Submerged Arc Welding

Transcription

1 3. Submerged Arc Welding 2003

2 3. Submerged Arc Welding 26 flux hopper electrode contact piece In submerged arc welding a mineral weld flux layer protects the welding point and the freezing weld from the influence of the surrounding atmosphere, Figure 3.1. The arc burns in a cavity filled with ionised gases and vapours where the droplets from the continuouslyfed wire electrode are transferred into the weld pool. Unfused flux can be extracted from behind the welding head and subsequently recycled. br-er3-01e.cdr Process Principle of Submerged Arc Welding Figure 3.1 Main components of a submerged arc welding unit are: the wire electrode reel, the wire feed motor equipped with grooved wire feed rolls which are suitable for the demanded wire diameters, a wire straigthener as well as a torch head for current transmission, Figure 3.2. Flux supply is carried out via a hose from the flux container to the feeding hopper which is mounted on the torch head. Depending on the degree of automation it is possible to install a flux excess pickup behind the torch. Submerged br-er3-02e.cdr Figure 3.2 AC or DC current supply wire straightener wire feed rolls flux supply indicators wire reel power source welding machine holder Assembly of a Welding Equipment

3 3. Submerged Arc Welding 27 alloy type Mn MnMo Ni NiMo NiV NiCrMo br-er3-03e.cdr commercial wire electrodes S1 S2 S3 S4 S2Mo S3Mo S4Mo S2Ni1 S2Ni2 S2NiMo1 S3NiMo1 main alloying elements Mn Ni Mo Cr V 0,5 1,5 2,0 1,5 2,0 1,5 2,0 0,5 0,5 0,5 0,5 0,5 S3NiV1 1,5 0,15 S1NiCrMo2,5 S2NiCrMo1 S3NiCrMo2,5 0,5 1,5 2,5 2,5 0,6 0,6 0,6 0,8 0,5 0,8 From a diameter of 3 mm upwards all wire electrodes have to be marked with the following symbols: S1 Si Mo S6: : : I _ Figure 3.3 IIIIII Example: S2Si: II _ S3Mo: III arc welding can be operated using either an a.c. power source or a d.c. power source where the electrode is normally connected to the positive terminal. Welding advance is provided by the welding machine or by workpiece movement. Identification of wire electrodes for submerged arc welding is based on the average Mn-content and is carried out in steps of 0.5%, Figure 3.3. Standardisation for welding filler materials for unalloyed steels as well as for fine-grain structural steels is contained in DIN EN 756, for creep resistant steels in DIN pr EN (previously DIN 8575) and for stainless and heat resistant steels in DIN pr EN (previously DIN ). The proportions of additional alloying elements are dependent on the materials to be welded and on the mechanical-technological demands which emerge from the prevailing operating conditions, Figure 3.4. Connected to this, most important alloying elements are manganese for strength, DIN EN 756 mat.-no. S S S S2Si S2Mo S2Ni1 S2Ni2 S3NiMo1 Reference analysis approx. weight % C = 0,08 Si = 0,09 Mn = 0,50 C = 0,10 Si = 0,10 Mn = 0 C = 0,11 Si = 0,15 Mn = 1,50 C = 0,10 Si = 0,30 Mn = 0 C = 0,10 Si = 0,15 Mn = 0 Mo = 0,50 C = 0,09 Si = 0,12 Mn = 0 Ni = 1,20 C = 0,10 Si = 0,12 Mn = 0 Ni = 2,20 C = 0,12 Si = 0,15 Mn = 0 Mo = 0,50 Ni = 0 Properties and application For lower welding joint quality requirements;in: boiler and tank construction, pipe production, structural steel engineering, shipbuilding For higher welding joint quality requirements; in: pipe production, boiler and tank construction, sructural steel engineering, shipbuilding. Fine-grain structural steels up to StE 380. For high-quality welds with medium wall-thicknesses. Fine-grain structural steels up to StE 420. Especially suitable for welding of pipe steels, no tendency to porosity of unkilled steels. Fine-grain structural steels up to StE 420. For welding in boiler and tank construction and pipeline production with creep-resistant steels. Working temperatures of up 500 C. Suitable for higher-strength fine-grain structural steels. For welding low-temperature fine-grain structural steels. Non-ageing. Especially suitable for low-temperature welds. Non-ageing. For quenched and tempered fine-grain structural steels. Suitable for normalising and/or re-quenching and tempering. molybdenum for high-temperature br-er3-04e.cdr strength and nickel for toughness. Figure 3.4

