Patent Publication Number: US-2007095433-A1

Title: Method and apparatus for treating cracks in slabs

Description:
FIELD OF THE INVENTION  
      The present invention relates to a method of treating cracks in slabs during processing and, in particular, steel slabs.  
     BACKGROUND OF THE INVENTION  
      In a steel mill, after a steel slab is cast, it must be cooled. As it cools, cracks appear on the slab. When rolling plate, these cracks tend to propagate into the finished plate creating defects. The current process for dealing with these cracks is to take the slabs off line and allow them to cool. A procedure known as “scarfing” is then used to remove the cracks.  
     SUMMARY OF THE INVENTION  
      According to one aspect of the present invention there is provided a method for treating cracks in slabs, which involves a step of positioning at least one cutting torch along a slab processing line. The at least one cutting torch being positioned to cut a slab portion where cracking commonly occurs from the slab at it passes along the slab processing line.  
      According to another aspect of the present invention there is provided an apparatus for treating cracks in slabs, which includes a torch support with at least one torch mounted on the torch support. A tracking system is connected to the torch support, which is adapted to provide consistent vertical and horizontal positioning for the torch support relative to a slab moving along a slab processing line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein:  
       FIG. 1  is a perspective view taken from a downstream vantage point of an apparatus for treating cracks in slabs constructed in accordance with the teachings of the present invention.  
       FIG. 2  is a perspective view taken from an upstream vantage point of the apparatus for treating cracks in slabs illustrated in  FIG. 1 .  
       FIG. 3  is a perspective view taken from a side vantage point of the apparatus for treating cracks in slabs illustrated in  FIG. 1 .  
       FIG. 4  is an upstream elevation view of the apparatus for treating cracks in slabs illustrated in  FIG. 1 .  
       FIG. 5  is a top plan view of cutting torches from the apparatus for treating cracks in slabs illustrated in  FIG. 1 .  
       FIG. 6  is a side elevation view of cutting torches from the apparatus for treating cracks in slabs illustrated in  FIG. 1 .  
       FIG. 7  is a perspective view of cutting torches positioned along the top surface of slabs. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The preferred embodiment, an apparatus for treating cracks in slabs generally identified by reference numeral  10 , will now be described with reference to  FIGS. 1 through 6 .  
      Structure and Relationship of Parts:  
      Referring to  FIG. 1 , apparatus  10  includes a movable torch support  12 . Referring to  FIG. 4 , two pairs of cutting torches are mounted on torch support  12 . Each pair has a leading torch  14  and  15  and a trailing torch  16  and  17 , respectively. It will be understood that different numbers of torches may be present, such as only one pair of torches, or four pairs, one for each corner  36  of a slab  26 . Referring to  FIGS. 5 and 6 , each cutting torch  14 ,  15 ,  16 , and  17  is pivotally mounted on torch support  12  for pivotal movement about a horizontal pivot axis  18  and about a vertical pivot axis  20 . Referring to  FIG. 2 , there is a tracking system in the form of a flanged roller  22  connected to torch support  12 . Flanged roller  22 , which is water cooled stainless steel, tracks the edge  24  of a slab  26  moving along a slab processing line  28  to provide consistent vertical and horizontal positioning for torch support  12  relative to slab  26 . Referring to  FIG. 3 , torch support  12  is carried by a telescopic cylinder  30  which is adapted to move torch support  12  toward and away from slab processing line  28 , thereby providing lateral adjustment to smit the width of slab  26 . An inner tube  31  slides inside an outer tube  33  and is actuated by a hydraulic cylinder  35  to accomplish this. Inner tube  31  is water-cooled and acts as a water supply manifold for torches  14 ,  15 ,  16  and  17 . Hydraulic cylinder  35  has a linear transducer mounted internally (not shown) to provide position feedback. The PLC can then be programmed for various widths of slabs and the system can automatically adjust to pre programmed slab widths. As leading torches  14  and  15  and trailing torches  16  and  17  are each independently operable, only leading torches  14  and  15  need be activated when only small cracks arc present. It is preferred that a pneumatic nozzle (not shown) be directed at slab  26  and adapted to blow excess slag created during the scarfing operation from the surface  34  of slab  26 .  
