Narrow Gap Welding, Electrogas - and. Electroslag Welding

Transcription

1 6. Narrow Gap Welding, Electroga - and Electrolag Welding

2 6. Narrow Gap Welding, Electroga- and Electrolag Welding 77 Up to thi day, there i no univeral agreement about the definition of the term Narrow Gap Welding although the term i actually elf-explanatory. In the international technical Proce characteritic: - narrow, almot parallel weld edge. The mall preparation angle ha the function to compenate the ditortion of the joining member - multipa technique where the weld build-up i a contant 1 or bead per pa - uually very mall heat affected zone (HAZ) caued by low energy input Advantage: - profitable through low conumption quantitie of filler material, ga and/ or powder due to the narrow gap - excellent quality value of the weld metal and the HAZ due to low heat input - decreaed tendency to hrink br-er6-01e.cdr Figure 6.1 Narrow Gap Welding Diadvantage - higher apparatu expenditure, epacially for the control of the weld head and the wire feed device - increaed rik of imperfection at large wall thicknee due to more difficult acceibility during proce control - repair poibilitie more difficult ISF 00 literature, the proce characteritic mentioned in the upper part of Figure 6.1 are frequently connected with the definition for narrow gap welding. In pite of thee definition difficultie all quetion about the univerally valid advantage and diadvantage of the narrow gap welding method can be clearly anwered. The numerou variation of narrow gap welding are, in general, a further development of the conventional welding technologie. Figure 6. how a claification with emphai on everal important proce characteritic. Narrow gap TIG welding with cold or hot wire addition i mainly applied a an orbital proce method or for the joining of highalloy a well a nonferrou metal. Thi method i, however, hardly applied in the practice. The other procee are more widely pread and are explained in detail in the following. ubmerged arc electrolag narrow narrow gap welding gap welding traightened wire electrode (1P/L, P/L, P/L) ocillating wire electrode (1P/L) twin electrode (1P/L, P/L) lengthwie poitioned trip electrode (P/L) br-er6-0e.cdr Figure 6. linearly ocillating filler wire triphaped filler and fuing feed ga-hielded metal arc narrow gap welding electroga linearly ocillating wire electrode electroga bent, longitudinally poitioned trip electrode MIG/MAGprocee (1P/L,P/L,P/L) Survey of Narrow Gap Welding Technique Baed on Conventional Technologie tungten innert ga-hielded narrow gap welding hot wire addition (1P/L, P/L) cold wire addition (1P/L, P/L) flat poition vertical up poition all welding poition ISF

3 6. Narrow Gap Welding, Electroga- and Electrolag Welding 7 In Figure 6., a ytematic ubdiviion of the variou GMA narrow gap technologie i hown. In accordance with thi, the fundamental ditinguihing feature of the method i whether the proce i carried out with or without wire deformation. Overlap in the tructure reult from the application of method where a ingle or everal additional wire are ued. While mot method are uitable for ingle pa per layer welding, other method require a weld build-up with at leat two pae per layer. A further ubdiviion i made in accordance with the different type of arc movement. D GMA narrow gap welding no wire-deformation br-er6-0e.cdr long-wire method (1 P/L, P/L) thick-wire method (1 P/L, P/L) twin-wire method rotation method explanation: P/L: Pa/Layer GMA narrow gap welding wire-deformation tandem-wire method (1 P/L, P/L, P/L) twited wire method coiled-wire method corrugated wire method with mechanical ocillator corrugated wire method with ocillating roller corrugated wire method with contour roll zigzag wire method wire loop method A: method without forced arc movement B: method with rotating arc movement C: method with ocillating arc movement D: method with two or more filler wire ISF 006 A B C In the following, ome of the GMA narrow gap technologie are explained: Uing the turning tube method, Figure 6., ide Figure 6. wall fuion i achieved by the turning of the contact tube; the contact tip angle are et in degree of between and 1 toward the torch axi. With an electronic tepper motor control, arbitrary tranvere-arc ocillating motion with defined dwell period of ocillation and ocillation frequencie can be realied - independent of the filler wire propertie. In contrat, when 1 - wire reel - drive roller - wire mechanim for wire guidance - inert ga hroud - wire guide tube and hielding ga tube 6 - contact tip br-er 6-0e.cdr Figure Principle of GMA Narrow Gap Welding corrugated wire method with mech. ocillator 1 - wire reel - mechanical ocillator for wire deformation - drive roller - inert ga hroud - wire feed nozzle and hielding ga tube 6 - contact tip - 10 Survey and Structure of the Variation of Ga-Shielded Metal Arc Narrow Gap Welding the corrugated wire method with mechanical ocillator i applied, arc ocillation i produced by the platic, wavy deformation of the wire electrode. The deformation i obtained by a continuouly winging ocillator which i fixed above the wire feed roller. Amplitude and frequency of the wave motion 00

