Clasp utilizing attractive force of permanent magnet
This application is related to the following co-pending applications of the applicant: Ser. No. 477,838 filed Mar. 25, 1983, now U.S. Pat. No. 4,453,294 a continuation of Ser. No. 309,762 filed Oct. 8, 1981 (now abandoned), which was a continuation of Ser. No. 89,134 filed Oct. 19, 1979 (now abandoned); Ser. No. 222,984, filed Jan. 7, 1981; Design Ser. No. 258,039, filed Apr. 27, 1981. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a clasp utilizing the attraction of a permanent magnet, and more particularly to obviating such inconveniences as disruption of magnetic records by magnetic flux from such clasps by preventing the flux lines of the magnet from leaking externally. 
     2. Description of the Prior Art 
     There have been proposed various clasps which utilize the attraction of a permanent magnet, and almost all of them are conventionally aimed at effectively using the magnetic attraction of a permanent magnet rather than taking counter-measures to prevent disruption of magnetic records by the permanent magnet. 
     As great innovations have been achieved in the recording technology recently and magnetic recording means such as tapes, cards or notes have become household items, safeguarding those means demands special attention and care. 
     We have entered an era where articles having magnetic records are used daily, such as various magnetic tapes and magnetic disks to tickets for transportation, admission tickets, or cash cards for bank accounts. 
     The content of such magnetic records as recording tapes, etc., however, can be lost because they are easily destroyed when placed under the influence of the magnetic flux lines of a magnet and the occurrence of such a disruption can not easily be observed from outside appearance. 
     BRIEF SUMMARY OF THE INVENTION 
     The clasp according to the present invention was contrived especially as a counter-measure for the above mentioned problems. It can obviate the disruption of magnetic records contained in tapes, etc. by minimizing the leakage of magnetic flux from a magnet used in a clasp and by preventing the magnetic polar surface of the magnet from contacting directly the tapes, etc. 
     The present invention is characterized in that the lines of magnetic induction inherent to a magnet is converged on the magnetic attraction end surface rather than diverged to outside in order to maximize the attracting power of the magnet which has only a specific number of magnetic induction lines. It is characterized more particularly in that the magnetic induction lines of a permanent magnet used are induced at respective poles to form magnetic fields and prevented from diverging to outside so that the paths of those magnetic induction lines are directed at a center hole bored on the magnet. 
     The present invention has been embodied as a clasp or lock for bags, boxes, bands or chains and is expected to have wide potentiality in application for various fields such as handbags, suitcases, daypacks, purses and pouches, belts, shoulder bag straps, necklaces, pendants, etc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be further described in greater detail with reference to the accompanying drawings wherein; 
     FIG. 1 is a cross sectional view to show the operational effects of a female clasp part of an embodiment of the present invention, 
     FIG. 2 is a perspective exploded view of a male/female clasp, 
     FIG. 3 is a perspective exploded view of the parts of the clasp of FIG. 2, 
     FIGS. 4 to 6 are cross-sectional views of embodiments of the invention to show how to construct the magnetic paths, 
     FIG. 7 a cross-sectional view of another embodiment, 
     FIGS. 8 to 14 are cross-sectional views to show other various embodiments of the clasp according to the present invention and 
     FIGS. 15 to 18 are cross-sectional views to show still further embodiments of the invention. 
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will now be explained together with the operational effects attained by them. 
     In FIG. 1 a female part a is shown in cross section for facilitating understanding of the typical operational feature of the clasp according to the present invention wherein a permanent magnet 1 having a hole 1a along the magnetic pole surface is provided with a ferromagnetic metal plate 2 on one of the magnetic poles in a manner to close the said hole 1a, a ferromagnetic metal plate 3 having a hole 3a communicating with the hole 1a is provided on the other magnetic pole surface and the metal plates 2 and 3 and the magnet 1 are encased integrally in a case 4 made of a non-magnetic material. 
     The case 4 is constructed so as to form a hollowed-out dish shape at the upper surface as shown and is provided with tabs 4a and at the peripheral edge thereof and a hole 4b at the center with a collar 4b&#39; on the internal edge thereof which protrudes into the hole 3a and also abuts against the surface thereof. The parts mentioned above are assembled integrally by successively attaching the metal plate 3, the magnet 1 the metal plate 2 by bending the tabs 4a inwardly toward the metal plate surface 2. A protruding peripheral edge 4c is constructed by bending the end of the internal bottom of the case 4, or the end which abuts against the outer periphery of the metal plate 3, toward the direction which perpendicularly crosses the magnetic pole surface of the magnet 1. 
     When a ferromagnetic protrusion 2a is provided at the hole 1a of a female part of the structure mentioned above, the magnetic induction lines of magnet 1 are generated as illustrated by a dot-and-dash line and are not diverged externally at all. By providing the metal plates 2 and 3 on the magnetic pole surface of the magnet 1 the magnetic induction lines are made to converge to the metal sheets 2 and 3 to form separate and respective magnetic fields. The converged magnetic induction lines are further made to communicate with respective magnetic fields via the protrusion 2a which has the least magnetic resistance and thus is suitable as the path therefor. 
