Welding welding and metal cutting
Topic. Welding and cutting of metals. Class 1
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Section II METALS WELDING.
Advantages and disadvantages of welded joints. Types of welds and joints
Gas welding of metals, equipment, materials used for gas welding, welding technology
Electric arc welding, its types, welding technology, equipment
General concepts and types of welding
Welding of metals is widely used in the national economy of our country. Electric welding is the most widespread type of metal welding. The beginning of its development should be considered as the discovery of electric arc by the great Russian physicist and the first Russian electrical engineer, academician V.G. Smirnoff. В. Petrov in 1802. He was the first to give instructions on the use of electric arc for electric lighting and melting of metals.
The great merit in the invention of electric welding of metals belongs to talented Russian inventors N.N. Krylov. Н. Benardos and N. Г. Slavyanov (in 1882) used welding with a metal electrode. Benardos proposed the use of an electric arc for welding with a carbon electrode, and in 1888 the. Slavyanov used welding with a metallic electrode). They were the first in the world who invented welding machines and automatic machines, developed the main principles of automatic welding under a layer of flux.
Nowadays, welding has almost completely superseded riveting, and in some cases, welded construction has replaced casting and forged assemblies.
The advantages of welding is that its use saves metal, time and labor, as well as reduces the cost of component assemblies. Welded structures due to the elimination of additional connecting elements have less weight compared to riveted ones, and when welded structures are replaced by cast structures, the saving in weight reaches 50%. In addition, replacing riveting by welding eliminates a number of operations: marking holes, riveting, etc. д. Welding only requires deburring of seams.
Welding is the process of permanently joining metals by heating them locally to a melting state or to a plastic state.
In fusion welding, the metal on the edges of the parts to be welded melts, mixes with the molten metal of the electrode rod and, as it cools, forms a welded joint.
In plastic welding, the metal of the surfaces to be joined is heated only to a softened, plastic state. To form a welded joint, a mechanical force must be applied, causing plastic deformation in the parts to be joined.
According to the type of energy used to heat the metal welding is divided into chemical and electrical. During chemical welding, heating of the welded parts is due to the energy of chemical reactions. Chemical welding is subdivided into flame, gas and termite welding.
In gas welding, metal is heated by a flame of burning gas. In termite welding heat for heating parts is produced by burning of thermite, which is a mechanical mixture of metal aluminum powder and iron scale. At thermite welding the temperature reaches 3000 ° C.
Electrical welding is divided into electric arc and contact welding. In electric arc welding, heating of the metal is due to combustion of the electric arc, and in resistance welding. at the expense of the passing current.
Advantages and disadvantages of welded joints. Types of welded joints and seams
Advantages and disadvantages of welded joints
Types of welded joints in comparison with riveted joints
1) The simplicity of the weld design and lower labor intensity;
3) possibility of joining parts of any shape;
5) low-noise technological process;
6) comparatively easy possibility of automating the process;
7) in general, welded connection is cheaper than riveted one.
1) the occurrence of residual stresses in the welded elements;
3) insufficient reliability under significant vibration and shock loads.
The following joints are used at welding: butt joints (fig. 1.1), overlap, T-joints and side or corner joints. When welding butt weld depending on the thickness of the metal to be welded it is subjected to cutting to ensure complete melting of the edges of welded products. Cutting the edges of small thickness metal is not required, and the edges are joined with a small gap (Fig. 1.2). If the thickness of metal is large (6-80mm) electric arc welding is carried out with V.fig. 1.2) or X-shaped cutting of edges with a gap between the welded items of 2-4 mm to improve penetration and blunting of 2-4 mm to prevent penetration of sheets. X-shaped cut is used to reduce metal deformation, which is achieved by a more uniform heating of metal due to the symmetrical weld, as well as to save electrodes.
Fig. 1.2. Methods of edge preparation for welding
Seams are subdivided in accordance with their position (fig. 1.3) on the bottom, horizontal. vertical and overhead.
Seams can be formed according to the form of cross-section (fig. 1.4, а ) normal 1. loosened 2 and reinforced 3.
Depending on the position of the weld in relation to the acting force, the welds are subdivided into overhead welding (vertical, vertical and overhead) and bevel welding (vertical and overhead) 1. flank joints 2 and oblique 3 (fig. 1.4, б ).
