CONTINUOUS ROLLING METHOD

Abstract: A continuous rolling mill is constructed by arranging driven horizontal rolling mills and undriven vertical rolling mills alternately and determining the values of the thickness of the rolled material between adjacent stands, the inter-­ axial distance between work rolls, and the diameter of the work roll to satisfy predetermined relationships.

Description: The present invention relates to a continuous rolling method for rolling blooms of steel or non-ferrous metal into billets as materials for various products or rolling said billets into various products. Heretofore, continuous-cast blooms are normally used in rolling, for example, bar steel. In a Blooming Mill, a continuous-cast bloom is rolled into billets, reheated, and thereafter rolled and formed into various products in a steel Bar Mill or Wire Rod Mill. The rolling mill used heretofore in a Blooming Mill is normally a continuous rolling mill in which horizontal mills and vertical mills are arranged alternately. In this arrangement, both the horizontal and the vertical mills are driven both in the steel Bar Mills and the Wire Rod Mills. The term "horizontal mill" as used in the specification and claims is to be understood to mean a rolling mill of the construction having a pair of work rolls disposed in parallel in the widthwise direction of the rolled material to hold it between them from both sides to thereby apply reduction to the rolled material in the thicknesswise direction. The term "vertical mill" as used herein and in the claims is to be understood to mean a rolling mill of the construction having a pair of work rolls disposed vertically to the surface of the rolled material to hold the longitudinal edges of it between them to thereby apply reduction to the rolled material in the widthwise direction. The expression "a rolling mill is driven" as used herein is to be understood to mean that the work rolls mentioned above are driven to rotate. A vertical mill requires three times or more equipment cost than that of a horizontal mill of the same power because a work roll driving device is to be located in the upper portion of the mill housing. For the same reason, the vertical mill is more than five meters in height and, accordingly, the mill house is inevitably higher and longer. Therefore, vertical mills require much more costs than horizontal mills both in equipment proper and in building of their houses. In order to overcome this disadvantage, the present applicant has proposed in JP-A-58/187203, considered to represent the closest prior art, the technical idea of making vertical mills undriven in a continuous rolling mill having horizontal mills and vertical mills arranged alternately. However, the technical idea of merely making the vertical mills undriven is not sufficient because the rolled material would buckle between the driven horizontal mills and the undriven vertical mills on the downstream side to make continued rolling operation difficult. For this reason, the reduction of area in an undriven vertical mill is predetermined to be 66% or lower than that of a driven horizontal mill on the upstream side. In such arrangement, the total reduction in thickness achieved by the horizontal mills becomes nearly twice the total reduction in width achieved by the vertical mills. Therefore, when a billet or product of square section is required, it is necessary to use flat material of rectangular section because material of square section cannot be used in such arrangement. On the other hand, requirements for the quality of materials for bar steel are very strict and, particularly, decrease of non-metallic inclusion and central segregation is an important problem. Rolling of materials such as slabs is not allowed because it leads to an increase in central segregation. Blooms widely used have generally sectional sizes from thickness 300 mm x width 300 mm to thickness 300 mm x width 400 mm. It is difficult to apply the technical art disclosed in the above-mentioned patent application to such blooms of square or nearly square section. GB-A-2,078,581 discloses a continuous rolling mill comprising a first pair of horizontal work rolls, a first pair of vertical work rolls, a second pair of horizontal work rolls and a second pair of vertical work rolls, all in series. All the work rolls are driven. The spacing between the pairs of work rolls is between 1.0 to 2.0 times the maximum roll diameter D max of the work rolls when new. In one embodiment in which the work rolls have become worn and are consequently reduced in diamater to 435 mm the thicknesses h of the rolled material between the nips of successive pairs of work rolls P₁ to P₄ are as follows: The corresponding values h/D (where D = diameter of work rolls) are as follows: JP-A-59/92101 discloses a continuous rolling mill comprising a pair of undriven vertical work rolls disposed between a preceding pair of driven horizontal work rolls and a succeeding pair driven horizontal work rolls. An object of the present invention is to provide a continuous rolling method in which substantially equal reductions of transverse cross-sectional area of the rolled material can be obtained by undriven vertical mills and driven horizontal mills of a continuous rolling mill assembly having horizontal mills and vertical mills disposed alternately. The invention provides a method for continuously rolling material in a continuous rolling mill assembly, the continuous rolling mill assembly comprising (2n+1) stands (S₁ to S 2n+1 ) wherein n is an integer equal to or greater than