Abstract:
A midsole molding apparatus which enables production of a high-quality midsole is provided. The apparatus includes a through hole, which passes laterally through a midsole used for a shoe, to be integrally formed, preventing traces of forming the through hole from being left in the through hole and on the periphery of the through hole and a shaft mold crossing the inner space of upper and lower molds, forming extending portions such that the ends of the shaft mold extend beyond the boundary of the inner space, and seating the extending portions in press recesses of the upper and lower molds to seal the insides of the molds so as to prevent raw material from leaking from inside the molds when foaming and forming a midsole, to prevent parting lines and burrs from forming on the inner surface of the through hole passing laterally through the midsole.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation application, claiming the benefit under §365(c), of an International application filed on Mar. 24, 2016 and assigned application number PCT/KR2016/003014, which claimed the benefit of a Korean patent application filed on Mar. 24, 2015 in the Korean Intellectual Property Office and assigned Serial number 10-2015-0040479 and of a Korean patent application filed on Mar. 24, 2016 in the Korean Intellectual Property Office and assigned Serial number 10-2016-0035064, the entire disclosure of each of which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a midsole used for a shoe, and more particularly, to a midsole including a through-hole formed through a side thereof. 
         [0003]    In detail, the through-hole is integrally formed through a side of the midsole without forming any traces on surrounding portions of the through-hole. 
       BACKGROUND 
       [0004]    In recent years, various designs and functions of shoes are demanded according to the various needs of consumers. Even in the sport industry as well as the outdoor industry, there have been proposed shoes having a light weight as well as a distinctive function. 
         [0005]    As a method of lightening a shoe, a midsole may be formed by injection-foaming an EVA material such that the weight of the midsole is lightened. 
         [0006]    According to a method of manufacturing a midsole by injection foam molding, after a liquid raw material containing a foaming material is injected into a mold having a size slightly smaller than that of the midsole to be manufactured, heat and pressure are applied to the mold, such that chemical reaction is made inside the mold, thereby performing molding in a shape of a midsole. By opening the mold after a predetermined time period, the molded article in the mold is instantaneously expanded at the same time as the mold is opened, so that a midsole having a desired size is produced. Such a method of manufacturing a midsole through the injection foaming method has been well known in the art and thus, the details will be omitted. 
         [0007]    Meanwhile, at present, to pierce the side of a midsole, a midsole which are separated into two pieces of which each or one has a groove formed in a predetermined shape or depth is prepared and then, the pieces of the sole are assembled by means of adhesive or the like, thereby manufacturing a side pierced midsole. 
         [0008]    However, according to such a method, since the midsole is implemented by bonding, it is difficult to not only manufacture the midsole but also ensure the quality of the product, and the effect of buffering by the through-hole formed through the side of the midsole is deteriorated. 
         [0009]    Therefore, to solve the problem described above, the applicant of the present application had proposed a midsole in which a through-hole is integrally formed at a side thereof, so that the midsole has excellent buffering function and the manufacturing difficulty caused due to adhesion is overcome. (Korean Unexamined Patent Publication No. 10-2013-0027610 A). 
         [0010]    However, in the injection foam molding method described above, it is very difficult to smoothly form a through-hole perforated in the lateral direction. The reason is that a shaft mold is required to penetrate through the center of a mold to integrally form the through-hole perforated in the lateral direction in the midsole, and an error occurs in the structure in which the shaft metal mold is closely attached to the inner wall of the mold so that it is difficult to manufacture a complete product. 
         [0011]    That is, in order to form the through-hole in the lateral direction of the midsole, the shaft mold for forming the through-hole in the midsole is installed inside the mold for molding the midsole. In the case where the midsole is molded at a constant temperature and pressure, for example, by a foaming method in the state that the shaft mold is installed inside the mold and is not tightly closed to the mold, a gap is generated between the mold and the shaft mold installed inside the mold and the molded material enters the gap, so that the through-holes of the midsole are partially or fully blocked. Thus, a separate processing means is required to remove such a material formed in the gap. 
