Continuous rolling method and facility thereof

Abstract: A continuous rolling method characterized by comprising the steps of: Moving together both said travelling flash butt welder (3) and said travelling grinding machine (4) which are movable separately, during flash butt welding; carrying out the flash butt welding while the flash butt welder (3) and the grinding machine (4) travel a specified stroke (SW) for welding; moving the travelling grinding machine (4) backward together with the travelling flash butt welder (3) to meet the welded part and returning the travelling flash butt welder (3) to a waiting position, after completed the welding; and removing the burr on the welded part, while the travelling grinding machine (4) changes separately the travelling direction opposite-side, and travels a specified stroke (SG), after the welded part arrived at a specified position.

Description: Background of the invention Field of the invention The present invention relates to a method and a facility to continuously roll billets directly supplied from a continuous casting machine. Such a method with the features of the pre-characterizing clause of claim 1 is known from Patent Abstracts of Japan JP-A-58 006702. An apparatus with the features of the preamble of claim 3 is known from DE-A- 2 836 338. Description of the Related Art The hot direct rolling (HDR) method is known as a rolling method to produce wire rod, steel bar, or shape steel at high efficiency under an energy saving condition. The HDR method directly charges the continuously cast billets to the rolling mill in an as-cast state, or charges them to the rolling mill line after heated to an adequate temperature through a heating system, in order to conduct continuous rolling. The method, however, rolls the billets successively one by one so that the production yield is poor giving a 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 "unexamined Japanese patent publication"). According to the disclosure, a billet which was continuously cast is once cooled, then is heated to an adequate temperature through a heating system. The rear end of the billet coming from the furnace is welded by flash butt welding with the front end of the succeeding billet coming from the furnace using a travelling flash butt welder. Then a scarfer is applied to remove burr from the welded part. The thus joined continuous billet is re-heated by an induction heating unit, and is continuously rolled in a rolling mill line. The 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 essential. As a result, the conventional method has disadvantages of inducing an inverse effect to energy saving necessitating a large scale production line and a great cost. Alternatively, a method to conduct billet heating and re-heating in a single furnace is proposed (JP-B-57-11722), (the term "JP-B" referred to herein signifies "examined Japanese patent publication").The method is the same as that of the above-described conventional method insofar as both a billet heating process and a 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 production line. In general arrangement, the billet casting line crosses the rolling line. When billets are continuously cast in a plurality of strands, they are charged onto the joining line using chain conveyers or the like. That type of arrangement, however, raises a problem of requiring a large floor area for the facilities. Further, in the methods described in JP-A-52-43754 and in JP-B-57-11722 the burrs on welded part are forcefully peeled off using a tool such as a forming tool, so that the wear of the tool becomes severe and the methods are not suitable for practical application. For conducting continuous rolling of the billets directly charged from a continuous casting machine, a series of steps are applied, which comprise: the step of scale removal from the billet surface using mechanical or hydraulic pressure de-scaling; continuous joining of the billets travelling at the rolling speed using a flash butt welding method; grinding the billet to remove burrs generated during the flash butt welding in a travelling state of billet; heating the billet by an induction heater; and continuous rolling. To conduct continuous HDR using current technoloy, most types of continuous casting machines adopt 2 to 4 strands and 1 to 4 tons of billet weight, from the standpoint of balancing the capacity of the continuous casting machine and the capacity for rolling. On the other hand, recent rolling capacities mostly fall into a range of from 60 to 100 tons/hour. Based on the state of the art, it is desirable that also the HDR continuous casting responds to the rolling capacity range with the above-described billet size. In case small size billets are rolled in a high efficiency rolling line, the cycle time covering billet-welding and burr-removal should be sufficiently short. The relation between the billet weight x (ton/billet), the rolling capacity y (ton/hour), and