4 3. Submerged Arc Welding 28 Wire electrode DIN EN S2Mo DIN main no. The identification of wire electrodes for submerged arc welding is standardised in DIN EN 756, Figure 3.5. Symbols of the chemical composition: S0, S1...S4, S1Si, S2Si, S2Si2, S3Si, S4Si, S1Mo,..., S4Mo, S2Ni1, S2Ni1.5, S2Ni2, S2Ni3, S2Ni1Mo, S3Ni1.5, S3Ni1Mo, S3Ni1.5Mo br-er3-05e.cdr Figure 3.5 Identification of a Wire Electrode in Accordance with DIN EN 756 During manufacture of fused welding fluxes the individual mineral constituents are, with regard of their future composition, weighed and subsequently fused in a cupola or electric furnace, Figure 3.6. In the dry granulation process, the melt is poured stresses break the crust into large fragments. During water granulation the melt hardens to form small grains with a diameter of approximately 5 mm. lime quarz rutile bauxite magnesite roasting kiln silos balance coke raw material coke molten metal air tapping electrical furnace coal-burning stove granulation tub As a third variant, compressed air is additionally blown into the water tank cylindrical crusher screen foaming air resulting in finely blistered grains with drying oven low bulk weight. The fragments or grains are subsequently ground and br-er3-06e.cdr balance screened thus bringing about the desired grain size. Figure 3.6

5 3. Submerged Arc Welding 29 rutile Mn - ore fluorspar magnesite alloys sintering furnace silos ball mill mixer balance dish granulator gas drying oven heat treatment furnace screen cooling pipe balance br-er3-07e.cdr Figure 3.7 During manufacture of agglomerated weld fluxes the raw materials are very finely ground, Figure 3.7. After weighing and with the aid of a suitable binding agent (waterglass) a pre-stage granulate is produced in the mixer. Manufacture of the granulate is finished on a rotary dish granulator where the individual grains are rolled up to their desired size and consolidate. Water evaporation in the drying oven hardens the grains. In the annealing furnace the remaining water is subsequently removed at temperatures of between 500 C and 900 C, depending on the type of flux. The fused welding fluxes are characterised by high homogeneity, low sensitivity to moisture, good storing properties and high abrasion resistance. An important advantage of the agglomerated fluxes is the relatively low manufacturing temperature, Figure 3.8. The technological properties of the welded joint can be improved by the addition of temperature-sensitive deoxidation and alloying constituents to the flux. Agglomerated fluxes have, in general, a lower bulk weight (lower consumption) which allows the use of components which are reacting among br-er3-08e.cdr Properties uniformity of grain size distribution grain strength homogeneity susceptibility to moisture storing properties resistance to dirt current carrying capacity slag removability high-speed welding properties multiple-wire weldability flux consumption 1) assessment : -- bad, - moderate, + good, ++ very good 2) core agglomerated flux Figure 3.8 Fused fluxes 1) --/+ -/+ -/++ -/+ Agglomerated fluxes 1) -/++ -/++ 2) -- /++ -/+ -/++ -/++

