METHOD OF MANUFACTURING METAL BARS AND APPARATUS THEREFOR

Abstract: An intermediate billet, which has been rolled by a rough roll train of a bar rolling mill, is finish rolled to obtain N pieces of strands connected to one another through thin connecting portions. Next, strands at opposite ends are cut off at the connecting portions by slit rolls, and subsequently, strands at opposite ends out of a plurality of intermediate strands, which have not been cut off, are cut off at the connecting portions by the slit rolls. Thenceforth, the cut-off of strands at opposite ends at the connecting portions is repeated, whereby all of the strands are cut off at the connecting portions by the slit rolls, and subsequently, the strands thus cut off are simultaneously rolled, to thereby manufacture N pieces of metal bars at the same time.

Description: Technical Field : The present invention relates to methods and apparatuses for producing metal bars wherein at least four strands of metal bars, particularly steel bars, are obtained by simultaneously rolling from a single billet. Background Art : A steel bar of 9 to 20 mm in diameter as a concrete bar for reinforcing concrete is produced in large quantities. In this context, the bar includes not only a bar whose cross section is substantially round, but also a bar whose cross section is slightly oval or square-shaped and a ribbed bar which is the above-mentioned bar, on which ribs are formed. Said bars are produced by a bar rolling mill generally having 16 to 20 stands in the following manner: The bar rolling mill is roughly composed of a roughing rolling train and a finishing rolling train. In the roughing rolling train, a preformed billet is produced by rolling a billet of 100 to 150 mm in diameter and thus reducing a cross-sectional area of the billet to 70 to 95 % thereof. Then, a final product is obtained by rolling said preformed billet in the finishing rolling train. The method wherein a strand of metal bar is produced from a single billet in this way is popular. However, such a method is not effective in productivity of the bars. Therefore, the following methods as methods for producing a plurality of bars from a single preformed billet in a finishing rolling train have been proposed: (1) A method for simultaneously producing three strands of bars from a single preformed billet in a finishing rolling train, which is disclosed in JP-A-1-53121 (hereinafter referred to as the "Prior Art 1"). In the method of the "Prior Art 1", a finishing rolling train is composed of 4 stands K 4 , K 3 , K 2 , and K 1 . The K 4 and K 3 stands roll a preformed billet to produce three strands of bars 2a, 2b and 2c connected to each other by means of thin connecting portions 2d and 2e as shown in Figure 9 (A). A pair of slit rolls cuts the three strands of bars 2a, 2b and 2c along the connecting portions, and then K 2 stand, composed of a pair of calibered rolls, rolls the three cut strands of bars 2a, 2b and 2c to produce bars of oval cross section as shown in Figure 9(B), and the K 1 stand, composed of a pair of rolls with a finishing caliber (a bore type), rolls the three strands to produce final product bars 3a, 3b, and 3c as shown in Figure 9(C). Figure 9(A) shows a state of rolling a billet at the stand K 3 . Figure 9(B) shows a state of strands having been cut off by means of a pair of slit rolls, following the K 2 stand. Figure 9(C) shows the shapes of bars 3a, 3b and 3c after the bars have been rolled at the stand K 1 . The "Prior Art 1" is limited to simultaneously producing three strands of bars from a single preformed billet by means of such a finishing rolling train. (2) A method for simultaneously producing four strands of bars from a single preformed billet, which is disclosed in JP-A-2-21882 (hereinafter referred to as the "Prior Art 2"). This document is regarded as being the closest prior art. The "Prior Art 2" was developed by the applicant of the present invention to enhance the productivity of the method of the "Prior Art 1". According to the method of the "Prior Art 2", bars are produced as follows: Four strands 4a, 4b, 4c and 4d connected to each other by thin connecting portions 4e, 4f and 4g are formed as shown in Figure 10(A) by means of stands K 4 and k 3 . The four strands 4a, 4b, 4c and 4d as shown in Figure 10(B) are cut off along the central connecting portion 4f by means of a first pair of slit rolls (6) between stands K 3 and K 2 as shown in Figure 11. Then, four bars 4a, 4b, 4c and 4d as shown in Figure 10(C) are obtained by cutting off along the connecting portions (4e, 4g) by means of two pairs of second slit rolls (7, 8). Subsequently, bars 5a, 5b, 5c and 5d as final products, as shown in Figure 10(D), are produced by simultaneously rolling the four bars 4a, 4b, 4c and 4d. Processes of rolling and cutting the strands are shown in Figures 10(A) to 10(D) and the positions