Preparation before welding of aluminum and aluminum alloys, and precautions for welding machines

【Summary Description】 Groove processing using mechanical processing methods. The surface of the groove after processing shall be smooth without burrs and flashes. Groove form is generally V-shaped, no blunt edge, groove angle should be 70~75 ℃. Butt welds of different wall thicknesses shall have a transition section of 14O. Preparation before welding Before welding, remove the welding wire, welded pipe groove and the oil stain and oxide film within 30~50mm inside and outside the groove. The removal sequence and method are as follows: use acetone or carbon tetrachloride and other organic solvents to remove oil stains on the surface, and the removal range inside and outside the groove should not be less than 50mm. After oil stains are removed, the welding wire adopts chemical method, the groove is easy to use mechanical method, and the test tube also uses chemical method to remove the surface oxide film. On the mechanical side, the surface of the groove and its vicinity can be cleaned by filing, scraping, grinding or brushing with a stainless steel wire of about 0.2mm until the metallic luster is exposed. The cleaning range on both sides shall not be less than 30mm from the groove edge, and the tools used shall be degreased regularly. Chemical methods. Soak in 5-10% NaOH solution at 70°C for 30-60 seconds, or soak in 5-10% NaOH solution at normal temperature for 3 minutes. Then, it was soaked in about 15% HNO3 (room temperature) for about 2 minutes, and then washed with warm water. Or rinse it with cold water and let it dry completely. The welding wire that has undergone a reliable surface treatment and is not oxidized or contaminated can be directly used without the above treatment. The cleaned groove and welding wire shall not be contaminated before welding. If there is no effective protective measures, welding should be carried out within 8 hours. Otherwise, it should be cleaned again. When assembling the pipeline, the inner wall should be flush, without burrs and chips, and the misalignment should conform to B ≤ 0.5mm. The internal welded joints are not lined, and the clearance should be equal to zero as much as possible, especially at the overhead welding position. The inner wall of the pipeline should be rounded by 1~1.5mm. Welding machine and other precautions The welder must be an AC TIG welder with steep external characteristics and sufficient capacitance. Moreover, the parameters are stable, the adjustment is flexible, and the performance is safe and reliable. It should also have a device for arc starting, arc stabilizing and eliminating DC components. The current and voltage meter on the welding machine shall be verified by the metering department. Before using the welding machine, check whether the grounding is good, whether the cooling water and gas circuit are unblocked, and its various functions must be guaranteed to work normally. The welding place shall be kept clean. In addition to windproof, rainproof and snowproof facilities, relative humidity ≤ 80% and ambient temperature> 5 ℃ shall be ensured during welding.

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