Patent Document

BACKGROUND 
     The present invention relates to a magnetic tack for fastening items to soft-magnetic surfaces. Soft-magnetic materials are known in the field of magnetism to be ones onto which a permanent magnet (called a hard-magnetic material) will stick. 
     Magnetic snap fasteners are known for use as closures. U.S. Pat. Nos. 5,722,126 and 5,933,926, issued to Applicant, entitled “Magnetic Snap Fasteners”, relate to magnetic snap fasteners of different configurations. These fasteners comprise a male and a female section which are magnetically coupled at a single position. These fasteners have projections or rivets on each section which engage to assist in the magnetic attraction between the male and female sections by closing a magnetic circuit. The projection or rivets may have holes extending therethrough. 
     U.S. Pat. No. 4,453,294, issued to Morita, entitled “Engageable Article Using Permanent Magnet”, as reexamined and confirmed under Reexamination Certificate B1 U.S. Pat. Nos. 4,453,294, and 4,021,891, also issued to Morita, entitled “Magnetic Lock Closure,” as reexamined and confirmed under Reexamination Certificate B2 U.S. Pat. No. 4,021,891, relate to a magnetic closure wherein a solid projection on a first half of the closure engages a solid projection on a second half of the closure, which also contains a circular magnet. The Morita &#39;294 and Morita &#39;891 patents essentially describe the same product. These patents show solid projections or rivets. Further, British Patent Specification No. 1,519,246, published Jul. 26, 1978, discloses a magnetic closure, wherein the projections are partially hollow. None of these prior patented devices are practical for use by themselves to attach items to a soft magnetic surface, such as a wall, since they do not have a convenient means for grasping the fastener to put it on or remove it from the wall. The backs of these devices have attachment means for mounting the fasteners to handbags and the like in male/female pairs. These attachment means are not suited to grasping by a hand. 
     It also is known to use flat magnets, usually containing an advertising gimmick, to fasten items to soft-magnetic surfaces. These flat magnets generally do not possess enough magnetic force to fasten and support more than a single sheet of paper to a surface. 
     Conventional thumb tacks can, of course, be used to fasten paper items to non-metallic surfaces. Thumb tacks pierce the documents being tacked and damage them. Their dangerous sharp points are a hazard to children and adult users. Also, conventional thumb tacks are not designed with the ability to support and fasten large packs of paper to a surface and cannot be used to fasten paper items to a metallic surface, such as a refrigerator, or white board. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     In view of the aforementioned shortcomings of conventional flat magnets, thumb tacks and magnetic snap fasteners, it is an object of the present invention to provide a magnetic tack for fastening items to soft-magnetic surfaces. 
     It is another object of the present invention to provide a magnetic tack with the utility and ability to support packs of paper and without damaging the paper. 
     It is also an object of the invention to provide a child proof and safe tack. 
     To these and other ends, the present invention contemplates a magnetic tack for fastening an item, such as paper, to a soft-magnetic surface, such as a white board, home refrigerator, wall strip, or other magnetically attractable apparatus or device to which the magnetic tack can stick. The tack includes a plate of soft-magnetic material and a non-magnetic cover which encase a magnet. A knob is secured to the plate to assist in handling the tack. A pin or projection can extend through a hole in the magnet to create a magnetic circuit that will channel magnetic flux in such a manner that the magnet will use its power with improved efficiency. The projection may be hollow or solid. The pin can connect the knob to the magnetic tack. Alternatively, the plate can incorporate sidewalls which conduct magnetic flux to create a magnetic circuit that will channel magnetic flux in such a manner that there will be reduced loss of magnetic power due to flux leakage. As another alternative, the magnetic tack can incorporate both a pin and sidewalls. The knob can be joined to the encased magnet in a variety of ways which may include rivets, screws, glue, solder, welding, or any other form of joining. 
     The advantages of the invention will become apparent from the detailed description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of a magnetic tack in accordance with the invention. 
     FIG. 2 is an exploded view of the magnetic tack of FIG.  1 . 
     FIGS. 3 a  and  3   b  are a top view and a side cut-away view, respectively, of the circular magnet used in FIG.  1 . 
     FIGS. 4 and 5 are a top view and a side cut-away view, respectively, of the non-magnetic cover used in FIG.  1 . 
     FIG. 6 is a cross-sectional view of a part of the magnetic tack of FIG.  1 . 
     FIG. 7 is an elevational view of the knob used in FIG.  1 . 
     FIG. 8 is a cross-sectional view of another embodiment of a tack with a projection which may be press fitted to the body of the tack. 
     FIG. 9 is a cross-sectional view of a tack with a projection which may be screwed into the body of the tack. 
     FIG. 10 is a cross-sectional view of a tack with a projection which may have a crush rivet for attachment to the body of the tack. 
     FIG. 11 is a cross-sectional view of an alternative embodiment of the tack incorporating a plate with side walls. 
