Method for removing burr in continuous rolling process and apparatus thereof

Abstract: A method for removing burr in a continuous rolling process of the first aspect of the present invention comprises the steps of: joining the rear end of a preceding billet (10) with the front end of a succeeding billet (10) using the flash butt welding method while running both thereof; and grinding a burr on the welded part of the joined portion using a plurality of grinders (31) while the billets running and while rotating the grinders and moving thereof synchronously with the travelling speed of the billets. and A grinding machine for continuously rolling a round billet (20) comprises: a travelling body (11) shuttling along the direction of the round billet movement; a turret ring (55) supported by the travelling body in a rotatable state thereof; a plurality of grinding devices (51) arranged in a movable manner within a radius of the turret ring; and grinders (31) of the grinding device, which are set at a tilted angle against the center axis of the turret ring.

Description: Field of the Invention The present invention relates to a method and an apparatus for removing burr in a continuous rolling process where billets are joined together by flash butt welding. Description of the Related Art There are several proposals on the method for removing burr from billets welded together to conduct continuous rolling. Examples of these methods are disclosed in JP-A-37541(1977) and JP-B-13361(1982), (the terms "JP-A-" and "JP-B-" referred to herein signify "unexamined Japanese patent publication" and "examined Japanese patent publication", respectively). However, they only describe examples of trimmer for burr-removal, and they do not disclose concrete method for grinding the burr. As for the removal of burrs from the welded parts of round billets welded together using flash butt welding method, JP-A-20492(1977) disclosed a method in which an edge face of rotating grinder contacts the surface of a round steel rod, and the surface of the round rod is ground by a revolution of the grinder around the rod center axis. In a system of flash butt welding of billets followed by continuous rolling, the on-line removal of burr from a flash butt weld part is necessary to conduct within a short time, and the bur-removing operation is required to sustain for a long period of time. Nevertheless, the methods disclosed in JP-A-37541(1977) and JP-B-13361(1982) did not disclose concrete method for grinding burr and did not deal with the burr on a flash butt weld part, though they proposed conceptual methods of burr-removal. In addition, the method proposed by JP-A-20492(1977) relates to the flash butt welding method, but the method has problems of offsetting the grinding center position owing to the abrasion of grinder and of lack of slag treatment. Thus the method is incapable of continuous grinding for a long period, and has no applicability to on-line commercial operation. The present invention was completed to solve the above-described problems. The first object of the present invention is to provide a method for removing burr on a flash but weld part, which method allows to remove burrs on a plurality of billets successively on an on-line basis. For a successive on-line operation of burr removal using grinding method in a continuous rolling process, there are various issues to solve as listed below. 1) Control of rotation and turning of grinder, and completion of grinding of the grinding machine; 2) Sensor positioning and trigger setting for enabling the control; 3) Escape control of a roll while a burr passing thereunder; and 4) Means for supporting and feeding the billet within a moving range thereof between the welding unit and the grinding machine. These issues, however, did not solved. The second object of the present invention is to solve the above-described issues and to present a control method for a running grinding machine, which control method realizes successive removal of burrs generated during the flash butt welding in a continuous rolling process. In a continuous rolling process where the successively cast billets are joined together at the inlet of a rolling mill using the flash butt welding method to form a continuos billet and where an endless rolling is conducted using thus joined billet in a rolling line, the rolling of as-welded billet cannot give satisfactory product because the uplifted portion on the welded part is left on the product as scab and other defects. Consequently, the burr on the welded part is required to remove before entering the rolling mill. Grinding was proved as a most effective means of burr-removal. A critical issue in that case is successive treatment of ground slag generated from successive grinding cycles without allowing accumulation thereof. The successive treatment of the slag is a neck of the adoption of the grinding method in continuous rolling process. Owing to the important issue that was not solved, the method is not brought into practical application, though the method is known by its usefulness. The present invention successfully solved the above-described important issue, and the third object of the present invention is to provide a method for successively treating ground slag in a continuous rolling process. In a process of continuous rolling of continuously cast billets, there is a known burr-removing unit (JP-A-43754(1977) and JP-B-11722(1982)) where a running flash butt welding unit is used to successively joint billets using the flash butt welding method and where the burrs generated during the welding are removed using bite or the like. That type of burr-removing unit uses a total bite because the unit deals with square billets so that the unit has a problem of severe abrasion of bite. On the other hand, there is a method dealing with round steel rods (JP-A-20492(1977), for example) where a plurality of grinders are used for removing burr by turning the grinders around the steel rod. That type of burr-removing unit has, however, a structure to insert the unit from lateral direction to the steel rod. Owing to the structure, a single grinder among plurality thereof is able to open/close while others are stationary. As a result, when the grinders are abraded, the center of grinding circle become offset from the center axis of the steel rod. In addition, since the rotational axis of the grinder is parallel to the axial line of the steel rod, the slag of ground chips scatters at an right angle to the steel rod axis and adheres to the grinder, and makes the slag collection difficult. Thus the on-line successive burr-removal is difficult. Use of grinder for removing burr from flash butt weld part is optimum for a billet continuous rolling process. The reason is that the time required for removing burr is very short and that a feature of grinding with grinder, or maintaining a stable grinding performance for a long period even after the grinder is abraded, is fully used. There are problems in the use of grinder for removing burrs from flash butt weld parts. These problems include that successively appearing burrs on the billet welded parts are necessary to remove during on-line running movement, and that, since a lot of ground slag scatter as spark during the burr grinding operation, the slag treatment is required to adequately treat, and that the operating state is requested to quickly respond to the size change of billet. The above-described patent publications do not provide any effective means to solve these problems. The present invention solved these problems, and the fourth object of the present invention is to provide a travelling burr-removal apparatus that grinds the burrs on welded parts of round billet successively and efficiently using grinders in a continuous rolling of round billet process. When successively cast billets are joined together at the inlet of the rolling mill using the flash but welding method to form a continuous billet, and when thus formed billet is then rolled without treating the welded part thereof, the uplift of welded part becomes scab or the like to remain on the product surface to result in a defective product. Accordingly, the burr on the welded part is necessary to be removed before entering the rolling mill. For a square billet, a burr-removal apparatus is disclosed in JP-A-43754(1977) and JP-B-11722(1982). The disclosed burr-removal apparatus uses total bites or bites each of which faces individual sides of the square billet to remove burr on the welded part. That type of burr-removal apparatus has, however, disadvantages