of the slit rolls on the plane are shown in Figure 11. The method of the "Prior Art 2" has some difficulties in that this method is confined to a method of simultaneously producing four bars. The present invention provides a method for producing metal bars, which solves said problems and is further improved, and it is an object of the present invention to provide a method for simultaneously producing at least four metal bars and an apparatus therefor. Disclosure of the Invention : The present invention proposes a new construction of a finishing rolling train and a new rolling method for producing metal bars wherein the conventional roughing rolling train is used. The stands of a finishing rolling train are stands K 4 , K 3 , K 2 and K 1 arranged in series in the rolling direction. 1 ○ A flat preformed billet is supplied from a roughing rolling train to the stand K 4 in a finishing rolling train. The last roll stand in the roughing rolling train is the stand K 5 . 2 ○ If N strands of bars are planned to be produced the stand K 4 is composed of a pair of upper and lower rolls each having (N - 1) of convex portions. The preformed billet is rolled to have concave portions by means of the rolls having the convex portions so that each cross section of the divided portions has substantially the same area. 3 ○ The stand K 3 is composed of a pair of caliber rolls. The two outer calibers of the rolls of the stand K 3 have sections of an oval shape longer in width. An intermediate caliber of the rolls of the stand K 3 usually has a section of a diamond shape. The rolls of the stand K 3 , however, could have calibers of an oval shape, longer in the vertical directions. In the stand K 3 , strands corresponding to the shapes of calibers are formed. 4 ○ The present invention has a major feature in the arrangement of pairs of slit rolls positioned adjacent to the stand K 3 . The first pair of slit rolls having two edges is placed just behind the stand K 3 to cut off two outer strands of the preformed billet along connecting portions of the strands. Subsequently, when four strands of bars are simultaneously produced, the center connecting portion of the strands is cut by means of the second pair of slit rolls. When five strands of bars are simultaneously produced, the strands are cut off by the second pair of slit rolls with two edges. When six or seven strands of bars are simultaneously produced, a third pair of slit rolls is placed behind the second pair of slit rolls. The present invention has a feature in that the connected strands are sequentially cut off by means of the pairs of slit rolls from both the outer strands toward the central strands. This is because cut strands cannot be separated from each other when two strands or more are cut simultaneously. 5 ○ After all the strands have been cut off from each other, all the strands are subjected to an ordinary oval rolling by means of the stand K 2 . Accordingly, a pair of upper and lower rolls having the same number of oval calibers as that of strands, which are simultaneously rolled, are arranged in the stand K 2 . 6 ○ The stand K 1 for carrying out the finishing rolling is placed behind the stand K 2 . The strands having been rolled by means of the stand K 2 are rolled on the stand K 1 so that the strands can have dimensions and shapes of final products. Accordingly, a pair of upper and lower rolls having calibers of dimensions and shapes of the final products are arranged in the stand K 1 . Brief Description of the Drawings : Figure 1 is a top plan view showing an arrangement of the finishing rolling train of an apparatus for producing metal bars by the present invention. Figures 2(A) to 2(G) are explanatory views showing the roll calibers of each stand in the finishing rolling train as shown in Figure 1. Figure 3 is a top plan view of an arrangement of the first and the second slit rolls placed just behind a stand K 3 . Figure 4 is an explanatory view showing a caliber of the first pair of slit rolls. Figure 5 is an explanatory view showing a caliber of the second pair of slit roll. Figure 6 is an explanatory view showing the slit roll guide composed of the first pair of slit rolls and the second pair of slit rolls as shown in Figures 3 to 5. Figures 7(A) to 7(H) are explanatory views showing the processes of deformation of the strands by roll calibers from the roll stands K 5 to K 1 in the case of simultaneously rolling five strands of bars. Figures 8(A) to 8(I) are explanatory views showing the processes of deformation of the strands by roll calibers from the roll stands K 5 to K 1 in the case of simultaneously rolling six strands of bars. Figures 9(A) to 9(C) are explanatory views showing the processes of rolling in the "Prior Art 1". Figures 10(A) to 10(D) are explanatory views showing the processes of rolling in the "Prior Art 2". Figure 11 is an explanatory view showing an arrangement