Non-oxidation continuous heat treatment furnace with shielding gas is widely used abroad for intermediate heat treatment and final product heat treatment in production process. Because a bright surface without oxidation can be obtained, the traditional pickling process is cancelled. Adopting this heat treatment process not only improves the quality of steel pipe, but also overcomes the environmental pollution caused by pickling.
According to the current development trend of the world, bright continuous furnaces are basically divided into three types:
(1) roller bottom bright heat treatment furnace. This furnace type is suitable for heat treatment of large and large steel pipes, and the output per hour is more than 1.0 tons. Protective gases that can be used are high purity hydrogen, decomposed ammonia and other protective gases. A convection cooling system can be equipped to quickly cool the steel pipes.
(2) mesh belt type bright heat treatment furnace. This furnace type is suitable for small-diameter thin-walled precision steel pipes, and the output per hour is about 0.3- 1.0 tons. The length of steel pipe can reach 40 meters, and it can also be processed into coiled capillary.
(3) muffle furnace type bright heat treatment furnace. The steel pipe is installed on the continuous handle and heated in the muffle pipe, which can treat high-quality small-diameter thin-walled steel pipe at a lower cost, and the output per hour is about 0.3 tons or more.
Technology of Stainless Steel Welded Pipe-Argon Arc Welding
Stainless steel welded pipe requires deep penetration, no oxide inclusions, and as small as possible the heat affected zone. Tungsten inert gas argon arc welding has good adaptability, high welding quality and good penetration, and its products are widely used in chemical industry, nuclear industry and food industry.
The disadvantage of argon arc welding is its low welding speed. In order to improve the welding speed, many methods have been developed abroad. Among them, the welding method of multi-electrode and multi-torch is developed from single electrode and single torch and applied to production. In 1970s, Germany first adopted a number of welding guns arranged in a straight line along the weld direction, forming a long heat flux distribution, which significantly improved the welding speed. Generally, argon arc welding with a three-electrode torch is adopted, and the wall thickness of the welded steel pipe is more than or equal to S≥2mm, so the welding speed is 3-4 times higher than that with a single torch, and the welding quality is also improved. The combination of argon arc welding and plasma welding can weld steel pipes with large wall thickness. In addition, the welding speed can also be improved by using high-frequency pulse welding power supply in argon gas with hydrogen content of 5- 10%.
Multi-torch argon arc welding is suitable for welding austenitic and ferritic stainless steel pipes.
Stainless steel welded pipe technology-high frequency welding
High frequency welding has been used in the production of carbon steel welded pipes for more than 40 years, but it is a relatively new technology for welding stainless steel pipes. The economy of its production makes its products more widely used in architectural decoration, household appliances and mechanical structures.
High-frequency welding has higher power supply, and can achieve higher welding speed for steel pipes with different materials, different outer diameters and different wall thicknesses. Compared with argon arc welding, it is more than 10 times of its highest welding speed. Therefore, the production of general stainless steel pipes has high productivity.
Because of the high speed of high frequency welding, it is difficult to remove burrs in welded pipes. At present, high-frequency welding of stainless steel pipes is not accepted by chemical and nuclear industries, which is also one of the reasons.
From the welding materials, high frequency welding can weld various types of austenitic stainless steel pipes. At the same time, the development of new steel grades and the progress of forming welding methods have also successfully welded ferritic stainless steel AISI409 and other steel grades.
Welded pipe technology-combined welding technology
Various welding methods of stainless steel welded pipe have their own advantages and disadvantages. How to combine several welding methods to form a new welding process to meet people's requirements for the quality and production efficiency of stainless steel welded pipe is a new trend in the development of stainless steel welded pipe technology.
After exploration and research in recent years, the composite welding technology has made progress, and the production of stainless steel welded pipes in Japan, France and other countries has mastered certain composite welding technology.
The combined welding methods include argon arc welding and plasma welding, high frequency welding and plasma welding, high frequency preheating and three torch argon arc welding, and high frequency preheating and plasma welding and argon arc welding. Composite welding is of great significance to improve welding speed. For the high-frequency preheating combined welded steel pipe, the weld quality is equivalent to that of conventional argon arc welding and plasma welding, the welding operation is simple, the whole welding system is easy to realize automation, and this combination is easy to connect with the existing high-frequency welding equipment, with low investment cost and good benefits.
Influence of TIG flux on weld formation (1)
TIG welding has been widely used in production. It can obtain high-quality welds, which are usually used for welding nonferrous metals, stainless steel, ultra-high strength steel and other materials. However, TIG welding has some disadvantages, such as penetration (≤3mm) and low welding efficiency, so multi-pass welding is needed for thick plates. Although increasing welding current can increase the penetration depth, the increase of weld width and weld pool volume is much greater than the increase of weld depth.
