Abstract:
A plurality of materials are rolled in an upstream stand. While the transfer speed of a succeeding material and the front end position thereof are detected, the transfer speed and the rear end position of a preceding material are detected by a measuring roll. The transfer speed of the succeeding material is controlled by adjusting at least the drive speed of the pinch rolls so that the front end of the succeeding material contacts the rear end of the preceding material at a specified position in a travelling welder. The rear end of the preceding material is joined with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material. The welded portion on the continuous material is ground and/or cut to remove burrs therefrom. After removing the burrs, the continuous material is continuously rolled by a down-stream stand.

Description:
This is a Division of application Ser. No. 09/511,086 filed Feb. 23, 2000 now U.S. Pat. No. 6,273,324 issued Aug. 14, 2001, which is a Division of application Ser. No. 08/876,651 filed on Jun. 16, 1997, now U.S. Pat. No. 6,089,441 issued Jul. 18, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for continuous rolling by continuously welding the rolled materials at an intermediate stage of a rolling line after applying several passes of rolling of billets, and relates to an apparatus therefor. 
     2. Description of the Related Art 
     A known continuous rolling method to produce wire, rod, or to shape steel with energy-saving and high efficiency comprises the steps of discharging billets from a heating furnace one at a time, welding the rear end of a preceding billet with the front end of a succeeding billet by a single unit travelling flash-butt welder, removing the burr from the welded portions using a scarfer or the like, heating the thus formed continuous billet to a temperature necessary for rolling in an induction heating furnace, then continuously rolling the continuous billet in a rolling mill group: (disclosed in, for example, unexamined Japanese patent publication No.52-43754 (1977)). Alternatively, there is a continuous rolling method in which billets discharged from a heating furnace are joined together by welding to form a continuous billet, and the continuous billet is heated again in the heating furnace, wherein also a single unit travelling flash-butt welder is used: (disclosed in, for example, examined Japanese patent publication No.52-11722 (1982)). 
     Shortening the cycle time for treating a single billet is an important issue in the continuous rolling of billets. In this respect, the weight of an ordinary billet is in a range of from 0.5 to 2 ton, and the necessary cycle time to treat a single billet is less than 1 min. to assure a production capacity of 70 to 80 ton/hr or more. Since conventional continuous rolling processes use only one on-line travelling flash-butt welder, as described above, the welding time inherent to the travelling flash-butt welder is difficult to shorten. Consequently, it is impossible to realize a cycle time of less than 1 min. in the prior art. 
     A possible method to shorten the time cycle is to incorporate two travelling welder units to realize a shorter cycle time operation. However, a system of two travelling welders increases investment cost and requires large capacity of power source. Another possible method is to reduce the cross sectional area of the billet through rolling in a specific number of rolling mill groups, to provide the intermediate rolled materials in a free state, to adjust the position of the intermediate rolled materials, and to perform the weld-joining to reduce the welding time. These methods, however, have a disadvantage that, when the intermediate rolled materials become long, the methods cannot be adopted-owing to the limitation of interstand distance: 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method of continuous rolling which shortens the cycle time of billet treatment without requesting a large-scale modification of existing facilities, and to provide an apparatus therefor. 
     The first method for continuous rolling comprises the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after being rolled in the first rolling mill group by a set of pinch rolls, detecting the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; after the front end of the succeeding material contacted with the rear end of the preceding material, joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; removing burr from a welded section on the continuous material; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step. 
     The first apparatus of continuous rolling comprises: a first rolling mill group for successively rolling a plurality of materials; a travelling welder for joining a rear end of a preceding material with a front end of a succeeding material by flash-butt welding to form a continuous material while moving itself at a speed synchronous with the transfer speed of the materials; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; a second rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; wherein the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement. 
     The second method for continuous rolling comprises the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after being rolled in the first rolling mill group by a set of pinch rolls, controlling the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; after the front end of the succeeding material contacted with the rear end of the preceding material, joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; grinding a welded section on the continuous material to remove burr therefrom; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step. 
