GB1564295A

GB1564295A - Overhead submerged arc welding process

Info

Publication number: GB1564295A
Application number: GB36784/76A
Authority: GB
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1975-09-11
Filing date: 1976-09-06
Publication date: 1980-04-02
Also published as: DE2640270C3; FR2323487B1; NO762992L; NO143088B; DE2640270A1; DE2640270B2; NO143088C; FR2323487A1

Description

(54) OVERHEAD SUBMERGED ARC WELDING PROCESS (71) We, KOBE STEEL LIMITED, a corporation organised under the laws of Japan, of 3-18, I-chome, Wakinohama-cho, Fujiai-ku, Kobe-city, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an overhead submerged arc welding process for welding plates together wherein a flux for submerged arc welding is supplied to the underside of the plates in the region to be welded and the welding is effected while feeding a consumable electrode from the underside of the plates.

Overhead welding has conventionally been accomplished by means of hand welding, TIG welding, MIG welding and CO2 gas shielded welding. However. the conventionally known processes have disadvantages in that the amount of deposit in a single path is small, that a number of steps is required, that soundness of weld can not be easily obtained, and that there is an environmental problem for the operators.

For this reason, overhead welding has been considered not to be suitable for welding relatively thick plates such as welding of the bottom shell plates in the shipbuilding industry. It has. therefore, been proposed to apply the submerged welding technique which gives a large amount of welded metal in a single path to such the use. For example, there has been disclosed in CBAPOYHOE NrPON3BO7CTBO, No. 11 (1958), pages 19 to 23. an overhead submerged welding process which is applied for welding a pipe. According to the above mentioned reference. there is disclosed a submerged welding process using a flux hopper which supplies a circulated flux for submerged welding to the welding line and in the vicinity thereof and a consumable electrode extending through the flux hopper for effecting submerged welding from the underside of the pipe without using a backing strip, wherein the inner surface of the welding joint pipe is welded at a first place and the pipe is then rotated by 180 degrees to be welded from the upperside thereof by means of a flat welding, whereupon dropping of the molten metal is prevented by the welded metal formed by the overhead submerged arc welding process even when any backing strip is not used on the inner wall of the pipe. The quality of the welded portion formed by the overhead submerged arc welding process is determined by the composition and the grain size of the flux which is supplied from the underside of the welding line, and also depends on the method of supplying the flux to the groove and in the vicinity thereof. In order to suitably supply the flux into and in the vicinity of the groove from the underside, it is necessary to press the flux onto the vicinity of the welding arc at a suitable pressure and to supply fresh flux as the welding is advanced and to remove the consumed and slagged flux. Smooth cyclic operations for supplying and removing the flux should be accomplished. The overhead submerged arc welding process has not yet been practically applied for effecting a butt welding of thick plates because of various problems such as those set forth above.

Accordingly, there is a demand for the development of an overhead submerged arc welding process which may be easily practised and which gives a sound weld.

According to the invention, there is provided an overhead submerged arc welding process for welding plates together wherein a flux for submerged arc welding is supplied to the underside of said plates in the region to be welded and the welding is effected while feeding a consumable electrode from the underside of said plates, the relationship between a flux supply duct and said plates being such that the distance d from the under surfaces of said plates to a circular opening at the top end of the flux supply cylinder and the diameter D of said opening is represented by the formula 2'D/d~15.

In the accompanying drawings: Fig. 1 is a diagrammatical view showing an overhead submerged arc welding process according to the present invention; Fig. 2 is a view showing a second overhead submerged arc welding process according to the present invention: Fig. 3 is a view diagrammatically showing a further embodiment of the process of the present invention; Fig. 4 is a view diagrammatically showing another embodiment of the process of the present invention; Fig. 5 is a sectional view showing somewhat diagrammatically the macrostructure of a welded portion formed by an embodiment of the process of the present invention; Fig. 6 is a view diagrammatically showing a further embodiment of the process according to the present invention; Fig. 7 is an enlarged view showing the embodiment shown in Fig. 6; Fig. 8 and 9 are views diagrammatically showing a further embodiment of the process according to the present invention; Fig. 10 and 11 are views diagrammatically showing a further embodiment of the process according to the present invention: Figs. 12(a) and 12(b) are views illustrating two further embodiments of the process according to the present invention; Fig. 13 is a view diagrammatically showing a further embodiment of the process according to the present invention: Figs. 14(a) to 14(c) illustrate an embodiment of the process according to the present invention: Figs. 15(at to 15(c) illustrate an embodiment of a process of the present invention utilizing a follower mechanism; Figs. 16(a) and 16/by illustrate diagrammatically a speed control mechanism for use in an embodiment of the process of the present invention.

