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Preface Manual metal arc welding, known as MMA welding for short, is one of the oldest welding processes still in use today. It goes back to research carried out by Slawjanow who in 1891 was the first to use a metal rod that was simultaneously the arc carrier and the welding additive, rather than the standard carbon electrode that had been used for arc welding up until that point. The first stick electrodes were not coated and were therefore difficult to weld with. Later on the electrodes were coated with materials that made welding easier, protected the weld metal and had a metallurgic affect...

ew/7? The electrode is the welder's tool. The welder moves the arc burning on the electrode in the weld groove side walls, thus melting the edges of the groove (Figure 2). Different current intensities are required depending on the type of groove and the thickness of the parent material. The stick electrodes are available in different diameters and lengths, since their diameter and length determine the current loading possible. Table 1 shows the standardised dimensions as specified in DIN EN 759. Higher welding currents can be used with larger core wire diameters. 2.3 Electrode types There are...

The EWM MMA Primer 2.4 Properties of the coating types The composition and the thickness of the coating have a significant effect on the welding characteristics. This relates both to the stability of the arc and to the material transition during welding and the viscosity of slag and molten bath. The size of the drop being transferred in the arc is of particular significance. Figure 3 shows a scheme diagram of the drop transferin the four basic types of coatings [1]. The cellulose type (Figure 3, c) has a medium- to large-drop material transfer. The coating consists primarily of organic components...

The EWM MMA Primer able to ignite without the core wire touching the workpiece. A spontaneous reignition of this type is always important if the welding process is being frequently interrupted, e.g. with short seams. In addition to the pure rutile type, there are several mixed types in this group of electrodes. Of particular note is the rutilecellulose type (RC) in which part of the rutile has been replaced with cellulose. As cellulose combusts during welding, less slag is produced. This type can therefore also be used for vertical-down welding (vertical-down position). However, it also has good...

The EWM MMA Primer squeezed and is hard to remove. The slag from the RA type itself is porous and breaks into small pieces under the slag hammer, and then these pieces can be easily removed. The special properties of rutile electrodes (R, RR), namely good re-ignition, easy slag removal and good seam appearance, determine their main applications. These are tacking work, as well as welding fillet welds and final passes where complete slag removal and good seam appearance are critical. The rutile-cellulose type (RC) can be welded in all positions including verticaldown. This means it has universal...

A low hydrogen content is important when welding steel with a tendency towards hydrogen-induced crack formation, such as high-tensile steel. The code for the hydrogen content provides the necessary information here. Similar identification systems also exist for high-tensile electrodes (DIN EN 757), creep resistant electrodes (DIN EN 1599) and for stainless electrodes (DIN EN 1600). For creep resistant and stainless electrodes, however, both the strength properties and the creep resistance and corrosion properties of the weld metals must match those of the parent metals. The general rule here...

Electrode designations irrespective to DIN EN 499 EWM HIGHTEC WELDING GmbH Dr. Günter-Henle-Str. 8, D-56271 Mündersbach/Ww., Germany www.ewm.de Codes for the strength and expansion properties of the weld metal Temperature for min. notch impact energy 47J °C No requirements +20 0 -20 -30 -40 -50 -60 1. All positions 2. All positions except vertical-down 3. Butt weld in flat pos., fillet weld in flat and horizontal vertical pos. 4. Butt weld in flat pos. fillet weld in flat pos. 5. Position as for 3. plus vertical down pos. Codes for the impact energy of the weld metal Coating acid cellulose rutile...

The EWM MMA Primer 4.2 Placement of the weld groove side walls The groove edges are normally bevelled by oxyacetylene cutting for unalloyed and low-alloy steels. High-alloy steels and metals that can be MMA welded, can be fusion cut using a plasma arc. It is not absolutely necessary to remove the oxide skin produced by thermal cutting, but may be required in special cases. If there are special requirements in terms of observing low tolerances, mechanical undercutting of the edges of parts to be joined may be recommended. This applies to circumferential welds in particular. The modern options...

a) Continually falling characteristic b) Vertically falling characteristic (constant current characteristic) Figure 11 Characteristics for MMA welding for MMA welding have a falling, static characteristic, and with conventional power sources (such as for the PICO 162, Figure 10) generally continuously falling and with electronic power sources falling vertically in the work area (Figure 11). This ensures that with the unavoidable changes in length of the arc with MMA welding, the most important parameter for the quality of the welding connection – the current intensity – is changed only slightly...

Rectivier (diode) Rectivier (diode) Figure 14 Block diagram of a 3rd generation inverter – clock frequency up to 100kHz into small particles by switching on and off by means of transistorss using a clock frequency of up to 100 kHz. This chopping process is necessary so that the current can be transformed. The chopped current is then discharged as alternating current into a transformer. This produces a square-wave alternate current on the secondary side with the corresponding frequency. This is then rectified and smoothed using a choke. The high frequency of the current being transformed permits...