         [0012]    That is, although the injection molding method is characterized in that molding is performed at a very high pressure, when the shaft mold is simply placed to be tightly closed to the inner wall surface of the upper and lower molds, since a gap is formed between the shaft and the inner wall of the mold, the result of molding is not good. Even if a mold is manufactured by precision machining in the production of a mold, a bur is generated in the result of molding. 
         [0013]    Therefore, after the molding is completed, the post-processing is necessarily required, so that the mold manufacturing cost is excessive and the production cost of the outsole is increased due to excessive labor as well as excessive working equipment and working time. 
         [0014]    In addition, to form the through-hole perforated in the lateral direction of the midsole, the mold opening structure is formed in the same line as the shaft mold installed inside the mold, so that the parting line is exposed on the inner wall of the through-hole of the molded midsole. 
         [0015]    Meanwhile, when the midsole is individually molded by injection foam molding, a defect may occur in the midsole. That is, after rapid foaming by the opening of the mold in the production process, the volume is reduced due to the temperature change caused by making contact with external air having a relatively low temperature while being cooled, thereby causing a dimensional defect. 
         [0016]    The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure. 
       SUMMARY 
       [0017]    To solve the problems described above, one object of the present invention is to improve the completeness of a molded article without a need of post-processing a portion of a through-hole after the completion of molding by preventing a molding trace from being formed on the though-hole and the surrounding portions of the through-hole even though the through-hole is integrally formed in a lateral direction of a midsole. 
         [0018]    In addition, another object of the present invention is to allow a pair of midsoles to be manufactured with a single mold such that the manufacturing time of the midsole is reduced and a dimensional defect is prevented from being generated between the pair of midsoles. 
         [0019]    To achieve the above-described objects, according to the present invention, there is provides a midsole forming device which includes inner spaces formed by an upper mold and a lower mold and foam-molds a midsole by injecting a raw material into the inner spaces. The midsole forming device includes a shaft mold intersecting the inner spaces of the upper and lower molds; an extension portion provided to the shaft mold, wherein the extension portion is formed on an end portion of a shaft to extend beyond boundaries of the inner spaces of the upper and lower molds; and press grooves formed on the upper and lower molds to surround the extension portion of the shaft mold such that an injection foam molding is performed without generating a parting line and a bur on an inner surface of a through-hole perforated in a lateral direction of the midsole. 
         [0020]    According to the midsole forming device of the present invention, by manufacturing the midsole through injection foam molding, it is possible to provide a sole that is lightweight, excellent in impact absorption and excellent in restoring force. In addition, it is possible to provide a high-quality midsole since there is no trace of molding in the through-hole and the surrounding portions of the through-hole even though the through-hole for damping is formed integrally with the midsole. 
         [0021]    In addition, the structure of the damping portion provided with the through-hole may be formed in in various shapes such as a bar shape, a ball shape and the like, or in such a shape that a heel does not exist, thereby satisfying both design and functionality. 
         [0022]    In addition, since the size of the midsole may be easily adjusted by controlling the amount of the raw material to be injected during molding and the midsole may be manufactured in various sizes besides the standard sizes which are usually used, the inventory burden may be reduced and the satisfaction of the consumers may be improved. 
         [0023]    In addition, since a parting line is not formed on the inner surface of the through-hole and any burs do not exist, the durability of the through-hole and the quality of the product may be improved, and since the post-processing of the corresponding part is not necessary in the production process, it is possible to reduce labor and reduce the manufacturing cost of the sole, thereby ensuring price competitiveness. 