     The second apparatus for continuous rolling comprises: a first rolling mill group for successively rolling a plurality of materials; a set of pinch rolls for pinching a succeeding material after being rolled and for detecting the transfer speed of the pinched material; a front end detector located at inlet of the pinch rolls for detecting a front end of the succeeding material; a measuring roll for detecting the transfer speed of a preceding material which is transferred before the succeeding material; a rear end detector located at inlet of the measuring roll for detecting a rear end of the preceding material; a travelling welder located at down-stream side of the measuring roll for joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding to form a continuous material while moving itself at a speed synchronous with the transfer speed of the continuous material; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; a secondary rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; and a drive control unit to which signals from the pinch rolls, the front end detector, the measuring roll, and the rear end detector are entered, and in which the rotational speed of the pinch rolls or both the rotational speed of the pinch roll and the rolling speed of the first rolling mill group are determined so as to enable the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder, and these determined variables are controlled; wherein the pinch rolls, the measuring roll, the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 illustrates the continuous rolling apparatus in the first mode according to the present invention. 
     FIG. 2 is a time chart of motion of the continuous rolling apparatus in the first mode according to the present invention. 
     FIG. 3 illustrates the continuous rolling apparatus in the second mode according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     1. The First Mode: 
     FIG. 1 illustrates the apparatus for continuous rolling of a mode according to the present invention. The figure shows a fourth-stand  10  and a fifth stand  11  in the rolling mill group. The first stand (not shown) through the fourth stand  10  are assumed to form the roughing mill group, and the fifth stand  11  and succeeding stands are assumed to form the intermediate rolling stands. Between the fourth stand  10  and the fifth stand  11 , there are serially arranged a travelling hot saw  21 , a descaler  22 , a table  23 , a travelling flash-butt welder  24  (hereinafter referred to simply as the “travelling welder”), a travelling burr-removing machine  25 , and a travelling induction heating unit  26 . 
     The following is the description of the functioning state of the apparatus of FIG. 1. A material  50  leaves the fourth stand  10  and enters the travelling hot saw  21  where the front end thereof is crop-cut. The crop-cutting is done to obtain a suitable shape (or existence of no significant collapse at its edge) for succeeding flash-butt welding (FBW). Even when a travelling cutting machine is applied instead of the hot saw, the cutting machine minimizes the collapse of material. The material  50  after passing the fourth stand  10  becomes free. Then the material  50  is sent by the table  23  to catch up with the rear end of the preceding material when the rear end arrives at the center of home position of the travelling welder  24 . The descaler  22  located at the inlet of the travelling welder  24  and removes scale at the clamped portions on front end and rear end of the transferred materials. The travelling burr-removing machine  25  is located after the moving end of the travelling welder  24 . The travelling burr-removing machine  25  conducts burr-removal at the welded portion of the materials welded by the travelling welder  24  while moving. The materials welded by the travelling welder  24  are cooled at their clamped portions during welding. The travelling induction heating unit  26  located at inlet of the fifth stand  11  heats the cooled portions, then the travelling induction heating unit  26  sends the materials to the fifth stand  11 . 
     The cut of the material at its rear end is conducted at a point that the rear end passes through the home position of the travelling hot saw  21 . At that moment, if the material is in a completely free state (or in a state that the material passed through the fourth stand and that the material is not clamped by the travelling welder  24 ), then the cutting in a stopped state is also possible. 
     FIG. 2 is a time chart illustrating an example of motion of continuous rolling apparatus of FIG.  1 . For example, the material ( 2 ) discharged from the fourth stand  10  is crop-cut at its front end by the travelling hot saw  21 . At that moment, the material ( 2 ) is still caught by the fourth stand  10 , so the travelling hot saw  21  conducts the cutting action while moving at a speed synchronous with the transfer speed of the rolled material. When the material ( 2 ) is passed through the fourth stand  10 , the table  23  feeds the material ( 2 ) so that the front end thereof catches up with the rear end of the preceding material ( 1 ) at a point that the rear end of the preceding material ( 1 ) arrives at the center of the waiting position in the travelling welder  24 . During the feeding period, the rear end of the material ( 2 ) passes through the travelling hot saw  21  so that the rear end of the material ( 2 ) is cut. The cutting of the rear end of the material ( 2 ) may be conducted while moving thereof. Since, however, during the moving period, the material ( 2 ) is in a free state, the cutting may be done by stopping the movement of the material and may be done in a stopped state, if only the cycle time allows. 
