Metallurgical processes in melting welding

 

What are metallurgical processes?

 Metal welding has long been used in industry, and the most popular is melting welding using an electric arc. This manual method of joining metals was invented in the 80s of the last century, and since then new welding equipment and other types of electrodes have appeared. The process itself has changed: now a special electrode is used for high-alloy alloys and the seam area is protected with inert gases.

 Nowadays, more than 20 types of electric welding are available for the welder, for example, in an electrolyte, a plasma jet, under the protection of argon. Even the classical method, in which an electric arc contacts a metal through an electrode, has been modified to connect dielectric materials or metallic parts. This technology of fusion welding is called indirect arc welding.

The essence of the melting welding process

 Fusion welding is a method of joining work pieces by melting touching surfaces without compression. The energy source must provide sufficient power to melt the edges of the parts and the filler material. To form a welding bath, which is a mixture of liquid metals, the flame is concentrated on a small area of the joint. When moving the place of application of thermal energy along the connection line after cooling, a welding seam is created along the entire length.

Together with the metal, impurities melt, so slag forms on the surface of the bath. The upper layers are heated above the melting point, which leads to a change in the structure and mechanical characteristics of the seam after cooling. The advantages of fusion welding include versatility and the ability to connect dissimilar metals.

 Varieties and methods of metal melting welding

 The types and methods of fusion welding are so diverse that scientists have learned to subordinate plasma for fusing and cutting metals. The proposed method is based on blowing a jet of inert gas through two electrodes, creating a large arc discharge. The gas from the neutral channel enters the arc, as a result of which the gas molecules are ionized, creating a high-temperature plasma jet. The power of the jet is regulated by variations with the composition of the gas or a change in pressure.

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 The advantage of plasma is that it can cut stainless and aluminum alloys, which is impossible in the usual gas-oxygen way.

 Not only new welding methods appeared, but also the technique developed. The industry required the rapid production of hundreds of template parts, and therefore automatic arc welding appeared.

 To solve the technological problem and increase productivity, automatic submerged welding was invented. The principle was that the welding wire was closed under a special substance-a flux-which protected the welding site from the influence of the atmosphere and formed a welding seam. Fusion welding and pressure welding have their own characteristics.

 And automatic welding allows you to:

 Increase the productivity of work, thanks to the use of a large current strength and large diameter electrodes. The flux protects the welding area, and also prevents the metal from splashing. This allows you to save on the material and form a smooth seam.

Due to the fact that there are no losses from stubs and splashing, not only metal, but also electrically conductive wire is saved.

The heat of the arc is used more efficiently, so there is a saving of electricity.

 Semi-automatic welding

 As a further development of the automatic method, semi-automatic welding was developed. In it, the arc is moved along the seam manually, and the wire is fed automatically. The equipment for electric fusion welding has become popular at every enterprise. Especially where welding of housing structures containing a large number of angular joints is required.

 There are developments that allow welding even in the upper position. In order for the welding bath to remain in its place, it is held by a copper disk.

Electrostatic welding

 Gradually, automatic arc welding was transformed into electroslag welding. With this method, low power consumption is obtained, and due to the high current strength, it is possible to weld metals of large thickness.

 The main advantage of electrostatic welding is that it is not necessary to prepare the edges of the parts.

 This welding is also divided into several types, the weld area is protected by a flux or a gas medium. The most popular protection is made of argon, which does not allow the metal to oxidize at the weld site. Later, more modern types of welding appeared, for example, vi bro-arc surfacing. It allows you to apply a thin layer of metal to the part.

Types of fusion welding

 Depending on the heat source, the main types of fusion welding include electric and gas. According to the method of execution, the electric type is divided into several varieties.

Gas station

 Gas fusion welding due to smooth heating allows you to connect blanks made of cast iron, non-ferrous metals, high-carbon steel. The gap between the parts is filled with filler wire, which melts together with the base metal. The joint is heated by the flame of the burner, which is formed by the combustion of a mixture of oxygen with a combustible gas:

 acetylene;

butane;

propane;

with hydrogen;

with kerosene or gasoline vapors.

 Gas welding scheme

Gas welding does not require electricity, so repair work can be carried out even in an open field. The disadvantage is the inability to work with work pieces with a thickness of more than 5 mm.

 Electric arc

 Electric arc welding is performed due to the heat of the arc, which occurs when a current passes through the electrode and the work piece. A welding bath is formed from the molten metal of the parts and the electrode or filler wire. After cooling, a seam is formed. Varieties are classified according to the following characteristics:

the type of current is alternating or constant; when there is a minus on the electrode, the polarity is direct, if plus ― reverse;

type of electrode ― melting, non-melting;

the level of mechanization ― manual, semi-and fully automatic;

the type of arc ― direct action (between the metal and the electrode), indirect (between two electrodes);

the method of protecting the welding site is an inert gas, flux, electrode coating.