         [0024]    Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0026]      FIG. 1  is an exploded perspective view illustrating a structure of a molding apparatus according to the present invention; 
           [0027]      FIG. 2  is a view illustrating an opened mold in a state that a midsole is molded by a molding apparatus according to the present invention; 
           [0028]      FIG. 3  is a front view of  FIG. 2 ; 
           [0029]      FIGS. 4 to 8  are sectional views illustrating a step of molding a midsole using a molding apparatus according to the present invention; 
           [0030]      FIGS. 9 and 10  are perspective views illustrating a shaft mold according to another embodiment of the present invention; 
           [0031]      FIGS. 11 to 14  are views illustrating a midsole manufactured by a midsole forming device according to an embodiment of the present invention; and 
           [0032]      FIGS. 15 to 21  are views illustrating a midsole manufactured by a midsole forming device according to another embodiment of the present invention. 
       
    
    
       [0033]    Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
       DETAILED DESCRIPTION 
       [0034]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
         [0035]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents. 
         [0036]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0037]    According to the best mode of the present invention, there is provided a midsole forming device which includes inner spaces  120  and  220  formed by an upper mold  100  and a lower mold  200  and foam-molds a midsole by injecting a raw material into the inner spaces, the midsole forming device including: 
         [0038]    a shaft mold  300  intersecting the inner spaces  120  and  220  of the upper and lower molds  100  and  200 ; 
         [0039]    an extension portion  340  provided to the shaft mold  300 , wherein the extension portion  340  is formed on an end portion of a shaft  320  to extend beyond boundaries of the inner spaces  120  and  220  of the upper and lower molds  100  and  200 ; and 
         [0040]    press grooves  140  and  240  formed on the upper and lower molds  100  and  200  to surround the extension portion  340  of the shaft mold  300  such that an injection foam molding is performed without generating a parting line and a bur on an inner surface of a through-hole perforated in a lateral direction of the midsole. 
         [0041]    In addition, there is provided a midsole which includes a heel portion located rearward of a support capable of pressing a concave portion of a sole and a toe portion, and is foam-molded to realize a low weight, wherein the heel portion of the midsole is relatively thicker than the toe portion to endure a load when a shearing force is applied during walking, the midsole including: 
         [0042]    recess portions and protrusion portions repeatedly formed on the heel portion; 
         [0043]    a though-hole perforated in a lateral direction of the protrusion portion for damping; and 
         [0044]    an assembly means provided on the toe portion in a planar state to assemble a damping ball which is separately molded. 
         [0045]    Hereinafter, the present invention will be described in detail with reference to accompanying drawings as follows. 
         [0046]    As shown in  FIG. 1 , the present invention includes a shaft mold ( 300 ) between upper and lower molds  100  and  200 . When the upper and lower molds  100  and  200  are engaged with each other for molding, the shaft mold is interposed between the upper and lower molds such that a though-hole  2  perforated in the lateral direction of a midsole  1  may be integrally formed. 
         [0047]    Inner spaces  120  and  220  may be formed in the upper and lower molds  100  and  200  to correspond to each other, respectively. The inner space  120  of the upper mold  100  is provided to mold an upper surface of the midsole  1  and the inner space  220  of the lower mold  200  is provided to mold a lower surface of the midsole  1 . 
         [0048]    The upper and lower molds  100  and  200  may be coupled in position to each other by guide pins  110  and  210 . A raw material is injected into the inner space between the upper and lower molds  100  and  200  in the state that the upper and lower molds are closed (shut), such that the midsole  1  is foam-molded. 
         [0049]    A shaft mold  300 , which is provided to cross the inner spaces  120  and  220  when the upper and lower molds  100  and  200  are closed, may allow a through-hole  2  perforated in the lateral direction of the midsole  1  to be integrally molded when the midsole  1  is molded in the mold. 
         [0050]    In this case, the shaft mold  300  may be provided as many as the number of through-holes  2  to be formed in the midsole  1 . In the structure of the shaft mold  300 , a shaft  320  may be provided to intersect the inner spaces  120  and  220  of the upper and lower molds  100  and  200 , and an extension portion  340  may be provided on an end portion of the shaft  320  to extend beyond the boundaries of the inner spaces  120  and  220  of the upper and lower molds  100  and  200 . 