Influence of TIG flux on weld formation (2)
Active TIG welding method has attracted worldwide attention in recent years. This technology is to coat a layer of active flux on the weld surface before welding. Under the same welding specification, the penetration can be greatly improved (up to 300%) compared with conventional TIG welding. For 8mm thick plate welding, a large penetration or penetration can be obtained at one time without groove, and for thin plate, the welding heat input can be reduced without changing the welding speed. At present, A-TIG welding can be used to weld stainless steel, carbon steel, nickel-based alloy and titanium alloy. Compared with traditional TIG welding, A-TIG welding can greatly improve productivity, reduce production cost and reduce welding deformation, and has a very important application prospect. The key factor of A-TIG welding is the choice of active agent composition. At present, the commonly used active agent components are mainly oxides, chlorides and fluorides, and different materials have different active agent components. However, due to the importance of this technology, the composition and formula of the active agent have patent restrictions in PWI and EWI, and are rarely reported in public publications. At present, the research on A-TIG welding mainly focuses on the mechanism of activator and the application technology of activation welding.
Influence of TIG flux on weld formation (3)
At present, there are three kinds of active agents developed and used at home and abroad: oxides, fluorides and chlorides. The active agents developed by PWI for titanium alloy welding in the early days are mainly oxides and chlorides, but chlorides are toxic, which is not conducive to popularization and application. At present, the active agents used for welding stainless steel and carbon steel abroad are mainly oxides, while the active agents used for welding titanium alloy materials contain certain fluoride components.
Influence of TIG flux on weld formation (4)
Effect of one-component activator on weld formation of stainless steel;
(1) For the weld coated with SiO _ 2 activator, with the increase of SiO _ 2 coating amount, the weld width gradually narrows, and the arc crater becomes longer, narrower and deeper. The remaining height on the back of the weld becomes higher. At the joint of coated and uncoated active agents, weld metal accumulates more. Among all activators, silica has the greatest influence on weld formation. ? (2) NaF and Cr2O3 have no obvious influence on weld formation. With the increase of coating content, the weld width changes little, and the arc pit changes little. Compared with the weld without activating agent, the weld width has no obvious change, but the arc pit is larger than that without activating agent. ? (3) With the increase of TiO2 _ 2 coating amount, the appearance of weld has little change, and the weld joint has no obvious change, which is similar to that without activating agent.
However, the formed weld surface is relatively flat and regular, and there is no undercut phenomenon, which is better than the weld formation without activating agent. ? (4) Calcium fluoride has great influence on weld formation. With the increase of CaF2 coating content, the weld formation becomes worse, the arc pit changes little, and the weld width changes little. However, with the increase of CaF2 content, defects such as undercut appear. ? (5) Compared with no activating agent, the above five activating agents can increase the weld penetration, and with the increase of coating amount, the penetration will also increase accordingly. However, when the coating amount reaches a certain value, the penetration depth increases to saturation, then increases and decreases.
Influence of TIG flux on weld formation (5)
Advanced series high-speed and high-efficiency MIG/MAG twin-wire welding technology
This process can weld carbon steel, low alloy steel, stainless steel, aluminum and other metal materials. It is an advanced welding technology with high speed, high efficiency and wide application.
High-speed welding and high deposition rate welding are the development direction of welding technology in the future, and MIG/MAG twin-wire high-speed and efficient welding is one of the hot spots, which will be more and more widely used in industrial production.
Principle of tandem twin-wire welding
The tandem twin-wire welding system consists of two welding machines, two wire feeders and a welding torch, which can be used in conjunction with automatic special plane or welding robot. Two wire feeders feed two welding wires into two independent conductive nozzles in the welding gun through two wire feeding tubes respectively, and they are melted in a double arc to form a molten pool.
Technological characteristics of tandem twin-wire welding
1, high performance welder, 100% welding current at temporary load rate 1000A, pulse current1500a;
2. Digital double pulse power supply, programmable, connected to PC and printer;
3. The specification parameters of each welding wire can be set separately, and the material and diameter can also be different;
4. The wire feeding speed of each welding wire can reach 30m/min；; ;
5, the deposition efficiency and welding speed are greatly improved;
6. When the deposition efficiency increases, keep the heat input low;
7, arc stability, droplet transition is controlled;
8, welding deformation is small;
9. Small splash;
10, welding data monitoring and management;
1 1, using standard gas, with less gas consumption;
12, wide application range and high productivity.