     The travelling welder  24  begins to move at a point when the front end of the succeeding material ( 2 ) catches up with the rear end of the preceding material ( 1 ), and conducts flash-butt welding (FBW) after clamping materials ( 1 ) and ( 2 ) together. According to the chart of FIG. 2, the rolling cycle of each billet is selected to 40 sec. including 20 sec. for welding and 18 sec. for returning. Since the material being treated in this step is an intermediate material, the cross sectional area of the material is narrower than that of the billet (about one fourth after the fourth stand), and the welding time is short. After completing the welding step, the travelling burr-removing machine  25  conducts burr-removal while moving. FIG. 2 shows a burr-removal cycle of 12 sec. including 6 sec. for burr-removal and 6 sec. for returning. 
     The travelling induction heating unit  26  located at the inlet of the fifth stand  11  conducts heating and soaking of the materials. Since, however, the time for the material to leave the fourth stand  11  and enter the fifth stand is 120 sec. or less, and since there is not significant temperature reduction, heating and soaking of the locally cooled portion at clamped portions are important. In this respect, it is effective that the induction heating unit  26  is also a travelling type, if space allows. 
     2. The Second Mode: 
     FIG. 3 illustrates the apparatus for continuous rolling of a mode according to the present invention. The figure shows a fourth stand  10  and a fifth stand  11  in the rolling mill group. The first stand (not shown) through the fourth stand  10  are assumed to form the rough roll group. A travelling cutting machine  21  is located at the upstream side of the exit of the fourth stand  10 . A set of pinch rolls  27  which is controllable in the driving speed thereof is located at the downstream side of the travelling cutting machine  21 . A measuring roll  28 , a descaler  22 , a travelling flash-butt welder  24  (hereinafter referred to simply as “travelling welder”), and a travelling burr-removing machine  25  are arranged in series at the downstream side of the pinch rolls  27 . A travelling induction heating unit  26  is located at the inlet of the fifth stand  11 . Since the mode has a short distance between stands, very little temperature reduction of the material occurs and, therefore, no stationary induction heating unit for heating the material is required. 
     At the inlet of the travelling cutting machine  21 , the pinch rolls  27 , and the measuring roll  28 , a respective material detector  30 ,  31 , and  32 , is positioned. The detector  30  detects the front end and the rear end of material, and the detection signal generated by the detector  30  is used to control the movement of the travelling cutting machine  21 . The detector  31  detects the front end of the material, and the detector  32  detects the rear end of the material. The drive control unit  40  receives the detection signals generated by the detector  32 , the rotary encoder  42  attached to the drive motor  41  which drives the pinch rolls  27 , and the rotary encoder  43  attached to the measuring roll  28 , and controls the drive motor  44  of the fourth stand  10  and the drive motor of the pinch rolls  27  based on the received detection signals. The drive control unit  45  receives the detection signal generated by the detector  30  to control the travelling cutting machine  21 . 
     The following is the description of a functioning state of the apparatus of FIG. 3. A material rolled in the fourth stand  10  arrives at the detector  30  where the arrival of the front end of the material is detected. The drive control unit  45  drives the travelling cutting machine  21  based on the detection signal to conduct crop-cutting of the front end of the material. When the detector  30  detects the rear end of a material, the travelling cutting machine  21  is controlled for its movement in a similar manner to conduct crop-cutting of the rear end of the material. The cutting is done to obtain a suitable shape (or existence of no significant collapse at its edge) for succeeding flash-butt welding (FBW). Accordingly, the travelling cutting machine  21  is requested to be the one that generates very little collapse at the cutting edge. A travelling saw may be applied as the travelling cutting machine  21 . The material which was crop-cut at its end in the travelling cutting machine  21  then arrives at the detector  31  where the arrival of the front end thereof is detected. On arrival of the front end of the material at the detector  31 , the material is pinched by the pinch rolls  27  at a slightly rear side from the front end thereof. 
     The speed of the material at that moment at the exit of fourth stand  10  is set to a slightly higher value than the inlet speed of the continuous material to the fifth stand  11  (determined by therotary encoder  43  in the measuring roll  28 ), and the pinch rolls  27  are also driven synchronously with the speed of the material. 
