Welding repair of mechanical parts is more difficult than that of steel structure parts, because welding repair parts not only need to meet the requirements of strength and rigidity, but also need to meet the requirements of overall size, shape and position accuracy and machinability after repair. For the welding repair of large and complex parts, the welding repair process must be formulated and strictly implemented according to the wear and damage conditions of the parts. Generally, the key points of parts welding repair process are as follows.
① Pre welding planning. In addition to equipment planning, pre welding planning mainly includes preparation of welding groove and preheating of weldment.
Y-groove is used for single side welding (plate thickness ≤ 30mm), double V-groove is used for double side welding (plate thickness > 30mm), and U-groove is used for butt welding of shaft parts. Groove is formed by machining, or by gas cutting or gouging, but oxide skin must be eliminated. The groove shall be clean and free of oil stain and rust. The groove of butt welding shall be symmetrical to ensure good positioning. The groove of the crack depends on the depth and length of the crack, which shall be convenient for welding and reduce the filler metal.
The preheating temperature of the welding repair parts is determined by the carbon content of the base metal. Some steels which maintain austenite structure at normal temperature have no hardening condition and can not be preheated.
② Tack welding. When one side of the shaft parts or some parts welded and butted has been broken from the whole, the butt position of the parts to be welded shall be accurate to prevent excessive deformation during welding. For this reason, tack welding shall be carried out first: spot welding shall be carried out with the welding rod whose diameter is smaller than that of welding, and then the position shall be corrected again, and spot welding shall be carried out at several symmetrical points.
③ Selection of weld passes and electrode diameter. The wide or deep weld needs to be completed with multiple weld layers, and the weld procedures are interwoven. The functions can be improved, and the annealed weld bead can be applied. The weld bead shall be welded symmetrically. For the thicker part of the welding layer, the welding rod with good toughness or austenitic stainless steel welding rod shall be used to weld near the working size first, then the welding rod shall be used to weld to the required size, and machining allowance shall be reserved if necessary. For multi pass welding, the first 1-3 passes of fine-diameter electrode can be used to fully weld the bottom corner, and then the rest passes can be completed with coarse-diameter electrode. The diameter of the bead shall be smaller than that of the electrode used for welding, so as to control the temperature of the part during the bead welding.
1、 First, explain the processing method of stainless steel parts for everyone:
Stainless steel parts are widely used in equipment and machinery, and their processing methods and processes are becoming more and more advanced. Here are six processing methods of key stainless steel parts:
1. Forging method: use the swaging machine to stretch at the end or part of the pipe to reduce the outer diameter. The common swaging machines are rotary type, connecting rod type and roller type;
2. Bulge method: one is to place rubber in the pipe, and shrink it with a punch to make the pipe protrude; the other is to bulge the pipe with hydraulic pressure, and fill the middle of the pipe with liquid. The liquid pressure bulges the pipe into the required form, which is mostly used in the production of wave pipe;
3. Bending forming method of stainless steel elbow: there are three commonly used methods, one is stretching method, the other is stamping method, the third is roller method, there are 3-4 rollers, two unchanging rollers, one adjusting roller, adjusting unchanging roller distance, forming article pipe fittings is bending;
4. Stamping method: the pipe end is expanded to the required size and form by the core with taper on the punch;
5. Rolling method: usually without mandrel, suitable for the inner circular edge of thick wall pipe;
6. Roller method: the core is placed in the pipe, and the outer circumference is pushed and pressed by roller, which is used for round edge processing.
2、 Requirements of stainless steel parts for welding technology:
Due to the different sizes of stainless steel parts, the special welding places of stainless steel parts shall be followed, and the heat input shall be reduced as much as possible. Therefore, manual arc welding and argon arc welding shall be used. For d > Φ 159mm, argon arc welding shall be used as the backing and manual arc welding cover. D ≤ Φ 159 mm. Requirements for welding technology of stainless steel parts are as follows:
1. In manual arc welding, DC reverse connection is used for welding machine and DC positive connection is used for argon arc welding;
2. Before welding, the welding wire shall be brushed with stainless steel wire to remove the oxide skin on the surface and washed with * *; the welding rod shall be dried at 200-250 ℃ for 1H and used as needed;
3. Before welding, the oil stain within the 25 mm boundary line on both sides of the workpiece groove shall be cleaned, and the 25 mm boundary line on both sides of the groove shall be washed with * *;
4. During argon arc welding, the diameter of nozzle is Φ 2 mm, and the specification of tungsten electrode is Φ 2.5 mm;
5. When argon arc welding stainless steel, the reverse side must be filled with argon for protection to ensure the reverse forming. The flow rate is 5-14l / min and the flow rate of argon on the opposite side is 12-13l / min. During backing welding, the thickness of the weld shall be thin, with excellent fusion with the root, and it shall be in a gentle slope shape during arc closing. If there are arc closing shrinkage holes, they shall be ground off with a grinder. Make sure to start and extinguish the arc in the groove, and fill the crater during arc extinguishment to prevent the crater crack.