Fig. 1.4. Joint profiles ( а ) and design welds ( б )
Gas welding of metals, equipment, materials used for gas welding, welding technology
Gas welding is a process of obtaining permanent connection by melting the edges of the welded metal with combustible gas in a stream of oxygen. Gas welding is widely used in the manufacture of thin-walled structures, as well as for repair of machinery.
Welding and metal cutting
Welding. The process of obtaining a permanent connection with or without local heating, using the forces of molecular adhesion. The use of welding saves metal (it is much more economical than riveting, casting). Welding is widely used in industry and construction. It is used to manufacture metal structures, reinforcing frames, metal tanks, bridge trusses, and other products.
In welding, a distinction is made between the following types of joints: butt, overlapping, angular, T-shaped (Fig. 12.12).
Depending on how the metal is joined at the time of welding, there are two main types of welding:
Fig. 12.12. Types of welded joints: а. butt welds; б. overlap welding; в. Angles; г. T-beams
- ? pressure welding, When the metal is brought to a plastic state and squeezed;
- ? fusion welding, where the metal is heated above the melting point and then welded without mechanical action.
High local heating during welding causes a significant change in the structure of the metal. The smaller the heat-affected zone around the weld, the higher the properties of the weld.
Depending on the source of heating, a distinction is made between electrical and chemical welding.
Electric welding. This welding is based on the use of heat generated by the passage of electric current. Electrical welding is subdivided into:
- ? resistance welding (or contact welding), in which the electric current emits heat at the expense of ohmic resistance (in the contacts of the welded parts);
- ? electric arc, based on using the heat generated by the electric arc in welding.
In resistance welding Electrical current is applied to the two products to be welded. When they are in contact, heat is released, which softens the metal, and under load they are welded. Three kinds of contact welding are used: spot, roller and butt welding.
Spot welding used for overlap welding of grids and frames. The total thickness of items welded in this way shall not exceed 20 mm.
Roller welding is used for joining sheet metal.
Butt welding is used to join metal rods of reinforcing bars.
The practical use of the electric arc to weld metals was carried out by Russian engineers H.Н. Benardos and H.Г. Slav.
By Benardos method (Fig. 12.13, а) electric arc is excited in the atmosphere between the carbon electrode and the weld-
Fig. 12.13. Diagram of arc electric welding: а. mode H.Н. Benardosa; б. mode H.Г. Slavyanov; 1. holder; 2. electrode; 3. the electric arc; 4. additive material; 5. part to be welded; 6. plate; 7. flexible wire
piece. This method uses direct current. the positive pole is connected to the workpiece to be welded, the negative pole to the carbon electrode. The filler material is introduced into the workpiece separately. This method of welding is widely used in welding of non-ferrous metals.
Slavianov’s method(Fig. 12.13, б). the main type of welding, used to connect the elements of metal building structures. When the product and the metal electrode come into contact, an electric arc arises between them with a temperature of over 5000 °С. At this temperature, the electrode metal is converted into a fine droplet liquid state and transferred to the workpiece to be welded. The metal of the product is also melted to a certain depth, which is called depth of penetration, forming a homogeneous alloy with the weld metal, resulting in a high strength joint.
Despite its great popularity, electric arc welding has a number of significant drawbacks:
- ? low welding speed due to the large heating zone of the metal, which causes warping of the product;
- ? porosity of the weld and burnout of alloying components during oxidative processes;
- ? the difficulty of welding metals with different physical and mechanical properties.
To eliminate the disadvantages noted in recent years, chemical welding in a shielding gas or submerged arc is used.
Chemical welding. This welding is made at the expense of the heat of chemical reactions and is divided into gas и termite.
At gas welding the heat source is a product of combustion of a mixture of oxygen and combustible gas or liquid propellant. Currently the following flammable gases are used: acetylene, hydrogen, oil-gas, natural gas, as well as gasoline, benzene and kerosene vapors, etc.
Acetylene-oxygen welding is the most economical and efficient. Acetylene С2Н2 is a colorless gas with a density of 906 kg/m 3. which is obtained by the action of water on calcium carbide CaC2 2H20. Ca(OH)2.
At pressure of 17,5 MPa and above acetylene is explosive.
The complete combustion of acetylene in oxygen creates a flame with a temperature of about 3200 ° C.
Special welding heads are used for welding, in which acetylene is mixed with oxygen (Fig. 12.14) and burns at the outlet of the torch. The welding process is carried out by surfacing the filler metal on the heated acetylene-oxygen flame of the seam.
The filler material for gas welding is a steel wire of diameter 2. 8 mm with a carbon content of 0.15 to 1.5%, depending on the composition of the weld metal. To reduce the degree of oxidation of the weld during welding fluxes are used (borax and boric acid).
