How to deal with cracks that occur during the repair welding of sand holes in the casing of mechanical pumps?

Cracks that occur as a result of welding repairs to sand holes in pump volutes may be caused by the following reasons: 1. Excessive heat input during welding: If too much heat is introduced during welding, it causes the temperature in the welded area to rise rapidly; the areas surrounding the molten metal are also affected by this heat. When the weld cools down, rapid cooling can lead to the formation of internal stresses, which in turn result in cracks. 2. Inappropriate selection of welding materials: You mentioned using E308-16 electrodes; generally, these electrodes are suitable for welding 304 stainless steel. However, if there are specific requirements regarding the area to be repaired or if there is a mismatch in the material composition, it may lead to welding failure. 3. Improper preheating and post-heating treatments: Welding of stainless steel typically requires proper preheating and post-heating treatments to avoid welding stress and welding deformation. If these measures are not properly implemented, it may increase the likelihood of cracks. 4. Internal structure issues in metals: Microscopic defects such as inclusions and pores may exist within castings, and these defects can expand under the influence of high heat input to become cracks. 5. Excessive cooling rate: If the cooling rate is too fast after welding, it can cause the structure in the weld zone and the heat-affected zone to become brittle and hard, making cracks more likely to form. Solution: 1. Optimize welding parameters: Adjust the welding current and welding speed to avoid excessive heat input. 2. Preheating and slow cooling: Proper preheating of the workpiece before welding, and taking measures to cool it down slowly after welding, such as covering it with insulating blankets or sand. 3. Selection of welding materials: Ensure that electrodes suitable for the material of the workpiece are used, and check whether the electrodes have expired or are damp. 4. Post-weld heat treatment: After welding is completed, the volute undergoes appropriate post-weld heat treatment, such as annealing or solution treatment, to relieve welding stresses and optimize the metal structure in the welded area. 5. Welding techniques: Improve welding techniques, such as using segmented, staggered, or multi-layer multi-pass welding methods to reduce the risk of cracks. 6. Crack repair: If a crack has formed, the cracked area needs to be ground or removed, after which it is re-welded using appropriate welding materials and techniques. Finally, it is recommended to perform a thorough cleaning before performing patch welding, in order to remove oil, rust, and other contaminants. During the operation, it is also necessary to follow best practices for welding stainless steel, such as avoiding contamination and ensuring good ventilation. If the problem still cannot be resolved, it is recommended to consult a welding process expert or welding engineer with relevant experience. .