         [0051]    In addition, press groove  140  and  240  may be formed on the upper and lower molds  100  and  200  to surround the extension portion  340  of the shaft mold  300 . 
         [0052]    That is, preferably, the shaft  320  is formed in a circular or elliptic shape. An upper surface of the shape  320  is tightly closed to the press groove  140  of the upper mold  100  based on the horizontal center of the shaft  320  and a lower surface of the shape  320  is tightly closed to the press groove  240  of the lower mold  200  based on the horizontal center of the shaft  320 , such that the mold is smoothly opened or closed and the molding is performed in the state that the extension portion  340  of the shaft  320  is tightly closed into the press grooves  140  and  240 . 
         [0053]    Thus, when the midsole  1  is molded, it is possible to prevent the raw material from leaking out due to the foaming pressure inside the mold and to prevent the through-hole  2  from being clogged. In addition, it is possible to prevent the parting line of the mold from occurring on the inner surface of the through-hole  2  and to prevent a bur from being generated on the surface of the midsole. 
         [0054]    Meanwhile, when the shaft  320  and the extension portion  340  are formed on a platform  360  that is operated to move up or down, the platform  360  is operated to move up and down when the upper and lower molds  100  and  200  are closed or opened, such that the shaft mold  300  may be separated from the mold. 
         [0055]    In this case, the platform  360  may be mounted on the upper or lower mold  100  or  200  such that the plate form  360  is operated to move up and down. The platform  360  may be mounted to have an elastic restoring force by a restoring element  362 . 
         [0056]    The platform  360  of the shaft mold  300  is mounted on the upper or lower mold  100  or  200  to have the elastic restoring force by the restoring element  362 , such that the molded article is separated and protrudes from the upper or lower mold when the mold is opened after molding is completed. 
         [0057]      FIGS. 4 and 8  are sectional views illustrating a sequence of manufacturing a midsole according to the present invention. To injection-mold the midsole  1 , after the upper and lower molds  100  and  200  are closed to be shut and closed, a raw material is injected into the mold to perform injection molding. In the state where the raw material is injected, the chemical reaction occurs in the mold so that the raw material is molded while being foamed. When the mold is opened after a set time, the molded article is separated from the upper and lower molds  100  and  200  while the platform  360  of the shaft mold  300  is ejected, so that the molded article is cooled while being expanded, so the manufacture of the midsole is completed. 
         [0058]    In this embodiment, the platform  360  is mounted on the lower mold  200  to move up and down, and the upper and lower molds  100  and  200  are respectively provided with receiving grooves  160  and  260  to enable the platform  360  to enter the upper and lower molds  100  and  200 , respectively, but the present invention may be variously modified depending on the productivity or the manner of opening and closing the upper and lower molds. 
         [0059]    In addition, the upper and lower molds  100  and  200  are preferably formed with one pair of inner spaces  120  and  220  to enable a pair of midsoles to be simultaneously fabricated. To this end, the shaft mold  300  may be formed with shafts  320  having extension portions  340  and symmetrically formed at both sides of the platform  360 , and the upper and lower molds  100  and  200  may be formed symmetrically with press grooves  140  and  240  which are symmetrically formed to receive the extension portions  340  of the symmetrical shafts, so that a pair of midsoles  1  may be simultaneously manufactured under a same molding condition. 
         [0060]    That is, according to the injection foam molding method, the size, weight, and elasticity of the molded article may be changed depending on the minute difference in the molding conditions such as the injection amount of the raw material, the temperature difference, the density, and the like. In addition, the pair of midsole  1  may be simultaneously molded by providing the shaft mold  300  on both sides of one platform  360 , so that a pair of midsoles having no deviation may be manufactured. 
