Patent Publication Number: US-10330386-B2

Title: Steel sheet heating method and steel sheet heating apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a steel sheet heating method and a steel sheet heating apparatus for heating a steel sheet. 
     BACKGROUND ART 
     Hot press molding, which is increasingly employed as, for example, a method for molding a steel sheet such as the material of an automobile component using a high-tensile steel sheet, can mold a steel sheet in a stage of low deformation resistance by molding it at high temperature, and furthermore can provide a component etc. with high strength and high shape accuracy by press molding without causing molding defects such as deformation after molding, by hardening by quenching based on rapid cooling using the jetting of cooling water. 
     In such a hot press molding method, press molding is performed such that a steel sheet is heated at a prescribed temperature, for example 700° C. to 1000° C., in a heating furnace before press molding and then the steel sheet is conveyed to a hot press molding apparatus. 
     As the technology of heating thus using a heating furnace, conventionally, a mechanism in which a steel sheet is heated by heaters provided in, for example, an upper portion and a lower portion of the interior of a furnace while the steel sheet is horizontally supported by rollers and conveyed by the rollers in the furnace has commonly been used (Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2009-155691A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the conventional technology mentioned above, since a steel sheet is conveyed by rolling rollers, the steel sheet may meander in the furnace. Furthermore, the rollers constitute a shield, and the radiation efficiency is poor and rapid heating is difficult. In addition, it is necessary to roll the rollers constantly even at times other than conveyance in order to soak the rollers so that they are not thermally deformed, and the energy efficiency is poor. Moreover, due to the thermal shock near the entrance of the furnace and the thermal stress produced by the unevenness of heating, there has been a concern that the roller will be degraded or damaged. If the roller is damaged, the operation of the furnace stops. Furthermore, for a surface-plated steel sheet, there have been concerns that the plating material will adhere to the roller in the melting temperature range and further the plating material adhering to the roller will adhere to the steel sheet again. 
     The present invention is made in view of these points, and an object of the present invention is to solve the issues mentioned above by a manner in which a steel sheet is brought into a furnace and is heated in a state of being fixedly supported in the vertical direction, instead of the conventional manner in which a steel sheet is conveyed in a furnace while being horizontally supported by rollers. 
     Solution to Problem 
     In order to achieve the above object, the present invention provides a steel sheet heating method that heats a steel sheet to be pressed before hot press molding, the steel sheet heating method including: bringing the steel sheet into a heating furnace including a heater on an inside surface of the heating furnace in a state where the steel sheet is supported in a vertical direction while an unnecessary portion of the steel sheet that becomes unnecessary after molding is fixedly supported by a support member; and performing heating at a prescribed temperature in the heating furnace, then taking the steel sheet out of the heating furnace, and after that removing the unnecessary portion. 
     The “after that” herein is not limited to the time immediately after being taken out of the heating furnace, and may be the time of performing hot press molding after the taking-out. 
     Examples of the “fixed support” in the present invention include holding the unnecessary portion mentioned above with a clamp and hanging the unnecessary portion by locking it with the support member. It is preferable that the steel sheet be fixedly supported at two or more places. This is because the steel sheet can thereby be prevented from bending when the steel sheet has a long-length shape, for example. When the steel sheet has a long length, for example when the length in the longitudinal direction of the steel sheet is more than 1 m, the steel sheet is preferably fixedly supported at both ends thereof. 
     According to the present invention, since a steel sheet is heated in the heating furnace in a state of being fixedly supported in the vertical direction by the support member, there is no harmful effect like conventional ones occurring in relation to the use of rollers, and the radiation efficiency is good and also the energy efficiency is good. Furthermore, by the fixed support in the vertical direction by means of the support member, the bending of the steel sheet can be suppressed. Here, the unnecessary portion that becomes unnecessary after molding refers to a portion that becomes unnecessary as a product after the steel sheet is molded. The “fixedly supporting the unnecessary portion by means of the support member” refers to fixedly supporting the whole or part of the unnecessary portion by means of the support member. 