     FIGS. 12 a,    12   b  and  12   c  are a top view and cross-sectional views of another alternative embodiment of the tack incorporating a plate with side walls, and a center pin. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals represent the same or similar elements. 
     As shown in FIGS. 1 and 2, magnetic tack  1  includes a knob  10 , a non-magnetic cover  16  secured to a circular plate  14 , and a circular magnet  15  contained between plate  14  and cover  16 . Pin or projection  20  connects to knob  10 . 
     As shown in FIG. 2, circular plate  14  may be made of a ferromagnetic material and includes central hole  14   a,  top side  14   b,  and bottom side  14   c.    
     As shown in FIGS. 2 and 7, knob  10  has a knob head  11  and knob body  12 . Knob  10  is positioned against circular plate  14 . Knob  10  can be of any convenient shape. Knob  10  may be made of any material. 
     As shown in FIGS. 2,  3   a,  and  3   b,  circular magnet  15  is toroidal in shape and has a central hole  15   a.  Magnet  15  may be made of any “hard” (permanent) magnetic material. Circular magnet  15  is encased by plate  14  and by non-magnetic cover  16  as shown in FIGS. 2,  4 ,  5 , and  6 . 
     Cover  16  has top side  16   d  and side wall  17  and circumscribes magnet  15 . Flange  16   c  on bottom side  16   b  of cover  16  helps contain circular magnet  15 . Continuous flange  18  on top side  16   d  also maintains magnet  15  in place relative to plate  14 . The continuous flange  18  holds the magnet  15  in place more securely than if prongs or tabs are used. However, it is within the scope of the invention to use a plurality of prongs or tabs. Preferably, continuous flange  18  extends about the entire periphery of non-magnetic cover  16 . Non-magnetic cover  16  and circular magnet  15  have central holes  16   a  and  15   a,  respectively, which are substantially axially aligned with center hole  14   a  of washer plate  14 . 
     A projection or pin  20  extends through magnet  15  and is secured to knob body  12  from the bottom side  14   b  of plate  14 . The pin  20  shown in FIG. 8 is press fitted into knob body  12 . Projection or pin  20 , sometimes called a rod, rivet or screw, is made of a soft-magnetic material. The existence of pin  20  serves to facilitate the magnetic attraction of the device to a soft-magnetic surface by making a magnetic circuit that channels magnetic flux from magnet  15 . Pin  20  may be solid or hollow, that is, having an interior bore. The advantage of using a solid pin is explained in U.S. Pat. Nos. 4,021,891 and 4,453,294. The advantages of using a hollow pin are explained in U.S. Pat. Nos. 5,722,126 and 5,933,926. The disclosures of those patents are incorporated herein by reference. It is also within the scope of the invention to use a partially hollow pin as shown, for example, in British Patent Specification No. 1,519,246. Some of the components used in the magnetic tack may be interchangeable with those used in the magnetic snaps shown in the aforesaid patents. The top surface of pin  20   a  should preferably extend through the magnet annulus  15   a  and cover  16  and be flush with bottom surface of cover  16   b  but this is not required. 
     In another embodiment, as shown in FIG. 9, knob body  12  is affixed to the cover/magnetic/plate assembly by pin  30  that is screw-fitted into knob body  12 . 
     In another embodiment, as shown in FIG. 10, knob head  10  has an internal undercut  50 . Knob body  12  is affixed to the cover/magnetic/plate assembly by a kwik rivet stem pin  40 . The kwik rivet stem pin  40  is crush fitted into knob body  12 . 
     An alternative embodiment shown in FIG. 11 depicts a magnetic tack with solid magnet  22 , soft magnetic material plate  23  with side walls  23   a,  cover  24 , and knob  10 . The side walls  23   a  serve to facilitate the magnetic attraction of the device to a soft-magnetic surface by making a magnetic circuit that channels magnetic flux from magnet  22 . Knob  10  is attached by an appropriate means, such as gluing, soldering, or welding. 
     Another embodiment is shown in FIGS. 12 a  and  12   b.  It is similar to the embodiment of FIG. 11 except that non-magnetic cover  25  is attached to plate  23  having side walls  23   a.  This embodiment has a series of tabs  26  extending through slots  27  in plate  23 . Tabs  26  are folded over to fasten the cover to the plate  23 . Knob  10  is attached by an appropriate means, such as gluing, soldering, or welding. In place of the tabs shown, the cover can be press fit into side walls  23   a,  or it can be glued, soldered, or welded in place to side walls  23   a.    
     Still another embodiment combines both side walls and a pin, as shown in FIGS. 11,  12   a,    12   b  and  12   c.  Cover  28  can attach either inside or outside the side walls  23   a.  Knob  10  can be attached by any of the methods previously described. 
     Various changes and modifications may be effected by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims. As an example, the flange in the non-magnetic cover can be a series of tabs, rather than a continuous piece. As another example, the knob may be welded to the top side of the plate rather than secured to the pin.

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