Abstract:
An induction foil cap sealing system includes a ferrite core having a plurality of openings therethrough and a mounting plate with a plurality of openings therethrough which are aligned with the plurality of openings in the ferrite core. Air is directed to flow through the openings to draw heat away. A litz wire coil is disposed proximate to the ferrite core which produces an electromagnetic field within the ferrite core. The ferrite core and litz wire coil are adapted to direct the electromagnetic field toward abject to heat it.

Description:
This application is based on and claims priority to U.S. Provisional Patent Application Ser. No. 60/199,717, filed Apr. 26, 2000, entitled “Induction Foil Cap Sealer” which is related to patent application Ser. No. 09/138,159, filed Aug. 21, 1998, entitled “Induction Foil Cap Sealer” which is a continuation of patent application Ser. No. 08/966,305, filed Nov. 7, 1997, now abandoned, which is related to patent application Ser. No. 60/030,488, filed Nov. 15, 1996, now abandoned, the entire contents of all are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an induction sealing apparatus which seals a foil sheet or liner to the opening of a container and, more particularly, to an induction sealing apparatus which is air cooled and which does not require the use of thermally conductive material disposed within ferrite cores of the apparatus to facilitate heat removal. 
     2. Related Art 
     Induction sealing units for sealing and hermetically sealing or tamper-proof sealing containers with foil liners are typically included in conveyer systems for high volume applications. A discussion of the general principles of inductive sealing is disclosed in pending application Ser. No. 09/138,159, the entire contents of which is incorporated by reference. 
     Conventional systems comprise an induction head which includes ferrite materials arranged to channel and direct the electromagnetic field towards the foil liner. An electric current is induced in the foil liner which heats the foil to a temperature sufficient to bond the foil to the rim of the container. As the foil and rim cool, the foil is firmly joined to the rim providing a securely sealed container. 
     Induction sealing systems generate a significant amount of excess thermal energy and have to be cooled in some way. Some systems use water cooling while others circulate air across heat sinks to draw heat away from the core. 
     In air cooled systems, a thermally conductive material is disposed within the ferrite core in order to conduct the heat generated within the core to heat sinks which are used to transfer the thermal energy to the air used to cool the unit. This thermally conductive material adds to the cost and weight of the device and is subject to mechanical failure and cracking. Heat sinks are usually made of metal and are produced with a plurality of fin projections to help dissipate the excess heat produced within the ferrite core. Exposed fins are subject to breakage which reduces the effectiveness of the heatsinks. Also, the use of extensive heatsinks add to the complexity and weight of the device. 
     Water cooled systems are necessarily more complicated and more costly. Water cooled systems require plumbing and a pumping system to circulate the water throughout the induction sealing head. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an induction sealing unit which does not require thermally conductive materials disposed within the ferrite core and is thus less expensive to produce than the prior art. 
     The present invention also provides an induction sealing head which utilizes an air cooled slotted ferrite core to minimize the use of complex heat sink configurations. 
     The present invention also provides an induction sealing head which is more energy efficient than conventional induction sealers. 
     The present invention also provides an induction sealing unit that is easy to use, manufacture and maintain. 
     The present invention attains these features by providing a sealing unit having a horizontal mounting plate, a ferrite core having openings formed therethrough, disposed on the mounting plate and a litz wire coil disposed proximate to the ferrite core for producing an electromagnetic field. The ferrite core and litz wire coil are adapted to direct an electromagnetic field toward a foil used to seal an opening of a container. The horizontal mounting plate has openings coinciding with the openings within the ferrite core to provide air flow through and around the core and sealing head. 
    
    
     Other features and advantages of the present invention will become apparent from the following description of the invention which refer to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there are shown in the drawings an embodiment which is presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentality shown. 
     FIG. 1 shows a front view of an induction sealing conveyor system employing an air cooled sealing head which is constructed in accordance with the principles of the present invention. 
     FIG. 2 is a top view showing slots in a metallic plate used in the sealing head of the present invention. 
     FIG. 3 is a bottom view of the sealing head used in present invention showing the litz wires and the slots. 
     FIG. 4 is a side view of the sealing head of the present invention. 
     FIG. 5 is a sectional view along section lines  5 — 5  of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings wherein like numerals indicate like elements, there is shown in FIG. 1 an induction sealing unit designated generally as  100 . Sealing unit  100  comprises housing  102  and sealing head  103 . The components within housing  102  include capacitor  106 , intake fan  110 , outtake fan  114 , transformer  118  electrically connected to the capacitor  106  and a power supply  152  electrically connected to transformer  118 . Sealing head  103  comprises a horizontal mounting plate  126 , two vertical mounting plates  170  (only one of which can be seen in FIG.  1 ), a ferrite core  120  and a litz wire coil  108  electrically connected to transformer  118 . 
     Referring to FIGS. 4 and 5, ferrite core  120  is constructed from both “E”-shaped and “I”-shaped ferrites ( 120   e  and  120   i  respectively) to form a channel shape which includes bottom tab sections  122  and a center spine  124 . Center spine  124  is constructed of the “I”-shaped ferrites  120   i  bonded together and centrally aligned along the longitudinal axis (i.e. the axis extending from the left to the right sides of ferrite core  120  as shown in FIG. 1) of ferrite core  120 . 