     In the method, the steel sheet may be moved in a vertical direction in the heating furnace. 
     Furthermore, tension may be applied to the steel sheet fixedly supported. 
     According to another aspect, the present invention provides a steel sheet heating apparatus that heats a steel sheet to be pressed before hot press molding, the steel sheet heating apparatus including: a heating furnace capable of accommodating the steel sheet in a vertical state; and a conveyance apparatus that allows the steel sheet to pass through a conveyance path of the heating furnace in a state of being supported in a vertical direction by a support member. The heating furnace includes the conveyance path of the steel sheet formed between side walls facing each other and a heater that is provided on at least one surface of the side walls and heats the steel sheet. The conveyance apparatus includes the support member that fixedly supports an unnecessary portion of the steel sheet that becomes unnecessary after molding and a moving mechanism that moves the support member along a rail provided from above an upstream side of an entrance to above a downstream side of an exit of the heating furnace. 
     In this case, a vertical drive mechanism that moves the support member in a vertical direction may be further included. 
     In addition, a shearing mechanism that shears the unnecessary portion on the downstream side of the exit of the heating furnace may be further included. 
     Furthermore, a mechanism that applies tension to the steel sheet fixedly supported may be further included. 
     Advantageous Effects of Invention 
     According to the present invention, there is no harmful effect like conventional ones occurring in relation to the use of rollers when a steel sheet to be pressed is heated before hot press molding, and the radiation efficiency is good and also the energy efficiency is good. Furthermore, a steel sheet to be pressed can be heated more uniformly than in the past. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a steel sheet heating apparatus according to an embodiment. 
         FIG. 2  is an illustration diagram of a heating furnace in the steel sheet heating apparatus of  FIG. 1  as viewed from the entrance side in the conveyance direction. 
         FIG. 3  is a front view of a support member. 
         FIG. 4  is a front view of a steel sheet supported by a support body of the support member. 
         FIG. 5  is a front view of a main portion of a steel sheet showing another example of an extension member. 
         FIG. 6  is an illustration diagram schematically describing the steel sheet heating apparatus and a hot press molding apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinbelow, embodiments of the present invention are described.  FIG. 1  shows an overview of a steel sheet heating apparatus  1  according to an embodiment; a heating furnace  10  in the steel sheet heating apparatus  1  of the embodiment includes side wall bodies  12  and  13  in a facing manner individually on both sides of a base  11 , and the long, narrow space between the side wall bodies  12  and  13  forms a conveyance path  14  of a steel sheet K. Heaters  15  and  15  are provided on the inside of the side wall bodies  12  and  13 , respectively ( FIG. 1  is depicted with part of the heating furnace  10  broken off for convenience of illustration). 
     As the heater  15 , for example, an electric heater, a far-infrared heater, a near-infrared lamp, an induction heating means, or the like may be used. Although in the embodiment the heater  15  is provided individually on both surfaces of the side wall bodies  12  and  13 , the heater  15  may be provided only on one side wall surface depending on the type, size, shape, etc. of the steel sheet. 
     A conveyance apparatus  20  of the steel sheet heating apparatus  1  according to the embodiment includes a forward rail housing  21  provided from above the entrance  10   a  side of the heating furnace  10  (the back side of the drawing) to above the exit  10   b  side of the heating furnace  10  (the front side of the drawing) and a backward rail housing  22  provided parallel to the forward rail housing  21 . Each of the forward rail housing  21  and the backward rail housing  22  is supported by support columns  23 . A support member moving path  24   a  and a support member moving path  24   b  in a curved line form in a planar view, which serve also as a horizontal rail, are stretched between the ends of the forward rail housing  21  and the backward rail housing  22 . 