         [0061]    In addition, when the shaft  320  formed on the platform  360  is formed of a hollow tube, the adhesion of the upper and lower molds to the press grooves  140  and  240  may be further improved by the elastic force of the shaft  320  itself. When the foam molding is performed in the state that the upper and lower molds  100  and  200  and the shaft mold  300  are closed, the raw material may be further prevented from being leaked through the gap between the molds due to the foaming pressure. 
         [0062]    In addition, the extension portion  340  may be provided with a coating layer  342  on the surface thereof to improve the adhesion strength with the press grooves  140  and  240 . 
         [0063]    The surface of the coating layer  342  may be Teflon-coated to improve the adhesion strength, or may be formed with metal or special plastic, thereby improving the adhesion strength with the press grooves  140  and  240 . 
         [0064]    Hereinafter, the midsole according to an embodiment manufactured by using the midsole foaming apparatus will be described in more detail with reference to  FIGS. 11 to 14 . 
         [0065]    The midsole  1  of the present invention may be formed through injection-foam-molding by injecting various kinds of synthetic resins capable of foaming into a mold as raw materials. It is preferable to use a thermosetting synthetic resin as a raw material of the midsole. 
         [0066]    The midsole  1  is provided with a plurality of through-holes  2  perforated in the lateral direction in order to have a buffering force and is molded without any parting lines and burrs in the peripheries of the through-holes  2  as well as the inner walls of the through-holes  2  to allow the through-hole to have a beautiful outer appearance. 
         [0067]    That is, when the molding is performed while the mold  300  is engaged between the upper mold  100  and the lower mold  200  in the above-described molding apparatus, since the extension portion  340  of the shaft mold  300  is inserted into the press grooves  140  and  240 , the raw resin may be basically prevented from being leaked to the inlet of the through-hole  2  due to the foaming pressure. In addition, since the upper and lower surfaces of the extension portion  340  are strongly pressed by the press grooves  140  and  240  to be in close contact with each other and the area of the tightly closed surface is large, even when the foaming pressure is strongly inside the mold, the raw material may be prevented from being leaked and the quality of the molded article may be improved. 
         [0068]    In addition, a plurality of protrusions  4  and an inlet portion  5  are repeatedly formed on the lower surface of the midsole  1  such that the midsole  1  may move flexibly. The protrusion  4  is formed with the through-hole  2 , such that the buffering capacity of the midsole may be further improved. 
         [0069]    In this case, the protrusion portion  4  may protrude in a hemispherical ball shape. 
         [0070]    When the heel portion of the midsole  1  is inclined inwardly in an arcuate shape for the purpose of stepping on the ground during walking, the inclined surface of the heel first touches the ground and pulls the back muscles in the walking step. In the next walking step, while the weight is tilted forward when the toes step on the ground, the entire muscles of the leg are pulled and pressed while the body weight is moved forward, so that the walking exercise effect may be improved and balanced walking may be achieved. 
         [0071]    In addition, as shown in  FIGS. 15 to 21 , another midsole which may be formed by the molding apparatus of the present invention is as follows. 
         [0072]    The midsole  1  includes a heel portion  10  located rearward of a support  3  capable of pressing a concave portion of the sole and a toe portion  20 . The midsole  1  is foam-molded to realize a low weight. The heel portion  10  of the midsole  1  is formed to be relatively thicker than the toe portion  20  to endure a load when the shearing force is applied during walking. 
         [0073]    In addition, the heel portion  10  is formed with repeating recess portions  5  and protrusion portions  4 . The protrusion portion  4  includes a through-hole  2  perforated in the lateral direction for damping. The toe portion  20  includes an assembly means for assembling a damping ball  30  which is separately molded in a planar state. 
         [0074]    The recess portions  5  and protrusion portions  4  repeatedly formed on the heel portion  10  of the present invention are preferably spaced apart from each other by a degree that the protrusion portion  4  is deformed back and forth while being crushed by the load caused by the generation of the shearing force during walking. Such an interval may allow the shearing force during walking transferred from the heel to the toe during walking to be easily operated. 
