Welding methods commonly used for titanium alloy welding are: argon arc welding, submerged arc welding, vacuum electron beam welding, etc. Tungsten arc welding is used for the thickness below 3 mm, and argon arc welding is used for the welding of more than 3 mm. The purity of argon is not less than 99.99%, and the content of air and water vapor in argon is strictly controlled. Surface treatment for degreasing, descaling and descaling before welding. Because titanium and titanium alloys have high chemical activity and are easily contaminated by oxygen, nitrogen, and hydrogen, they cannot be welded by electrode arc welding, oxyacetylene (or oxypropane, etc.) gas welding, C02 welding, or atomic hydrogen welding.
The welding of titanium alloy pipes by argon arc welding is usually all-site welding on site, which is much more difficult than the welding of stainless steel pipes.The welding zone of titanium and its alloys above 400 ℃ must be protected, because its chemical properties are particularly lively. It is easy to absorb harmful gases, resulting in a decrease in the performance of the material and even cracks. Therefore, pay special attention to the following items when welding:
- 1.When welding titanium pipes and titanium alloy pipes by argon arc welding, the welding materials are basically selected based on the principle of equal strength.If no suitable welding materials can be found, the method of cutting from the parent material can be used to solve it; and argon gas The selection will directly affect the hardness and toughness of the weld, and also have a significant effect on the generation of welding cracks, so it is required to select (especially pure titanium) high-purity argon (99.99%).
- 2. Welding titanium tube cutting and breaking production should adopt cold working method, and it should not be overheated and discolored. Use the grinding wheel or stainless steel wire wheel to polish the metallic luster within the range of not less than 20mm on the inner and outer surfaces of the groove. Use the scraper to trim the burrs of the groove and then polish it to avoid hanging the wire during cleaning.
- 3. The quality of cleaning when welding titanium alloy directly affects the welding cracks and pores, usually pickled first (3% HF + 35% HNO3 + H2O), then rinsed with clean water, and finally dried, use acetone or Wipe with alcohol. The welded joints must be welded immediately after cleaning, no more than 4h, otherwise they need to be cleaned again. Rubber gloves cannot be used for cleaning, and white clean cotton gloves should be used.
- 4. The protection of the welding area is very important when welding titanium alloy pipes and titanium alloy pipes, similar to the welding of stainless steel pipes, but the requirements for gas protection are more strict. The argon filling in the pipe should continue until the end of the welding, until the temperature of the welding area drops below 350 ℃ It can be stopped; the argon protection on the front of the tube adopts a large-diameter nozzle and an extended drag cover. In order to improve the protection effect, when the welding is completed, the drag cover does not end. You must wait for the temperature to fall below 200 ° C to stop the gas supply. Lower the hood.
The operation method of TIG welding of titanium alloy tubes is basically similar to stainless steel. When the full penetration is ensured, the welding line energy should be as small as possible, that is, the straight welding gun and the filler wire should be quickly welded. Welding operations mainly pay attention to the following points:
- 1. Before welding, replace it with a period of time in advance. You can use the open flame detection method to check the welding port and confirm that the gas in the tube is completely argon before welding. Adopt short arc welding without swinging welding torch and welding wire. When covering the face, it is to swing, but only slightly and slowly. The end of the welding wire cannot be separated from the protection range during the welding process, otherwise the end of the welding wire will be oxidized. If it is found that the end of the welding wire has been oxidized, the oxidized part must be cut off before use. After the welding is stopped, the gas supply should be delayed until the temperature of the welding zone drops below 300 ℃. When welding, the arc starting and closing points must be carried out within the breach, and no arc starting and closing on the base material is allowed.
- 2. When feeding the wire, the welding wire cannot be fed one by one quickly, and the welding wire should be sent slowly and evenly into the molten pool, otherwise it will cause gas turbulence and affect the protection effect. When welding, the distance between the nozzle and the nozzle is as low as possible without affecting the line of sight. The angle is about 75 °, but the tungsten pole cannot be caught by the tungsten electrode and the base material. The angle between the welding wire and the nozzle is 12 ° Around. During the welding process, the temperature between the layers must be strictly controlled. The first layer of the US and South Korea should wait for the temperature to drop to room temperature before continuing to weld the next layer. There should be a gap of 0.5 ~ 1mm between the rubber plugging plate and the inner diameter of the pipe, which can play a role in replacing the air in the pipe before welding, releasing excess argon gas and cooling during welding. When welding, the surface color of the welding seam should be observed at all times, silver-white is the best, followed by golden, purple, blue, gray, gray-white.
- 3. The welding environment is very important. The welding site must be kept dry and clean. The ambient temperature during welding should be controlled above 18 °; the welding area is free of wind, and the welding pool and heat-affected zone are absolutely forbidden to seep, Otherwise, there must be shielding measures to prevent the welding seam from being polluted and affecting the welding quality. In short, it is important to weld titanium and its alloy pipelines from the selection of welding materials, beveling and grinding, cleaning and drying, environmental measures, gas protection, process parameters, welding operations and other aspects. Qualified welded joints.