Patent Publication Number: US-9889574-B2

Title: Sheet groove cutter capable of operation without use of ruler

Description:
TECHNICAL FIELD 
     The present invention relates to a groove cutter for floor sheets which can form a concave groove, necessary for bonding tightly the adjacent floor sheets by use of a welding rod, on the seam formed by the adjacent floor sheets, and in particular relates to a groove cutter for floor sheets wherein a concave groove at a seam, which is formed bridging over the floor sheets, can be formed rapidly and accurately without using a ruler. 
     BACKGROUND OF THE INVENTION 
     Generally, when floor sheets are bonded to a base sheet of floor, in order to bind a seam of individual floor sheets tightly, a method of pouring a heat melted welding rod into the said seam is used. In this case, since the floor sheets are laid so closely each other from the beginning, it is difficult to press directly the heat melted welding rod into the narrow gap, which exists at the seam, from the top of the seam. Therefore, even if the welding rod had been pressed into the gap, the heat melted welding rod merely becomes firm on the surface of the seam in a state of being raised (See,  FIG. 1 ). If this raised area is simply whittled away to flat the floor surface, the original seam appears again and the floor surface just returns to the original state. Therefore, it is practically impossible to bind each floor sheet tightly by using such method. 
     Generally, a U-shaped or V-shaped groove is cut at the seam part by using a hand cutter or the like (See,  FIGS. 2 and 3 ), then the heat melted welding rod is poured into the groove (See,  FIG. 4 ), and the raised area on the surface is whittled away to finish the surface flatly (See,  FIG. 5 ). According to this method, except when it is difficult to cut a groove having desired depth since sheets are thin or hard, it is possible to bind sheets tightly to some extent. 
     In either case, it is required that the concave groove is formed uniformly along a seam without being displaced to right or left from a center of the seam by means of the above groove-cutting work. Therefore, in order for the seam to be placed at the center of a U-shaped or V-shaped blade of cutter, a ruler is usually set parallel to the seam, and the groove is cut contacting the blade of cutter with the ruler. With regard to this method, if the seam is short in length, it does not take time or care to work so much. However, when a floor space is larger and a seam is longer in length, there is a disadvantage that it takes an immense amount of time and effort and also an operating cost becomes huge. 
     In order that the groove can be cut easily on the seam of sheets, a grooving tool having a guiding function is proposed (for instance, Patent document 1). By using this tool, a relatively stable operation can be performed due to a support structure having a two contact points consisting of a blade edge and a guiding roller against sheet surfaces. However, since the distance between the support points and a grip is long, there are disadvantages that not only the stability is limited but also a tool itself is easy to break. 
     In addition, a floor grooving device equipped with rollers having a function for a guiding seam, at the front end portion and the rear end portion of the device itself is proposed (Patent document 2). With regard to this device, there was a disadvantage that this device causes a risk to cut off the part other than the seam of the floor in the process of operation, since the front roller, which is the seam guide, is apt to run off from the seam. Furthermore, there were other disadvantages that the device cannot follow the seam sufficiently, since the rear roller, even though a width of it is wider than that of the above front roller, is not always stable in the wide cut groove which is formed by a blade equipped just behind the roller provided at front of the device, and also the device cannot sufficiently correspond to surface irregularities of floor. And also, there was one more disadvantage that, the rear roller, and if the second blade is provided at the rear, the second blade should also be detached when a curved groove is formed, which is a troublesome operation. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent document 1: Japanese Unexamined Utility Model Publication Jitsu kai hei 6-57606 
     Patent document 2: U.S. Pat. No. 6,640,446 
     As a result of extensive studies for improving the above conventional disadvantages, the inventors of the present invention found that, when a nonrotating thin fixed plate which is inserted into the seam formed between sheets to guide the tool along the seam is provided, and also a blade is provided behind that plate in order to cut the seam part so as to have a concave-shaped groove, and further a wheel having a width matched to a groove formed by the above blade, or a fixed member of which cross-sectional shape at the end fits into the above groove is provided near the rear end of tool, not only this tool can follow the seam very well, but also it can be improved in following the surface irregularities of the floor, maintaining a light operability and the depth of groove formed at the seam can be uniformed better than ever. The inventors also found that it becomes difficult for a welding rod pressed into the seam for filling up to detach by forming the second groove inside the above first groove, and that the bond between sheets can be tightened much better than ever by the second groove, and further found that, by making the tool bottom near the front end having the thin plate incline at a suitable angle moderately toward the end upward and making the thin plate nonangular-shaped so as to incline the tool forward easily, it becomes possible to operate the tool easily along the seam by inclining the tool forward even when the seam is curved, thereby achieving the present invention. 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Therefore, the first object of the present invention is to provide a groove cutter for floor sheets wherein it is possible to be operated easily corresponding with the surface irregularities of floor without using a ruler or the like and a groove having excellent uniformity of depth can be cut rapidly and accurately at the seam of floor sheets. 
