An investigation on bridging larger welding gaps between workpieces occurring in practice due to structural requirements or to defects in weld edge preparation is described. Some characteristic cases from practice where a larger root gap should be bridged or the space between two or three workpieces should be filled with a greater quantity of filler material are described. Submerged-arc welding with twin-wire and triple-wire electrodes was applied.Opisano je istraživanje premoštenja zazora između komada za zavarivanje, koji se u praksi pojavljuju zbog konstrukcijskih zahtijeva ili grešaka prilikom pripreme stranica šavova. Opisani su neki karakteristični primjeri iz prakse, gde je bilo potrebno širi zazor ili prostor između dva ili tri komada za zavarivanje premostiti pomoću veće količine dodatnog materiala. Upotrebljeno je zavarivanje pod prahom uz upotrebu dvostruke i trostruke žičane elektrode

J. Tušek

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METALURGIJA 42 (2003) 1, 21-25 21J. TUŠEK: BRIDGING OF WELDING GAPS IN WELDING WITH A MULTIPLE-WIRE ELECTRODEReceived - Primljeno: 2002-02-20Accepted - Prihvaćeno: 2002-06-15Original Scientific Paper - Izvorni znanstveni radISSN 0543-5846METABK 42 (1) 21 (2003)UDC - UDK 621.791.573.5.053=20ŠEKJ. Tušek, Faculty of Mechanical Engineering, Ljubljana, SloveniaBRIDGINGOF WELDING GAPS IN WELDING WITH A MULTIPLE-WIRE ELECTRODEAn investigation on bridging larger welding gaps between workpieces occurring in practice due to structuralrequirements or to defects in weld edge preparation is described. Some characteristic cases from practicewhere a larger root gap should be bridged or the space between two or three workpieces should be filled with agreater quantity of filler material are described. Submerged-arc welding with twin-wire and triple-wire electrodeswas applied.Key words: bridging, welding gap, weld root, twin arc, joint contact tube, multiple-wire electrodePremoštenje zazora pri zavarivanju s višežičanom elektrodom. Opisano je istraživanje premoštenja zazoraizmeđu komada za zavarivanje, koji se u praksi pojavljuju zbog konstrukcijskih zahtijeva ili grešaka prilikompripreme stranica šavova. Opisani su neki karakteristični primjeri iz prakse, gde je bilo potrebno širi zazor iliprostor između dva ili tri komada za zavarivanje premostiti pomoću veće količine dodatnog materiala. Upotrebljenoje zavarivanje pod prahom uz upotrebu dvostruke i trostruke žičane elektrode.Ključne riječi: premošćivanje, zazor vara, korijen vara, dvostruki električni luk, zajednička kontaktna vodilica,višežičana elektrodaINTRODUCTIONIn welding a root pass of a butt joint, the weld edgepreparation is very important to perform high-quality weld-ing. This particularly applies to automatic submerged arcwelding with a twin wire or triple wire and for gas shieldedarc welding where no transverse movement of the weld-ing gun is possible. In welding of thin and medium thickplates, any tiny defect in the weld edge preparation, evenup to 1 mm size, may be fatal. In practice, there are somenonstandard welded joints with uncommon welding gaps.LITERATURE REVIEWBridging of welding gaps and filling up of larger weldedjoints occur in practice quite often, but they remain almostuntreated in literature.In spite of a quite detailed survey of journals and con-ference papers, only one article could be found in litera-ture which explicitly reports on bridging of root gaps insubmerged arc welding [1]. The author welded root passesbetween workpieces of 5 to 20 mm in thickness with gapsof 0 to 10 mm in width. As filler material for bridginggaps, he applied a wire with a diameter of 5 mm and, inaddition to a shielding flux, also metal powder (∅  1 mm).The investigations conducted led to a conclusion that insubmerged arc welding with the metal powder addition, itis possible to bridge welding gaps twice as large as thewire diameter. It is, of course, necessary to weld with ad-equate welding parameters, particularly high arc voltage(40 - 48 V), i. e., with a long arc.Welding of larger welded joints or of passes for which agreater quantity of filler material is required has been some-what more often discussed in the literature. In the first group,there is welding with a strip electrode. In the literature thereare some papers describing a successful application of sub-merged arc welding with a strip electrode, still the processhas not been widely used in practice [2-6].The second group of processes, with which bridgingof welding gaps to a certain extent and