NL2004244A

NL2004244A - Method of manufacturing flux-filled welding wire.

Info

Publication number: NL2004244A
Application number: NL2004244A
Authority: NL
Inventors: Toru Ikegami
Original assignee: Kobe Seiko Sho Kobe Steel Kk
Priority date: 2009-02-18
Filing date: 2010-02-15
Publication date: 2010-08-19
Also published as: KR20100094411A; NL2004244C2; CN101804534B; CN101804534A

Description

METHOD OF MANUFACTURING FLUX-FILLED WELDING WIRE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a flux-filled welding wire.

2. Description of the Related Art A flux-filled welding wire (also called a "flux cored wire (FCW)") manufactured by filling flux in a tubular band steel (hoop), which serves as a sheath, is generally used as an arc welding wire for full-automatic or semiautomatic welding. There are two types of FCWs, i.e., one type addressed by the present invention and having a juncture (also referred to as a "seam" hereinafter) in the hoop, and the other type having no seam, i.e., the seamless type. Because the latter seamless type requires a higher manufacturing cost, the FCW having the seam is more widely used. The FCW having the seam means a welding wire in which the tubular hoop is enclosed, as illustrated in Figs. 2 and 9B described later, without joining it at the seam by welding, for example. In the following description, the flux-filled welding wire having the seam is also simply called the "flux-filled welding wire" or the "FCW".

A general method of manufacturing the flux-filled welding wire includes, as illustrated in Figs. 9A and 9B which are described in detail later, a step of unwinding a coiled hoop (band steel) 100 and shaping it into a U-forraed hoop (tube) 100a, a step of filling flux 106 in the U-formed hoop 100a, which is running on a manufacturing line, midway the shaping thereof, and a step of drawing a tubular shaped wire 100b filled with the flux 106 and further winding it into a coiled flux-filled welding wire as a product. Those steps are successively performed on the same line in order mentioned above. Details of those steps are disclosed in, e.g., Japanese Unexamined Patent Application Publication No. 10-109190 and Japanese Patent No. 3959380.

A continuous manufacturing line for such a flux-filled welding wire includes a butt joint forming line, as a front-end process, in which hoops (band steels) serving as stocks (starting materials) are connected to each other by butt welding at their ends in the longitudinal (lengthwise) direction to increase a length of the coiled stock hoop.

The reason is that an increase in the length of the coiled stock hoop is effective in cutting a time required for work of replacing the hoop coil in the continuous manufacturing line for the flux-filled welding wire and in increasing line efficiency.

From the viewpoint of manufacturing efficiency, the stock hoop having a relatively small width is usually manufactured by shearing (slitting) a steel sheet (cold-rolled steel sheet), which has a relatively large width, into a plurality of stock hoops divided in the transverse (widthwise) direction thereof.

In the hoops manufactured by shearing the steel sheet (cold-rolled steel sheet), however, burrs (projected edges) are inevitably generated at both transverse ends of each hoop with at the time of the shearing. In a usual hoop, because a shearing line in the longitudinal direction is provided by each of both (two) transverse ends of the hoop in the state after the shearing, the burrs are generated along both the transverse ends (shearing lines) of each hoop while extending in the longitudinal direction of the hoop.

In each of the hoops obtained at both the transverse ends of the steel sheet, the shearing line in the longitudinal direction is provided by either (one) transverse end of the hoop, the burr is generated along the either transverse end (shearing line) of the hoop.

The burr still exists (remains), though reduced in size, even after the hoop has been shaped and drawn into the tubular wire. The direction (orientation) in which the burr projects is changed depending on which surface of each of the stock hoops to be connected is put on the upper side in the butt joint forming line as the front-end process. Accordingly, depending on the upward or downward orientation of the stock hoops to be connected, i.e., depending on the orientation of the burr, the burr projects outward, as described later, from a seam portion of the flux-filled welding wire, which corresponds to the transverse ends of the hoop where the burrs are present.

A height of the burr from the hoop surface (i.e., a burr height or a projection height) is as very small as about several hundreds μτη or below in the stage of the final flux-filled welding wire after being drawn. Therefore, when the flux-filled welding wire has a large diameter in excess of 2.0 ιτΰηφ, the burr height is much smaller than the wire diameter and the problem of causing deterioration in roundness of the wire hardly occurs in practice.

In flux-filled welding wires having relatively small diameters of 2.0 mm<j) or less and being more widely used, however, even the very small burr imposes a considerable influence upon the wire roundness. Stated another way, if the burr projects outward of the flux-filled welding wire, the wire roundness would significantly deteriorate in the longitudinal direction of the wire.

For that reason, as the wire diameter reduces, the performance in supplying the wire, which is unwound from a wire coil and fed to a welding machine during welding work, is adversely affected to a larger extent. In highly-efficient welding work such as carbon-dioxide shield arc welding and MIG welding, the above-mentioned influence increases because the supply of the unwound wire to the welding machine needs a higher running (feed) speed of the wire and higher accuracy in the wire supply over a larger length or a longer time.

Such a tendency similarly occurs in the process of manufacturing the flux-filled welding wire. More specifically, the hoop (band steel) is usually conveyed through the process (i.e., on a line thereof) with vertically opposite surfaces of the hoop (band steel) being directed upward and downward, respectively. However, when a burr is generated on the lower surface side of the running hoop (band steel) and is directed downward, the generated burr in the hoop or the wire contacts feed rollers and interferes with smooth running of the hoop or the wire in some cases. Such an influence is more significant in a higher-efficient manufacturing line for the flux-filled welding wires having smaller diameters, in which the hoop and the flux-filled welding wire are conveyed at a higher running speed.

