A continuous rolling method

Abstract: Billets 10 which were continuously cast in a continuous casting machine 1 are directly supplied to the joining line 12. The scale on the billets is removed by the de-scaling apparatus 3. Then the rear end of the preceding billet is welded with the front end of the succeeding billet using a travelling flash butt welder 4 to produce a continuous billet. The burr on the welded part 15 is removed by the grinders 51-53 in the travelling burr-removing apparatus 5. The continuous billet is heated in an induction heater 6, then is continuously rolled in the rolling mill line.

Description: Background of the Invention Field of the Invention The present invention relates to a method of HDR continuous rolling wherein hot billets cast by a continuous casting machine are supplied maintaining high temperature as cast directly to rolling mill, continuously joined and subsequently continuously rolled to produce steel bars and wire rods. Description of the Related Art Hot direct rolling (HDR) method is known as a rolling method for producing wire rods, steel bars, or shape steel at high efficiency under an energy saving. The HDR method directly supplies continuously cast billets to a rolling mill in an as-cast state, or supplies them to a rolling mill line after heated to an adequate temperature through a heating system, continuously roll those billets. Since method, however, rolls the billets successively one by one so that the production yield is poor giving an short length of product. Accordingly, a continuous rolling method in which billets are continuously joined together before rolling has recently been tried to further improve the efficiency. That type of continuous rolling method is disclosed in JP-A 52-43754, for example, (the term "JP-A" referred to herein signifies "Japanese unexamined patent publication"). According to the disclosure, a billet which was continuously cast is once cooled, then is heated to an adequate temperature in a heating furnace. A rear end of the billet coming from the furnace is jointed with the front end of the succeeding billet coming from the heating system using a travelling flash butt welder. Then a scarfer is applied to remove burr from the butt-welded part. Thus joined continuous bullet is re-heated by an induction heater, and is continuously rolled in a rolling mill line. A conventional continuous rolling method, however, does not directly connect the billet cast line with the billet rolling line. Consequently, both the billet heating process and the billet re-heating process are indispensable. As a result, the heat hold by billet cannot be utilized, which is a disadvantage of the method from the energy saving point of view and which results in a large scale production line and a great cost. Alternatively, a method for conducting billet heating and re-heating in a single furnace is proposed (JP-B 57-11722(1982)), (the term "JP-B" referred to herein signifies "Japanese examined patent publication"). The method is the same with that of the above-described conventional method on the point that both billet heating process and billet re-heating process are necessary. In addition, the method requires to bring out the billet from the furnace to the opposite direction against the rolling direction before joining it with another billet, then requires to change the direction of the billet charge to enter the joining process, the welded part burr-removing process, the re-heating process (in the same furnace), and the rolling process. Accordingly, the method gives large heat loss and unavoidably needs a large scale installation and a great cost. Furthermore, the methods described in JP-A-52-43754 and in JP-B-57-11722 are the ones which forcefully peel off the burr on the welded part using a tool such as a forming tool, so the wear of the tool becomes severe, resulting in an unsuitable practical application. Summary of the Invention The present invention aims to solve the above-described problems and to actualize a continuous rolling at high efficiency under energy saving while minimizing the scale of production line. The object of the present invention is to provide a method of HDR continuous rolling by combining the above-described direct supply rolling method and the continuous rolling method to enhance the characteristics of two methods. The continuous rolling method of the present invention comprises the steps of: casting billets by a continuous casting machine; supplying the billets successively one after another from the continuous casting machine to a rolling mill while the billet holding heat obtained through casting; joining a rear end of the preceding billet with a front end of the succeeding billet the billets forming a continuous billet using the flash butt welding method during travelling to produce continuous billet; removing