especially increas-ing of  melting rate and consequently easier filling of weld-ing grooves  can be achieved, consists of submerged-arcwelding with additional metal powder [7-11].The third group of processes, which permit bridgingof welding gaps and make easier the making of filler passes,includes different submerged-arc welding processes withMETALURGIJA 42 (2003) 1, 21-2522J. TUŠEK: BRIDGING OF WELDING GAPS IN WELDING WITH A MULTIPLE-WIRE ELECTRODEmultiple wires. We are acquainted with processes, such asmultiple-wire welding, multiple-head welding and weld-ing with an additional hot and cold wire [12-16].NONSTANDARD WELDING EDGES AND GAPSFigure 1. shows eight nonstandard welded joints withuncommon welding gaps, which in some cases require evenan asymmetrical weld. For each welded joint an ideal weldshape is indicated as well. This, however, can not be ac-complished with a single-wire electrode or in a single run.An approximately ideal weld shape may be obtained  bywelding  with  a multiple-wire electrode, with a suitablearrangement of the wires in the joint contact tube.In the first four cases (Figure 1. - A, B, C, D) a com-paratively large welding gap could be bridged by weldingwith a twin-wire electrode. The wire arrangement in thecontact tube should be parallel to the welding direction(Figure 2.).The optimum wire diameter, distance between the wiresand welding parameters should be selected in order to pro-duce a uniform weld with a flat and smooth weld face.Welds A, C, and D (Figure 1.) are symmetrical, whichmeans that melting conditions in both arcs, if the twin-wire electrode was used, were the same. The wire exten-sion lengths and the arc lengths were the same too.Case B (Figure 1.) is somewhat specific. The arc lengthsand the  wire  extension lengths of two wires were differ-ent (Figure 3.). Taking into account that the wire feedspeeds of both wires and the currents in both wires werethe same, it may be concluded that the electric resistancein the first arc  was higher than in the second one. Thismeans that the power of the first arc was higher than thatof the second one and that a larger quantity of the parentmetal was melted, which was very favourable in this case.In cases E, F, H, and G (Figure 1.), the welds were weldedwith a triple-wire electrode. In three cases (F, G, H) a com-paratively large welding gap with low penetration is required;therefore, the wire arrangement should be parallel in thewelding direction (Figure 4.). The distance between the wiresand the welding parameters should be selected so as to makea uniform weld with a smooth weld face.In case E (Figure 1. E) an asymmetrical weld is to bemade. This can be obtained by welding with a triple-wireelectrode with triangular wire arrangement (Figure 5.).The left workpiece (Figure 1. E) had a much highermass than the right one, and consequently a stronger heatdissipation. Two wires were, therefore, travelling alongthe thicker workpiece, and only one wire along the thinnerworkpiece (Figure 7.).WIRE ARRANGEMENT IN THE CONTACT TUBEBecause of the intricate shapes of the joint  assemblies(Figure 1.), it is recommended to use two or three wires ina joint contact tube. The wires may be arranged in a lineor in a triangular form in the case of three wires.A                                      BC                                      DE                                       FG                                       HFigure 1.Slika 1.Non-standard welded joints with uncommon welding gapsNenormirani zavari s neuobičajenim rasporom šavovaFigure 2.Slika 2.Wire arran-gement in the contact tube in  welding  with a twin-wire electro-de: 1 - weldi-ng wire; 2 - arc; 3 work-piece; 4 - wel-ding directi-on;  - distan-ce between wires;  - ele-ctrode exte-nsion length;  - wire dia-meterRaspored ži-ca u kontakt-noj vodilici prilikom za-varivanja s dvostrukom žičanom ele-ktrodom: 1 - žica za zava-rivanje 2 - e-lektrični luk; 3 - radni ko-mad; 4 - smj-er zavarivanja;  - udaljenost između žica; - dužina iz-vučenog (slobodnog) djela žice;  - promjer žicebLdb L dwwb21dL344METALURGIJA 42 (2003) 1, 21-25 23J. TUŠEK: BRIDGING OF WELDING GAPS IN WELDING WITH A MULTIPLE-WIRE ELECTRODEFigure 2. shows the contact tube with two wires. Thewires were arranged parallel to reference to the weldingdirection and had the same wire feed speed, a joint powersource, and a joint regulation. The distance between thewires was determined taking into account the welding pa-rameters, the form of weld edge, and the diameter of thewelding