Abstract:
The present invention provides an apparatus for measuring flatness of a hot rolled strip based on a contact load of the hot rolled strip to split rolls of a looper in the hot rolling process. The split rolls are assembled in a bracket such that each split roll can be separated from the bracket. A normal-movement control unit for moving the split rolls in the normal direction, and a tangent-movement control unit for moving the split rolls in the tangent direction are porvided at a side of the bracket bearing the split rolls. An impact absorption unit is mounted at a support that is movably connected to the tangent-movement control unit. A pre-pressure application unit is provided at the support to prevent a sensor cap and a load sensor from being released. A heat-shielding ring surrounds the load sensor to prevent the load sensor from being overheated.

Description:
This application is a 35 USC 371 of PCT/KR00/00771 filed Jul. 15, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to an apparatus for measuring flatness of hot rolled strips in a rolling mill and, more particularly, to a contact-typed strip flatness measuring device which protects load sensors from heat or impact while controlling surface points of split rolls to move up and down. 
     (b) Description of the Related Art 
     Generally, metal strips produced through hot-rolling slabs should be kept to be even in flatness along the width thereof. 
     An automatic shape controller based on a shapemeter has been frequently employed for use in controlling the strip flatness during the hot rolling process. FIG. 1 illustrates a rolling mill with such an automatic shape controller. In the automatic shape controller, a shapemeter  1  measures the shape change in the target hot rolled strip S through generating laser, and detects the strip flatness based on the measured shape change. The detected value of the strip flatness is input into a calculator  4  that calculates a control value. Then, depending upon the control value, a bender controlling unit  5  controls pressure of a bender  2  installed at the last stand, thereby controlling the strip flatness. 
     However, in the above strip flatness control technique, the strip flatness is basically controlled by taking the shape change of the hot rolled strip S as a criterion, and such a shape change largely differs from the practical value of strip flatness. Therefore, in such a technique, the strip flatness cannot be measured in a correct manner. Furthermore, when the frontal end portion of the hot rolled strip S transported over a roller table  3  is coiled around a coiler  6 , the hot rolled strip S is flattened under strain due to the difference in relative speeds between the last stand B and the coiler  6 . Accordingly, the shapemeter  1  cannot measure the strip flatness after the hot rolled strip S is coiled around the coiler  6 . 
     In order to solve such problems, a contact-type strip flatness measuring device has been suggested. In the device, the strip flatness is measured through detecting reduction in the hot rolled strip while directly contacting it. 
     Split looper rolles are arranged along the width of the hot rolled strip S, and a load sensor is attached to each split roll to detect load distribution of the hot rolled strip S. The detected load distribution is converted to a value of strip flatness, and makes feedback to a flatness control system, thereby controlling flatness across the hot rolled strip S. 
     When the load distribution signal issued from the strip flatness measuring device makes feedback to the flatness control system on line, uniform flatness can be obtained over the entire length of the hot rolled strip S. 
     However, such a contact-type load distribution measuring device should perform its intrinsic functions in poor working conditions such as high temperature, high humidity, and high vibration. Furthermore, it should ensure sufficient device stability and reliability, and detect the load distribution in a stable manner. 
     FIG. 2 illustrates a contact-type strip flatness measuring device installed at the Hoesch steel mill of German (Herman J. Kopineck, “Rolling of hot strips with controlled Tension and Flatness,” Hot strip profile and flatness seminar, Nov. 2-3, 1988, Pittsburg Pa.). As shown in FIG. 2, a load sensor  12  is provided at an end portion of a support  11  bearing a split roll  10  to detect the load applied to the split roll  10 , thereby measuring the strip flatness. 
     However, in such a device, since the difference in the maximum loads at tension and compression (hereinafter referred to as the “peak load”) is so great that the load sensor  12  is liable to be broken at repeated sensing operations, resulting in lowered precision and reduced device life span. 
     FIG. 3 illustrates another contact-type measuring device disclosed by George. F. Kelk in “New developments improve hot strip: Shapemeter-Looper and Shape Actimeter”, Iron and Steel Eng., August, 1986, pp. 48-56. As shown in FIG. 3, a compression-type load sensor  22  is provided at the bottom side of a shaft support  21  bearing a split roll  20 . In this structure, the tensile load applied to the split roll  20  does not influence the load sensor  22  so that the peak load can be reduced. However, since the strip flatness measuring device should play its intrinsic functions as a looper before it detects the load applied to the hot rolled strip S along the width thereof, the looper excessively moves up and down when uneveness in mass between the neighboring stands is present due to the great difference in relative speeds between the stands. In this case, the looper collides with an upper or lower damper so that strong impact is applied to the strip flatness measuring device, resulting in reduced life span of the load sensor  22 . 
     In this connection, a stopper  23  is provided at the strip flatness measuring device to prevent the load sensor  22  from being applied with an over-load. 
     However, when the maximum load is applied to the load sensor  22 , the compressed displacement is too small to make sufficient distance for preventing the load sensor  22  from being applied with the over-load. Thus, the mechanical means of protecting the load sensor  22  based on the stopper  23  has a limit in application in that whenever the device suffers slight deformation, the stopper  23  should be controlled each time. 
     Furthermore, the strip flatness measuring devices shown in FIGS. 2 and 3 are interposed between the rolling stands, and the temperature of the hot rolled strips S amounts to 800 to 1200° C. In these conditions, the load sensor extremely sensitive to heat should be protected from the heat in a stable manner. If not, errors in meaurement are inevitably followed by. 