burr formed by the flash butt welding on the welded part of the continuous billet using a grinding machine during travelling; heating the continuous billet to a specified temperature using an induction heater; and rolling the heated continuous billet through the rolling mill line. The method further comprises the step of removing scale on the billet before applying the flash butt welding using a hydraulic pressure de-scaling apparatus or a mechanical de-scaling apparatus. In the above-described method, a plurality of grinders are arranged along the outer periphery of the billet under a condition of an equal inclination angle and of inclination against the center axis of the continuous billet to remove the burr from the welded part. In the above-described method, a plurality of grinders are arranged separately along the travelling direction of the continuous billet to remove the burr from the welded part. Brief Description of the Drawings Fig. 1 shows a schematic drawing of a HDR continuous rolling apparatus for the present invention. Fig. 2 shows a schematic drawing of a travelling flash butt welder for the present invention. Fig. 3 is a side view partly in section of internal clamp of the above-illustrated flash butt welder. Fig. 4 is a front view of the internal clamp of the above-illustrated flash butt welder illustrated in Fig. 3. Fig. 5(a) is a sectional view of a continuous billet before removing burr from a welded part. Fig. 5(b) is a sectional view of a continuous billet after the burr is removed. Fig. 6 shows a schematic front view of a travelling burr-removing apparatus for a round billet. Fig. 7(a) is a schematic side view of a travelling burr-removing apparatus for a square billet. Fig. 7(b) is a schematic front view of a travelling burr-removing apparatus for a square billet. Description of the Preferred Embodiment Fig. 1 is a schematic drawing of an HDR continuous rolling facility of the present invention illustrating flat arrangement of individual components. In Fig. 1, the reference numeral 1 denotes a continuous casting machine. In this embodiment the continuous casting machine has two strands. A casting line 11 and a rolling line 13 are parallel in each other. The billets 10 which are continuously cast by the continuous casting machine 1. The billets are transferred onto the chain conveyer 2 which is located orthogonally to a billet joining line 12. The billet joining line 12 is linearly connected to an upstream end of the rolling line 13. On the joining line 12, there arranged a de-scaling apparatus 3, a travelling flash butt welder 4, a travelling burr-removing apparatus 5, and an induction heater 6 in the order from the upstream. The reference numeral 7 is a rolling mill line composing of a plurality of rolling mill stands structuring a rolling line 13. The de-scaling apparatus 3 removes the scale from the billet 10 using, for example, injection of high pressure water or a rotating brushing machine. The de-scaling improves electric conduction during flash butt welding, and prevents damage of an electrode face. The portion to de-scale on the billet 10 is not necessarily covers the whole length of the billet, and it may be limited to the front end part and the rear end part of the billet 10 where the electrode for flash butt welding touches. The both of end faces on the billet 10 are preferably de-scaled. Fig. 2 shows a schematic drawing of a travelling flash butt welder. Fig. 3 is a side view partly in section of internal clamp of the flash butt welder. Fig. 4 is a front view of the internal clamp of the above-illustrated flash butt welder. The welder 4 is provided with a stationary head 41 and a moving head 42 within a travelling body 40, and with a plurality of hydraulic cylinders 43a, 44a, and 43b, 44b to clamp the preceding billet 10a and the succeeding billet 10b, respectively, on each head. A clamp body on the hydraulic cylinder 43a and the hydraulic cylinder 43b, which are close to the billet ends form the electrode 45, 46, respectively. The stationary head 41 and the moving head 42 are connected each other by a plurality of upset hydraulic cylinders 47. The hydraulic cylinders 43a, 43b for driving the electrodes are positioned as near to the edges of the billet as possible. Fig. 5(a) is a sectional view of a welded part 15 formed by flash butt welding of the rear end of the preceding billet 10a with a front end of the succeeding billet 10b using the welder 4. The upset of flash butt welding raises the welded part 15 from the external periphery, so the burr 15a is removed by the travelling burr-removing apparatus 5 described below. Fig. 5(b) shows the billet after removing the burr from the welded part. Fig. 6 shows a schematic drawing of a travelling burr-removing apparatus for a round billet. Fig. 7(a) is a schematic side view of a travelling burr-removing apparatus