The above-described problem of the burr being generated in the hoop with the shearing of the steel sheet (cold-rolled steel sheet) has been recognized, instead of the field of the flux-filled welding wire, on the side manufacturing the band steel as the starting material, i.e., in the field of manufacturing the band steel (band steel sheet) by shearing the steel sheet. Apparatuses for removing a burr generated at an end of band steel at the time of shearing a steel sheet have hitherto been proposed as disclosed in, e.g., Japanese Unexamined Patent Application Publication No. 10-315108 and No. 2007-22983.

Further, with respect to gap control in a welded portion, which is required when joining steel sheets to each other by laser welding, Japanese Unexamined Patent Application Publication No. 1-118389, for example, proposes a technique for flattening the burr that imposes a difficulty in the gap control. With the proposed technique, such a difficulty is overcome by previously flattening the burr by using a pressing member, e.g., a roller, when ends of thin plates, e.g., steel sheets, including burrs generated thereat are butted and joined to each other by laser welding.

Meanwhile, the problem of the burr being generated in the flux-filled welding wire has hitherto hardly been reported in public, and actions to cope with that problem have not been proposed in the field of the flux-filled welding wire. The reason is presumably in that the burr height is as small as about several mm (or as very small as about several hundreds μπι in the stage of the finished flux-filled welding wire after being drawn). In other words, it is inferred that the burr being so small in size has hardly caused the problem in the past, which is worthy to report in public, as described above, depending on a situation where the flux-filled welding wire is manufactured in a relatively large diameter and the line running speed in the manufacturing process is relatively low, or depending on welding work conditions required for the flux-filled welding wire.

However, the problem of the burr has become an issue to be overcome from the viewpoint of not only welding quality, but also manufacturing efficiency, as discussed above, in the highly-efficient welding work using the flux-filled welding wires with smaller diameters and the highly-efficient process of manufacturing the flux-filled welding wires with smaller diameters.

SUMMARY OF THE INVENTION

In view of the above-described state in the art, an object of the present invention is to provide a method of manufacturing a flux-filled welding wire, which can solve the problem of a burr being inevitably generated in a hoop (band steel) at the time of shearing a steel sheet (cold-rolled steel sheet) from the viewpoint of not only welding quality, but also manufacturing efficiency.

To achieve the above object, the present invention provides a method of continuously manufacturing a flux-filled welding wire having a small diameter of 2.0 mm<t> or less and having a seam by using, as a stock, a long band steel which is obtained by successively butting longitudinal ends of individual band steels, obtained by shearing a steel sheet, with each other and connecting the butted ends by welding, the method including the steps of, when the individual band steels are connected to each other, butting the longitudinal ends of the individual band steels with each other and connecting the butted ends by the welding in a state that burrs generated with the shearing of the steel sheet and extending at transverse ends of each band steel in a longitudinal direction thereof are oriented in the same direction with respect to the butted band steels, and when the flux-filled welding wire is manufactured with the connected band steels forming a sheath, placing the butted band steels such that the burrs are not present in orientation facing outward of the welding wire in a seam portion of the flux-filled welding wire.

Herein, the expression "oriented in the same direction with respect to the butted band steels" means that the burrs are directed upward, for example, in each of the butted band steels. Also, the expression "the burrs are not present in orientation facing outward of the welding wire" means that the burrs are oriented to face the interior of the flux-filled welding wire.

In the above method of manufacturing the flux-filled welding wire, preferably, the welding is arc welding, and welding work is performed in a state that tab plates are placed, from both sides, in contact with a butted portion in which the longitudinal ends of the individual band steels are butted with each other.

According to the present invention, the problem of the burr being inevitably generated in the hoop (band steel) at the time of shearing the steel sheet (cold-rolled steel sheet) can be eliminated from the viewpoint of not only quality of welding using the flux-filled welding wire, but also efficiency in manufacturing the flux-filled welding wire.

As discussed above, the direction (orientation) in which the burr projects is changed depending on which surface of each of the stock hoops to be connected is put on the upper side in the butt joint forming line as the front-end process. Also, in the process of manufacturing the flux-filled welding wire, as in the butt joint forming line, the hoop (band steel) is usually conveyed through the process (i.e., on a line thereof) with vertically opposite surfaces of the hoop (band steel) being directed upward and downward, respectively. Therefore, the orientation of the burr is practically given only in one of two cases, i.e., one case where the burr is generated on the lower surface side of the running hoop (band steel) and is directed downward, and the other case where the burr is generated on the upper surface side of the running hoop (band steel) and is directed upward.

Even in the past, therefore, it may have often happened without the intention that the longitudinal ends of the band steels are butted and connected to each other while the burrs generated with the shearing of the steel sheet and extending along the transverse ends of each of the band steel are directed upward of the band steel, and that the connected band steels are used as the long stock band steel to form the flux-filled welding wire with the burrs being directed to the interior of the wire.

In the field of manufacturing the flux-filled welding wire, however, there are hardly known techniques which are addressed to the problem of the burrs being generated extending along the transverse ends of the stock band steel. Such a situation is partly attributable to the fact that because the burr remaining in the seam portion of the flux-filled welding wire having the seam becomes smaller as the diameter of the manufactured welding wire reduces, as discussed above, the burr cannot be observed in some cases just by visually checking a cross-section of the wire and cannot be noticed without efforts of carefully observing or checking the cross-section while paying particular attention to the burr.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view illustrating a state where band steels (hoops) are butted and joined to each other according to a method of the present invention;

Fig. 2 is a schematic sectional view of a flux-filled welding wire according to the present invention, which is manufactured by using the band steels joined to each other according to the method illustrated in Fig. 1;

Fig. 3 is a perspective view illustrating a state where band steels are butted and joined to each other according to a known method;

Fig. 4 is a schematic sectional view of a known flux-filled welding wire which is manufactured by using the band steels joined to each other according to the method illustrated in Fig. 3;

Fig. 5 is a schematic view illustrating a butt-welding joint forming line for the band steels;

