Problems needing attention for welding spiral duct fan:
1. Preparation before welding
(1) According to the form of plate thickness, the groove shall be cut by machining, plasma arc cutting or carbon arc gouging. In order to avoid splashing metal damage, lime powder shall be coated on both sides of the groove when carbon arc gouging, beveling and manual arc welding are used.
(2) V-shaped groove shall be adopted for groove form, and small welding current shall be adopted, so as to prevent intergranular corrosion of stainless steel.
(3) In order to meet the same performance of the joint, the welding material shall be selected according to the principle of "equal composition". At the same time, it shall be noted that there shall not be too much ferrite in the joint, so as to enhance the heat crack and intergranular corrosion resistance of the joint.
(4) Strict tack welding shall be adopted and the principles of "short and thick" and "spot welding without penetration" shall be followed.
2. Welding technical requirements
(1) DC reverse connection shall be adopted for manual arc welding and DC positive connection shall be adopted for argon arc welding.
(2) Before welding, the welding wire shall be brushed off the oxide scale on the surface with stainless steel wire, cleaned with acetone, and then dried for use at any time.
(3) During backing welding, the weld thickness shall be as thin as possible, which is conducive to good fusion with the root; The arc closing shall be in a gentle slope shape. If there is arc closing shrinkage, it shall be ground off with a grinder. Arc striking and quenching shall be carried out in the groove. During arc quenching, the arc pit shall be filled to prevent arc pit cracks.
(4) In order to prevent carbide precipitation sensitization and intergranular corrosion, the interlayer temperature and cooling rate after welding should be strictly controlled, so the interlayer temperature during welding is required to be controlled below 60 ℃.
(5) Argon arc welding crank technology shall be used as much as possible during welding. This technology can well control the surface color and shape of welding layer, and the welding effect is ideal.
The spiral air duct shall avoid opening at the air duct weld and its edge. The next step is to remove the slag at the weld after welding, brush the metal luster with stainless steel wire brush or copper wire brush, then pickle and passivate with pickling paste, and then clean it with hot water.