     The forward rail housing  21  and the backward rail housing  22  basically have the same configuration; a detailed description thereof is given as follows based on the forward rail housing  21  shown in  FIG. 2  and  FIG. 3 : the forward rail housing  21  houses a chain conveyor  21   b  serving as a drive mechanism on the upper side of the interior of a main body unit  21   a  in which the lower surface side is opened and the cross section is shaped like a trench, and houses a rail body  21   c  on the lower side. As shown in  FIG. 1 , the chain conveyor  21   b  is stretched between a gear sprocket  25  provided on the support member moving path  24   a  side and a gear sprocket  26  provided on the support member moving path  24   b  side, and moves cyclically between the forward rail housing  21 , the support member moving path  24   a,  the backward rail housing  22 , and the support member moving path  24   b  by the operation of a drive source  28  such as a motor connected to the gear sprocket  25  via a shaft  27 . 
     A support member  30  in the embodiment is supported directly by the rail body  21   c.  As shown in  FIG. 3 , the support member  30  includes two hanging members  31  and  32 . The hanging members  31  and  32  have the same configuration, and thus the hanging member  31  is taken representatively for description; as shown in  FIG. 2 , the hanging member  31  is provided with a rail running member  33  and a cylinder  34 , at a bracket  31   a.    
     The rail running member  33  includes an engaging unit  33   a  engaging with the chain conveyor  21   b  and a running unit  33   c  provided with rollers  33   b  capable of running the rail body  21   c  mentioned above. The cylinder  34  is fixed to the bracket  31  a, and a rod member  34   a  that extends and contracts by the operation of the cylinder  34  is suspended below the bracket  31   a  and has a support body  34   b  at its lower end. Therefore, the support body  34   b  moves vertically by the operation of the cylinder  34 . 
     As shown in  FIG. 4 , a plurality of protrusions  35  are provided on a lower portion of the support body  34   b  in the vertical direction (in the example of the drawing, on four places). The steel sheet K is locked with the protrusions  35  and is supported between the support bodies  34   b  and  34   b  of the hanging members  31  and  32 . That is, extension members Ka and Kb that have no relation to the original product, i.e. are unnecessary portions that become unnecessary after molding, have been formed at both ends of the steel sheet K in advance, and a locking portion  36  to be locked with the protrusion  35  of the support body  34   b  is formed in the extension members Ka and Kb; and by the locking portion  36  being locked with the protrusion  35 , the steel sheet K is locked with the protrusions  35  and is supported between the support bodies  34   b  and  34   b  of the hanging members  31  and  32 . 
     In the example of the embodiment, the extension members Ka and Kb are in a T-shaped configuration, and the inside thereof is notched to form the locking portions  36 ; but instead, as shown in  FIG. 5 , the steel sheet K may be supported between the support bodies  34   b  and  34   b  of the hanging members  31  and  32  in such a manner that a hole  37  is formed in the extension member Ka extending from an end of the steel sheet K in the horizontal direction and the protrusion  35  of the support body  34   b  is inserted into the hole  37 . 
     Instead of thus supporting the steel sheet K by hanging the steel sheet K between the support bodies  34   b  and  34   b  of the hanging members  31  and  32  using the extension members Ka and Kb, for example, a clamping mechanism (not shown) that clamps the extension members Ka and Kb may be provided in the hanging members  31  and  32 , and thus the extension members Ka and Kb may be clamped to fixedly support the steel sheet K in the vertical direction. 
     As shown by the broken line of  FIG. 3 , a tension application mechanism  39  that includes a cylinder  38  and rods  38   a  and  38   a  protruding on both sides may be provided between, for example, the rod members  34   a  and  34   a  of the two hanging members  31  and  32 . By putting the cylinder  38  of the tension application mechanism  39  into operation, the rods  38   a  extend and contract to allow the spacing between the hanging members  31  and  32  to become wider; thereby, tension can be applied to the steel sheet K supported between the support bodies  34   b  and  34   b  of the hanging members  31  and  32 . 
     Referring to  FIG. 1  again for description, the steel sheet heating apparatus  1  includes, as mentioned above, the forward rail housing  21  and the backward rail housing  22  provided parallel to the forward rail housing  21 , and the backward rail housing  22  has the same configuration as the forward rail housing  21 . 