Fig. 6 is an explanatory perspective view illustrating butt welding work performed in the butt-welding joint forming line for the band steels by using tab plates;

Fig. 7 is an explanatory plan view illustrating a state where the tab plates are welded to a butt-welded portion of the joined band steels;

Fig. 8 is an explanatory perspective view illustrating a way of cutting away, from the band steels, the tab plates which are welded to the butt-welded portion of the joined band steels;

Fig. 9A is an explanatory view illustrating a continuous manufacturing process for the flux-filled welding wire having a seam, and Fig. 9B is an explanatory view illustrating sectional forms of the hoop and the wire in respective shaping steps in the continuous manufacturing process of Fig. 9A; and

Fig. 10 is a photo showing a section of the flux-filled welding wire according to the present invention, which is manufactured in accordance with the manufacturing process, illustrated in Figs. 9A and 9B, by using the band steels joined to each other according to the method illustrated in Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 illustrates a state where hoops (band steels) are butted to each other. A long hoop obtained after joining butted ends of individual hoops by welding is then used as a stock hoop (starting material) in a continuous manufacturing line for a flux-filled welding wire. Fig. 2 illustrates a cross-section of the flux-filled welding wire manufactured by using the stock hoop obtained with the joining method according to the present invention, which is illustrated in Fig. 1.

In Fig. 1, left and right hoops 1 and 1 are set on a table in a welding step, denoted by 20, of a butt joint forming line (described later) such that longitudinal ends of the hoops are butted with each other. The left and right hoops 1 and 1 have respectively burrs 2 and 2, which are generated with shearing of a steel sheet and which are extended along both transverse ends of each of the hoops 1 and 1 in the longitudinal direction thereof while orienting in the same direction (upward in Fig. 1).

In the embodiment of the present invention, illustrated in Fig. 1, the hoops 1 and 1 are butted with each other in a state that respective hoop surfaces la on the side including the burrs 2 and 2 are positioned to face upward and the burrs 2 and 2 are directed upward of the hoops 1 and 1.

With ordinary shearing of a steel sheet, the burrs 2 and 2 generated at both the transverse ends of the hoops 1 and 1 are all oriented in the same direction, i.e., upward or downward.

After the hoops 1 and 1 have been, as described above, butted and joined to each other at their butted ends by welding on the butt joint forming line (table) 20 with the respective burrs 2 and 2 being directed upward (i.e., upward of the hoops 1 and 1 or upward as viewed in Fig. 1), the joined hoops 1 and 1 are directly wound into a coil while the burrs 2 and 2 are kept directed upward. In any of the case where the coiled hoops are unwound and fed, as they are, to be used as the stock hoop in the continuous manufacturing line for the flux-filled welding wire, and the case where the unwound stock hoop is used in a more complicated process including further winding and unwinding steps midway, the hoops are conveyed on the continuous manufacturing line with the burrs 2 and 2 being directed upward (i.e., upward of the hoops 1 and 1).

As illustrated in the cross-section (transverse section) of Fig. 2, therefore, in the cross-section of a manufactured flux-filled welding wire 3a, the hoop surfaces la on the side including the burrs 2 and 2 are positioned on the inner side of the wire and smooth hoop surfaces lb not including the burrs 2 and 2 are positioned on the outer side of the wire.

As a result, the burrs 2 and 2 extending in the longitudinal direction of the hoops 1 are all directed to the interior of the flux-filled welding wire 3a (i.e., toward flux 4 therein) in a seam portion 5 corresponding to the transverse ends of each band steel (hoop) 1 at which the burrs 2 and 2 are present. Herein, the word "all" means all of the burrs 2 and 2 which are present at the transverse ends of all the band steels 1 while extending in the longitudinal direction of the band steels 1 (i.e., the welding wire).

Thus, the burrs 2 and 2 generated in the seam portion 5 of each of the band steels 1, which form a sheath of the flux-filled welding wire 3a, at the time of manufacturing the band steels 1 by shearing the steel sheet are not present in orientation facing outward of the welding wire. Consequently, the burrs 2 and 2 are not projected, even though their sizes are reduced to become very small, outward of the hoop (sheath) 1 of the wire. In other words, even though the very small burrs 2 and 2 are present, they are all directed to the interior of the flux-filled welding wire 3a.

Therefore, satisfactory roundness of the flux-filled welding wire 3a is ensured, whereby the performance in uncoiling and feeding the wire for supply to a welding machine in welding work is not adversely affected and better performance is obtained in the wire supply even when the wire is drawn to have a diameter as small as mentioned above.

On the other hand, Figs. 3 and 4 are similar views to Figs. 1 and 2, respectively, but illustrate the related art in which the orientation of the burrs 2 and 2 differs from that in Figs. 1 and 2. In Fig. 3, left and right hoops 1 and 1 are butted with each other on a butt joint forming line (table) 20, and burrs 2 and 2 generated at both transverse ends of each of the hoops 1 and 1 while extending in the longitudinal direction thereof are oriented in the same downward direction. Thus, in the related art illustrated in Fig. 3, the hoops 1 and 1 are butted with each other in a state that respective hoop surfaces la on the side including the burrs 2 and 2 are positioned to face downward and the burrs 2 and 2 are directed downward of the hoops 1 and 1.

After the hoops 1 and 1 have been, as described above, butted and joined to each other at their butted ends by welding on the butt joint forming line (table) 20 with the respective burrs 2 and 2 being directed downward, the joined hoops 1 and 1 are directly wound into a coil while the burrs 2 and 2 are kept directed downward. In any of the case where the coiled hoops are unwound and fed, as they are, to be used as the stock hoop in the continuous manufacturing line for the flux-filled welding wire, and the case where the unwound stock hoop is used in a more complicated process including further winding and unwinding steps midway, the hoops are conveyed on the continuous manufacturing line with the burrs 2 and 2 being directed downward.

