Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of mounting a resin-molded member. 
     2. Description of the Related Art 
     Generally, in audio and video apparatus, a magnetic tape is often used to record and play back information. The magnetic tape is wound around a pair of reels and conveyably retained within a cassette case. 
     For example, as shown in  FIG. 6 , a magnetic tape cassette  100  employed for business use at a broadcasting station includes an upper half  102  and a lower half  104  that form a case. A pair of reels  109  is rotatably supported inside the case. Each reel comprises a lower flange  105 , a hub  106  that is integrally fixed to an upper portion of the lower flange  105 , and an upper flange  108  that is mounted to an upper portion of the hub  106 . A magnetic tape T is wound around the pair of the reels  109 . A window  103  made of a clear plate is disposed at the upper half  102 . 
     A pair of reel holders  112  for pressing the reels  109  and a pair of compression coil springs  110  for pressing the reel holders  109  are interposed between the upper half  102  and the reels  109 , and the reels  109  are urged toward the lower half  104  by the reel holders  112 . The reel holders  112  respectively engage with a pair of the center caps  114 , and the center caps  114  are engaged with opening edges  103 M formed on the window  103 . 
     As shown in  FIG. 7 , a pivot  116  is disposed at the central portion of the upper surface of the hub  106 , and the upper portion of the pivot  116  has a spherical surface. The pivot  116  is pressed by the reel holders  112  to swingably retain the reels  109 . Further, the pivot  116  is molded integrally with the hub  106 , and is often made of a general-use material such as acrylnitrilbutadiene (ABS) resin or polystyrene (PS). 
     The reel holder  112  is a hat-shaped member and has an inner bottom surface  112 B abutting the pivot  116 , and is often made of a general-use polyacetal (POM) resin. 
     From a viewpoint of traveling stability or durability of a tape, it is preferable that the pivot  116  and the hub  106  are molded into different members, and having the member including the pivot  116  mounted to the hub  106 . 
     However, if the pivot  116  and the hub  106  are molded into different members, fitting portions or engagement portions of the member including the pivot  116  and the hub  106  need to be formed and assembled with high precision. Further, each of the components must be stored until shrinkage due to molding of each component stops. Therefore, a problem has been caused in that productivity deteriorates. 
     This problem is not limited to reels used for the magnetic tape cassette  100 , but often occurs with a mounting member (the hub body  106  or the member including the pivot  116 ) and a member to be mounted (the hub body  106  or the member including the pivot  116 ), at least one of which is a resin-molded. 
     SUMMARY OF THE INVENTION 
     In view of the aforementioned facts, an object of the present invention is to provide a method of mounting a mounting member to a member to be mounted, at least one of which is resin-molded, with high productivity. 
     A first aspect of the present invention is a method of mounting a mounting member onto a member to be mounted, at least one of which is resin-molded, comprising the steps of: molding the mounting member and the member to be mounted; and mounting the mounting member to the member to be mounted, utilizing post-molding shrinkage. 
     For example, if the mounting member is a resin-molded member, when the mounting member is molded, the dimension is larger so as to correspond to post-molding shrinkage of the mounting member which has just been molded. The mounting member which has just been molded is aligned with the member to be mounted, and mounted thereto. 
     For example, if both of the mounting member and the member to be mounted are resin-molded members, the mounting member and the member to be mounted are molded at different times. Both members can be mounted to each other by utilizing post-molding shrinkage. 
     Accordingly, neither pressing of the mounting member into the member to be mounted nor forming of fitting portions of the members with high precision is needed. Accordingly, since post-molding shrinkage is utilized, components can be assembled without being stored immediately after molding. Consequently, the molded mounting member and the member to be mounted are mounted to each other with high productivity, and components or the like can be assembled. This mounting method is especially advantageous when large members are mounted. 
     A mounting formation of the mounting member and the member to be mounted is not limited to, but can be in a fitted state or a state with a predetermined clearance. 
