GB1579748A - Narrow weld-groove welding process and apparatus therefor - Google Patents

Description

(54) NARROW WELD-GROOVE WELDING PROCESS AND APPARATUS THEREFOR (71) We, BABCOCK-HITACHI KABUSHIKI KAISHA, a Japanese Body Corporate of 6-2, 2-chome, Otemachi, Chiyoda-ku, Tokyo, 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-: This invention relates to a narrow weldgroove welding process and an apparatus therefor, in which two pieces of metal are placed in opposed relation so as to define a weld-groove therebetween, and a bare consumable electrode welding wire is fed into the weld-groove through a contact tube, thereby producing a metal arc, for instance in a shield gas or a flux, for depositing a welding wire on the surfaces of metal pieces to be joined.

Hitherto, there has been proposed a MIG (Metal Arc Inert Gas) welding process for thick steel plates, with a narrow weldgroove defined between the opposed surfaces thereof, in which process a welding wire of a small diameter has imparted to it elastic deformation tending to cause bending, and then the wall surface of a weldgroove on one side is welded, followed by welding on the other. However, this attempt suffers from disadvantages in that a contact tip of a contact tube inserted into a weld-groove is liable to consume excessively; an arc produced during the welding of a wall of a weld-groove on one side is free from weaving, thus resulting in lack of penetration or high temperature cracking; and undesired stability or consistency in feeding a welding wire results. In contrast thereto, there has been proposed an attempt (the Japanese Patent Publication No. Sho50-20031) in which the tip of a welding wire is oscillated or weaved. However, this latter attempt is not a satisfactory solution to this problem, because there should be provided a mechanism for weaving a contact tube in a weld-groove in its entirety, and thus this attempt is not suitable for a narrow weld-groove welding. A still another attempt is disclosed in the Japanese Patent Publication No.

Sho49-17946, in which a welding wire is imparted an elastic deformation tending to cause bending in a given direction beforehand, and then the welding wire is wound around a rocking plate, while the rocking plate is rocked and rotated through a given angle about a feeding axis of a welding wire, so that the tip of the welding wire being fed into the weld-groove may be weaved. However, this attempt poses still another problem that a bending and feeding mechanism for a welding wire is large in size, and the undesirable inconsistency in feeding a welding wire results because various mechanisms have to be inserted or incorporated in a range from a welding wire source to an arc point, and the direction of welding is irreversible due to the arrangement of wire bending.

The following are various gas shielding processes employable in a narrow weldgroove MIG welding process.

(a) A gas nozzle is placed outside of a weld-groove, so that a shield gas is injected through a gas nozzle towards a welding zone, thereby shielding from atmosphere.

(b) A gas nozzle surrounding a contact tube is inserted into a weld-groove for shielding a weld zone from atmosphere.

(c) Gas is injected from a side hole in a gas nozzle, in addition to the injection of gas through a nozzle tip, as in a manner disclosed in the paragraph (b).

(d) A first shield gas is injected towards a weld zone through a passage running in parallel with a guide path for guiding a welding wire, while a second shield gas is injected from a surface outside of the weld-groove.

However, according to processes (a) and (d), a shield gas is injected and supplied from a surface outside of a weld-groove, so that a limitation is imposed on a thickness of metals to be joined. According to the processes (b) and (c), a gas nozzle surrounding a welding wire is inserted into a weld-groove, so that a limitation is imposed on the width of a weld-groove, when the width is desired to be reduced.

Hitherto, several welding processes of this type have become known in Japan.

(One example is the Battelle process developed in U.S. Battelle Memorial Institute.) A majority of the welding processes of this type use a contact tube adapted to guide a welding wire into a welding groove, except for high current MIG welding process using a welding wire of a large diameter.

The diameter of a welding wire used is on the order of 1 mm, and a welding current which approximates critical value required for spray transfer of molten metal droplets is selected, with the result that there is necessarily produced spatters (this term is defined as slag or molten droplets splashed from an arc or crater), so the spatters thus produced cling to the tip of a contact tube or an injection exit of a nozzle, thereby exerting adverse effect on welding characteristics. In addition, a welding current to be used is limited to a value approximating a critical current, so that the resulting weld droplet-transferring mode is not suited for all position welding.

In addition, MIG welding processes, when used for a narrow weld-groove welding, suffer from defects as are incurred to the other welding processes, for instance, lack of fusion into a base metal, blow holes, slag inclusion, lack of penetration or fusion in a preceding-layer or underlayer of beads.

According to the present invention there is provided a narrow weld-groove welding process, wherein a bare consumable electrode welding wire is fed through a contact tube into a weld-groove defined between the opposed surfaces of two pieces of metal and an arc is produced, including the steps of imparting a wavy plastic deformation to said welding wire immediately before it is fed into said contact tube and moving said wire through said contact tube, while maintaining the wavy plastic deformation, whereby the tip of said welding wire on being fed out through said contact tube is automatically alternated between said opposed surfaces of said metal pieces, with the progress of welding and the feeding of said welding wire, with the tip of said welding wire being alternately directed in opposite directions and wherein the welding wire is fed to the contact tube by roller means and the wavy plastic deformation is imparted to the welding wire by a welding wire guide, which is rocked relative to the roller means, the wire being passed directly and without intervening feeding means from the guide to the roller means and from the roller means to the contact tube.

The invention provides, in another aspect, welding apparatus for performing narrow weld-groove welding including a contact tube, roller means to feed a bare consumable electrode welding wire through the contact tube into a weld-groove defined between the opposed surfaces of two pieces of metal, and a welding wire guide rockable relative to the roller means to impart a wavy deformation to said welding wire immediately before it is fed into said contact tube, said roller means and wire guide being so arranged that in use wire is passed directly and without intervening feeding means from the guide to the roller means and from the roller means to the contact tube.