billet treatment cycle time Ts for continuous rolling is expressed by eq. (1). y = (3600/Ts) · x The treatment time per 1 billet in a plant which has a rolling capacity of 60 (ton/hour) for 1 (ton) billet is calculated from eq. (1) as: Ts = 3600 (s) ÷ ( 60(ton/hour) x 1(ton/billet)) = 60(s/billet) This value is the shortest target cycle time. The time necessary to complete the flash butt welding is the sum of the welding time (15s) and the clamping and positioning time (25s), or a total of (40s). Therefore, the margin is 20 s. If the grinding time using a grinder takes 15 s, and if the flash butt welder and the grinding machine are integrated, the total time consumed becomes 55 s, which leaves only 5 s as the margin. Conclusively, the flash butt welder and the grinding machine have to be returned to the waiting position within the 5s that are left to establish the time cycle. Such a short time is, however, almost insufficient for return travelling. As a result, with the integrated type of flash butt welder with a grinding machine, it is impossible to realize the cycle time of 60s. Further prior art is known from DE 28 36 338 A1 which discloses an arrangement of a travelling welder and a grinding machine, which arrangement is to achieve a large difference between casting intervals and the time for welding as well as for travelling the welder. Finally, Patent Abstracts of Japan JP 58-006702 was considered. It discloses a switching turntable between a surface heater and a rolling facility. Summary of the Invention It is an object of the present invention to provide a method of and a facility for continuous rolling that take invariable billet treatment cycle times into account, so as to reduce the overall treatment time. This object is solved by a method comprising the features of claim 1, and a facility comprising the features of claim 3. Advantageous further embodiments are defined in the respective dependent claims. Brief Description of the Drawings Fig. 1 is a graph showing the relation of billet weight, rolling capacity, and billet treatment time of the present invention. Fig. 2(a) shows the position of the integrated flash butt welder and grinding machine of the present invention at the beginning of the welding step. Fig. 2(b) shows the position of the integrated flash butt welder and grinding machine of the present invention at the completion of the welding step. Fig. 2(c) shows the position of the integrated flash butt welder and grinding machine of the present invention at the beginning of the grindíng step. Fig. 2(d) shows the position of the integrated flash butt welder and grinding machine of the present invention at the completion of the grinding step. Fig. 3(a) shows the position of the separated flash butt welder and grinding machine of the present invention at the beginning of the welding step. Fig. 3(b) shows the position of the separated flash butt welder and grinding machine of the present invention at the completion of the welding step. Fig. 3(c) shows the position of the separated flash butt welder and grinding machine of the present invention at the beginning of the grinding step. Fig. 3(d) shows the position of the separated flash butt welder and grinding machine of the present invention at the completion of the grinding step. Fig. 4 illustrates an example of a facility to perform the method of the present invention. Fig. 5 illustrates another example of a facility to perform the method of the present invention. Fig. 6 shows a schematic drawing of a continuous rolling facility of the present invention. Fig. 7 shows a sectional-side view of a travelling flash butt welder of the present invention. Fig. 8 shows a side view partly in section of the clamp section of the travelling flash butt welder of the present invention. Fig. 9 shows the front view of the clamp section of the travelling flash butt welder of the present invention. Fig. 10(a) is a sectional view showing the state before removing burr from the welded part of the billet, using the facility of the present invention. Fig. 10(b) is a sectional view showing the state after removing burr from the welded part of the billet, using the facility of the present invention. Fig. 11 shows the front view of a travelling burr-removal apparatus for round billets in the facility of the present invention. Fig. 12(a) is a side view of a travelling burr-removal apparatus for square billets in the facility of the present invention. Fig. 12(b) is the front view of a travelling burr-removal apparatus for square billets in the facility of the present invention. Fig. 13 is a schematic drawing illustrating another arrangement of turn tables in the facility of the present invention. Description of the Preferred Embodiments "Method for continuous rolling" The layout of the welder and the grinding machine is grouped into the integrated mode and the separated mode as described. Fig. 2(a) through Fig. 2(d) show the integrated mode where a welder 