of suffering severe abrasion on the bite and of taking too much time for replacement of bite, so that type of burr-removal apparatus cannot be applied for a continuous rolling process that has a strict limitation on time cycle. On the other hand, a grinding method using grinders is proved most effective to solve these problems. That type of method, however, generates a lot of ground slag so that a design for easy treatment of the slag is required. That is, the arrangement of grinders is requested to assure the scattering of the ground slag to a specified direction. The present invention was completed to respond to these problems, and the fifth object of the present invention is to provide an apparatus for removing burr on a welded part of a square billet, which apparatus is best fit to the continuous rolling process of suare billet. Finally, DE 28 36 338 A1 discloses a continuous rolling arrangement comprising a moveable welding machine and a moveable hot barker. The welding machine travels together with advancing billets and along a guide track. The barker is provided at the end of the guide track, so that movement thereof in the direction of advance of the billets is not possible. Thus, it is an underlying technical problem of the present invention to provide a method for removing burr and an apparatus for removing burr for enabling quicker continuous rolling of billets. In accordance with the present invention, this problem is solved by a method for removing burr in a continuous rolling process comprising the features of claim 1, and by a grinding machine having the features of claim 10. Advantageous further embodiments are recited in the respective dependent claims. Brief Description of the Drawings Fig. 1 is a schematic drawing of an example of the present invention showing the relation between the travelling grinding machine for removing burr on the welded part and the flash butt welding unit. Fig. 2 is a schematic front view of the travelling grinding machine for removing burr on the welded part of round billets in the present invention. Fig. 3(a) shows a sectional view of a burr generated at the joint section of the billets using a flash butt welding unit. Fig. 3(b) shows a cross sectional view of a burr generated at the joint section of the billets, after removing the burr using a flash butt welding unit. Fig. 4(a) shows a schematic side view of the travelling grinding machine for removing burr on the welded part of square billets. Fig. 4(b) shows a schematic front view of the travelling grinding machine for removing burr on the welded part of square billets. Fig. 5 is an illustrative drawing showing the scattering direction of the ground chips generated by grinding of burr on the welded part of billets using a travelling grinding machine. Fig. 6 is a schematic drawing of another travelling grinding machine for implementing the present invention. Fig. 7(a) shows the state that the sensor detects a welded part in the present invention. Fig. 7(b) shows the state that a welded part arrives at beneath the grinder. Fig. 8 is a control block diagram of the travelling grinding machine of Fig. 6. Fig. 9 is an illustrative drawing of lift mechanism of the support roll of the present invention. Fig. 10 shows the arrangement of the billet transfer mechanism of the present invention. Fig. 11(a) shows the arrangement of vehicles and other equipment at a waiting position of the present invention. Fig. 11(b) shows the arrangement of vehicles and other equipment at a weld-completion position. Fig. 11(c) shows the arrangement of vehicles and other equipment at a starting position for grinding. Fig. 11(d) shows the arrangement of vehicles and other equipment at a grind-completion position. Fig. 12 is a longitudinal cross sectional view of the hood for implementing the means for treating the ground slag of the present invention. Fig. 13 is a front view of the hood for implementing the means for treating the ground slag of the present invention. Fig. 14 shows an example of arrangement of grinders for a round billet. Fig. 15(a) is a front view of the grinders for a square billet. Fig. 15(b) is a side view of the grinders for a square billet. Fig. 16 is a front view of another travelling grinding machine of the present invention. Fig. 17 is a side view of the travelling grinding machine of Fig. 16. Fig. 18 is an illustrative drawing showing the state of setting the grinders. Fig. 19 is a schematic drawing of an HDR type continuous rolling unit for a round billet. Fig. 20 is a side view of another travelling grinding machine of the present invention. Description of the Preferred Embodiment 1. Example of a first embodiment of the present invention (Preferred mode 1 of the present invention) Fig. 1 is a schematic drawing of the travelling burr-removal apparatus and the relating equipment thereof for the flash butt welding method of an example of the preferred mode of the present invention. Fig. 2 is a front schematic view of the travelling burr-removal apparatus of Fig. 1. In the figures, the flash but welder 20 is provided with the clamp 21 which fastens the preceding billet 10, the clamp 22 which fastens the succeeding billet 11, and the welding power source 23. The flash butt welding is conducted by applying a welding current between the rear end of the billet 10 and the front end of the billet 11, which billets are in a pressure welding state, via the clamps 21 and 22. The flash butt welder 20 is supported in a manner that the unit 20 is freely movable along the travelling direction of the billets 10 and 11, thus the flash butt welder 20 moves synchronously with the movement of the billets 10 and 11 when the welding operation begins. At downstream of the flash butt welder 20, the travelling grinding machine 30 for removing burr is located. The travelling grinding machine 30 grinds the burr on the welded part, which burr was formed during the flash butt welding operation. The travelling grinding machine 30 is provided with grinders 31 through 33 which are supported in a rotatable and revolutionary state along the circumferential direction of the billet, and provided with the motors 36 and 37 which drive the grinders 31 and 32, respectively. The grinder 33 is also driven by a motor, though the driving motor is not shown in Fig. 1. The travelling grinding machine 30 is also supported in a monvable state along the travelling direction of the billets 10 and 11, and the travelling grinding machine 30 moves when the grinding operation begins synchronously with the travelling billets 10 and 11. In the apparatus shown in Fig. 1 and Fig. 2, the billets 10 and 11 came from a continuous casting unit (not shown) or a heating furnace (not shown) are separately fastened by the clamps 21 and 22 at the rear end and the front end thereof, respectively. Then the pressure welder 25 brings the rear end of the billet 10 and the front end of the billet 11 close each other. The welding current is supplied from the welding power source 23 at the state that a part of the rear and front ends contact each other to perform the flash butt welding. At that moment, the flash butt welder 20 performs the flash butt welding while travelling by itself. Fig. 3(a) is a cross sectional schematic view of the welded part 12 in a state that the rear end of the preceding billet 10 and the front end of the succeeding billet 11 are welded together by the flash butt welding method using the flash butt welder 20. As seen in the figure, the welded part 12 is uplifted on the circumferential wall owing to the upset at flash butt welding. The uplifted burr 13 is removed by grinding using the travelling burr-removal apparatus 30. Fig. 3(b) shows the state after removed the burr. When the travelling burr-removal apparatus 30 detects the welded part 12 of billet, it starts travelling toward downstream and moves the constantly rotating grinders 31 through 33 toward the center of the billet using hydraulic cylinders or the like, thus presetting the billet 10. Then, the billets 10 and 11 are further transferred to downstream. When the welded part of the billet reaches beneath the grinders 31 through 33, the drive current of the drive motors 36 and 37 suddenly increases. By the sudden increase in the current, the arrival of the welded part 12 is detected, and the grinders 31 through 33 starts removing the burr 13 on the welded part 12. At that moment, the grinders 31 through 33 revolute circumferential direction of the billet (in this example, the revoluting angle is 120 deg + α, α is a margin), and remove the whole burr 13 by