In the case of tungsten argon arc welding, since the argon protective layer is flexible, it is easily damaged by external factors and its protection effect is mainly related to the following factors:
(1) Gas flow rate: For a nozzle with a certain aperture, the greater the gas flow rate, the stronger the ability of the protective layer to resist the influence of flowing air. However, when the flow rate is too large, the protective layer will generate irregular flow, which will easily cause the air to get involved, but the protection effect will be reduced, so the gas flow rate should be properly selected. For example, a nozzle having a pore diameter of 5-14 mm has an argon flow rate of 5-15 L/min.
(2) Nozzle diameter: When the nozzle diameter and the gas flow rate increase simultaneously, the protection zone must increase. However, when the nozzle diameter is too large, some weld positions are not easy to weld or obstruct the welder's line of sight, thus affecting the welding quality. The diameter of the nozzle for manual tungsten argon arc welding is 5-14mm.
(3) Distance from nozzle to workpiece: The farther the nozzle is from the workpiece, the worse the protection effect; on the contrary, the closer the distance is, the better the protection effect, but too close will affect the welder's line of sight, and the operation is inconvenient. Generally, it is suitable to take a nozzle to workpiece distance of 10 mm.
(4) Welding speed and external airflow: Due to the influence of air resistance on the protective gas layer, the welding speed is too fast or the lateral airflow is encountered during welding, the protective layer may be deviated from the tungsten and the molten pool, thereby protecting The effect is worse, so the proper welding speed should be chosen. In order to improve the protection effect, the tungsten hydrogen arc welding should be operated indoors or without wind.
(5) Welded joint form: Different welding forms will have different protective effects on the gas, see Figure 2-9. When welding butt joints and T-joints, the argon gas is blocked and reflected back, so the protection effect is better; while the lap joints and corner joints are easy to invade the arc area due to air, so the protection effect is poor.
(6) Welded metal materials: For metals and their alloys (titanium and titanium alloys) that are very sensitive to oxidation and nitriding, better protection is required for argon arc welding. The specific measures are: increase the diameter of the nozzle, use a drag cover to increase the protection area, and use special equipment to protect the front and back of the weld.
In addition, the welding current, the arc voltage, the inclination angle of the torch, and the feeding condition of the filler wire have a certain influence on the protection effect. In short, in order to obtain a weld with satisfactory quality, the above factors should be considered in the welding.
