Patent Publication Number: US-2012040035-A1

Title: Captive screw fabrication mold

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to captive screw fabrication technology and more particularly, to a captive screw fabrication mold, which prevents overflow of the applied molten material into the tool groove in the top protrusion at the top side of the head of each lock screw when molding a knob on the head of each lock screw for captive screw. 
     2. Description of the Related Art 
     When fastening panel frames together, a positioning screw formed of a cap-shaped knob, a ring and a screw nail is usually used. During installation, the screw nail and the ring are secured to the first panel frame, and then the cap-shaped knob is rotated to drive the screw nail into the second panel frame, and then a hand tool is used to fasten tight the screw nail, affixing the first and second panel frames together. This panel frame joining method can be used in a machine tool to join panel frames together. The power drive and speed-adjustment unit of a machine tool are generally provided inside the housing. When the power drive or speed-adjustment unit fails, or when an adjustment of the speed is necessary, the panel frames must be unlocked. When unlocked the panel frames, the positioning screws may be missed accidentally. 
     To facilitate detachable installation, captive screws are developed. Conventional captive screws are commonly formed of a cap member, a screw, a spring member and a mounting barrel, and adapted for locking into plate on a first panel frame, enabling the easy installation and removal of attached pieces without release of the screw. However, after insertion of the screw into the cap member during the assembly process, a secondary processing process is necessary to secure the metal cap member to the head of the screw, wasting much time and labor. Further, the cap member may be permanently deformed when fastening the cap member and the screw together. 
     To avoid this problem, plastic cap member may be used and directly molded on the head of the screw. The plastic cap member has damp-proof and anti-corrosion characteristics. Further, the plastic cap member can be made in any of a variety of colors. However, because the screw is made through a cold forging processing process, the head and threaded shank of the screw may be not kept in a perfect concentric relationship. Further, the screw head a tool groove on the top side of the head. The tool groove can be a keystone groove, crossed groove, hexagonal groove, or key groove for the positioning of a keystone tip screwdriver, Phillips tip screwdriver, hexagonal wrench, open-end wrench, socket wrench, or ratchet wrench. When molding the plastic cap on the head of the screw, the molten material may flow into the tool groove of the screw. If the tool groove is stuffed with the applied material, the finished captive screw will become a defective product, not operable by a hand tool (such as a screwdriver). 
     Therefore, it is desirable to provide a way that prevents overflow of the applied molten material during molding of a cap member on the head of a screw for captive screw, improving the yield and quality of the fabrication of captive screws. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is therefore an object of the present invention to provide a captive screw fabrication mold, which prevents overflow of the applied molten material during molding of a cap member on the head of a screw for captive screw, improving the yield and quality of the fabrication of captive screws. 
     To achieve this and other objects of the present invention, a captive screw fabrication mold comprises a bottom die having a tubular post vertically disposed in each bottom die cavity thereof for holding a lock screw for molding, and an upper die that has an annular rib vertically downwardly suspending in each upper die cavity thereof for stopping against the head of the lock screw in the associating bottom die cavity around the top protrusion of the lock screw to isolate the molding chamber in each upper die cavity, avoiding overflow of the applied molten material into the tool groove in the top protrusion of each lock screw. 
     Further, an annular groove is defined on the top side of the head of the lock screw between the top protrusion of the lock screw and the molded cap-shaped knob at the head of the lock screw so that a user can insert a tool into the tool groove in the top protrusion of the lock screw accurately without touching the cap-shaped knob, facilitating operation of the attached tool. 
     Further, the vertical length of the annular rib has a certain height so that so that a gap is left inside the annular rib between the upper die and the top wall of the top protrusion of the lock screw when the upper die is closed on the bottom die to stop the annular rib against the top wall of the top protrusion of the lock screw, avoiding damaging the top protrusion. 
     Further, the annular rib in each upper die cavity can be formed integral with a sliding block in one respective stepped sliding slot, and a spring member is provided in the sliding slot and stopped against sliding block to impart a downward pressure to the sliding block against the head of the lock screw. Thus, the annular rib can be positively stopped against the top wall of the head of the lock screw around the top protrusion without causing any damage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a captive screw fabrication mold in accordance with the present invention. 