     For that reason, a cooling nozzle  24  is provided at the strip flatness measuring device to spray cooling water to the load sensor  22 . However, in case the spraying of the cooling water becomes poor due to breakage or alien materials, there is a problem in that the preparation for such a case is absent. 
     Furthermore, the hot rolled strips are differentiated in the load distribution depending upon their shapes. Therefore, when the strip flatness measuring device is used for a long time, the plural numbers of split rolls  10  and  20  are rubbed in a different manner so that they become differentiated in horizontal height, and errors in detection with respect to the load applied thereto are made. 
     In order to solve such a problem, the strip measuring device shown in FIG. 2 is provided with a height control bolt  13  for controlling the tangent-movement thereof around a rotation shaft  14 , and the strip measuring device shown in FIG. 3 with a wedge-shaped control member  25  for controlling the tangent-movement. 
     However, in such a case, as shown in FIG. 4A, deviation in rubbing dR between the split rolls  10  and  20  is made. Even though such a deviation in rubbing is controlled, as shown in FIG. 4B, deviance in controlling dR′ is present so that the load sensors  12  and  22  for detecting the load applied to the hot rolled strip S incorrectly detect such a load while making serious errors in the flatness detection signal. That is, in the one-directional control technique, the horizontal height of the measuring device cannot be controlled in a correct manner. 
     Meanwhile, in case the rubbed split rolls should be repaired or replaced by a new one, long repair or replacement time is required, lowering productivity. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a strip flatness measuring device which can protect a load sensor from the external factors, and control the relative heights between split rolls while securing precesion in measurement. 
     This and other objects may be achieved by a strip flatness measuring device including a looper with a plurality of split rolls. The split rolls are assembled in a bracket such that each split roll can be separated from the bracket. A normal-movement control unit for moving the split rolls in the normal direction, a tangent-movement control unit for moving the split rolls in the tanget direction are provided at a side of the bracket. A support is movably connected to the tanget-movement control unit, and an impact absorption unit is installed at the support. A sensor cap is installed at a side of the support while pressurizing a load sensor. A pre-pressure application unit is provided between the support and a base of the looper to previously compresses the sensor cap against the load sensor, thereby preventing the load sensor from being released from the sensor cap. 
     In the above structure, even though deviation in rubbing occurs at the split rolls, the normal-movement control unit and the tangent-movement control units can precisely control the relative heights between the split rolls. 
     Furthermore, the load sensor is protected from the external impacts by way of the impact absorption unit and the pre-pressure application unit so that it can detect load distribution in a stable manner. The load sensor is also protected from the heat through mounting a heat-shielding ring around the load sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or the similar components, wherein: 
     FIG. 1 is a perspective view of a rolling mill with a usual strip flatness measuring device; 
     FIG. 2 is a side view of a contact-type strip flatness measuring device according to a prior art; 
     FIG. 3 is a side view of a contact-type strip flatness measuring device according to another prior art; 
     FIGS. 4A and 4B illustrate the technique of compensating deviation in rubbing occurred at split rolls in the contact-type strip flatness measuring devices shown in FIGS. 2 and 3; 
     FIG. 5 is a cross sectional view of a contact-type strip flatness measuring device with a load sensor according to a preferred embodiment of the present invention; 
     FIGS. 6A and 6B are amplified sectional views of the load sensor shown in FIG. 5; and 
     FIGS. 7A and 7B illustrate the technique of compensating deviation in rubbing occurred at split rolls in the contact-type strip flatness measuring device shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of this invention will be explained with reference to the accompanying drawings. 
     The strip flatness measuring device according to the present invention is provided at a looper  30  between the rolling mills A and B shown in FIG.  1 . The looper  30  gives tension to the hot rolled strip S while rotating by 90 degree or less in the clockwise or anti-clockwise direction with respect to a rotation shaft  31 . Looper rolls  33  are fixed at the end portion of the looper  30  such that they directly contact the hot rolled strip S. The looper rolls are segmented by two external dummy rolls, and three measuring rolls disposed between the dummy rolls to measure the load applied to the hot rolled strip S. The three measuring rolls will be hereinafter referred to as the “split rolls”  35 . 
     FIG. 5 is a cross sectional view of a contact-type strip flatness measuring device according to a preferred embodiment of the present invention. 
     As shown in FIG. 5, the contact-type strip flatness measuring device roughly includes an impact absorption unit  40  for absorbing the impact applied to a load sensor  37 , a pre-pressure application unit  50  for applying pressure to a sensor cap  46 , a tangent-movement control unit  60  for moving the split rolls  35  up and down, a normal-movement control unit  70  for moving the split rolls  35  back and forth, and a split roll fixation unit  80  for fixing the split rolls  35 . 
     The impact absorption unit  40  is installed at an inner groove of a support  42  that rotates around a support shaft  41 . A cylindrical-shaped rubber pad  43  is fixed to the inner groove of the support  42  using bolts  45  via washers  44 . The washers  44  have protrusions holding the sensor cap  46 . The load sensor  37  for measuring the load applied to the split rolls  35  is fixed to a sensor block  47  that is in turn fixed to a base  39  with a cylindrical shape. 
     A heat-shielding ring  48  is externally screw-coupled to the sensor block  47  to protect the load sensor  37  from the heat at the hot rolling temperature of 800-1200° C. The heat-shielding ring  48  protects the load sensor  37  through filling up the gap between the sensor block  47  and the sensor cap  46 . In addition, a usual cooler may be selectively provided at the strip flatness measuring device to cool it through spraying cooling water thereto. 