     The second object of the present invention is to provide a groove cutter for floor sheets, which can be operated along the curved seam easily. 
     The third object of the present invention is to provide a groove cutter for floor sheets wherein the second groove can be cut continuously inside the first groove by one time operation. 
     Means to Solve the Problems 
     The above objects of the present invention were attained by a groove cutter for floor sheets which is a tool capable of being operated without using a ruler and can cut a seam, which is created when sheets are laid sequentially on the surface of floor base with an adhesive agent, so that a groove formed along the seam can bridge over both adjacent sheets, comprising a front part, a middle part, a rear part, wherein the front part has a thin guide plate, which is to be inserted into the seam and guides the said tool along the seam when pushing the tool forward, at the front end, and at least one blade to cut a concave groove at the seam part of the above sheet, which is provided behind the guide plate so as to be detachable, and also a stabilizing member provided at the rear part, which is to be inserted into the concave groove, to stabilize a direction of movement of the tool along the seam; and the method for cutting groove at the seam of sheets, wherein by means of one time operation, shallower groove than the thickness of the sheet is formed by the first blade, then a deeper groove is formed by the second blade inside the groove formed by the above first blade. 
     The groove cutter for floor sheets of the present invention may provide a blade, which may be detachable or slidable in and out, at the rear part so that when the tool is turned 180 degrees, that is, it is the opposite direction, the said blade is able to act as the blade for cutting a concave groove at the seam part, and a bottom part of the front part having the thin guide plate may also be provided so as to be able to slide back and forth. 
     In addition, a pair of rollers and/or wheels running on the surface of the sheet may be provided on the right and left side, near the stabilizing member of the rear part of the tool, and an independent grip may be provided mainly over the middle part. Furthermore, it is preferable to provide the first blade just behind the guide plate, and to provide the second blade having a narrower width than the first blade behind the first blade so as to be free to detach and so as to be able to cut much deeper groove inside the groove formed by the first blade. 
     Furthermore, it is preferable that the stabilizing member set at the rear part is a wheel having a width almost corresponding to the groove formed by the blade(s), or the fixed member having a cross-sectional shape almost corresponding to a cross-sectional shape of the groove. Also, it is preferable that the bottom surface of the front end part having the guide plate inclines upward, and the above guide plate, without having angles, is designed to have a smooth shape in order to be able to incline the tool forward easily along the inclined surface. 
     Moreover, the groove cutter for floor sheets of the present invention may have the constitution of the invention, wherein the front end portion which is set before the first blade provided at the front part and has the guide plate, is detachable from the tool or 90 degrees or more turnable upward, and when the said front end portion is detached or is turned 90 degrees or more upward, the first blade at the front part sticks out from the tool. 
     Effect of the Invention 
     By using the groove cutter of the present invention, a concave groove can be easily and accurately obtained at the seam existing between the sheets without using a ruler or the like, and the concave groove also can be easily and accurately obtained along the seam and at the seam, which is created between the sheets attached to base sheets having small surface irregularities or formed as curved seam from a design-centric viewpoint, although it was difficult in these cases to obtain the concave groove beautifully even though the ruler or the like was used. In addition, in cases of cutting further groove inside the groove cut first, by means of the present invention, the working efficiency of grooving welding operation can be remarkably improved and adjacent sheets are bound much stronger each other than ever, since the melted welding rod pressed into the groove can hardly be detached from the groove formed at the seam of the floor sheets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view indicating the state wherein the seam part having no cutting groove is only covered by a melted welding rod. 