         FIG. 2  is a sectional view, in an enlarged scale, of the captive screw fabrication mold shown in  FIG. 1 . 
         FIG. 3  is a schematic sectional side view of a part of the captive screw fabrication mold in accordance with the present invention, showing a lock screw inserted through the post in one bottom die cavity of the bottom die and the annular rib in the associating upper die cavity of the upper die pressed on the top wall of the head of the lock screw. 
         FIG. 4  corresponds to  FIG. 3 , showing a molten material filled in the upper die cavity of the upper die and the associating bottom die cavity of the bottom die. 
         FIG. 5  is an exploded view of a captive screw according to the present invention. 
         FIG. 6  is a sectional assembly view of the captive screw shown in  FIG. 5 . 
         FIG. 7  is an applied view of the captive screw according to the present invention. 
         FIG. 8  illustrates an alternate form of the captive screw fabrication mold in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1˜3 , a captive screw fabrication mold in accordance with the present invention comprises a bottom die  1  and an upper die  2 . 
     The bottom die  1  comprises a plurality of bottom die cavities  10  inwardly curved from the top wall thereof and arranged at selected locations, a post  11  vertically disposed in each bottom die cavity  10  at the center, a vertical through hole  110  axially extending through the post  11  in each bottom die cavity  10  in communication with the space outside the bottom die  1 , a step  101  located on the peripheral wall of each bottom die cavity  10 , a series of teeth  102  located on the step  101  in each bottom die cavity  10 , a curved surface portion  103  formed in each bottom die cavity  10  between the associating teeth  102  and the associating post  11  at the bottom side and extending around the associating post  11 , a bottom main flow passage  13  located on the top wall thereof, a plurality of bottom sub flow passages  12  located on the top wall thereof and extending across the bottom main flow passage  13 , and a plurality of bottom filling grooves  121  located on the top wall thereof and respectively connected between the bottom sub flow passages  12  and the bottom die cavities  10 . 
     The upper die  2  comprises a plurality of upper die cavities  20  inwardly curved from the bottom wall thereof and arranged at locations corresponding to the bottom die cavities  10  of the bottom die  1 , an annular rib  21  vertically downwardly suspending in each upper die cavity  20  and defining with the peripheral wall of the associating upper die cavity  20  a molding chamber  201 , a series of teeth  2011  disposed in the molding chamber  201  in each upper die cavity  20 , a upper main flow passage  23  located on the bottom wall thereof, a plurality of upper sub flow passages  22  located on the bottom wall thereof and extending across the upper main flow passage  23 , a plurality of upper filling grooves  221  located on the bottom wall thereof and respectively connected between the upper sub flow passages  22  and the upper die cavities  20 , and a filling hole  24  cut through top and bottom walls thereof in communication with the upper main flow passage  23  for the filling of a molten material. 
     The captive screw fabrication mold is adapted for molding a cap-shaped knob  34  on each of a number of lock screws  3 . The lock screw  3  has a threaded shank  31 , a head  32  located on one end of the threaded shank  31 , a top protrusion  33  raised from the top wall of the head  32  opposite to the threaded shank  31  and a tool groove  331  formed in the top protrusion  33  and capable of being engaged by a driving tool or implement, such as a screwdriver (not shown). After insertion of one lock screw  3  in the vertical through hole  110  in the post  11  in each bottom die cavity  10  of the bottom die  1  and closing of the upper die  2  on the bottom die  1 , a molten material is filled through the filling hole  24  into the upper die cavities  20  and the bottom die cavities  10 , molding a cap-shaped knob  34  on the head  32  of each lock screw  3 . 
     During application, the threaded shank  31  of each lock screw  3  is inserted into the vertical through hole  110  in the post  11  in one bottom die cavity  10  of the bottom die  1  to let the head  32  of the each lock screw  3  be rested on the topmost edge of the respective post  11 . Thereafter, the upper die  2  is closed on the bottom die  1  to press the annular rib  21  in each upper die cavity  20  on the top wall of the head  32  of each lock screw  3  around the top protrusion  33 , thereby isolating the respective molding chamber  201 . At this time, the upper filling grooves  221 , upper sub flow passages  22 , upper main flow passage  23  and filling hole  24  of the upper die  2  are kept in communication with the bottom filling grooves  121 , bottom sub flow passages  12  and bottom main flow passage  13  of the bottom die cavities  10 . 