         [0075]    By forming the protrusion portion  4  to be larger than the recess portion  5 , the through-hole  2  perforated in the lateral direction for damping may be easily formed. In addition, it is possible to stably walk when the heel portion steps on the ground at a starting of walking. 
         [0076]    In addition, an inner groove  4 a for mounting an outsole A is formed on the bottom surface of the protrusion portion  4 . The inner groove  4 a allows the outsole A to be easily mounted and is formed at such a depth that the midsole  1  does not produce friction against the ground when the outsole A is in close contact with the ground. 
         [0077]    Although the through hole  2  is formed on the protrusion portion  4  for damping according to one embodiment of the present invention, the same object may be achieved even when the damping means is implemented by another method. 
         [0078]    In addition, the damping ball  30  according to the present invention mounted on the assembly means of the toe portion  20  may be formed of a rubber material which is not easily damaged even when the damping ball  30  is in direct friction against the ground during walking, so that it may be not required to install a separate outsole. 
         [0079]    The rubber material in the present invention means a material which is excellent in friction and does not easily worn away. Various materials having such functions may be used. 
         [0080]    In addition, when the damping ball  30  is mounted on the toe portion  20  of the midsole  100  by assembling it, to secure the excellent quality as well as the easiness of mounting and the rigidity in the mounted state, the assembly means is formed with an opening hole  21  formed in the bottom surface corresponding to the toe portion  20  of the midsole  1  and support grooves  22  formed in either one side or both sides of the upper end of the opening hole  21 . 
         [0081]    In addition, the damping ball  30  includes a support shaft  31  formed on an upper end of a ball  33 , which is tightly closed to a ground, to be tightly closed to an opening groove and a adhesion wing  32  formed on one side of two side of an upper end of the support shaft  31 , such that the support shaft  31  and the adhesion wing  32  are tightly fitted into the opening hole  21  and the support groove  22  constituting the assembly means. 
         [0082]    Although one embodiment of the ball  33  shown and described in the present invention is described as a perforated member penetrating through one side, the perforated member in the present invention may have excellent resilience in a collapsed state and these functions may be used in various forms possible. 
         [0083]    In addition, the damping ball  30  includes two support shafts  31   a  and  31   b  to enhance supporting force and to make the damping ball  30  closer to the bottom surface of the midsole in a state that the damping ball  30  is mounted on the assembly mean of the midsole. The support shafts  31   a  and  31   b  are spaced apart from each other by a predetermined distance such that the support shafts  31   a  and  31   b  are formed at left and right sides of the ball  33  having a through-hole, respectively. An adhesion wing  32 , which spreads outward from each of the support shafts  31   a  and  31   b , is provided, so that the ball  33  of the damping ball  30  is positioned closer to the bottom surface  7  of the midsole  1 , thereby realizing a sense of security when worn and providing excellent supportability with the ground in the assembled state. 
         [0084]    According to the present invention, the opening groove  21 , which is formed to be opened upward from the bottom surface  110  of the midsole  1 , may be spaced apart from the bottom surface of the toe portion of the midsole  1  by a predetermined distance. However, it is required to form the opening groove at a constant depth α. In this case, if possible, the depth α of the opening groove  21  is equal to or deeper than a length β of the support shaft  31  such that the damping ball  30  may be tightly closed to the bottom surface  110  of the midsole  1  by allowing the support shaft  31  to fixedly adhere into the opening groove  21  in a state that the support shaft  31  is extended. 
         [0085]    Thus, as shown in  FIG. 17 , when the damping ball  30  adheres to the midsole  1  by expanding the support shaft  31  of the damping ball  30 , of course, pressing force is generated in the adhesion state, so that the adhesion strength may be enhanced and the tight adhesion of the support shaft  31  with the bottom surface  7  of the midsole  1  may be excellent. 