Rice. 12.14. Scheme of gas welding:
1. filler material; 2. The material to be welded; 3. clad metal; 4. burner housing; 5,7. Acetylene and oxygen hoses; 6. oxygen cylinder; 8. acetylene
Welding welding and metal cutting
The essence and types of manual arc welding, basic physical and chemical processes occurring in the arc zone and welded metal are considered. Provides information on welding materials, modern equipment, and shows the peculiarities of welding technology of various metals and alloys. Examines possible defects in welded joints, how to prevent, control, and eliminate them. Safety information is given. May be used in vocational training of production workers.
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Chapter 1. Fundamentals of welding theory. § 1. Metal welding classification. § 2. Basic types of welded joints. § 3. Chemical and physical processes in welding § 17. § 4. Welding stresses and strains. § 5. Ways of reducing welding stresses and strains. § 6. Weldability of metals and alloys.
Chapter 2. Welding consumables. § 7. Welding wire. § 8. Electrode classification. § 9. Calculation of electrode consumption
Chapter 3. Power sources for arc welding. § 10. Welding arc. § 11. Requirements for welding arc power sources and their classification. § 12. AC power supplies. § 13. DC power sources. § 14. Specialized welding arc power sources and installations.
Chapter 4. Welding station auxiliary equipment.
Chapter 5. Manual arc welding procedure. § 15. § 12 Welding preparation. § 16. Fusion techniques. § 17. Bottom position welding techniques. § 18. Welding technique on the horizontal and ceiling planes. § 19. Selecting welding current and electrode diameter.
Chapter 6. Special methods of manual arc welding. § 20. High productivity manual welding methods. § 21. Submerged-arc welding.
Chapter 7. Welding carbon and alloyed steels. § 22. Welding of low-carbon and low-alloy steels. § 23. Welding of carbon steels. § 24. Welding of high-alloy steels.
Chapter 8. Welding of cast iron, non-ferrous metals and their alloys. § 25. Cast Iron Welding. § 26. Welding aluminum and its alloys. § 27. Welding copper and its alloys. § 28. Welding of titanium and its alloys. § 29. Welding of nickel and its alloys.
Chapter 9. Welding technology of hard alloys. § 30. The essence of the surfacing process. § 31. Ways of surfacing. § 32. Features of surfacing technique. § 33. Selecting the chemical composition of the weld metal.
Chapter 10. Welding of Basic Structures. § 34. Requirements for welded joints. § 35. Classification of welded structures. § 36. Peculiarities of Welding of Some Structures. § 37. Welding technology of main gas pipelines.
Chapter 11. Welding at Low Temperatures.
Chapter 13. Defects and quality control of welded joints. § 38. Defects of welded joints. § 39. Weld inspection. § 40. Inspection of welded product.
Chapter 14.The rationing of work in manual arc welding. Chapter 15. Safety measures at the plant.
Welding Welding and Metal Cutting
In the textbook are given basics of technology of arc, electroslag, contact and gas welding, oxygen and electric arc cutting; features of welding technology of alloyed steels, non-ferrous metals and their alloys, cast iron, plastics, as well as methods and modes of pipeline welding. The 4th edition contains changes concerning equipment and materials, the description of contact welding machines has been extended; a chapter on “surfacing work” has been introduced.
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Section 1. Electrical Fusion Welding and Arc Cutting.
Chapter 1. Classification and essence of arc welding.
Chapter 2. Electric welding arc. § 1. Basic concepts. § 2. Thermal properties of the welding arc § 3. Fusion welding and metal transfer in the arc
Chapter 3. Sources of power of welding arc. § 4. Basic requirements. § 5. Welding Converters. § 6. AC welding machines. § 7. Welding rectifiers. § 8. Installation and maintenance of welding equipment.
Chapter 4. Metallurgical processes in welding. § 9. The concept of weldability. § 10. Main reactions in the weld zone. § 11. Crystallisation of weld pool metal. Chapter 5. Welding wire and electrodes. § 12. Welding wire. § 13. Metallic electrodes.
Chapter 6. Manual arc welding technology. § 14. Weld Joints and Seams. § 15. Welding mode selection and weld technique. § 16. High productivity welding processes. § 17. Welding strains and stresses.
Chapter 7. Automatic and semi-automatic submerged arc welding. § 18. Bottom line and advantages. § 19. Welding fluxes. § 20. Submerged-arc welding equipment. § 21. Welding Technology. § 22. Electro Slag Welding.