     Further, the teeth  2011  in the molding chamber  201  in each upper die cavity  20  of the upper die  2  and the teeth  102  on the step  101  in each bottom die cavity  10  of the bottom die  1  can be made having a V-shaped, U-shaped, arched, semi-circular, wave-like or trapezoidal cross section. 
     Further, the post  11  in each bottom die cavity  10  of the bottom die  1  can be a cylindrical post, rectangular post or polygonal post. 
     Further, the top protrusion  33  of the lock screw  3  is a flat, circular protrusion concentrically located on the top wall of the head  32 . Further, the tool groove  331  of the lock screw  3  can be a keystone groove, crossed groove, hexagonal groove, or key groove for the positioning of a keystone tip screwdriver, Phillips tip screwdriver, hexagonal wrench, open-end wrench, socket wrench, or ratchet wrench. The excellent concentricity between the head  32  and top protrusion  33  of the lock screw  3  enables the top protrusion  33  of the lock screw  3  to be accurately inserted into the annular rib  21  in the respective upper die cavity  20  of the upper die  2  upon closing of the upper die  2  on the bottom die  1 . Thus, when molding a cap-shaped knob  34  on the head  32 , the applied molten material is kept in the molding chamber  201  in each upper die cavity  20  and prohibited by the annular rib  21  in each upper die cavity  20  from flowing to the top protrusion  33  of each loaded lock screw  3 . 
     Referring to  FIGS. 4˜6  and  FIG. 1  and  FIG. 3  again, during application of the present invention, a molten material (molten plastic or rubber) is filled through the filling hole  24  into the upper die cavities  20  and the bottom die cavities  10  through the upper main flow passage  23  and bottom main flow passage  13  and the upper sub flow passages  22  and bottom sub flow passages  12  via the bottom filling grooves  121  and upper filling grooves  221  to fill up the molding chamber  201  in each upper die cavity  20  of the upper die  2  and each bottom die cavity  10  of each bottom die  1 , thereby forming a cap-shaped knob  34  on the head  32  of each loaded lock screw  3 . Subject to the design of the teeth  2011  in the molding chamber  201  in each upper die cavity  20  of the upper die  2  and the teeth  102  on the step  101  in each bottom die cavity  10  of the bottom die  1  and the design of the curved surface portion  103  in each bottom die cavity  10  of the bottom die  1 , the cap-shaped knob  34  that is molded on the head  32  of each lock screw  3  has a toothed design on the periphery and a bottom coupling flange  341  inwardly curved from the bottom side thereof. Each lock screw  3  that has a cap-shaped knob  34  molded thereon can then be assembled with one barrel  37  and one spring member  36  to form a captive screw  4 . 
     When molding a cap-shaped knob  34  on the head  32  of each lock screw  3  in the captive screw fabrication mold, the annular rib  21  in each upper die cavity  20  of the upper die  2  is pressed on the top wall of the head  32  of the respective lock screw  3  around the top protrusion  33  to isolate the respective molding chamber  201 , avoiding flowing of the applied molten material to the tool groove  331  in the top protrusion  33  of each loaded lock screw  3 . The excellent concentricity between the head  32  and top protrusion  33  of the lock screw  3  enables the top protrusion  33  of the lock screw  3  to be accurately inserted into the annular rib  21  in the respective upper die cavity  20  of the upper die  2  upon closing of the upper die  2  on the bottom die  1 . Therefore, the top protrusion  33  of the lock screw  3  will not be damaged by the corresponding annular rib  21  when closing the upper die  2  on the bottom die  1 , and the tool groove  331  in the top protrusion  33  of each loaded lock screw  3  is kept clean. After molding of a cap-shaped knob  34  on the head  32  of each lock screw  3 , an annular groove  35  is defined on the top side of the head  32  of each lock screw  3  between the top protrusion  33  and the cap-shaped knob  34 . Thus, a user can insert a tool into the tool groove  331  in the top protrusion  33  of the lock screw  3  accurately without touching the cap-shaped knob  34 , facilitating operation of the attached tool. Thus, the invention greatly improves the yield and quality of the fabrication of captive screws  4 . 