pairs of slit rolls in the "Prior Art 2". The Best Mode for Carrying out the Invention : An embodiment of the present invention will now be described in detail with reference to the appended drawings. In Figure 1, reference numeral 9 denotes a final stand K 5 in a roughing rolling train. The final stand has a pair of vertical rolls (hereafter referred to as "V roll") and finally controls the shape of a preformed billet supplied to the next stand K 4 . Reference numeral 11 denotes a stand K 4 , 13 a stand K 3 16 a first pair of slit rolls, 17 a second pair of slit rolls, 18 a stand K 2 and 20 a stand K 1 . An ordinary roughing rolling train (not shown) is arranged before the stand K 5 . Following the K 1 stand, a finishing billet yard is laid out, which includes cutting devices and cooling beds. Roll calibers arranged in the stands as shown in Figure 1 and a process of deformation of strands are described with specific reference to Figure 2. Figure 2(A) shows a shape of a roll caliber of said stand K 5 and a shape of a preformed billet 10. The stand K 5 provides a shape of the preformed billet 10 by means of a pair of V rolls required for rolling in the stand K 4 . Figure 2(B) shows an oval caliber rolls 11 and the strands divided into four in the case of simultaneously rolling four strands. The caliber roll 11 has three convex portions 11a, 11b and 11c as shown in Figure 2(B) and divides the preformed billet 10 into four strands 12a through 12d having a substantially equal cross sectional area. In this case, the depth of the convex portions is from 1 to 4 mm, and the four strands are sufficiently connected to each other with shallow cleavages. The depth of the cleavages is from 10 to 20 % of the thickness of the strand 12. The four strands divided are substantially square-shaped or oval in shape. Figure 2(C) shows that the connected four strands are further rolled by the stand K 3 . Both the outer roll calibers 13a and 13d are of oval shape or box-shaped and the roll calibers 13b and 13c at the intermediate portion are diamond-shaped in principle. Accordingly, both the outer strands 14a and 14d are box-shaped and the two strands 14b and 14c at the intermediate portion are diamond-shaped. The four strands are connected to each other by means of thin connecting portions (hereinafter referred to as the "connecting portion") 14e through 14g. Figure 2(D) shows that the connecting portions 14e and 14g of the connecting portions are cut by means of a first pair of slit rolls. Figure 2(E) shows the four strands 14a through 14d after the center connecting portion 14f has been cut by means of a second pair of slit rolls. Figure 2(F) shows roll calibers 18a through 18d and strands 19a through 19d in the stand K 2 . The stand K 2 has oval roll calibers so that the four strands as shown in Figure 2(E) are rolled to be adapted to the final rolling, whereby four strands 19a to 19d of oval shape are formed. Figure 2(G) shows roll calibers 20a through 20d on the stand K 1 for carrying out the final rolling. When the final product is a round bar, the roll caliber is a round caliber. When the final product is initially of oval shape or square-shaped, the roll calibers in the stand K 1 are required to have the shape of the final product. When the final product is a ribbed bar, the roll caliber should be a caliber which gives ribs on the bars. Approximate dimensions of the preformed billet are shown to show specific examples of the present invention. In the above examples, initially, a square billet of 150 mm in each side was rolled by means of a roughing rolling train. A preformed billet 10 obtained in the final stand K 5 had a box-shape with a breadth of 41.24 mm and a thickness of 13.48 mm and the central portion of the preformed billet was swelling. Accordingly, the roll calibers also were box-shaped. A roll caliber in the stand K 4 had a breadth of approximately 48.1 mm and had an oval shape as a whole, the maximum thickness of which was about 10.5 mm. The roll caliber had convex portions 11a through 11c at positions where the roll caliber was divided into about four equal portions. The breadth of each of the divided strands was from 11.5 to 12.5 mm. Each of both the outer roll calibers 13a and 13d in the stand K 3 had a breadth of about 7.9 mm and a thickness of 9.5 mm and had an oval shape. Diamond-shaped roll calibers 13b and 13c at the intermediate portion had a breadth of about 11.4 mm and a thickness of 12 mm. The connecting portions had a breadth of about 0.8 mm and a thickness of 1 mm or less. Roll calibers 18a through 18d in the stand K 2 had a breadth of 17.8 mm and a thickness of 6.6 mm and were flat oval-shaped. Roll calibers 20a through 20d in the stand K 1 were round calibers of about 8.9 mm in diameter. In consequence, a bar of about 8.8 mm in diameter as a final product could be produced. Said dimensions were only a part of