Manual arc welding: technology, GOST
When creating metal structures, manual arc welding is widely used.
It is the process of creating a permanent joint by melting a metal.
The essence of the welding process
Welding consists in creating an arc between the coated protective electrode and the weld pool. Ignition is performed by quickly touching and leading a small distance from the surface of the metal rod. From the heat of the arc that appears, it melts and forms a weld. Together with the electrode, its coating melts, forming a protection from gas and slag, which protects the metal from oxidation. After each stage of welding, slag coating is removed from the surface of the seam.
The limited length of the electrode causes an interruption of the welding process, as it is constantly necessary to change it to a new one. Interruptions in work cause defects in the weld.
The manufacturer of the electrodes indicates the recommended limits for the change in the magnitude of the required current, depending on the properties of the coating, the thickness of the rod and the welding position.
When the rod is heated, the coating melts too, creating a stream of gas directed to the weld pool. As a result, droplets of molten metal are transferred to it. The movement of the gas is so intense that it moves the metal from the bottom up when welding in a ceiling position.
Type and thickness of parts to be welded
Manual arc welding is applicable to unalloyed and alloyed steels with a thickness of up to 50 mm in the production of single or small-scale products. Thin metal (less than 1.5 mm) is quickly melted and "collapses" until the weld pool appears. It needs special tools.
The strength of the weld metal compound decreases with increasing carbon content.
It is beneficial to use manual welding for products with a thickness of 3-20 mm. The exceptions are single seams of complex configuration.
For the electrodes, special materials of the rod and the coating layer containing slag-forming, stabilizing and other substances are selected.
Coverage assignments are as follows.
- Slag production, which envelops the weld pool and molten metal droplets, protecting them from oxidation by oxygen of air and the influence of water vapor.
- The formation of a protective gas formed during the combustion of the organic component of the coating.
- Perform deoxidization of the weld metal. In addition, in the coating can be alloying additives, passing from slag to metal droplets.
Electrodes for manual arc welding are of a certain type, corresponding to the specified mechanical characteristics of the weld metal. The letter E with the number in the designation of its type indicates the magnitude of the temporary resistance (kg / mm2). The presence of the letter A is characterized by high ductility and toughness.
Position of welding in space
Welding is allowed in all positions, but the most convenient is the lower one, which does not require high qualification of the performer. Large diameter electrodes can be used here, and the current can be high, which allows the process to be made more productive. In the ceiling and vertical positions of the seam, metal droplets are held only by surface tension. The size of the weld pool is reduced and a smaller electrode diameter is required.
Welder working conditions
The process of electric welding can be performed in a variety of conditions: indoors, outdoors, on structures, pipelines and other objects.It does not require the supply of water, gas, and of the materials used, only electrodes are required. A power source is required for operation. Cables can be removed from it for a long distance. At the same time, energy losses for their heating increase. In remote locations, electric generators driven by gasoline or diesel engine can be used.
Snow, rain and wind are interferences, and protection of the working area is required of them.
Type of welding current
Manual arc welding is carried out on alternating or direct current. Special electrodes are used for this, but they can be universal, designed for both types of current.
Direct current allows you to create a more stable arc, and it is more convenient to work with it. Molten metal has the best wetting effect, and the seam forms a uniform. Therefore, this method is necessary for welding small items or thin sheets.
Defects of welded joints
The quality requirements of the compounds in the metal are subject to technical requirements and standards are established. If there are deviations from them that lead to a decrease in the efficiency of structures and reliability, then defects appear. For reasons of occurrence they are divided into two groups.The first is the defects arising in the crystallization of the metal, as well as its cooling: cracks, pores, slag inclusions, deterioration of the properties of the metal on the seams and near them. The 2nd group includes defects associated with improper preparation and violation of the welding mode: undercuts, lack of penetration, influxes, burn-throughs, craters, deviations of welds from the calculated dimensions.
Manual arc welding: welded joints
To create a reliable connection when the thickness of the metal is not less than 7 mm, it is necessary to prepare the edges of the blanks. With their help, a complete penetration of the blanks is provided.
On thin metal, 1 or 2 seams are made, and on large thicknesses, a root pass is first performed, and then the cavity is filled with weld rollers.
GOST "Manual arc welding" (5264-80) regulates how to cut the edges of the parts, depending on what type of connection is selected. In shape, there are V, K, X-shaped edges. The seam can be carried out from one or two parties.
The edge can be cut down with a chisel, but the quality is achieved the lowest. Smooth and clean they are obtained on special planing or milling machines. If this is not possible, use oxygen cutting.
Particular attention is paid to cleaning the edges from rust, scale and other contaminants.This is done with a steel brush. To facilitate the use of preheating areas of the flame of a gas burner.
Types of welded joints are determined by the mutual arrangement of parts and can be as follows:
- butt joint
GOST "Manual arc welding. Weld joints" (5264-80) distinguishes types of welds by position in space.
- Lower - the easiest and most reliable. Details are located under the electrode. It is important not to melt the workpiece.
- Horizontal - the detail is located at an angle of 0-600, and welding is carried out in the horizontal direction.
- "In the boat" - installation of the part tilted and welding in the corner.
- Vertical - the seam is made upwards. The work is complicated due to the runoff of the metal.
- Ceiling - the seam is located on top. Welding is carried out with short pulses at low current.
The seams on the finished products are checked for compliance with the requirements of GOST. Manual arc welding should not lead to the formation of defects, and the geometric and mechanical characteristics of the joints must be maintained within the specified limits.
Equipment for manual arc welding is primarily a special apparatus, which can be:
- transformer with rectifier;
Special popularity gained welding inverters. The functions of forcing the arc and anti-sticking allow you to make relatively high-quality seams even for beginners. High cost does not stop buyers, due to high technical characteristics and greater reliability.
On the market, you can buy professional devices with high performance and for home use, when there is no need for continuous operation.
Manual arc welding technology
For manual welding, it is first ignited by touching or striking. Then the electrode is retracted a short distance so that the arc is constantly burning. The technology of manual arc welding consists in moving the rod in three planes:
- approach and removal of the electrode from the surface of the workpiece by oscillating movements;
- movement in the direction of the seam formation;
- forming a metal roll by moving the electrode across the weld axis.
Manual arc welding
For pipes, conventional joint methods and joint positions are used. They must comply with GOST "Manual arc welding. Welded joints" (5264-80).Pipe joints are subject to special requirements so that they are airtight and withstand the specified pressure of the pumped medium.Therefore, they are trying to weld the pipes in the lower position, and the product turns from time to time. Their training is to create perpendicular ends with a dull -2.5 mm and bevel edges at an angle of 60-700.
Welding is carried out mostly butt-joint, and for this purpose, they first tack at 4 places of the pipe. If its diameter exceeds 300 mm, the distance between the welding sections is about 200 mm. Tack length is about 50 mm. After perform the welding of the pipe around the entire circumference.
Manual arc welding is performed to connect parts in small-scale and individual production. To obtain high-quality connections, it is necessary to have a suitable apparatus and electrodes, as well as to have the skills to prepare parts and perform welding.