         FIG. 2  is a cross-sectional view indicating the state wherein a U-shaped groove is cut at a seam of floor sheets. 
         FIG. 3  is a perspective view looking from the upper side, indicating the state wherein a U-shaped groove is formed at the seam of the floor sheets. 
         FIG. 4  is a perspective view looking from the upper side, indicating the state wherein a heat melted welding rod is poured into a U-shaped groove formed at the seam of floor sheets. 
         FIG. 5  is a perspective view looking from the upper side, indicating the state wherein the heat melted welding rod is poured into the U-shaped groove formed at the seam of floor sheets to solidify and then the welding rod area raised from the surface is whittled away to flat the surface. 
         FIG. 6  is a left side view indicating an example of the groove cutter of the present invention. 
         FIG. 7  is a bottom view of bottom of the groove cutter in  FIG. 6 . 
         FIG. 8  is a left side view indicating a case wherein the front plate can move back and forth. 
         FIG. 9  is a bottom view of the groove cutter itself in  FIG. 8 . 
         FIG. 10  is a view indicating an example of the front plate. 
         FIG. 11  is a view indicating an example of the rear plate. 
         FIG. 12  is a front view of the groove cutter in  FIG. 8  wherein the front plate is omitted. 
         FIG. 13  is a back view of the groove cutter in  FIG. 8  wherein the rear plate is omitted. 
         FIG. 14  is a view explaining the usage state of the groove cutter of the present invention. 
         FIG. 15  is a front view of an embodiment of the groove cutter where bottom surface of the front end part having the guide plate is inclined upward. 
         FIG. 16  is a cross-sectional view taken along the chain line  16 - 16  in  FIG. 15 . 
         FIG. 17  is a front view of an embodiment of groove cutter of  FIG. 15  wherein the front part  20  is turned 90 degrees upward and wherein the thin guide plate is omitted. 
         FIG. 18  is a cross-sectional view taken along the chain line  18 - 18  in  FIG. 17 . 
         FIG. 19  is a cross-sectional view taken along the chain line  19 - 19  in  FIG. 17 . 
         FIG. 20  is a side view of the embodiment of the groove cutter shown in  FIG. 17 . 
         FIG. 21  is cross-sectional view taken along the chain line  21 - 21  in  FIG. 15 . 
         FIG. 22  is a side view of the embodiment of the groove cutter shown in  FIG. 15 . 
         FIG. 23  is a left side perspective view of an embodiment of the groove cutter shown in  FIG. 15 . 
         FIG. 24  is a left side perspective view of an embodiment of the groove cutter shown in  FIG. 17 . 
         FIG. 25  is a close up side view of a guide plate with a smooth shape, having no corners, and inclined upward. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereafter, the present invention is explained according to Examples, however, the present invention is not limited by these Examples. In this regard, the groove cutter for floor sheets of the present invention will be described and explained simply as “a tool” in the present specification. 
       FIG. 6  is an example of side view of the groove cutters of the present invention for the case of manufacturing the body integrally except the bottom and the movable portions. In the views, numeral  1  is the tool body of the present invention,  2  is the grip,  3  is the front part,  4  is the middle part,  5  is the rear part,  6  is the thin guide plate guiding the seam of floor sheets,  7  is the cutting blade for the U-shaped or V-shaped concave groove,  8  and  8 ′ are groove-like or tube-like spaces set for equipping the groove-cutting blade,  9  and  9 ′ are screw bolts for detaching the groove-cutting blade or adjusting a position of the groove-cutting blade,  10  is the bottom part covering the whole area of the above front, middle and rear parts. It is preferable that the middle part is designed so as not to contact with the floor sheets, in order to move the tool lightly when used and in order to follow well the surface irregularities of floor base, like the present Examples. In addition, it is preferable that the front end of the front part inclines upward like the present Examples in order to correspond easily to the curved seam of the floor sheets. Numeral  11  is the wheel which functions as the stabilizing member against the movement direction of the tool when the tool is used in cases where the seam of floor sheets is a straight line,  12  is the wheel shaft. This wheel  11  is naturally placed in the storage space for placing the said wheel set in the body. When a fixed member is used as the stabilizing member, the above storage space is not needed. In this case, the above fixed member may be set as appropriate using known fixation means: for instance, a male screw is set at the rear end portion of the fixed member whose cross-sectional shape corresponds to that of the groove, and also a screw hole screwed together to the said male screw is provided at the body bottom in order to screw together both for fixation. 