4 6. Narrow Gap Welding, Electroga- and Electrolag Welding 79 plate thickne: gap preparation: elctrode diameter: amperage: pule frequency: arc voltage: welding peed: wire ocillation: ocillation width: hielding ga: primery ga flow: econdary ga flow: number of pae: 00 mm quare-butt joint, 9 mm flame cut 1. mm 60 A 10 HZ 0 V cm/min -1 0 min mm 0% Ar/ 0% Co l/min 0 l/min approx. 70 can be varied over the total amplitude of ocillation and the peed of the mechanical ocillator or, alo, over the wire feed peed. A the contact tube remain tationary, very narrow gap with width from 9 to 1 mm with plate thicknee of up to 00 mm can be welded. br-er6-0e.cdr ISF 00 Figure 6. Figure 6. how the macro ection of a GMA narrow gap welded joint with plate (thickne: 00 mm) which ha been produced by the mechanical ocillator method in approx. 70 pae. A highly regular weld build-up and an almot traight fuion line with an extremely narrow heat affected zone can be noticed. Thank to the correct etting of the ocillation parameter and the precie, centred torch manipulation no idewall fuion defect occurred, in pite of the low idewall penetration depth. A further advantage of the weave-bead technique i the high crytal retructuring rate in the weld metal and in the baemetal adjacent to the fuion line an advantage that gain good toughne propertie. Two narrow-gap welding variation with a rotating arc movement are hown in Figure 6.6. When the rotation method i applied, the arc movement i produced by an eccentrically protruding wire electrode (1. mm) from a contact tube nozzle which i rotating with frequencie between 100 and 10 Hz. When the wave br-er 6-06e.cdr Figure 6.6 rotation method piral wire method wire reel - drive roller - mechanim for nozzle rotation - inert ga hroud - hielding ga nozzle 6 - wire guiding tube wire reel - wire mechanim for wire deformation - drive roller - wire feed nozzle and hielding ga upply - contact piece Principle of GMA Narrow Gap Welding

5 6. Narrow Gap Welding, Electroga- and Electrolag Welding 0 wire method i ued, the 1. mm olid wire i being piralwie deformed. Thi happen before it enter the rotating roll wire feed device. With a turning peed of 10 to 10 rev per minute the welding wire i deformed. The effect of thi i uch that after leaving the contact piece the deformed wire create a piral diameter of. to.0 mm in the gap adequate enough to weld plate with thicknee of up to 00 mm at gap width between 9 and 1 mm with a good idewall fuion. tandem method 1 0 twin-wire method 1 Figure 6.7 explain two GMA narrow gap welding method which are oper- 6 ated without forced arc movement, where a reliable idewall fuion i obtained either by the wire 1 - wire reel - deflection roller - drive roller - inert ga hroud - hielding ga nozzle 6 - wire feed nozzle and contact tip br-er 6-07e.cdr Figure wire reel - drive roller - inert ga hroud - wire feed nozzle and hielding ga upply - contact tip Principle of GMA Narrow Gap Welding 1-1 deflection through contant deformation (tandem wire method) or by forced wire deflection with the contact tip (twin-wire method). In both cae, two wire electrode with thicknee between 0. and 1. mm are ued. When the tandem technique i applied, thee electrode are tranported to the two weld head which are arranged inide the gap in tandem and which are indefigure pendently electable. When the twin-wire method i applied, two parallel witched electrode are tranported by a common wire feed unit, and, ubequently, adjuted in a common word-type torch at an incline toward the weld edge at mall pace behind each other (approx. mm) and molten. In place of the SA narrow gap welding method, mentioned in Figure 6., the method with a lengthwie poitioned trip electrode a well a the twin-wire method are explained in more detail, Figure 6.. SA narrow gap welding with trip electrode i carried out in the multipa layer technique, where the trip electrode i deflected at an angle of approx. toward the edge in order to avoid colliion. After completing the firt fillet weld and lag removal the oppoite fillet i made. Solid wire a well a cored-trip electrode with width between 10 00