grinding on the circumference of the billet. The revolutionary motion is conducted by, for example, supporting the whole travelling grinding machine 30 within a supporting device such as a turret ring in a rotatable state, as shown in Fig. 1. (Preferred mode 2 of the present invention) Fig. 4(a) and Fig. 4(b) are a schematic plan view and a schematic front view of another example of the travelling grinding machine of the present invention, respectively. Fig. 1 and Fig. 2 show an example of travelling burr-removal apparatus 30 for removing burr on a round billet. Fig. 4 shows an example dealing with a square billet. In Fig. 4, the grinders 41 through 44 are arranged to encircle the square billet 14, and are arranged at an tilted angle to the billet axis thereeach. The right and left grinders 41 and 42 are positioned distant from the top and bottom grinders 43 and 44 in a travelling direction of the billet to avoid mechanical interference between each pair thereof. Accordingly, in this case, the burr 13 is removed by two steps grinding operation. (Preferred mode 3 of the present invention) Unless the slag generated from grinding of burr using the grinders 31 through 33 of the travelling grinding machine 30 shown in Fig. 1 is adequately removed, a long period of grinding operation cannot be sustained. To answer the requirement, the grinders 31 through 33 or the grinders 41 through 44 of the above-described travelling grinding machine of the present invention are arranged at a tilted angle against the travelling direction of the billet to ease the slag treatment. Fig. 5 illustrates the scattering direction of slag during grinding operation. As seen in the figure, since the slag 50 scatters to a direction different from the travelling direction of billets 10 and 11. Accordingly, the slag 50 is collected by installing an adequate dust collecting duct at downstream of the scattering slag. A preferred tilted angle of the grinders is in a range of from 15 to 30 degrees. The arrangement of tilted grinders has advantages of easing the slag treatment and of allowing to increase the grinding width for the width of grinder. According to the present invention, the burrs on the welded parts of billets joined together by flash butt welding are ground by a plurality of rotating grinders while travelling the billets and while moving the grinders synchronously with the run of the billets. Consequently, a feature of the grinding by grinders, or a feature of sustaining constant grinding state even after the grinders are abraded, maintains its effectiveness, thus assuring the burr-removal for a long period of operation. In addition, the grinders move synchronously with the run of the billet so that the on-line grinding treatment is attained without interfering the run of the billet. As a result, on-line continuous burr-removal is performed for a plurality of billets, which makes the method suitable for the continuous rolling process. 2. Example of a second embodiment of the present invention (Preferred mode 1 of the present invention) Fig. 6 is a schematic drawing of the travelling grinding machine of an example of a mode of the present invention. Fig. 7(a) and Fig. 7(b) illustrate the action of the travelling grinding machine. The travelling grinding machine 30 grinds burr on a welded part, which was formed by the flash butt welding. The travelling grinding machine 30 is provided with the grinders 31 through 33 which are supported in a rotatable state, with the drive motors 36 through 38 to rotate the grinders 31 through 33, and with the lifting cylinder 27 and the slide guide section 28 to move each of the grinders 31 through 33 to the center of the billet. At the time of the grinding operation, the grinders 31 through 33 are locked at the preset position around the circumference of the billet. Fig. 6 and Fig. 7 show the lifting cylinder 27 and the slide guide section 28 only for the grinder 31, though similar devices of cylinder and slide guide are installed for each of the grinders 32 and 33. The travelling grinding machine 5 is supported in a movable state along the travelling direction of the billet, and, when the grinding starts, the travelling grinding machine 30 moves synchronously with the movement of the billet. The target billet in this example is a round billet, and the grinders 31 through 33 are supported in a revolutionary state along the circumference of the billet. Fig. 8 is a schematic drawing of the control system of the travelling grinding machine 5. The travelling grinding machine 30 is provided with a welded-part detection sensor 90 which detects the welded parts on the billets welded together by the flash butt welding method. The output of the sensor 90 enters the control unit 91. Based on the input signal, the control unit 91 conducts a specified computing processing, and generates the resulted control signal to the drive circuits 92 through 95. The drive circuit 92 drives the drive motor 96 which moves the body of travelling grinding machine 30 synchronously with the rolling speed during the travelling grinding operation. The drive circuit 93 drives the motors 36 through 38 which continuously rotate the grinders 31 through 33. The drive circuit 94 drives the lifting cylinder 27. The drive circuit 95 drives the drive motor 97 (not shown in Fig. 6) which revolutes the grinders 31 through 33. The action of the travelling grinding machine 30 is described below referring to Fig. 6 through Fig. 8. 1) On receiving the weld-completion signal from the travelling flash butt welder 4, the control unit 91 drives the drive motor 96 using the drive circuit 92 to move the grinding machine 30 to upstream side. At that moment, the control unit 91 also moves the travelling flash butt welder 4 to upstream side. 2) When the welded-part detection sensor 90 detects a welded part of the billet, the control unit 91 drives the drive motor 96 in a reverse rotational direction using the drive circuit 92, and moves the grinding machine 30 to downstream side while accelerating the grinding machine up to the rolling speed. Then, the control unit 91 drives the lifting cylinder 27 using the drive circuit 94 to pre-clamp the billet. (Refer to Fig. 7(a).) 3) The control unit 91 detects the arrival of the welded part 10 to beneath the grinders 31 through 33. When the welded part 10a arrives at beneath the rotating grinders 31 through 33, (refer to Fig. 7(b)), the drive current of the drive motors 36 through 38 which rotate the grinders 31 through 33 shows a sudden increase. The control unit 91 detects the arrival of the welded part 10a by sensing the sudden increase in the drive current while entering the drive current from the drive circuit 93. The control unit 91 also tracks the position of the welded part 10a on the basis of the distance between the grinding point 21a and the welded-part detection sensor, of the moving speed of the travelling grinding machine body, and of the rolling speed. 4) The travelling grinding machine locks the lifting cylinders 27 of the grinders 31 through 33 and begins the grinding operation while travelling thereof at a synchronous speed with the rolling speed. 5) Simultaneously with the beginning of grinding, the control unit 91 drives the drive motor 96 using the drive circuit 95 and starts the turning of the grinders 31 through 33. In this example, the grinders 31 through 33 are arranged at an equal space therebetween on a circumference, so the revolution angle is 120 degrees. 