wire. The minimum distance was equal to 5 mmand the maximum one to 9 mm. In welding with greaterdistances between the wires, a uniform weld of high qual-ity and nice shape was difficult to obtain. In welding withsmaller distances, the welding gap was difficult to bridgeand a much too narrow weld was obtained.The welding parameters and the distance between thewires shall be chosen in such a way that a uniform cavitylarge enough to permit all the necessary metallurgical,chemical, and physical processes between the weld pool,slag, and gases.In bridging of a welding gap of a lap joint or a buttjoint composed of two different thicknesses (Figure 1. B),a twin wire can be used (Figure 3.). In this case too, thewires had the same wire feed speed and carry the samecurrent. The resistance in the two wires being different,the arc lengths and arc powers were different, which af-fected the weld shape.In welding of two or more workpieces using a large gap,three wires arranged in the line or in the triangular form canbe used. The wire arrangement depends on the type ofwelded joint to be made. Figure 4. shows the contact tubewith three wires arranged in the line and Figure 5. in theform of a triangle. In both cases (Figures 4. and 5.), the21dwL oL wv  = w1 vI  = IR  + R  = R  + RL  < LL  > LR  < R  P  < Pw21 2w1 o1 w2 o2w1 w2o1 o2o1 o2o1 o2Figure 3.Slika 3.Asymmetrical welded joint made with a twin-wire elec-trode: 1 - first wire; 2 - second wire;  - wire diameter;  - wire speed;  - current;  - electric resistance in wire;  - electric resistance in arc;  wire extension length;  - arc length;  - arc powerNesimetričan zavar, zavaren pomoću dvostruke žičane elektrode: 1 - prva žica; 2 -  druga žica;  - promjer žice;  - brzina žice;  - električna struja;  električni otpor u žici;  - električni otpor u luku;  - dužina izvučenog (slobodnog) djela žice;  - dužina električnog luka;  - jakost električnog lukad vI R RL LPdI RR LL Pw ww ow ooww wo wo ovLA1 243Figure 4.Slika 4.Contact tube with parallel arrangement of  three wires; 1 - welding wires; 2 - view ; 3 - contact tube; 4 - welding di-rection;  - wire extension lengthKontaktna vođica s tri usporedno postavljene žice; 1 - žice za zavarivanje; 2 - pogled ; 4 - smjer zavarivanja;  - dužina izvučenog djela žiceALA Lb 221b130° - 180°Figure 5.Slika 5.Triangular wire arrangement for welding asymmetrical workpieces;  - distance between wires; 1 - welding wires; 2 - contact nozzle; 3 - possible welding directionRaspored žica u obliku trokuta za zavarivanje nesimetri-čnih radnih komada;  - udaljenost između žica; 1 - žice za zavarivanje; 2 - kontaktna vođica; 3 - mogući smjer za-varivanjabbMETALURGIJA 42 (2003) 1, 21-2524J. TUŠEK: BRIDGING OF WELDING GAPS IN WELDING WITH A MULTIPLE-WIRE ELECTRODEwires had the same wire feed speed and a joint regulation,and  a single power source was used. With reference to  thewelding direction, the line of wires can be arranged in thesame direction, at a right angle, or at an angle ranging be-tween 0 ° and 90 °. Figure 5. shows possible welding direc-tions with reference to the wire arrangement for  the devicewith three wires arranged in the form of a triangle.MACRO SECTIONS OF THE WELDSFigure 6. shows macro sections of root passes weldedwith the same parameters, the same distance between thewires, but with different sizes of welding gaps. The weld-ing gaps were 0 mm, 2 mm, 3.5 mm, and 6 mm wide.There was no preparation of the welding edges.Regarding the fact that the welding parameters wereconstant during welding, the energy input in the filler ma-terial and the parent metal was constant too.Consequently, the melting rate, i. e., the weight of thefiller material melted in a unit of time, was constant aswell. Because of a specific “direct” melting of the parentmetal the quantity of the parent metal melted even slightlyincreased with an increase in the welding gap width.The weld geometry changed as well with a change ofthe welding gap. The penetration depth increased, the weldreinforcement decreased whereas the penetration width prac-tically did not change with the increase in the welding gap.On the basis of the results obtained, the optimum dis-tance between the wires was established. For plates of 10mm in thickness and wires of 2 mm in diameter, this dis-tance was equal to 7 mm. The optimum welding param-eters depended not only on the wire diameter andworkpiece thickness but also on the welding gap widthand were in the range showed in Figure 3.Figure 7. shows a welded joint (Figure 1. E) and thearrangement