     A second aspect of the present invention is a method of mounting a mounting member onto a member to be mounted, the mounting member and the member to be mounted being components of a magnetic tape cassette that are assembled together in the magnetic tape cassette, and at least one of which is resin-molded, the method comprising the steps of: molding the mounting member and the member to be mounted; and assembling the mounting member and the member to be mounted together, utilizing post-molding shrinkage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a developed perspective view of a magnetic tape cassette according to a first embodiment of the present invention; 
         FIG. 2  is a side cross-sectional view showing a pivot member that has just been resin-molded being mounted on a hub body that has been resin-molded and cooled; 
         FIG. 3  is a side cross-sectional view showing the pivot member of the first embodiment fitted onto the hub body; 
         FIG. 4  is a side cross-sectional view showing a pivot member that has been resin-molded and cooled being inserted into an opening in a hub body that has just been resin-molded, according to a second embodiment of the present invention; 
         FIG. 5  is a side cross-sectional view showing the pivot member fitted into the hub body, according to the second embodiment of the present invention; 
         FIG. 6  is a developed perspective view of a structure of a conventional magnetic tape cassette; and 
         FIG. 7  is a side cross-sectional view of a reel of the conventional magnetic tape cassette. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Description of reels that are housed in a magnetic tape cassette according to embodiments of the present invention will now be given. 
     First Embodiment 
     First, description of a first embodiment of the present invention will be given. As shown in  FIG. 1 , a magnetic tape cassette (betacam L cassette)  10  that is used for business use by a broadcasting station includes an upper half  12  and a lower half  14  that form a case. 
     A pair of reels  20  is rotatably supported inside the case. Each of the pair of the reels  20  has a lower flange  24 , a hub  26  that is integrally fixed to an upper portion of the lower flange  24 , and an upper flange  28  that is mounted to an upper portion of the hub  26 . A magnetic tape T is wound around the reels  20 . Clear plate windows  13 A and  13 B are disposed at the upper half  12 . 
     A hat-shaped reel holder  32 A, which abuts an internal bottom surface of the reel  20 A, and a compression coil spring  30 A, which presses the reel holder  32 A, are interposed between the upper half  12  and the reel  20 A (see  FIG. 1 ). The reel holder  32 A urges the reel  20 A toward the lower half  14  and engages with a center cap  34 A that engages with an opening edge of an opening  13 MA formed in the window  13 A. 
     A reel holder  32 B and a compression coil spring  30 B are similarly interposed between the upper half  12  and the reel  20 B. The reel holder  32 B urges the reel  20 B toward the lower half  14 . The reel holder  32 B engages with a center cap  34 B, and the center cap  34 B engages with an edge of an opening  13 MB formed in the window  13 B. 
     A pair of guide rollers  44  is disposed in the vicinity of an opening  16  at the front side of the magnetic tape cassette  10  to guide the magnetic tape T when it is played or rewound. Each of the guide rollers  44  is formed into a so-called barrel shape and includes an outer periphery that swells at an intermediate portion thereof. 
     The magnetic tape cassette  10  includes tape pads  46  that slidably contact and press an undersurface of the magnetic tape T with an appropriate urging force to thereby prevent the magnetic tape T from slackening. 
     The magnetic tape cassette  10  includes a pair of shafts  50  that are typically fixed to and project from an inner wall surface  14 U of the lower half  14 . Each of the shafts  50  penetrates a through hole  44 H that is formed along the central axis of each guide roller  44 . The guide rollers  44  are axially and rotatably supported around the shafts  50 . 
     As shown in  FIGS. 2 and 3 , the hub  26  includes a hub body  52 , and a hat-shaped pivot member  54  which is fitted onto and covers the hub body  52  from above. 
     A substantially semispherical pivot  36  is integrally molded with the central portion of a pivot member  54  at the upper side thereof. The pivot  36  is pressed by, for example, the reel holder  32 A to thereby swingably retain the reel  20 . The hub body  52  is formed by a general resin such as acrylnitrilbutadiene (ABS) or polystyrene (PS), and the pivot member  54  is made of a highly slick resin such as polyacetal (POM) resin. 
