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Electric welding. Basics of electric welding. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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Сварка - this is a technological process that allows you to connect two parts with an integral connection. Electric welding is based on the ability of metals to melt and fuse under the influence of an electric arc.

welding arc - long-term electric discharge in an ionized mixture of gases and vapors of various materials between the electrode 1 and the product 3, which are under voltage.

The composition of the arc includes (Fig. 17.1): the anode region; pillar; cathode region.

Rice. 17.1. welding arc

Arc temperature (5000-7000 °C) allows you to melt all metals and alloys. On the surface of the anode and cathode, the temperature of the arc decreases to 3500-4000 °C.

The electric arc is excited by a short circuit of the welding arc and subsequent rapid removal of the electrode from the workpiece.

Arc length almost equal to the diameter of the electrode rod.

The dependence of the arc voltage on the welding current is called the static current-voltage characteristic (CVC).

Rice. 17.2. Static current-voltage characteristic of the welding arc

The main types of electric welding are:

• electric welding with a piece (or consumable) electrode;
• semi-automatic electric welding with wire;
• argon-arc welding with a non-consumable electrode;
• contact welding.

Arc welding related to fusion welding. In this type of welding, the melting of the base and filler metals is carried out by an electric arc burning between the electrode and the metal being welded.

The molten base and filler metals (electrode, wire or tape) form a weld pool, as a result of the crystallization of the metal of which a weld is formed. The source of heat in arc welding is a welding arc - a stable electric discharge in a highly ionized mixture of gases and metal vapors used in welding, characterized by high current density and high temperature.

At the heart of semi-automatic and automatic gas-shielded welding is the same process that is used in manual arc welding.

The main difference is the continuous supply of the consumable electrode, which is the wire.

In semi-automatic welding, several types of protection of the product and the weld pool from oxidation are used.:

• welding in shielding gases;
• welding with flux-cored or fluxed wire;
• submerged arc welding.

The most commonly used in industry, in repair work and for domestic purposes are semi-automatic welding in shielding gases, which is mainly due to the relative cheapness of consumables. Some of these machines have the ability to weld with fluxed wire. But submerged arc welding is mainly used for large industrial and mass production.

Argon arc welding - arc welding, in which argon is used as a shielding gas. Apply argon-arc welding with non-consumable tungsten and consumable electrodes. Argon-arc welding with a tungsten electrode can be manual and automatic.

Welding is possible without feed and with filler wire feed. This process is intended mainly for metals less than 3-4 mm thick. Most metals are welded with direct current of direct polarity. Aluminum welding is carried out on alternating current.

With direct polarity (plus on the product, minus on the electrode):

• better conditions for thermionic emission;
• higher resistance of the tungsten electrode;
• higher permissible current limit.

The permissible current when using a tungsten electrode with a diameter of 3 mm is:

• with direct polarity 140-280 A;
• at alternating current 100-160 A;
• with reverse polarity 20-40 A.

The straight polarity arc easily ignites and burns steadily at a voltage of 10-15 V in a wide range of current densities.

With reverse polarity:

• the arc voltage increases;
• the stability of its combustion decreases;
• the resistance of the electrode decreases sharply;
• heating and electrode consumption increase.

These features of the reverse polarity arc make it unsuitable for direct use in the welding process.

An electric arc of reverse polarity has an important technological property: during its action, oxides and impurities are removed from the surface of the metal being welded.

This phenomenon is explained by the fact that, with reverse polarity, the metal surface is bombarded with heavy positive argon ions, which, moving under the influence of an electric field from plus (electrode) to minus (product), destroy oxide films on the metal being welded, and leaving the cathode (product surface) electrons contribute to the removal of destroyed oxide films.

The process of removing oxides is called cathode sputtering.

The specified property of the arc of reverse polarity is used when welding Al and Al alloys having strong oxide films. But since the resistance of the tungsten electrode is low with a direct current of reverse polarity, an alternating current is used for this purpose.

In this case, the removal of the film, i.e., cathode sputtering, occurs when the workpiece to be welded is the cathode.

When welding with a non-consumable electrode on alternating current, the advantages of an arc of direct and reverse polarity are realized to a certain extent, i.e., this ensures the stability of the electrode and the destruction of oxide films.

The arc is initiated by closing the electrode and metal with a carbon rod or by a short-term discharge of high frequency and voltage using an oscillator.

manual welding perform an inclined burner angle forward, the angle of inclination to the surface of the product is 70-80°. The filler wire is fed at an angle of 10-15°. At the end of welding, the arc is gradually broken to fill the crater, with manual welding - by its gradual stretching, with automatic welding - with a special crater welding device, which ensures a gradual decrease in the welding current. To protect the cooled metal, the gas supply is stopped 10-15 seconds after the current is turned off.

Connection types, basically, are selected depending on the thickness of the welded metal. The edges are not cut for parts whose thickness completely allows the joint to be welded with an arc.

TIG welding without filler wire used for small thicknesses. Thicker metal requires edge cutting, since flanging is difficult to perform on a thickness of more than 2-2,5 mm.

For thicknesses greater than 6-8 mm, one-sided cutting of edges is used, often with a lining to ensure complete penetration. With a thickness of parts over 20 tmm, two-sided cutting is performed.

If with such a thickness it is impossible to carry out bilateral welding (for example, pipes of large thickness and small diameter), a U-shaped or cup-shaped one-sided cutting of the edges is made and welding is carried out in several passes. But this somewhat reduces the internal quality of the welds, increases the amount of deposited metal.

Beginning and end of the seam perform on attached technological strips, which are removed after welding. The beginning and end of the seam is removed using technological strips.

There are usually the most defects at the beginning and at the end.:

• melting;
• unmelted crater;
• errors of a non-stationary weld over the cross section;
• arc ignition defects, etc.

Before welding, the edges are cleaned from dirt, scale, rust to a metallic sheen. After welding, the seam is cleaned with a steel brush, giving it the desired appearance and often revealing defects.

Hack and predictor Aviator. The presence of flux crust residues and oxides on the surface of the weld contributes to the corrosion destruction of the weld.

In some cases, a seam made on an aluminum alloy is coated with an anti-corrosion solution. Shielded welding mode is chosen depending on the thickness and grade of the metal to be welded, the diameter and grade of the electrode wire, taking into account the provision of fine droplet transfer of the electrode metal.

When welding steels, the diameters of tungsten electrodes and the optimal current values ​​​​are selected according to the tables given in the relevant reference books.

In argon-arc welding of high-alloy steels with a tungsten electrode, electrode wires of the same composition are used as filler metal as for submerged arc welding of this steel.

Author: Koryakin-Chernyak S.L.

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