     A pre-pressure application unit  50  has a role of defining the rotation angle of the support  42  at a predetermined degree. The pre-pressure application unit  50  includes a bolt  51  coupling the end portion of the support  42  with the end portion of the base  39 , a spherical nut  52  fixing the bolt  51  to the base  39 , and a disk spring  54  inserted between the support  42  and a head  53  of the bolt  51 . A spherical groove  55  is formed at the side of the support  42  contacting the disk spring  54 . A stopper  56  is coupled to the bolt head  53  to control the rotation angle of the support  42 . 
     A tangent-movement control unit  60  turns a bracket  71  fixing the shaft of the split rolls  35  around a bracket shaft  72  up and down. The tangent-movement control unit  60  includes a left clevis  61  rotatably coupled to the bracket  71 , a right clevis  62  rotatably coupled to the support  42 , and a bidirectional control bolt  63 . In this structure, when the control bolt  63  is locked or released, the left and right devises  61  and  62  become closer to each other, or distant from each other. 
     The normal-movement control unit  70  has a role of moving the bracket  71  fixing the shaft of the split rolls  35  left and right. The normal-movement control unit  70  includes a slide base  74  fixed to the body of the split rolls  35 , a bracket slide  75  coupled to the bracket  71 , and a control bolt  76  for controlling the movement range of the bracket slide  75  left and right. The bracket  71 , and the bracket slide  75  are rotatably fixed around a bracket shaft  72  such that they move together. That is, when the bracket slide  75  moves left and right, the bracket  71  moves left and right. Whereas, when the bracket  71  is rotated, the bracket slide  75  does not rotate together. 
     The split roll fixture  80  has a role of making the split rolls  35  to be easily locked or released. The split roll fixture  80  couples two separate split roll fixing plates  81  with a bracket fixing plate  83  via fixation bolts  82 . 
     In operation, when a hot rolled strip S passes over the split rolls  35 , the load applied to the split rolls  35  compresses the split rolls  35 . Such a compression power is transmitted to the load sensor  37  via the bracket  71 , the tanget-movement control unit  60 , and the support  42 . 
     The plural numbers of split rolls  35  can be easily locked or released via the corresponding fixation bolts  82 . Therefore, in case one of the split rolls  35  needs to be repaired, it can be instantly replaced by a new one. 
     When uneveness in mass between the rolling stands A and B occurs during the hot rolling process, the looper  30  moves up or down around the shaft  31 . In case the looper  30  excessively moves down, it collides with the lower damper while applying impact to the strip flatness measuring device. In this situation, the load sensor  37  suffers momentary impact. 
     At this time, the impact absorption unit  40  absorbs the impact applied to the strip flatness measuring device. Therefore, the load sensor  37  can correctly measure the rolling reduction ratio of the hot rolled strip S transmitted up to the sensor cap  46 . 
     Meanwhile, when the looper  30  excessively moves up, and collides with the upper damper, as shown in FIG. 6A, the load sensor  37  is released from the sensor cap  46 . When such a situation is repeated, the lock and release of the load sensor  37  into and from the sensor cap  46  are repeated. In this case, the load sensor  37  suffers repeated momentary impacts while being reduced in life span. 
     The pre-pressure application unit  50  solves such a problem. The pre-pressure application unit  50  previously compresses the support  42  against the base  39 , thereby preventing the load sensor  37  from being released from the sensor cap  46  due to the impact applied to the looper  30 . Therefore, even though a momentary impact is applied to the support  42 , the load sensor  37  can correctly measure the applied load without being released from the sensor cap  46 . 
     The hot rolled strip S passes over the looper  30  usually at the temperature range of 800-1200° C. and hence, the thermal-sensitive load sensor  37  is liable to be reduced in life span. In this connection, the heat-shilding ring  48  is disposed between the support  42  and the sensor block  47  to shield the heat directly applied to the load sensor  37 . The heat-shilding ring  48  has a double structure while bearing a role of protecting the load sensor  37  from the heat as well as a role of functioning as a variable stopper. 
     The split rolls  35  suffers rubbing due to friction against the hot rolled strip S. Therefore, it is required that the height between the split rolls  35  should be periodically controlled in a correct manner. 
     The tangent-movement control unit  60  controls the relative heights between the split rolls  35 , and the normal-movement control unit  70  controls the left and right distance between the split rolls  35 . 
     As shown in FIG. 7A, in case deviation in rubbing between the split roll  35  bearing higher rubbing ratio and the split roll  35  bearing lower rubbing ratio is present, as shown in FIG. 7B, the surface of the split roll  35  is controlled to move in the tanget direction using the bidirectional control bolt  63  of the tangent-movement control unit  60 , and to move in the normal direction using the control bolt  76  of the normal-movement control unit  70 . When the bidirectional control bolt  63  is controlled, the surface of the split roll  35  moves to the C 1  point shown in FIG.  7 B. In contrast, when the control bolt  76  is controlled, the surface of the split roll  35  moves to the C 3  point. In case the surface point of the split roll is controlled only with the bidirectional control bolt  63 , the maximum control point becomes to be the C 2  point Accordingly, in order to control both surface points of the rubbed split roll  35 ′ and the non-rubbed split roll  35 , the tangent-movement control unit  60  and the normal-movement control unit  70  should be used together. 
     Meanwhile, when the sensor cap  46  returns to its initial state, the load sensor  37  senses the shape change of the hot rolled strip S in the upper direction, thereby correctly measuring the flatness of the hot rolled strip S. 
     The flatness of hot rolled strips S was measured through detecting correct distribution of the load applied to each split roll  35  and making feedback the detected values to the strip flatness control system. The results are given in Tables 1 and 2. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 (Comparison in flatness of strips with a width of 900-1100 mm) 
               