 Electric arc welding scheme

 The metal of the melting electrode should be the same as that of the work pieces or similar in composition. When it is impossible to determine the steel grade, it is cooked with a transition (buffer) electrode. It is also used to connect elements made of steel with different compositions. Tungsten, graphite, and carbon rods are used as a non-melting electrode. The filler wire and the parts to be welded must be similar in chemical composition.

See also: Classification of knitting wire

The technological process of indirect arc welding

 During it, an arc occurs between two electrodes attached to the holder. Electricity does not go into the metal, and the deposition occurs due to a closely located burning arc. You can adjust the level of metal deposition by approaching or distancing the electric arc.

 Indirect welding is in demand for low-carbon steels, non-ferrous metals, in the manufacture of small parts.

 When it comes to smelting a small and very precise tool from metal, a very slow heating in the melting zone is necessary. This effect can be achieved by atomic-hydrogen welding with indirect heating on the metal.

 The principle is that hydrogen is supplied between two tungsten electrodes with a diameter of 1.5 to 4 mm, when metals are welded by melting. The gas, falling into the arc, turns from diatomic hydrogen into an atomic form. This process requires the expenditure of energy that hydrogen takes from the arc. Then, touching the metal, the hydrogen turns into a normal form and releases energy. Thus, a welding bath is formed at the junction, in which the metals are joined. Atomic-hydrogen welding is similar in its qualities to plasma welding.

Requirements for the quality of welding seams

 The list of requirements for welded joints is determined by the purpose of the finished product. However, there are mandatory requirements according to which the weld must be performed. In terms of hardness and strength, it should not be inferior to the metal of the work pieces.

 For visual inspection, the seam is cleaned of slag and scale, which are formed during melting welding. The width of the seam should be the same along the entire length, the surface should be finely scaly. It is not allowed to have surges, gaps, narrowing. If there are pores or cracks on the metal, the seam is rejected.

 The type of fusion welding is chosen depending on the tasks to be solved. When you often have to work outdoors, portable arc devices or a gas burner with cylinders will be more convenient. When working in one place, it is better to choose a semi-automatic option, and for mass production it is automatic.

 The book provides a classification of welding processes and a comparative description of various welding methods. The issues of weld ability of the base metal and the causes of defects in welded joints, argon welding of aluminum are considered. Information is given about welding materials, equipment and modes used for welding and surfacing various structures made of carbon, low-alloy and alloy steels, light metals and alloys. The information about the methods of non-destructive quality control of welded joints is given .

The principle of operation of the welding machine

It is quite affordable for a summer resident, the owner of a private house or garage, to perform welding work independently. The choice of the type of household welding machine depends on what and how it is required to connect reliably.

 welding works

 Consultations and advice from sellers, of course, will help you navigate the variety of commercial offers. However, the buyer's personal awareness and the most basic knowledge will help to ask the right questions and understand the answers to them.

 In this article, you will find basic information about what welding is and what the principle of operation of the welding machine is based on.

 What is welding?

 The process of inseparable connection of several parts into a single whole through heating, deformation and the use of filler materials (electrodes) is called welding.

 The materials of the solid components to be joined are heated to a state where inter molecular or inter atomic bonds occur at the welding site. A similar effect can be achieved by applying pressure on the surface at the place of the desired connection.

 The combination of pressure and heating allows you to optimize and regulate the welding process. Moreover, the higher the temperature, the less pressure is required. When the melting temperatures of the materials of the connected parts are reached, the need for pressure on them disappears altogether.

 welding process

The welding method, being dependent on a number of factors, affects the choice of welding equipment.

 In this article, we are not talking about industrial, but about household welding machines that can be bought in stores. Therefore, we will limit ourselves to the description of the equipment in which the principle of electric arc welding is implemented, and semi-automatic welding machines, for welding which a gas medium is required.

 The principle of operation of the welding transformer

 Welding machines of this type operate on alternating current, the strength of which is regulated by changing the voltage using a step-down transformer. As a result, reliable power is provided to the welding arc, the temperature of which can be several thousand degrees Celsius.

 transformer for welding

 In most designs, the voltage reduction to the level required to maintain the stability of the welding arc is achieved by moving one of the windings along the magnetic core. The resulting operating voltage, as a rule, does not exceed 80V at the initial levels of 220-380V. The inductive resistance of the windings changes and thus the value of the welding current is regulated.

 In addition to this, designs with a movable magnetic shunt or transistors are also used.