3 and a grinding machine 4 travel together in integrated mode. Fig. 3(a) through Fig. 3(d) show the separated mode where the welder 3 and the grinding machine 4 travel independently. (1) For the case of integrated mode The integrated mode is applied in case the billet treatment cycle time is 90 sec. or more. The movement of the integrated machines is described in the following. At the beginning of the welding step, both the welder 3 and the grinding machine 4 are at their waiting position (refer to Fig. 2(a)). The flash butt welding of a billet is performed while both the welder 3 and the grinding machine 4 travel together through the predetermined welding stroke SW (refer to Fig. 2(b)). The travelling time for the stroke SW takes 40 sec. as described before. The burr removal step begins in the position in which the welding step is completed and upon arrival of the welding part (refer to Fig. 2(c)). The grinding is completed during the period that both the welder 3 and the grinding machine 4 travel together through the grinding stroke SG (refer to Fig. 2(d)). The time until the welding part arrives (the waiting time) is 10 sec., and the travelling time of the grinding machine 4 is 15 sec. Accordingly, the flash butt welding and the grinding of burr are completed within 65 sec. so that the remaining time becomes (90 - 65 = 25 sec.) Both the welder 3 and the grinding machine 4 have to be returned to their waiting position within 25 sec. The timing of 25 sec. is sufficient for completing the time cycle. (2) For the case of separated mode The separated mode is applied when the billet treatment cycle time is 90 sec. or less. When the welder 3 and the grinding machine 4 are separated from one other, the welder 3 can separately be returned to its waiting position after the welding step is completed, as shown in Fig. 3. Accordingly, even if the target cycle time is 60 sec., the residual time of 20 sec. is fully used for the transfer of the welder 3. In addition, after the welding step is completed, the grinding machine 4 also once travels backward along with the welder 3, (backward travelling distance L), to meet the welded part in a position suitable for starting the grinding action, (refer to Fig. 3(c)). If, after completing the welding step, the grinding machine 4 waits until the welded part arrives at the position for starting the grinding action, the cycle time is consumed ineffectively. So the grinding machine 4 goes to meet the welded part to prevent useless consumption of cycle time. The backward travelling time is about 5 sec. Consequently, the remaining time at the completion of grinding becomes [60 - (15 ÷ 5) = 40 sec.], which allows the grinding machine 4 to return to its waiting position with a sufficient margin of time. As described above, in the case of a 100 ton/hour rolling facility, the separated mode gives a cycle time of 60 sec. or longer if only the billet weight is 1.67 ton (100 ÷ ( 3600 x 60 = 1.67 ton/billet)) or more, as shown in Fig. 1, and the above-described method is applicable. In the case of the integrated mode, however, the mode is only applicable for the billet weight of 2.5 ton or more. Therefore, the integrated mode is applicable only for the billet having 2.5 tons or more of weight. The present invention is described in more detail referring to the embodiments. The conditions are the following. Example 1 Rolling capacity 90 ton/hour Weight and size of billet 2 ton, 154 x 154 (square) x 10.8 m Feed cycle 80 sec. Feed speed 10.8/80 = 0.135 m/sec Continuous casting machine (CCM) 3 strands, 0.135/3 x 60 = 2.7 m/min. Rolling mill line Rough train 4 stands Intermediate train 8 stands Finish train 4 stands Total 16 stands Product Reinforcing bar D13 - D38 Example 2 Rolling capacity Max. 100 ton/hour Weight and size of billet 3 ton, 210 (round) x 11.1 m Feed cycle 108 sec. Feed speed 11.1/108 = 0.103 m/sec Continuous casting machine (CCM) 2 strands, 0.103/2 x 60 = 3.1 m/min. Rolling mill line Rough train 6 stands Intermediate train 6 stands Finish train 6 stands Total 18 stands Product Reinforcing bar D18 - D41 Wire rods 5.5 - 16 mm dia. (Example 1) A facility arrangement shown in Fig. 4 was applied to roll for manufacturing reinforcing bars. The reference numeral 1 is CCM, 2 is a table which feeds billets succeedingly, 3 is the welder, 4 is the grinding machine for burr removal, 5 is an induction heater, 6 is a roughing train of 4, 7 is an intermediate train, 8 is a finishing train, 9 is a cooling bed, 10 is a facility for cutting and bundling. Example 1 is an example of separated mode (the welder 3 and the grinding machine 4 travel separate from each other) to shorten the cycle time of billet treatment. CCM 1 has 3 strands, and the handled billet has a size of 154 x 154 mm and of 10.8 m of length, and a weight of 2.0 tons. The flash butt welder 3 is directly connected to the CCM downstream thereof. The billets which were cut in each strand are fed successively in the order of