unity, and having horizontal rolling mills (H) and vertical rolling mills (V) arranged alternately in a series in which: a horizontal rolling mill having a pair of driven horizontal work rolls is disposed at each of the odd-numbered stands inclusive of the first and last stands; a vertical rolling mill having a pair of undriven vertical work rolls is disposed at each of the even-numbered stands inclusive of the second stand; each pair of undriven vertical work rolls achieves a reduction in transverse cross-sectional area of the rolled material which is at least 83% of the reduction in transverse cross-sectional area achieved at its immediately preceding pair of driven horizontal work rolls, and the following conditions are satisfied: 0.1≦αµρ¨di/Di≦αµρ¨0.4 Li/Di≦αµρ¨4.0 where Di : outer diameter of each work roll of horizontal mill i, di is the thickness of the rolled material which is released from the ith horizontal rolling mill, Li is the interaxial distance between the nip of the work rolls of the ith horizontal rolling mill and the nip of the work rolls of the adjacent downstream vertical rolling mill, and i = 1,3,5 ... 2n+1. Preferred embodiments are defined in the dependent claims. In the continuous rolling method according to the present invention using the continuous rolling mill comprising horizontal and vertical mills disposed alternately with or without ordinary rolling mills added thereto, material can for example be rolled in a single pass or in reversing passes with rotation by 90° about the rolling direction between passes. In the continuous rolling mill according to the present invention having undriven vertical mills, in order to obtain the same reduction effect as by the continuous rolling mill having driven vertical mills, the distance Li between the axis of the roll of the driven horizontal mill by which the rolled material is pushed and the axis of the roll of the undriven vertical mill into which the rolled material is pushed, and the thickness di of the material between them are predetermined in the ranges defined by said formulae (1) and (2). With the values of Li and di in these ranges, the undriven vertical mill provides a reduction of area equivalent to or approaching the reduction of area achieved by the driven horizontal mills without buckling the material. After the rolled material has been released from the driven horizontal mill by which the material was pushed, the material is pulled out of the undriven vertical mill by the driven horizontal mill disposed on the downstream side of said undriven vertical mill. In this case, a tensile force is exerted on the rolled material and the result of the rolling is dependent upon the presence of slip in the driven horizontal mill. The slip can be easily prevented by increasing the area of contact between the work rolls and the rolled material and roughening the surface of the rolls, to thereby increase the coefficient of friction between the rolls and the rolled material. Particularly, the slip prevention effect is increased simply by using a box groove to restrain the edges of the rolled material. The invention will be better understood from the following description by way of example only taken in connection with the accompanying drawings in which: Fig. 1 is a plan view illustrative of the schematic arrangement of a continuous rolling mill assembly for use in a method according to the present invention; Fig. 2 is a side view of a smallest unit continuous rolling mill assembly for use in a method according to the present invention; Fig. 3 is a graph illustrative of the relationship of reduction of area of driven and undriven rolling mills in a prior art continuous rolling mill; Fig. 4 is a graph illustrative of the relationship of reduction of area of driven and undriven rolling mills according to the present invention; Fig. 5 is a plan view illustrative of an example of application of the continuous rolling method according to the present invention to Blooming Mills, and Fig. 6 is a plan view illustrative of an example of application of the continuous rolling method according to the present invention to steel Bar Mills. Certain preferred embodiments and examples of the present invention will now be described in detail with reference to the drawings, in which Fig. 1 is a plan view illustrative of a schematic arrangement of a continuous rolling mill 10. Rolled material 20 runs from right to left in Fig. 1. Stands of the continuous rolling mill 10 are numbered first, second, ... ith ... 2nth, and (2n+1)th from the upstream toward the downstream in the rolling direction and denoted by S₁ S₂ ... S i ... S 2n' and S 2n+1' respectively. Horizontal mills 1H, 3H, ... (2i-1)H ... (2n+1)H each comprising a pair of driven horizontal work rolls 11 are disposed at the odd-numbered stands S (2i-1) (i = 1, 2, 3 ... n+1) including the first stand S₁ and the last stand S 2n+1' respectively. Vertical mills 2V, 4V, ... 2iV ... 