     In the embodiment, as described above, the support member moving path  24   a  and the support member moving path  24   b  are stretched between the ends of the forward rail housing  21  and the backward rail housing  22 , and the hanging members  31  and  32  of the support member  30  that has been located on the backward rail housing  22  side can be moved to the forward rail housing  21  side, that is, to the entrance  10   a  side of the heating furnace  10 , via the support member moving path  24   b.    
     Furthermore, the hanging members  31  and  32  of the support member  30  that has been located on the forward rail housing  21  side, i.e. on the exit  10   b  side of the heating furnace  10 , can be moved to the backward rail housing  22  side via the support member moving path  24   a.  For the hanging members  31  and  32  to be inserted into the furnace, heat-resistant steel or the like with high heat resistance and thermal shock properties is used; and the hanging members  31  and  32  may be protected with a heat insulating material, which should usually be considered as a means for protecting the furnace equipment, and may be provided with a flow path inside and use a cooling means based on a cooling medium such as cooling water or air. 
     In the embodiment, a shearing mechanism  40  that shears the extension members Ka and Kb of the steel sheet K that has undergone the heating by the heating furnace  10  and is located on the exit  10   b  side of the heating furnace  10  while being supported by the hanging members  31  and  32  of the support member  30  is provided on the exit  10   b  side of the heating furnace  10 . 
     The shearing mechanism  40  includes a pair of shearing apparatuses  41  and  42 . The shearing apparatuses  41  and  42  have the same structure; for example, a detailed description of the shearing apparatus  42  is given as follows: the shearing apparatus  42  includes a base  43  and shearing members  44  and  45  provided perpendicular to the base  43  and facing each other. The shearing members  44  and  45  move along the base  43  by means of a drive mechanism (not shown), and can come close to and go away from each other freely. Blades  44   a  and  45   a  are provided on the facing surface sides of the shearing members  44  and  45 , respectively. Therefore, by the shearing members  44  and  45  coming close together, by means of the blades  44   a  and  45   a  thereof, the extension members Ka and Kb of the steel sheet K supported between the hanging members  31  and  32  can be sheared. 
     A conveyance robot  50  including an articulated arm that holds the steel sheet K supported by the hanging members  31  and  32  of the support member  30  may be placed on the exit  10   b  side of the heating furnace  10 . The conveyance robot  50  has the function of setting two clamp-type chucks  52  and  52  to ON or OFF by the rotational movement operation of a handle  51 . The conveyance robot  50  includes a moving mechanism (not shown) that can move from the position on the exit  10   b  side of the heating furnace  10  freely, and can convey the held steel sheet to a hot press molding apparatus described later. 
     The steel sheet heating apparatus  1  according to the embodiment is configured in the above manner; next, a steel sheet heating method using the steel sheet heating apparatus  1  is described. 
     First, the steel sheet K to be molded by hot press molding is supported at the hanging members  31  and  32  of the support member  30  located on the forward rail housing  21  side, on the entrance  10   a  side of the heating furnace  10 . Then, tension is applied to the supported steel sheet in the horizontal direction by the tension application mechanism  39  shown in  FIG. 3 . 
     In this state, the drive mechanism of the forward rail housing  21  is put into operation to drive the chain conveyor  21   b,  and thereby the hanging members  31  and  32  of the support member  30  supporting the steel sheet K are moved to the heating furnace  10 ; and the steel sheet K is heated to a prescribed temperature, for example 700° C. to 1000° C., by the heaters  15  in the heating furnace  10 . At this time, the cylinders  34  of the hanging members  31  and  32  may be put into operation to extend and contract the rod members  34   a,  and thus the steel sheet K supported at the hanging members  31  and  32  can be moved in the vertical direction. 
