted block. Not by adding weight on the lighter side of the impeller, but by reducing weight on the heavier side to achieve balance of the impeller. When reducing weight, milling or grinding with a grinding wheel can be used (when the removal amount is not large), but it is important to note that the depth of milling or grinding should not exceed one-third of the thickness of the impeller cover plate. The allowable deviation of the impeller after static balance shall not exceed the product of the outer diameter of the impeller and 0.025g/mm. For example, for an impeller with a diameter of 200mm, the allowable deviation is 5g.
Disassembly and assembly of coupling
(1) When removing the coupling, do not directly strike it with a hammer. Instead, use a copper rod as a cushion, and hit the coupling hub instead of the outer edge, as it is highly susceptible to damage. The most ideal way is to use a hook to disassemble the coupling. For small and medium-sized water pumps, the coupling is easy to remove due to its small interference fit. For larger water pumps, there is a significant interference fit between the coupling and the shaft, so the coupling must be heated during disassembly.
(2) When assembling couplings, pay attention to the key numbers (for couplings with two or more keys). When using a copper rod to strike, attention must be paid to the struck area. For example, when tapping the end face of the shaft hole, it is easy to cause the shaft hole to shrink, making it impossible for the shaft to pass through; Knocking on the outer edge of the wheel can easily damage the flatness of the end face, which will affect the accuracy of measurement when using a feeler gauge for alignment in the future. For couplings with large interference fit, they should be heated before installation.
(3) Coupling pins, nuts, washers, and rubber pads must ensure their respective specifications and sizes are consistent to avoid affecting the dynamic balance of the coupling. Corresponding markings should be made on the coupling bolts and corresponding coupling pin holes to prevent incorrect installation.
(4) The fit between the coupling and the shaft generally adopts a transition fit, which may result in a small amount of interference or clearance. For couplings with longer wheel hubs, a looser transition fit can be used, as the shaft hole is longer and the surface is rough and uneven, which will naturally produce some interference after assembly. If the fit between the coupling and the shaft is found to be too loose, affecting the concentricity of the hole and shaft, repair welding should be carried out. Punching or copper lining on the shaft is a temporary solution and cannot be considered an ideal method.