As illustrated in the cross-section (transverse section) of Fig. 4, therefore, in the cross-section of a manufactured flux-filled welding wire 3a, the hoop surfaces la on the side including the burrs 2 and 2 are positioned on the outer side of the wire. Hence, the burrs 2 and 2 extending in the longitudinal direction of the hoops are directed outward of the flux-filled welding wire 3a. Accordingly, even though the burrs 2 and 2 are reduced in size to be very small, they are projected outward of the hoop (sheath) of the wire.

Herein, the expression "the burrs 2 and 2 are reduced in size to be very small" includes the case that the burr size is reduced so small as to be not discernable by visual observation. It is highly probable that the burrs 2 and 2 become so small as to be not discernable by visual observation of the cross-section of the actual flux-filled welding wire 3a. This is because, in the actual process of manufacturing the flux-filled welding wire, the sizes of the burrs 2 and 2 are of course further reduced due to, e.g., an improvement in the shearing, a decrease in diameter of the wire, and a higher rate of wire drawing.

With the manufacturing method of the present invention, whether the gist of the present invention is satisfied can be determined even when the burrs are so small as to be not discernable by visually observing the cross-section of the actual flux-filled welding wire 3a. Stated another way, the • manufacturing method of the present invention makes it possible to determine or estimate the state that the burrs 2 and 2 are not present in orientation facing outward of the welding wire 3a in the seam portion 5, i.e., the state that the burrs are all present in orientation facing the interior of the welding wire 3a (i.e., toward the flux 4 therein), with no need of observing the cross-section of the actual flux-filled welding wire 3a by ensuring that vertically opposite surfaces of each of the stock hoops connected on the butt joint forming line as the front-end process are properly directed upward and downward (i.e., that the burrs 2 and 2 are properly oriented in the vertical direction).

As described above, the height of the burrs 2 and 2 is as small as about several mm in the stage of the stock hoops 1 and 1. After the stock hoops are drawn in the continuous manufacturing line for the flux-filled welding wire, the burr height is reduced to about several hundreds μπι, i.e., to such a level as hardly discernable by visual observation of the cross-section of the actual flux-filled welding wire 3a, However, if the burrs 2 and 2 are directed outward of the flux-filled welding wire 3a (i.e., positioned on the outer side thereof) even though they are so very small, the roundness of the wire deteriorates. In the case of the wire having a diameter as small as described above, the performance in uncoiling and feeding the wire for supply to the welding machine in the welding work is adversely affected and the wire supply performance is reduced. Also, in the manufacturing process for the flux-filled welding wire, smooth running of the hoops and the wire is impeded, which results in a difficulty in increasing a speed of the manufacturing line (i.e., running speeds of the hoops and the wire).

Butt Joint Forming Line:

The continuous butt joint forming line for producing the stock hoops, which are used in the continuous manufacturing line for the flux-filled welding wire in practice of the present invention, will be described below with reference to Figs. 5 to 8. Be it noted that the butt joint forming line, described below, is known from Japanese Unexamined Patent Application Publication No. 2004-50281 and No. 2005-95963, for example, and the known butt joint forming method can also be used to carry out the present invention.

In Fig. 5, the butt joint forming line includes a preprocessing step 10, the welding step 20 illustrated in Fig. 1, a heating process step 30, and a post-processing step 40, etc., which are successively arranged in order named from the right side as viewed in Fig. 5. In the preprocessing step 10 upstream of the welding step 2£, though not illustrated, there is disposed, for example, a shear for cutting away leading and tailing ends of an unwound hoop coil to provide a gap (groove) when two hoops are butted with each other.

In the welding step 20, there is installed an inert gas arc welding machine, such as a TIG welding machine or a YAG laser-beam welding machine. The heating process step 30 includes a resistance heating apparatus provided with an electrode and a conductive base. A hoop (band steel) is clamped between the electrode and the conductive base to perform annealing of the band steel by resistance heating.

In the post-processing step 40 downstream of the heating process step 30, there are disposed, for example, a hoop ear (lug) scraping apparatus (such as a grinder for removing the burrs), a reshaping apparatus such as a leveler (for correcting curves of the hoops), and a coloring apparatus for indicating the position of a butt-welded portion between the hoops. Those apparatuses are operated so as to perform respective predetermined processes as per intended.

In Fig. 5, the hoop 1 is led out (unwound) from a coil

Cl positioned at a line start end (rightmost end in Fig. 5) and is introduced to the welding step 20 through the preprocessing step 10. In the welding step 20, as illustrated in Fig. 6, opposed ends of two hoops 1 and 1 (i.e., a tailing end of a preceding hoop (band steel) 1 unwound from the coil and a leading end of a succeeding hoop (band steel) 1 unwound from the coil) are butt-welded to each other.

In the butt joint forming line for the band steels, as described above in connection with Fig. 1, two band steels as welding targets are placed on the line such that respective hoop surfaces la including the burrs 2 and 2 are oriented to face upward. Stated another way, the succeeding hoop 1 led out from the coil Cl is introduced to the line with the burrs 2 and 2 being directed upward and is butted with the leading hoop 1, which has already been led out from the coil Cl and placed on the line with the burrs 2 and 2 being directed upward.

The steps of butting the opposed ends of two hoops 1 and 1 and joining them to each other by welding are preferably performed by using tab plates 22, as illustrated in Fig. 6. When a butt joint is formed by arc welding, such as TIG arc welding or YAG laser-beam welding, using inert gas (shield gas), e.g., argon or helium, an arc is unstable at the start of welding work (i.e., at the ignition of arc). In the case of the hoops 1 and 1 each having a smaller thickness, therefore, it is more difficult to form a sound welded joint because of melting erosion (burning-out) at the butted ends, which is caused by an excessive current or an excessive input. An abnormality in joint quality also tends to occur at the extinction of an arc (i.e., at the stop of an arc current) when the welding work is brought to an end.