     In addition, in cases where a formed groove does not reach the floor base, a roller having a thin disk may be used as the stabilizing member so as to get into the seam of remaining sheets, and if necessary, a middle roller may further be set behind the first groove-cutting blade so as to get into the seam of remaining sheets. 
       FIG. 7  is a bottom view of the bottom part  10 , omitting the groove-cutting blade  7  from the tool shown in  FIG. 6 . Numeral  13  in the views is a pair of rollers attached in order to improve the stability of right and left direction of the tool when used. These rollers are omitted in  FIG. 6 . Numerals  14  and  14 ′ are openings where groove-like or tube-like spaces  8  and  8 ′ for attaching the blade appear at the bottom part, and groove-cutting blades  7  and  7 ′ are supposed to pass through these openings. Numeral  15  is a screw hole for fixing the bottom part to the body with a screw bolt. The number of fixation place and the position of fixation place can be designed as appropriate. It is preferable that a thread does not stick out from the bottom part by using a screw bolt having a flat thread. 
     Naturally, with regard to the tool of the present invention, all the nonmovable parts including the bottom part  10  can be manufactured integrally. Materials can be selected from among known materials appropriately, however, it is preferable in the present invention to use aluminum in particular. 
       FIG. 8  is an example wherein the body bottom part is directly designed so as not to contact the bottom part of the middle part with sheets. Particularly, this is the example wherein the front plate  20  having thin guide plate  6  at the front part of the body bottom part is attached so as to be movable back and forth and be detachable. In the present Example, the fixed member is attached as the stabilizing member  11 . 
       FIG. 9  is a view indicating an example of the bottom part, wherein in order to be able to withstand the friction against the sheets when used, plates comprised of materials having high hardness such as SUS are attached in a detachable way at the front bottom part and rear bottom part. In the present Example, the flange  16  is attached on both sides of left and right of front and rear parts so that the plate can be detached easily with a bolt. Numeral  17  is a screw hole for fixing the front plate  20  with a screw bolt,  18  is a screw hole for fixing the rear plate with a screw bolt. When the above plate having high hardness is not attached at the rear bottom part, it is preferable that the flange part itself or at least the surface thereof is reinforced with the abrasion-resistant materials. 
       FIG. 10  is a view indicating an example of the front plate  20  which can move back and forth at the front bottom. Numeral  21  in the views is an opening for passing through the groove-cutting blade  7  and corresponds to the opening  14  in  FIG. 7 . Both openings can be designed as appropriate so as to make a shape for taking chips out easily. Numeral  22  is a slit for moving the front plate  20  back and forth and fixing it at a predefined position with a screw bolt. 
       FIG. 11  is a view indicating an example of the rear plate  30 . Numeral  31  in the view is an opening for a screw bolt, which is screwed into the screw hole  18  provided at the body, in order to fix the rear plate  30 . If a stabilizing member is a wheel, this rear plate  30  is usually longer than the diameter of the above wheel so that a hole for the wheel can be provided in the rear plate  30 . However, if the stabilizing member  11  is a fixed member, the length thereof can be designed further freely in the same way as the present Examples. If the stabilizing member  11  is not attached to the rear plate  30 , but attached to the body directly, the rear plate  30  can be made much smaller. 
     The tool of the present invention can be operated with a hand by gripping a handle part. If the handle part shown in the above Examples is not provided in particular, the middle part of the body functions practically as the handle part. Such a tool is also one of embodiments of the present invention. Definitely, it is free to design the part consisting of the middle part and the rear part as the part having an easy-to-grip shape. The handle part  2  in the present Example is an all-in-one with the body wherein the body has an easy-to-grip shape by hollowing out the body circularly. However, the handle part  2  can be manufactured as an independent grip from the body and be fixed to the body appropriately using the fixing means. In either event, when the contact area of the tool bottom of the present invention with sheets is larger, not only the movement of tool is heavier while in use, but also it is difficult to follow the surface irregularities of floor base and it is difficult to form a groove having a uniform depth. Therefore, it is preferable to design so as to make the above contact area as small as possible. 