6) When the revolution completed, the travelling grinding machine 30 is moved to the waiting position, and the above control action is repeated again. (Preferred mode 2 of the present invention) If a burr on the welded part of the billet 10 passes over the rolls in an uplifted state, the billet will be uplifted by the burr on the billet, and may derail from the V-grooved roll. Therefore, the rolls which are located between the travelling flash butt welder 4 and the travelling grinding machine 30 are necessary to escape from the billet during the welded part passes thereon. Fig. 9 illustrates a mechanism for escaping the roll from the billet to satisfy the requirement. The roll 86 is located at downstream of the travelling flash butt welder 4 and at upstream of the grinding point 21a. When the welded-part detection sensor 90 detects the welded part 10a, the control unit 91 actuates the built-in timer to start counting the time. When the timer reaches the time-up point, then the control unit 91 drives the lifting cylinder 99 using the drive circuit 98. According to the example of Fig. 9, after the weld-part detection sensor 90 detected the welded part 10a and after a specified time has passed, and immediately before the welded part 10a passes over the roll 86, the control unit 91 drives the lifting cylinder 99 to descend the roll 86. After the welded part 10a passed over the roll 86, the control unit 91 ascends the roll 86. In this manner, when the welded part 10a passes over the roll 86, the roll concerned escapes from the billet. If that type of roll is mounted more than one, descending and ascending are repeated in the order from upstream rolls to downstream rolls. (Preferred mode 3 of the present invention) It is necessary to escape the rolls when a welded part of the billet passes thereover. To mount a plurality of ascending/descend ing rolls is not preferable from the viewpoint of investment cost and of complicated operation. Accordingly, the number of support rolls is necessary to minimize between the travelling flash but welder 4 and the travelling grinding machine 30. To do this, the present invention provides a support roll and controls separately the travelling flash butt welder 4 and the travelling grinding machine 30. Fig. 10 shows an arrangement of transfer mechanism for the continuous rolling billets of an example of another preferred mode of the present invention. At the uppermost upstream position, the fixed roll 70 is located, and the vehicles 61 through 63 which move along the rails 16, 16, are located immediately downstream to the fixed roll 70. The vehicles 61 through 63 have the support rolls 71 through 73, respectively. The travelling flash butt welder 4 which is positioned at directly downstream of the vehicle 63 has the support rolls 74 and 75. The travelling flash butt welder 4 is successively connected with the vehicles 61 through 63 by flexible connecting means (ropes, fore example). Thus, when the travelling flash butt welder 4 moves to downstream, it moves the vehicles 61 through 63 by towing them. When the travelling flash butt welder 4 moves to upstream, it moves the vehicles 61 through 63 to upstream by pushing them. The travelling grinding machine 30 also has the support rolls 76 and 77. The travelling flash butt welder 4 and the travelling grinding machine 30 also move on the rails 16, 16, during the operation thereof. Three vehicles 64 through 66 are located directly after the travelling grinding machine 30, which have the support rolls 78 through 80, respectively. The travelling grinding machine 30 is successively connected with the vehicles 64 through 66 by flexible connecting means (ropes, fore example). Thus, when the travelling grinding machine 30 moves to upstream, it moves the vehicles 64 through 66 upstream by towing them. When the travelling grinding machine 30 moves to downstream, it moves the vehicles 64 through 66 to downstream by pushing them. The fixing roll 81 is positioned directly after the vehicle 66. Fig. 11 (a) through (d) illustrate the arrangement of vehicles for each control stage of the travelling flash butt welder 4 and the travelling grinding machine 30. 1) Waiting position (Fig. 11(a)): First, the travelling flash butt welder 4 and the travelling grinding machine 30 are placed at the initial state, or the waiting position. At the waiting position, both the travelling flash butt welder 4 and the travelling grinding machine 30 are located at the uppermost upstream position. The distance among the support rolls 71 through 73 of the vehicles 61 through 63 which are connected to the travelling flash butt welder 4 is the shortest one. The distance among the support rolls 78 through 80 of the vehicles 64 through 66 which are connected to the welder 30 is the longest one to maintain the maximum distance for each other. 2) Weld-completion position (Fig. 11(b)): When the billet detector on the travelling flash butt welder 4 detects the rear end of the succeeding billet, the travelling flash butt welder 4 begins the welding treatment while moving itself to downstream synchronously with the rolling speed. At that moment, the control unit 91 drives the drive motor 96 using the drive circuit 92 to move the travelling grinding machine 30 to downstream at a synchronous speed with the rolling speed. When the welding treatment completed, the vehicles 61 through 63 is towed by the travelling flash butt welder 4 to become the maximum distance between each of the vehicles 64 through 66 under a state of maximum stretch of the distance among each of the support rolls 71 through 73. The vehicles 64 through 66 were pushed to downstream by the travelling grinding machine 30, thus the distance among each of the support rolls 78 through 80 becomes the minimum. 3) Grinding start position (Fig. 11(c)): When the welding completed, the travelling flash butt welder moves to upstream. At that moment, the control unit 91 receives a signal to indicate the weld completion from the travelling flash butt welder 4. Based on the signal, the control unit 91 moves the travelling grinding machine 30 to upstream. When the welded-part detection sensor 90 detects the arrival of the welded part of the billet, the control unit 91 stops the movement of the travelling grinding machine 30. After then, the travelling grinding machine 30 starts the grinding operation. At that moment, the distance among each of the vehicles 61 through 63 is at a slightly contracted state compared with the most stretched state, and the distance among each of the vehicles 64 through 66 is at a slightly stretched state compared with the most contracted state. Consequently, the support rolls 71 through 73 and 78 through 80 become corresponding distance to that of vehicles 61 through 66. 4) Grinding completion position (Fig. 11(d)): Although the travelling flash butt welder 4 is kept stopped at the grinding start position, the travelling grinding machine 30 conducts grinding the burr on the welded part while travelling itself to downstream. Since the travelling flash butt welder 4 stops, the vehicles 61 through 63 stay at the same position as that at grinding start. Vehicles 64 through 66 are, however, at a slightly contracted state compared with that at grinding start because the travelling grinding machine 30 moves to downstream. Accordingly, the support rolls 71 through 73 and 78 through 80 of the vehicles 61 through 66 have a distance each of them corresponding to the above-described arrangement. Since the stroke of the travelling grinding machine 30 is about 1500 mm, the maximum distance between the travelling grinding machine 30 and the travelling flash butt welder 4 corresponds to the stroke. Consequently, billets are satisfactorily supported even when there is not a support roll between the travelling flash butt welder 4 and the travelling grinding machine 30. When the welding completed, the travelling flash butt welder 4 and the travelling grinding machine 30 return to the above-described waiting position, and they repeat the above-described control action. In Fig. 10, the fixed roll 70, the support rolls 72, 75, and 79, and the fixed roll 81 are the drive rolls to assure the travelling of billets at a rolling speed. The support roll 75 of the welder 4 and the support roll 76 of the grinding machine 30 are supported in a free-lifting state and are descended when a welded part of billet passes thereover. According to a preferred mode of the present invention described above, on-line grinding treatment is achieved because the mode comprises the steps of: detecting a welded part on billets for continuous rolling, which billets were welded to join together by a travelling welder, using the travelling grinding machine located at downstream of the welder; presetting a plurality of grinders mounted to the travelling grinding machine and continuously rotating thereof to the billet immediately after detecting the welded part while moving the travelling grinding machine synchronously with a rolling speed of the billet ; detecting that the welded part of the billet arrived at a position of the grinders; and after detecting the arrival of the welded part of the billet, grinding a burr on the welded part by fixing the grinders at the preset position while travelling the travelling grinding machine with the speed of the billet rolling synchronously. According to another preferred mode of the present invention, the burr is effectively removed for total circumference of the billet because the burr on the welded part is ground using the grinders arranged on a circumference of the round billet at an equal distance therebetween while turning the grinders. According to a further preferred mode of the present invention, the welded part of the billet is avoided to pass over the support rolls while contacting each other owing to a control means of the support rolls including a step of descending the support roll located at directly downstream of the detection point after detecting the welded part of the billet, and ascending thereof after a specified period of time. According to still another preferred mode of the present invention, the billets are adequately supported without placing support roll between the travelling welder and the travelling grinding machine because the travelling welder is in a move-controlled state responding to the weld completion point and the grinding point to minimize the distance between the travelling welder and the travelling grinding machine. 