Referring now to Fig. 1 which shows a portion to be welded and the vicinity thereof and a screw feeder for supplying a flux for welding plates 1 spaced from each other by a groove having a root gap. Plates 1 and 1 to be welded are opposed across the groove having the root gap and are temporarily secured by a restrainer 11. A cylindrical duct 3 is disposed within an underside flux supply hopper 2 into which an underside flux 4 is preliminarily charged.

The top end of the duct 3, having a diameter D, is spaced from the underside of the plates 1 and 1 by a distance d. The duct 3 comprises a shaft 7, which is rotated by a belt 12 passed around a pulley 8, and a plurality of helical vanes 9 mounted on the shaft 7. Upperside flux 10 is spread over the groove. A consumable electrode wire 6 is fed through the shaft 7 and passed to the groove via a wire feeding tube 5. An overhead submerged arc welding operation is carried out while retaining the position of the screw feeder such that the relationship between the diameter D of the uppermost end of the duct 3 of the screw feeder and the distance d from the uppermost end of the duct 3 to the underside of the plates to be welded is maintained to be 2D/d 15.

In accordance with the present invention the relationship between the diameter D of the uppermost end of the duct of the screw feeder and the distance d from the uppermost end of the cylinder of the screw feeder to the undersides of the plates to be welded is maintained within the range of 2'D/d' I 5, since outside of this range the flux for overhead submerged arc welding (under flux) cannot be suitably supplied to and removed from the portion to be welded which results in formation of uneven bead or even dropping out of the molten metal. If Dld > 15, the underside flux is not discharged appropriately from the duct of the screw feeder since the discharge thereof is obstructed by the undersides of the plates to be welded, so that it becomes impossible to feed or supply fresh flux to the welded portion. On the other hand, if Dld < 2, although circulation of the flux is improved the pressure of the underside flux is not ,maintained at a constant level and it becomes difficult to support molten metal by the underside flux. The preferred range to obtain particularly good beads is 4~D/d' I 0.

For example, when the diameter of the upper end of the cylinder of the screw feeder is 140 mm, the distance d is preferably within the range of 1 4'd~35 mm.

Fig. 2 shows an embodiment of a flux supply device used for carrying out the process of the present invention. As shown, a supply hopper 2 is provided with a duct 3 disposed therein. A wire feeding tube 5 is disposed within the duct 3. One end of a flux transport line 15 is connected to the lower portion of the duct 3 for feeding a mixed flow of the flux for submerged arc welding with a gas for transporting the flux by pressure, while the other end thereof is connected to a flux storage tank 14 which is provided with a conduit 13 for supplying therethrough the gas for transporting the flux under pressure. A consumable electrode wire 6 is fed to the vicinity of the underside of the plates 1 to be welded, i.e. to the portion to be welded, by a wire feeder 16 through the wire feeding tube 5. A backing strip 17 may be disposed over the reverse sides or upper surfaces of the plates 1 in the vicinity of the welding line 20. A welding line follower 18 is provided so that the consumable electrode wire 6 follows the welding line 20. A gas vent partition 19 which surrounds the duct 3 over the upper end thereof may be provided for preventing the flux 4, which is pressed up to the portion to be welded, from being scattered.

Fig. 3 shows a process wherein a pulverized upperside flux 10 which is capable of forming an upper bead is used.

whereas Fig. 4 shows a process wherein a solid flux 17 (which acts as a backing strip) which is capable of forming upper bead is used. In Figs. 3 and 4, a hopper 2 contains a duct 3 and an underside flux 4 in powder form, which flux 4 is pushed up in a manner similar to that described with reference to Figure 1 onto the plates to be welded on the welding line and in the vicinity thereof. A consumable electrode wire 6 is fed through a wire feeding tube 5 supported at the centre of the duct 3 to establish an arc between the plates 1 and the wire 6 for effecting overhead submerged arc welding to form a reverse side bead on the upper surfaces of the plates 1.