Chapter 8. Arc welding under shielding gas. § 23. Essence and Benefits. § 24. shielding gases. § 25. Equipment for shielded gas welding. § 26. Argon arc welding process § 27. Carbon dioxide arc welding technology.
Chapter 9. Arc Cutting. § 28. Methods of cutting with consumable electrode. § 29. Cutting methods with a non-consumable electrode.
Section II. Gas welding and oxyfuel cutting.
Chapter 10. Gas welding. § 30. Welding station equipment. § 31. Welding torches.
Chapter 11. Welding flame. § 32. Welding and metal cutting gases. § 33. Welding flame.
Chapter 12. Welding Technology. § 34. Techniques for gas welding. § 35. Gas welding process.
Chapter 13. Oxygen Cutting. § 36. The essence of the oxygen cutting process. § 37. Equipment for oxyfuel cutting. § 38. Technology for oxyfuel cutting.
Section III. Pressure Fusion Welding.
Chapter 14. Contact welding technology. § 39. The essence of resistance welding. § 40. Butt contact welding. § 41. Pressure spot welding. § 42. Seam joint contact welding.
Chapter 15. Contact welding equipment. § 43. Butt-welding machines. § 44. Spot-welding machines. § 45. TIG welding machines.
Section IV. Peculiarities of Welding Technology of Various Materials. Hardfacing. Welding pipelines.
Chapter 16. Welding of alloyed steels. § 46. Weldability of alloyed steels. § 47. Welding of low-alloy steels. § 48. Welding medium and high alloyed steels.
Chapter 17. Welding of non-ferrous metals and their alloys. § 49. Peculiarities of welding of non-ferrous metals and their alloys. § 50. Welding of copper and its alloys. § 51. Welding aluminum and its alloys.
Chapter 18. Welding of cast iron. § 52. Peculiarities of welding cast iron. § 53. Hot Cast Iron Welding. § 54. Cold-welding of cast iron.
Chapter 19. Hardfacing work. § 55. Types of surfacing operations. § 56. Welding technology.
Chapter 20. Welding of polymers and plastics. § 57. Basic plastics and plastics. § 58. Welding Techniques.
Chapter 21. Welding piping. § 59. Nomenclature and range of pipes and fittings. § 60. § 53 Preparation of pipes for welding. § 61. Welding methods and conditions.
Section V. Welding quality control. Safety Precautions.
Chapter 22. Welding quality control. § 62. Main weld defects. § 63. Types of inspection of welded joints.
Chapter 23. Safety precautions. § 64. Electrical Welding Safety Fundamentals § 65. Safety rules for gas welding and oxyfuel cutting. § 66. Safety precautions during inspection testing of welds. § 67. Safety precautions at the construction and installation site. List of references.
The text of the book “Welding work: practical manual for electric and gas welder
Under conditions of scientific and technological progress it is especially important to develop the determining areas of science, technology and production. These may include welding and cutting of metals, which in many industries are one of the main factors determining the pace of technological progress, and have a significant impact on the efficiency of social production. There is practically no branch of machine building, instrument making and construction, where welding and cutting of metals are not applied.
Welded execution of many types of metal structures allowed the most efficient use of blanks obtained by rolling, bending, stamping, casting and forging, as well as metals with different physical and chemical properties. Welded structures compared to cast, forged, riveted, etc. п. are easier and less time-consuming. With the help of welding, permanent joints of almost all metals and alloys of different thickness from hundredths of a millimeter to several meters are made.
Founders of electric arc welding of metals and alloys are Russian scientists and inventors.
According to the level of development of welding production, USSR was the leading country in the world. And for the first time performed an experiment on manual welding, cutting, brazing and deposition of metals in open space.
Work is successfully carried out at the specialized Institute of Welding. named after V.V. Plekhanov Institute of Electric Welding, Russian Academy of Sciences, as well as at the Russian Academy of Sciences, Moscow. Е. О. Paton Institute of the Academy of Sciences of Ukraine (IES).
Growth of technological progress. introduction of complex welding equipment, automatic lines, welding robots, etc. д Requirements for general educational and technical training of workers-welders. The purpose of this book. to help students in vocational schools, educational and training workshops, as well as students in preparation for production master the profession of electric and gas welder.