An effective method for coping with those problems is to perform the welding work in such a way that the tab plates 22 are placed from both sides of a butted portion including the butted ends of the hoops 1 and 1 to be contacted with lateral surfaces of the butted portion. As illustrated in Fig. 6, the operations of butting the ends of the hoops 1 and 1 with each other and assembling the tab plates 22 to the hoops 1 and 1 from both the sides are performed by using a clamping (fixing) jig 23 as required. More specifically, after clamping the hoops 1 and 1 and the tab plates 22 and 22 together by the jig 23, the butt joint is formed by the inert-gas arc welding, such as TIG arc welding or YAG laser-beam welding with the use of a filler (filler metal) having the same composition base as the hoops 1 and 1. In the case of using the TIG arc welding, a tungsten electrode is preferably employed.

Supply of an arc current is started (for arc ignition) while a welding torch 21 is positioned to face one of the tabs 22 (on the left side). Then, the welding torch 21 is moved from the left to the right, as indicated by an arrow in Fig. 6, so that an arc is scanned along a butt joining line L. Thereafter, the supply of the welding current is stopped (for arc extinction) on the other tab plate 22 (on the right side). Thus, by causing one tab 22 to provide an arc ignition surface and the other tab 22 to provide an arc extinction surface, the welding work can be performed in a region along the butt joining line L in a stable arc state, and the butt joint can be formed free from defects such as melting erosion.

After the above-described butt welding, as illustrated in Fig. 7, a butt welded portion W is transferred to the heating process step 30 while the tab plates 22 are kept in a state welded to both the sides of the butt welded portion W. In the heating process step 30, the butt welded portion W is subjected to a heating process (temporary annealing). The heating process is intended to soften the butt welded portion W (i.e., the hardened structure therein) and is carried out by heating and holding the butt welded portion W to and in an Austenite temperature range for an appropriate time, and then cooling it in the atmosphere.

After heating and holding the butt welded portion W to and at the predetermined temperature and further cooling it in the atmosphere, the tab plates 22 are cut away, as illustrated in Fig. 8, in such a hot or warm condition that the butt welded portion W is held in the softened state.

When separating the tab plates 22, each tab plate 3 can be handled just by folding it upward or downward with respect to the hoops, as illustrated in Fig. 8. The butt welded portion W between the hoops 1 and 1, from which the tab plates 22 have been separated, has a sound shape free from damages, cracks, etc.

After the separation of the tab plates 22, main annealing is preferably performed on the butt welded portion W. The reason why the annealing is performed again after the separation of the tab plates 22 resides in forming a homogeneous annealed structure over the entire butt welded portion W in the transverse direction. The main annealing can be performed by heating and holding the butt welded portion W between the hoops 1 and 1 to and in the Austenite temperature range with resistance heating, and then slowly cooling it in a controlled manner. After the main annealing, the joined hoops are transferred to the post-processing step 40 in which they are wound around a coil winder C2, as illustrated in Fig. 5, after carrying out predetermined processes (such as reshaping and surface inspection). Continuous Manufacturing Process for Flux-filled Welding Wire:

The continuous manufacturing method for the flux-filled welding wire, according to the present invention, will be described below with reference to Figs. 9A and 9B. Fig. 9A schematically illustrates, partly in a plan view, the continuous manufacturing process for the flux-filled welding wire. Fig. 9B is an explanatory view illustrating sectional forms of the hoop and the wire in respective shaping steps in the continuous manufacturing process of Fig. 9A. Be it noted that the illustrated continuous manufacturing process for the flux-filled welding wire is also known, and the known continuous manufacturing process for the flux-filled welding wire can be used to carry out the present invention.

In Fig. 9A, a coiled hoop 100 corresponds to the hoops 1 which are connected into a long hoop in the butt joint forming line illustrated in Fig. 5. The coiled hoop 100 is conveyed to the continuous manufacturing process in a state wound around the coil winder C2 and is unwound by an unwinding machine (not shown).

(Washing and Degreasing Step)

First, the hoop 100 is washed and degreased in a washing and degreasing step 102 before being shaped. For example, when a stock steel sheet having a large width is shorn into the hoops 1 for use in manufacturing the flux-filled welding wire having a small diameter of 2.0 πτηφ or less, machining oil and other contaminants attach to the hoop surfaces and remain on the surface of the hoop 100. Those machining oil and other contaminants need to be previously removed in the washing and degreasing step 102 from the viewpoint of quality of the welding wire.

(Lubricant)

Then, in a lubricant applying step 103a in Fig. 9A, a small amount of lubricant or rust inhibiting oil is applied to the hoop 100 having been washed and degreased. In subsequent steps, i.e., a hoop shaping step, a step of shaping a U-formed hoop into a tubular wire, and a wire drawing step, a wire drawing lubricant containing a sulfur-based extreme pressure agent is used. The wire drawing lubricant can be selected, as appropriate, from among known non-hydrogen lubricants, such as a lubricant containing a sulfur-based extreme pressure agent, a wet lubricant containing a sulfur-based extreme pressure solid as a component and water as a solvent, and an oily lubricant containing a sulfur-based extreme pressure solid as a main component and a small amount of oil.

(Shaping)

The hoop 100 to which the lubricant has been applied as described above is shaped by a shaping roller row (group) 104a from the hoop having a cross-section in the form of a flat plate, indicated at A in Fig. 9B, to a hoop 100a having a U-formed cross-section indicated at B in Fig. 9B. In the shaping roller row (group) 104a of Fig. 9A, two shaping rollers are arranged in series as one example. The number of shaping rollers arranged in the shaping step is selected, as appropriate, depending on shaping conditions such as the width, the thickness and/or the hardness of the hoop 100. (Filling of Flux)

Flux 106 is supplied from a flux supply apparatus 105 to the hoop 100a having been shaped into the U-formed cross-section such that, as indicated at C in Fig. 9B, the flux 106 is filled (contained) in the U-formed space of the hoop 100a at a certain filling rate (void rate).