arrival to the welder 3 by the table 2 located in front of the welder 3. The average temperature of the billets was about 914°C. The welder 3 has a travelling stroke of about 7 m, and it carried out the welding of billets while travelling synchronously with the billet over a length of about 7 m at a speed of 0.135 m/sec entering the No. 1 stand under a condition of 90 ton/hour of rolling capacity. The average cycle time of the welder at that time was: Billet arrival - Clamping 12 sec Clamping - Welding completion 31 sec Welding completion - Unclamping 6 sec Total 49 sec Return travel of welder (at 0.35 m/sec) 26 sec Grand total 75 sec Therefore, the total average cycle time became 75 sec. After completion of the welding step, the burr removal on the welded part was carried out using the travelling grinding machine 4 which traveled separately from the welder 3 and which was located downstream of the welder 3. For the burr removal, two sets of grinders facing each other were used, and the time for burr removal was 21 sec, counting from the start of travelling from the waiting position. In the continuous rolling with separated mode, the rate-controlling time cycle was 75 sec. for the welder, and the average travelling stroke of the welder was 6.2 m. Since the billet-feeding cycle time at 90 ton/hour of rolling capacity was 80 sec., the welder had about 5 sec. for waiting (margin time) at the upstream waiting position, which allowed smooth rolling operation. The average billet temperature was 908°C at the inlet of the induction heater 5, and the induction heater 5 was controlled to maintain the billet temperature to an average 990 °C. The rolling line comprises, four stands of the roughing train 6, eight stands of the intermediate train 7, and four stands of the finish train 8, accounting for a total of 16 stands. The maximum speed was 12.9 m/sec for the minimum size D13 rolling (slit rolling). The rolled billets are divided by cutting for sending to the cooling bed 10. After having been cooled, they are transformed to the cutting and bundling apparatus 10 to become the product. All the products manufactured by the method met the specified properties of the product. (Example 2) A facility arrangement shown in Fig. 5 was applied for rolling in order to manufacture reinforcing bars and wires. Since the example used large billets and had a margin of cycle time, the welder 3 and the grinding machine 4 were integrated together. CCM 1 uses two strands, and the billet size was 210 mm dia. x 11.1 m length, with a weight of 3.0 tons. At downstream of CCM, a direct connection line of the grinding machine 4 integrated with the welder 3, and the induction heater 5 were arranged as shown in Fig. 5. Furthermore, as the rolling facility for HDR, tandem rolling lines were arranged which included eighteen stands of bar-rolling line and ten stands of block-mill 20 for wire rolling. Billets directly fed from CCM1 were sent via the table 2 located in front of the welder 3 to the welder 3 which was integrated with the grinding machine 4. The billet temperature at this point was about 990 °C. The welder 3 traveled together with the burr-removing grinding machine 4, and the maximum stroke was 8 m. When the rolling line was operated at its maximum capacity of 100 t/h, the billet feed cycle time was 108 sec., and the entering speed of the billet to the No.1 stand was 0.103 m/sec. The welder traveled synchronously with the billet entering speed to conduct the clamping of succeeding billet, welding the billet, and burr-removal. The cycle time of the operation was: Billet arrival - Clamping 14 sec Clamping - Welding completion 33 sec Welding completion - Unclamping 6 sec Unclamping - Grinding start 7 sec Grinding start - Grinding completion 12 sec Total 72 sec Return run of welder 30 sec Grand total 102 sec Therefore, the total average cycle time became 102 sec., and even at the maximum rolling capacity of 100 t/h, there was a margin of (108 - 102 = 6 sec.), which assured a stable continuous rolling. The average travelling distance of the welder at that time was 7.4 m. The average billet temperature at the inlet of the induction heater 5 after welding was 928°C. The induction heater 5 heated the billets to an average temperature of from 990 to 1010 °C for rolling. The rolling line comprises: the bar-line consisting of six stands in the roughing train, six stands in the intermediate train, and six stands in the finishing train, as well as a downstream rolling facility for wire rolling consisting of the block mill 20 containing ten stands. The bar-line carried out the slit rolling of two strands at 8.9 m/sec for D16, and one strand rolling at 12.4 m/sec for D19. In both cases, the rolling provided stable products with uniform properties which satisfied the mechanical property of the product. For the wire rolling, the product of continuous rolling was cut by the tab-shear 21 to produce coils of two tons. The products showed uniform