Detailed explanation of the welding method of copper

【Summary Description】 1. Common welding methods Welding copper methods include gas welding, manual carbon arc welding, manual arc welding and manual argon arc welding. Large structures can also be welded automatically. (1) Gas welding of copper Copper is the most commonly used butt joints, lap joints and T-joints as little as possible. Two kinds of welding wires can be used for gas welding, one is the welding wire containing deoxidizing elements, such as wire 201 and 202; the other is the general copper wire and the cutting strip of the base metal, the gas agent 301 is used as the flux, and the neutral flame should be used for gas welding of copper. (2) Manual arc welding of copper. When the thickness of the weldment is greater than 4mm, it must be preheated before welding, and the preheating temperature is generally about 400-500 ℃. With copper 107 electrode welding, the power supply should be DC reverse connection. When welding, short arc should be used, and the welding rod should not be swung laterally. The reciprocating linear motion of the welding rod can improve the forming of the welding seam. The long welding seam should be gradually withdrawn and the welding speed should be as fast as possible. During multi-layer welding, the slag between the layers must be completely removed. Welding should be carried out in a well-ventilated place to prevent copper poisoning. After welding, flat head hammer should be used to knock the weld to eliminate stress and improve the quality of the weld. (3) Manual argon arc welding of copper When red copper manual argon arc welding, the welding wire used is wire 201 (special red copper welding wire) and wire 202, and red copper wire, such as T2. Before welding, the oxide film, oil and other dirt on the welding edge of the workpiece and the surface of the welding wire must be cleaned to avoid defects such as pores and slag inclusion. Cleaning methods are mechanical cleaning and chemical cleaning method. When the thickness of the butt joint plate is less than 3mm, no groove shall be opened; When the plate thickness is 3~10mm, open V-shaped groove, groove angle is 60 ° ~ 70 °; When the plate thickness is greater than 10mm, open X-shaped groove, groove angle is 60 ° ~ 70 °; In order to avoid incomplete welding, generally no blunt edge is left. According to the plate thickness and groove size, the assembly clearance of butt joint is selected in the range of 0.5~1.5mm. Manual argon arc welding of red copper usually adopts DC positive connection, I .e. tungsten electrode is connected to negative electrode. In order to eliminate pores and ensure reliable fusion and penetration at the root of the weld, it is necessary to increase the welding speed, reduce argon consumption, and preheat the weldment. When the plate thickness is less than 3mm, the preheating temperature is 150~300 ℃; when the plate thickness is greater than 3mm, the preheating temperature is 350~500 ℃. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced. (4) Carbon arc welding of copper Carbon electrodes and graphite electrodes are used in carbon arc welding. The welding wire used for carbon arc welding of red copper is the same as that used for gas welding. It can also be cut from the base metal and flux used for gas welding of red copper, such as gas 301, etc. 2. Examples of copper welding Example 1. Manual tungsten argon arc welding of copper tubes A unit has 6 Φ180mm × 10mm copper pipe (brand T2) welding joints to be welded during equipment installation. Manual argon tungsten arc welding method has achieved good results. The welding process is as follows: Preparation before 1.1 welding 1.1.1 The welding equipment is WSE-350 AC/DC argon arc welding machine with DC connection. The Welding materials is made of copper welding wire (wire 201) with a diameter of 3mm. Argon purity ≥ 99.96%. 1.1.2 No gap shall be left when the groove is set. 1.1.3 The welding area of the copper pipe and the copper wire shall be free of oil, oxide layer, moisture, etc., and metallic luster shall be exposed. 1.1.4 Welding parameters: tungsten electrode: Φ3mm cerium tungsten electrode, nozzle: Φ14mm, welding current 160 ~ 180A, argon flow rate: 15L/min. 1.1.5 Preheating: Due to the large thermal conductivity and thermal expansion coefficient of red copper and its thermal brittleness, the groove of red copper pipe and the 60mm on both sides of the groove are preheated before welding. The preheating method adopts oxygen-acetylene flame heating, the preheating temperature is about 500 ℃, and the temperature measuring method is point contact thermometer. 1.1.6 Tack weld the pipe fittings at two places (divided into three parts according to the circumference of the pipe, two places are tack welding and one place is welding spot). The length of tack welding is ≥ 10mm and the welding height is 3mm. 1.2 welding The welding level is two layers, I .e. the bottom layer and the cover layer, which are both rotary welding. The welding position is from 10: 00 to 11: 30 on the clock, and the welding is randomly rotated up. 1.2.1 Base welding: Base welding adopts left welding method, and defects such as porosity, slag inclusion, welding flash and incomplete welding shall be prevented during welding. The angle between the welding wire and the pipe plane shall be as small as possible to enhance the argon protection effect, as shown in Fig. 7. The welding torch moves evenly, and the temperature of the molten pool should be controlled appropriately, not too high or too low, so that the welding process can proceed