the examples. Those dimensions are not limited and represented in approximate numerical values. Subsequently, the construction of pairs of slit rolls will now be described with specific reference to Figures 3 to 8. Figure 3 is a top plan view showing an arrangement of a first pair of slit rolls 16 and a second pair of slit rolls 17 placed just behind a stand K 3 . Reference numerals 16c, 16d and 17b denote guides for controlling the directions of movement of cut strands. Now, the strands 14a through 14d are cut off as shown in Figure 4. The present invention is characterized in that connecting portions of two strands 14a and 14d on the outer sides out of divided four strands 14a through 14d are cut off by means of two edges 16a and 16b of a first pair of slit rolls 16. The important points in the shape of the two edges 16a and 16b consist in that the edges are formed so that the cut strands 14a and 14d can be directed outwardly, as shown by the arrows in Figure 3. Subsequently, the two central strands 14b and 14c are cut off along the connecting portion 14f by means of the edge 17a of the second pair of slit rolls 17 as shown in Figure 5. The angle of the edge 17a of the second pair of slit rolls is formed so that the cut strand can be directed outwardly. As described above, the present invention includes the feature that initially both the outer strands are cut off and then two inside strands are sequentially cut off, in contrast to the Prior Art 2. As shown in Figures 3 to 5, a method is adopted wherein the strands are sequentially cut off from both the outer strands to the central portion thereof. This method has an advantage in that the position of the second pair of slit rolls 17 can be fixed in relation to the position of the first pair of slit rolls 16 independent of the rolling speed of the strands and that the cutting of the strands can be performed to change of the rolling speed and the like. As shown in Figure 6, the first pair of slit rolls 16 and the second pair of slit rolls 17 are accommodated into a housing 22. Reference numeral 23 denotes a guide for leading cut strands. The device as a whole is referred to as a slit roll guide. The above-described is an embodiment in the case where four bars are simultaneously produced. Figure 7 shows an embodiment wherein five bars are simultaneously produced. Figure 8 shows an embodiment wherein six bars are simultaneously produced. The method for simultaneously producing five bars or six bars is quite the same as the method for simultaneously producing four bars. However, additional explanation is given below as follows: Figure 7(A) shows a roll caliber 9a in a stand K 5 and a preformed billet 10. Figure 7(B) shows a process in which five strands 25a through 25e, each having equal cross sectional area, are rolled by means of a pair of rolls 24 in the stand K 4 . Figure 7(C) shows a process in which both the outer strands 27a and 27e are rolled to form strands of oval shape or of a box-shape, and intermediate three strands 27b through 27d are rolled to form strands of a diamond shape or oval shape which is longer in vertical directions, by means of a pair of rolls 26 in the stand K 3 . Figure 7(D) shows a process in which both the outer two strands 27a and 27e are cut off by means of two edges 28a and 28b of the first pair of slit rolls 28. Figure 7(E) shows a process in which connected three strands 27b, 27c and 27d are cut off by means of the second pair of slip rolls 29 having two edges 29a and 29b along the connecting portions 27g and 27h. Figures 7(F) to 7(H) show a process in which the cut strands 27a through 27e are rolled on the stands K 2 and K 1 . Figures 8(A) to 8(I) show roll calibers and deformation of the strands when six bars are simultaneously produced. Figure 8(A) shows the deformation of the billet in the stand K 5 Figure 8(B) shows the deformation of the strands in the stand K 4 . Figure 8(C) shows the deformation of the strands in the stand K 3 . Figure 8(D) shows a cutting procedure of the strands by means of the first pair of slit rolls 38. Figure 8(E) shows a cutting procedure of the strands by means of the second pair of slit rolls 39. Figure 8(F) shows a cutting procedure of the strands by means of the third pair slit rolls 40. If the number of bars to be simultaneously produced is N (N ≧ 4), 1/2 x N pairs of slit rolls are provided in the slit roll guide when N is an even number. When N is an odd number, 1/2 x (N - 1) pairs of slit rolls are provided in the slit roll guide. Figure 8(H) shows a rolling process at the stand K 2 . Figure 8(I) shows a rolling process at the stand K 1 . Industrial Applicability : As described above, the present invention is intended to simultaneously roll mainly four steel bars or more. It is clear that the present invention can be applied to the production of aluminium bars, copper bars and other metal bars in general.