     Further, the annular rib  21  in the respective upper die cavity  20  of the upper die  2  can be made having raised portions (not shown) located on the outer wall thereof so that the molded cap-shaped knob  34  can have decorative recessed portions on the outer wall thereof. The raised portions of the annular rib  21  can have a circular, oval, arched, geometric, polygonal profile or irregular profile. 
     Referring to  FIG. 7  and  FIGS. 5 and 6  again, after molding of the cap-shaped knob  34  on the head  32  of one lock screw  3 , the lock screw  3  is assembled with one barrel  37  and one spring member  36  to form a captive screw  4 . The barrel  37  comprises a top coupling flange  372  extending around the periphery of the top end thereof, a contracted bottom mounting portion  373  axially extended from the bottom end thereof, a stepped axial hole  370  extending through the top and bottom ends and a step  371  defined in the stepped axial hole  370 . During the assembly process, the spring member  36  is sleeved onto the threaded shank  31  of the lock screw  3  and stopped between the step  371  in the stepped axial hole  370  of the barrel  37  and the bottom wall of the head  32  of the lock screw  3 , and the bottom coupling flange  341  of the cap-shaped knob  34  is coupled to the top coupling flange  372  of the barrel  37 . When assembled, the cap-shaped knob  34  can be moved with the lock screw  3  axially relative to the barrel  37 . 
     During application of the captive screw  4 , the contracted bottom mounting portion  373  of the barrel  37  is fixedly bonded to a mounting through hole  50  on a first metal panel  5 . At this time, the user can thread the threaded shank  31  of the lock screw  3  into a mounting screw hole  60  on a second metal panel  6  to lock the first metal panel  5  to the second metal panel  6 . 
     Referring to  FIGS. 3 and 4  again, the vertical length of the annular rib  21  can be greater than the height of the top protrusion  33  of the lock screw  3  so that a gap  202  is left inside the annular rib  21  between the upper die  2  and the top wall of the top protrusion  33  of the lock screw  3  when the upper die  2  is closed on the bottom die  1  to stop annular rib  21  against the head  32  of the lock screw  3 , avoiding damage. 
     Referring to  FIG. 8  and  FIG. 1  again, as an alternate form of the present invention, the upper die  2  further comprises a plurality of locating holes, for example, threaded holes  205  located on the top wall thereof corresponding to the upper die cavities  20 , a plurality of stepped sliding slots  203  respectively axially connected between the threaded holes  205  and the upper die cavities  20 , a step  204  defined in each stepped sliding slots  203 , a sliding block  211  inserted into each stepped sliding slot  203  and stoppable by the step  204  in the associating stepped sliding slot  203 , a cap  26  threaded into each threaded hole  205  and a spring member  25  inserted in each stepped sliding slot  203  and stopped between the associating cap  26  and the associating sliding block  211  to impart a downward pressure to the associating sliding block  211  against the head  32  of the lock screw  3  in the associating upper die cavity  20 . The annular rib  21  in each upper die cavity  20  according to this embodiment is formed integral with the bottom wall of the sliding block  211  in the associating stepped sliding slot  203 . However, the annular rib  21  of each sliding block  211  has a height relatively greater than the embodiment shown in  FIGS. 3 and 4 . When the upper die  2  is closed on the bottom die  1  to stop the annular rib  21  of each sliding block  211  against the head  32  of the lock screw  3  in the associating upper die cavity  20 , the spring member  25  is compressed, and a relatively greater gap  202  is left in the annular rib  21  between the top protrusion  33  of the lock screw  3  and the bottom wall of the associating sliding block  211 , avoiding damage. When the upper die  2  is opened from the bottom die  1  after a molding operation, the external pressure is released from the spring member  25 , and therefore the spring member  25  returns to its former shape to return the associating sliding block  211  to its former position, i.e., to stop the associating sliding block  211  against the step  204  in the associating stepped sliding slot  203 . 
