Principle of operation of electrodes for welding
The principle of current transfer in such electrodes is simple. One of the ends is not covered for 3 cm so that it can be grasped by the holder for contact with the current circuit. The second end is slightly cleaned from the coating to create contact with the object when the arc is ignited.
During melting in the arc, complex processes occur. As a result of oxidation-reduction reaction in the gaseous medium, at the interface of slag, metal and arc, alloying, deoxidation and oxidation occur, which create a seam.
Classification of welding electrodes
The classification of welding electrodes is carried out according to the following criteria:
- thickness of the rod coating;
- web material;
- is a kind of slag that forms during melting;
- type of coating;
- purpose for welding special steels;
- properties of metal seam;
- polarity and type of current used for operation;
- allowable spatial positions of surfacing or welding.
Electrodes for manual arc welding should provide a stable burning and simple ignition of the welding arc. In addition, it is desirable that the coating of the electrode is melted correctly, and the coating of the seam with slag occurs evenly and is easily cleaned after the end of work. When working in the weld metal, pores and cracks should be avoided.
Before selecting electrodes for DC welding, you need to familiarize yourself with their classes:
- SSSI 13/45 - has a basic coating, and is used for low-alloy and carbon steels. With its help, it is possible to process metals having a large thickness, vessels operating under pressure, and to eliminate casting defects.
- SSSI 13/55 - has the same function as SSSI 13/45, and you can weld not only pressure vessels, but also building metal structures.
- OZS-12 - is used for working with low-carbon steel structures. The work can take place in any position, except for the vertical one.
- OZS-4 - makes it possible to work on an oxidized surface, suitable for low-alloy and carbon steels.
- МР-3С - suitable for the same steels as the previous type, in addition, it creates a neat seam, which facilitates the whole process of work.
Typology of coatings for welding electrodes
To make the right choice of welding electrodes, one must take into account all the finenesses of the coating, the type of metal and the type of weld. By type of coating, we can identify some types of welding electrodes, for which we indicate a few words about the composition and application.
Materials with acid coating contain oxide of iron, silicon, manganese and in some cases titanium. The weld metal has an increased tendency to form hot cracks. You can use these electrodes for AC and DC welding.
variants with basic coating consist of magnesium and calcium carbonate, CaF2 fluorspar. They become indispensable for the welding of hardening steels that are prone to cold cracks as a result of the action of hydrogen, passing into the peritoneal zone of the metal.
Such low oxidant coatings help to move alloy elements from the electrode to the seam. In addition, they are used for welding high-alloy steels. The weld metal thus welded is resistant to hot cracks. It is possible to combine rigid structures and use for thick joints when surfacing in several layers.
But they also have disadvantages: low arc stability, a tendency to pores when the arc in the welds increases during welding, if there is rust or scales on the surface of the metal.
Materials with cellulose coating are based on cellulose. The metal deposited by them includes an increased amount of hydrogen. They allow to carry out welding from the top down, while with other electrodes a poor-quality track is obtained with such an algorithm.
electrodes with rutile coating include rutile, which consists of titanium dioxide TiO2, as well as carbonates and aluminosilicates. Before work, they should be dried at 200-degree temperature for 1 hour, and only after 24 hours they can be worked with. They can cook steel, on the surface of which there is rust and scales, pores will not form. They are more resistant to hot cracking than electrodes with acid coating.
Their advantages are: easy ignition, high fatigue resistance of welding joints, low propensity for pores to appear during ignition and rapid elongation of the arc. Such electrodes can be cooked low-alloy and low-carbon steel;Do not cook structures that work at elevated temperatures.
