NGW - S73 - 2 - 71 As an NGW series planetary reducer, its base is mostly made of cast iron, Q345B low alloy steel and other materials. The welding quality directly affects the operation stability of the equipment. The specific precautions cover the whole process of pre-welding preparation, welding process and post-welding treatment, as follows:
1. Preparation before welding
Matching of materials and welding consumables: If the base is made of HT250 cast iron, use Z308 pure nickel-core welding rod; if it is Q345B low-alloy steel, give priority to E5015 low-hydrogen welding rod or ER50-6 welding wire. Before use of welding materials, low-hydrogen welding rods need to be baked at 350°C for 2 hours to remove moisture to prevent pores in the weld. At the same time, check the base material. Cast iron parts need to be cleaned of molding sand and oil stains, and low alloy steel needs to be confirmed to be free of defects such as rust and cracks.
Grooving and assembly processing: When the plate thickness exceeds 20mm, V-shaped or U-shaped grooves are used, the angle is controlled at 60° - 70°, and the blunt edge is set to 1 - 3mm to ensure penetration of the weld and reduce deformation. During assembly, calibrate with the reference plane of the machine base, use tooling fixtures to rigidly fix components, and control the misalignment of key mounting surfaces such as bearing seats within 0.5mm; the length of positioning welding should not be less than 25mm, the spacing should not exceed 300mm, and the height of the welding legs should be 1/2 of the formal weld to avoid cracking at the positioning location.
Preheating treatment: When the ambient temperature is lower than 5°C or the plate thickness exceeds 25mm, the low alloy steel frame is preheated to 100 - 150°C; the cast iron frame is partially preheated to 200 - 300°C before welding to prevent cold cracks due to excessive temperature difference during welding.
2. Welding process
Precise control of parameters: when welding cast iron with manual arc welding, the current is controlled at 90 - 130A; when welding low alloy steel, the MAG welding current is 180 - 240A and the voltage is 22 - 28V. During multi-layer and multi-pass welding, the interlayer temperature is maintained at 120-160°C to avoid embrittlement of the heat-affected zone; the welding speed is stable at 25-35cm/min. Too fast may lead to incomplete welding, and too slow may cause overheating and deformation of the weld.
Optimize the welding sequence: adopt a symmetrical welding method from the center outward, such as welding the main frame of the machine base first, then welding the ribs, and finally welding the welds around the bearing seat. Segmented reverse welding is used for long welds. The welds are segmented and welded from both ends to the middle to offset the welding shrinkage stress; for the easily deformed parts of the machine base, a reverse deformation angle of 0.5° - 1.5° is preset.
Operation of key parts: Bearing seat, sealing joint surface and other key parts, the first layer of welding seam should be operated with short arc, and the welding gun inclination angle is 75° - 85° to ensure root penetration. The width of the filling layer weld bead should not exceed 15mm to avoid excessive accumulation of welds and stress; clean the slag in real time during welding, and grind it with an angle grinder after each weld to prevent slag residue.
3. Post-weld treatment
Stress relief: To avoid rapid cooling of the machine base after welding, it can be covered with insulation cotton to slowly cool down. For larger machine bases, a vibration aging process is used to eliminate more than 85% of residual stress; if the machine base is used in important working conditions, annealing is performed when necessary to further reduce residual stress and prevent cracking during subsequent use.
Defect detection and repair: First visually inspect the weld to ensure that there are no obvious cracks, undercuts, or arc craters. The undercut depth does not exceed 0.5mm, and the weld reinforcement is 0-3mm. Ultrasonic testing is then used to detect T-joints and butt welds, which comply with the GB/T11345 standard; magnetic particle or penetrant testing can be used to detect fine cracks on the surface. If defects such as pores and slag inclusions are found, the defective areas need to be cleaned and then repaired by welding. After repaired welding, the cast iron parts need to be locally insulated and slowly cooled again.
Follow-up cleaning process: Use an angle grinder to remove spatter and welding slag around the weld, and grind the mounting surface and joint surface of the machine base. If it is a sealing part, oil-resistant sealant can be applied to the joint surface, and the dimensional accuracy of the machine base can be checked at the same time to ensure that it is assembled and matched with other parts of the reducer.
