Every novice welder is faced with the problem of choosing welding consumables. A wide variety of MMA electrodes are available on the market. By the name of the electrodes, it is completely unclear what material they are intended for welding, and in what modes. Let's try to figure out what is the difference between them, and most importantly - how to choose the right electrode for you.
Electrode marking
In addition to the name of the electrodes, you will find a marking on each pack of electrodes. All the necessary information is encrypted in the marking. For electrodes manufactured in Russia, marking of the following type is required:
In the example of marking, the numbers indicate the parameters:
1. Electrode type. Its strength characteristic is 420 MPa. For a better understanding, we can say this - the weld metal made with this electrode, a cross section of 1 mm2, will withstand 42 kilograms to break. That is, the higher the digital value in the marking, the stronger the seam.
The letter "A" after the strength characteristic denotes the increased resistance of the seam to shock and vibration loads. This is due to the reduced content of harmful impurities in the weld metal, namely, sulfur and phosphorus. If the letter "A" is absent, then the electrodes are of ordinary quality.
There is one exception - electrodes for welding special grades of high alloy steels. For these electrodes, instead of the strength characteristic, the chemical composition of the electrode rod is indicated. This is done so that the welder can select electrodes for a specific grade of high-alloy steel - after welding, the seam and the base metal will have the same properties.
2. Electrode name. For product identification. By the name, you can easily purchase the electrodes you need in the future if you have already worked with them.
3. Electrode diametera. Designation of the diameter of the metal rod of the electrode.
4. Purpose of the electrode:
- U - for carbon and low alloy steels
- L - for alloyed structural steels of increased strength
- T - used for alloyed heat-resistant steels
- B - for high-alloy steels with special properties
- H - surfacing electrodes
5. Electrode coating thickness:
- M - thin coating
- С - medium coverage
- D - thick coating
- G - extra thick coating
6. The group of indices assigned to the electrodes according to the test results. In this section, the welder will not gather important information for himself. The choice of electrode is not affected.
7. Electrode coating type:
- A - sour
- R - rutile
- B - main
- C - cellulose
8. Allowable spatial position when welding.
- 1 - welding in all positions
- 2 - in all, except vertical, if welding is done from top to bottom
- 3 - in all, except for vertical and ceiling
- 4 - welding only in the lower position
9. Current type and polarity:
From the table below, the welder can determine which current (DC or AC) and which polarity is applicable for welding with the selected electrodes. The number indicating the type and polarity of the current is in the far right column.
For the use of electrodes on alternating current, an important parameter is the open circuit voltage of the power source - Uxx. This parameter is indicated on the nameplate of any power supply. So, for example, if the number 5 is in the electrode marking, it means that the power supply for welding must have Uxx at least 70V.
In the column for direct current, the polarity is indicated opposite the number.
So, for electrodes with the number 0 in the marking, alternating current is not used, and direct current should only have reverse polarity ("+" on the electrode).
Electrode selection criteria
1. You need to know what kind of metal and how thick you are going to cook. In accordance with this, an electrode is selected for its purpose and diameter.
For simple carbon structural steels (most of all rolled metal products - corners, sheets, channel bars, etc.), we select electrodes with the letter "U" in point 4. For welding stainless steel - the letter "B".
The diameter is selected depending on the thickness of the workpiece. Optimal ratio - the value of the diameter is equal to the value of the thickness of the part.
2. The thickness of the coating affects the quality of the seam itself and the welding process itself. Thin coatings tend to light the arc easily, but the quality of the weld metal is reduced.
The thicker the coating of the electrode, the higher the quality of welding. But with an increase in the amount of coating, the electrode becomes heavier - it becomes more difficult to manipulate it.
3. An important parameter is the type of electrode coating.
Acid-coated electrodes are the cheapest, but also the lowest quality. When using them, cracks may form in the seam, as well as increased metal spatter during welding.
For many welders, rutile-coated electrodes are optimal. They provide good ignition of the arc, maintenance of its burning, good formation of a seam, easily detachable slag crust.
The main coating requires careful preparation of the surface of the parts before welding - remove scale, rust, oil contamination. The main coating is very moody - the arc is difficult to ignite, it is rather difficult to maintain it. But, on the other hand, electrodes with a basic coating give the most durable seams.
The cellulose coating does not tolerate overheating and is destroyed at the slightest sticking of the electrode. Its main advantage is good back bead formation when welding on one side. If you do not have access to the back of the seam, then these coated electrodes will provide better quality.
4. Do not forget about the type and polarity of the current. To avoid problems with starting the arc and maintaining its burning, follow the manufacturer's recommendations in accordance with the table above.