     The front part has thin guide plate  6  and has the opening  14  behind the guide plate  6 . Groove-cutter blade  7  passes through this opening and sticks out from the front bottom. In this case, if the distance between the said groove-cutting blade  7  and the above guide plate  6  is too small, it is difficult for chips to fall off from between the groove-cutting blade  7  and the above guide plate  6 . Therefore, it is necessary that the distance is at least longer than the depth of groove formed. However, in the case of reaching an obstacle such as a wall, this distance remains as a non-cut distance. Hence, in the present invention, in order to shorten the above remaining distance, it is preferable to design the distance between the above groove-cutting blade  7  and the above guide plate  6  is adjustable by using the front plate, which functions as the front bottom having the above guide plate and can move back and forth, or to design the above guide plate  6  part as a part which can completely detachable in order to lose the above remaining distance, or to design the above guide plate  6  part as a part which can move more than 90 degrees upward. 
     In this regard, the front bottom corresponding to the front plate part  20  having the above guide plate  6  contacts with sheets. Therefore, it is preferable that the front bottom part is as small as possible (short plate or short bottom part) in order to follow the surface irregularities of base floor under the sheets. 
     Furthermore, in the present invention, in order to solve the problem of the above remaining part of cutting, the same blade as the above blade can be attached at the rear end portion. This blade can also function as a stabilizing member in general use, when the stick out distance of this blade from the bottom surface of the tool is adjusted to the depth of the groove to be cut. This blade at the rear end portion can stick out all the time, however, it is preferable to attach slidably in and out, in order to enhance safety of the tool and keep the edge of the blade. For that purpose, a person skilled in the art would be able to make the above front blade detachable using known technique such as the screw bolt  9 ′ in the same way as using the screw bolt  9 . 
     In the present invention, by using the blade  7 ′ at the rear end portion which is equivalent to the blade used at the front part, and/or by attaching the wheel  11  having the width corresponding to the cut groove, or by attaching the stick-like or hemispherical stabilizing member  11  of which end cross-section corresponds to the cross-section of the groove, the stability for the direction of movement of the tool of the present invention can be ensured when used, however, the stability for crosswise direction of the tool cannot be sufficient by these technique. Therefore, it is preferable in the present invention that a pair of wheels, or a pair of rollers  13  which have a width larger than the wheel, is arranged on the right and left of the tool near the above stabilizing member  11 . When the wheels  11  are provided as a stabilizing member, the shaft  12  of aforementioned wheels or rollers can be the same shaft of the wheels  11 . Moreover, the above wheels  11  and rollers  13  may turn freely around the fixed rotating shaft  12  or may rotate integrally with the shaft  12 . Where, the direction of the shaft is a direction orthogonal to the longitudinal direction of tool. 
     As described above, by attaching the wheels or rollers  13 , the stability of the direction of movement and the direction orthogonal to it increases sufficiently when the tool of the present invention is used. In this case, in order not to make the use of tool heavier, due to occurring of unnecessary friction, or from the viewpoint of following easily the surface irregularities when a groove is cut, it is preferable to design the rear bottom surface in order not to contact with sheets in the same way as the middle part bottom surface. In addition, it is preferable to design so as for the radius of the above wheels or rollers  13  to be as small as possible in order to follow easily the surface irregularities of the floor. 
     By the way, in some cases, the seam  40  may often not be a straight line but a curved line. In order to be able to accommodate the groove-cutting along such curved seam, it is preferable in the present invention that the bottom end portion of front part having thin guide plate  6  is inclined upward toward the front (See.  FIG. 6 ). By doing this, when the inclined surface  19  of front end bottom surface is attached firmly to sheets, this attached surface alone attaches tightly to the sheet, and even if the seam of sheets are curved lines, the tool can follow easily the carved seam. In order to accommodate such a case, it is required that a groove-cutting blade having a different shape from a blade cutting a straight line seam is used, or if the same blade as the one for the straight line seam is used, that blade is designed to be adjusted and fixed to the body at an angle suitable for the case of curved seam. 
