Abstract:
A magnetic assembly and method permitting the use of low-cost magnets capable of being fabricated in an efficient and low-cost manner having a plate having a mounting surface and an opposing bottom surface, with a plurality of magnetizable elements, each of which is fitted in a fixture having plural radial wings for holding the magnetizable elements against the mounting surface, and with an over mold of a plastic material covering the mounting surface, the fixture and the bottom surface.

Description:
RELATED APPLICATION 
     This application claims priority from provisional application Ser. No. 61/610,611, filed Mar. 14, 2012. 
    
    
     BACKGROUND 
     Magnetic housing assemblies are used with magnetic advertising signs for automotive vehicles. Because the magnets must withstand forces taking place during the vehicle&#39;s motion without becoming dislodged, a strong construction is necessary; however, because the signs are used as temporary fixtures and are frequently removed from vehicles, magnet strength must not be so high as to defeat removal. Therefore for certain applications, it is desirable to use a plurality of thinner, lower-cost, magnets arranged in a permanent fashion inside a housing, so that the magnetic force is distributed across the housing&#39;s surface area. 
     To assure that the magnets do not shift during construction of the assembly and during use, it is necessary to permanently fix the magnets in place. Although glue is used as one method to fix magnets in place, the glue must be able to withstand high temperatures to which the finished housing will be subjected. Use of high temperature glue is relatively expensive as well as unnecessary for the routine use of the magnet. In order to avoid these problems alternate solutions are desirable. An earlier version of a magnetic assembly for automotive signs is disclosed in U.S. Pat. No. 7,618,013, a disclosure of this is incorporated here by reference. 
     SUMMARY 
     The present invention is directed to an improved magnetic assembly and method that permits the use of low cost magnets to be utilized in fabricating a magnetic mounting assembly useful, for example, in the attachment of signs to automobiles. One significant feature of this invention is the ability to fabricate the magnetic assembly efficiently and in a low cost manner. 
     In accordance with this invention, the magnetic assembly utilizes a base plate of a magnetizable metal having an inner surface and a side wall, and with plural magnetizable elements disposed on the inner wall. A magnet positioning fixture is provided with indentations for receiving the magnet elements, so as to hold the elements in proper position during assembly. The plate, the fixture and the magnets are over molded with a plastic cover forming an upper coating and a lower coating joined together along a side wall of the plate. The magnetizable elements are then magnetized. 
     Preferably, the plate is provided with apertures that permit the insertion of positioning pins that hold the plate and fixture in place during the over molding process. The plate, the fixture and the upper and lower coatings are provided with aligned central openings to permit a fastener to be inserted through the magnet assembly and engage an advertising sign of similar article after the magnet elements are properly magnetized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention is described by way of example with reference to the accompanying drawings in which: 
         FIG. 1  is a partial exploded cross-sectional view of a magnet assembly made according to the present invention attached to a portion of an advertising sign. 
         FIG. 2  depicts in an exploded view an exemplary configuration of the magnet assembly in accordance with the present invention. 
         FIGS. 3 and 4  are, respectively, a perspective view of the top and a plan view of the bottom of a sealed magnet assembly according to  FIG. 2 . 
         FIGS. 5 and 6  are, respectively, top and bottom perspective views of a magnet fixture shown generally as element  30  in  FIG. 2 . 
         FIG. 7  is a perspective view of a mounting plate of the assembly shown as element  16  in  FIG. 2 . 
         FIG. 8  is a bottom view of the mounting plate  16  shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more fully with reference to the accompanying drawings in which preferred embodiments of the invention are shown and described. It is to be understood that the invention may be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure may be thorough and complete, and will convey the scope of the invention to those skilled in the art. 
     With reference initially to  FIG. 1 , one embodiment of the invention is a magnet assembly  10  useful in removably attaching a sign  12  to a metallic structure  14 , such as the roof of a motor vehicle used in transporting an advertising sign. The assembly  10  in accordance with the present invention is installed through use of a fastener  42  into a molded extension  60  of the advertising sign  12 , with a flexible sleeve  62  interposed between the assembly  10  and a recess  64  in a lower portion  66  of the sign  12 . 
     Now noting  FIG. 2 , the magnet assembly  10  comprises the following elements: a plate  16  having a side wall  20  and an inner mounting surface  22 , a central opening  24  and slots  26  through which positioning pins may be inserted during the over molding process. The assembly  10  further includes plural magnet elements  28  that may be placed on the surface  22  of the plate  16  prior to being magnetized, thereby making the fabrication of the assembly  10  much more easily controlled. A magnet fixture  30  is placed snugly over the magnet elements  28  and across the inner wall  22  of the plate  16 , with the fixture  30  being defined by plural wings  38  as described further below. Once assembled and held in place by positioning pins extending through openings  26  of the plate  16 , the entire assembly  10  is over molded with an upper coating  46  and a lower coating  50  as is shown in  FIGS. 3 and 4 . In this example, three magnet elements  28  are placed across the surface  22  with each magnet  28  between adjacent slots  26 . Preferably, the plate  16  is cylindrical in shape. 
