Copper and its alloys (brass, bronze, etc.) are widely used in various industries (especially in electrical engineering and in the manufacture of pipes) as structural materials.
Copper is widely used in industry due to the fact that it is a good conductor of heat and current.
Copper conducts electricity and heat well, resists corrosion perfectly, has high plasticity and aesthetics. Anyone who often has to work with metals should know how to make copper.
Features of copper welding
The process of working with copper products depends largely on the presence in its composition of various impurities (lead, sulfur, etc.). The smaller the percentage of such impurities will be contained in the metal, the better it will weld. When working with copper, it is necessary to consider its following features:
The characteristics of copper.
- Increased oxidability. During the heat treatment of this metal with oxygen in the near-weld zone, cracks and brittle zones occur.
- The absorption of gases in the molten state of copper leads to the formation of poor-quality weld. For example, hydrogen, combining with oxygen during the crystallization of a metal, forms water vapor, as a result of which cracks and pores occur in the heat treatment zone, reducing the reliability of the weld.
- High thermal conductivity. This property of copper leads to the fact that its welding must be carried out with the use of a high-power heating source and with a high concentration of thermal energy in the weld area. Due to the rapid heat loss, the quality of weld formation decreases and the possibility of formation of sagging, undercuts, etc. increases.
- The large coefficient of linear expansion causes significant shrinkage of the metal during solidification, as a result of which hot cracks may form.
- With increasing temperature above 190 ° C decreases the strength and ductility of copper. In other metals, with increasing temperature, a decrease in strength occurs with a simultaneous increase in ductility. At temperatures from 240 to 540 ° C, the ductility of copper reaches the lowest value, as a result of which cracks can form on its surface.
- High fluidity makes it impossible to carry out high-quality one-sided welding on weight. To do this, you must additionally use gaskets on the back side.
The effect of impurities on the weldability of copper
Impurities found in copper have different effects on its weldability and performance characteristics. Some substances can facilitate the welding process and improve the quality of the weld, and some - to reduce. For the production of various copper products, the most popular is copper sheet grades M1, M2, M3, which in a certain amount contain sulfur, lead, oxygen, etc.
The greatest negative impact on the welding process has O2: the bigger it is, the harder it will be to achieve a high-quality weld. In the copper sheets M2 and M3 allowed concentration O2 no more than 0.1%.
A small lead concentration at normal temperature does not adversely affect the characteristics of the metal. With increasing temperature, the presence of lead in the same amount causes red brittleness.
Bismuth (Bi) practically does not dissolve in the solid metal. It covers copper grains with a brittle shell, as a result of which the welding seam becomes brittle in both hot and cold conditions. Therefore, the content of bismuth should be no more than 0.003%.
The most harmful impurity after oxygen is sulfur, because it forms a sulphide, which, being at the grain boundaries, significantly reduces the performance characteristics of copper and makes it reddisk. During heat treatment of copper with a high concentration of sulfur, it enters into a chemical reaction, which leads to the appearance of sulfuric gas, which during cooling makes the seam porous.
Phosphorus is considered one of the best deoxidizers. Its content in the copper billet not only does not reduce the strength characteristics of the seam, but also improves them. Moreover, its content should not exceed 0.1%, because otherwise copper becomes brittle. This should be considered when choosing a filler material. Phosphorus also reduces the ability of copper to absorb gases and increases its fluidity, and this can increase the speed of the work to be welded.Back to table of contents
The main methods of welding copper
The main methods of welding copper.
Copper can be welded in various ways, the most popular of which are:
- gas welding;
- automatic flux;
- argon arc;
- manual welding.
Whichever method is chosen, it is necessary to properly prepare the surfaces to be welded before starting work. Before welding copper, bronze, brass and other alloys, the welded edges and filler wire must be cleaned of dirt and oxidation to a metallic luster, and then degreased. Edges are brushed with brushes for metal or sandpaper. In this case, the use of coarse sandpaper is not recommended.
Etching of edges and wire can be carried out in acid solution:
- sulfuric - 100 cm3 on 1 l of water;
- nitrogen - 75 cm3 on 1 l of water;
- salt - 1 cm3 on 1 l of water.