6 3. Submerged Arc Welding 30 MS CS ZS RS AR AB AS AF FB Z MnO + SiO2 min. 50% CaO max. 15% manganese-silicate CaO + MgO + SiO2 min. 55% CaO + MgO min.15% calcium-silicate ZrO 2 + SiO 2 + MnO min. 45% ZrO2 min. 15% zirconium-silicate TiO 2 + SiO2 min. 50% TiO2 min. 20% rutile-silicate Al2O 3+ TiO2 min. 40% aluminate-rutilel Al2O 3+ CaO + MgO Al2O3 min. 40% min. 20% aluminate-basic CaF2 Al2O 3+ SiO 2+ ZrO2 CaF 2 + MgO max. 22% min. 40% min. 30% aluminate-silicate ZrO2 Al2O 3+ CaF2 min. 5% min. 70% aluminate-fluoride-basic CaO + MgO + CaF 2 + Mo SiO2 min. 50% max. 20% fluoride-basic CaF2 min. 15% other compositions themselves during the melting process. However, the higher susceptibility to moisture during storage andprocessing has to be taken intoconsideration. br-er3-09e.cdr Different Welding Flux Types According to DIN EN 760 Figure 3.9 The welding fluxes are, in accordance with their mineralogical constituents, classified into nine groups, Figure 3.9. The composition of the individual flux groups is to be considered as in principle, as fluxes which belong to the same group may differ MS CS ZS RS AR br-er3-10ae.cdr - high manganese and silicon pickup - restricted toughness values - high current carrying capacity/ high weld speed - unsusceptible to pores and undercuts - unsuitable for thick parts - suitable for high-speed welding and fillet welds acidic types - highest current carrying capacity of all fluxes - high silicon pickup - suitable for welding by the pass/ capping method of thick parts with low requirements basic types - low silicon pickup - suitable for multiple pass welding - current carrying capacity decreases with increaseing basicity - high-speed welding of single-pass welds - high manganese pickup/ high silicon pickup - restricted toughness values of the weld metal - suitable for single and multi wire welding - typical: welding by the pass/ capping pass method - average manganese and silicon pickup - suitable for a.c. and d.c. - single and multi wire welding - application fields: thin-walled tanks, fillet welds for structural steel construction and shipbuilding Figure 3.10a substantially with regards to their welding or weld metal properties. In addition to the groups mentioned above there is also the Z-group which allows free compositions of the flux. The calcium silicate fluxes are recognized by their effective silicon pickup. A low Si pickup has low cracking tendency and liability to rust, on the other hand the lower current carrying capacity of these fluxes has to be accepted. A high Si pickup leads to a high current currying capacity up to 2500 A and a deep penetration. Aluminate-basic fluxes have, due to the higher Mn pickup, good mechanical

7 3. Submerged Arc Welding 31 AB AS AF FB Z br-er3-10be.cdr properties. With the application of wire electrodes, as S1, S2 or S2Mo, a low cracking tendency can be obtained. Fluoride-basic fluxes are characterised by good weld metal impact values and high cracking insensitivity. Figures 3.10a and 3.10b show typical properties and application areas for the different flux types. Figure 3.11 shows the identification of a welding flux according to DIN EN 760 by the example of a fused calcium silicate flux. This type of flux is suitable for the welding of joints as well as for overlap welds. The flux can be used for welding of unalloyed and low-alloy steels, as, e.g. general structural steels, as well as for welding hightensile and creep resistant steels. The silicon pickup is % (6), while the manganese pickup is expected to be % (7). Either d.c. or a.c. can be used, as, in principle, a.c. weldability allows also for d.c. power source. The hydrogen content in the clean weld metal is lower than the 10 ml/100 g weld metal. - medium manganese pickup - good weldability - good toughness values in welding by the pass/ capping pass method - application field:unalloyed and low alloyed structural steels - suitable for a.c. and d.c. - applicable for multilayer welding or welding by the pass/ capping pass method - mainly neutral metallurgical behavior - manganese burnoff possible - good weld appearance and slag removability - to some degree suitable for d.c. - recommended for multi layer welds for high toughness requirements - application field: high-tensile fine grain structural steels, pressure vessels, nuclear- and offshore components - suitable for welding stainless steels and nickel-base alloys - neutral behaviour as regards Mn, Si and other constituents - mainly neutral metallurgical behaviour - however, manganese burnoff possible - highest toughness values right down to very low temperatures - limited current carrying capacity and welding speed - recommended for multi layer welds - application field: high-tensile fine-grain structural steeels - all other compositions Figure 3.10b welding flux DIN EN 760-SF CS 1 67 AC H10 DIN main no. flux/ welding method of manufacture F fused A agglomerated M mechanically mixed flux flux type (figure 3.9) hydrogen content (table 4) type of current metallurgical behaviour (table 2) flux class 1-3 (table 1) br-er3-11e.cdr Figure 3.11 Identification of a Welding Flux According to DIN EN 760