     The aforesaid two embodiments are simply exemplars of the present invention and not to be used as limitations. During the use of the captive screw fabrication mold, captive screws  3  are loaded in the bottom die cavities  10  of the bottom die  1 , and then the upper die  2  is closed on the bottom die  1  to force the annular rib  21  in each upper die cavity  20  against the head  32  of the respective lock screw  3  around the top protrusion  33  of the respective lock screw  3 , isolating the associating molding chamber  201  and avoiding flowing of the applied molten material to the tool groove  331  in the top protrusion  33  of each loaded lock screw  3 . Further, an annular groove  35  is defined on the top side of the head  32  of each lock screw  3  between the top protrusion  33  and the molded cap-shaped knob  34  so that a user can insert a tool into the tool groove  331  in the top protrusion  33  of the lock screw  3  accurately without touching the cap-shaped knob  34 , facilitating operation of the attached tool. 
     In actual practice, the captive screw fabrication mold of the present invention has the following advantages and features:
     1. An annular rib  21  is disposed in each upper die cavity  20  for stopping against the head  32  of the respective loaded lock screw  3  to isolate the associating molding chamber  201 , avoiding flowing of the applied molten material to the tool groove  331  in the top protrusion  33  of each loaded lock screw  3 . After molding of the cap-shaped knob  34  on each lock screw  3 , the tool groove  331  of each lock screw  3  is kept clean, facilitating operation of a tool means during installation of the finished captive screw.   2. An annular groove  35  is defined on the top side of the head  32  of each lock screw  3  between the top protrusion  33  and the molded cap-shaped knob  34  so that a user can insert a tool into the tool groove  331  in the top protrusion  33  of the lock screw  3  accurately without touching the cap-shaped knob  34 , facilitating operation of the attached tool.   3. The vertical length of the annular rib  21  can be greater than the height of the top protrusion  33  of the lock screw  3  so that a gap  202  is left inside the annular rib  21  between the upper die  2  and the top wall of the top protrusion  33  of the lock screw  3  when the upper die  2  is closed on the bottom die  1  to stop the annular rib  21  against the top wall of the top protrusion  33  of the lock screw  3 , avoiding damaging the top protrusion  33 .   4. In an alternate form of the present invention, the upper die  2  is made having a locating hole (threaded hole)  205  located on the top wall thereof corresponding to each upper die cavity  20 , a stepped sliding slot  203  in communication between each locating hole (threaded hole)  205  and the associating upper die cavity  20 , a step  204  defined in each stepped sliding slot  203 , a sliding block  211  inserted into each stepped sliding slot  203  and stoppable by the step  204  in the associating stepped sliding slot  203 , a cap  26  threaded into each locating hole (threaded hole)  205  and a spring member  25  inserted in each stepped sliding slot  203  and stopped between the associating cap  26  and the associating sliding block  211  to impart a downward pressure to the associating sliding block  211  against the head  32  of the lock screw  3  in the associating upper die cavity  20 ; the annular rib  21  in each upper die cavity  20  is formed integral with the bottom wall of a sliding block  211  that is inserted into each stepped sliding slots  203  and stoppable by the step  204  in the associating stepped sliding slot  203 , a cap  26  threaded into each threaded hole  205  and a spring member  25  inserted in each stepped sliding slot  203  and stopped between the associating cap  26  and the associating sliding block  211  to impart a downward pressure to the associating sliding block  211  against the head  32  of the lock screw  3  in the associating upper die cavity  20 , and the annular rib  21  in each upper die cavity  20  is formed integral with the bottom wall of the sliding block  211  in the respective upper die cavity  20 . Thus, the annular rib  21  can be positively stopped against the top wall of the head  32  of the lock screw  3  without causing any damage.   

     Although particular embodiment of the invention have been described in detail for purposes of illustration, it will be obvious that various modifications and enhancements may be made therein without departing from the spirit and scope of the present invention as defined in the disclosure and the claims.