     After the steel sheet K is heated to the prescribed temperature, the chain conveyor  21  b of the forward rail housing  21  is driven, and thus the hanging members  31  and  32  of the support member  30  supporting the steel sheet K are taken out of the heating furnace  10  and are moved to the space on the exit  10   b  side of the heating furnace  10 . The steel sheet K may be heated in the heating furnace  10  while being conveyed constantly, or may be heated in a state of being stationary in the heating furnace  10 . 
     After the hanging members  31  and  32  of the support member  30  supporting the steel sheet K have stopped in a prescribed position in the space on the exit  10   b  side of the heating furnace  10 , the conveyance robot  50  is brought close to the steel sheet K, and the steel sheet K is held by the chucks  52  and  52 . After that, the tension applied to the steel sheet K the tension application mechanism  39  is released; and the shearing apparatuses  41  and  42  are put into operation, and the extension members Ka and Kb of the steel sheet K supported between the hanging members  31  and  32  are sheared by the shearing members  44  and  45 . Thus, the conveyance robot  50  enters a state of supporting the steel sheet K from which the extension members Ka and Kb, which are unnecessary portions after molding, have been removed. 
     After that, as shown in  FIG. 6 , while the steel sheet K is held by the chucks  52  and  52 , the steel sheet K is conveyed by an articulated arm  53  of the conveyance robot  50  to a lower mold  63  of a molding and rapid cooling stage  62  of a hot press molding apparatus  60 , which stage performs press molding and rapid cooling treatment. Then, after the steel sheet K is set in a prescribed position, prescribed press molding by the pressing of an upper mold  64  and rapid cooling treatment are performed on the steel sheet K, and the steel sheet K is processed into a prescribed product. 
     Thus, by the embodiment of the present invention, the steel sheet K is brought into and heated by the heating furnace  10  including the heaters  15  on the surfaces of the side wall bodies  12  and  13  in a state where the steel sheet K is fixedly supported in the vertical direction via the extension members Ka and Kb, which are unnecessary portions that become unnecessary after press molding, by the hanging members  31  and  32  of the support member  30 ; therefore, as compared with a conventional system in which a steel sheet is heated while being supported in a horizontal state by rollers, firstly, the steel sheet K can be heated more uniformly than in the past without the steel sheet K meandering. Furthermore, since there is no shield between the heater  15  and the steel sheet K, the heat from the heater  15  can be given to the steel sheet K with good efficiency, and the radiation efficiency is good and more rapid heating than in the past is possible. In addition, since at times other than heating there is no need to put the support member  30  in movement, the energy efficiency is better than in the past. In addition, since rollers are not used, there is no possibility of shutdown due to damage to rollers. 
     Furthermore, in the embodiment described above, since the support body  34   b  supporting the steel sheet K can be moved vertically by putting the cylinder  34  of the support member  30  into operation, the heating unevenness can be suppressed by putting the cylinder  34  into operation to move the steel sheet K in the vertical direction while the steel sheet K is located in the heating furnace  10 , and thereby more uniform heating can be made. Therefore, also heating unevenness in the vertical direction due to the arrangement of heaters  15  and the variation in heating output characteristics can be prevented. 
     Furthermore, in the embodiment described above, since the steel sheet K to be heated is fixedly supported in the vertical direction via the extension members Ka and Kb by the hanging members  31  and  32  of the support member  30  and, in particular, is fixedly supported at two places of both ends, the steel sheet K does not bend even when the steel sheet K has a shape long in the horizontal direction. Furthermore, since tension is applied to the steel sheet K to be heated in the horizontal direction by the tension application mechanism  39 , the deformation due to the reduction in rigidity and the thermal expansion of the steel sheet K during heating can be suppressed. 
     Furthermore, since the extension members Ka and Kb of the steel sheet K used when the steel sheet K is fixedly supported in the vertical direction are unnecessary portions that become unnecessary after press molding, the steel sheet K itself can be heated uniformly in whole. Moreover, in the case where the steel sheet K is a plated steel sheet, even when it is heated in the melting temperature range, there is no concern that the molten plating material will adhere to the steel sheet K again. 