The U-form shaped hoop 100a having been filled with the flux 106 is further shaped into a tubular wire 100b, denoted by D in Fig. 9B, by another shaping roller row 104b. The shaping roller row 104b is arranged in the same conditions as those for the shaping roller row 104a. The tubular wire 100b has a seam 114, i.e., a gap defined by both the transverse ends of the hoop which are positioned adjacent to each other, the seam 114 extending in the longitudinal direction of the wire 100b. The seam 114 remains as the gap even after the wire 100b is successively drawn into a wire 100c and a wire lOOd, which have gradually decreasing diameters, in a subsequent wire drawing step.

More specifically, the seam 114 remains even when the wire 100c in Fig. 9B (denoted by E) has a cross-section 114a of the butt type, illustrated in enlarged scale with a lead line extending from the wire 100c, in which both the transverse ends of the hoop are butted with each other. In another example, the seam 114 also remains even when the wire 100c in Fig. 9B (denoted by E) has a cross-section 114b of the lapped type, illustrated in enlarged scale with a lead line extending from the wire 100c, in which both the transverse ends of the hoop are lapped with each other.

Similarly, the seam 114 is present even in the FCW (flux cored wire) in the stage of a product.

(Wire Drawing and Lubrication)

Then, the shaped tubular wire 100b is drawn after applying a lubricant to the surface of the wire 100b in a lubricant applying step 103b. The lubricant used in this step 103b may be the same as or differ from the lubricant used in the above-described lubricant applying step 103a. Also, the lubricant applying step may be arranged not only before the wire drawing as denoted by 103b, but also during the wire drawing as required.

(Roller-die Wire Drawing) A roller-die wire drawing step illustrated in Fig. 9A is mainly divided into a primary wire drawing step and a secondary wire drawing step. With those wire drawing steps, the wire diameter is reduced to that of a product or a value near that of the product. As seen from E and F in Fig. 9B, the wire diameter is reduced from that of the wire 100c to that of the wire lOOd by the primary wire drawing. Further, as seen from F and G in Fig. 9B, the wire diameter is reduced from that of the wire lOOd to that of a wire 100e, which has the product diameter, by the secondary wire drawing.

The wire drawing step in Fig. 9A is divided, by way of example, into separate steps, i.e., the primary wire drawing step and the secondary wire drawing step. Whether to separate the wire drawing step as illustrated in Fig. 9A or to continuously draw the wire to the product, i.e., the wire having the product diameter, in one continuous step, including the primary wire drawing step and the secondary wire drawing step can be selected, as appropriate, depending on design conditions of the hoop, design conditions of the product FCW, productivity, etc. Further, in consideration of productivity balance between the primary wire drawing and the secondary wire drawing, it is possible to selectively arrange, as appropriate, plural lines of secondary wire drawing steps (C) with respect to one line of primary wire drawing step (B), or one line of secondary wire drawing step (C) with respect to plural lines of primary wire drawing steps (B).

The primary wire drawing step includes superhard-material-made roller die rows (groups) 201 to 206 in multiple stages (six stages or groups in the example of Fig. 9A). The secondary wire drawing step includes superhard-material-made roller die rows (groups) 401 to 405 in multiple stages (five stages or groups in the example of Fig. 9A). Also, the number of multiple stages of roller die rows to be arranged is selected, as appropriate, depending on the wire drawing conditions.

The primary wire drawing step in Fig. 9A is in-line connected to the above-described shaping step. The wire after the primary wire drawing is temporarily wound into a coil 106. Further, the secondary wire drawing step is performed by unwinding the wire from the coil 106, as illustrated in Fig, 9A.

The secondary wire drawing step is in-line connected to a means (step) 108 for physically removing the above-mentioned lubricant and an oil applying means 109. As an alternative, a skin-pass finish wire drawing step using a bored die 501 may be inserted before the step of removing the lubricant for the wire drawing and the step of applying the oil in some cases. The steps subsequent to the wire drawing using the roller dies, including the finish wire drawing step 501, the lubricant removing step 108, and the oil applying step 109, are performed in-line (i.e., continuously on the same line). If those steps are performed off-line as separate steps, productivity and production efficiency of the entire manufacturing process for the product FCW would be significantly reduced and the advantage of the high-speed wire drawing using the roller die groups would be impaired to a large extent.

After applying the oil to the product FCW in the secondary wire drawing step, the product FCW is wound, as denoted by 110, by a coil winder. Further, the product FCW is wound again around a wire spool or loaded into a pail pack in a not-shown step. In the wire drawing step of Fig. 9A, reference numeral 111 denotes a capstan which is arranged downstream of each roller die row to smoothly guide the drawn wire, thus ensuring continuous and high-speed wire drawing.

Comparing with the bored die in which the wire passes through a single small-diameter bore, the roller die (wire drawing apparatus) is advantageous in that a shearing force applied to a lubrication layer on the die surface is relatively small and the problem of loss of a lubricant coating is less apt to occur. Further, the roller die is free from the problems of solidification and clogging of the lubricant, which are often caused in the bored die. Hence, the roller die can ensure continuous and high-speed wire drawing.

The roller die and the bored die are preferably made of cemented carbides (superhard materials), such as a WC-based superhard alloy, a TiC-based superhard alloy, and a TiCN-based cermet, which are known as being high in strength, hardness and rigidity, and as being suitable for drawing the welding wire at a high speed.

The accuracy in shape of the wire 100e having the product diameter, indicated at G in Fig. 9B, not only adversely affects the performance in supplying the wire, but also greatly affects workability (operation efficiency) when the product FCW is additionally wound again around the wire spool (into the coiled hoop 100) or loaded into the pail pack.

