- How they work and how they differ
- The difference between the electrodes in the location of the seam
- Type and polarity of welding current
- Explanation of symbols
- Types of coatings
- Most popular brands
In the welding craft, the ability to choose the right electrodes depending on the type of joints and steel grade is a very important professional skill. In this article we will tell you about the main types of coating electrodes for MMA welding and explain how to use them for their intended purpose..
How they work and how they differ
The electrode is a simple metal rod that melts in an ignited electric arc and fills the seam between two parts, simultaneously heating their edges. The coating of the electrode, burning, ionizes the medium and maintains continuous arc burning. In addition, during combustion, the composition releases gases that displace oxygen from the weld pool, and forms a slag that floats to the surface of the molten metal and covers it, protecting it from corrosion, cracking and other negative effects during cooling..
Understanding the essence of the work of electrodes is very important to explain such a huge number of their varieties. They differ not only in the strength characteristics of the seam, but also in its position and the type of welding current used..
The difference between the electrodes in the location of the seam
Let us briefly recall how the orientation of the weld pool in space can change and how this affects the welding technique. The most convenient is the lower position of the horizontal seam, which can be flat and fillet. In this case, the melt effectively fills the seam and chamfer, and a uniform slag crust forms on top, which is easily separated. Almost all brands of electrodes, with the exception of special ones, can be cooked in the lower horizontal position.
Vertical seams are more difficult to cook. Usually, a pull-up welding technique is used. Accordingly, the coating of the electrode should be capable of fast and short-term ignition of the arc and efficiently guide the molten metal. Also, vertical seams can be cooked without tearing, but for this the coating must have a thickness greater than usual, so that a semicircular hole is formed at the contact point on the electrode.
The upper (overhead) location of the horizontal seam is considered the most difficult in MMA welding. It is almost impossible to weld such seams without tearing, more often they are deposited by the point method with an overlap of 3/4 of the previous weld. The coating of electrodes for ceiling seams promotes rapid melting of small portions of metal and the same rapid cooling. Slag from electrodes also behaves differently. For the most part, it flies off to the side (the electrode is held at an angle) and covers the previous sticking point. Ceiling welding electrodes are most sensitive to current and polarity compliance.
Type and polarity of welding current
As you know, inverters have alternating or direct current at the output, the latter having direct and reverse polarity of connection. Most electrode welding tasks are solved by reverse polarity, in which the electrode is connected to the positive “+” contact, and the part to the negative “-“. The peculiarity of reverse polarity is that electrons, continuously moving from the negative to the positive pole, heat the electrode and its coating, and the metal of the part is heated only by indirect radiation.
With straight polarity, the flow of the electrodes is directed from the electrode to the workpiece and heats it directly. The electrode burns out more slowly, adding small portions of molten metal to the bath. It is unreasonable to expect such a weld to efficiently fill a wide gap joint; straight polarity is used to join well-fitted parts with uniform weld thickness. For example, in this way it is good to weld metal sheets, the seam is minimally noticeable. Due to the higher temperature of the weld pool with straight polarity, it is optimal to weld massive parts for which the maximum heating depth is required.
AC welding is usually characterized by strong spatter of molten metal. The coating of electrodes for AC welding has additives to stabilize the arc and special alloying impurities that make the melt more viscous. The quality of the welded seam when working with electrodes on alternating current is considered the highest for RDS.
Explanation of symbols
There are two main specifications according to which electrodes are marked: domestic GOST 9466 and European standard ISO 2560. Each of them uses its own system of conventions.
Top line – T11-XXX-Y-ZN:
- T – type of electrodes, “E” for MMA welding;
- 11 – metal yield point in MPA;
- XXX – brand of electrodes;
- Y is the diameter of the electrode;
- Z – the purpose of the electrode (Y – low-alloyed and carbonaceous up to 60 kgf / mm, L – alloyed over 60 kgf / mm);
- N – coating thickness.
Bottom line – E-AAA-B-C-D:
- E-AAA – type and standard index that determine the strength characteristics of the seam;
- B – type of coverage;
- C – seam position;
- D – current characteristics.
T XX Y SS 01:
- T – designation of the type of electrodes, “E” – for MMA welding;
- XX is the yield point of the metal in MPA;
- Y – index of resistance to impact destruction in MPA;
- SS – type of electrode coating;
- 0 – index of surfacing productivity, type of current and polarity;
- 1 – seam position index.
Types of coatings
The acidic coating (A) strongly melts the weld pool, due to which the metal is susceptible to cracking when solidified. Currently superseded by rutile acid.
The main (B, C) coating provides a high toughness of the metal in the bath and uniform heating of the part. Such electrodes are intended for welding loaded structures, however, they should be calcined before use to avoid the formation of pores in the metal..
The cellulose (C, C) coating burns out in the arc almost completely, almost without forming a slag. This type of electrodes is one of the few that can weld vertical seams from top to bottom..
The basis of the rutile (P, R) coating is titanium dioxide. The electrodes are optimal for pull-off welding: they ignite well and hold the arc, they evenly weld the metal. Rutile coating provides full control over the welding process and allows you to vary the arc length over a wide range.
Rutile-cellulose (RC, RC) coatings inherit the positive qualities of both types. It is these electrodes that are used for installation in cramped conditions, they leave an aesthetic facial seam that does not require further processing.
Most popular brands
The lower the seam complexity, the more convenient the electrodes are in work, some literally cook themselves. These, first of all, include the famous E46 of the MONOLITH trademark, they are also ANO-36, popularly called “school” electrodes. Cooking with them is really simple: the rutile-cellulose coating holds the arc well even at very low currents, the metal is transferred by small and medium drops, filling the bath well. However, one should not approach critical structures with such electrodes: due to the increased silicon content, the seam loses its plasticity and toughness.
It is recommended to weld joints and joints operating outdoors, including metal-frame structures with hinged cladding, using electrodes, the coating of which contains alloying additives. Such seams have a much higher yield point, and they are subject to corrosion to a much lesser extent due to their low pH value. An example of such a brand is OK-48. They have a basic coating and melt the metal to a viscous-liquid state, setting the optimal degree of heating, and are suitable for welding in any position. If you need a penetration of 12 mm and more, it is recommended to pre-weld the seam with organic coated electrodes such as ANO-7 and ANO-8.
For welding structures with oscillatory types of loads and pressure vessels, OK 61.35 electrodes are used. Their coating is basic, the metal is very tough when melted, the seam is practically insensitive to intercrystalline corrosion.