Fig. 5 shows the section of a weld which is obtained by welding the plates in accordance with an embodiment of the present invention. An upper bead 21 is formed by welding the uppermost portion of the groove having a shape of an inverted letter Y at the first place by means of an overhead submerged arc welding step.

Subsequently, beads 22 and 23 are laminated underneath the bead 21 by means of one or more further overhead submerged arc welding steps to complete the welding process and to obtain a three-layered welding.

Fig. 6 shows a modified example of an overhead submerged arc welding device for use in the process of the present invention and having an upper flux feeder. Fig. 7 is an enlarged view of this embodiment showing the shape of the groove and an upper flux supply nozzle. Referring now to Figs. 6 and 7, plates 1 and 1 to be welded have root surfaces separated by a root gap and are temporarily fixed by a restrainer 11. Rails 29 are laid beneath the plates 1 parallel to the groove, and a welding truck 30 runs on the rails 29. Mounted on the truck 30 are a wire feeder 16 for feeding a consumable electrode wire 6 from a wire reel 24 via a wire feeding tube 5 to the weld portion, a flux supply duct 3 surrounding the wire feeding tube 5, and a hopper 2 surrounding the duct 3, and further an upper flux spreader for spreading an upper flux 10 over the upper surfaces of the plates to be welded. The arrangement of the hopper 2, flux supply duct 3, wire feeding tube 5 and wire 6 is similar to that described with reference to Figure 1. The upper flux spreader serves to mix a gas fed through a gas feeding conduit 28 with the upper flux in an upper flux feeding tank 25 and to pass the mixed flow of the gas and the upper flux through a mixed flow transport conduit 26 to the upper flux spreading nozzle for allowing the flux to be spread over the upper surface of the welding line. The process of the present invention using this device will now be described.

After confirming that a sufficient amount of the under flux 4 which has been pushed up by the under flux supply device is supplied to the groove and the vicinity thereof, the upper flux supply is commenced. Then, an arc is established between the wire 6 and the plates 1 to be welded. If the upper flux 10 contains iron powder or iron alloy powder, the flux 10 in the vicinity of the arc is retained without falling down through the gap of the groove by the action of a magnetic field created by the welding current. As a result, constant spreading of the upper flux is ensured to result in the formation of a good upper bead on the upper surface of the plates 1 to be welded. The height and width of the spread upper flux may be readily changed by adlusting the distance of the upper flux supply nozzle 27 from the plates 1 to be welded. When the nozzle is positioned at a suitable level, the upper flux 10 may be supplied and there is no need for recovering the upper flux after the completion of the welding operation. It has been confirmed that stable spreading of the upper flux may be effected if the width of the opening of the upper flux supply nozzle 27 is larger than 2 mm. Sufficient root gap of the groove is 4 mm or more in consideration of the thickness of the plate and clearance. The same flux may be used both as the upper and under fluxes, and an eccentric roller may be mounted on the upper flux supply nozzle 27 at the vicinity of its foremost end for moving the nozzle 27 in upward and downward directions.

Figs. 8 and 9 show another embodiment of the process of the present invention. Fig.

8 is a cross-sectional view of the welded portion, while Fig. 9 is an elevational view thereof. Plates 1 to be welded are secured by a restrainer 11 and the plates 1 are spaced by a groove having a root gap. An under flux 4 from the under flux supply hopper 2 is pushed up into and in the vicinity of the groove to be charged into the gap in a manner similar to that described with reference to Figure 1 while the upper flux 10 is passed through an upper flux supply conduit 26 to the position over the welding line to be spread over the welding line and charged into the gap formed between the plates I to be welded and a slidable backing strip 31 supported by a support member 32. The upper flux supply conduit 26 and the support member 32 extend through the root gap of the groove.

The upper flux is spread forwardly of the welding position which moves in the direction shown by the arrow in Fig. 9. If an upper flux 10 containing iron and/or iron alloy powder is used, the flux is prevented from falling down through the gap by the action of the magnetic force created between a wire 6 fed through the welding nozzle 5 and the plates 1 to be welded.