8 3. Submerged Arc Welding 32 The flux classes 1-3 (table 1) explain the suitability of a flux for welding certain material groups, for welding of joints and for overlap welding. The flux classes also characterise the metallurgical material behaviour. In table 2 defines the identification table 1 flux class unalloyed and low-alloyed steel general structural steel high-tensile & creep resistant steels stainless and heat resistant steels Cr- & CrNi steels welding of joints hardfacing pickup of elements as C, Cr, Mo br-er3-12e.cdr Figure 3.12 table 4 identification H5 H10 H15 table 2 metallurgial behaviour burnoff pickup or burnoff pickup identification figure Parameters for Flux Identification According to DIN EN hydrogen content ml/100g all-weld metal max proportion flux in all-weld metal % over 0,7 0,5 up to 0,7 0,3 up to 0,5 0,1 up to 0,3 0 up to 0,1 0,1 up to 0,3 0,3 up to 0,5 0,5 up to 0,7 over 0,7 figure for the pickup or burn-off behaviour of the respective element. Table 4 shows the gradation of the diffusible hydrogen content in the weld metal, Figure Figure 3.13 shows the identification of a wire-flux combination and the resultant weld metal. It is a case of a combination for multipass welding where the weld br-er 3-13e.cdr wire-flux combination DIN EN S 46 3 AB S2 standard no. wire electrode and/or wire-flux combination for submerged arc welding Figure 3.13 strength and fracture strain (table1 and 2) Identification of a Wire-Flux Combination According to DIN EN 756 chemical composition of the wire electrode type of flux (figure 3.10) impact energy (table 3) metal shows a minimum yield point of 460 N/mm² (46) and a minimum metal impact value of 47 J at 30 C (3). The flux type is aluminatebasic (AB) and is used with a wire of the quality S2.

9 3. Submerged Arc Welding 33 The tables for the identification of the tensile properties as well as of the impact energy are combined in Figure table 1 identification table br-er3-14e.cdr table 2 identification 2T 3T 4T 5T identification temp. for minimum impact energy 47J C Figure 3.14 Identification for strength properties of multipass weld joints minimum yield point n/mm minimum base metal yield strength N/mm tensile strength N/mm up to up to up to up to up to 720 minimum fracture strain % Identification for strength properties of welding by the pass/ capping pass method welded joints minimum tensile strength N/mm Identification for the impact energy of clean all-weld metal or of welding by the pass/ capping pass method welded joints Z no demands A The chemical composition of the weld metal and the structural constitution are dependent on the different metallurgical reactions during the welding process as well as on the used materials, Figure The welding flux influences the slag viscosity, the pool motion and the bead surface. The different combinations of filler material and welding flux cause, in direct dependence on the weld parameters (current, voltage), a different melting behaviour and also different chemical reactions. The dilution with the base metal leads to various strong weld pool reactions, this being dependent on the weld parameters. The diagram of the characteristics for 3 different welding fluxes assists, in dependence of the used wire electrodes, to determine the pickup and burn-off behaviour of the element manganese, Figure For example: A welding flux with welding flux slag br-er 3-15e.cdr Figure 3.15 droplet reaction dilution weld pool reaction weld metal Metallurgical Reactions During Submerged Arc Welding welding filler metal welding data base metal welding data welding data

10 3. Submerged Arc Welding 34 Mn-pickup S1 % 2,0% 3,0% Mn in wire S2 S3 S4 S5 S6 the mean characteristic and when a wire electrode S3 is used, has a neutral point where neither pickup nor burn-off occur. Mn-burnoff br-er 3-16e.cdr Figure 3.16 Manganese-Pickup and Manganese-Burnoff During Submerged Arc Welding The pickup and burn-off behaviour is, besides the filler material and the welding flux, also directly dependent on the welding amperage and welding voltage, Figure By the example of the selected flux a higher welding voltage causes a more steeply descending manganese characteristic at a constant neutral point. Silicon pickup increases with the increased voltage. The influence of current and voltage on the carbon content is, as a rule, negligible. Inversely proportional to the voltage is the rising characteristic as regards manganese in dependence on the welding current, Figure Higher currents cause the characteristic curve to flatten. As the welding voltage, the welding current also has practically no influence on the location of the neutral point. Silicon pickup decreases with increasing current intensity. pickup/ burnoff X in weight % br-er3-17e.cdr Figure 3.17 weld flux LW 280 current intensity 580 A welding speed 55 cm/min % Mn wire % Si wire neutral point % C wire

11 3. Submerged Arc Welding 35 weld flux LW 280 arc voltage 29 V welding speed 55 cm/min The Mn-content of the weld metal can be determined by means of a welding flux diagram, Figure neutral point In this example, the two points on the pickup/ burnoff X in weight % % Mn wire % Si wire 450 A % C wire axis which determine the flux characteristic are defined for the parameters 600A welding current and 29V welding voltage, with the aid of the auxiliary straight line and the neutral point curve (Mn NP ). In this case, the two points are positioned at 0.6% Mn and 1.25% Mn SZ. Dependent on the manganese content of the used filler material, the pickup or burn-off con- br-er3-18e.cdr tents can be recognized by the reflection with respect to the characteristic line Figure 3.18 (0.38% Mn-pickup with a wire containing 0.5%Mn, 0.2% Mn-burnoff with a wire containing 1.75%Mn). flux diagramm LW 280, manganese wire electrode 4 mm Ø acc. to Prof. Thier The structure of the characteristic line for the determination of the silicon example: I = 580 A U = 29 V Mn SZ1 = 0.48 % Mn Mn = 1.69 % Mn SZ2 pickup content, is, in principle, exactly the same as described above, Figure As silicon has only pickup properties and therefore no neutral point exists, the second auxiliary straight line must be considered for the determination of the second characteristic br-er3-19e.cdr line point. Figure 3.19