2nV each comprising a pair of undriven vertical work rolls 12 are disposed at the even-numbered stands S 2i (i = 1, 2, ... n) including the second stand S₂, respectively. Among the continuous rolling mills 10, a mill comprising a smallest number of stands includes rolling mills 1H, 2V and 3H, and is hereafter called the smallest unit continuous rolling mill 10m. A rolled material portion 20i between the (2i-1)th stand S (2i-1) and the (2i)th stand S 2i (i = 1, 2, ... n), that is between two adjacent stands has the thickness di, and the interaxial distance between the work rolls 11 and 12 of said adjacent stands is denoted by Li. The diameter of the horizontal rolls of the horizontal mill of the (2i-1) stand S (2i-1) is denoted by Di. Fig. 2 is a side view of the smallest unit continuous rolling mill 10m usable in a method according to the present invention, in which the undriven vertical rolling mill 2V is disposed between the driven horizontal mills 1H and 3H, and these mills 2V, 1H and 3H are fixed closely in mutual connection with each other. The horizontal work rolls 11 and the vertical work rolls 12 are supported by roll chocks 111 and 121 of the mills, respectively. In the continuous rolling method according to the present invention, as mentioned above, the values of the thickness di of the rolled material portion between two adjacent stands, the interaxial distance Li of the rolls, and the outer diameter Di of the roll are limited so as to be within the range of condition defined by the formulae (1) and (2) for the reason to be described hereunder. Result of the rolling by pushing depends upon buckling of the material and presence of slip in the horizontal rolls. In the first place, the buckling stress at which buckling occurs in the material is inversely proportional to the square of the interaxial distance Li of the rolls and is proportional to the first power of the thickness di of the material. On the other hand, the stress in the material as it is pushed is required to enable the idle vertical mill to roll and increases substantially in proportion to the reduction of area by the vertical mill. Therefore, a large reduction of area is made possible in the undriven vertical mill when the interaxial distance Li of the rolls of the driven horizontal mill and the undriven vertical mill is as small as possible and the thickness of the material released from the horizontal mill is as large as possible. The interaxial distance Li of the rolls is smallest in the case where the rolls of the horizontal and the vertical mills are in contact with each other. In order to obtain the same reduction of area in the horizontal and the vertical mills under this condition, the thickness di of the material must be equal to or larger than 0.1 times the diameter Di of the roll. On the other hand, when the thickness of the material is equal to or larger than 0.4 times the diameter Di of the roll, biting of the material in the horizontal mill is insufficient. Accordingly, when the thickness di of the material released from the horizontal mill is 0.4 times the roll diameter, the interaxial distance Li of the rolls of the horizontal and the vertical mills must be equal to or smaller than four times the roll diameter in order to obtain the same reduction of area by the horizontal and the vertical mills. For the reason described above, the conditions required to obtain nearly the same reduction of area by the horizontal and the vertical mills are: 0.1 ≦αµρ¨ di/Di ≦αµρ¨ 0.4 Li/Di ≦αµρ¨ 4.0 The continuous rolling method according to the present invention can be used for various purposed such as blooming, steel bar, wire rod, hot rolling and so forth. Further, in the continuous rolling method according to the present invention, when required, a material may be rolled in a single pass or in reversing passes or turned by 90° about the rolling direction. The continuous rolling method according to the present invention can include a conventional continuous rolling step on the downstream side of the series of horizontal and vertical rolling mills. An example of improvement in reduction of area by the continuous rolling method according to the present invention will now be described. In this example, rolling operation was carried out under the conditions: horizontal and vertical work roll diameter Di = 300 mm, thickness of rolled material on exit side of horizontal mill di = 45 - 105 mm (di/Di = 0.15 - 0.35), interaxial distance between horizontal and vertical work rolls Li = 1300 mm, 715 mm (Li/Di = 4.33, 2.38), rolling temperature 1100°C, and low carbon killed steel used as the material. The relationship between the reduction of area by the driven mills and the reduction of area by the undriven mills in this example is shown in Figs. 3 and 4, in which Fig. 3 shows the results of the case using a prior art continuous rolling mill in which vertical mills are undriven and Fig. 4 shows the results of the case using the continuous rolling method according to the present invention. In the case of the prior art rolling mill of Li = 1300 mm (Li/Di = 4.33), the reduction of area by the vertical mill is approximately 70% of the reduction of area by the horizontal mill as shown in Fig. 3. On the other hand, in the case of the rolling according to the present invention of Li = 715 mm (Li/Di = 2.38) can be as high as 100% as shown in Fig. 4. The continuous rolling method according to the present invention will now be described in detail with reference to certain examples of practice thereof. Example of Application to Blooming Mills Rolling was carried out using the continuous rolling mill 10 shown in Fig. 5 having the arrangement described below and under the conditions described below: Number of stands: seven 1st, 3rd, 5th and 7th stands S₁ S₃, S₅ and S₇ were driven horizontal mills (1H, 3H, 5H and 7H) 2nd, 4th and 6th dtands S₂ S₄ and S₆ were undriven vertical mills (2V, 4V and 6V). Interaxial distance Li between the work rolls : 1.4 m Overall length of the continuous rolling mill: 8.4 m Outer diameter Di of a horizontal or vertical roll: 900 mm Thickness di of the rolled material between adjacent stands: 340 - 220 mm Bloom (starting material): thickness 400 mm x width 