The welding process according to the invention may include the further steps of spreading the surface of a pool of molten metal by gas ejected through a secondary gas nozzle at the rear of the contact tube as viewed in the advancing direction of said contact tube and pushing back said molten metal pool by gas ejected through a primary gas nozzle positioned in front of said contact tube in that direction. Likewise, the apparatus of the invention may include a primary gas nozzle positioned in front of the contact tube in the advancing direction thereof and a secondary gas nozzle positioned behind the contact tube in that direction, such that in use, gas ejected through the secondary tube can spread the surface of a pool of molten metal and gas ejected through the primary tube can push back the molten pool.

In order that the invention may be more clearly understood, the following description is given, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an outline of the process and apparatus therefor, according to the present invention; Figure 2 (a) is a longitudinal crosssectional view of a contact tube for use in the present invention Figure 2-B is a cross-sectional view taken along the line B-B of Figure 2-A; Figures 3-A to 3-C are views illustrative of the weaving locuses of an arc, shown in cross-section taken along the line B-B of Figure 2; Figure 4 is a longitudinal cross-sectional view showing a nozzle for use in a narrow weld-groove MIG welding process according to the present invention; Figure 5 is a cross-sectional view taken along the line V-V of Figure 4; Figure 6 is a perspective view showing an alternative arrangement of an apparatus embodying the present invention; Figure 7 is a cross-sectional view, partly broken, of a mechanism for imparting a welding wire elasticity tending to cause bending; Figure 8 is a cross-sectional view taken along the line VIII--VIII of Figure 7; Figure 9 is a perspective view showing the construction of a narrow weld-groove welding apparatus according to the present invention; Figure 10 is a cross-sectional view showing a welding nozzle portion, in addition to the formation of a wavy wire and a displacement of the tip of the wire; Figure 11 and Figure 12 are crosssectional views showing the positional relationship between a weld bead and nozzle openings, taken along the line XI-XI of Figure 10; Figure 13 is an enlarged side view of an arcuate tube in a welding wire supply means according to the present invention; Figure 14 is a longitudinal crosssectional view showing a welding apparatus and beads produced in a narrow weldgroove welding process and apparatus therefor according to the prior art; Figure 15 is a transverse cross-sectional view of the bead; Figure 16 is a cross-sectional view of a contact tube useful in apparatus according to the present invention, taken along the line XXIII-XXIII of Figure 17; Figure 17 is a longitudinal crosssectional view of the contact tube of Figure 16 taken along the line XXIV-XXIV of Figure 16; Figures 18, 19, 20 are transverse crosssectional views of primary or secondary gas nozzle, showing various shapes of gas passages; Figure 21 is a transverse cross-sectional view of a bead showing penetration of a weld; and Figure 22 is a longitudinal crosssectional view showing one example, in which the injecting directions of gases through two or more gas passages are varied.

Figure 1 is a perspective view showing the entire arrangement of one embodiment of an apparatus according to the present invention. Referring to Figure 1, shown at 1 is a consumable electrode welding wire, at 2 straightening rollers, at 3 first feeding rollers, at 4 a conduit, at 5 a welding wire bending guide tube, at 6 a rocking plate, at 7 a rocking motor, at 8 a roller drive motor, at 9 second feeding rollers, and at 10 a contact tube. The welding wire 1 is straightened by means of the straightening rollers 2 into a linear form, and then delivered from the first feeding rollers 3.

The welding wire 1 thus delivered from the first feeding rollers 3 is guided through the conduit 4 and directed into the welding wire bending guide tube 5. The guide tube 5 runs along the outer periphery of the rocking plate 6 up to the entrance of the second feeding rollers 9. The welding wire 1 thus guided through the guide tube 5 is supplied through the feeding rollers 9 into a nozzle hole provided in the contact tube 10 to be described later. Shown at 8 is a roller drive motor adapted to drive the second feeding rollers 9, and at 7 is a rocking motor adapted to rock the rocking plate 6. When the rocking plate 6 is rocked about its one end in the direction at a right angle to the surface of the figure, the welding wire 1 has imparted to it a wavy plastic deformation due to a combination of the downward feeding of the wire by means of the second feeding rollers 9 positioned immediately before or upstream of the contact tube 10a with the rocking motion of the rocking plate 6.

Figure 2 shows a detailed construction of a contact tube for use in the present invention. Figure 2 (a) is a cross-sectional view thereof and Figure 2 (b) is a crosssectional view taken along the line lIB-lIB. In Figure 2, shown at 1 is a welding wire, at 5 a welding wire bending guide tube, at 9 feeding rollers, at 10a a contact tube, at 10b a contact tip, at 11, 11' metals to be joined, at 12 a backing material, at 16 a nozzle hole of an elongated cross-section with part circular ends, at 17 injection holes through which to inject an inert gas such as argon towards a weld-groove, and at 18 water passages for circulating cooling water therethrough.

The nozzle hole 16 is of an elongated cross-section in the direction at a right angle to the opposed walls or surfaces of metals 11, 11'. The welding wire 1 is fed through the nozzle hole 16, while maintaining wavy plastic deformation, from the side of the feeding rollers 9 towards the backing material 12. The welding wire 1 which has been fed into a weld-groove through the lower opening of the nozzle hole 16 tends to restore the full plastic deformation imparted by the feeding rollers due to elasticity of the welding wire as shown in Figure 2 (a). The amplitude of weaving of the tip of a welding wire along the width of the weld-groove is dependent on a rocking angle of the rocking plate as well as an extension of the welding wire (length of welding wire protruding from the contact tube tip). This permits sufficient penetration of a weld on a corner formed by the backing material 12 and opposed surfaces of metals to be joined.

With the progress of welding, an arc produced at the tip of a welding wire automatically reciprocates or weaves between the opposed surfaces of the metals 11, 11'.