6 6. Narrow Gap Welding, Electroga- and Electrolag Welding 1 br-er6-0e.cdr h f w h p w v w a Figure 6. α o x a z trip electrode twin-wire electrode H SO tick out a x α h w vw a H z h w p Submerged Arc Narrow Gap Welding gap width electrode deflection ditance of trip tip to flank twiting angle bead hight bead width weld peed electrode deflection tick out ditance torch - flank gap width bead height bead width penetration depth and mm are ued. The gap width i, depending on the number of pae per layer, between 0 and mm. SA twin-wire welding i, in general, carried out uing two electrode (1. to 1.6 mm) where one electrode i deflected toward one weld edge and the other toward the bottom of the groove or toward the oppoite weld edge. Either a ingle pa layer or a two pa layer technique are applied. Dependent on the electrode diameter and alo on the type of welding powder, i the gap width between 1 and 1 mm. Figure 6.9 how a comparion of groove hape in relation to plate thickne for SA welding (DIN 1 part ) with thoe for GMA welding (EN 969) and the untandardied, mainly ued, narrow gap welding. Depending on the plate thickne, ignificant difference in the weld cro-ectional dimenion occur which may lead to ubtantial aving of material and energy during welding. For example, when welding thicknee of 10 mm to 00 mm with the narrow gap welding technique, 66% up to 7% of the weld metal weight are aved, compared to the SA quare edge weld. 10 double-u butt weld SA-DU weld preparation (UP DIN 1) quare-edge butt weld SA-SE weld preparation (UP DIN 1) 10 The practical application of SA narrow gap welding for the production of a flanged calotte joint for a reactor preure veel cover i depicted in Figure The inner diameter of the preure veel i more than,000 mm with double-u butt weld GMA-DU weld preparation (Indexno..7.7 DIN EN 969) br-er6-09e.cdr Comparion of the Weld Groove Shape narrow gap weld GMA-NG weld preparation (not tandardied) Figure

7 6. Narrow Gap Welding, Electroga- and Electrolag Welding wall thicknee of 00 mm and with a height of 0,000 mm. The total weight i,000 ton. The weld depth at the joint wa 670 mm, o it had been neceary to elect a gap width of at leat mm and to work in the three pa layer technique. workpiece wire guide electrode hielding ga arc + - weld pool Cu-hoe weld metal water weld advance deignation: poition: plate thickne: material: gap width: electrode: amperage: voltage: weld peed: hielding ga: ga-hielded metal arc welding (GMAW acc. DIN 1910 T.) vertical (width deviation of up to ) 6-0 mm quare-butt joint or V weld eam 0 mm double-v weld eam unalloyed, lowalloy and highalloy teel - 0 mm only 1 (flux-cored wire, for lag formation between copper hoe and weld urface) Ø mm 0-60 A - V - 1 m/h unalloyed and lowalloy teel CO or mixed ga (Ar 60% and 0% Co ) highalloy teel: argon or helium br-er6-10e_w.cdr ISF 00 br-er6-11e.cdr Electroga Welding Figure 6.10 Figure 6.11 Electroga welding (EG) i characteried by a vertical groove which i bound by two watercooled copper hoe. In the groove, a filler wire electrode which i fed through a copper nozzle, i melted by a hielded arc, Figure During thi proce, are groove edge fued. In relation with the acending rate of the weld pool volume, the welding nozzle and the copper hoe are pulled upward. In order to avoid poor fuion at the beginning of the welding, the proce ha to be tarted on a run-up plate which cloe the bottom end of the groove. The hrinkhole forming at the weld end are tranferred onto the run-off plate. If poible, any interruption of the welding proce hould be avoided. Suitable power ource are rectifier with a lightly dropping tatic characteritic. The electrode ha a poitive polarity. 00