of three wires in welding with a triple-wireelectrode. With the triple-wire electrode, the problem wassolved ideally by welding the workpieces in a single pass.Two workpieces with different masses and of differentshapes were welded together. In the thicker workpiece,dissipation  of heat was much stronger than in the  thinnerone, therefore a risk of excessive penetration in the thin-ner workpiece and a too small penetration depth in thethicker one occurred. With a single-wire electrode, theworkpieces shown can be multi-pass welded.Two wires, together with the arcs, travel one after an-other over the thicker workpiece, introduce into it moreenergy and melt it. In this way, a penetration deep enoughcan be obtained on the thicker workpiece. Over the thin-ner workpiece, only one wire travels, introduces into itless energy which, with satisfactory penetration depth,causes less deformation. With an adequate choice of thedistances between  wires  b1  and b2 (Figure 7.), a uniform,asymmetric weld with a nice weld face was obtained.Welding is carried out with a relatively high welding speedand a low energy input. The macro section of the relevantwelds is shown in Figure 8.CONCLUSIONSWith the investigation presented in the present paper itwas established very clearly that welding gaps and weld-ing edges can be bridged and multiple-wire welded withdifferent number of wires and a different arrangement ofthe wires in the joint contact tube.Conclusions can be summarised as follows:1. The weld geometry is influenced mostly by the wirearrangement in the contact tube;2. The most satisfactory results of bridging root gaps canbe obtained in twin-wire electrode welding when theb2b 1AView A1Figure 7.Slika 7.Scheme of triple-wire electrode welding of two workpie-ces of different thickness and shape;  - distance between wires; 1 - welding directionShematski prikaz zavarivanja s trostrukom žičanom elektrodom dva različito debela i različito oblikovana radna komada;  - udaljenost između žica; 1 - smjer zava-rivanjabbFigure 8.Slika 8.Macrosection of an asymme-trical weld.  = 3 x 260 A,  = 29 V,  = 0.7 m/min,  = 2 mmMakrografska epruveta nesi-metričnog zavara;  = 3x260 A,  = 29 V,  = 0.7 m/min,  = 2 I Uv dIU v dw ww w10 mm10 mmFigure 6.Slika 6.Submerged arc welds made with a twin-wire electrode in  various welding gaps:  = 2 x 200 A,  = 32 V,  = 0.5 m/min,   = 2 mm;  workpiece thickness = 10 mmZavarivanje pod prahom s dvostrukom žičanom elektro-dom u različitim zazorima šavova:  = 2 x 200 A,  = 32 V,  = 0.5 m/min,  = 2 mm; debljina radnog komada = 10 mmI U vI Udwww wdvMETALURGIJA 42 (2003) 1, 21-25 25J. TUŠEK: BRIDGING OF WELDING GAPS IN WELDING WITH A MULTIPLE-WIRE ELECTRODEREFERENCES1. Y. A. Chernov, V. I. Mishenko, A. P. Pavlov: Svarochnoe proizvod-stvo, 62 (1981), 11, 27-282. H. Boske, J. Keller, V. Komiichau: Schweißtechnik, Berlin, 39(1980) 8, 346-3473. U. Franz, G. Maechtig, G. Moebius, M. Feverhak: Schweißtechnik,Berlin, 21 (1971) 12, 535-5394. F. Eichhorn, K. Blasig: Schweißen und Schneiden, 36 (1984), 5,205-2095. L. I. Oparin: Avtomaticheskaja Svarka, 22 (1970), 3, 19-236. W. Huwer: Industrie-Anzeiger, 95 (1973), 59, 1391-13937. R. F. Arnoldy: Welding Journal, 42 (1963), 11, 885-8918. R. J. De Haeck: Welding Journal, 50 (1971), 10, 689-7009. S. Sakaguchi, T. Yamaguchi, C. Shiga: One Pass Submerged ArcWelding with Flux Containing Iron Powder for Thick Steel Plates.Doc. XII-1156-90. International Institute of Welding, Montreal, 199010. U. Strand: Svetsaren, 43 (1989), 1, 3-411. D. S. Taylor: Review International, 10 (1991), 1, 9-1112. T. Ashton: Welding Journal, 33 (1954) 4, 350-35513. H. Heinke, H. Schlerfer, U. Franz, H. D. Wendler: Schweißtechnik,Berlin, 17 (1967), 9, 386-39214. J. Tušek: Functions of Electrodes in the Formation of Weld in Triple-Electrode Submerged Arc Welding. Doc. 212-696-88. InternationalInstitute of Welding, Wien, 198815. V. Kralj, J. Tušek: Varilna tehnika, 35 (1986), 1, 5-1016. J. Sordi: Oerlikon-Schweißmitteilungenwires are arranged in the direction transverse to thedirection of welding;3. In triple-wire electrode welding, larger gaps can be“filled” in a single pass;4. With the triangular wire arrangement, asymmetricwelds can be obtained, which is very favourable inwelding of workpieces of different masses and shapes;5. Multiple-wire welding shows higher energy efficiency;the energy input in the weld per unit volume is lower.

Premoštenje zazora pri zavarivanju s višežičanom elektrodom

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