Figure 3 is a cross-sectional view taken along the line lIB-lIB of Figure 2-A, showing the weaving locus or pattern of an arc in this case. Shown at 13 in Figure 3 (a) is an arc locus in case the nozzle hole 16 is of an elongated cross-section in the direction at a right angle to the opposed surfaces of metals 11, I 11', as shown in Figure 2. An arrow mark shows the advancing direction of welding. Shown at 14 in Figure 3 (b) is an arc locus, in case the center line of an elongated cross-section of the nozzle hole 16 is inclined to the direction at a right angle to the opposed surfaces of metals 11, Il', in which the arc locus is not symmetric with respect to the advancing direction of welding. However, in this case, as well, there may be achieved a stable arc locus, and thus this version of welding process may be used as required, with the achievement of deposited metals of a high quality. Shown at 15 in Figure 3 (c) is an arc locus resulting, in case the center line of an elongated cross-section of the nozzle hole 16 runs in the direction at a right angle to the opposed surfaces of metals 11, 11' as in the case of Figure 3 (a), and yet the rotational speed of the rocking motor 7 is so controlled as to be stopped intermittently, thereby forming a rectangular wave form of an arc locus. As a result, the dwelling time of an arc on the opposed surfaces of metals 11, 11' may be extended, thereby insuring sufficient penetration of welds on corner portions. In addition, the procedures 3(b) and 3(c) may be combined in use. The adjustment of dwelling time of an arc may be controlled by changing a mode of speed control of the rocking motor 7. As is apparent, the position of an arc may be automatically weaved between the opposed surfaces of metals, with the progress of welding and feeding of a welding wire, and in addition the dwelling time of an arc on the opposed surfaces of metals may be adjusted as desired, so that the welding according to the present invention permits efficient welding and provides a wide application.

In other words, all position welding may be applied to pipes of a large thickness and diameter.

The following numerical values are given as examples of the narrow weld-groove according to the present invention: * thickness of metals to be joined .. .. 150 mm * length of weld-groove in the welding direction . . .1000 mm * width of weld-groove . .. .. . 10 mm * arc locus . ............. Figure 3 (a) * weaving width or amplitude . .... about 7 mm * inert gas . Ar mixed CO2 * flow rate of gas Ar: 40 litr/min, CO2: 10 litr/min * welding speed 300 mm/min In the above welding condition, there may be obtained a weld of a quality acceptable for JIS - one grade.

As is apparent from the foregoing description of the present invention, a welding wire is imparted a wavy plastic deformation, immediately before being fed into a contact tube, and then the wire is fed through the nozzle hole of an elongated cross-section while maintaining a wave form, thereby enabling a weaving action of a welding wire within a weldgroove, so that an arc may be automatically weaved between the opposed surfaces of metals. As a result, a consistent feeding of welding wire becomes possible, even in case the thickness of metals are increased, and in addition the weaving direction of an arc may be maintained constant. In addition, the weaving direction of an arc may be changed to meet an intended application, thus allowing complete penetration of a weld on the walls of a weld-groove as well as welding in any position. Meanwhile, description has been had to the MIG welding process. However, the present invention is by no means limited to this instance but may be applied to submerged arc welding. In short, the present invention may be applied with the same result to any type of welding, as far as a bare welding wire is used for a narrow weld-groove welding.

Embodiments of nozzles for use in narrow weld-groove MIG welding will be described with reference to Figures 4 and 5.

Referring to Figures 4 and 5, shown at 21 is a contact tube made of a copper alloy, an outer diameter and inner diameter thereof being 5 mm, and 3 mm, respectively. Shown at 22 is a cooling water feeding tube and, at 23 a cooling water return tube. Accordingly, cooling water is circulated in arrow directions through the tubes 22, 23 for cooling a nozzle and improving electric conductivity thereof, in addition to prevention of burning of a heat resisting, electrically insulating material 30 to be described hereinafter. Shown at 24 is a shield gas supply tube, and thus a gas con taining 80No argon gas, and 20 70 carbon dioxide gas may be directed to a weldgroove portion for injection towards a deposited metal. Shown at 25, 26 are impure-gas suction and discharge tubes for introducing and discharging impure gases into and from a weld-groove. A vacuum is maintained in the impure gas suction and discharge tubes 25, 26 for withdrawing impure gases under suction, so that even a shield gas injected through a nozzle exit of a small diameter may be well spread around a weld at a low flow speed, with the aid of the aforesaid suction, thereby protecting a weld, without exerting an adverse effect on a deposited metal. The tubes 21 to 26 are arranged flatwise, and brazing is applied to respective tubes to be joined together, after which the outer surfaces of the tubes are covered with a heat resisting, electrically insulating material 30, such as glass fibers. The diameters of the respective tubes 21 to 26 are so selected as to be equal to the outer diameter of the contact tube 21. Shown at 27 is a weld bead. In the embodiment, the width of a weld-groove is selected as being 8 mm.

Shown at 28 is a metal to be welded.

Shown at 1 is a welding wire of 1.2 mm in diameter. Although not shown, the welding wire 1 is imparted a wavy plastic deformation, immediately before being fed into the contact tube 21, thus allowing a weaving motion of the tip of a welding wire after being fed into a weld-groove. This insures sufficient penetration of a weld into a base metal.

As can be seen from the foregoing, there are arranged flatwise in side by side relation the contact tube 21 adapted to feed a welding wire into a weld-groove, the cooling water feeding tube 22 and its return tube 23 which are positioned sidewise thereof, shield gas feeding tube 24, and impure gas suction and discharge tube 25, and another suction and discharge tube 26, which are positioned on the opposite ends of the set of tubes. As a result, the width of a weld-groove may be reduced to a considerable extent. In addition, the impure gases around a weld portion may be withdrawn under suction and discharged outside, so that despite shield gas being injected through a nozzle exit of a small diameter, the gas may be directed towards the bottom of a weld-groove following a satisfactory flow pattern. This improves the purity of a shield gas, and the shield gas may be fed only through a weld-groove towards its bottom. In addition, gas suction and discharge openings are provided adjacent to the bottom of a weldgroove, so that no limitation arises for the thickness of metals to be joined, while permitting satisfactory feeding of a shield gas. Furthermore, since a fume or smoke produced during welding may be discharged, observation and monitoring of an arc may be attained with ease.