8 6. Narrow Gap Welding, Electroga- and Electrolag Welding The application of electroga welding for lowalloyed teel i more often than not - limited, a the toughne of the heat affected zone with the complex coare grain formation doe not meet ophiticated demand. Long-time expoure to temperature of more than 100 C and low crytalliation rate are reponible for thi. The ame applie to the weld metal. For a more wide-pread application of electroga welding, the High-Speed Electroga Welding Method ha been developed in the ISF. In thi proce, the gap cro-ection i reduced and additional metal powder i added to increae the depoition rate. By the increae of the welding peed, the dwell time of weldadjacent region above critical temperature and thu the brittlene effect are ignificantly reduced. deignation: poition: plate thickne: gap width: material: electrode: amperage: voltage: welding peed: lag hight: br-er6-1e.cdr Figure copper hoe 7. water cooling. weld eam 9. Run-up plate Electrolag Welding 1. bae metal. welding boom. filler metal. lag pool. metal pool reitance fuion welding vertical (and deviation of up to ) 0 mm (up to,000 mm) - mm unalloyed, lowalloy and highalloy teel 1 or more olid or cored wire Ø.0 -. mm plate thickne range per electrode: fixed 0-0 mm ocillated: up to 10 mm 0-00 A per electrode - V 0. - m/h 0-0 mm Figure 6.1 how the proce principle of Electrolag Welding. Heating and melting of the groove face occur in a lag bath. The temperature of the lag bath mut alway exceed the melting temperature of the metal. The Joule effect, produced when the current i tranferred through the conducting ~ Figure 6.1 powder lag ignition with arc powder fuion lag molten pool weld metal tart of welding welding end of welding br-er6-1e.cdr ISF 00 Proce Phae During ES Welding bath, keep the lag bath temperature contant. The welding current i fed over one or more endle wire electrode which melt in the highly heated lag bath. Molten pool and lag bath which both form the weld pool are, ideway retained by the groove face and, in general, by 00

9 6. Narrow Gap Welding, Electroga- and Electrolag Welding water-cooled copper hoe which are, with the complete welding unit, and in relation with the welding peed, moved progreively upward. To avoid the inevitable welding defect at the beginning of the welding proce (inufficient penetration, incluion of unmolten powder) and at the end of the welding (hrinkhole, lag incluion), run-up and run-off plate are ued. The electrolag welding proce can be divided into four proce phae, Figure 6.1. At the beginning of the welding proce, in the o-called ignition phae, the arc i ignited for a hort period and liquefie the non-conductive welding flux powder into conductive lag. The arc i extinguihed a the electrical conductivity of the arc length exceed that of the conductive lag. When the deired lag bath level i reached, the lower ignition parameter (current and voltage) are, during the o-called Data-Increae-Phae, raied to the value of the tationary welding proce. Thi occur on the run-up plate. The ubequent actual welding proce tart, the proce phae. At the end of the weld, the witch-off phae i initiated in the run-off plate. The olidifying lag bath i located on the run-off plate which i ubequently removed. The electrolag welding with conumable feed wire (channel-lot welding) proved to be very ueful for horter weld. The copper liding hoe are replaced by fixed Cu cooling bar and the welding nozzle by a teel tube, Figure 6.1. The length of the heathed teel tube, in general, correpond with the weld eam length (mainly horter than.00 mm) and the teel tube melt during welding in the acending lag bath. Dependent on the plate thickne, welding can be carried out with one ingle or with everal wire and trip electrode. A feature of thi proce variation i the handine of the welding device and the eaier welding area preparation. Alo curved eam can be welded with a bent conumable electrode. A the groove width can be ignificantly reduced when comparing welding cable = ~ br-er 6-1e.cdr drive motor workpiece workpiece cable workpiece Figure 6.1 run-off plate workpiece wire or trip electrode fuing feed nozzle run-up plate copper hoe workpiece copper hoe Electrolag Welding with Fuing Wire Feed Nozzle Electrolag fuing nozzle proce (channel welding) poition: vertical plate thickne: 1 mm material: unalloyed, lowalloy and highalloy teel welding conumable: wire electrode: Ø. - mm trip electrode: 60 x 0. mm plate electrode: 0 x60 up to 10 x 10 mm fuing feed nozzle: Ø 10-1 mm welding powder: lag formation with high electrical conductivity 00

