What are the Main Points of Gas Welding Repair Welding of Gray Cast Iron?

The weldability of gray cast iron is poor. During the welding process, the welded joint is prone to stress cracks; the weld is prone to porosity; easy to generate insoluble SiO2; easy to appear brittle and hard white structure; due to the liquid metal fluidity of gray cast iron Very good, can only be welded in the flat welding position. As a Grey Iron Casting Company, share with you.

Because the temperature of the gas welding flame is much lower than the arc temperature, the heating and cooling of the castings during welding are relatively slow, which can effectively prevent white holes, cracks and pores. Therefore, the welding quality is high, and it is easy to machine cutting after welding. The disadvantages of gas welding are low productivity, high cost, poor working conditions, and difficult penetration of large castings.

Preparation before welding

If the casting defect is a crack, find both ends of the crack and drill a crack arrest hole (usually about 6mm in diameter). The methods to find cracks include: look with a magnifying glass. When the cracks are not obvious, you can heat it with a flame at 200～300℃, and it will be displayed after it cools down. The kerosene penetration method is used, that is, the oil stains on the surface are wiped off after applying kerosene, and then sprinkled. Put a thin layer of talcum powder (quick lime powder) and tap it with a small hammer to vibrate to show the traces of the cracks; use the hydraulic test method to find the cracks.

Grey Cast Iron Casting

Use carbon arc gouging, gas welding flame, grinder slotting, and thoroughly remove defects. Commercially available gray cast iron welding wire: HS401, and CJ201 for flux can be used as the welding wire. In order to better eliminate defects such as pores and slag inclusions, a larger flame energy rate should be selected. In general, when the thickness of the casting is 20-50mm, the nozzle diameter is 3mm and the oxygen pressure is 0.6MPa; when the thickness of the casting is less than 20mm, the nozzle diameter is 2mm and the oxygen pressure is 0.4MPa.

Welding operation

Gray cast iron gas welding adopts neutral flame or slight carbonized flame, and the carbonized flame can be used at the end of welding to slow down the welding seam. This can reduce the burning loss of C and Si, eliminate the excessively thick oxide film, and reduce the cooling rate to prevent white mouth tissue.

For some small defects at the edges, corners and edges of the casting, cold welding can be used directly. To avoid excessive melting of the base material, even when using flames to remove defects, the molten wood must be removed to prevent the melt from being too hard after cooling. When welding, always pay attention to the fusion condition. The base metal should be penetrated first and then the welding wire should be added to form a well-bonded joint. When small pores and white spot inclusions are found in the molten pool during the welding process, a small amount of flux can be added to the molten pool to help remove slag inclusions. In general, it is necessary to increase the temperature of molten iron, use flame to melt into the depth of the molten pool, so that the gas and inclusions will float, and use welding wire or ruler to scrape away the inclusions. During the welding process, the flame must always cover the molten pool to avoid excessive oxidation caused by air entrapment. When welding, the distance between the flame core and the molten pool should be kept at 10-15mm. Continuously use the welding wire to gently agitate the molten pool to help the gas and slag float out. Our company also has Grey Cast Iron Casting on sale, welcome to contact us.