As a welding power source for supplying a current to the welding wire 1, there has been proposed a pulsed arc welder not shown, which may supply a pulse wave current of 120 Hz. A combination of the aforesaid power source with a welding nozzle according to the present invention permits the complete transferring of a droplet in a relatively low current range, thereby avoiding spatters, with the result of freedom of adhesion of spatters to a contact tip and a shield-gas exit of a nozzle, unlike the prior art welding apparatus.

In this embodiment, a weld zone in the bottom portion of a weld-groove alone is shielded, and tubes are joined flatwise, so that a narrow weld-groove welding is enabled for metals having an increased thickness, thus providing a weld zone of a consistent quality with the accompanying many industrial advantages.

Description will now be given of the second embodiment of the narrow weldgroove MIG welding process according to the present invention.

The feature of this embodiment is that a welding wire is imparted a wavy plastic deformation, immediately before being fed into a nozzle hole of an elongated crosssection, and then the wire is fed into the nozzle hole while maintaining elasticity tending to cause waving, so that the tip of a welding wire being fed through the tip of a nozzle is weaved automatically, with the direction of the tip being alternately changed in opposite directions, in response to the weaving motion thereof.

Figure 6 shows an alternative arrangement of the apparatus embodying the present invention.

Figure 7 shows, in cross-section, a mechanism for providing a welding wire with a wavy plastic deformation.

Referring to Figures 6 and 7, shown at 41 is a rocking nozzle, at 42 a drive source for the rocking nozzle, i.e., a rocking motor, at 43 a worm gear adapted to rotate, along with a rotary shaft of the rocking motor 42, at 44 a rocking shaft adapted to rotate in response to the rotation of the worm gear 43 and coupled to the worm gear 43, at 45 a welding wire feeding motor serving as a drive source for the feeding rollers, 46, at 47 press rollers adapted to rotate in response to the rotation of the feeding rollers 46 in contact with the outer peripheries of the feeding rollers, at 48 a contact tube adapted to receive a welding wire 1, which wire is being fed from the feeding rollers and press rollers 47, and at 49 metals to be joined.

The welding wire I is supplied from above the rocking nozzle 41, while the rocking nozzle 41 effects a rocking motion following a sector pattern in a plane as shown in Figure 7, through the medium of worm gear 43 and rocking shaft 44, according to the cyclic normal and reverse rotations of the rocking motor 42. This imparts a wavy plastic deformation to the welding wire 1. The welding wire 1 which has passed through the feeding rollers 46 and the press rollers 47, wherein the wire is imparted a downward force and forced into a nozzle hole in the contact tube 48 positioned immediately downstream of rollers 46, 47, and then the wire 1 is moved through the nozzle hole, while being elastically restrained from its wavy plastically deformed state to cause waving on its exit into the weld-groove. The welding wire which has entered the weld-groove restores its fully wavy deformation due to its elasticity. In this respect, the nozzle hole provided in the contact tube 48, as shown at 52 in Figure 8, is of an elongated crosssection with part circular ends so that the weaving motion of the weld wire is restricted by a major axis of the elongated cross-section.

Figure 8 is a cross-sectional view taken along the line VIll-VIll of Figure 7.

Figure 8 (A) refers to a case where the direction of a major axis of an elongated cross-section is at a right angle to the width of a weld-groove, while Figure 8 (n) refers to a case where the direction of a major axis is slant to the width of the weldgroove. Shown at 40 Figure 8 are arc locuses in the respective cases. More particularly, the welding wire 1 which has been fed into a weld-groove through a lower exit of a nozzle hole 52 of an elongated circular cross-section, while maintaining a wavy plastic deformation, tends to be directed along the major axis of the elongated cross-section due to the elasticity of the wire. In this case, the amplitude of the weaving of a welding wire is controlled by a rocking angle of the rocking nozzle and an extension of the welding wire from the tip of a nozzle in a weld-groove. This permits sufficient penetration of a weld into the corner portions formed between a backing material 53 and opposed surfaces base metals 49. In addition, the progress of welding an arc produced at the tip of a welding wire automatically weaves between the opposed surfaces of metals to be joined. Shown at 40 in Figure 8 is a weaving locus of an arc in this case, while an arrow designates the advancing direction of welding. In case the major axis of an elongated cross-section of a nozzle hole 52 is slant to the vertical direction, as shown in Figure 8 (B), then the arc locus resulting is not symmetric with respect to the advancing direction of welding. However, a stable or consistent arc locus may be attained in this case as well, so that a deposited metal of a good quality may be obtained according to its intended application. For instance, the arc locus shown in Figure 3 (A) is best suited for a flat position welding, vertical position welding and overhead position welding, while the arc locus of Figure 8 (B) is suited for a horizontal position welding.

As is apparent from the foregoing description of this embodiment, a welding wire for MIG welding process is imparted a wavy plastic deformation, immediately before being fed into a contact tube, and then moved through the nozzle hole having an elongated cross-section, while maintaining a wavy deformation, thereby permitting the weaving motion of the tip of a welding wire within a weld-groove, with the result that an arc may be automatically weaved between the opposed walls of the weldgroove. As a result, there may be achieved stable or consistent feeding of a welding wire into the weld-groove, with the weaving direction of an arc maintained constant. In addition, the weaving direction of an arc may be changed as required, and there may be achieved sufficient penetration of a weld into the walls of a weld-groove. The aforesaid embodiment according to the present invention solved many problems experienced with the prior art welding processes, in which a welding wire is imparted an elasticity tending to cause bending in a given direction by means of bending rollers, and then the welding wire is wound around a rocking plate, while the rocking plate in its entirety is rocked and rotated through a given angle about the feeding axis of a welding wire, thereby causing the tip of a welding wire to weave within a weld-groove. More specifically, the following disadvantages of the prior art processes may be avoided i.e., a bending and feeding mechanism for a welding wire is complex and large in size; since various mechanisms are placed between a welding wire feeding source and an arc point, there results the failure in stability in feeding of a welding wire, because of an elasticity tending to cause bending in the wire in a given direction, the advancing direction of welding is not reversible; and the weaving of a welding wi apparatus, in which the formation of a wavy welding wire and the feeding thereof are accomplished at the same time.

