Aluminum is very widely used in the construction and installation of various devices. Often there is a need to connect aluminum products. This issue can be solved only after it has been decided how aluminum can be boiled.
The scheme of spot welding of aluminum.
Due to the presence of an oxide film, before cooking aluminum, a special surface treatment is required at the welding site. Preliminary cleaning of the aluminum surface from oxide is necessary for any method. The full cleaning cycle includes several steps. At first, the edges of the product being welded are cleaned of dirt and slightly rounded at the top.
At the second stage of preparation should be processed with a solvent. As solvents, it is better to use alkaline solutions or organic solvents. White spirit, technical acetone, solvents PC-1 or PC-2 are suitable for cleaning aluminum alloys. The alkaline composition is recommended in the form of the following mixture: 50 g of trisodium phosphate, 50 g of soda ash, 30 g of liquid glass per 1 l of water. This composition is preferably heated to 60 °.
The third stage consists in machining the surface with a metal brush. The brush can be made of steel wire with a diameter of 0.1 mm. After machining the surface, it is advisable to process the solvent again. The welding process should be started no later than 3 hours after processing, otherwise the film is formed again.Back to table of contents
The principle of operation of electric arc welding.
Welding of metals using an electric arc with consumable electrodes using inverters is one of the most common types of living conditions. Aluminum should be welded in this way when certain conditions are met. Work begins after a thorough preparation of the surface of the material. Welding itself is carried out by a direct current of reverse polarity.
For aluminum welding it is necessary to use special electrodes such as OZA, OZA-1, OZR, OZR-2, OZANA, OZANA-1. Before cooking the metal, it is recommended to dry the electrodes, keeping two hours at a temperature of 200 °. Electrodes have a low melting point and do not require a large welding current. The current maintained in the arc zone is calculated from the condition of 25-30 A per 1 mm of the diameter of the electrode. During work, the transverse movement of the electrode should be minimized.
To improve the quality of the weld, aluminum should be heated to 400 ° before welding. If it is necessary to weld large parts, then only the welding zone is heated. After completion of the welding process, slow cooling is performed, which reduces the risk of microcracks in the weld.
At present, new Al-350n electrodes, which are specifically designed to weld aluminum, are on sale. The diameter of the electrodes 3.2 mm. When welding aluminum with a thickness of up to 3 mm, the welding current is selected in the range of 70-110 A, and with a thickness of 4-5 mm - up to 160 A. The arc length is shortened.
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It is recommended to provide a gap between the electrode and the welded surface within 1-3 mm.
Features of the use of carbon electrodes
The scheme of the carbon electrode for welding.
Electric arc welding using carbon (or graphite) electrodes is usually used for welding local damage (scrap, crack, etc.) or for connecting narrow products, such as an electrical bus. Special carbon electrode is used in conjunction with the filler material. The additive is a rod or wire on which the flux is applied. Aluminum should be welded with such electrodes on direct current of direct polarity.
Another specific type of electrode for aluminum welding is coated metal electrodes. They are a welding wire coated with a layer of a mixture of fluoride and chloride salts.Back to table of contents
Electric arc welding in inert environment
Aluminum welding by electric arc method does not always ensure a high-quality weld due to enhanced oxidation of the heated welding zone. Electric arc welding in an inert environment somewhat complicates the process, but it allows to improve the quality and reliability. High purity argon is used as an inert medium; therefore, such welding is often called argon arc welding. Sometimes a mixture of argon and helium is used. With this method, the electrode is in a special burner, from the nozzle of which argon is fed.
Argon arc welding can be performed using both consumable and non-consumable electrodes. In the first case, the process differs from conventional electric arc welding only in the presence of an inert environment. Non-consumable tungsten electrodes are more commonly used. In the process of work involved filler wire, which plays the role of consumable metal. If it is necessary to boil aluminum, then filler wire of the type HELL, AO, AK with a diameter of 2-5 mm is used. When welding aluminum alloys, aluminum-magnesium additives are used, and the magnesium content in the additive should exceed its presence in the alloy being welded.Back to table of contents
The scheme of gas welding aluminum.
The low melting point of aluminum allows gas welding to be used successfully. In this case, welding is performed by melting the base metal and additive in the open gas flame of the burner. The flame in the burner is maintained by a constant supply of combustible gas mixed with oxygen. By adjusting the size of the flame, it is possible to ensure a smooth and slow heating of the metal, which is important for aluminum. Gas welding is less speed welding than other types, but it can provide good quality if you need to weld aluminum.
A filler rod or wire is used as a consumable material for gas welding. For the manufacture of additives used pure aluminum or silumin with a low content of silicon. When the silicon content is within 4-6%, the necessary shrinkage and good melt flow are ensured. When welding aluminum alloys with magnesium for the additive used a similar material, but the magnesium content in it should not exceed 6%. When welding duralumin an additive is used in the form of rods from duralumin or silumin. The diameter of the filler rod is selected taking into account the thickness of the metal being welded: when the thickness of aluminum is up to 3 mm, the diameter of the bar is chosen 2-3 mm, at a thickness of 3-5 mm - 3-4 mm, up to 7 mm - 4-4.5 mm.
To protect against oxidation, which is especially important in view of the receipt of heated oxygen in the welded zone, flux is used. When welding aluminum and its alloys, flux based on fluoride or lithium chloride has proven itself well.
In the composition of high-quality fluxes, the content of these salts is 15-30%. After completion of the work, the flux residues must be removed, since it can lead to the destruction of the weld.Back to table of contents
The equipment used in aluminum welding is determined by the type of welding selected. Each of them is characterized by its own sets of equipment. Electric arc welding is carried out with the use of inverters, providing the supply of direct current. For argon arc welding, you can use a welding transformer that provides alternating current. For gas welding, special kits are used, including an acetylene generator. Gas (oxygen, argon, helium) is stored in special cylinders.
Scheme of the electric welding apparatus.
When welding it is impossible to do without the following tool:
- emery wheel;
- emery sandpaper;
- metal brush;
Aluminum can be welded using different methods. The choice of method depends on the qualifications of the person making the welding, the availability of equipment, the size and type of aluminum products, the requirements for quality of welding.
In general, if it is decided to boil aluminum, a number of specific features should be taken into account; but the process may well be carried out in domestic conditions.