GENERAL INFORMATION ABOUT WELDING, WELDED JOINTS AND SEAMS
BRIEF DESCRIPTION OF THE MAIN TYPES OF WELDING
General information on basic welding
Welding is the process of obtaining permanent joints by establishing the inter-atomic bonds between the welded parts at their heating or plastic deformation, or the combined action of both (in accordance with the existing standards).
There are two main most common types of welding: fusion welding and pressure welding.
The essence of fusion welding is that the metal on the edges of the welded parts is melted under the action of the heat source. The heating source can be an electric arc, gas flame, molten slag, plasma, laser beam energy. In all types of fusion welding, the liquid metal formed by one edge of the weld is combined and mixed with the liquid metal of the other edge, creating a total volume of liquid metal, which is called the weldpool. After the metal of the weld pool solidifies, a weld is obtained.
The essence of welding pressure consists in the plastic deformation of the metal along the edges of the welded parts by compressing them under load at a temperature below the melting point. The weld is formed as a result of plastic deformation. Only plastic metals like copper, aluminum, lead, etc., can be well welded by pressure welding. (cold welding).
Among the great variety of different types of fusion welding, the leading place is occupied by arc welding, in which the source of heat is an electric arc.
In 1802. Russian scientist B. В. Petrov discovered the phenomenon of electric arc discharge and pointed out the possibility of using it to melt metals. With his discovery, Petrov initiated the development of new branches of technical knowledge and science, which later gained practical application in electric arc lighting, and then in electric heating, melting and welding of metals.
In 1882. scientist-engineer N. Н. Benardos, working on creation of big accumulator batteries, discovered the method of arc welding of metals using a non-consumable carbon electrode. He developed a method of arc welding in shielding gas and arc cutting of metals.
Scientist-engineer N. Г. Slavyanov in 1888. He suggested welding with a fusible metallic electrode. Slavyanov is associated with the development of metallurgical bases of electric arc welding, creation of the first automatic arc length regulator and the first welding generator. He proposed fluxes for obtaining high quality weld metal. (In Moscow Polytechnic Museum there is Slavyanov’s authentic welding generator and exhibited samples of welded joints.)
In 1924-1935 the technology of submerged-arc welding was developed. mostly used manual welding electrodes with thin ionizing (chalk) coating. During these years, under the leadership of academician V. П. The first Russian-made boilers and hulls of several ships were manufactured under the supervision of Vologdin. From 1935 to 1939, the first thick-walled electrodes were used. thick-coated electrodes began to be used. For the electrode rods, alloyed steel was used, which enabled welding to be used for manufacturing industrial equipment and building structures. In the process of the development of welding production, under the leadership of E. О. Paton (1870-1953), submerged-arc welding technology was developed. Submerged-arc welding allowed increasing the productivity of the process by 5-10 times, ensuring a good quality of the welded joint due to increasing the power of the welding arc and reliable protection of molten metal from the ambient air, mechanizing and improving the technology of welded structures manufacturing. In the early 50s, the Electric Welding Institute named after V.V. Plekhanov began to manufacture. Е. О. The electroslag welding was developed by Professor K.O. Paton, which made it possible to replace cast and forged large-size parts with welded ones; workpieces became more transportable and easier to assemble/install.
Industrial application since 1948. Methods of arc welding in inert shielding gases were developed: manual. with a nonconsumable electrode, mechanized and automatic. with a nonconsumable and a consumable electrode. In 1950-1952 the methods of arc welding were developed in our country. in CNIITmash in cooperation with the Moscow Higher Technical School and the IES named after V.I. Mechnikov. Е. О. Welding of low-carbon and low-alloy steels in carbon dioxide was developed by Paton Institute. the process is highly productive and provides a good quality of welded joints. Carbon dioxide welding makes up about 30% of all welding work in our country. The development of this method of welding was headed by Prof. K. O. Kovalev, Doctor of Science. Ф. Lubawski.
Electric arc welding is a method of metal joining based on using electric arc. The arc heats and melts the metal to form a weld. Can be heated to over 6000 degrees. This is enough to melt most existing metal types.
Electric arc technology is widely used in the welding and cutting of metals. Can be manual, semi-automatic and automatic.
Manual electric arc welding (a.k.a. RDS). welding with manual labor and an electrode. The welder holds the electrode and sends it to the welding area, forms the weld and monitors the process himself. In semi-automatic welding, a welding wire is used as an electrode, which is fed into the welding area with a special mechanism. In this process, the welder still follows the arc himself. And in automatic welding, both wire feeding and arc movement are performed by automatic equipment.
