A practical guide for an electric and gas welder

  

Welding works: A practical guide for an electric and gas welder

 Introduction:

In the conditions of scientific and technological progress, the development of the fields of science, technology and production that define it is especially important. These can 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 mechanical engineering, instrument making and construction in which welding and cutting of metals would not be used.

 The welded design 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 various physical and chemical properties. Welded structures are lighter and less labor-intensive compared to cast, forged, riveted, etc. With the help of welding, one – piece joints of almost all metals and alloys of various thicknesses are obtained-from hundredths of a millimeter to several meters.

 The founders of electric arc welding of metals and alloys are Russian scientists and inventors.

 According to the level of development of welding production, the USSR was the leading country in the world. And for the first time he carried out an experiment on manual welding, cutting, soldering and spraying of metals in outer space.

 The work is being successfully carried out at the specialized institute of welding profile – the E. O. Paton Institute of Electric Welding of the Academy of Sciences of Ukraine (IES).

 The growth of technical progress – the commissioning of complex welding equipment, automatic lines, welding robots, etc. - increases the requirements for the level of general education and technical training of welders. The purpose of this book is to help students of vocational schools, educational and course complexes, as well as students who are preparing for production to master the profession of an electric and gas welder.

 Section one

 GENERAL INFORMATION ABOUT WELDING, WELDED JOINTS AND SEAMS

 Chapter 1

 BRIEF DESCRIPTION OF THE MAIN TYPES OF WELDING

 1. General information about the main types of welding

 Welding is the process of obtaining permanent joints by establishing interatomic bonds between the parts being welded when they are heated or plastic deformed, or the combined action of both (in accordance with 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 along the edges of the welded parts is melted under the influence of the heat of the heating source. The heating source can be an electric arc, a gas flame, molten slag, plasma, or the energy of a laser beam. In all types of fusion welding, the resulting liquid metal of one edge is combined and mixed with the liquid metal of the other edge, creating a total volume of liquid metal, which is called a welding bath. After solidification of the metal of the welding bath, a weld is obtained.

 The essence of pressure welding consists in plastic deformation of metal along the edges of the parts to be welded by compressing them under load at a temperature below the melting point. The weld is obtained as a result of plastic deformation. Only plastic metals are well welded by pressure welding: copper, aluminum, lead, etc. (cold welding).

 Among the wide 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, the Russian scientist V. V. Petrol discovered the phenomenon of electric arc discharge and pointed out the possibility of using it for melting metals. With his discovery, Petrov laid the foundation for the development of new branches of technical knowledge and science, which later received practical application in electric arc lighting, and then in electric heating, melting and welding of metals.

 In 1882, the scientist-engineer N. N. Bernardo, working on the creation of large batteries, discovered a method of electric arc welding of metals with a non-melting carbon electrode. He developed a method of arc welding in protective gas and arc cutting of metals.

 The scientist-engineer N. G. Slavyanov in 1888 proposed to produce welding with a melting metal electrode. The name of Slavyanov is associated with the development of the metallurgical foundations of electric arc welding, the creation of the first automatic arc length controller and the first welding generator. They were offered fluxes for obtaining high-quality metal welds. (The Moscow Polytechnic Museum has an authentic Ulyanovsk welding generator and exhibits samples of welded joints.)

 In 1924-1935, mainly manual welding with electrodes with thin ionizing (chalk) coatings was used. During these years, under the leadership of Academician V. P. Volgograd, the first domestic boilers and hulls of several ships were manufactured. From 1935-1939, thick-coated electrodes were used. Alloy steel was used for the electrode rods, which made it possible to use welding for the manufacture of industrial equipment and building structures. During the development of welding production, under the leadership of E. O. Paton (1870-1953), the technology of submerged welding was developed. Submerged arc welding allowed to increase the productivity of the process by 5-10 times, to ensure good quality of the welded joint by increasing the power of the welding arc and reliable protection of the molten metal from the ambient air, to mechanize and improve the production technology of welded structures. In the early 50s, the E. O. Paton Institute of Electric Welding developed electrostatic welding, which made it possible to replace cast and forged large-sized parts with welded ones; the blanks became more transportable and convenient for assembly and installation.

 Since 1948, the methods of arc welding in inert protective gases have been used commercially: manual – with a non-melting electrode, mechanized and automatic-with a non-melting and melting electrode. In 1950-1952, the welding of low – carbon and low-alloy steels in the carbon dioxide environment was developed at TSNIITMASH with the participation of the MVTU and the E. O. Paton NPP-a high-performance process that ensures good quality of welded joints. Carbon dioxide welding accounts for about 30 % of all welding operations in our country. The development of this welding method was led by Doctor of Sciences, Professor K. F. Lyubavsky.

