Welding of titanium tube heat exchanger tube plate

During assembly, use acetone to carefully clean the oil, water, and impurities on the surface of the tube and orifice plate. The requirement for orifice plates is that the aperture is greater than the pipe diameter by 0.5mm to ensure clearance. Before welding, the site should be strictly cleaned to reduce the content of iron ions in the air. Secondly, the welding equipment should be carefully cleaned, and the surface of the workpiece should be thoroughly cleaned with sandpaper and acetone and dried. The time interval between cleaning and welding should not exceed 2 hours. After drying, clean with a white silk cloth before welding can be carried out. Strengthen on-site wind prevention measures and enhance protection effectiveness.

In order to ensure uniform protection of the three welding zones, first carefully check whether each air outlet on the welding gun nozzle is unobstructed. 4-5 layers of fine copper mesh have been covered around the holes to achieve uniform airflow protection. In order to improve the cooling speed, shorten the residence time at high temperatures, and obtain good protection, utilizing the fast heat absorption characteristics of pure copper and the non melting nature of titanium and titanium alloys in other metals (except silver), in order to achieve rapid cooling, more than 20 quasi 20mm x 50mm pure copper rods were processed, and 4mmx20mm holes were drilled in the centers of both ends of the copper rods. The main purpose is to quickly absorb heat during the welding process by inserting the copper rods at the titanium tube ends, And timely release the small holes into the space to accelerate the cooling speed of the three areas of titanium metal welding. In addition, the small holes also make it easy to access (the copper rod extends into the titanium tube at a depth of 1mm). Pure copper not only plays a role in heat absorption and cooling, but also plays a role in sealing and protecting. Due to the low thermal conductivity and poor heat dissipation of titanium, small welding process parameters are selected to reduce heat input, appropriately extend the residence time of the molten pool, and reduce the generation of pores. In order to improve the protection effect of the welding pool, the arc ignition should be preceded by air supply for more than 5 seconds, and the gas should be stopped for more than 10 seconds after arc extinguishing. During welding, the angle between the welding gun and the front and rear of the tube plate is 75 °~85 °, and the angle between the tungsten electrode and the tube wall is 0 °~15 °. Arc striking is carried out on one side of the welding plate. After the first droplet of molten metal melts on the weld seam, normal welding begins and the arc is generally lowered by about 2mm to improve the protection effect and increase the penetration depth. The arc extinguishing should be placed on a copper rod, and the air supply should continue for more than 10 seconds after the arc extinguishing to achieve good protection and cooling purposes. To prevent overheating and deformation of the tube plate and facilitate heat dissipation and cooling, dispersed and symmetrical welding is adopted.

During the welding process of the titanium tube heat exchanger tube sheet, through continuous exploration, the following experience has been summarized: due to the good fluidity of titanium after melting, which is higher than other metals except silver, it is recommended to start the arc at 1 o'clock and weld counterclockwise until 11 o'clock using high-frequency arc extinguishing to increase the arc extinguishing frequency to prevent the droplet from flowing too fast, affecting the welding quality and weld appearance, Avoid uneven thickness of the weld seam. When extinguishing the arc, it should pass through the ignition point by 4-6 mm and extinguish the arc on the copper rod to prevent the formation of arc pits. In summary, in the welding of titanium tube heat exchanger tube sheets, it is effective to use a large nozzle water-cooled welding gun, utilize the fast heat absorption characteristics of pure copper rods, and accelerate the cooling speed of the weld seam. The adopted process measures and operating methods have ensured the overall welding quality of the titanium tube heat exchanger, achieved good results, and achieved significant economic benefits.