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1. Pump shaft runout standards: 1) The taper and ellipticity of the shaft journal shall not exceed 1/2000 of the shaft diameter. However, it must not exceed 0.05 mm at most, and the surface must be free of defects. 2) If the shaft bending exceeds the allowable value, it can be straightened using mechanical or heating methods. The allowable runout values for the shaft are shown in the table below (unit: mm): at the shaft diameter, in the middle of the shaft at 1500 revolutions per minute, in the middle of the shaft at 3000 revolutions per minute. For multi-stage pump shafts: ≤0.02, ≤0.10, ≤0.08, ≤0.05. 2. Methods for straightening the pump shaft: 1) Cold straightening method: (1) Straightening using a hand-cranked screw press. This method can be employed when the shaft diameter is small and the degree of bending is high. First, place the shaft inside a triangular notched block to support it, or on a machine tool using thimbles to hold both ends of the shaft, then turn the vertex of the bent convex surface upward. Use a screw press to press on the peak of the protrusion and push downward until the shaft is straightened. (2) Straightening by tapping with a twisting rod: This method can be used when the diameter is large and the bending is slight. This method uses a twisting rod to cold-form the curved concave surface of the shaft, causing the surface at this area to extend and become straighter. The twisting rod should be made of a material with a lower hardness than that of the pump shaft, or a copper sleeve should be fitted onto a harder material; the edges of the twisting rod must have rounded corners. In the straight-axis position, the concave side of the shaft faces upward, supporting the vertex of the convex side that experiences the maximum bending. Apply downward pressure at both ends using tensioning devices, then strike the twisting rod with a 1-2 kilogram hammer to cause the concave material of the shaft to stretch under the impact. When twisting and beating, start by striking from the center of the lowest concave surface, gradually moving toward the sides, and proceed along one-third of the circular arc; however, the intensity of striking should increase as one moves closer to the center. The straightening amount of the shaft is generally proportional to the number of blows. Note that the shaft alignment is faster at the initial tapping, and slower thereafter. When tapping, be careful to handle the twisting rod properly to avoid damaging the surface of the shaft. (3) Straightening with a screw jack: When the bending amount of the shaft is not large (below 1% of the shaft length), it can be straightened in its cold state using a screw jack. During straightening, taking into account the springback of the shaft, it is necessary to over-straighten it slightly to ensure that the shaft remains fairly straight after correction. The accuracy of this method can reach 0.05–0.15 millimeters per meter. (4) Straightening with steel wire rope 2) Local heating method: Place the bent surface facing up, wrap it with asbestos cloth, and then heat it rapidly using a blowtorch or gas welding. The heating temperature is about 100°C lower than the material’s critical temperature. After rapid heating, the metal undergoes plastic deformation, which shortens its surface length; although it is stretched upon cooling, it can no longer return to its original state. This results in a reverse bending in the direction opposite to the original bending, thereby flattening the convex surface and achieving a straight axis. Better results are achieved if heat is applied to the concave surface to assist its thermal expansion and elongation. The heating method should be carried out at a constant speed and at equal intervals (about 20 millimeters from the axis surface), by rotating outward from the center and then inward toward the center, in order to maintain uniform temperature. The heating area and shape are heated using an axial opening method (long in the axial direction and short in the radial direction) to ensure uniform temperature in the radial direction and prevent the shaft from twisting. When heating using the radial opening method (long in the radial direction and short in the axial direction), the straight-axis effect is significant. During alignment, first place the shaft flat on two supports with the convex side of the bent portion facing up, and wrap the area of maximum bending with wet asbestos cloth. This asbestos cloth has rectangular openings: either axial openings of 0.15d×0.2d or radial openings of 0.35d×0.2d (where d is the diameter of the axis). The openings are then heated for 3–5 minutes using an oxy-acetylene flame (with a high-powered welding torch and an oxygen pressure of 4–5 atmospheres). Once the temperature reaches 500–600°C, the heated area is covered with dry asbestos cloth and kept at that temperature for 10–15 minutes. Finally, compressed air is used to blow on the area in order to cool it down rapidly. The bending variation of the shaft can be measured using a dial indicator. If straightening does not succeed on the first attempt, it can be repeated. After straightening, the shaft should undergo low-temperature annealing at the heated area: the shaft is rotated and slowly heated to 300–350°C, where it is held for more than an hour. Afterwards, the heated area is wrapped with asbestos cloth to allow it to cool down slowly to 50–70°C, thereby eliminating internal stresses. The amount of change in the shaft during straightening is related to the material properties of the shaft itself. During heating, the bending deflection at the shaft end gradually increases to a maximum, which is due to the metal expansion resulting from heating of the protruding part. After cooling, the bending deflection at the shaft end gradually decreases to a minimum, which is due to the rapid cooling of the protruding parts causing the metal fibers to shorten. 3) Internal stress relaxation method: The principle is based on the relaxation property of metal materials; that is, when the stress in a part decreases at high temperatures, its elastic deformation decreases while the proportion of plastic deformation increases. In this case, by applying a load in a certain direction, it is possible to control the direction and magnitude of its deformation. When the load is removed, since plastic deformation dominates, there is little springback, thereby achieving a straight shaft. Induction coils are commonly used for heating tools, and annealing treatment should also be carried out after the shaft is straightened. This method is often used on large shafts. 4) Mechanical heating with the straight-axis method: First, fix the shaft with the convex side facing upward, then apply an external load to press the bent shaft downward, thereby creating compressive stress on the convex side; subsequently, heat the concave side to straighten the shaft. This method is only applicable to shafts with low degree of curvature.