Referring to Figures 9, 10 11 and 12, the welding wire 1 is supplied from a wire reel past a conduit 62 to a welding device 63 according to this embodiment. In this case, there may be provided a wire feeding means having a drive rollers additionally, for achieving smooth paying-out of wire from a wire reel. The welding device 63 consists of a welding wire supply means 64 and roller means 65 including a welding nozzle. These components are supported on a frame not shown. The welding wire fed into the conduit 62 is then fed into an arcuate conduit 69 running along the periphery of a frame 68 secured to a shaft 67 of the frame 66. The wire-receiving end of the arcuate conduit 69 is rotatably supported by the frame 66, with the attaching portion thereof being positioned on an extension line of the shaft 67. The configuration of the arcuate conduit 69 is smoothly curved, so that the welding wire may be delivered from the other end, i.e., an end 70 on the side of a nozzle smoothly. The frame 68 swings through a given angle at a given speed about the shaft 67, being driven by a connecting arm 72 coupled to a speed change geared motor 71. The axis of a swinging motion of the frame 68 through a swing angle 2 is positioned on a plane including the two axes of two rollers. The shaft of a drive roller of the above two rollers is connected to a reduction gear shaft within a casing of the roller means 65, which shaft is coupled to the change geared motor 75. The welding wire 1 is formed into a wavy wire la having a given pitch which depends on the swing angle and speed of the arcuate conduit 69 in the wire supply means 64, and the r.p.m. of the roller 74 (wire feeding rate) in the roller means 65, which is associated therewith. The wavy welding wire la is passed through a welding nozzle 77, and one end ib thereof extends from the contact tube hole 78 outside in a manner the wire may contact the inner wall surface of the tube 78 for supplying a current therethrough, thereby forming a steady arc in a weld-groove portion to provide weld beads. Thus, the wire is consumed progressively. The welding nozzle hole 78 should be of a cross-section having a major axis and minor axis for accommodating the feeding of a welding wire, for instance, elongated with circular end, ellipse, and rectangle. The major axis should run at a right angle or aslant to the direction to form beads, depending on a welding condition. Two or more inert gas supply holes 79 and cooling water passages 80 are provided in the welding nozzle 77 adjacent to the welding nozzle hole 78. In this manner, a continuous but stable arc is produced between the end of the wavy wire la and a weld zone, thereby providing welds free of a defect in the metal plates 76a, 76b. In short, the welding device according to this embodiment of the present invention features that there are provided a welding wire supply means adapted to swing about one axis, and a set of roller means adapted to continuously supply a welding wire into a welding nozzle hole, thereby drawing the welding wire from the welding wire supply means into a wavy form.

According to this embodiment, a wavy wire may be readily obtained by means of the welding wire supply means which swings through a given angle at a given speed, and two sets of roller means. As a result, this enables the narrow weld-groove MIG welding, particularly for thick plates, without causing a defect, and with a desired rapidness and positiveness. The two sets of roller means in this welding device enable the formation and drawing of a wavy wire at a time, and the welding device is simple in construction, free of a trouble and easy in handling. The axis 61 of the conduit 62 is coaxial with the shaft 67 of the swinging guide means 68. The direction of the axis 61 should be substantially in parallel with the axes of a set of rollers 74, 76. This fact is essential to the effect that a welding wire drawn through the rollers 74, 76 be waved and maintain its wave configuration in a common plane accurately, and that the welding wire be smoothly introduced into the welding nozzle hole 78. A low profile welding device may be provided, because of the feeding of a welding wire which runs substantially in parallel with the axes of rollers. In addition, the welding device permits vertical-position welding. The axis 61 should preferably be positioned in a plane including the axes of two rollers 74, 76, in parallel with the shafts of rollers 74, 76.

In short, the following features are of importance: (1) A process in which a welding wire is drawn by roller means and supplied to a welding nozzle in a wave form, characterized in that the welding wire is supplied from a direction which is substantially in parallel with the shafts of rollers, past a swing guide means to the roller means.

(2) A welding wire supply device for use in a welding device, in which a welding wire is drawn by roller means in a wave form, and supplied to a welding nozzle, characterized by a swing guide means adapted to receive a welding wire from the direction parallel with the shafts of rollers in the aforesaid roller means and supply same to the aforesaid roller means.

According to this embodiment, the feeding of a welding wire may be accomplished smoothly, and a low profile welding device may be achieved. In addition, welding positions other than flat position are enabled. Particularly, there may be achieved welds, rapidly and positively, in a narrow weld-groove MIG welding process, without a defect.