 In the same years, French scientists developed a new type of electric fusion welding, called electron beam welding.

 This method of welding is also used in our industry. For the first time in outer space, automatic welding and cutting was carried out in 1969 by cosmonauts V. Kubasov and G. Shonin. Continuing these works, in 1984 cosmonauts S. Savitskaya and V. Dzhanibekov conducted manual welding, cutting and soldering of various metals in outer space.

 Melting welding also includes gas welding, in which the heat of the flame of a mixture of gases burned with a burner is used for heating (in accordance with existing standards). The gas welding method was developed at the end of the last century, when the industrial production of oxygen, hydrogen and acetylene began. During this period, gas welding was the main method of welding metals and provided the most durable joints. Gas welding with the use of acetylene has become the most widespread. With the development of the railway network and car building, gas welding could not provide structures with increased reliability. Arc welding is becoming more widespread. With the creation and introduction of high-quality electrodes for manual arc welding into production, as well as the development of various methods of automatic and mechanized arc welding under flux and in the environment of protective gases, contact welding, gas welding was displaced from many industries. Nevertheless, gas welding is used in many industries in the manufacture and repair of products made of thin-sheet steel, welding of products made of aluminum and its alloys, copper, brass and other non-ferrous metals and their alloys; surfacing works. A type of gas-flame processing is gas-thermal cutting, which is widely used when performing procurement operations when cutting metal.

Pressure welding refers to contact welding, which also uses the heat released in the contact of the parts being welded during the passage of an electric current. There are point, butt, seam and relief contact welding.

 The main methods of contact welding were developed at the end of the last century. In 1887, N. N. Benardos received a patent for methods of spot and seam contact welding between carbon electrodes. Later, these methods of contact welding, improved by the use of electrodes made of copper and its alloys, became the most common.

 Contact welding occupies a leading place among mechanized welding methods. In the automotive industry, contact spot welding is the main method of connecting thin-sheet stamped structures. The body of a modern passenger car is welded in more than 10,000 points. A modern airliner has several million welded points. Butt welding is used to weld the joints of railway rails, the joints of main pipelines. Seam welding is used in the manufacture of gas tanks. Relief welding is the most high-performance method of welding reinforcement for reinforced concrete structures.

 The feature of contact welding is a high heating rate and obtaining a weld. This creates conditions for the use of high-performance in-line and automatic assembly lines for car components, heating radiators, instrument elements and radio circuits.

 Security questions:

 What is called welding and what are the main two types of welding you know?

2. Tell us about the essence of fusion welding and pressure welding.

 

3. Tell us about the new types of welding.

4. What do you know about the use of gas welding?

5. What do you know about contact welding and its advantages?

2. Classification of fusion welding

Melting welding, depending on the various methods, the nature of the sources of heating and melting of the edges of the parts to be welded, can be divided into the following main types:

electric arc, where the heat source is an electric arc;

elector slag welding, where the main source of heat is molten slag, through which an electric current flows;

electron-beam, in which the heating and melting of the metal is produced by the flow of electrons;

laser technology, in which metal is heated and melted by a focused powerful beam of micro particles-photons;

gas, in which the heating and melting of metal occurs due to the heat of the flame of a gas burner.

A more detailed classification can be carried out according to other characteristics, highlighting welding with a melting and non-melting electrode, an arc of direct and indirect action; an open arc, under a flux, in a protective gas environment, an arc plasma.

The classification of arc welding is also made depending on the degree of mechanization of the welding process, the type and polarity of the current, etc.

According to the degree of mechanization, there are manual, mechanized (semi-automatic) and automatic welding. Each of the types of welding in accordance with this classification is characterized by its own method of ignition and maintaining a certain arc length; manipulation of the electrode to give the weld the desired shape; the method of moving the arc along the seam line and stopping the welding process.

In manual welding, these operations are performed by a welder manually without the use of mechanisms (Fig. 1).

When welding on a semi-automatic melting electrode, the operations for feeding the electrode wire into the welding zone are mechanized, and the remaining operations of the welding process are carried out manually by the welder (Fig. 2).

In automatic welding, operations are mechanized to excite the arc and move it along the seam line while maintaining a certain arc length (Fig. 3). Automatic welding with a melting electrode is usually performed with a welding wire with a diameter of 1-6 mm; at the same time, welding modes (welding current, arc voltage, arc movement speed, etc.) are more stable. This ensures the quality of the weld along its length, but requires more thorough preparation for the assembly of parts for welding.