Welding of metals is one of the most important operations in the manufacture and operation of metal structures. The manufacture of complex metal parts, patterned products, products made of high-alloyed steels is the lot of professionals who know well how to weld metal correctly. After all, electric welding is the most common type that has many advantages.
Schemes of electric arc welding.
In life, it is often necessary to connect or repair simple metal parts - pipes, profiles, strips, simple structures. Acquainted with how to cook metal by electric welding, any person is able to do all the work on their own.
The Basics of Electric Welding
Electric welding is based on the process of joining metal parts by melting the edges of parts adjacent to each other and filling this area with molten metal. Melting of the metal produced by an electric arc. The arc between the electrode and the surface of the workpiece is created by applying a constant current of high power.
Scheme spot welding.
The set of the welding machine includes an inverter, transformer, cable, holder. The inverter is designed to convert AC to DC. With the help of a transformer the required strength of the welding current is provided. The current is regulated depending on the thickness of the workpiece to be welded, the type of metal and the type of electrode and ranges from 30 to 400 A.
The electrode is a metal wire (the most common diameter is 3-5 mm), covered with a special coating. Its length is usually 250-500 mm. The coating in the process of welding plays the role of an inert environment. The composition of the coating usually includes a mixture of metals (nickel, manganese, iron) and minerals (alumina, magnesia, limestone).Back to table of contents
Electric welding process
Equipment and tools required for welding:
- welding machine;
- set of electrodes;
- protective shield;
- metal brush;
- emery sandpaper;
- patterns and probes.
The sequence of the process of electric welding is developed as follows. A positive pole (anode) is connected to the electrode through the holder and a constant electric current is applied. An electric arc is formed in the gap between the electrode and the surface of the workpiece, which melts all the metal falling into its zone of action.
The scheme of the welding machine for electric welding.
At the same time, the base metal of the electrode is melted. This metal in the form of droplets fills the space between the melted edges of the workpiece in the weld pool - as a result, a weld is formed. Under the influence of high temperature, a gas cloud arises from the evaporation of the coating. This cloud due to its chemical inertness protects the molten metal from interaction with air. On top of the weld slag appears from the products of the decomposition of the coating, which forms an additional protective layer against oxidation. The weld gradually cools, and the metal in it crystallizes. So connection of preparations is provided.Back to table of contents
The first step is to select the electrode and set the amount of welding current. As a rule, electrodes are used with a diameter of 3.2 or 4 mm. Then it is necessary to measure the thickness of the workpiece with a caliper to set the amperage. The electrode with a diameter of 3.2 mm can be used with a workpiece thickness up to 3 mm, and the current intensity is set to 90 A. Use an electrode with a diameter of 4 mm for blanks up to 4 mm thick; at the same time, the current with a workpiece thickness of up to 3 mm is 100 A, and with a thickness of 3-4 mm it is 120 A.
Before welding, it is necessary to prepare the welding area. For this, the workpiece is cleaned of dirt and external coatings (paint, primer, etc.). The site of direct work is necessary to clean the grinder, sandpaper or file to the base metal. The workpiece is fixed.Back to table of contents
The main types of trajectories of transverse vibrations in arc welding.
The welding process begins with the formation of an arc between the electrode and the surface of the workpiece. For this purpose, the holder is set at an angle of 60º to the surface of the workpiece and is lightly held along it until sparks appear. If sticking of the electrode occurs, it is released by a slight tilt from side to side. After the appearance of sparks, the electrode rises above the surface to a height of 5 mm.
An arc should be formed between the electrode and the surface of the workpiece. The minimum arc length is 3 mm, but it is recommended to ensure an optimal arc length of 5 mm. If a stable arc does not form, increase the strength of the welding current. The arc must be maintained all the time welding with a given size. An increase in the arc length is not permissible, since oxidation processes or nitration reaction may develop in the increased gap, molten metal droplets splash, porosity may occur in the weld. In the process of welding, the length of the electrode decreases, but it is necessary to keep the length of the arc unchanged, smoothly bringing the remainder to the surface.Back to table of contents
Weld seam formation
The formed arc is directed to the beginning of the work site and melts the metal. The weld is formed by a smooth slow longitudinal movement of the electrode along the welding line. By the form of its movement, the seams can be divided into several types.
Types of welds.
- The simplest one is a thread seam; it is obtained only with the longitudinal direction of motion. The width of such a seam is 2-3 mm. This seam has a low quality and can be used only in non-critical details.
- Better, but also not guaranteeing reliability is the seam formed by the movement of the electrode in two directions, longitudinal and transverse. The width of such a seam is up to 15 mm. The projection of the movement of the electrode is a zigzag or sinusoid. In this case, the electrode is slowly advanced along the welding line and at the same time is moved transversely from side to side by a width of 10-15 mm.
- Reliable welding seam is formed when the electrode moves in three directions. Longitudinal and transverse movement is maintained, but when the extreme positions are reached on both sides of the welding line, the electrode is shifted back by 10-20 mm. This ensures reciprocating movement, which allows you to re-process the seam. Step to the next shift is 30-50 mm. In the projection, such a movement in three directions is a spiral line or ornament.
When forming a weld, the electrode is guided at an angle of 75-80º to the surface of the workpiece in the direction of the welding line and strictly at an angle of 90 ° in the direction away from the welding line.Back to table of contents
How to weld after stopping?
In the process of welding there is a need to change the electrode or stop welding for other reasons. At the point of stopping, a depression is formed, called a crater. Resume work should be in the following order:
Diagram of the effect of the angle of inclination on the welding seam.
- At a distance of 12 mm from the crater arc ignites.
- The arc slowly moves to the crater.
- The location of the crater is thoroughly boiled by oscillating movements of the electrode.
- Then the welding process continues as usual.
Welding is usually carried out in several layers. With a blank thickness of up to 6 mm, 2 layers are sufficient, with a thickness of 6-12 mm - 3 layers, with a thickness of more than 12 mm - 4 layers. The direction of movement of the electrode in the layers varies.
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After the end of welding, the seam is processed, the excess is knocked off with a chisel or processed by a grinder and a file.
It should be remembered that welding is a dangerous process, therefore it is necessary to use protective equipment. A shield with a protective glass is necessary to protect the eyes from bright flashes of the arc and face from melted splashes. Clothing must be tight and melt proof. Hands should be tight protective gloves. It is necessary to consider the presence of electrically conductive parts, which must be reliably isolated. It is forbidden to work near flammable materials.
Electric welding is one of the most common and effective types of welding. Welding metal in simple designs is quite under the power of any person.