      Operation:  
      Referring now to  FIGS. 1 through 6 , apparatus  10  is provided as described above. Referring to  FIG. 1 , the method of using apparatus  10  to treat cracks in slabs  26  begins by positioning cutting torches  14 ,  15 ,  16  and  17  along slab processing line  28 . It is preferred that these cutting torches be positioned along the caster runout table. Referring to  FIG. 4 , cutting torches  14 ,  15 ,  16 , and  17  are positioned to cut a corner  36  from slab  26  where cracking commonly occurs at it passes along slab processing line  28 . They are arranged in pairs including a leading torch  14  and  15  and a trailing torch  16  and  17  mounted with each pair cutting a different corner  36  of slab  26 . There may be one pair, two pairs, or a pair for each corner. The cutting speed of scarfing torches  14 ,  15 ,  16 , and  17  is adjusted to suit the speed of slab processing line  28 . For example, the speed at which the system makes the cut varies front 1″ per minute to 65″ per minute or faster. The torches can be adjusted to match the speed of the casting operation. Suitable cutting torches to use as torches  14 ,  15 ,  16 , and  17  are as oxygen/natural gas torches such as Oxy-Arc brand, OXY2 Series, P/N OXY2AW with a 2″ body and 10″ barrel and Oxy-Arc CC130 cutting tips. These torches are water cooled with a stainless steel body. Potentially the same results can be achieved by other methods of cutting such as Plasma Arc or laser.  
      Referring to  FIGS. 5 and 6 , leading torch  14  and trailing torch  16  are able to pivot upwardly or downwardly about a horizontal pivot axis  18  at an angle within an approximate range of angles between 0 degrees and 35 degrees, and pivoted inwardly or outwardly about a vertical pivot axis  20  toward the slab within a preferred range of angles of 15 degrees and 35 degrees. These parameters apply to each pair of torches present. The torches  14  and  16  are placed at an angle measured from horizontal surface  34  of slab  26  vertically down and from edge  24  of slab  26  measured horizontally out. The torches work in a range of angles depending upon the speed of the casting operation and the temperate of the slab. Fine adjustments can be made to the angles to obtain the optimum cut. Brackets  38  that holds the torches allow for vertical, angular, and rotational adjustment. In a preferred position, leading torch  14  is pivoted upwardly about horizontal pivot axis  18  at an angle of approximately 15 degrees and pivoted about vertical pivot axis  20  inwardly toward slab  26  at an angle of approximately 25 degrees, while trailing torch  16  is pivoted about horizontal pivot axis  18  upwardly at an angle of approximately 2 degrees, and pivoted about vertical pivot axis  20  inwardly toward slab  26  at an angle of approximately 25 degrees. However, there will be a range of angles that torches  14  and  16  will perform adequately and these angles can be fine-tuned.  
      An approximate 4″ stand-off distance between the cutting torch tip and the slab is the optimal distance to produce the desired cut quality. Also the center oxygen stream from the torch, which is approximately ⅜″ in diameter is preferably directed at the corner of the slab with 75% of the stream being below the corner of the slab.  
      By way of a qualitative discussion, the angles can be seen in  FIG. 4 , which shows torches  14  and  16  mounted in brackets  38  that position them so that the cutting stream is a steep angle against the direction of travel of slab  26 . This enables torches  14  and  16  to maintain a puddle and the cut. Lead torch  14  typically produces a 45 degree chamfer on corner  36  of slab  26 . The amount of material removed can be adjusted depending upon the depth of the cracks that need to be removed. The torch angle or stand-off distance to slab  26  can be adjusted to accommodate any size of crack, as discussed above. Trailing torch  16  is laid at a very slight angle from horizontal, and a steep angle against the direction of travel of slab  26 , so that it skims off a wedge shaped portion of slab  26  to remove any cracks that have propagated into the material beyond corner  36  that was removed by lead torch  14 . As mentioned above, pairs of torches can be placed at all four corners  36  of slab  26  to remove cracks on all four corners.  