Claims: A method for simultaneously producing N strands of metal bars from a single preformed billet, where (N is at least four), comprising the steps of: (1) forming the single preformed billet in a roughing rolling train of a bar rolling mill; (2) then, rolling, in a finishing rolling train of said bar rolling mill, said preformed billet into N strands having substantially the same cross-sectional area and connected to each other by means of thick connecting portions; (3) then, rolling said N strands into N strands connected to each other by means of thin connecting portions; characterised by (4) cutting off each of strands positioned on the both outermost sides from said N strands along the respective thin connecting portions by means of a pair of slit rolls; (5) subsequently cutting off each of strands positioned on the both outermost sides from remaining strands not yet cut off along the respective thin connecting portions by means of a respective further pair of slit rolls; (6) repeating said cutting as defined in the step (5) until all the remaining strands of said N strands are cut off along the respective thin connecting portions, when N is odd; (7) cutting off last two strands of said remaining strands not yet cut off along the thin connecting portion, when N is even; and (8) then, simultaneously rolling said cut-off N strands into N strands of metal bars. The method of claim 1 wherein at step (3) each of the strands positioned on the both outermost sides of said N strands is rolled into an oval or box cross-section, and each of remaining strands is rolled into a diamond cross-section, all of said strands being connected to each other by means of the thin connecting portions. The method of claim 1 or 2 wherein said N strands comprises four strands. The method of claim 1 or 2 wherein said N strands comprises five strands. The method of claim 1 or 2 wherein said N strands comprises six strands. A slit roll guide, which is placed at an intermediate position of a finishing rolling train of a bar rolling mill, for simultaneously producing N strands of metal bars where (N is at least four), characterised in that is comprises: (1) when N is odd 1/2 x (N-1) pairs of slit rolls arranged in series in a rolling direction, each roll of said 1/2 x (N-1) pairs of slit rolls having a pair of laterally spaced cutting edges; (2) when N is even 1/2 x N pairs of slit rolls arranged in series in a rolling direction, each roll of the first (1/2 x N)-1 pairs of slit rolls out of said 1/2 x N pairs of slit rolls having a pair of laterally spaced cutting edges, and each roll of the last 1/2 Nth pair of slit rolls out of said 1/2 x N pairs of slit rolls having a single cutting edge; (3) said plural pairs of slit rolls, each pair of which has said pair of cutting edges, being arranged in series in a rolling direction so that a distance between said pair of cutting edges of each pair of slit rolls sequentially becomes smaller in the rolling direction; (4) when N is even said last 1/2 Nth pair of slit rolls, which has said single cutting edge, being arranged at a last position in a rolling direction; and (5) said cutting edges of said plural pairs of slit rolls being parallel to the rolling direction. A finishing rolling train for simultaneously producing N strands of metal bars, where (N is at least four), comprising: (1) first to fourth roll stands (K 4 , K 3 , K 2 and K 1 ) arranged in series in a rolling direction, each of said first to fourth roll stands having a pair of calibered rolls for rolling strands of metal bars; and (2) a slit roll guide as defined in claim 6 arranged between said second roll stand (K 3 ) and said third roll stand (K 2 ). A bar rolling mill for simultaneously producing N strands of metal bars, where (N is at least four), comprising: (1) a roughing rolling train; and (2) a finishing rolling train as defined in claim 7 installed directly following said roughing rolling train.

Inventors: MATSUO GIICHI, SAKAI AKIRA, MATSUO, GIICHI, SAKAI, AKIRA
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1991
Main classification: B21B1
IPC codes: B21B1, B23D19, B21B15, B21B27