3. Example of a third embodiment of the present invention (Preferred mode of the present invention) Fig. 12 is a schematic drawing illustrating a continuous treatment of ground slag of the present invention. Fig. 13 is a front view of the hood. In these figures, the continuous billet 11 moves to the arrow direction. The flash butt welder (not shown) located at upstream side conducts continuous flash butt welding. Reference numeral 9 denotes the welded part 9, and reference numeral 10a denotes the burr on the welded part. The grinding machine 30 which travels along the billet moving direction has a plurality of grinding devices 51 which has the grinders 31 and 32 to remove the burr 10a while revoluting along the circumference of the welded part 9. The turret ring 55 is supported by the roller 34 on the travelling body 54 in free-rotational state, which turret ring 55 has the motor 36 of the grinding device 51. The ground slag 120 generates during the grinding of the burr 10a, which slag 120 scatters to downstream to a specified direction within a specified range. The grinders 31 and 32 come close to or apart from the billet 1 by a lifting means or a swing means (both means are not shown). The hood 100 is located on the travelling body 54 while facing the scattering direction of the ground slag 120. The shape of the hood 100 has a wide front opening 101 around the billet 1, and a gentle slope inner face from the edge of the opening 101 to connect the vertical impinging face 102. The impinging face 102 receives most part of the ground slag 120. In addition, the impinging face 102 has an opening 103 through which the billet 1 passes. The opening 103 is provided with a billet cover 104 having an adequate length to cover the billet. The front edge of the billet cover 104 has a rise 25 which rises toward outside therefrom. Spray nozzles 106 are mounted at adequate positions in the hood 100 to cover the whole inside surface of the hood 100 with flowing water film 107. A discharge opening 108 is opened at bottom of the hood 100. The burr-removing grinding is conducted while the grinding machine 30 travels synchronously with the moving speed of the billet 11. The spray nozzles 106 in the hood 100 sprays water in advance to cover the whole inner face of the hood 100 with the flowing water film 107. The grinders 31 and 32 grind the burr 10a on the welded part 9 while rotating to the arrow direction and while revoluting around the circumference of the billet 11. The ground slag 120 generated by the grinding scatters to downstream in a cone shape pattern as shown in Fig. 12. Since the hood 100 is located facing the scattering direction of the ground slag 120, the ground slag C scattering in a conical pattern enters the opening 101 and collides against the impinging face 102, which slag is immediately cooled by the flowing water film 107 and is discharged along with the water film 107 through the bottom opening 108. The discharge opening 108 opens at above the drain channel 110, for example, so the slag can be accumulated at a specified place via the drain channel 110. The billet 11 moves through the opening 103 on the impinging face 102. The opening 103 is provided with the billet cover 104, and the front edge of the cover 104 forms a rise 105, so the flowing water film 107 does not contact with the billet 11 but the film flows down along the billet cover 104 while going around the billet 11. As a result, the temperature of the billet 11 does not reduce, and heat loss is prevented. In this manner, the burrs 10a of the welded parts 9 on successively arriving billets are ground while collecting the generated ground slag 120 by the hood 100 having a specially designed shape and structure and while removing the collected slag 120 along with the flowing water film 107 on the inner face of the hood. Consequently, the ground slag is continuously treated without accumulating thereof. Fig. 2 and Fig. 14 show an example of arrangement of a grinder 31 against the round billet 10. Fig. 2 is a front view, and Fig. 14 is a top view. As shown in these figures, it is preferable to place the grinder 31 at a tilted angle against the axis of the round billet 10. With that type of placing, the scattering direction of the ground slag is assured to a obliqe direction, and the grinding width to the welded part 9 is widened. Fig. 15(a) and Fig. 15(b) illustrate an example of the arrangement of grinders 41 through 44 against the billet 12. Fig. 15(a) is a front view, and Fig. 15(b) is a side view. In that case, a preferable arrangement of the grinders 41 through 44 is to position each pair thereof along the axial direction of the square billet 12 separating each pair of them. Generally the length of a side of the square billet 11 will be larger than the width of a grinder, so the grinders 41 through 44 are constructed in a movable state along the direction of side length during the grinding operation. The grinding is performed by two-steps: right and left sides, and top and bottom sides. With the parallel arrangement of the grinders 41 through 44 to the axial line of the square billet 12, the ground slag generated from the upstream grinders 41 through 44 is prevented from hitting the grinding machine at downstream. The scattering direction of the ground slag is oblique angle to the axial line of the square billet 12. As described above, the continuous treatment method of ground slag of the present invention for removing burr on the welded part of billet using the grinding with grinders comprises the steps of: regulating the direction of scattering ground slag in a specified downstream direction; collecting the ground slag using the hood covered with a flowing water film inside thereof; and flowing down the collected slag along with the flowing water film. Therefore, the method of the present invention allows the continuous treatment of ground slag without accumulating thereof, thus realizes the treatment of ground slag, which was an issue in prior art. As a result, the effectiveness of the grinding with grinders in the continuous rolling process is maximized. 4. Example of a fourth embodiment of the present invention (Preferred mode of the present invention) Fig. 16 is a front view of an example of the travelling burr-removal apparatus of the present invention, and Fig. 17 is a side view of the unit. The travelling burr-removal apparatus 30 for removing burr comprises the travelling body 54 which has the turret ring 55 thereon. The turret ring 55 is provided with three grinding devices 51 which are separately driven to rotate and are movable to a radial direction of the turret ring 55. Each of the grinders 31 through 34 is tilted at a specified angle against the center axis of the round billet 10 as shown in Fig. 18. With the tilted angle, a grinder having relatively thin thickness can grind the burr 10a on the welded part 9 to a wide width thereon. Since the scattering direction of generated slag 120 is a oblique angle against the center axis of the round billet 10, the separation and collection of the slag 120 is easily performed. The travelling body 54 travels on the rails 16 laid along the billet moving direction at a specified stroke. The servo-motor 96 for driving travelling is actuated by mating the pinion 18 on the motor output shaft with the rack on the side of the rails 16. The turret ring 55 is structured by frames, and is supported at its bottom by the supporting rollers 125 in a rotatable state on the travelling body 54. The rear side of the turret ring 55 is supported by the longitudinal frame 58 which stands on the travelling body 54. The longitudinal frame 58 is provided with the turret drive motor 97. The turret ring 55 rotates around the center axis of the round billet 10 by mating the pinion 111 mounted to the output