① Check the position and length of the crack first, and clean the oil stain, oxide scale and other impurities at the crack site with carbon tetrachloride to avoid blowholes and slag inclusion during welding.
(2) at both ends of the crack, drill a drill with a diameter of φ 3 ~ 5 mm to stop the crack. For cracks in thick-walled parts, the diameter of the drill bit can be larger. At the same time, use a flat chisel to gouge the grooves with cracks of 7 ~ 11.
2) gas welding process
① during gas welding repair, white structure is easy to appear due to the burning loss of carbon, silicon and other elements. In order to compensate the burning loss of elements, promote the graphitization of weld metal, and obtain weld metal with basically the same chemical composition and metal structure as the base metal, high-silicon cast iron gas welding covered electrode should be used, or waste piston rings (oil rings and plated rings cannot be used) can be used as substitutes. The diameter of covered electrode is φ 3 ~ 4 mm.. The flux is CJ21 cast iron gas welding flux.
② The welding torch and welding nozzle are generally medium or small, and the diameter of welding nozzle is between φ 1.5 ~ 2.2 mm.. The flame is neutral flame or acetylene has residual neutral flame to reduce the burning loss of carbon and silicon and ensure the chemical composition of weld metal.
(3) Before welding, put the cylinder head in a charcoal furnace, evenly and slowly heat it at about 5~6℃, and keep the temperature for about 1h. When preheating before welding, it is best to put the crack part to be repaired face down in the charcoal furnace for sufficient preheating.
④ Use a horizontal position when welding to prevent metal loss.
⑤ When welding is started, the flame is aimed at the bottom of the crack in the welding repair part, so that more than two-thirds of the thickness of the welded crack is melted, and then covered electrode is dipped in the flux and put into the solution pool and stirred at any time, so that bubble impurities can completely float out. At the same time, the flame should move back and forth around the weld to ensure that the temperature near the weld metal is not too low. Each crack should be welded by one gas, and the welding operation should be rapid and reliable.
⑥ repair the weld surface and root. Its operation is to use flame to heat it in spots to make it partially melt, and the left hand holds the iron plate to cooperate, so that the weld surface is scraped flat and smooth, and it is flush with the base metal surface.
3) Post-welding treatment
After welding, put it in a charcoal furnace for heat preservation, so as to eliminate the stress caused by cold shrinkage and prevent the white spot, and the temperature is the same as the preheating temperature. When the temperature rises slowly and evenly to the specified temperature, block it around with iron sheets to make the furnace temperature drop slowly.