     After the succeeding material is pinched by the pinch rolls  27 , the transfer speed and the front position of the succeeding material are detected by the pinch rolls  27 . That is, the transfer speed of the material is detected by the rotary encoder  42 , and the front end of the material is detected by the detector  31 , thereby tracking the movement of the material using a drive control unit  40  to detect the transfer speed and the front end position of the succeeding material. As for the preceding material, the transfer speed is detected by the rotary encoder  43  in the measuring roll  28 , and the rear end position is detected by the detector  32 , thus tracking the movement of the preceding material using the drive control unit  40  to detect the transfer speed and the front end position of the succeeding material. The drive control unit  40  computes the transfer speed of upstream material so as the front end of the succeeding material and the rear end of the preceding material contact each other at a target position before the travelling welder  24  based on the relative relation between the transfer speed and front end position of succeeding material and the transfer speed and rear end position of preceding material, then controls the rotational speed of the drive motor  44  of the fourth stand  10  and the drive motor  41  of the pinch rolls  27 . 
     Through the control described above, the rear end of preceding material and the front end of succeeding material make contact with each other at a target position. The drive control unit  40  detects the contact of materials from the increased torque (increased drive current) on the pinch rolls  27  or from the thrust force applied to the pinch rolls  27  toward the upstream side, and controls the transfer speed (rolling speed) at the upstream side to synchronize with the rolling speed at the down-stream side. At a moment that the succeeding material and the preceding material arrive at the home position of the travelling welder  24  in a state of adjoining and synchronously running thereof, the travelling welder  24  begins the welding of these materials while moving by itself synchronously with the transfer speed of the materials. The descaler  22  which is located at the inlet of the travelling welder  24  performs descaling at the clamped portion at both the front end and rear end of the transferred material. After the travelling welder  24 , there is positioned the travelling burr-removing machine  25  which conducts burr-removal at the portion welded by the travelling welder  24  in a moving mode. The material welded by the travelling welder  24  is cooled at its clamped portion during welding. The induction heating unit  26  located at the inlet of the fifth stand  11 , however, heats the locally cooled portion before transferring the material to the fifth stand  11 . 
     According to the above-described welding process, the transfer speed of the succeeding material is controlled against the transfer speed of the preceding material responding to respective welding condition for flash-butt welding and for upset-welding. The control is performed through the control of upset cylinder which is built in the travelling welder  24 . The speed control of the upstream (succeeding) material corresponding to the control of the upset-cylinder differs with variables such as billet size, intermediate material size, and distance between the welder and the upstream stand. 
     1) In the case wherein the rear end of the succeeding material passes through the fourth stand  10  and that the succeeding material becomes free before the welding begins, (or that the succeeding material passed through the fourth stand  10  and the succeeding material is not clamped by the travelling welder  24 ), the welder clamps the succeeding material, then the pinch rolls  27  release the material. That is, the case occurs for a short intermediate material passed through the fourth stand  10 . The case is controlled in a similar procedure as prior art. 
     2) In the case wherein the cross sectional area of intermediate material is relatively narrow and the length thereof is long, (50 sq. to 100 sq.), the speed variation is absorbed by a material loop height between the fourth stand  10  and the pinch rolls  27 . Since the speed variation in that case is slight, the necessary height of material loop is very small (100 to 200 mm), the material loop height is easily formed if only the distance between the fourth stand  10  and the pinch rolls  27  is secured. 
     3) In the case wherein the cross sectional area of the intermediate material is wide and the length thereof is large, the formation of material loop height is difficult so that the speed control is applied by an integral motion of the fourth stand  10  and of the pinch rolls  27 . Since the change cycle of transfer speed of the material is at a level of several Hz, conventional tension control is applicable. 
     As described above, according to the present invention, materials that were reduced in their cross sectional area by rolling in the first rolling mill group are joined together by flash-butt welding in a travelling welder to form a continuous material, and the burr on the welded portions of the continuous material is removed, followed by continuous rolling of the continuous material in a second rolling mill group. Accordingly, shortening of billet treatment cycle time is realized without requesting significant modification of existing facilities, and a succeeding material rolled in and discharged from the first rolling mill group is pinched by a set of pinch rolls, and the transfer speed and the front end position of the succeeding material are detected, also the transfer speed and the rear end position of the preceding material are detected. Then the transfer speed of the succeeding material is controlled so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder through the adjustment of the drive speed of the pinch rolls or both the drive speed of the pinch rolls and the first rolling mill group. Thus, the materials which were reduced in the cross sectional area thereof by rolling are successively welded together by the travelling welder to form a continuous material. As a result, the welding time is shortened, the continuous welding of billets is performed independent of billet size and intermediate material length, and the cycle time for treating billets is shortened. Since the method according to the present invention is not limited by billet size, the method is applicable to a rolling mill group having relatively short distance between both stands.