Figs. 10 and 11 show another embodiment of the present invention. Fig. 10 is a sectional view of the plates to be welded which lie in the vicinity of the groove, while Fig. 11 is a side elevation of the apparatus used to carry out the process of the invention. Plates I to be welded are temporarily secured together by a restrainer 11. An under flux 4 is pushed up into and in the vicinity of the groove by a screw feeder S. When the plates 1 to be welded are thick, an upper flux 10 is charged into the groove downwardly or sidewardly. The under flux 4 circulates through an under flux supply hopper 2 and a cylinder 3 provided with helical vanes. At the centre of the cylinder 3 is disposed a wire feeding tube 5 through which a consumable electrode wire 6 is fed.

Forwardly of the direction along which welding is advanced, there is disposed another tube 34 for feeding a filler wire or filler metal 33 which is fed from a reel 36 through said nozzle 34 by a feeding motor 36. The wire 6 is fed from a wire reel 24 through the tube 5 by a feeding means 16.

The helical vanes contained in the duct 3 of the screw feeder S for pushing up the under flux 4 is rotated by a motor 37 through a belt 12 which is stretched over a pulley 8 and another pulley 38 mounted to the output shaft of the motor 37. At the forward position of the filler wire feeding nozzle 34 is mounted a groove gap detecting mechanism 39 which serves also as a groove follower apparatus by which the width of the groove is sensed to be fed back to the filler wire feeding motor for adjusting the feeding speed of the filler wire and thereby for uniformalizing the formation of the upper bead and for preventing thrusting of the wire 6 therethrough. Particularly, such thrusting of the wire 6 may be more easily prevented by using a flexible strip-shaped electrode which may be readily bent in the weld advancing direction. Such a flexible electrode is thus readily bent when it abuts against the filler wire 33.

Figs. 12(a) and 12/by show overhead submerged arc welding processes according to the present invention wherein a support member is used. In the embodiment shown in Fig. 12(a) a glass tape 40 which may be melted by an arc is applied on the groove as a support member, whereas in the embodiment shown in Fig. 12/by a thin steel plate 40' is used as a support member on which layers of iron powder 10' and flux powder 10 or a single layer of a flux 10 containing iron powder are preliminarily spread. When an overhead submerged arc welding operation is carried out with the constructions described above. the iron powder 10' or the thin steel plate 40' is subjected to the arc so as to be melted and through thrust of the electrode wire 6 may be advantageously prevented. When long plates are welded, the width of the groove gap is not constant but varied, so that even if the welding is accomplished under constant conditions, the formed upper bead is uneven. Evenly formed upper bead may be obtained by adjusting the amount of the iron powder spread over the groove. In detail, the amount of the iron powder is increased at the positions where the width of the groove gaps is broad since at such a position upper beads are readily formed, whereas the amount of iron powder is decreased at the positions where the width of the groove gaps is narrow, since at such positions upper beads are hardly formed. By adjusting the amount of iron powder as mentioned above, a uniform upper bead may be formed even when the width of the groove gap varies.

Fig. 13 shows a side elevation of an apparatus used for practising a further embodiment of the process according to the present invention. As shown, a flat welding apparatus is disposed over the plates 1 to be welded and an overhead submerged arc welding apparatus is disposed under the plates 1. Firstly, the flat welding apparatus disposed over the plates 1 will be described.

On the plates 1 are laid rails 41 on which a welding truck 42 is movably arranged. A consumable electrode wire 44 wound around a wire reel 43 is fed through each of two welding torches 46 by a wire feeding apparatus 45. An upper flux 10 has preliminarily been spread over the groove.

The overhead submerged arc welding apparatus is basically the same as that shown in Fig. Il except for the filler wire feeding means. In operation of the process of this embodiment of the present invention, a flat arc welding is carried out in the first place in such a manner that an unmelted portion remains at the lower part of the groove between the plates 1, and then the unmelted portion is successively welded from the undersides of the plates 1 so long as the undersides of the plates are still hot by means of an overhead submerged arc welding. In accordance with the process set forth above, beads which are extremely intimately fitted with each other and which have a good appearance may be formed, since the undersides of the plates to be welded are heated by the preceding flat welding operation and a flux is continuously supplied in the vicinity of the electrode wire for facilitating formation of the beads.

When a flat arc welding and an overhead submerged arc welding are carried out in the direction of the arrow denoted in Fig.

13, the distance between the welding electrode of flat welding and the overhead submerged arc welding electrode is an important factor. The preferred distance I is smaller than 500 mm. If the distance 1 exceeds 500 mm, an increase in welding speed cannot be expected since the preheating effect due to the preceding flat welding operation is insufficient, which results in lack of penetration by the overhead submerged arc welding operation.