     Provision of the metal sheets 2 and 3 eliminates possible generation of magnetic induction lines outside the female part a and leads to such advantageous effects as the maximum lines of magnetic induction of the magnet are converged to one location, thereby eradicating the inconveniences entailed by the leakage of magnetic induction lines as in the prior art. 
     Even if a magnetic recording means such as a magnetic tape x is placed near the female part a, the magnetic record therein would not become destroyed by the magnetic induction lines of the magnet 1 at all, thus presenting a new and convenient possibility that magnetic tape or cards of this type can be handled in the same area as the female clasp means. More particularly, the magnetic disruption lines of the magnet 1 are converged on the metal plates 2 and 3 to form a closed circuit via the protrusion 2a to prevent the leakage from the magnet 1, the metal plates 2 and 3. The magnet 1 and the metal plates 2 and 3 are simultaneously housed in a case made of non-magnetic materials so as to eliminate the possibility for magnetic tapes or cards coming into contact with the magnet 1 or the metal sheets 2 and 3. 
     The magnetic tapes, etc. are forced to contact with the female clasp a only through the magnetic gap of a thickness equal to the case 4 even if they are brought close thereto, thereby completely preventing the records contained therein from becoming destroyed. 
     Provision of the protruding periphery 4c on the case 4 results in a wider magnetic gap y between the magnetic pole surface and the tape x, thereby providing a safeguard on the magnetic pole surface where magnetic disturbance most often occurs. The protruding periphery is further advantageous in that it effectively prevents tapes x etc. from falling into the hole 1a which is the only place magnetic induction lines are exposed so as to effectively prevent the destruction of the record therein. The protrusion 4c further prevents the lateral displacement of a male clasp part b which is separately provided. It can completely prevent undesired disengagement of the clasps caused often by lateral forces exserted in pulling or peeling off which is heretofore considered the most formidable problem. 
     The male clasp part b is engageable within the protrusion 4c of the female clasp part a, and comprises a ferromagnetic metal plate 5 closely attracted on the magnetic pole surface and protrusion 5a of ferromagnetic material which contacts with the top end of the protrusion 2a within the hole 1a. As shown in FIG. 4, the parts are integrally assembled by inserting a rod of a small diameter on the protrusion 5a through the metal plate 5 and a washer 6 which is engaged on the metal sheet 5 and by upsetting the top protruding end 5a&#39;. 
     The female clasp part a is also assembled by mounting a washer 6 on the metal plate 2, inserting a rod of a small diameter on the protrusion 2a through the metal plate 2 and a washer 6 and by upsetting the protruding end 2a&#39;. 
     The fastening washer 6 as illustrated in FIG. 15 is adapted to extend legs 6a and 6a through such materials as leather 7, to which the clasp according to the present invention is applicable, and through slots in a washer 8 to have the legs bent over the washer 8 for retaining the female and male clasp parts to the material. 
     In the embodiment shown in FIG. 5 the protrusion 2a is omitted and the protrusion 5a of the male member b is made to directly contact with the metal plate surface 2 which is the bottom surface of the hole 1a for attraction. In the embodiment shown in FIG. 6, the protrusion 5a is omitted and the protrusion 2a is adapted to directly contact and be attracted on the metal plate 5. 
     FIG. 7 shows still another embodiment wherein the metal plate 3 is directly pressed on and retained by the bent periphery of the protrusion 4c on cylindrical case 4 for integrating the magnet 1, and the metal plates 2 and 3. This embodiment has an exposed surface on the metal plate 3. In this embodiment it is aimed to cut down moulding cost of the case by utilizing the protruding periphery 4c as a preventive spacing means for tapes x. 
     In the embodiments shown in FIGS. 8 to 14, various attachments for the female/male clasp members described above are illustrated. 
     In the embodiment shown in FIG. 8, a connecting tube 9 of a flute type is attached to the female/male members either by welding or with tabs 4a to form an attaching means for the members on leather or other materials. 
     In the embodiment shown in FIG. 9 the above mentioned connecting tube 9 of a flute type is provided with a closed end to be used in the same manner as shown in FIG. 17. In the embodiment illustrated in FIG. 10 the connecting tube 12 is provided with a washer 12a so that the diverging end of tube 12 is engaged by the collar which is formed by bending the washer 12a around the diverging end. The washer is then attached to the female/male members by the same upsetting method and means as described above for the members 2a&#39; and 5a&#39;. A connecting tube 11 in the form of a flute with or without bottom may be separately provided so as to be inserted into the tube 12, which is flattened for engagement as shown in FIG. 18. 
     In the embodiments shown in FIGS. 11 to 13, the rod of small diameter on the protrusions 2a and 5a are constructed as threaded rods 2a&#34; and 5a&#34; to be attached to leather or other materials by such methods as screwing FIG. 11, nut tightening FIG. 12, or hammering in FIG. 13. 
     In the embodiment shown in FIG. 14 the rod of small diameter on the protrusions 2a and 5a is made in the form of a pointed pin rod 2a&#34; and 5a&#34; is adapted to be attached to leather and other materials by pressing or thrusting therein.