Commonly used welding methods
(1) Thermal welding method
The hot welding method is a welding method in which the weldment is heated to 600-700℃ in whole or partly before welding, and kept at a certain temperature during the welding process, and then slowly cooled in the furnace after welding.
Features: When using the thermal welding method, the weldment is cooled slowly and the temperature distribution is uniform, which is beneficial to eliminate the white mouth structure, reduce stress and prevent cracks. However, the hot welding method has high cost, complicated process, long production cycle, and poor labor conditions during welding, so it should be used as little as possible.
Commonly used welding methods are gas welding and electrode arc welding. Gas welding commonly used cast iron gas welding wire, such as HS401 or HS402, with flux CJ201 to remove oxides. The gas welding preheating method is suitable for repair welding of small and medium- sized thin-walled parts. Electrode arc welding uses cast iron core cast iron electrode Z248 or steel core cast iron electrode Z208. This method is mainly used for repair welding of cast iron parts with a large thickness (greater than 10mm).
The welding equipment of thermal welding method mainly includes heating furnace, welding torch, electric furnace, etc. The welding process is as follows:
1) Pre-welding preparation and preheating: remove the oil and scale around the defect to expose the metallic luster of the substrate; open the groove, generally the groove depth is 2/3 of the weldment wall thickness, and the angle is 70° ～120°;
Put the weldment into the furnace and slowly heat it to 600～700℃ (not exceeding 700℃).
2) Welding: Use a neutral flame or a weak carbonized flame (do not let the molten iron flow to one side during welding), and after the base metal has penetrated, melt it into the electrode metal; if there are white bright spots in the molten pool, stop filling Fill in the electrode metal, add an appropriate amount of flux, and use the welding rod to remove the debris before continuing welding; in order to obtain a smooth weld, the weld should be slightly higher than the surface of the cast iron, and the slag will overflow outside the weld Remelt, and when the temperature is cooled to a semi-melted state, use a welding wire to smooth the higher part along the surface of the casting.
3) Cooling after welding: Generally, it should be slowly cooled to room temperature with the furnace (usually more than 48h), and it can also be covered with asbestos cloth (board) or charcoal dust to make the weld form a uniform structure and prevent cracks.
(2) Gas welding method
The temperature of the gas welding flame is much lower than the arc temperature, so the heating and cooling of the weldment is relatively slow, which is beneficial to preventing the white structure and cracks of the gray cast iron during welding. Therefore, the quality of castings repaired by gas welding is generally better, because gas welding has become a common method for repairing cast iron.
Compared with electrode arc welding, gas welding has higher labor intensity and greater deformation of the weldment, and it is difficult to weld through large castings;
Gas welding castings are of good quality and easy to cut. Many small and medium-sized gray castings in many factories are still repaired by gas welding.