Welding operation skills of copper and brass

【Summary Description】 Copper has excellent properties such as electrical conductivity, thermal conductivity, corrosion resistance, ductility and certain strength. It is widely used in electrical, electronic, chemical, food, power, transportation and aerospace industries. In pure copper (copper) to add more than 10 kinds of alloying elements to form a solid solution of all kinds of copper alloys, such as zinc for brass; nickel for cupronickel; silicon for silicon bronze; aluminum for aluminum bronze and so on! Copper and copper alloys can be connected by brazing, resistance welding and other processes. In today's developed industry, fusion welding has occupied a dominant position. The welding of copper and copper alloy is easy to be realized by welding rod arc welding, TIG welding, MIG welding and other technological methods. There are four main elements that affect the weldability of copper and copper alloys: One is the effect of high thermal conductivity. The thermal conductivity of copper is 7 to 11 times larger than that of carbon steel. When the process parameters used are similar to those of welding carbon steel with the same thickness, the copper material is difficult to melt, and the filler metal and the base metal cannot be fused well. Second, the hot cracking tendency of welded joints is large. During welding, copper and impurities in the molten pool form a low melting point eutectic, which makes copper and copper alloys have obvious hot brittleness and produce hot cracks. Third, the defects of pores are much more serious than those of carbon steel, mainly hydrogen pores. Four is the change of welding joint performance. Grain coarsening, plasticity decreased, corrosion resistance decreased. 1. Welding of red copper 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 Butt joints are most commonly used for welding copper, and lap joints and T-joints are used 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, using Gas agent 301 as a flux. Neutral flame shall be used for gas welding of copper. (2) Manual arc welding of copper In manual arc welding, red copper electrode copper 107 is used, and the welding core is red copper (T2, T3). The edge of the welding place shall be cleaned before welding. 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 weld. Long welds shall be welded by step-back method. 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 is opened; When the plate thickness is 3~10mm, open a V-shaped groove with a groove angle of 60~70; When the plate thickness is greater than 10mm, open an X-shaped groove with a groove angle of 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 the 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. There is also carbon arc welding of copper. The electrodes used in carbon arc welding are carbon electrodes and graphite electrodes. 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. Welding of brass Brass welding methods are: gas welding, carbon arc welding, manual arc welding and argon arc welding. (1) gas welding of brass Due to the low temperature of the gas welding flame, the evaporation of zinc in brass during welding is less than that during electric welding, so gas welding is the most commonly used method in brass welding. The welding wire used in brass gas welding are: wire 221, wire 222 and wire 224, etc. These welding wires contain silicon, tin, iron and other elements, which can prevent and reduce the evaporation and burning of zinc in the molten pool, which is conducive to ensuring the performance of the weld and preventing pores. Gas welding brass commonly used flux of solid powder and gas flux, gas flux by boric acid methyl ester and methanol composition; flux such as gas agent 301. (2) Manual arc welding of brass In addition to copper 227 and copper 237, self-made welding rods can also be used for welding brass. When brass arc welding, DC power source should be used for positive connection, and the electrode should be connected to the negative electrode. The surface of the weldment shall be cleaned carefully before welding. Generally, the groove angle should not be less than 60~70 °. In order to improve the weld formation, the weldment should be preheated at 150~250 ℃. Short arc welding should be used during operation, not for horizontal and back and forth swing, only for linear movement, welding speed to be high. Brass weldments in contact with corrosive media such as seawater and ammonia must be annealed after welding to eliminate welding stress. (3) Manual argon arc welding of brass Brass manual argon arc welding can use standard brass welding wire: wire 221, wire 222 and wire 224, or materials with the same composition as the base metal as filling materials. Welding can be connected with DC or AC. When welding with AC, the evaporation of zinc is lighter than when DC is connected. Usually do not have to preheat before welding, only plate thickness difference is relatively large before preheating. The welding speed should be as fast as possible. After welding, the weldment should be heated to 300~400 ℃ for annealing treatment to eliminate the welding stress and prevent the weldment from cracking during use. (4) Brass Carbon Arc Welding When brass carbon arc welding, wire 221, wire 222, wire 224 and other welding wires are selected according to the composition of the base metal, and self-made brass welding wires can also be used for welding. Welding can use gas 301, etc. as a flux. Welding should be short arc operation to reduce zinc evaporation and burning loss. DC TIG welding process is widely used in copper and copper alloy welding, welding wind forming good, good quality inside and outside, under the protection of argon, the molten pool is pure, less pores, thermal cracking effect is small, easy to operate. When the thickness is ≤ 4mm, it is not necessary to preheat before welding, but directly preheat with argon gas. When the temperature of the molten pool is close to 600 ℃, filler wire can be added to melt the base metal to realize welding. For copper with a thickness greater than 4mm, pure copper should be preheated at 400-600 ℃. Copper alloy welding preheating 200-300 ℃. 