shaft of the turret drive motor 97 with the ring gear 112 at the rear side of the turret ring 55. The billets 10 are continuously joined together by a preceding travelling flash butt welder (not shown). A plurality of grinding devices 51 each of which is separately driven are mounted on the support 115. Each support 115 is supported at the front side of the turret ring 55 via the slide table 116 in a free-sliding state. The slide table 116 is connected with the turret ring 55 by a hydraulic cylinder 39 for moving. Thus, by moving the grinders 31 through 33 to the radial direction of the turret ring 55, the grinder devices 51 are configured in a concentric pattern around the center axis of the round billet 10 allowing displacing thereof. The grinder 31 is driven to rotate by the grinder drive motor 36 mounted on the support 115 via the belt 36a. A bead sensor 90 is located at upstream of the grinder 31 to detect the billet welded part 9. A dust collection hood 100 is located at downstream of the grinder 31, and a plurality of water spray nozzles 106 on inside face of the hood 100. Owing to the hood 100 and the water spray from the water spray nozzles 106, the spark of ground slag generated during the burr removing operation is cooled, and the ground slag are collected. Thus the collected slag is discharged through the drain pipe 108 into drain channel or the like. The support roll 113 of the continuous billet 10 descends when the welded part 9 passes thereover. The lifting means of the support roll 113 is not shown. The reference numeral 114 denotes the heat isolation hood. The grinding machine 30 for removing burr as structured described above is installed as a part of the continuous rolling facility for round billet, for example, as shown in Fig. 19. Fig. 19 shows a schematic drawing of a continuous rolling mill of HDR (Hot Direct Rolling) type. The continuous casting machine 1 in the figure is, in this example, a continuous casting machine of two strand type. The turn table 2 is installed at the base end side of the connection line 1b of the round billet 10, which turn table 2 shifts the billet 10 thereon while turning thereof onto the center line 201. The reference numeral 3 is the de-scaling unit to remove the scale by, for example, injecting high pressure water against thereof. The reference numeral 4 is the travelling flash butt welder which travels at a specified stroke S1. Succeeding to the welder 4, the travelling grinding machine 30 of the present invention is installed. The reference numeral 6 is the induction heating unit to heat the continuous billet after removing burr to a specified temperature. The reference numeral 7 is a series of rolling mills comprising a plurality of rolling mill stands to structure the rolling line. The reference numeral 1a denotes the casting line, and 1c denotes the rolling line. The joining line 1b of the billet 10 and the rolling line 1c are connected in series. The reference number 202 is the rotational center of the turn table 2, which center fits the joining line 1b. The action of travelling grinding machine 30 is described below along with the description on the action of the above-described HDR continuous rolling facility. The round billets 10 which were continuously cast by the continuous casting machine 1 are transferred onto the turn table by one at the single turn thereof, and the billet 10 is shifted to match the center line 201 of the turn table 2 and to match the joining line 1b during the single turn thereof. Then the round billet 10 is directly fed to the joining line 1b one by one. The directly supplied billets 10 are subjected to de-scaling and are successively welded at the front end of the preceding billet with the rear end of the succeeding one while travelling thereof using the flash butt welding method. The state of billet welding is shown in Fig. 3(a), which indicates that the burr 10a rose above the circumference of the billet. The height H of the burr 10a is normally 7 to 15 mm. Accordingly, the rolling of billet while leaving such a burr 10a nontreated results in a defect on the product. For removing the burr 10a, the grinders are used in the travelling grinding machine 30 to remove the burrs quickly and successively. That is, when the sensor 90 detects the position of the welded part 9, the travelling grinding machine 30 begins to move to downstream, and the grinders 31 of the grinding device 51 begin to rotate, and further the hydraulic cylinder 39 moves the grinder device 51 toward the center of the billet to preset the grinding depth. When the continuous billet 1 further moves to downstream and when the billet welded part 9 arrives at directly beneath the grinder 31, the driving current of the grinder drive motor 36 shows a sudden increase in current, which notifies the arrival of the welded part 9. When the welded part 9 arrives at directly beneath the grinder 31, the rotating grinder 31 is fixed at the preset position, and the grinder device 51 is revoluted around the continuous billet 10 using the turret ring 55 to remove the burr 10a on the whole circumference of the continuous billet 10. Since the grinder 31 is set at a tilted angle against the billet center axis and the grinder 31 revolutes around the continuous billet 10, even a thin grinder 31 can remove the burr 10a at a wide width. Also since the scattering direction of the slag 120 is able to regulate in a oblique angle as shown in the figure, the slag 4 is easily collected. The burr-removal apparatus 30 conducts the removal of burr during the travelling period of stroke S2 as shown in Fig. 18. After completing the burr removal, the burr-removal apparatus 30 returns to the original position, and the successive burr removing action against the welded part 9 is performed following the above-described procedure. In this manner, the burr 10a of each welded part 9 is successively removed. The state after the completion of the burr removal is shown in Fig. 3(b). Since the welded part 9 is also rolled, the burr removal is not required to accurately finish but left at a rough finish. During the burr-grinding operation, a lot of slag 120 generates. A dust collection hood 100 is mounted at front side of the grinder 31, so the water spray through the water spray nozzles attached on the inside face of the hood allows to collect the slag 120 while cooling thereof. Furthermore, the slag 120 is discharged to outside through the drain pipe 108 so that the slag 120 is not emitted to the peripheral area of the apparatus 30. If the size of billet 1 changed, a plurality of grinders 31 through 33 are capable of displacing, so a quick response to the size change is applicable without adding special action. As described above, the travelling burr-removal apparatus of the present invention for a process of continuous rolling of the direct feed billets which were continuously cast comprises the steps of removing the burrs on the welded parts of the round billets which were continuously welded by the flash butt welding method using the grinders while travelling the billets. As a result, the on-line burr removal is conducted successively at a high productivity, at a short burr-removing time, for a long period of application. Since the grinders are set at a oblique angle against the center axis of the billet, the burr-removal is conducted at a wide range of burr, while regulating the scattering direction of slag, thus easing the separation and collection of scattered slag. Owing to the dust collection hood equipped with the water spray nozzles inside thereof, the slag can be separated and collected without emitting the slag during the burr removing operation. 