On the other hand, if the overhead submerged arc welding is carried out prior to the flat welding, the welding speed has to be decreased since the plates to be welded are not pre-heated, which also results in depression of efficiency.

Yet a further embodment of the process of the present invention is shown diagrammatically in Figs. 14(a) to 14(c). Fig.

14(a) is a diagrammatical view illustrating the principle of a position control process for the present invention, in which reference numeral 1 designates one of the plates to be welded, numeral 44 designates each of two wires for flat welding, numeral 6 designates an overhead submerged arc welding wire, 47 designates a temperature detector, numeral 48 designates a comparator and numeral 49 designates a driving motor for adjusting the position of the overhead submerged arc welding wire perpendicular to the weld line. Firstly, a flat arc welding is carried out in such a manner that an unmelted portion remains on the reverse sides, i.e. the undersides, of the plates 1 to be welded while allowing the wires 44 to follow the groove by means of an appropriate measure. Fig. 14(b) shows the results of measurements made for detecting the temperature distribution in the direction perpendicular to the welding line positioned rearwardly of the point at which arcing takes place. In Fig. 14(b), the ordinate represents the temperature and the abscissa represents the distance from the welding line.

The temperature distribution is substantially symmetrical with respect to the welding line. Temperature detectors S, and S2 which are combined with the following overhead submerged arc welding wire are disposed at positions respectively spaced perpendicularly from the welding line by appropriate distances, as indicated in Fig. 14(c), for example by a distance of 15 mm, for detecting output signals E, and E2 which are fed to the comparator 48 shown in Fig. 14/at to sense the difference E0=E1-E2 between the signals E, and E2. The position of the overhead submerged arc welding wire 6 along the direction perpendicular to the welding line may be adjusted by rotating the driving motor 49 in a forward or reverse direction depending upon whether the difference E0 is positive or negative.

Figs. 15/awl to 15(c) are diagrammatical views illustrating features of yet another embodiment of a position control process for the present invention. Fig. 15(a) shows a follower apparatus for tracing along the welding line. As shown in the figure, plates 1 and I to be welded are intimately abutted with each other and a square groove having substantially zero gap is formed therebetween. However, a slight gap is inevitably formed at the welding line even in the above butt welding combination. There is disposed a welding truck 50 which spreads over the welding line and which has a base 51 having rollers 52 at its sides and its central portion a through hole 53 into which a sleeve 54 is loosely inserted. The sleeve 54 is provided with a flange 55 at its lower end and is continuously biased upwardly by a compression spring 56. A flange 57 mounted to the central portion of the sleeve 54 is engaged with and stopped by the base 51, sd that the sleeve 54 is prevented from moving up beyond the necessary level. At the upper end of the sleeve is secured a support stand on which a pair of rollers 59 and a pair of detectors 60 are mounted. The ends of the detectors 60 which are biased upwardly through a support stand 58 are, therefore, spaced from the plates 1 by a constant gap by the action of the rollers 59. Each detector 60 is connected to a gas supply pipe 61 and a detected pressure transmitting pipe 62, and the supplied gas is ejected onto the surfaces of the plates 1 and 1 forming a vortex. The central portion of each vortex forms an eye similar to that of a typhoon and the pressure at the central portion is lower than atmospheric pressure. The pressure at the centre of the vortex varies depending upon the amount and the pressure of the ejected gas and the distance from the ejection port to the surfaces of the plates to be welded. It is preferred to eject the gas under suitably selected optimum conditions.

These detectors 60 and 60 are disposed on the positions opposing with each other with respect to the welding line, as shown in Fig.

15(at. However, the detectors should be spaced one from the other by a certain distance. because a considerable error is caused in the measurement of the pressures when these detectors are disposed so closely as to allow the right and left vortices to influence each other. However, accuracy in the following movement reduces when the detectors are set at positions too far from the welding line. It is, therefore, desired to dispose these detectors in such a manner that they are staggered in the fore and aft direction so as to increase the distance between the detectors while maintaining them close to the welding line. thereby reducing the interference between them as much as possible. In the apparatus shown in Fig. 15(a), rollers 59 are used for separating the detectors 60 from the plates 1 and 1.