             
          
           
               
                   
                   
                   
                 Note 
               
               
                   
                   
                   
                 Total 
               
               
                   
                   
                   
                 numbers of 
               
               
                   
                   
                   
                 collected 
               
               
                 Top (%) 
                 Middle (%) 
                 Tail (%) 
                 strips 
               
             
          
           
               
                 Before 
                 After 
                 Before 
                 After 
                 Before 
                 After 
                 before/after 
               
               
                 control 
                 control 
                 control 
                 control 
                 control 
                 control 
                 control 
               
               
                   
               
               
                 25.1 
                 47.2 
                 24.9 
                 57.4 
                 19.9 
                 55.0 
                 382/322 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 (Comparison in flatness of strips with a width of 1100-1350 mm) 
               
             
          
           
               
                   
                   
                   
                 Note 
               
               
                   
                   
                   
                 Total 
               
               
                   
                   
                   
                 numbers of 
               
               
                   
                   
                   
                 collected 
               
               
                 Top (%) 
                 Middle (%) 
                 Tail (%) 
                 strips 
               
             
          
           
               
                 Before 
                 After 
                 Before 
                 After 
                 Before 
                 After 
                 before/after 
               
               
                 control 
                 control 
                 control 
                 control 
                 control 
                 control 
                 control 
               
               
                   
               
               
                 78.0 
                 96 4 
                 77.0 
                 93.9 
                 67.8 
                 91.9 
                 469/591 
               
               
                   
               
             
          
         
       
     
     As indicated in Tables 1 and 2, the hot rolled strips that were controlled based on the inventive strip flatness measuring device exhibited evenness in flatness over the entire length thereof. 
     While the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.