and satisfactory properties. As described above, the method of the present invention adopts the separated mode in which the welder and the grinding machine travel separately, and lets the grinding machine travel to the inverse direction at the completion of the welding step. As a result, the time cycle is established even for the target billet weight of 1 to 2.5 tons and the target rolling capacity of 60 to 100 tons, and continuous rolling which is compatible with the actual plant capacity is available. The case of the integral mode of welder and grinding machine is applicable only when the billet weight is in the domain of the integral mode zone in Fig. 1 against the rolling capacity. "Continuous rolling facility" Fig. 6 shows a schematic drawing of an example any embodiment of an HDR continuous rolling facility of the present invention. The figure illustrates a flat arrangement of each apparatus. The reference number 1 is the continuous casting machine showing, as an example, a two strand continuous casting machine. The reference number 2 is the turn table located at the end of the billet joining line 12, with its center of rotation 20 matching the joining line 12. In this example, the casting line 11 and the joining line 12 cross each other orthogonally, though the angle of crossing is arbitrarily selected. A plurality of casting lines 11 are positioned symmetrically to the center of rotation 20 of the turn table 2 which has the function to shift the billet 10 which was transferred onto the turn table 2 during the rotation thereof and to align the billet 10 with the joining line 12. Although the shifting mechanism is not shown, a means to slide a row of support rolls mounted on the turn table 2 may be applied. The billet joining line 12 is connected linearly to the upstream side of the rolling line 13. The joining line 12 is provided with the turn table 2, the de-scaling apparatus 3, the travelling flash butt welder 4, the travelling burr-removal apparatus 5, and the induction heater 6, in the order of billet feeding. The reference number 7 is a rolling line consisting of plurality of rolling mill stands which constitute the rolling line 13. The de-scaling apparatus 3 conducts scale removal on the billet 10 using, for example, injection of high pressure water or a rotary brush. The scale removal operation improves the electric current conduction during the billet welding step and prevents damage on the electrode face. The area to remove scale on the billet 10 does not necessarily cover the whole length of the billet but may be limited to the front end and the rear end of the billet 10 where the flash butt welding electrode touches. Fig. 7 shows a schematic drawing of a travelling flash butt welder. Fig. 8 shows a side view partly in section of the clamp section of the welder. Fig. 9 shows the front view of the clamp section. The welder 4 is provided with the stationary head 41 and the moving head 42 in the travelling body 40. Each of the heads has a plurality of hydraulic cylinders 43a, 44a, and 43b, 44b, to clamp the preceding billet 10a and the succeeding billet 10b, respectively. The clamp body of the hydraulic cylinder 43a and of the hydraulic cylinder 43b, both of which are located near the ends of the billets, act as the electrodes 45 and 46, respectively. The stationary head 41 and the moving head 42 are joined together by a plurality of upset hydraulic cylinders 47. The hydraulic cylinders 43a, 43b for driving the electrode are positioned as close to the edges of the billet as possible. The reference number 48 is the base to which the stationary head 41 is mounted. Fig. 10(a) is a schematic sectional view of the welded part 15 formed by flash butt welding the rear end of the preceding billet 10a to the front end of the succeeding billet 10b using the above-described 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-removal apparatus 5 described below. Fig. 10(b) is the state after removing burr from the welded part. Fig. 11 shows the front view of a travelling burr-removal apparatus for round billets. Fig. 12(a) shows a side view of the travelling burr-removal apparatus for square billets. Fig. 12(b) is the front view of the apparatus. The travelling burr-removal apparatus 5 shown in Fig. 11 comprises a plurality of grinders 51 through 53 which separately rotate on a travelling body (not shown) and which are arranged along the outer periphery of the billet 10 at a uniform spacing, under a condition that each of the grinders 51 through 53 are arranged to have an angle of inclination relative to the center axis of the billet 10 and that each of the grinders 51 through 53 rotates around the billet 10. In addition, each of the grinders 51 through 53 is movable in the radial direction of the billet 10. By arranging each of the grinders 51 through 53 to be inclined relative to the center axis of billet 10, a relatively thin grinder can remove a wide range of burr 15a from the welded part 