5. Example of a fifth embodiment of the present invention (Preferred mode of the present invention) Fig. 20 is a side view of an example of the structure of burr-removal apparatus of the present invention. Fig. 4(a) and Fig. 4(b) are front view of the grinder arrangement against the square billet. The burr-removal apparatus 30 is provided with two pairs of grinding devices 51 and 52, total four devices, on the travelling body 11. Among them, a pair of the grinding devices is located at upstream to grind the right and left sides of the welded part 12a of the square billet 12, and the other pair is located at downstream to grind the top and bottom faces of the welded part 12a of the square billet 12. Each of the grinders 41 through 44 is positioned parallel to the longitudinal direction of the square billet 12. That is, the rotational axis 43a of the grinder is right angle to the axis of the square billet 12. The grinder 43 is driven by the motor 401 to rotate to the arrow direction so as the ground slag scatters to downstream direction. Each motor 401 is mounted on the slide base 402. In the grinding device 51 at upstream, the slide base 402 is vertically guided using the vertical base holder 56. In the grinding device 52 at downstream, the slide base 402 is horizontally guided using the horizontal base holder 48. For sliding the slide base 47, the sliding cylinder 57 connects the base holders 56 and 48. The sliding cylinder that connects the base holder 48 with the slide base 47 is not shown. With the configuration, the grinders 41 through 44 are capable of sliding along the longitudinal direction of a side of the square billet 12. Each of the grinders 41 through 44 is rotated by a belt transmission mechanism which is not shown. The casing 45 containing the belt transmission mechanism has the arm 46a. The front end of the arm 46a and the front end of the arm 46a which protrude from the motor casing are connected by a swing cylinder 460 to enabling the swing of the grinder 43 around the motor shaft 403. Owing to the configuration, the grinder 43 is able to come close to or separate from the square billet 12. The dust collecting hood 100 is mounted at downstream of the grinding devices 51 and 52 to collect the ground slag and to wash the slag down to the bottom of the hood. The dust collection hood 100 is equipped with the water spray nozzles 106 inside thereof to form a flowing water film on the inner face thereof. Since the slag scatters to a specified direction as described before, the dust collecting hood 100 accepts the scattered slag, and wash the collected slag down along the flowing water film 107 on the inner face of the hood. The support roller 113 for the square billet 12 descends during the welded part 12a passing thereover by a lifting means (not shown). The grinding machine 30 for removing burr as structured described above is installed as a part of the continuous rolling facilityu for square billet, for example, as shown in Fig. 19. Fig. 19 shows a schematic drawing of a continuous rolling mill of HDR (Hot Direct Rolling) type. The continuous casting machine 1 in the figure is, in this example, a continuous casting machine of two strand type. The turn table 2 is installed at the base end side of the joining line 1b of the square billet 12, which turn table 2 shifts the billet 12 thereon while turning thereof onto the center line 201. The reference numeral 3 is the de-scaling apparatus to remove the scale on the billet 12 by, for example, injecting high pressure water against thereof. The reference numeral 4 is the travelling flash butt welder which travels at a specified stroke S1. Succeeding to the welder 4, the travelling grinding machine 30 of the present invention is installed. The reference numeral 6 is the induction heating unit to heat the continuous billet after removing burr to a specified temperature. The reference numeral 7 is a series of rolling mills comprising a plurality of rolling mill stands to structure the rolling line. The reference numeral 1a denotes the casting line, and 1c denotes the rolling line. The joining line 1b of the billet 10 and the rolling line 1c are connected in series. The reference numeral 202 is the rotational center of the turn table 2, which center fits the joining line 1b. The action of travelling grinding machine 30 is described below along with the description on the action of the above-described HDR continuous rolling facility. The square billets 12 which were continuously cast by the continuous casting machine 1 are transferred onto the turn table 2 by one at the single turn thereof, and the billet 12 is shifted to match the center line 201 of the turn table 2 and to match the joining line 1b during the single turn thereof. Then the square billet 12 is directly fed to the joining line 1b one by one. The directly supplied billets 12 are subjected to de-scaling at the de-scaling apparatus 3 applying, for example, the injection of high pressure water, and are successively welded at the front end of the preceding billet with the rear end of the succeeding one while travelling thereof using the flash butt welding method. The state of billet welding is shown in Fig. 3(a), which indicates that the burr 10a rose above the circumference of the billet. The height H of the burr 12a is normally 7 to 15 mm. Accordingly, while leaving such a burr 12a nontreated, the rolling of billet results in a defect on the product. For removing the burr 12a, the grinders are used in the travelling grinding machine 30 to remove the burrs quickly and successively. That is, when a sensor (not shown) detects the position of the welded part 12a, the travelling grinding machine 30 starts to move to downstream, and the grinders 43 and 44 of the grinding device 51 starts to rotate. Firstly, the grinder device 51 at upstream moves the grinder 43 toward the center of the billet to preset the grinding depth using the swing cylinder 46c. When the continuous square billet 12 further moves to downstream and when the billet welded part 12a arrives at directly beneath the grinder 43, the driving current of the grinder drive motor 401 shows a sudden increase, which sudden increase in current notifies the arrival of the welded part 12a. When the welded part 12a arrives at directly beneath the grinder 43, the rotating grinder 43 is fixed at the preset position. When the length of a side of the square billet 12 is longer than the width of the grinder, the grinding device 51 is ascended or descended using the sliding cylinder 57 to grind the right and left sides of the billet welded part 12a, so the whole burr 12a on the right and left sides is ground to remove. After removing the right and left side burr, the grinder 41 stops its rotation, and leaves from the grinding position to go back to the original position by the action of the swing cylinder 460, and further returns to the original position by the action of the sliding cylinder 57. When the square billet 12 is transferred and arrives at the grinding device 52 at downstream, the grinding device 52 performs similar function with that of the grinding device 51. Thus the grinder 44 of the grinding device 52 grinds the burr on top and bottom sides of the billet welded part 12a to remove the burr. In this manner, the billet welded part 12a is firstly ground on right and left sides, then on top and bottom side to remove the burr. The necessary time for grinding in each stage is about 5 to 10 sec, which timing is sufficient to satisfy the time cycle of the continuous rolling of square billets. The travelling grinding machine 30 conducts the burr removal while travelling through a specified stroke S2, which is shown in Fig. 3, at a speed synchronous with the moving speed of the square billet. After completing the burr removal, the travelling grinding machine 30 returns to the original position to repeat the burr removal action to succeeding welded part 12a in a similar procedure as preceding one. Following the procedure, the burr 12b on each welded part 12a is successively removed. The state after the burr removal is shown in Fig. 3(b). Since the welded part 12a is also rolled, accurate finish is not necessary. Since the grinders 43 and 44 of the grinding devices 51 and 52 are set parallel to the longitudinal direction of the square billet 12, the ground slag generated during the grinding scatters downstream in a regulated direction. Accordingly, the ground slag generated by the grinder 43 of the grinding device 51 does not hit the downstream grinding device 52, and the ground slag coming from the grinding devices 51 and 52 is easily collected by the dust collecting hood 100. Furthermore, the collected slag is washed down with the flowing water film 107 which flows down on the inner face of the hood. Thus the treatment of ground slag becomes easy. If the size of square billet changes, prompt response is available without applying special action because only the change of swing and slide of the grinder 43 is required for the billet size change. As described above, the burr-removal apparatus of the present invention realizes the continuous rolling of square billets at a high productivity without raising problem of time cycle owing to the adoption of two pairs (front and rear) of grinding devices for grinding and removing the burrs on the welded parts of square billets. Since the scattering direction of the ground slag is restricted to a single direction, the collection and treatment of the ground slag is easily conducted.