for square billets and Fig. 7(b) is a schematic front view of the apparatus. The burr-removing apparatus 5 shown in Fig. 6 comprises a plurality of grinders 51 through 53 which are independently driven by motors and which are arranged along the outer periphery of a continuous billet 10c at a uniform spacing under a condition that each of the grinders 51-53 are arranged to have an inclined angle against the center axis of the continuous billet 10c and that each of the grinders 51-53 together rotates around the continuous billet 10c. In addition, each of the grinders 51 through 53 is movable in the radial direction of the continuous billet 10. By arranging each of the grinders 51-53 at an inclined angle against a center axis of billet 10, a relatively thin grinder can remove a wide range of the burr 15a from the welded part 15. For the case of round billet 10, by rotating a plurality of grinders 51-53 around the round billet 10, the burr 15a can be removed as shown in Fig. 5(b). For the case of a square billet 14, the grinders 54-57 are arranged around the square billet 14 as shown in Fig. 7(a) and Fig. 7(b), and each of the grinders are arranged at a tilted position while displacing the pair of right and left grinders, 54, 55, from the pair of top and bottom grinders, 56, 57, along the travelling direction of the square billet 14, thus avoiding mechanical interference between these pairs. Accordingly, the burr is removed by two-step operation in that case. Since the induction heater 6 and the rolling mill line 7 are known equipments, the detailed illustration is not given. The method of the present invention will be described along with the operation. As shown in Fig. 1 the billets 10 continuously cast by the continuous casting machine 1 and then are transferred onto, for example, the chain conveyer 2, or are taken out successively, then they are directly supplied successively to the joining line 12. The directly supplied billets 10 move while keeping nearly equal interval. First, on the de-scaling apparatus 3, the scale mainly on the ends, front end, and rear end of the billet is removed by hydraulic or mechanical means. Next, the preceding billet 10a and the succeeding billet 10b are separately clamped by the hydraulic cylinders 43a, 44a, and 43b, 44b, respectively, while the travelling flash butt welder 4 travels at nearly equal speed with that of the billets 10. Thus the upset hydraulic cylinder 47 brings the succeeding billet 10b close to the preceding billet 10a to contact each other. A large current is applied to both ends of the billets through the electrodes 45, 46, to send out flashes repeating short circuits and archings and to bring both ends to fused state. The upset hydraulic cylinder 47 applies upset to the succeeding billet 10b to join with the preceding billet 10a. The flash butt welder 4 conducts the flash butt welding during the period of travelling through the specified stroke S1 shown in Fig. 1 at a equal speed with that of the billet transfer. When the welding is completed, the flash butt welder 4 returns to the original position. The welder 4 repeats the flash butt welding to join thus the obtained continuous billet 10c with a further succeeding billet 10b. In this manner, the billets 10 are successively joined together by the flash butt welding. The burr 15a on the welding part 15 is continuously removed by the travelling burr-removing apparatus 5. That is, when the apparatus 5 detects the welded part 15 on the continuous billet 10c, it moves the grinders 51-53 which are kept to rotate at a constant speed toward the center of the billet using a hydraulic cylinder while the apparatus is travelling downstream. The grinders touch the billets 10c, and they are preset at the position. The billet 10c is further transferred to downstream. When the welded part 15 of the continuous billet 10c reaches the lower face of the grinders 51-53, the driving current of the drive motor suddenly increases, and the arrival of the welded part 15 is detected by the sudden change in current. When the welded part 15 reaches the lower face of the grinders 51-53, the rotating grinders 51-53 start to rotate around the continuous billet 10c, keeping the preset position. thus the burr 15a on the whole periphery of the continuous billet 10c is ground. Also the burr-removing apparatus 5 conducts the burr-removal during a period of travelling through the specified stroke S2 shown in Fig. 1. After completing the burr-removing cycle, the apparatus 5 returns to the original position, and repeats the burr-removing operation to the following welding part 15. Thus the burrs on the welded part 15 are continuously removed. In the case that square billets 14 are treated, the grinders 54 through 57 are arranged as shown in Fig. 7. By approaching the billet beginning from the upstream grinders 54, 55, the burr