For that reason, it is preferred that the wire having been drawn through the roller die rows is finally subjected to finish drawing by using the bored die 501. The wire drawing speed of the bored die is lower than that of the roller die. By constructing the secondary wire drawing line as described above, however, such a lower wire drawing speed of the bored die does not adversely affect the high-speed operation and continuity in the entirety of the wire drawing step and the FCW manufacturing process even when the finish wire drawing is finally performed by using the bored die. When the finish wire drawing is finally performed by using the bored die, the wire drawn through the roller die rows has a diameter near the product diameter, and the wire after being finish-drawn by the bored die has the same diameter as that of the final product.

(Lubricant Removing Means)

Subsequently, the above-mentioned lubricant is removed by the means 108 for physically removing the lubricant from the wire surface. The lubricant removing means 108 in Fig. 9A actually comprises an upstream-side stage, i.e., a lubricant removing means (not shown) for grinding and hitting the wire surface, and a downstream-side stage, i.e., a lubricant removing means (illustrated in the form of a box including rolls therein) using wiping rolls, such that the lubricant is removed in-line in two stages. The lubricant removing means for grinding and hitting the wire surface in the upstream-side stage serves to remove the lubricant from the wire surface by grinding the surface of the running wire and then dropping, e.g., a small piece of light material onto the running wire so as to strike against the wire. The lubricant removing means 108 using the wiping rolls in the downstream-side stage serves to remove the lubricant from the wire surface by using the wiping (scraping) rolls which are each provided on its surface with, e.g., a felt to wipe out the lubricant. Additional in-line operations for removing the lubricant can also be performed by using a means for removing the lubricant with washing, other type of physically removing means such as vibrating the wire, and/or an appropriate combination of those removing means. If the lubricant is not completely removed and remains on the wire surface or the FCW surface, arc stability deteriorates during the welding, thus causing welding defects.

(Oil Applying Means)

The wire 100e from which surface the lubricant has been removed is then introduced to the oil applying means 109 that applies a known lubricant for improving the wire supply performance to the wire surface, whereby an FCW product is obtained as denoted by W in Fig. 9B. The oil applying means 109 is required to uniformly coat a small amount of lubricant 113 in a short time, as illustrated in Fig. 9B, over the surface of the wire which is conveyed (moved) at a high speed. To that end, a forcibly oil applying means utilizing electrostatic oil application, for example, is preferably used in consideration of total hydrogen control. It is however general to employ a method of applying oil by bringing a felt impregnated with a lubricant, for example, into contact with the wire.

In the above-described example of Fig. 9A, the process including the step of shaping the hoop into the U-form, the step of filling the flux into the U-formed hoop, the step of shaping the ϋ-formed hoop into the tubular wire, and the primary wire drawing step for the tubular wire, and the process including the secondary wire drawing step and the step of applying the lubricant for wire feeding to the wire surface are performed respectively on the separated continuous lines (in-line). Depending on the production efficiency and the production conditions of the FCW manufacturing line, however, the primary wire drawing step and the secondary wire drawing step may be directly connected to each other such that the above-mentioned steps are all on the same continuous line (in-line). As an alternative, the above-mentioned steps until the primary wire drawing step may be performed on separate lines. For example, the process until the step 104b of shaping the U-formed hoop into the tubular wire and the primary wire drawing step for the tubular wire in Fig. 9A may be performed on separate lines. In the description of the present invention, the expression "the steps are successively performed in-line" means that the steps are successively performed in a continuous manner on a wire while the wire is conveyed.

(Hardness of Wire Surface after Finish Wire Drawing)

When an ordinary hoop made of a soft steel sheet is used in the above-described manufacturing process, the finish property of the FCW surface after the wire drawing is ensured, the coefficient of friction thereof is reduced, and hence the wire supply performance for the finished FCW is improved on condition that the surface of the wire (soft-steel hoop) after the finish wire drawing has hardness in the range of 150 to 260 Hv in terms of Vickers hardness. In the case of the roller die being made of the WC-based superhard alloy as in the present invention, such a range of Vickers hardness is relatively easy to obtain. If the hardness of the wire surface is less than 150 Hv in terms of Vickers hardness, the stiffness of the FCW would be too weak and the wire supply performance would deteriorate. Conversely, if the hardness of the wire surface is more than 260 Hv in terms of Vickers hardness, the FCW would be susceptible to a breakage. A breakage of the FCW at the start of winding around the spool (i.e., in the initial stage of the winding) would give rise to a trouble, i.e., a necessity of restarting the winding of the FCW.

In the above-described embodiment, the roller dies made of the superhard materials are used thoroughly in all the wire drawing steps except for the finish wire drawing.

However, other suitable dies than the roller dies made of the superhard materials and other suitable roll materials than those super hard materials can also be used in one or more portions or steps where the high-speed and continuous wiring drawing and shaping are not significantly affected. [Example 1]

One Example of the present invention will be described below. A flux-filled welding wire having a product diameter of 2.0 mm<|) was manufactured based on the butt joint forming processing and the conditions for the same, which have been described above with reference to Figs. 5 to 8, and the flux-filled welding wire manufacturing process and the conditions for the same, which have been described above with reference to Fig. 9A.

The manufacturing process was carried out by using a commercially available hoop made of a soft steel sheet, flux containing Fe-Cr and Zircon sand as main components, and a lubricant containing molybdenum disulfide as a sulfur-based extreme pressure agent. The manufactured hoop had a width W of 12 mm and a thickness t of 0.96 mm.