smoothly. The key is to pay close attention to the liquid flow of copper in the molten pool and grasp the timing of melting and penetration. When the molten pool metal slightly sinks, it indicates that the welding has been penetrated (the root forming is basically good). The "intermittent" wire feeding method is adopted for wire filling, I .e. the copper welding wire is fed and returned, which is "neat" and returned "clean". This state is always maintained for uniform forward welding. If the welding speed is slightly slow or the penetration is uneven, incomplete penetration or burn-through will occur, resulting in weld bead formation. The arc striking, joint and operation method are the same as those of the argon arc welding pipe. 1.2.2 Welding of cover surface layer: the welding torch swings left and right, and the welding wire is also fed with the movement of the welding torch. When the arc moves to both sides of the groove, it should pause for a while, and add welding wire to fill the groove and be 1.5~2mm higher than the pipe plane. Only when the welding torch and the welding wire match each other properly and swing evenly can the shape of the molten pool be controlled and the weld seam with good quality inside and outside. 1.3 considerations 1) It is strictly forbidden to "hit tungsten" (I. e. tungsten electrode and welding wire or tungsten electrode and molten pool contact) during welding. During welding, a large amount of metal fume and vapor will enter the molten pool during "tungsten beating", and a large number of honeycomb pores or cracks will be generated in the weld. In case of "tungsten beating" phenomenon, welding must be stopped, polished and welded again, and tungsten electrode shall be replaced or tungsten electrode tip shall be trimmed again until there is no copper spot metal. 2) The bonding jumper shall be firmly connected to prevent the surface of the tube from being scratched. 3) After the weld is slightly cooled, rotate the pipe fitting and pad it firmly. 4) Control the interlayer temperature. When it is found that welding is difficult to melt, it indicates that the temperature is low. It should be preheated to above 500 ℃ before welding, otherwise it is easy to produce incomplete fusion or poor fusion defects. 5) Under the condition of ensuring good fusion, the welding speed should be slightly faster, and the wire feeding is appropriate. Pay attention to the simultaneous melting and integration of the base metal and the welding wire to prevent defects such as incomplete fusion or poor fusion. 6) When the welding arc is extinguished, the welding torch cannot be lifted immediately, and the delayed gas stop protection function should be used to protect the molten pool to prevent pores. 1.4 post-weld treatment After inspection, there are no defects such as pores, cracks and slag inclusion, the welding area of the welded pipe joint is reheated to 600~700 ℃, and quenched with tap water to increase the plasticity of the welding area. Example 2. Oxygen-acetylene welding δ = 2mm thin copper plate Blast furnace circulating cooling pool water stop is made of δ = 2mm thin copper plate pair welding. During welding, because red copper has excellent thermal conductivity, or because the temperature is not enough to form a molten pool, the metal on the weld bead is not fused or not fused well. Either the temperature is too high, the welding area melts a large area, forming welding defects such as burn-through or welding flash. The welding of thin copper plate is a relatively "thorny" problem. According to the above situation, the welding method of "brass brazing" can solve this problem very well. Preparation before welding and operation process during welding are as follows: 1) 60mm on both sides of the weld shall be decontaminated and polished with a wire brush to expose metallic luster. 2) The welding parts shall not be beveled, and the clearance between the welding parts shall be less than 1mm. 3) Use Ф 3mm silicon brass welding wire (wire 224) and flux to 301 the flux. 4) Pad the welded part flat (the backing plate shall be made of flat steel plate and shall be thicker to prevent thermal deformation). 5) Preheating, two welders use medium welding guns, and the neutral flame heats the welding place at the same time, and the temperature reaches 500~600 ℃. One person welds while the other continues to heat in front of the welding position to ensure the stability of the welding process. 6) Neutral flame shall be used for preheating welders, and micro-oxidation flame shall be used for welding welders. 7) The positioning welding and formal welding shall be carried out continuously. The positioning distance shall be 60~80mm, and the positioning welding spot shall be smaller. 8) During heating and welding, pay close attention to the change of temperature in the welding area to prevent too high and too low. Generally, dark red (550~600 ℃) is appropriate for visual inspection. 9) The swing of the welding nozzle should be stable and move forward at a constant speed. The flame core (white spot) of the flame is 5~8mm higher than the melting pool. The contour of the flame should always cover the molten pool and avoid contact with air. Ensure that the brass fluid naturally and smoothly spread to both sides of the weld and dipped into the gap. 10) In order to make the structure of the welded joint crystal fine, improve the strength and toughness, after welding, use a small hammer to beat the welding meat properly. 11) Densification performance test shall be conducted after welding.

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