Features welding of various materials

Welding of mild steels
Good welded low carbon steel containing up to 0.25% carbon. Such compounds can be easily processed with cutting tools. To avoid overheating and the formation of hardening structures, using multi-layer welding with a long interval of time between the overlapping layers. Metal arc welding of 2 mm thickness are usually DC reverse polarity. Product thickness of 15 mm is subjected to heat treatment after welding. Welding thick metal "cascade" or "slide" with slowing the rate of cooling of metal and heat affected zone prevents the formation of hardening structures. Defective parts were welded seams are usually normal section of not less than 100 mm, or pre-heated to a temperature of 150 - 200 ° C.

Welding of carbon steels
Welding of steels is often fraught with the formation of cracks in the ground and in the weld metal. To get a quality connection, the following ratio between the diameter of the electrode and the welding current:
Electrode diameter, 2.53 mm
Current, A40-60 50-7580-100
Diameter electrodes, mm 4,5,6
Welding current, A 130-150170-200200-280

Welding of sheet steel
When the thickness of the base metal of 2 mm use manual metal arc welding often causes the formation of burn-through. To avoid this, you must follow these guidelines:
- Welding seams apply electrodes of small diameter (1.6-2 mm);
- Current should be minimal - 50-70 A;
- To sustain the arc to connect the oscillator;
- To prevent burn-through educational use flanging edge welded sheets.
Welding sheets having different thickness, recommended by a smooth transition from a thick metal to thin, using an oscillator.