In the welding device shown in Figures 9, 10, I 1, 12, the arcuate conduit 69 running along the outer periphery of the swing guide means 68 changes, through an angle of 90 , the direction of a welding wire which has been directed through the conduit 62 in parallel with the metal plates 76a, 76b (in the horizontal direction) and allows downwards running of the wire at a right angle to a plane including axes of two rollers 74. However, an excessive change in the direction of a welding wire in an attempt to reduce the size of a welding device results in excessive deformation of the welding wire to be supplied to a welding nozzle, thereby hindering smooth movement of a welding wire through the welding nozzle hole 78. Accordingly, the curvature of the arcuate conduit 69 should be smooth, and in addition, the radius of curvature of the conduit should be such as not to cause deformation beyond the elastic limit. The wire is fed out of the arcuate conduit, which is shown in side view in Figure 13 to have a straight guide tube 82 from which wire is passed to a curved tube 89 ending in a tip 90 from which wire emerges at right angles to tube 82. Tube 89 is mounted on a frame 88 pivotally mounted, and is the end of the tube 89, on a frame 86. Tube 82 supplies the wire straight, and the wire is then waved due to the swinging motion of the swing guide means 68 (89) and the cooperation of the rollers 74.

Because of the arcuate conduit of the aforesaid arrangement, the feeding of a welding wire may be accomplished smoothly, and there may be achieved a low profile welding device, thus enabling various welding positions and formation of a desired wave form for a welding wire.

Particularly, there may be obtained a satisfactory narrow weld-groove MIG welding without a defect, rapidly, positively.

Further embodiments according to the present invention are shown in Figures 14 to 22, which are intended to improve the defects in welds obtained from a narrow weld-groove MIG welding according to the present invention.

Figure 14 gives detailed obscrvation of a molten pool and an arc in prior art MIG welding. A molten pool 92 is positioned under the wire 1, being somewhat biased against the advancing direction of welding.

With the progress of welding, there are formed beads 93 which are continuous, solidified layers, of metal, following a molten pool in the direction against the advancing direction of welding. A molten metal assumes an elliptic form in crosssection, because of a large surface-tension, as shown in Figure 14. The contact angle e between an under-layer 94 and the surface of a bead where it contacts the under-layer 94 is larger than 90 , thus providing poor wettability. The example shown in Figure 15 which is a cross-sectional view taken along the line XXll-XXlI of Figure 14 provides poor wettability between the bead 93 and the metal 95, presenting a danger of undercut and slag inclusion on a corner portion (a).

Hitherto, the supply of inert gas is effected through a passage 107 around a contact tube 96, as shown in Figure 14, or through a second passage 107a surrounding the passage 107 for sufficiently shielding a weld zone from atmosphere. The object of the supply of inert gas in the prior art welding is to shield a weld zone from air, rather than to affect a molten pool, and thus is not intended to give some influence on the molten pool intentionally.

According to this embodiment of the invention, gas is used to adjust the contour of the molten pool, while it can, and generally will, also provide a shield for the weld zone. The contour adjustment reduces defects in welds obtained according to the narrow weld-groove MIG, welding processes.

This embodiment according to the present invention will be described with reference to MIG welding. Figure 16 is a cross-sectional view of a welding apparatus, as viewed from the front in the advancing direction of welding, taken along the line XXIIl-XXlll of Figure 17.

The transverse cross-section of the contact tube 96 is of an elongated rectangular cross-seciton, and is formed with a hole 96a of a rectangular cross-section for ac commodating a welding wire therethrough.

The contact tube 96 is high in electrical conductivity, while a welding wire which has been waved according to the device de scribed earlier is supplied from above through the hole 96a, continuously. Thus, beads are formed, with an arc produced at the lower end of the wire which is being weaved transversely of a weld-groove, and the welding wire is consumed, accordingly.

Figure 17 is a cross-sectional view taken along the line XXIV--XXIV of Figure 16, in which a primary gas nozzle 97 is pro vided in close contact with a contact tube forwardly in the advancing direction of welding. An inert gas passage as shown in Figure 17 is of an elongated rectangular cross-seciton, as shown in Figure 18 which is a partial section on line 95 of Figure 17 or is of a plurality of gas passages provided in a block as shown in Figure 19.

Alternatively, two or more tubes may be joined together as shown in Figure 20 in the block form. Figures 19 and 20 are sections similar to that of Figure 18 of alternative embodiments. Cooling water tubes 98 are positioned in close contact with the contact tube 96 in the rear thereof, as viewed in the advancing direction of welding, while a secondary gas nozzle 99 is positioned in further rear position of the cooling water tube 98 in close contact therewith. The secondary gas nozzle should be of a shape similar to that of the primary gas nozzle 97. In addition, the configuration of a gas passage therefor may be either one of those shown in Figures 18 to 20.

The distance from the axis of the contact tube to the secondary gas nozzle is greater than that from the axis of the contact tube to the primary gas nozzle.

Description will be made to a molten pool produced by a welding apparatus according to this embodiment. The longitudinal cross-sectional built-up contour of a molten pool in the prior art welding, in which a weld zone is shielded from air by inert gas, is shown by the chain line at 100 in Figure 17. In this embodiment, the secondary gas nozzle 99 in the welding apparatus is positioned at a given spacing from the end of a welding wire, so that a molten pool 101 is spread under a gas pressure from the secondary gas nozzle, so that the surface of the molten pool assumes a concave cross-sectional contour as shown at 100a. In addition, the primary gas nozzle 97 is positioned in a given positional relationship to the end of a welding wire, so that a molten metal, in a molten pool which has been forced forwards by inert gas being injected from the secondary gas nozzle, is pushed back by the inert gas, thereby providing the pronounced concave cross-sectional contour 100a, as shown in Figure 21. Satisfactory penetration is achieved between a high temperature molten metal and a region 103 of an under-layer 102 in contact therewith, and a sufficient penetration 104 is also achieved between a molten metal and a base metal, as shown at 100a in Figure 21, being free of undercut and slag inclusion.

In this manner, there may be formed beads 105 which are free of defect, as the welding nozzle goes on. In addition, for the primary or secondary gas nozzle provided with two or more gas passages spaced apart in the welding direction as shown in Figure 22, there may be provided gas passages 1061, 1062, 1062 which are adapted to deflect the direction of gas being injected, thereby effectively pushing back the surface of a molten pool or spreading the molten pool. Alternatively, the flow rates of gas through these gas passages may be varied, thereby facilitating deformation of a molten pool.