12 3. Submerged Arc Welding 36 Weld preparations for multipass fabrication are dependent on the thickness of the flux diagramm LW 280, silicon wire electrode 4 mm Ø acc. to Prof. Thier example: I = 580 A U = 29 V Si = 0.16 % Si SZ plates to be welded, Figure If no root is planned during weld preparation and also no support of the weld pool is made, the root pass must be welded using low energy input. auxiliary straight line br-er3-20e.cdr Figure 3.20 auxiliary straight line When welding very thick plates which are accessible from both sides, the double-u butt weld may be applied, Figure Before the opposite side is welded, the root must be milled out (gouging/sanding). This type of weld cannot be produced by flame cutting and is, as milling is necessary, more expensive, although exact weld preparation and correct selection of the welding parameters lead to a high weld quality. Another variation of heavy-plate welded joints is the so-called steep single-v butt weld, Figure The very steep edges keep the welding volume at a very low level. This technique, however, requires the application of special narrow-gap torches. The geometry during slag detachment and preparation geometry br-er 3-21e.cdr Figure 3.21 weld buildup and manual metal arc welding manual metal arc welding manual metal arc welding Welding Procedure Sheets for Single-V Butt Welds, Single-Y Butt Welds with Broad Root Faces and Double-V Butt Welds

13 3. Submerged Arc Welding 37 preparation geometry br-er3-22e.cdr Figure 3.22 weld buildup side 1 side 2 Welding Procedure Sheet for Double-U Butt Welds manual metal arc welding turning and sanding manual metal arc welding turn turn turn also during reworking weld-related defects may cause problems. Here, high demands are made on torch manipulation and process control. Special narrow-gap welding fluxes facilitate slag removal. The most important welding parameters as regards weld bead formation are welding current, voltage and speed, Figure A higher welding current causes higher deposition rates and energy input, which leads to reinforced beads and a deeper penetration. The weld width remains roughly constant. The increased welding voltage leads to a longer arc which also causes the bead to be wider. The change in welding speed causes - on both sides of an optimum - a decrease of the penetration depth. At lower weld speeds, the weld pool running ahead of the welding arc acts as a buffer between arc and base metal. At high speeds, the energy per unit length decreases which leads, besides lower penetration, also to narrower beads. GMA welding GMA welding welding welding oscillated br-er3-23e.cdr Welding Procedure Sheet for Square-Edge Welds Figure 3.23

14 3. Submerged Arc Welding 38 penetration depth t in mm p br-er3-24e.cdr constant: w constant: I constant: I t p welding current ( I) arc voltage (U) w t e welding speed (v) plate thickness: wire electrode: flux: t p w weld width b in mm consumption kg flux / kg wire consumption kg flux/ kg wire br-er3-25e.cdr 2,4 2,2 2,0 1,8 1,6 1,4 1,2 0,8 0,6 0,4 0,2 0 1,6 1,4 1,2 0,8 0,6 0,4 0, A) flat weld - I square butt joint fused composition fluxes agglomerated fluxes current intensity (A) B) fillet weld fused composition fluxes agglomerated fluxes current intensity (A) Figure 3.24 Figure 3.25 Weld flux consumption is dependent on the selected weld type, Figure Due to geometrical shape, the flux consumption of a fillet weld is significantly lower than that of a butt weld. Because of their lower bulk weight, the specific consumption of agglomerated fluxes is direction of welding lower than that of fused fluxes. Two different control L 1 L 2 concepts allow the regulation of the arc L 3 length (the principle is shown in Figure 3.26). The applica- br-er3-26e.cdr Figure 3.26 Control of the Arc Length tion of the appropriate control system is

