How to operate electric brazing

Welding technology of copper and copper alloys

Copper has excellent conductivity, thermal conductivity, corrosion resistance, ductility and strength.It is widely used in electrical, electronic, chemical, food, power, transportation and aerospace industries.Add more than 10 kinds of alloying elements to pure copper (red copper) to form various kinds of copper alloys with solid solution, such as adding zinc to make brass;Add nickel to white copper;Adding silicon is silicon bronze;Alcan for aluminum bronze and so on. 

Copper and copper alloy can be connected by brazing, resistance welding and other technological methods.It is easy to realize the welding of copper and copper alloy by welding electrode arc welding, TIG welding and MIG welding.There are four main factors influencing the weldability of copper and copper alloy.The thermal conductivity of copper is 7-11 times higher than that of carbon steel. When the process parameters adopted are similar to that of welded carbon steel of the same thickness, the copper is difficult to melt.Second, the hot crack tendency of welding joint is large.During welding, copper and its impurities in the molten pool form eutectic with low melting point, which makes copper and copper alloy have obvious hot brittleness and generate hot crack.The third is that the defect of producing pores is much more serious than that of carbon steel, and if hydrogen pores.The fourth is the change of welding joint performance.Grain coarsening, plasticity decreasing, corrosion resistance decreasing, etc.

1. Welding of red copper

(1) manual arc welding edge of red copper.

When the thickness of the welding part is more than 4mm, it must be preheated before welding. The preheating temperature is generally around 400-500℃.Use copper 107 welding rod welding, power supply should use dc reverse connection.Welding should use a short arc, the welding rod should not be transverse swing.Welding rod for the reciprocating linear motion, can improve the weld forming.Long welds shall adopt the step - by - step back method.The welding speed should be as fast as possible.When multi-layer welding, the slag between layers must be thoroughly removed.Welding shall be done in a well-ventilated place to prevent copper poisoning.After welding, the flat hammer is applied to strike the weld to eliminate the stress and improve the weld quality.

(2) manual argon arc welding of red copper

In manual argon arc welding of red copper, the wires used are 201(special red copper wire) and 202, and also use red copper wire, such as T2.Before welding the welding edge of the workpiece and the surface of the welding wire oxidation film, oil and other dirt must be cleaned to avoid the generation of porosity, slag and other defects.The cleaning methods are mechanical cleaning and chemical cleaning.When the thickness of the butt joint plate is less than 3mm, the groove shall not be opened;When the thickness of the plate is 3 ~ 10 mm, v-groove is opened and the groove Angle is 60-70;When the thickness of the plate is greater than 10 mm, X groove is opened, and the groove Angle is 60-70;In order to avoid incomplete welding, generally do not leave blunt edge.According to the plate thickness and groove size, the assembly clearance of the butt joint should be within 0.5 ~ 1.5 mm.Manual argon arc welding of red copper usually adopts dc positive connection, that is, tungsten negative connection.In order to eliminate the porosity and ensure the reliable fusion and penetration of the root of the weld, it is necessary to improve the welding speed, reduce the consumption of argon, and preheat the weld.When the thickness of the plate is less than 3mm, the preheating temperature is 150-300℃;When the thickness of the plate is greater than 3 mm, 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.

(3) carbon arc welding of red copper. Carbon arc welding USES carbon electrode and graphite electrode.The welding wire used in copper-carbon arc welding is the same as that used in gas welding. It can also be used as base material cutting strip.

2. Welding of brass

Brass welding methods are: gas welding, carbon arc welding, manual arc welding and argon arc welding. 

(1) manual arc welding of brass

In addition to using copper 227 and copper 237, welding brass can also use homemade electrode. 

In brass arc welding, the direct current power supply should be adopted, and the electrode should be connected to the negative electrode.The surface of the weld should be cleaned carefully before welding.Groove Angle should not be less than 60-70 in general, in order to improve the weld forming, welding parts to preheat 150-250℃.During operation, short arc welding shall be used, instead of swinging horizontally or back and forth, only moving in a straight line. The welding speed shall be high.Brass welds in contact with corrosive media such as seawater and ammonia must be annealed after welding to eliminate welding stress. 

(2) manual argon arc welding of brass

Brass manual argon arc welding can be performed with standard brass wire: wire 221, wire 222 and wire 224, or with filler material of the same composition as the base metal. 

Welding can be either direct or alternating current.With ac welding, the evaporation of zinc is lighter than with direct current welding.Usually do not preheat before welding, only when the thickness of the difference is large.The welding speed should be as fast as possible.After welding, the welders should be heated at 300-400℃ for annealing treatment to eliminate the welding stress, so as to prevent the welders from cracking during use. 

(3) brass carbon arc welding

When brass carbon arc welding, wire 221, wire 222, wire 224 etc. are selected according to the component of base material, and self-made brass wire can also be used for welding.Welding can use gas agent 301 as flux.Welding shall be short-arc operation to reduce evaporation and burning loss of zinc. 

Dc TIG welding technology is widely used in the welding of copper and copper alloys, with good welding air forming and good internal and external quality. Under the protection of argon gas, the molten pool is pure, with few pores and little influence of hot crack, and it is easy to operate.When the thickness is less than 4mm, it is not necessary to preheat before welding, but directly preheat with argon. When the temperature of the melting pool approaches 600℃, it is possible to add filler welding wire to melt the base material, so as to realize welding.For copper with thickness greater than 4mm, the pure copper should be preheated at 400-600 ℃.Preheat copper alloy welding 200-300℃.The 300TSP, 315TX dc TIG welder can weld copper alloys such as pure copper, silicon bronze, phosphor bronze, brass and white copper.The 300WP5 and 300/500wx4 ac/dc TIG welder can be used for ac TIG welding aluminum bronze (removing oxide film on the surface with ac square wave) and dc TIG welding the above copper. 

In recent years, the use of MIG method welding copper and copper alloy construction more and more, especially for the thickness of ≥3mm aluminum bronze, silicon bronze and white copper best choose MIG welding method.The thickness of 3~14mm or >14mm of copper and copper alloy almost always to choose MIG welding, because of high deposition efficiency, melting depth, welding speed (generally 3~4 times of TIG welding), to achieve high efficiency, high quality, low cost of economic benefits.Before welding, the preheating temperature of copper should be reached (400~600℃ pure copper, 200~300℃ copper alloy), the welding wire is chemically similar to the base material, and the purity of argon gas is ≥99.98%