     As illustrated in  FIG. 2 , the magnet fixture  30  is placed snugly over the magnet elements  28  and the inner surface  22  of plate  16 . As a result, the transverse and longitudinal movement of each magnet element  28  is limited by the fixture  30 . Referring to  FIGS. 5 and 6 , the fixture  30  comprises a top side  32 , a bottom side  34 , a central opening  36  and a plurality of wings  38  that are spanned outwardly from the central opening  36 . As shown in  FIGS. 5 and 6 , the fixture  30  comprises a non-metallic and non-magnetic material, with the fixture made of plastic. The bottom side  34  of the fixture  30  has indentations  40  that snugly engage with the magnet elements  28  through wings  38 . The wings  38  at the bottom side  34  include corresponding indentations  40  dimensioned to accommodate the magnet elements  28 . The fixture  30 , and in particular the wings  38 , provides a uniform and even surface for equal distribution of the magnets  28  on the bottom inner surface  22  of the plate  16 . 
     The plate  16  and the fixture  30  each include a central opening ( 24  and  36 , respectively) cooperating to receive the fastener  42  therethrough, such as the screw illustrated by way of example with reference again to  FIG. 1 , when fastening the mounting assembly  10  to an object such as the sign  12 . 
     In the embodiment of  FIG. 2 , the plastic overcoating  46  is defined by an upper coating  48 , a lower coating  50  and a sidewall coating  52 . The upper coating  48  is in seamless contact with the side wall  22  of the plate  16 . The upper coating  48  carries crimps or tabs  56 . The tabs  56  extend from the peripheral portion  54  of the upper coating  48  for providing a compression-fit contact between the housing  16  and the magnets  28 . The upper coating  48  further comprises a central indentation  58  and a central opening  60  in the center of the central indentation  58 . As herein described and as illustrated in  FIGS. 3 and 4 , the central indentation  58  and the central opening  60  are formed in the center of the upper coating  48 , and are cylindrical in shape. 
     The upper coating  48  further comprises a plurality of apertures  62  having similar shapes as the magnet elements  28  and the wings  38 , but fractionally larger in dimension than the corresponding magnet elements  28  and wings  38 . When the upper coating  48  is formed over the cover  30 , the cover  30  rests with its top side  32  touching the inside surface  22  of the plate  16 . Accordingly, the coatings  48  and  50  hold the plate  16  and the fixture  30  in place and provide a structural framework during fabrication and overmolding of the assembly  10 . 
     As shown in  FIG. 4 , the lower coating  50  is cylindrical in shape, comprises a central opening  63  and plural pin holes or slots  68  to permit the use of pins to hold the assembly unit in place during assembly of the plate  16 , the magnets  28 , the fixture  30  and the overmolding of the upper and lower covers  48  and  50 . 
     When fully assembled, only outside surfaces of the upper coating  48 , the outside surface of the lower coating  50 , and a circumferential outside surface  52  along side wall  20  are exposed. The fastener  42  is extended through the central opening  63  of the upper and lower coatings  48  and  50  when fastening the magnet assembly  10  to an object such as the sign  12 . 
     In one specific example, the coatings  48  and  50  comprise a material such as polyolefin or thermal plastic with a durometer rating between about 60-90, or any other similar polymeric coating depending on the contemplated application. After fabrication the completed magnet assembly  10  may then be subjected to a magnetic field, which magnetizes the magnet elements  28 . 
       FIG. 2  illustrates an individual polygonal-shaped magnet  28  which may be used in the completed assembly  10 . A person skilled in the art will recognize that magnets come in a number of shapes including toroidal, semi-toroidal as well as various polygonal and irregular shapes. The shape shown is illustrative of these possibilities. In one specific embodiment, the magnet elements  28  are each a rectangular prism, and by way of example only, is on the order of 1″×0.5″×0.125″ in size. The magnets  28  may comprise neodymium or any other suitable magnetizable material. The plate  16  is a circular disk in shape, and may be made of steel coated with zinc plating, for example. 
     With regard to the method of assembly, reference is again made to  FIG. 2  where the plate  16 , the magnets  28 , and the fixture  30  are assembled and oriented as illustrated. In this illustration, the wall  22  is shown with the central opening  24  and plurality of apertures  26  facing the inside surface  22  of the plate  16 . As illustrated in  FIG. 2 , the magnet elements  28 , or a substrate capable of being magnetized, are then inserted in the plate  16 , with the bottom surface of each magnet resting on the surface  22 . In a next step, the fixture  30  is inserted into the plate  16  in which the magnet elements  28  have previously been placed. The central opening  36  of the fixture  30  is aligned with the central opening  24  of the plate  16 . In the next step, the coatings  46  and  50  are deposited in a mold to cover the assembly  10 . 
     With reference again to  FIG. 1 , the assembly  10  is used to removably fasten the advertising sign  12  to the structure  14  such as a surface of a vehicle. In that regard, a portion of the sign as disclosed in U.S. Pat. No. 5,711,100 is illustrated in  FIG. 1  by way of example, the entire specification and drawings for which are incorporated herein by reference. 
     Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiment disclosed, and that modifications and alternate embodiments are intended to be included within the scope of this invention.