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A 1150hP synchronous motor imported from the UK needs to be replaced with a rotating shaft due to operational failure. 40Cr steel of φ220 × φ2490mm is selected, and the whole material is tempered before cutting. After the semi-finishing, the distance between the two bearings is inadvertently (1620mm). The car is 5mm shorter, as shown in Figure 1. In order to avoid major losses, the shaft has been repaired and repaired. Since the shaft is already in the semi-finished stage, the grinding surface has only a grinding allowance of 0.3mm to 0.5mm. The non-grinding surface has reached the requirements of the drawing size, so that the workpiece can not be used in the post-weld heat treatment process after welding, but the quality cannot be guaranteed. After the following welding repair method is adopted for the rotating shaft, the quality and quality are guaranteed. Requirements.
2 Preparation before welding (1) The surface of the rotating shaft before welding should be carefully cleaned, and all impurities such as oil which will generate hydrogen should be strictly removed.
2毫米。 (2) Select J857 electrode, φ3. 2mm. Before welding, the electrode is dried in the furnace at 250-300 ° C for 2 h, and the water in the electrode is removed as needed.
(3) Reverse connection method is adopted on the DC welding machine.
3 welding repair process (1) The entire rotating shaft was placed in an oven and preheated to 300 ° C and taken out.
(2) Hang the rotating shaft on the roller bracket. The roller should be supported on the outer circumferences of φ135 and φ140 on the shaft, and the turning clamp should be installed.
(3) Using symmetrical interlaced welding, each segment is divided into 8 segments, and each layer of the connector should be staggered and filled with craters. The current value is 90A~
100A, slow welding speed to prevent overheating of the shaft and reduce penetration and heat affected zone. With continuous welding, the weld width should be greater than 6mm, 2mm above the surface of the shaft, the welding order of the first and second layers is shown in Figure 2, the third layer is the same as the first layer, the fourth and second The layers are the same, and the rest are analogous.
(4) Immediately after welding, use two gas torches to heat the area within 100mm~120mm on both sides of the welding position, and continuously rotate the shaft to make the heating even and avoid deformation.
(5) Using a semiconductor thermometer to detect, when the temperature reaches 550 ~ 600 ° C, and then keep warm for 1 h, then the shaft is suspended into the oven at 300 ° C, and then cooled to room temperature with the furnace. Its purpose is to eliminate welding stress, reduce the content of diffusible hydrogen, and improve the metallographic structure of the heat affected zone.
After the welding repair, the hardness test is carried out. The hardness of the outer circle of φ115mm in the welding repair zone is HB248; the hardness of the outer circle of φ130mm is HB254. The motor shaft is soldered and finished, and the synchronous motor is installed. It has been running for more than 5 years and is running normally.
Welding repair of large motor shaft
1 Introduction Figure 1 1 150hP synchronous motor shaft Figure 2 welding order