Assume that a distance of an axis of a contact tube to an axis of the primary gas nozzle is "e", and a distance of the axis of the contact tube to the axis of the secondary gas nozzle if "f". Then, f > e.

In other words, best results may be obtained, in casef is larger than e. The cooling water tubes 98 should not necessarily be limited to the instance shown, but may be such as to surround the contact tube 96, so that the distances f and e may be suitably selected. It is preferable that the primary gas nozzle, contact tube, cooling water tube, and secondary gas nozzle be in intimate contact with each other for improving the heat radiation and the thermal conductivity thereof, in addition to reduction in size of the welding apparatus. This embodiment provides the following features: (1) A narrow weld-groove welding process, in which the surface of a molten pool is spread by gas being injected through a secondary gas nozzle positioned in the rear of a contact tube as viewed in the advancing direction of a contact tube, and a molten metal in a molten pool is pushed back by gas being injected through a primary gas nozzle in front of the contact tube.

(2) A narrow weld-groove welding apparatus, in which one or more primary gas nozzles are positioned in front of a contact tube, while a cooling water tube is positioned in the rear of the contact tube in intimate contact therewith, and one or more secondary gas nozzles are positioned in the rear of the cooling water tube.

(3) A narrow weld-groove welding apparatus, in which there are provided two or more primary gas nozzles having varying injecting directions of inert gas, and secondary gas nozzles having varying injecting directions of inert gas.

(4) A narrow weld-groove welding apparatus, in which a distance of an axis of a contact tube to an axis of the secondary gas nozzle is larger than a distance of an axis of the contact tube to the axis of a primary gas nozzle.

According to this preferred feature of the present invention (which is the subject of Application No. 20309/78, Serial No.

1 579 749, divided herefrom), the surface of a molten pool may be suitably spread and pushed back thereby providing a con cave surface for a molten pool; sufficient or proper penetration may be achieved for a base metal and an under-layer; slag inclusion, undercut, blow holes may be minimized; the size of a welding apparatus may be reduced; flat position welding may be accomplished with ease; and horizontal position welding and other positions welding are also accomplished with ease, with the aid of a well retained molten pool due to the narrow weld-groove.

WHAT WE CLAIM IS:- 1. A narrow weld-groove welding process, wherein a bare consumable electrode welding wire is fed through a contact tube into a weld-groove defined between the opposed surfaces of two pieces of metal and an arc is produced, including the steps of imparting a wavy plastic deformation to said welding wire immediately before it is fed into said contact tube and moving said wire through said contact tube, while maintaining the wavy plastic deformation, whereby the tip of said welding wire on being fed out through said contact tube is automatically alternated between said opposed surfaces of said metal pieces, with the progress of welding and the feeding of said welding wire, with the tip of said welding wire being alternately directed in opposite directions and wherein the welding wire is fed to the contact tube by roller means and the wavy plastic deformation is imparted to the welding wire by a welding wire guide which is rocked relative to the roller means, the wire being passed directly and without intervening feeding means from the guide to the roller means and from the roller means to the contact tube.

2. A narrow weld-groove welding process according to claim 1, wherein the wavy plastic deformation is imparted to a welding wire, immediately before said welding wire is fed into a hole which has an elongate cross-section with part circular ends and which is provided in said contact tube.

3. A narrow weld-groove welding process according to claim 1 or 2, wherein the roller means includes two rollers and the welding wire guide is a passage which is rocked about an axis substantially parallel to the axes of said rollers.

4. A narrow weld-groove welding process according to claim 3, wherein the passage guides the welding wire to the rollers from an entry portion extending in a direction substantially parallel to the roller axes, but this wire does not acquire plastic deformation in the passage.

5. A narrow weld-groove welding process according to claim 3, wherein the passage is perpendicular to the axes of the rollers and is rocked in a plane perpendicular to said axes.

6. A narrow weld-groove welding process according to any preceding claim applied to the MIG welding process, wherein a metal arc is produced in an inert gas atmosphere.

7. A narrow weld-groove welding process according to any one of claims 1 to 5 applied to the submerged-arc welding process, wherein a metal arc is produced in a flux for welding.

8. A narrow weld-groove welding process, according to any one of claims 1 to 6 and including the further steps of spreading the surface of a pool of molten metal by gas ejected through a secondary gas nozzle at the rear of the contact tube as viewed in the advancing direction of said contact tube and pushing back said molten metal pool by gas ejected through a primary gas nozzle positioned in front of said contact tube in that direction.

9. Welding apparatus for performing narrow weld-groove welding including a contact tube, roller means to feed a bare consumable electrode welding wire through the contact tube into a weld-groove defined between the opposed surfaces of two pieces of metal, and a welding wire guide rockable relative to the roller means to impart a wavy deformation to said welding wire immediately before it is fed into said contact tube, said roller means and wire guide being so arranged that in use wire is passed directly and without intervening feeding means from the guide to the roller means and from the roller means to the contact tube.

10. Welding apparatus according to claim 9, wherein the contact tube has, to receive the welding wire, a hole which is elongate with part circular ends in crosssection.

11. Welding apparatus according to claim 9 or 10, including guide means in the form of a passage for the welding wire and rollers to draw the wire through the passage and drive the wire into the contact tube, the passage being rockable about an axis.

12. Welding apparatus according to claim 11, wherein the passage extends to receive welding wire from a direction generally parallel to the axes of the rollers and to deliver it to the rollers and including means to rock the passage about an axis parallel to said axes.

13. Welding apparatus according to claim 11, wherein the passage is perpendicular to the axes of the rollers and is rockable in a plane perpendicular to said axes.