Electric arc welding and cutting
Currently, about 70% of all welding work is performed by fusion methods, among which electric arc welding is the most common, which is used in the manufacture of road, rail, sea and river transport and in the manufacture of pipelines. Electric arc welding allows to weld almost all structural steels, gray and malleable cast iron, copper, aluminum, nickel, titanium and their alloys.
The invention of arc welding was invented by Russian scientists. The arc discharge phenomenon was first discovered in 1802. Russian academician V. В. Petrov. In 1882. Russian inventor N. Н. Benardos proposed the use of an electric arc to weld metal with a carbon electrode. For this purpose, graphite (carbon) electrode 2 (fig. 6.6, а) with filler metal from the rod / or without it are connected to the current source 3. This method does not melt the electrode.
In 1888. mining engineer N. Г. Slavyanov replaced the graphite electrode with a metal one (Fig. 6.6, б), and since then, 99% of all arc welding work is done using the H. Г. Slavyanov. The arc is excited between the electrode 4 and base metal and melts them to form a common bath, in which all the molten metal is mixed.
A welding arc is an electrical discharge that exists for a long time between electrodes that are energized. One of the electrodes can be a product. In this case, the arc is called a direct arc. If the arc burns between two electrodes with no electrical connection to the workpiece (but close to it), then such an arc is called an indirect arc.
Direct arc is more efficient than indirect arc.
Electric discharge of welding arc occurs in a mixture of gases and metal vapors, is characterized by high temperature (6000-15 000 K), strong glow, high current flow (1 to 3000 A) and relatively low voltage (10-50 V). Arc power ranges from 0.01 to 150 kW. This range allows it to be used for welding both the smallest and largest products.
Under normal conditions, the gas gap between the electrodes is a non-electrically conductive. Appearance of arc and its stable burning depend on many factors and depends on the degree of ionization of the arc gap. Ionization occurs due to the intense flux of electrons generated by thermionic and photoelectron emission.
coated electrodes are used for manual welding. The coatings can be stabilizing, protective or alloying.
Electrodes can be of thin, medium, thick and extra thick according to coating thickness (GOST 9466-75). Thin coatings are stabilizer coatings. They consist of chalk and liquid glass. The calcium in the chalk releases in the plasma of the arc, ionizes it and thus contributes to a stable combustion of the arc.
Medium, thick and extra thick coatings ensure stable ignition of the arc, as well as protection and alloying of the metal. The composition of these wrappings is chosen so that a gas environment is created around the arc, protecting the electrode metal 5 (Fig. 6.6, в), flowing in the arc, and the metal of the trough 8 from oxidation and dissolution of gases in it. As the electrode melts, the cladding slag and slag 7 evenly covers the weld 6, protecting metal from oxidation and nitrogen saturation. In addition, the slag slows down the cooling of the metal, which contributes to the release of dissolved gases and sealing of the weld. If necessary, ferroalloys are added to the cladding for alloying. Thus, these coatings include ionizing (e.g., chalk), gas-forming (flour), slag-forming (feldspar) substances as well as deoxidizers (ferromanganese) and alloying components.
In all cases where a welded structure must withstand high loads, electrodes with thick and extra thick coatings are used, which provide strength and toughness of the seam, not inferior to the base metal.
The current used in the arc can be constant or alternating. Stability of arc combustion at direct current is higher than at alternating current, since in the latter case, when the voltage passes through zero and the polarity reversal at the beginning and the end of each half-period, the arc gap temperature decreases, causing deionization of gases. The stability of AC arc combustion is significantly increased if easily ionizable chemical elements, such as potassium, calcium, etc., are introduced into the arc gap through the coating or wire.
DC arc welding, when the negative pole of the voltage source is connected to the electrode and the positive pole of the voltage source is connected to the workpiece, is called arc welding direct polarity. Welding when the electrode is connected to the positive pole of the current source, and the workpiece. to the negative, is called an arc welding reverse polarity. The arc of direct polarity is characterized by greater heat release on the workpiece, and of reversed polarity. on the electrode.
AC arc welding, including non-consumable electrode, and manual arc welding are used for non-ferrous metals.
In Fig. 6.7 shows the static volt-ampere characteristic of the arc, i.e. е. relation between arc voltage and arc current at constant arc length and electrode diameter.
On the site 1 Increased current leads to a sharp voltage drop. Here the arc is of low stability, its use is limited.
On site 2 Increasing the current does not increase the arc voltage. This is because under these conditions