300TSP,315TX DC TIG welding machine can weld pure copper, silicon bronze, phosphor bronze, brass, white copper and other copper alloys. The 300WP5 and 300/500WX4 AC/DC dual-purpose TIG welding machines can weld aluminum bronze with AC TIG (remove surface oxide film with AC square wave) and the above copper with DC TIG. In recent years, the construction of welding copper and copper alloy by MIG method is more and more, especially for aluminum bronze, silicon bronze and white copper with thickness ≥ 3mm, it is best to use MIG welding method. Thickness of 3~14mm or> 14mm copper and copper alloy almost always use MIG welding, because of high deposition efficiency, large penetration, welding speed (generally 3~4 times TIG welding), to achieve high efficiency, high quality, low cost of economic benefits requirements. Before welding, the copper material shall meet the preheating temperature requirements (pure copper 400~600 ℃, copper alloy 200~300 ℃), the welding wire and the base metal shall be sufficiently similar in chemistry, and the purity of argon shall be ≥ 99.98. • Brass is a copper-zinc alloy, because the boiling point of zinc is low, only 907 ℃, so the welding process is very easy to evaporate, which has become the biggest problem of brass welding. Under the action of high temperature, the evaporation of zinc during electrode arc welding is as high as 40%, and a large amount of zinc evaporation leads to the decrease of mechanical properties and corrosion resistance of welded joints, and also increases the sensitivity to stress corrosion. Evaporated zinc in the air is immediately oxidized into zinc oxide, the formation of white smoke, to bring great difficulties to the operation, but also affect the welder's health, therefore, welding brass places, should strengthen ventilation and other protective measures. The weldability of brass is poor, and there will be problems such as pores, cracks, evaporation and oxidation of zinc during welding. In order to solve these problems, the welding wire containing silicon is often used in welding, because silicon will form a dense silicon oxide film on the surface of the molten pool, which hinders the evaporation and oxidation of zinc and prevents the invasion of hydrogen. After welding, it can be annealed at 470~560 ℃ to eliminate stress and prevent "self cracking. 2, brass welding methods commonly used in the production of brass welding method is welding rod arc welding and argon arc welding, the process points are as follows: (1) The welding rod adopts bronze core welding rod, such as ECuSn-B(T227) and ECuAl-C(T237). Brass castings with low repair welding requirements can be used with pure copper cored electrodes, such as ECu(T107). The power supply adopts DC positive connection, and the V-groove angle shall not be less than 60 ° ~ 70 °. When the plate thickness exceeds 14mm, the surface of the weldment should be carefully cleaned before welding to remove all oil impurities that will generate hydrogen. Short arc welding should be used during operation, and the welding rod does not swing horizontally and back and forth, but only moves along the straight line of the weld. The welding speed should be fast and should not be less than 0.2~0.3 m/min. During multi-layer welding, the oxide film and slag between layers shall be removed. The copper liquid of brass has high fluidity, so the solution pool is preferably in a horizontal position. If the solution pool must be inclined, the inclination angle should not be greater than 15 degrees. (2) Argon arc welding manual tungsten argon arc welding, the welding wire adopts tin brass welding wire HSCuZ-1(HS221), iron brass welding wire HSCuZn-2(HS222), silicon brass welding wire HSCuZn-4(HS224). These wires are high in zinc and have a large amount of smoke during welding. Also available bronze wire HSCuSi(HS211), HSCuSn(HS212). Because the evaporation of zinc destroys the protective effect of argon, a larger nozzle aperture and argon flow rate should be used when welding brass. Preheating is generally not required before welding. Preheating is only required when welding joints with a thickness greater than 10mm and joints with a large difference in welding edge thickness. The latter only preheats the thicker part of the weldment edge. The power supply can be DC positive connection or AC. When welding with AC power, the evaporation of zinc is small. The welding parameters should adopt larger welding current and faster welding speed. The welding parameters of 16~20mm thick brass plate are: welding current 260 ~ 300A, tungsten electrode diameter 5mm, welding wire diameter 3.5~4.0mm, nozzle aperture 14~16mm, argon flow rate 20 ~ 25L/min. In order to reduce the evaporation of zinc, the filler wire and weldment can be "short-circuited" during operation, arc ignition and arc maintenance on the filler wire, as far as possible to avoid the arc directly acting on the base metal, the base metal is mainly heated and melted by the heat transfer of the molten pool metal. When welding, Single-layer welding should be carried out as much as possible. For joints with a plate thickness of less than 5mm, it is best to finish welding at one time. After welding, the weldment should be heated to 300~400 ℃ for annealing treatment to eliminate welding stress and prevent brass components from cracking during use.

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