15. For. the case of a round billet 10, by rotating a plurality of grinders 51 through 53 around the round billet 10, the burr 15a can be removed as shown in Fig. 10(b). For the case of a square billet 14, the grinders 54 through 57 are arranged around the square billet 14 as shown in Fig. 12(a) and Fig. 12(b), and each of the grinders is 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 charge direction of the square billet 14, thus avoiding mechanical interference between these pairs. Accordingly, the burr is removed by a two-step operation in that case. Since the induction heater 6 and the rolling mill line 7 are known equipment, detailed illustration is not given. The action of the above-describe HDR continuous rolling facility is described below. The billets 10 which were continuously cast by the continuous casting machine 1 are successively transferred onto the turn table 2, then each of the billets 10 is shifted in its direction so as to align the center line 21 to match the joining line 12. After the alignment, the billets 10 are directly and successively supplied to the joining line 12. The directly supplied billets 10 travel while keeping nearly equal intervals. First, on the de-scaling apparatus 3, the scale mainly on the edges, the front end, and the 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 a speed nearly equal to 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 generate 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 the preceding billet 10a. The flash butt welder 4 conducts the flash butt welding during the period of travelling through the stroke S1 given in Fig. 6 at a speed nearly equal to 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 the thus 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 each welding part 15 is continuously removed by the travelling burr-removal apparatus 5. That is, when the apparatus 5 detects the welded part 15 on the continuous billet 10c, it moves the grinders 51 through 53 which are kept to rotate at a constant speed toward the center of the billet using an adequate hydraulic cylinder or the like while the apparatus is travelling downstream. Then the apparatus 5 presets to the billet 10c. The billet 10c is further transferred downstream. When the welded part 15 of the billet 10c reaches the lower face of the grinders 51 through 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 through 53, the rotating grinders 51 through 53 are fixed to the preset position, and further they are rotated around the billet 10c, whereby the burr 15a on the whole periphery of the billet 10c is ground. The burr-removal apparatus 5 also conducts burr-removal during a period of travelling through the predetermined stroke S2 shown in Fig. 6. 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. 12(a) and Fig. 12(b). By approaching the billet beginning from the upstream grinders 54, 55 while rotating the grinders 54 through 57, the burr on the right and left sides, then the burr on the top and bottom sides are removed in a 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-removal apparatus 5 and is transferred into the induction heater 6 where the billet 10c is heated to a temperature of from 990 to 1010 °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 supplied to successively 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 only a single stage, 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 flash butt welding induces no problem of material strength. Furthermore, since the burr-removal at the welded part 15 is carried out by grinders, the burr-removing time becomes short. The grinding with grind stone grinders has a feature that the grinding performance sustains for a long time even under an abraded state of the grinders. Since the method relays the casting line 11 and the joining line 12 by the turn table 2, both lines can be connected at an arbitrary crossing angle, which gives a wide freedom of production line arrangement. When the casting line 11 and the joining line 12 are arranged in parallel, two turn tables 2a, 2b may be applied as illustrated in Fig. 13. The reference number 2c is a relay line consisting of a series of transfer rolls. As described above, the present invention adopts a series of continuous rolling steps for the directly supplied billets which were continuously cast, and high efficiency continuous rolling under an energy saving condition is achieved without increasing the length of the production line. In addition, the billet welding time and the burr-removing time at the welded part are shortened, so the cycle time is shortened. Furthermore, the casting line and the joining line are relayed using a turn table, so the freedom of production line arrangement increases, the application to the existing facilities is readily conducted, and a buffer function to time cycle is available. Conclusively, the facility and method of the present invention provide significant effects as a practical application.