In the butt joint forming process, as the preferable process conditions described above with reference to Figs. 5 to 8, the hoops 1 and 1 were butted with each other on the butt joint forming line (table) 20 with their burrs 2 and 2 being directed upward, and the stock hoops 1 and 1 connected by welding their butted ends are directly wound into a coil while the burrs 2 and 2 are kept directed upward. The welding to form the butt joint was performed by using a TIG arc welding machine with the aid of the tab plates 22 illustrated in Fig. 6, the argon inert gas, and the tungsten electrode.

The coil of the long stock hoop obtained by connecting the butted ends of individual hoops by welding was transferred to the continuous manufacturing line for the flux-filled welding wire and was uncoiled to be directly used as the stock hoop. Then, the flux-filled welding wire was manufactured by successively running the stock hoop on the continuous manufacturing line with the burrs 2 and 2 being directed upward (i.e., projected upward of the hoops 1 and 1).

A cross-section of the flux-filled welding wire thus manufactured to have a product diameter of 1.2 ιτιπιφ is illustrated in Fig. 10 as a cross-section photo with a magnification of 100. As seen from Fig. 10, the flux-filled welding wire according to the present invention is a flux-filled welding wire having a seam and manufactured in accordance with the above-described manufacturing method such that the burrs are not present in orientation directing outward of the welding wire in the seam portion of the band steel (hoop) which forms a sheath of the flux-filled welding wire. In other words, a smooth hoop surface free from the burrs is positioned on the outer side of the wire.

More specifically, in comparison with Fig, 2, the size of each burr in Fig. 10 is so small as to be not discernable by visual observation. During the above-described butt joint forming process and before the start of the wire drawing in the FCW manufacturing process illustrated in Fig. 9A, the burrs are certainly directed upward of the hoops 1 and 1. Therefore, when the very small burrs are present in the seam portion of the flux-filled welding wire illustrated in Fig. 10, those burrs are all as a matter of course present in orientation directing to the interior (i.e., toward the flux 4 therein) of the flux-filled welding wire. Accordingly, even though the presence of the burrs cannot be discerned by visual observation, it is certainly ensured that the flux-filled welding wire having the small diameter, illustrated in Fig. 10, satisfies the gist of the present invention.

A maximum primary wire drawing speed and a maximum secondary wire drawing speed in such a range as enabling the wire drawing steps to be stably performed were 300 m/min and 1000 m/min, respectively. Also, shape accuracy (roundness) of the FCW after being wound into a coil had a variation of less than ± 5μιη as a result of measuring the roundness of the FCW at successive sampling points by using a roundness meter RONDCOM30B made by Tokyo Seimitsu Co., Ltd.

Further, as a result of evaluating the wire supply performance for the manufactured FCW, smooth and satisfactory operations were proved without interruption of the wire supply. In addition, as a result of evaluating welding performance in the butt welding between two soft steel sheets (each having a thickness of 1 mmt), arc was stable thoroughly the welding, no welding defects were found in a welded portion, and toughness of a butt joint portion was satisfactory.

The wire supply performance was checked by evaluating the performance in supplying the wire to a universal carbon-dioxide shield welding machine by using a universal wire supplying machine. Also, weldability was evaluated by performing carbon-dioxide shield welding under welding conditions of a welding current of 300 A, a welding voltage of 32 V, a welding speed of 30 cm/min, and a carbon-dioxide shield gas flow of 25 L/min.

As seen from the above-described results, the advantages of the present invention are ensured in that satisfactory roundness of the flux-filled welding wire is obtained and that the performance in uncoiling and feeding the wire for supply to the welding machine in welding work is not adversely affected and better performance is obtained in the wire supply even in the case of the wire having a diameter as small as mentioned above. Also, in the manufacturing process for the flux-filled welding wire, smooth running of the hoops and the wire is not impeded and a higher speed of the manufacturing line (i.e., higher running speeds of the hoops and the wire) can be realized.

According to the present invention, the method of manufacturing the flux-filled welding wire and the flux-filled welding wire can be provided which ensure satisfactory roundness of the flux-filled welding wire and which does not adversely affect the performance in uncoiling and feeding the wire for supply to the welding machine in welding work and hence can improve the performance in the wire supply even in the case of the wire having a diameter as small as mentioned above. As a result, the present invention can be suitably applied to the continuous manufacturing process for the flux-filled welding wire, which is required to have high production efficiency and quality guarantee.

Claims

A method for continuously manufacturing a flux-filled welding wire with a small diameter of 2.0 mm0 or less and having a seam, using, as a starting material, a long steel band obtained by the longitudinal ends of individual steel bands, obtained by cutting a steel sheet, successively placing them against each other and joining the adjacent ends by welding, the method comprising the steps of: when the individual steel bands are connected to each other, the longitudinal ends of the individual steel bands to lie against each other and the connecting lying ends by welding in a state in which burrs formed during the cutting of the steel sheet and extending along the transverse ends of each steel band in a longitudinal direction thereof are oriented in the same direction with respect to the adjacent steel bands; and if the ilux-filled welding wire, wherein the connected steel bands form a sheath, is produced, the adjacent steel bands are positioned so that the burrs are not present in an outward-facing orientation of the welding wire in a seam portion of the flux-filled welding wire.

The method for manufacturing the flux-filled welding wire according to claim 1, wherein the welding is arc welding, and welding is performed in a state in which tab plates are placed on either side, in contact with an adjacent portion in which the longitudinal ends of the individual abutting steel bands.

3. A flux-filled welding wire with a small diameter of 2.0 mm0 or less and provided with a seam, the wire made using a long steel band as a starting material, obtained by cutting the longitudinal ends of individual steel bands, obtained by cutting a steel sheet , successively placing against each other and joining the adjacent ends by welding, the longitudinal ends of the individual steel bands being connected to each other in a state in which burrs arise during the cutting of the steel sheet and present in the output steel band in the upward direction of each steel band directed, and wherein the burrs are not present in outward facing orientation in a seam portion of the steel band that forms a sheath of the welding wire.