     The guide plate  6  (See.  FIG. 6 ) attached to the front part by fixing means such as welding is inserted into the seam of sheets where a groove is not cut, therefore, the insert depth thereof needs 1 mm or more, however, does not need to reach the bottom of sheet. By inserting the guide plate  6 , it is possible to move the tool along the seam. Therefore, if the seam of sheets  40  is a curved line, the front guide plate  6  alone is inserted into the seam of sheet. In this regard, the thickness of target sheets for using the tool of the present invention is usually 3 mm˜7 mm. 
     In the tool of the present invention, the groove-like or tube-like space  8  is provided on the body upper backwardly from the opening  14 . For instance, U-shaped groove-cutting blade  7  is inserted in this space  8 , then, after adjusting appropriately the blade direction and the blade length sticking out from the bottom surface, it is fixed by a known method such as a screw bolt  9 .  FIGS. 12 and 13  are a front view and a back view of a groove cutter corresponding to the embodiment of  FIG. 18  wherein the front and back plates are omitted. 
     As is shown in  FIG. 14 , when gripping the handle part of tool of the present invention, inserting the above guide plate  6  into the seam of sheets  40  and pushing it forward, a concave groove is cut on the seam of sheets  40  by U-shaped groove-cutting blade  7  set behind the guide plate  6 . The chips  41  of cut sheets move upward along the groove of U-shaped groove-cutting blade  7  and after going through the opening  14  and being guided upward from the tool body, it is removed. In the present invention, it is preferable to make the opening  14  a mortar-like shape so that it can have a function of guiding the chips, and the chips do not block up. 
     In the present invention, the second blade (not shown) having narrower width than that of the first blade may be arranged behind the blade provided at the front part (the first blade) so that much deeper groove can be cut in the groove formed by the first blade. In this case, it is required that the groove formed by the first blade is relatively shallow, and the sticking out distance of the second blade from the bottom surface of the tool body is adjusted so that the groove depth cut by the second blade can be shorter than the thickness of the sheet. 
     In this embodiment, after a groove is formed by the first blade a narrower groove than the first groove width is then formed at the bottom of the first groove by the second blade. The depth of groove on the seam of sheets  40  increases by this procedure, and the groove structure having longitudinal cross-sectional shape, wherein a middle part of it is narrow, can be realized. As a result, the welding rod  50 , which is welded and pressed into the seam, hardly detaches and the binding strength at the seam of sheets increases than that of simple groove structure. In this case, it is preferable to provide an opening, which is able to guide the chips, for such second blade. 
     INDUSTRIAL APPLICABILITY 
     By using the groove cutter of the present invention, it is possible to create a concave groove along the seam of sheets easily and accurately without using a ruler. In addition, it is possible to create a groove having a uniform depth by improving the following properties for small surface irregularities of floor, and to perform groove-cutting of curved seam emphasizing design thereof easily and accurately, and also to further create a groove inside the first cut groove by means of one time operation, which were difficult when a ruler was used. Therefore, not only the working efficiency of conventional groove-cutting welding operation can be remarkably improved, but also the welding rod, which is melted and pressed into the groove, can create a stronger binding strength between sheets since the rod hardly detaches from the groove. 
     Thus, the present invention is quite useful for industry. 
     EXPLANATION OF NUMERAL 
     
         
           1 . Body 
           2 . Handle part 
           3 . Front part 
           4 . Middle part 
           5 . Rear part 
           6 . Thin guide plate 
           7 ,  7 ′ Concave groove-cutting blade 
           8 ,  8 ′ Groove-like or tube-like space provided for equipping the groove-cutting blade 
           9 ,  9 ′ Detachable•adjustable screw bolt for groove-cutting blade 
           10 . Bottom area covering the whole area of front part, middle part and rear part. 
           11 . Stabilizing member 
           12 . Wheel shaft 
           13 . Roller 
           14 ,  14 ′ Opening for passing through the blade 
           15 . Screw hole for fixing the bottom area to the body with a screw bolt 
           16 . Flange 
           17 . Screw hole for fixing the front plate with a screw bolt 
           18 . Screw hole for fixing the rear plate with a screw bolt 
           19 . Inclined surface 
           20 . Front plate 
           21 . Opening provided in the front plate 
           22 . Slit provided in the front plate 
           30 . Rear plate 
           31 . Opening for fixing the rear plate  30  to the screw hole  18  of the body with a bolt 
           40 . Seam of sheet 
           50 . Welding rod