Claims: A continuous rolling method comprising the steps of: descaling billets (10) which are directly sent from a continuous casting machine (1), said continuous casting machine being part of a continuous rolling facility; continuously welding the billets (10) using a travelling flash butt welder (4); grinding burr on the welded part of the billet by means of a grinding machine (5), in order to remove said burr; heating the billets (10) to a target temperature range using an induction heater (6); and continuously rolling said billets; characterized by: conducting said step of grinding burr using a travelling grinding machine (5); determining on the basis of a rolling capacity of the continuous rolling facility a standard cycle time for welding and for grinding the billets, and on the basis of billet weight a billet treatment cycle time; determining whether the billet treatment cycle time exceeds the standard cycle time; if the billet treatment cycle time is determined to exceed the standard cycle time, conducting said steps of flash butt welding and grinding burr for each billet in an integrated mode of the travelling flash butt welder and the travelling grinding machine; if the billet treatment cycle time is determined to not exceed the standard cycle time, conducting said steps of flash butt welding and grinding burr for each billet in a separated mode of the travelling flash butt welder and the travelling grinding machine. The method of claim 1, characterized by, in said separated mode, moving together both said travelling flash butt welder (4) and said travelling grinding machine (5) which are moveable separately, during flash butt welding; carrying out said step of flash butt welding while the flash butt welder (4) and the grinding machine (5) travel a specified stroke for welding; moving the travelling grinding machine (5) backward together with the travelling flash butt welder (4) to meet the welded part and returning the travelling flash butt welder (4) to a waiting position, after completing the welding; and separating the travelling grinding machine (5) from the travelling flash butt welder (4) by changing the travelling direction of the travelling grinding machine to the opposite side and making it travel for a specified stroke, after the welded part arrived at a specified position, and carrying out said step of removing burr while the travelling grinding machine (5) travels said specified stroke. A continuous rolling facility for carrying out the method according to claim 1 or 2 comprising: a turn table (2) which connects a casting line (11) for supplying billets (10) to a joining line (12) for continuously joining said billets (10), which turn table is located upstream of the joining line (12) in a linear position relative thereto and is adapted to transfer the billets supplied from upstream of the turn table to the joining line; a de-scaling apparatus (3) for removing scale from the billets (10); a travelling flash butt welder (4) for continuously joining a rear end of a preceding billet with a front end of a succeeding billet, by flash butt welding; an apparatus (5) for removing burr on the welded part of said billets (10); and an induction heater (6) for heating said continuously joined billets (10), the facility being characterised in that said apparatus for removing burr is a traveling grinding machine (5) which can move in an integrated mode and in a separated mode which said traveling flash butt welder (4). The facility of claim 3, wherein the number of turn tables (2) is greater than one, and wherein these turn tables transfer the billets (10) to the joining line (12). The facility of claim 3, wherein the de-scaling apparatus (3) is a hydraulic pressure de-scaling apparatus. The facility of claim 3, wherein the de-scaling apparatus (3) is a mechanical de-scaling apparatus. The facility of claim 3, wherein the number of grinders (51, 52, 53) in the travelling grinding machine is geater than one, and wherein these grinders (51, 52, 53) are arranged along an outer periphery of the billet (10) at equal angles of inclination relative to the center axis of the billets. The facility of claim 3, wherein the number of grinders (51, 52, 53) is more than one, and wherein these grinders (51, 52, 53) are arranged separately along the travelling direction of the billets (10). The facility of claim 6, wherein the mechanical de-scaling apparatus (3) is a brush type de-scaling apparatus.

Inventors: AOYAMA SOICHI, OKUSHIMA KOJI, SAKAI AKIRA, AOYAMA, SOICHI, OKUSHIMA, KOJI, SAKAI, AKIRA, Aoyama, Soichi, c/o Int. Prop. Dep., Okushima, Koji, c/o Int. Prop. Dep., Sakai, Akira, c/o Int. Prop. Dep.
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1996
Main classification: B21B15
IPC codes: B21B1, B23K11, B21B15, B24B5, B21B45