However, the detectors 60 may be directly mounted on the base 51 and the distance between the detectors 60 and the plates 1 may be alternatively retained by the rollers 51. Vortices are also formed on the surface of the plates to be welded by the action of the vortices ejected from the detectors. If the welding apparatus deviates from the welding line to such an extent that either of the detectors 60 gradually approaches the welding line and finally comes to the position just below the welding line, the condition of the vortex ejected from the closer detector is disturbed by the influence of the atmospheric air or due to the escape of the vortex through the slight gap inevitably formed between the abutting surfaces although they appear to be intimately fitted with each other as shown in Fig. 15(a), and the pressure at the central portion of the vortex approaches the atmospheric pressure. Fig. 15(b) is a graph showing this phenomenon. In Fig. 15(b), there are shown variations in the differences from the atmospheric pressure when one of the detectors 60 is moved from left to right or from right to left beyond the welding lines formed by a square or I-shaped groove having respectively gaps of 0.1 mm, 0.5 mm and 2 mm. The line depending from the central point of the abscissa corresponds to the centre of the welding line. The more remote the points represented in the figure are from the central line, the more remote are the positions of the detector from the welding line. As may be clearly understood from the graph, the detected pressure approaches the atmospheric pressure when the detector is positioned just below the welding line, and the pressure is reduced as the detector is positioned farther from the welding line and reaches a stable condition when the detector is separated from the welding line by a distance of from 4 to 5 mm. Further, it should be appreciated that the pressure variation curves are substantially symmetrical with respect to the centre line. It has been found that a satisfactory accuracy for the following movement of the welding apparatus cannot be obtained until the detectors are spaced from the welding line by the distance of more than about 3 mm, since the detected pressures fluctuate when the detectors come to positions separated from the welding line by distances less than about 3 mm even for an I-shaped groove having no apparent gap and the end surfaces of the plates to be welded are abutted with each other. As the gap becomes broader the width of fluctuation of the detected pressure is broadened to occupy a more remote position from the welding line and at the same time the degree of the pressure fluctuation becomes greater. However.

highly accurate following movement of the welding apparatus may be effected even when the gap is broad as long as each of the detectors is separated from the welding line by a distance of from 4 to 5 mm, since at such a position the detected pressure is maintained in a stable condition, as may be clearly understood from the graph.

Fig. 15(c) is a block diagram of a system for operating on the detected pressures, wherein the detected pressures are converted to an electric signal. Reference symbols S, and S2 desig the groove may be reduced for improving efficiency of the process.

WHAT WE CLAIM IS: 1. An overhead submerged arc welding process for welding plates together wherein a flux for submerged arc welding is supplied to the underside of said plates in the region to be welded and the welding is effected feeding a consumable electrode from the underside of said plates, the relationship between a flux supply duct and said plates being such that the distance d from the under surfaces of said plates to a circular opening at the top end of said flux supply duct and the diameter D of said opening is represented by the formula 2~D/d < 15.

2. A process as claimed in Claim I, wherein the flux for submerged arc welding is supplied from a flux supply apparatus which comprises a flux containing hopper, a screw provided with a plurality of helical vanes arranged in the flux containing hopper for supplying the flux from the flux containing hopper onto the under surfaces of the plates to be welded and for pressing the flux against the same; and a driving means for rotating the screw.

3. A process as claimed in Claim 1, wherein welding is effected while supplying and pressing the flux to the undersurfaces of the plates to be welded by means of gas pressure.

4. A process as claimed in any preceding claim, wherein a flux containing iron powder and/or iron alloy powder is used as the flux for overhead submerged arc welding.

5. A process as claimed in any preceding claim, wherein an overhead submerged arc welding is effected by supplying a pulverized flux for overhead submerged arc welding onto and in the vicinity of an overhead welding groove without a root gap from the underside of the plates to be welded and spreading a pulverized flux which can form an upper bead over the upper surface of the welding line and over the vicinity of the welding line.

6. A process as claimed in any of Claims I to 4, wherein an overhead submerged arc welding is effected by supplying a pulverized flux for overhead submerged arc welding and overlaying a solid flux which can form an upper bead on and near the welding line.

7. A process as claimed in any of Claims I to 4, wherein the uppermost portion of the welding groove is welded in the first place by means of an overhead submerged arc welding, and thereafter beads of welded metal are laminated on the under surface of the bead formed by the overhead sumberged arc welding step by at least one overhead submerged arc welding step.

