Gas welding refers to a group of fusion welding methods. To carry out the welding process may use different fuels, respectively, which can distinguish between hydrogen-oxygen welding, gasoline-oxygen, etc. The overwhelming importance Oxyacetylene welding; other; fuels are of limited use. The significant difference of technological gas welding of welding - more, smooth and slow heating of the metal. This is the main difference between the gas flame from the welding arc is in some cases, the defect in the other - the advantage of a gas flame and identifies the following key areas of its application for welding: 1) steel of small thickness, 0.2-5 mm 2) non-ferrous metals, 3 ) metals that require welding mild gradual heating and slow cooling, such as many tool steels, and 4) metals that require heating during welding, such as iron and some grades of specialty steels, 5) for brazing, 6) for certain types of surfacing works.
Thanks versatility, relative simplicity and portability of equipment gas welding is very suitable for many types of repairs. Relatively slow heating of the metal gas flame rapidly reduces gas welding performance with increasing thickness of the metal and steel at a thickness of 8-10 mm above the gas welding is usually economically unprofitable, although technically still possible welding of steel thickness of 30-40 mm. During slow heating heats a large volume of the base metal adjacent to the weld pool, which, in turn, causes significant deformation (warping) of welded products. This important fact makes gas welding is technically impractical, not to mention I have about the economic disadvantages for such objects as building steel structures, bridges, railroad cars, ship hulls, large frame machines, etc. Slow heating also causes prolonged exposure to the metal zone of high temperatures, which leads to overheating, consolidation of grain a slight decrease of the mechanical properties of metals. Significant deformation of the metal, resulting in a gas cooking, limit the choices of rational forms of welded joints. Of the various forms of welds performed by arc welding, gas welding if used, usually only a simple butt joint. Fillet welds and joints and lap-fillet welding is used for the gas only when necessary because of the difficulties posed by significant deformation of the metal, characteristic of gas welding. They are used as the butt joints without the bevel edge, with no flare and flare edges (very convenient connection for gas welding), and with one-and two-sided bevel edges.
Burner is usually regulated to operate on a normal flame. The thermal effects of fire on the metal depends not only on the power of the flame, but also on the angle of inclination of the axis of the flame to the metal surface. The most intense flame effect, when its axis normal to the surface of the metal. With decreasing angle of inclination of the thermal effect of the flame is reduced and distributed over a larger area. Thus, besides the selection of the appropriate size burner, the welder can smoothly adjust the thermal effect of the flame to the metal, making the flames more than a soft or hard, changing the angle of the flame to the surface of the product. With increasing thickness of the metal taken to increase the angle of fire and reduce it to a decrease in the thickness of the metal.
Gas welding can be carried out in the bottom, vertical and overhead positions. Filler rods for gas welding of different composition are used, respectively, the nature of the base metal. The wire diameter is selected according to the thickness of the base metal.
Filler wires for gas welding of steels used is the same as for the electrodes in arc welding, and is manufactured according to GOST 2246-80. For gas welding low carbon steel wire used stamps Sv-08 Sv-Sv-08A and 15G. For welding of cast iron produced a special cast iron sterezhenki with a high content of carbon and silicon. For the deposition of hard wear-resistant coatings are manufactured of cast tungsten carbide rods.
Protection for gas welding
electrode coatings exchange used in arc welding, gas welding fluxes used quite widely, the use of which is necessary for the gas welding of cast iron, nonferrous metals and some special steels. Fluxes are added to the bath to dissolve the oxides and the formation of low-melting slag, good pop on the surface of the bath. Fluxes can be introduced into reductants and additives, alloying the weld metal. Fluxes are used in the form of powders and pastes, applied to the base metal or filler rod. Effect of fluxes on the chemical oxide can be physical and I, but often between them is difficult to draw a clear boundary.
Chemical fluxing action is the formation of metal oxides with a low-melting compounds are stable at high temperatures. For chemical fluxing metal oxides of basic character, such as ferrous oxide FeO, oxides in fluxes introduced acidic, such as silicon dioxide SiO2 (quartz sand, pounded glass window) and boric anhydride B2O3 (borax, boric acid). For fluxing acidic oxides such as silicon dioxide, SiO2, used compounds that provide the basic oxides. For this purpose, commonly used baking soda and potash Na2CO3 K2CO3, yielding, respectively, in the main zone of welding oxides Na2O and K2O. For flux-solvent used mainly halide salts of alkali and alkaline earth metals, NaCl, KC1, LiCl, CaCl2, NaF, KF, CaF2 and others ., as well as phosphate and carbonate salts of sodium. To enhance the flux of the solvent, they often add sodium bisulfate or potassium NaHSO4 and KHSO4.
The use of gas welding is extensive and varied. Gas welding is used in aircraft, where the predominant metal welding of small thickness (1-3 mm) in the manufacture of chemical equipment. It is important to forge welding in pipe laying and installation of a variety of purposes, particularly small-diameter, 100 mm. Gas welding is an indispensable powerful tool to repair and to this end is widely used in the repair shop for all modes of transport, agriculture, etc.
The quality of welded joints, gas welding performed higher than when the electrodes with a thin arc of coated ionizing, but a few inferior arc welding, electrodes made with quality. The main reason for a reduction of strength of welded joints is that when gas welding is not made of weld metal alloying, whereas in arc welding of high-quality electrodes containing coating alloys, produced a rather large doping. Thus, the gas protection afforded by reducing the welding zone of the flame to get a quality weld is less effective than the qualitative effect of electrode coatings in arc welding.
Gas welding performance, significant at small thickness of the base metal, rapidly decreases with increasing thickness. For small thicknesses (0.5-1.5 mm), gas welding performance can exceed the arc. With the increase of metal thickness to 2-3 mm in the rate of gas and arc welding are equalized, then the difference in speed increases rapidly with increasing thickness of the metal in favor of welding. For small thicknesses, the absolute consumption of gas per 1 m of the weld is small, the total cost of 1 m of the weld may be less than with other welding methods. With increasing thickness of the base metal is rapidly growing cost of gas and time spent on the weld seam 1 meter and gas welding arc becomes more expensive, the difference in cost increases rapidly with increasing thickness of the base metal. Thus, cost-gas welding is most appropriate for the welding of small metal thicknesses.
See also:
Gas Welding Technology
Gas Welding Article
Welding Torches
Universal welding torch GS
Technical Oxygen
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