15 3. Submerged Arc Welding 39 U U 0 U S U U 0 U S br-er3-27e.cdr drop (slightly descending characteristic). At a constant wire feed speed the initial arc length is independently regulated by the increased burn-off rate which again is a consequence of the high current. The reaction of the internal regulation to process disturbance is very fast. This process is self regulating and does not require any machine expenditure. I A A I S I K I external regulation ( U-regulation) U Figure 3.27 U A I S internal self regulation I A ( I-regulation) I I I I I dependent on the available power source characteristics. The external regulation of the arc length by the control of the wire feed speed requires a power source with a steeply descending characteristic, Figure In this case, the shortening of the arc caused by some process disturbance, entails a strong voltage drop at a low current rise. As a regulated quantity, this voltage drop reduces the wire feed speed. Thus, the initial arc length can be regulated at an almost constant deposition rate. In contrast, the internal regulation effects, when the arc is reduced, a strong current rise at a low voltage backing flux ceramic backing bar flux copper backing In submerged arc welding of butt joints, it is, depending on the weld preparation, necessary to support the br-er3-28e.cdr Figure 3.28 Examples of Weld Pool Backups

16 3. Submerged Arc Welding 40 liquid weld pool with a backing, Figure This is normally done with either a ceramic or copper backing with a flux layer or by a backing flux. Dependent on the shape of the backing bar, direct formation of the underside seam can be achieved. When welding circumferential tubes, b 1 α 1 = 0 br-er3-29e.cdr Figure α 2 α 3 b 2 b 3 t 1 t 2 t 3 inclusion the inclination angle of the electrode has a direct influence onto the formation of the weld bead, Figure For external as well as for internal tube welds, the best weld shapes may be obtained with an adjusted angular position of the torch. If the advance is too low, the molten bath runs ahead and produces a narrow weld with a medium-sized ridge, too high an advance causes the flowback of the molten bath and a wide seam with a formed trough in the centre. The processes described here for external tube welds are, the other way round, also applicable to internal tube welds. To increase the efficiency of submerged arc weld- single wire tandem ing, different process variations are applied, Figure In multiwire welding, where up parallel twin wire tandem, twin wire to 6 wires are used, each welding torch is operated from a separate power source. In twin wire br-er3-30e.cdr Figure 3.30 Process Variations of Submerged-Arc Welding

17 3. Submerged Arc Welding 41 welding, two wire electrodes are connected in one iron powder/ chopped wire cold wire torch and supplied from one power source. Dependent on the application, the wires can be hot wire strip arranged in a parallel or in a tan- br-er3-31e.cdr Process Variations of Submerged-Arc Welding dem. Figure 3.31 In submerged arc welding with iron powder addition can the deposition rate be substantially increased at constant electrical parameters, Figure The increased deposition rate is realised by either the addition of a currentless wire (cold wire) or of a preheated filler wire (hot wire). The use of a rectangular strip instead of a wire electrode allows a higher current carrying capacity and opens the method also for the wide application range of surfacing. However, the mentioned process variations can be combined over wide ranges, where the electrode distances and positions have to be appropriately optimised, Figure Current type, polarity, geometrical coordination of the individual weld heads and the selected weld parameters also have substantial influence on the weld result. tandem welding three-wire welding three-wire, hot wire welding four-wire welding br-er3-32e.cdr Figure 3.32 = = = WH 1. WH 1. WH WH 2. WH HW WH 3. WH 3. WH

18 3. Submerged Arc Welding 42 deposition rate weld metal 100 kg/h single wire tandem A 3500 current intensity 12 kg/h 9 6 single wire+ metal powder single wire+ hot wire double wire 4,0 mm 5,0 mm 3,0 mm A 800 current intensity three-wire voltage = 30 V four-wire speed = 40 cm/min wire protrusion = 10d length The description of these individual process variations of submerged arc welding shows that this method can be applied sensibly and economically over a very wide operating range, Figure It is a high-efficiency welding process with a deposition rate of up to 100 kg/h. Due to large molten pools and flux application positional welding is not possible. br-er3-33e.cdr Figure 3.33 When more than one wire is used in order to obtain a high deposition rate, arc interactions occur due to magnetic arc blow, Figure Therefore, the selection of the current type (d.c. or a.c.) and also sensible displacements phase between the individual welding torches are very important. ( _ ) (_ ) + + ( ) + ( + ) br-er3-34e.cdr Figure 3.34 elektrode arc + _ workpiece _ + Magnetic Interaction of Arcs at Tandem Welding + _