Claims: Method for removing burr in a continuous rolling process, comprising the steps of: joining a rear end of a preceding billet (10) with a front end of a succeeding billet (11) by flash butt welding and while the preceding billet as well as the succeeding billet are travelling; and grinding with a plurality of grinders (31, 32, 33; 41, 42, 43, 44) a burr (13) on the welded part (10a) of the joined preceding and succeeding billets while the joined billets travel and the grinders rotate and move synchronously with the travelling speed of and in the same direction as the joined billets. The method of claim 1, further comprising: detecting a welded portion (10a) on billets by using a sensor (90) mounted onto a travelling grinding machine (30), the travelling grinding machine being located downstream of the step of welding; pre-setting the continuously rotating plurality of grinders (31, 32, 33; 41, 42, 43, 44), the grinders being mounted to the travelling grinding machine (30), to the billet immediately after detecting the welded portion, the step of pre-setting being carried out while the travelling grinding machine moves in a downstream direction of the joined billets (10, 11); accelerating the travelling grinding machine (30) to a travelling speed of the joined billets (10, 11); detecting that the welded portion (10a) of the joined billets arrives at a position of the plurality of grinders; and carrying out said step of grinding a burr by fixing the grinders at the pre-set position, after detecting the arrival of the welded portion of the joined billets. The method of claim 1 or 2, further comprising, for a round billet and in said step of grinding a burr on the welded portion, revolving the plurality of grinders (31, 32, 33), said grinders being arranged at equal intervals on a circumference of the round billet, spaced apart by a specified angle. The method of any of the preceding claims, wherein, for a square billet, said step of grinding a burr on the welded portion is carried out by using grinders (41, 42, 43, 44) which are arranged in pairs, one pair (41, 44) being arranged above and below, the other pair (42, 43) being arranged at both sides of the square billet, one pair being spaced from the other pair along the travelling direction of the square billet. The method of claim 3 or 4, wherein the grinders are arranged with their grinding direction tilted (0) relative to the travelling direction of the billet. The method of any of claims 3 to 5, further comprising a step of descending a support roll (86) after detecting the welded portion of the joined billets, this support roll being located directly downstream of the detection point, and ascending the support roll (86) after a specified period of time. The method of any of claims 3 to 6, further comprising moving the travelling grinding machine (30) against the travelling direction of the billets (10, 11) until the welded portion (10a) of the joined billets is detected, said step of moving being carried out after completing said step of welding, said method further comprising after said step of moving and at the beginning of said step of grinding, moving a travelling welder (4) in the travelling direction of the joined billets (10, 11) and synchronously with said travelling speed of the joined billets. The method of any of the preceding claims, further comprising the steps of: scattering ground chips (120) generated by grinding a burr on a welded portion (10a) of two billets (10, 11) towards a downstream direction of the travelling billets and within a limited direction away from said downstream direction, said step of scattering being carried out during moving a travelling grinding machine (30); placing a hood (100) downstream of the travelling grinding machine (30) while facing the hood against the scattering direction of the ground chips; forming a water film (107) on an inner surface of the hood by flowing water down along said inner surface; and collecting the scattered ground chips (120) by means of the hood (100) for continuously flowing down the ground chips along with the water film. The method of claim 8, wherein the hood has an opening (101, 103) for passing the billets therethrough and a billet cover (104) at the opening (103) for preventing the billets from being exposed to the water film. Grinding machine for a continuous rolling process of billets, comprising: a travelling body (54) shuttling along the travelling direction of the billets (10, 11); support means (55, 125) being supported by the travelling body (54); a plurality of grinding devices arranged movably with respect to the support means; and grinders (31, 32, 33; 41, 42, 43, 44) of the grinding devices; for round billets, said grinders (31, 32, 33) are set in a tilted direction (0) relative to the travelling direction of the billet, or, for square billets, two pairs of grinders are provided, one pair (41, 44) being spaced apart from the other (42, 43) along the travelling direction of the billets. The grinding machine of claim 10, wherein the support means is a turret ring (55) and can be supported by the travelling body in a revolving state of the turret ring; and said grinders (31, 32, 33; 41, 42, 43, 44) are set in a tilted direction (0) relative to a central axis to the turret ring. The grinding machine of claim 10, wherein, for square billets, two pairs (51, 52) of grinding devices, one pair being located at a front side, the other pair at a rear side of the travelling body; means (47, 48, 402, 56) for moving the grinding device in a direction parallel to the square billet; and means (46a, 46b, 46c) to make the grinders move towards and away from the square billet are provided. The grinding machine of any of claims 10 to 12, further comprising a dust-collecting hood (100) having a water spray nozzle (106) inside thereof. The grinding machine of any of claims 10 to 13, further comprising a sensor (90) for detecting the welded portion (10a) on billets (10, 11), said sensor being arranged upstream of the grinding device (30, 51, 52).

Inventors: ANAI HIDENORI, AOYAMA SOICHI, HAMURA NOBUYOSHI, MATSUO GIICHI, OKAWA SUSUMU, OKUSHIMA KOJI, SAKAI AKIRA, SUGAWARA YUKI, USHIODA BUNNOSUKE, WATANABE YUJI, ANAI, HIDENORI, AOYAMA, SOICHI, HAMURA, NOBUYOSHI, MATSUO, GIICHI, OKAWA, SUSUMU, OKUSHIMA, KOJI, SAKAI, AKIRA, SUGAWARA, YUKI, USHIODA, BUNNOSUKE, WATANABE, YUJI
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1996
Main classification: B21B15
IPC codes: B21B1, B21B15, B24B5