     The reels  20  are formed by molding the hub body  52  and the lower flange  24  integrally with each other, and then molding the pivot member after a predetermined amount of time. The amount of predetermined time is equivalent to a period in which the hub body  52  cools naturally and almost stops shrinking, and is ordinarily a day or so. 
     For example, considering that shrinkage of the hub body  52  is generally 5/1000 when the hub body  52  is formed by acrylnitrilbutadiene (ABS)resin, the pivot member  54  is molded such that an inner diameter D of the freshly molded pivot member  54  and an outer diameter d of a portion of the hub body  52  after cooling, which portion is fitted into the pivot member  54 , substantially correspond to each other. Namely, the dimension of the metal mold with which the hub body  52  is molded is predetermined considering that shrinkage of the outer diameter d of the fitting portion of the hub body  52  after cooling becomes 995/1000 as compared to the freshly molded pivot member  54 . 
     The pivot member  54 , which has just been molded, is capped over the hub body  52 , and clamps the hub body  52  due to the shrinkage of the pivot member  54 . 
     Therefore, neither pressing of the pivot member  54  into the hub member  52  nor molding of the fitting portion with high dimensional precision is needed. Accordingly, even if the pivot member  54  and the hub member  52  are molded into different members, the reels  20  can be manufactured with high productivity. 
     As long as the pivot member  54  can be fitted onto the hub body  52 , the internal diameter D of the pivot member  54  which has just been molded, can be slightly larger than the outer diameter d of the fitting portion of the hub body  52  after cooling. Accordingly, further allowance of dimensions of fitting portions of the pivot member  54  and the hub body  52  becomes possible. Further, the lower flange  24  and the hub body  52  can be molded into different members, and the hub body  52  is fitted into the lower flange  24 . 
     Second Embodiment 
     Description of a second embodiment of the present invention will now be given. In the present embodiment, portions identical to those shown in the first embodiment of the present invention are denoted by the same reference numerals and description thereof is omitted. 
     The second embodiment is similar to the first embodiment except that, as shown in  FIG. 4 , configurations of a pivot member  64  and a hub body  62  that structures a hub  66  are different from those in the first embodiment, and the pivot member  64  is molded before the hub body  62  is molded. 
     A substantially semispherical surface  64 S is formed at the top of the pivot member  64  and contacts the inner bottom surfaces of, for example, the reel holders  32 A (see  FIG. 1 ). A recess  64 H that engages with the hub body  62  is formed around the pivot member  64  at the central portion thereof. 
     An opening  62 M into which the pivot member  64  is fitted is formed in the upper central portion of the hub body  62 . 
     To manufacture the hub  66 , the pivot member  64  is first molded, and then the hub body  62  is molded after a predetermined amount of time. 
     The hub body  62  is molded such that a diameter D of the opening  62 M of the hub body  62 , which has just been molded, and an outer diameter d of a lower end  64 L of the pivot member  64  after cooling becomes almost the same. 
     The pivot member  64 , which has just been molded, is inserted into the opening  62 M and fitted into the hub body  62  due to shrinkage of the hub body  62 . 
     Accordingly, neither pressing of the pivot member  64  into the hub body  62  nor molding of the fitting portions of the pivot member  64  and the hub body  62  with high dimensional precision is needed. Consequently, even if the pivot member  64  and the hub body  64  are molded into different members, reels  70  can be manufactured with high productivity. 
     Similar to the first embodiment, as long as the pivot member  64  can be fitted into the hub body  62 , the diameter D of the opening  62 M, which has just been molded, can be slightly larger than the outer diameter d of the lower end  64 L of the pivot member  64  after cooling. 
     Although the invention has been described with reference to specific embodiments, the invention is not limited to any of the details of description, unless otherwise specified, but must be constructed broadly within its spirit and scope as set out in the accompanying claims. 
     Since the invention is structured as described above, the mounting member can be mounted with high productivity. Further, the components which are just molded can be assembled without being temporarily stored for cooling.

Technology Category: g