After the etching procedure, the blanks are washed in water and alkali and then dried with hot air. If the thickness of the workpiece is more than 1 cm, then it must first be heated with a gas flame, arc, or other method. Joints for welding are connected with tacks. The gap between the joined elements must be the same throughout the whole section.Back to table of contents
Gas welding of copper products
The scheme of gas welding copper.
With the help of copper welding by gas welding and subject to the technology of work, you can get a high-quality weld with good performance characteristics. In this case, the maximum strength of the joint will be about 22 kgf / mm2.
Due to the fact that copper has a high thermal conductivity, for its welding it is necessary to use the following gas flow rate:
- 150 l / h with a thickness of not more than 10 mm;
- 200 l / h with a thickness of more than 10 mm.
To reduce the formation of copper oxide and to protect the product from the occurrence of hot cracks, welding should be carried out as quickly as possible and without interruptions. As an additive, wire made of electrical copper or copper with a silicon content (not more than 0.3%) and phosphorus (not more than 0.2%) is used. The diameter of the wire should be about 0.6 thickness of the sheets to be welded. The maximum allowable diameter is 8 mm.
When welding is carried out, it is necessary to distribute heat so that the filler material melts a little earlier than the workpiece.
Fluxes are used to deoxidize the metal and clean it from slag, which are introduced into the weld pool. They also process the ends of the wire and the edges of the plates to be welded on both sides. To grind the grains of the weld metal and increase the strength of the seam after the work is completed, it is forged. If the thickness of the workpiece is not more than 5 mm, the forging is carried out in a cold state, and at a thickness of more than 5 mm - at a temperature of about 250 ° C. After forging, the seams are annealed at a temperature of 520-540 ° C with rapid cooling with water.Back to table of contents
Automatic submerged arc welding
Automatic submerged arc welding scheme.
This welding method is performed by a conventional welding machine at a direct current of reverse polarity. If ceramic flux is used, then you can work on alternating current. To weld copper no more than 1 cm thick, ordinary fluxes can be used. If the thickness is more than 1 cm, then dry granulation fluxes should be used.
In most cases, all the work is done in 1 pass, using copper wire. If the seam should not have high thermophysical indicators, then to increase its strength, the connection of bronze and copper is carried out with bronze electrodes. In order for the molten metal not to spread and a seam on the reverse side of the workpiece is formed, flux pillows and graphite linings are used.
Welding of brass is carried out under low voltage, because the probability of zinc evaporation will decrease with decreasing arc force. Bronze welding is performed by direct current of reverse polarity. The height of the flux is limited or the flux of large granulation is limited (up to 3 mm).Back to table of contents
Argon arc welding of copper
Schematic diagram of argon arc welding.
Argon arc welding is widely used for the manufacture of copper structures of varying complexity. To obtain a reliable compound, top grade argon or its mixture with helium is used as a protective gas. In everyday life, such welding is performed with tungsten electrodes. In the role of the additive is usually wire, laid butt.
Argon arc welding with a tungsten electrode is carried out at a constant current of reverse polarity. The electrode must be oriented strictly in the joint cavity. If the workpiece has a thickness of more than 5 mm, then it is preheated to 320-420 ° C. Copper thinner can be cooked without preheating. Some modes of argon-arc welding are shown in the table.
|The thickness of the workpiece, mm||Electrode diameter, mm||Welding current, A||Arc voltage, V||Gas consumption, l / min|
Manual welding of copper products
Manual welding scheme.
This process is performed on a direct current of reverse polarity. Blanks with a thickness of no more than 4 mm can be welded without cutting edges, up to 1 cm - with cutting on one side. With greater thickness, experts recommend using an X-shaped cutting.
Electrodes of the types MM3-2, Central Bank-1, MN-4, etc. are used for welding bronze and brass. Electrodes with a coating “Komsomolets-100” are of great popularity. The thermal conductivity of the weld when welding with coated electrodes is significantly reduced. When using such a wire, a part of the alloying components penetrates into the seam, which reduces its electrical conductivity several times.
Manual arc welding of brass is used quite rarely. This is due to intense evaporation in the process of zinc. When welding brass billet preheated. The welding of bronze with coated electrodes is carried out with direct current of reverse polarity with or without heating. It uses currents from 160 to 280 A.