10 6. Narrow Gap Welding, Electroga- and Electrolag Welding with conventional procee, and a trip haped filler material with a conumable guide piece i ued, thi welding proce i rightly placed under the group of narrow gap welding technique. technological meaure metallurgical meaure Likewie in electroga welding, the electrolag welding proce i alo characteried by a large molten pool with a imultaneouly - low heating and cooling rate. Due to the low cooling rate good degaing and thu almot porefree hardening of the lag bath i poible. Diadvantageou, however, i the formation of a coare-grain tructure. There are, however, poibilitie to improve the weld propertie, Figure 6.1. pot weld heat treatment continuou normaliation furnace normaliation br-er 6-1e.cdr Figure filler wire. copper hoe. lag pool. metal pool. water cooling 6. lag layer 7. weld eam. ditance plate 9. potheating torch 10. ide plate 11. heat treated zone br-er 6-16e.cdr Figure 6.16 decreae of peak temperature and dwell time at high temperature increae of welding peed reduction of energy per unit length increae of depoit rate application of everal wire electrode, metal powder addition decreae of groove volume V, double-v butt joint, multi-pa technique Poibilitie to Improve Weld Seam Propertie increae of purity reduction of S-, P-, H-, N- and O - content and other unfavourable trace element temperature C ES Welding with Local Continuou Normaliation application of uitable bae and filler metal addition of uitable alloy and micro-alloy element (nucleu formation) C-content limit Mn, Si, Mo, Cr, Ni, Cu, Nb, V, Zr, Ti To avoid potweld heat treatment the electrolag welding local continuou normaliation ha been developed for plate thicknee of up to approx. 60 mm, Figure The welding temperature in the weld region drop below the A r1 - temperature and i ubequently heated to the normaliing temperature (>A c ). The pecially deigned torche follow the copper hoe along the weld eam. By reaon of the reidual heat in the workpiece the neceary temperature can be reached in a hort time. 00

11 6. Narrow Gap Welding, Electroga- and Electrolag Welding 6 In order to circumvent an expenive potheat weld treatment which i often unrealitic for ue on-ite, the electrolag high-peed welding multilayer technique ha been developed. Similar to electroga welding, the weld cro-ection i reduced and, by application of a twin-wire electrode in tandem arrangement and addition of metal powder, the weld peed i increaed, a in contrat to the conventional technique. In the heat affected zone toughne value are determined which correpond with thoe of the unaffected bae metal. The lag bath and the molten pool of the firt layer are retained by a liding hoe, Figure The weld preparation i a double-v butt weld with a gap of approx. 1 mm, o the carried along liding hoe eal the lag and the metal bath. Plate preparation i, a in conventional electrolag welding, excluively done by flame cutting. Thu, the advantage of eaier weld preparation can be maintained br-er6-17e.cdr 10 1 magnetic creening metal powder addition tandem electrode water cooling copper hoe (water cooled) 6 lag pool 7 molten pool olidified lag 9 welding powder addition 10 weld eam ES-welding in pae with liding hoe ISF 00 br-er6-1e.cdr 1 magnetic creening metal powder upply three-wire electrode water cooling copper hoe (water cooled) 6 lag pool 7 molten pool olidified lag 9 welding powder upply 10 weld eam firt pa 1 econd pa ES-welding of the outer pae ISF 00 Figure 6.17 Figure 6.1 For larger plate thicknee (70 to 100 mm), the three pae layer technique ha been developed. When welding the firt pa with a double-v-groove preparation (root width: 0 to 0 mm; gap width: approx. 1 mm) two liding hoe which are adjuted to the weld 00

12 6. Narrow Gap Welding, Electroga- and Electrolag Welding 7 groove are ued. The firt layer i welded uing the conventional technique, with one wire electrode without metal powder addition. When welding the outer pae flat Cu hoe are again ued, Figure 6.1. Three wire electrode, arranged in a triangular formation, are ued. Thu, one electrode i poitioned cloe to the root and on the plate outer ide two electrode in parallel arrangement are fed into the bath. The ingle a well a the parallel wire electrode are fed with different metal powder quantitie which a outcome permit a welding peed time higher than the peed of the ingle layer conventional technique and alo lead to trong increae of toughne in all zone of the welded joint. If wall thicknee of more than 100 mm are to be welded, everal twin-wire electrode with metal powder addition have to be ued to reach depoition rate of approx. 00 kg/h. The electrolag welding proce i limited by the poible crack formation in the centre of the weld metal. Reaon for thi are the concentration of element uch a ulphur and phophor in the weld centre a well a too fat a cooling of the molten pool in the proximity of the weld eam edge. 00