Gas welding is one of the earliest methods used for the repair of cast iron components. Since the flame temperature of gas welding (approximately 3150°C) is lower than that of arc welding (about 6000°C), the heat is not as concentrated. Additionally, the heating degree and duration can be controlled more freely, allowing for a slow heating and cooling process. This helps in the graphitization of the metal in the repair area and the escape of gases from the weld seam, resulting in better welding quality. Furthermore, gas welding equipment and materials are readily available, making it widely used for the repair of various castings.
Gas Welding Equipment and Tools
Gas welding typically uses an oxygen-acetylene flame as the heat source. The required equipment and tools are relatively simple, mainly consisting of oxygen, acetylene gas, a welding torch, and some auxiliary tools.
The welding torch is the main tool in gas welding. Its function is to mix acetylene gas and oxygen in a specific ratio, then emit the mixed gases through the nozzle to produce a stable flame with a certain heat and composition. The torch should be lightweight, safe, and reliable. The flame produced should be small in volume with concentrated temperature, allowing for flexible flame adjustments during operation to achieve different flame properties.
Repairing Cast Iron Components
1. Gas welding should use a weak reducing flame or neutral flame to reduce silicon and manganese loss and prevent the formation of a thick oxide layer.
2. Complete fusion must be achieved, and the flame should always cover the molten pool. The distance between the flame center and the molten pool should be 15-20mm.
3. If small gas bubbles or bright oxidation appears in the molten pool, a small amount of welding powder can be added, and the flame should be used to heat the molten pool to help the bubbles and oxide inclusions float up. These can then be removed with the welding rod or scraped out.
4. After the weld seam is formed, the flame should be used to heat the seam and reduce the cooling rate to prevent the formation of white iron.
Repairing Non-Ferrous Alloy Castings
1. Aluminum Alloy Castings: Gas welding should be performed in a draft-free environment with a temperature not lower than 15°C.
2. Brass Castings: A weak oxidative flame should be used for the repair, ensuring a layer of zinc oxide film covers the surface of the molten pool to prevent evaporation.
3. Tin Bronze Castings: Tin bronze is thermally brittle, so the casting should be preheated before welding, and it should not be moved immediately after welding.
4. Aluminum Bronze Castings: The casting should be preheated to 500-600°C before welding. Larger defects should be repaired first, followed by smaller ones. For long and deep defects, the casting can be tilted 15°for uphill welding.
Post time: Feb-21-2025