      Apparatus  10  is also designed so that the depth of the cut can be adjusted. The depth and length of the cracks to be removed may vary depending on the type of material, casting process, and any cooling or quenching process. Thus, the adjustment system allows torches  14 ,  15 ,  16 , and  17  to be positioned at varying heights to increase or decrease the amount of material removed. With a two-torch system, leading torch  14  is used to cut off corner  36  of slab  26  at 45°. The amount of corner  36  cut off can be adjusted from ¼″ to 1″ or larger. Trailing torch  16  follows lead torch  14  and is used to cut surface  34  of slab  26  from corner  36  in towards the center  40  of slab  26 . The thickness of material removed and the length of material removed from the edge of slab  26  towards center  40  can also be adjusted to remove different crack lengths and depths. The amount typically removed is from ⅛″ to ⅜″ thick and 2″ to 4″ in length measured from corner  36  of slab  26  towards center  40 .  
      In order to maintain a consistent cutting depth, a horizontal and vertical tracking system adjusts torches  14 ,  15 ,  16  and  17  as slab  26  passes through slab processing line  28 . The system consists of fanged rollers  22 , mounted on pivot points  42 , that keep a constant pressure against corner  36  of slab  26 . Torch holders  14  are mounted to rollers  22  so that as slab edge  24  moves up and down, torches  14 ,  15 ,  16  and  17  track slab  26 . This ensures a consistent thickness of cut in both directions. The system also adjusts to various slab widths by sliding torch supports  12  in and out. Inner tube  31  slides inside outer tube  33  and is actuated by hydraulic cylinder  35  to accomplish this. It will be appreciated that there are other means of accomplishing this horizontal and vertical tracking. For example, an electronic system could be employed using proximity sensors.  
      The torches are positioned to remove the corners of the slab because this is generally where the cracks originate. The system is designed so that the cutting of each corner can be controlled independently. In some instances cracking may occur on the top of the slab and not the bottom thus the top cutting can be operated with the bottom turned off.  
      Depending upon the material being produced and the cracks that develop, the system can run with a pair of torches  14  and  16  operating at the same time, or with one of the pair operating independently. If there were a pair for each corner of slab  26 , a total of eight torches could be running simultaneously. If the product being produced needs only the corner cut off, the lead torch of each pair can be operated by its self, or conversely, if the precuts requires only the surface to be removed, the trailing torch of each pair can be operated without the lead torch. Thus, depending upon the cracks in the product, the cut profile can be adjusted to accommodate.  
      It will be appreciated that for minor cracks, the “cutting” by the cutting torches can merely involve melting the material to remove cracks.  
      Referring to  FIG. 7 , when treating cracks on surface  34  of slab  26  cutting torches  44  are positioned to scarf along surface  34  of slab  26 . In some circumstances, it may be preferable to have cutting torches  44  oscillate, as represented by arrows  46 , representing movement perpendicular to the movement of slab  26 . When cutting torches  44  oscillate, they can cover more of surface  34  in order to keep pace with the movement of slab  26 , while cutting less material off surface  34 . Cutting torches  44  are also capable of rotation as with the torches previously described. Other features described above may also be used with cutting torches  44  where practical.  FIG. 7  also shows two additional torches  50  for concurrently scarfing corners along edge  24 .  
      Advantages:  
      The above described method that enables scarfing “on line” as the slab exits the caster onto the caster runout table substantially reduces steel plate production costs. There is no longer a need to cool the slab enough to allow workers to manually scarf the corners and then waste energy re-heating the slab to the rolling temperature. There are no longer labour costs incurred in handling the slabs to take them off line, manually scarfing the slab and then return them to the line. In cases where the slab must be removed from the line, the scarfing may occur before removal or after. For example, the slab temperature may vary from ambient temperature to 2100° F. Thus the apparatus can be used on line while the steel is being produced or off line if the slabs have cooled. Although the present invention was developed to meet the particular needs of the steel industry, its teachings will be equally applicable to other metal materials that are formed into slabs prior to being further processed.  
      Although major advantages are to be obtained by integrating the method and apparatus into a steel making process that involves the formation of the steel slab, it will be appreciated that steel rolling plants that acquire their slabs from elsewhere can still obtain advantages by including the method and apparatus in their slab processing line.  
      In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.  
      It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the Claims.