[China Aluminum Network] pre-weld cleaning: When welding aluminum and aluminum alloys, the oxide film and oil stains on the surface of the workpiece weld and wire must be removed strictly before welding.
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1) chemical cleaning chemical cleaning, high efficiency, stable quality, suitable for clean welding wire and small size, batch production of the workpiece. Available dip method and scrub method two. Can be used acetone, gasoline, kerosene and other organic solvents to the surface of the oil, with 40 °C ~ 70 °C 5% ~ 10% NaOH solution caustic washing 3min ~ 7min (a little longer but not more than 20min pure aluminum), flow water rinse, then use The 30% HNO3 solution at room temperature to 60°C is pickled for 1 minute to 3 minutes, rinsed with flowing water, air-dried or dried at low temperature.
2) Mechanical cleaning: Mechanical cleaning is often used when the workpiece has a large size, a long production cycle, multi-layer welding or chemical cleaning. First use acetone, gasoline and other organic solvents to wipe the surface to remove oil, and then directly use a copper wire brush with a diameter of 0.15mm to 0.2mm or a stainless steel wire brush to brush until the metal luster is exposed. Generally, it is not suitable to grind with grinding wheel or ordinary sandpaper, so as to avoid the sand particles remaining on the metal surface, and the defects such as slag inclusion will be generated when welding. In addition, the surface to be welded can be cleaned with a spatula, a trowel, or the like.
After cleaning, if the storage time is too long (such as more than 24h) should be re-treated.
2. Backing plate: The strength of aluminum alloy is very low at high temperature, and the flow properties of liquid aluminum are good. The weld metal will easily fall down during welding. In order to ensure penetration without collapse, welding pads are often used to support the weld pool and nearby metal. Pads can use graphite plates, stainless steel plates, carbon steel plates, copper plates or copper bars. An arc-shaped groove is formed on the surface of the pad to ensure that the weld seam is formed on the reverse side. It is also possible to weld double-sided molding without single-sided welding of the backing plate, but it is required that the welding operation be skilled or adopt advanced technological measures such as strict automatic feedback control of arc welding energy.
3, preheating before welding: thin, small aluminum generally do not have to preheat, the thickness of 10mm ~ 15mm can be preheated before welding, according to different types of aluminum preheat temperature can be 100 °C ~ 200 °C, available oxygen acetylene Flames, electric furnaces or torches are heated. Preheating can reduce the deformation of the weldment, reduce the porosity and other defects.