     In the embodiment described above, since the extension members Ka and Kb are, immediately after heating, sheared and removed in the steel sheet heating apparatus  1  by the shearing mechanism  40  installed in the steel sheet heating apparatus  1 , the extension members Ka and Kb, which are unnecessary portions, can be removed in a state of high temperature and low strength, and there is no influence on the shape, quality, and performance of the product after molding. The extension members Ka and Kb left on the hanging members  31  and  32  of the support member  30  after shearing may be collected to a collection box or the like via a chute (not shown) or the like. In the case where the press mold can be provided with a shearing mechanism, the extension members Ka and Kb may be sheared and removed simultaneously with the pressing in the hot press molding apparatus  60 . 
     The hanging members  31  and  32  of the support member  30  after the steel sheet K is conveyed by the conveyance robot  50  in the above way may be moved to the backward rail housing  22  side through the support member moving path  24   a  and then moved to the entrance  10   a  side of the heating furnace  10  through the support member moving path  24   b,  and the steel sheet K to be processed next may be set at the hanging members  31  and  32  of the support member  30  again in a prescribed position on the entrance  10   a  side of the heating furnace  10 . 
     As is clear from  FIG. 1 , the steel sheet heating apparatus  1  uses the heating furnace  10  that heats the steel sheet K in a vertical state from both sides, and the forward rail housing  21  and the backward rail housing  22  of the conveyance apparatus  20  are installed above the heating furnace  10 ; therefore, the occupied floor area is much smaller than that of a conventional horizontal support-type heating furnace, and thus a large number of steel sheet heating apparatuses  1  can be juxtaposed. Therefore, productivity is very good in operation with the same floor area. 
     Furthermore, in the embodiment described above, the movement of the hanging members  31  and  32  of the support member  30  is based on the chain conveyor  21   b  installed in the forward rail housing  21  and the backward rail housing  22 , and an arrangement in which the drive mechanism is installed outside the heating furnace  10  and the forward rail housing  21  does not receive radiant heat directly from the opening of the heating furnace as shown in  FIG. 2  is possible; thus, the thermal effect from the heating furnace  10  on the drive system can be suppressed to a minimum. When a thermal shield is provided as appropriate, the support member  30  itself may be equipped with a self-propelled drive mechanism, as a matter of course. 
     The preferred embodiment(s) of the present disclosure has/have been described above with reference to the accompanying drawings, whilst the present disclosure is not limited to the above examples. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful for the heating of a steel sheet before the steel sheet is molded by hot press molding. 
     REFERENCE SIGNS LIST 
     
         
           1  steel sheet heating apparatus 
           10  heating furnace 
           10   a  entrance 
           10   b  exit 
           11  base 
           12 ,  13  side wall body 
           14  conveyance path 
           15  heater 
           20  conveyance apparatus 
           21  forward rail housing 
           21   a  main body unit 
           21   b  chain conveyor 
           21   c  rail body 
           22  backward rail housing 
           23  support column 
           24   a,    24   b  support member moving path 
           25 ,  26  gear sprocket 
           27  shaft 
           28  drive source 
           30  support member 
           31 ,  32  hanging member 
           31   a  bracket 
           33  rail running member 
           33   a  engaging unit 
           33   b  roller 
           33   c  running unit 
           34  cylinder 
           34   a  rod member 
           34   b  support body 
           35  protrusion 
           36  locking portion 
           37  hole 
           38  cylinder 
           38   a  rod 
           39  tension application mechanism 
           40  shearing mechanism 
           41 ,  42  shearing apparatus 
           43  base 
           44 ,  45  shearing member 
           44   a,    45   a  blade 
           50  conveyance robot 
           51  handle 
           52  chuck 
           53  articulated arm 
           60  hot press molding apparatus 
           62  molding and rapid cooling stage 
           63  lower mold 
           64  upper mold 
         K steel sheet 
         Ka, Kb extension member