         [0086]    Thus, various shoes may be designed according to the size and arrangement of the damping balls  30  on the bottom surface of the midsole, and various functional shoes may be provided by the hardness difference of the damping balls. 
         [0087]      FIG. 18  is a view showing the damping ball  30  having the support shaft  31  and the adhesion wing  32  which fixedly adheres to the bottom surface of the midsole  1  according to another embodiment of the present invention, where the upper surface of the midsole  1  is opened to facilitate assembling work in a state that the opening holes  21   a  and  21   b  and the support groove  22  are formed, and an insole B is provided on the upper surface of the midsole  1  as an essential element in a state that the adhesion wing  32  fixedly adheres to the support groove  22  after assembling. 
         [0088]    That is, the upper surface of the bottom surface of the midsole  1  in which the opening holes  21   a  and  21   b  and the receiving groove  22  are formed is opened, so that the supporting shaft  31  of the cushioning ball  30  and the adhesive blade  32  may improve the easiness of fitting assembly. 
         [0089]    As shown in  FIG. 19 , according to the present invention, the midsole includes two opening holes  21   a  and  21   b  by opening the bottom surface of the midsole  1  for coupling the damping ball  30  including two support shafts  31   a  and  31   b . The support groove  22  communicating with the opening holes  21   a  and  21   b  is formed outside each of the opening holes  21   a  and  21   b . The reinforcing shafts  23  are formed at each center of the opening holes  21   a  and  21   b  to enhance a support force of the support shafts  31   a  and  31   b  spaced apart from each other. 
         [0090]    The reinforcing shafts  23  are provided to enhance support and adhesion forces of the support shafts  31   a  and  31   b  while the two support shafts  31   a  and  31   b  formed on the damping ball  30  are spaced apart from each other. The reinforcing shafts  23  are provided with sealed through-holes to allow the damping ball  30  having the two support shafts  31   a  and  31   b  to have elasticity. 
         [0091]      FIG. 20  is a view showing an embodiment in which the elastic direction of the cushioning ball is maintained as the forward direction during the elastic operation and the midsole is slim. Curved grooves  111  are further provided outward of the opening holes  21   a  and  21   b  formed on the bottom surface  110  of the midsole  100  such that an upper portion of a ball  33  of the damping ball  30  is partially inserted into the bottom surface  110  of the midsole in a state that the damping ball  30  is coupled to the midsole  100 . An upper end of the ball simultaneously adheres to the curved groove  111  in a state that the support shafts of the damping ball are fitted into the opening holes  21   a  and  21   b . The support shafts of the damping ball are prevented from being tilted left or right even when the damping ball is subject to twisting due to a sudden change of force applied to the damping ball  30  in a state that a user wears a shoe having the midsole  1  and it is possible to make the midsole slim. 
         [0092]    In addition, according to the present invention, the curved groove  6  is equally applicable to even the case where the opening holes  21   a  and  21   b  are a single number or a pair. 
         [0093]    In addition, the thickness of the support shaft  31  of the damping ball  30  and the size and elasticity of the ball  33  of the damping ball  30  are variously selected to allow the midsole  1  to be suitable for various types of shoes so that the productivity may be improved and the cost may be reduced. 
         [0094]    For example, the damping ball  30  may be assembled in a block type on a predetermined portion of the bottom surface  110  of the midsole ( 100 ). The ball  33  of each damping ball  30  having a strong resilience may be attached to an outside of the midsole to correct a splay-footed step and to an inside of the midsole to correct a pigeon-toed step, such that incorrect steps are naturally corrected during walking. 
         [0095]    This is proposed as one embodiment, and it is possible to provide a shoe without a heel when the sizes of the balls of the damping ball are different from each other. When applying the midsole to a slippery shoe, it is possible to provide various types of midsole as well as ankle stretching. 
         [0096]    While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.