14. A welding apparatus according to any one of claims 9 to 13 and including a cooling medium tube and a return tube for circulating cooling medium therethrough

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

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. cave surface for a molten pool; sufficient or proper penetration may be achieved for a base metal and an under-layer; slag inclusion, undercut, blow holes may be minimized; the size of a welding apparatus may be reduced; flat position welding may be accomplished with ease; and horizontal position welding and other positions welding are also accomplished with ease, with the aid of a well retained molten pool due to the narrow weld-groove. WHAT WE CLAIM IS:-

1. A narrow weld-groove welding process, wherein a bare consumable electrode welding wire is fed through a contact tube into a weld-groove defined between the opposed surfaces of two pieces of metal and an arc is produced, including the steps of imparting a wavy plastic deformation to said welding wire immediately before it is fed into said contact tube and moving said wire through said contact tube, while maintaining the wavy plastic deformation, whereby the tip of said welding wire on being fed out through said contact tube is automatically alternated between said opposed surfaces of said metal pieces, with the progress of welding and the feeding of said welding wire, with the tip of said welding wire being alternately directed in opposite directions and wherein the welding wire is fed to the contact tube by roller means and the wavy plastic deformation is imparted to the welding wire by a welding wire guide which is rocked relative to the roller means, the wire being passed directly and without intervening feeding means from the guide to the roller means and from the roller means to the contact tube.

2. A narrow weld-groove welding process according to claim 1, wherein the wavy plastic deformation is imparted to a welding wire, immediately before said welding wire is fed into a hole which has an elongate cross-section with part circular ends and which is provided in said contact tube.

3. A narrow weld-groove welding process according to claim 1 or 2, wherein the roller means includes two rollers and the welding wire guide is a passage which is rocked about an axis substantially parallel to the axes of said rollers.

4. A narrow weld-groove welding process according to claim 3, wherein the passage guides the welding wire to the rollers from an entry portion extending in a direction substantially parallel to the roller axes, but this wire does not acquire plastic deformation in the passage.

5. A narrow weld-groove welding process according to claim 3, wherein the passage is perpendicular to the axes of the rollers and is rocked in a plane perpendicular to said axes.

6. A narrow weld-groove welding process according to any preceding claim applied to the MIG welding process, wherein a metal arc is produced in an inert gas atmosphere.

7. A narrow weld-groove welding process according to any one of claims 1 to 5 applied to the submerged-arc welding process, wherein a metal arc is produced in a flux for welding.

8. A narrow weld-groove welding process, according to any one of claims 1 to 6 and including the further steps of spreading the surface of a pool of molten metal by gas ejected through a secondary gas nozzle at the rear of the contact tube as viewed in the advancing direction of said contact tube and pushing back said molten metal pool by gas ejected through a primary gas nozzle positioned in front of said contact tube in that direction.

9. Welding apparatus for performing narrow weld-groove welding including a contact tube, roller means to feed a bare consumable electrode welding wire through the contact tube into a weld-groove defined between the opposed surfaces of two pieces of metal, and a welding wire guide rockable relative to the roller means to impart a wavy deformation to said welding wire immediately before it is fed into said contact tube, said roller means and wire guide being so arranged that in use wire is passed directly and without intervening feeding means from the guide to the roller means and from the roller means to the contact tube.

10. Welding apparatus according to claim 9, wherein the contact tube has, to receive the welding wire, a hole which is elongate with part circular ends in crosssection.

11. Welding apparatus according to claim 9 or 10, including guide means in the form of a passage for the welding wire and rollers to draw the wire through the passage and drive the wire into the contact tube, the passage being rockable about an axis.

12. Welding apparatus according to claim 11, wherein the passage extends to receive welding wire from a direction generally parallel to the axes of the rollers and to deliver it to the rollers and including means to rock the passage about an axis parallel to said axes.

13. Welding apparatus according to claim 11, wherein the passage is perpendicular to the axes of the rollers and is rockable in a plane perpendicular to said axes.

14. A welding apparatus according to any one of claims 9 to 13 and including a cooling medium tube and a return tube for circulating cooling medium therethrough

and positioned adjacent to one side of the contact tube, a shield gas supply tube positioned adjacent to the other side of said contact tube for supplying a shield gas to said weld-groove; and an impure-gas suction and discharge tube positioned outwardly of said cooling-medium return tube and said shield gas supply tube for receiving and discharging impure gas, said tubes all being arranged flatwise in parallel relation to each other, and the surfaces of said tubes being covered with heatresisting, electrically insulating material.

15. Welding apparatus according to any one of claims 9 to 13 including a primary gas nozzle positioned in front of the contact tube in the advancing direction thereof and a secondary gas nozzle positioned behind the contact tube in that direction, such that, in use, gas ejected through the secondary tube can spread the surface of a pool of molten metal and gas ejected through the primary tube can push back the molten pool.

16. A narrow weld-groove welding process apparatus, according to any one of claims 9 to 13, including a primary gas nozzle positioned in front of the contact tube in the direction of advance thereof, a cooling medium tube positioned behind said contact tube in that direction and in intimate contact therewith and a secondary gas nozzle positioned behind said cooling medium tube such that, in use, gas ejected through the secondary tube can spread the surface of a pool of molten metal and gas ejected through the primary tube can push back the molten pool.

17. A narrow weld-groove welding apparatus according to claim 15 or 16, wherein the distance from the axis of said contact tube to the axis of said secondary gas nozzle is greater than the distance from the axis of said contact tube to the axis of said primary gas nozzle.

18. A narrow weld-groove welding apparatus according to claim 15, 16 or 17, wherein there are two or more primary gas nozzles having different ejecting directions for inert gas and two or more secondary gas nozzles having different ejecting directions for inert gas.

19. A narrow weld-groove welding process substantially as hereinbefore described with reference to any of Figures 1 to 13 and 16 to 22 of the accompanying drawings.

20. A welding apparatus substantially as hereinbefore described with reference to and as shown by any of Figures 1 to 13 and 16 to 22 of the accompanying drawings.