300 mm Billet (product): thickness 180 mm x width 180 mm Pass schedule: shown in Table 1. It will be seen that the ratio of the percentage reduction in transverse cross-sectional area achieved by each vertical undriven stand to the percentage reduction in transverse cross-sectional area achieved by each preceding horizontal driven stand is equal to or greater than 0.83 in each instance. For comparison, construction and rolling results of the prior art continuous rolling mill are described below. Those not specifically described below were the same as those described above. Li: 5.0 m Overall length of the continuous rolling mill: 30 m Billet (product): thickness 180 mm x width 220 mm Pass schedule: shown in Table 2 It will be seen that the ratio of the percentage reduction in transverse cross-sectional area achieved by each vertical undriven stand to the precentage reduction in transverse cross-sectional area achieved by each preceding horizontal driven stand is less than or equal to 0.62 in each instance. Example of Application to Steel Bar Mills Rolling of steel bar was carried out in an arrangement in which the continuous rolling mill 10 was disposed as a roughing tandem mill upstream of a conventional intermediate tandem mill 30, under the following conditions: Number of stands: seven 1st, 3rd, 5th and 7th stands S₁ S₃ S₅ and S₇ were driven horizontal mills 2nd, 4th and 6th stands S₂ S₄ and S₆ were undriven vertical mills Interaxial distance Li between the work rolls: 0.9 m Overall length of the continous rolling mill: 5.4 m Outer diameter Di of horizontal or vertical work roll: 550 mm Thickness di of the rolled material between adjacent stands: 140 - 90 mm Billet (starting material): diameter 180 mm Steel bar (product): diameter 75 mm Pass schedule: shown in Table 3. In this example, work rolls of box groove having strong side restriction were used as horizontal rolls and work rolls of box groove having weak side restriction were used as vertical work rolls. For comparison, construction and rolling results of the prior art continuous rolling mill having all driven stands are described below. A roughing tandem mill comprising six stands having horinzontal and vertical mills arranged alternately was used. Li: 4.5m Overall length of the tandem mill: 25 m Pass schedule: shown in Table 4.

Claims: A method for continuously rolling material (20) in a continuous rolling mill assembly (10), the continuous rolling mill assembly comprising (2n+1) stands (S₁ to S 2n+1 )wherein n is an integer equal to or greater than unity, and having horizontal rolling mills (H) and vertical rolling mills (V) arranged alternately in a series in which: a horizontal rolling mill having a pair of driven horizontal work rolls (11) is disposed at each of the odd-numbered stands inclusive of the first and last stands; a vertical rolling mill having a pair of undriven vertical work rolls (12) is disposed at each of the even-numbered stands inclusive of the second stand; each pair of undriven vertical work rolls (12) achieves a reduction in transverse cross-sectional area of the rolled material (20) which is at least 83% of the reduction in transverse cross-sectional area achieved at its immediately preceding pair of driven horizontal work rolls (11), and the following conditions are satisfied: 0.1≦αµρ¨di/Di≦αµρ¨0.4 Li/Di≦αµρ¨4.0 where Di : outer diameter of each work roll of horizontal mill i, di is the thickness of the rolled material which is released from the ith horizontal rolling mill, Li is the interaxial distance between the nip of the work rolls of the ith horizontal rolling mill and the nip of the work rolls of the adjacent downstream vertical rolling mill, and i = 1,3,5 .....2n+1. A continuous rolling method as claimed in claim 1 in which each pair of undriven vertical work rolls (12) achieves a reduction in transverse cross-sectional area of the rolled material (20) which is at least 90% of the reduction in transverse cross-sectional area achieved at its respective immediately preceding pair of driven horizontal work rolls (11). A continuous rolling method as claimed in claim 1 or claim 2 in which a pair of driven horizontal work rolls (11) are arranged to reduce the transverse cross-sectional area of the rolled material (20) by more than 20% as it passes between them. A continuous rolling method as claimed in any of claims 1 to 3 in which a pair of undriven vertical work rolls (12) reduce the transverse cross-sectional area of the rolled material (20) by at least 22.6% as it passes between them. A continuous rolling method as claimed in any preceding claim wherein said material (20) is of square cross-section before it enters said first stand (S₁). A continuous rolling method as claimed in any preceding claim, in which the rolled material (20) is rolled in conventional rolling mills (30) downstream of said series of horizontal and vertical rolling mills (11, 12). A continuous rolling method as claimed in any preceding claim wherein said material (20) is rolled in a single pass. A continuous rolling method as claimed in any of claims 1 to 6 wherein said material (20) is rolled in reversing passes and is turned by 90° about its rolling direction between passes. A continuous rolling method as claimed in any preceding claim wherein said horizontal work rolls (11) are grooved. A continuous rolling method as claimed in any preceding claim in which said material (20) is steel.

Inventors: HAYASHI, CHIHIRO, KUSABA, YOSHIAKI
Applicants: SUMITOMO METAL INDUSTRIES, LTD.
Application year: 1985
Main classification: B21B1
IPC codes: B21B1