Welding of non-ferrous metals
Copper welding is complicated by the presence of impurities present in its composition, high thermal conductivity, and the ability to strongly oxidized in the molten state. In addition, the copper absorbs hydrogen in the molten state. Inside a work area bubbles form water, which are the cause of a large number of microcracks. This phenomenon is called hydrogen disease copper. Prevents disease reduced the amount of hydrogen in the weld zone by baking electrodes and fluxes, and the use of protective gas.
Products used for malootvetstvennyh MMA carbon electrode. Carbon electrodes are used with a thickness up to 15 mm copper. Graphite electrodes are used for thick piece. Welding electrodes is, sharpened to a cone is 1/3 of its length, DC straight polarity of the current density at the electrode of 200-400 A / cm. Recommended that a long-arc welding and filler metal immersed in the bath and kept at 30 ° to the product at a distance of 6 mm from the work piece. The electrode is better kept at 75-90 ° to the work piece. Produced during welding carbon dioxide is insufficient protection of the metal from oxidation.
As protection has worked well with the filler material deoxidising - phosphorus, or flux, consisting of 94% of calcined borax and 4-6% magnesium metal. The surface of the rod moistened with liquid glass, then applied flux in the form of powder and dried.
If the thickness of the workpiece than 5 mm, the cutting angle on the edges should be 70-90 °. When welding, use graphite or asbestos lining. The gap between the edges should be 0.5 mm, the electrode should be held at an angle of 10-20 ° to the vertical. If the thickness of the compound is about 5 mm, stamping his unheated, with very thick use heating to 800 ° C and subsequent rapid cooling. To avoid the loss of mechanical properties of butt welds are in the same layer on one side.
If you prefer manual welding with coated electrodes, it leads to a direct current reverse polarity short arc without transverse vibrations. For the best in welding recommended reciprocating electrodes. If you lengthen the arc, it will cause an increase in spraying and influence the formation of the joint. The mechanical properties of the compounds of this decline.
When the thickness of the copper pieces to 4 mm welding is carried out without the section edges and heating. For metal thickness greater than 5 mm are required pre-heating to a temperature 250-300 ° C and one-sided cutting edge with an angle of 60-70 °, followed by toning them up to 1.5-3 mm. X-shaped cutting is recommended for thick. When welding copper electrodes often use "Komsomolets-100", the most widespread, which is used as the pivot of copper wire M1 and M copper electrodes with a diameter of 3 mm is rarely used, since they have low mechanical strength.
High-performance electrodes of ASC-1 and ASC-2 provide welding unheated blanks with a thickness up to 15 mm. If you use a small heating (250-400 ° C), these electrodes can be used for welding of thick copper products. Different types of brass vary the welding, so the technology of welding bronze quite different. The chemical composition of the weld metal should be similar to the composition of the filler. Welding is carried out by direct current reverse polarity, short lengths of moving.
Brass is used in welding electrodes brand ST. The melting point of brass - 800-1000 ° C. Welding is the DC reverse polarity, short arc. Seam-welded exposed peening and annealed at 600-660 ° C: it is necessary to align the chemical composition of the weld and make fine-grained structure.
Due to its high corrosion resistance, heat resistance, and heat resistance of nickel and its alloys are important structural materials that are used in different industries.
Nickel and alloys can be welded by arc, gas and other types of welding. If the thickness of the workpiece is less than 5 mm, the welding is carried out without cutting edges. With a thickness of 6 to 12 m is used v-shaped groove, and with a thickness greater than 12 mm - s-shaped, with an opening angle of 60-70 ° and dulling 2-4 mm, depending on the thickness of the base metal.
Clearances for welding should not exceed 1-1.5 mm. Edges before welding cleaned to bright metal and degreased with acetone or aviation gasoline.
Since nickel and its alloys have high electrical resistance, welding wire radius should be reduced by 1.5-2 times compared with the departure of the electrode when welding. The main difficulties in welding of nickel and its alloys - the tendency to the formation of pores and cracks of crystallization. This is due to the transition metal from a solid to a liquid state, which resulted in the formation of insoluble products in the formation of pores in the weld metal. Welding technique should provide protection for the fusion of air and good deoxidation cooking bath.
One effective measure is the short arc welding (up to 1.5 mm), which sharply reduced suction gas from the atmosphere. To prevent the formation of pores on the fusion line, you need to be preheated before welding metal to a temperature of 250-300 ° C, followed by air cooling.
Sheet thickness of more than 1.5 mm the basic coated electrode DC reverse polarity. In order to reduce stress in the weld and prevent overheating of the electrode, use a lower current (compared with a current used for welding of steel).
Welding is in the lower position, the transverse vibrations of the electrode should not exceed three times the diameter of the electrode. When accidental breaking arc turns her on stripped from the slag seam, stepping back from the crater of 5-6 mm. Welding is done in one pass. For thick welded edges are multipass welding after cooling connections and a thorough cleaning of the previous layer of slag and spatter.
If you prefer semi-automatic welding, its lead consumable electrode gas-shielded DC reverse polarity. As a protective environment is argon and helium. Improves the quality of welds introduction to argon and 20% hydrogen. Standard semi-automatic welding lead to the burner, which is tilted forward at an angle of 10-15 ° from the vertical. In order to weld not form pores, recommended welding wire, alloy 3% titanium or additives of rare earth elements.
Warn burnout and promote formation as backing flux pads or copper mold lining. Welding starts and ends on a technological standard with groove and a thickness equal to the thickness of the base metal.
Low thermal conductivity and low melting point of lead require low heat input welding. Welding of lead can be in any position, but the product is tilted over 10-15 ° metal is leaking out of the tub, which affects the formation of welds. Acceptable is the lowest position for which you need to focus and lead welding products.
Since lead has a higher density and it is probable failures bath recommended sliding plate-forming rings. Edge products before welding wipe gasoline or carbon tetrachloride, and cleaned to bright metal scraper on the width of 20-25 mm.
Workpiece thickness of 2 mm welded flanged edges of a height equal to the thickness of the base metal, with a thickness of 8 mm lead - without cutting edges, with greater thickness is beveled edges with a total opening angle 60-70 ° with no gap in the joint and blunting 03.04 mm. Sometimes perform two-way edge preparation. Welding lead held carbon electrode in inert gases - consumable and non-consumable electrodes, and oxyacetylene welding. Welding of carbon electrodes runs on DC straight polarity.
During welding, the electrodes are perpendicular or inclined at 10-15 ° from the vertical in the direction of movement of welding.