8. A process as claimed in any of Claims I to 4, applied for welding a joint having a root gap by means of an overhead one-side submerged arc welding, wherein a flux containing iron powder and/or iron alloy powder is used as the flux for forming an upper bead thereby allowing the iron powder and/or iron alloy powder to bridge over the root gap along the line of magnetic force created by a welding current to support the flux for forming an upper bead, and that a flux for submerged arc welding is supplied in the vicinity of the consumable electrode from the underside of the welded portion and pressed thereto.

9. A process as claimed in Claim 8, wherein the flux for forming the upper bead is supplied on the upper surfaces of the plates to be welded positioned forwardly relative to the direction of the overhead submerged arc welding operation.

10. A process as claimed in Claim 9, wherein a backing strip is disposed over the welding line spaced from the plates to be welded by a predetermined gap and a flux for forming the upper bead is supplied into said gap positioned forwardly relative to the direction of the overhead submerged arc welding operation.

11. A process as claimed in any preceding claim, wherein the overhead submerged arc welding is effected by preliminary charging and/or delivering a filler wire or filler metal into a groove having a root gap which is broader than the diameter of a consumable electrode, and by effecting straight motion of the consumable electrode along the welding line.

12. A process as claimed in any of Claims 1 to 10. applied for welding a groove having a broad root gap by means of a one-side overhead submerged arc welding process, wherein a supporting member which is allowed to melt by the welding heat is disposed in the groove and a flux for forming the upper bead is spread over the upper surface of the supporting member or into and in the vicinity of the root gap beyond the supporting member.

13. A process as claimed in any of Claims I to 10 applied for welding a groove having a broad root gap by means of a one-side overhead submerged arc welding process, wherein a supporting member which is allowed to melt by the welding heat is disposed over the broad root gap and a flux for forming the upper bead is spread over the upper surface of said supporting member or into and in the vicinity of the root gap beyond said supporting member.

14. A process as claimed in any of Claims 1 to 4, for welding a groove having an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the groove may be reduced for improving efficiency of the process. WHAT WE CLAIM IS:

1. An overhead submerged arc welding process for welding plates together wherein a flux for submerged arc welding is supplied to the underside of said plates in the region to be welded and the welding is effected feeding a consumable electrode from the underside of said plates, the relationship between a flux supply duct and said plates being such that the distance d from the under surfaces of said plates to a circular opening at the top end of said flux supply duct and the diameter D of said opening is represented by the formula 2~D/d < 15.

abutting portion to form butt welded portion welded on each side, wherein a preceding welding is carried out by a flat arc welding in such a manner that unmelted portions remain at the lower part of the groove and the unmelted portions are subsequently welded by means of an overhead submerged arc welding.

15. A process as claimed in Claim 14, wherein the temperatures of the under surfaces of the plates to be welded due to the welding heat of the preceding flat welding operation are measured at two points on either side of the welding line to be compared with each other for detecting the measured temperature difference following which the measured temperature difference is used to control the movement of the consumable electrode for overhead submerged arc welding so that the electrode proceeds along the welding line to effect the subsequent welding.

16. A process as claimed in Claim 14, wherein a welding torch is moved in a direction perpendicular to the welding line to be followed by disposing along the welding line detectors which are movable integrally with the welding torch while maintaining a constant distance from the surface of the plates to be welded at positions opposing one another on both sides of the welded line and positioned in the vicinity of the welding line, and by ejecting a vortex of a gas onto the upper surfaces and/or the under surfaces of the plates to be welded, detecting the pressures of the vortex created by the detectors, comparing the pressure detected on either side of the welding line by a comparator to obtain a comparison signal, and moving the welding torch in such a manner that the detected pressure difference is maintained smaller than a predetermined value.

17. A process as claimed in Claim 14, wherein the running speed of the overhead submerged arc welding electrode is controlled by detecting the temperature at two arbitrary positions of the plates to be welded by means of temperature detecting members disposed to move with the overhead submerged arc welding electrode which is desired to run in synchronism with the welding electrode for flat welding running along the welding line at a predetermined speed, and discriminating the position of the overhead submerged arc welding electrode relative to that of the welding electrode for flat welding with reference to the temperatures detected.

18. An overhead submerged arc welding process substantially as herein described with reference to Figure 1 or 2 with or without reference to any of Figures 3 to 161by of the accompanying drawings.