on right and left sides are removed at first. Secondarily the burr on top and bottom sides are removed in two step grinding. As described above, the continuous billet 10c is subjected to the burr-removing action on each welded part 15 in the travelling burr-removing apparatus 5 and transferred into the induction heater 6 where the continuous billet 10c is heated to a temperature of from 950 to 1050 °C, and further the heated continuous billet 10c is treated by continuous rolling in the rolling mill line 7. Accordingly, the continuously cast billets 10 are directly charged successively to pass through the de-scaling step, the travelling flash butt welding step, the travelling burr-removing step, the heating step, and the continuous rolling step. Thus the billet heating step is a single process to heat up only by 100°C-200 °C, which significantly contributes to energy saving and which enables high efficiency continuous rolling without increasing the scale of the production line. Since the flash butt welding is performed while the directly supplied billet holds the high temperature at around 800 to 900°C, the necessary preheating time for the flash butt welding is shortened, which then shortens the welding time and shortens the cycle time. The adoption of the flash butt welding eliminates the possibility of inclusion of impurities in the welded part on upsetting, and the change in structure is very slight, thus the joint strength is brought to nearly equal with that of the mother material (billet). The flash butt welding induces no problem of product character. Furthermore, the burr raised by upset at the welded part of the external periphery of the billet is removed by grinders during the billet travelling period, so the burr-removal is readily carried out within a short time of burr-removing. The grinding with grind ing wheels has a feature that the grinding performance sustains for a long time even under an abraded state of the grinders. The continuous billets thus joined together are heated to a temperature of from 950 to 1050°C in an induction heater, then they are continuously rolled by the rolling mill line. As described above, the present invention adopts a series of continuous rolling steps for the directly supplied billets which were continuously cast, high efficiency continuous rolling under an energy saving condition is achieved without increasing the scale of production line. In addition, the billet welding time and the burr-removing time at the welded part are shortened at HDR condition, so the cycle time is shortened.

Claims: A continuous rolling method comprising the steps of: casting billets (10) by a continuous casting machine (1); supplying the billets (10) successively one after another from the continuous casting machine (1) to a rolling mill (7, 13) while the billets (10) holding heat obtained through casting; joining a rear end of the preceding billet (10a) with a front end of the succeeding billet (10b) forming a continuous billet (10c) using the flash butt welding method (4) during travelling to produce continuous billet (10); removing burr (15a) formed by the flash butt welding (4) on the welded part (15) of the continuous billet (10) using a grinder (5) during travelling; heating the continuous billet (10) to a specified temperature using an induction heater (6); and rolling the heated continuous billet (10) through the rolling mill line (7, 13). The method of claim 1 further comprising the step of removing scale on the billet before applying the flash butt welding using a hydraulic pressure de-scaling apparatus. The method of claim 1 further comprising the step of removing scale on the billet before applying the flash butt welding using a mechanical de-scaling apparatus. The method of claim 1, wherein a burr on the welded part is removed by arranging plurality of grinders along outer periphery of the billet at an equal angular spacing and at an inclined angle against a center axis of the continuous billet. The method of claim 1, wherein a burr on the welded part is removed by arranging plurality of grinders along the travelling direction of the continuous billet while displacing the grinder location. The method of claim 2, wherein a part of the billet for removing scale is a part that contacts with electrodes for flash butt welding. The method of claim 2, wherein the mechanical de-scaling apparatus is a brush de-scaling apparatus. The method of claim 4 or claim 5, wherein the grinders are grinding wheels.

Inventors: AOYAMA SOICHI, MATSUO GIICHI, SAKAI AKIRA, AOYAMA, SOICHI, MATSUO, GIICHI, SAKAI, AKIRA, Aoyama, Soichi, c/o Intellectual Prop. Dept., Matsuo, Giichi, c/o Intellectual Prop. Dept., Sakai, Akira, c/o Intellectual Prop. Dept.
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1996
Main classification: B21B15
IPC codes: B24B5, B21B1, B23K11, B21B45, B21B15