Welding of aluminum and its alloys
Pure aluminum is of limited use because of their low strength and high ductility. In daily life are used aluminum alloys - duralumin and silumin. When welding aluminum on the surface of the molten metal is formed refractory film of aluminum oxide, which hinders the process of fusing with each other metal particles. The difference between the melting point of aluminum oxide (2050 ° C) and the melting point of aluminum (658 ° C) creates technical difficulties during welding.
Regardless of the method of welding products must undergo special training. Degrease the surface and remove them from the film of aluminum oxide. Similarly prepare the filler wire and electrode rods before applying the coating on them.
Degreasing is carried out using solvents such as aviation fuel or technical acetone. The next stage - mechanical cleaning or chemical etching, which removes the oxide film. Degreasing and etching spend no more than 2-4 hours before welding.
For non-critical products used carbon electrode manual welding with direct current straight polarity. If the metal has a thickness of 2 mm, the welding are no additives and no cutting edge, with metal thicknesses over 2 mm welding is done with a gap equal to the thickness of the welded sheets 0.5-0.7 or groove. Manual welding with coated electrodes perform in the production of technical designs of aluminum alloys and AMts AMg and silumin. At moderate currents required penetration is provided by using direct current straight polarity with preheating (for medium thickness - 250-300 ° C, for large thicknesses - up to 400 ° C). Aluminum welding speed should be higher than the rate of welding steel. It is a continuous process within the same electrode due to the fact that the film of slag on the crater at the end of the electrode prevents re-ignition of the arc.
Welding current is taken to a maximum of 60 A for 1 mm diameter electrode - this will ensure the sustainability of the process and the minimum loss splash. Electrodes previously dried at a temperature of 150-200 ° C for 2 hours
In manual TIG welding with non-consumable tungsten electrode is used in dry moisture argon premium on AC. If the thickness of the weld metal is 5.6 mm, then the diameter of 1.5-5 mm electrodes.
Welding technique here has its own characteristics. Between the electrode and filler wire must be maintained at an angle of about 85-90 °. When applying additives used reciprocating. Effective protection is achieved by optimum gas consumption. Metal thickness up to 10 mm are welded right: This technique reduces overheating the base metal.

Welding of pipelines
The main way of rotating joint welding of pipelines or individual tubes in a continuous hand welding electrodes. The advantage of this fusion are easy to work and the ability to use it in different environments.
Welded pipes, which are used during installation process, and the main production lines, have an outer diameter of 4-1620 mm wall thickness 0,3-25 mm. Welded pipes produced with direct longitudinal or spiral weld.
Rolled pipe is made of mild open-hearth steel with a tensile strength of 350-550 MPa. Industry produces pipe outside diameter 114-426 mm and a wall thickness of 4,5-20 mm.
The main pipelines of oil refineries and pipelines for transportation of liquid and aggressive media assembled from rolled pipe, made of heat-resistant alloy and stainless steels.
Aluminum tubes are designed for long-distance pipelines and pipelines refineries that are in environments that cause corrosion. Assortment for these pipes are provided outer diameter 120-280 mm and a wall thickness of 10-30 mm. To build the trunk and factory production lines are special fittings. They are used to the angles of rotation, the branch sites, etc. These parts are triangles, Specifications, doubles, tees, reducers, made of 20 steel by pulling or pressing. Applied and welded fittings. , Specifications squares produced with 48-529 mm outer diameter with a wall thickness 4.5-12 mm and the average radius of 80-500 mm. Welded bends often made of several parts (Fig. 119).

Типы сварных отводов

Fig. 119. Types of welded bends.
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