     Referring now to FIG. 1, a plurality of the “E”-shaped ferrites  120   e  are joined open end to open end to form slots  116   v  which are aligned perpendicular to the longitudinal axis of ferrite core  120 . Slots  116   v  are vertically oriented along the two outer portions of ferrite core  120 . 
     Now referring to FIGS. 1 and 2, another plurality of the “E”-shaped ferrites  120   e  are also arranged open side to open side to form horizontal slots  116   h . Slots  116   h  are horizontally oriented and are aligned perpendicular to the longitudinal axis. Slots  116   h  provide air channels within ferrite core  120  and increase the surface area exposed to cooling air  200 , thereby allowing ferrite core  120  to be air cooled without the use of thermally conductive materials encasing ferrite core  120 . 
     In order to direct the electromagnetic field within core  120 , a conductor needs to be in intimate contact with the core, but the conductor must be electrically insulated from core  120 . Induction sealing unit  100  utilizes high frequency current which tends to flow near the surface of a conductor (known as “the skin effect”). Therefore, the conductor needs to be one suited for use with high frequencies. It is for this reason that the litz wire coil  108  is used as the conductor. 
     Preferably, litz wire coil  108  includes thousands of individually insulated electrical conductors surrounded by an insulating sheath, made from polyethylene, polypropylene, Teflon, or the like, which also electrically insulates litz wire coil  108  from the surrounding structures, including ferrite core  120 . 
     Litz wire coil  108  has a very low resistance to the flow of current as compared to the wire typically used in conventional induction sealers. This lower resistance allows the current to flow more efficiently and requires less power to operate. Litz wire coil  108  also generates less heat than the wire typically used, thereby making it easier to cool. 
     Litz wire coil  108  is sized such that the effective resistance per unit length is only about 0.1 to 0.01 of the resistance per unit length of the wire typically used in conventional induction sealers. Consequently, the heat produced within litz wire coil  108  (due to I 2 R losses) is reduced by a factor somewhere between 10-100 times allowing induction sealing unit  10  to be air cooled rather than liquid cooled. 
     Referring to FIGS. 3 and 4, litz wire coil  108  is attached so as to abut against the inner surface of ferrite core  120 . Litz wire coil  108  may be attached to ferrite core  120  with a heat resistant epoxy or by using temperature resistant strapping materials. Whatever method is used to attach litz wire coil  108 , it is important that litz wire coils  108  remain flush against the inner surface of ferrite core  120 . 
     Referring again to FIGS. 1 and 2, horizontal mounting plate  126 , which is formed from a metal with good thermal conductivity such as aluminum, supports ferrite core  120 . Cooling slots  126   h  are aligned with cooling slots  116   h  that are formed within ferrites core  120 . Slots  16   h  are aligned with respective slots  126   h  to provide cooling channels in ferrite core  120  through which cooling air  200  is circulated. 
     A first plurality of individual ferrites  120   e  are horizontally positioned and epoxied to the lower surface of horizontal mounting plate  126 . Horizontal mounting plate  126  is either unitarily formed with two vertical mounting plates  170  or alternatively, the two vertical mounting plates  170  can be attached to horizontal mounting plate  126 . Any method of attachment is acceptable as long as the joint can withstand thermal stress (i.e. welding, bolting, gluing, etc.) Another plurality of individual ferrites  120   e  are vertically mounted and epoxied along the inner surface of mounting plates  170 . The vertical slots  116   v  formed in ferrite core  120  increase the surface area of the ferrite core  120  exposed to cooling air flow  200 , but it is not necessary for air to flow through the vertical slots  116   v . However, it would be within the scope of this disclosure to cut slots corresponding to vertical slots  116   v  in the vertical mounting plates  170  to provide an airflow channel through the sides of ferrite core  120  if additional cooling is desirable. 
     Referring to FIGS. 1 and 4, heat is drawn from the vertically mounted ferrites  120   e  using a heat sink  128  which is in intimate contact along the outer longitudinal edges of mounting plates  126  and  170 . A plurality of fins  128   a  are inwardly exposed to cooling air flow  200  to draw heat away from the sides of ferrite core  120 . 
     Cooling air  200  is directed to flow within ferrite core  120  by an air circulation chamber  150  which is defined within housing  102 . Cooling air flow  200  is drawn in through intake fan  110 . A baffle  112  is mounted at an angle within air circulation chamber  150  to direct cooling air  200  down through horizontally mounted intake fan  110 . Air is then pushed through cooling slots ( 116   h  and  126   h ) thereby cooling core  120 , and also cooling components such as capacitor  106  and transformer  118 . Cooling air  200  also draws heat away from heat sink  128 . Cooling air is simultaneously pulled with vertically mounted outtake fan  114 . 
     Protective boot  138  encloses the bottom of sealing head  103  to protect litz wire coil  108  and ferrite core  120 . Protective boot  138  also directs air flow  200  to flow within ferrite core  120 . Fans  110  and  114  are preferably capable of moving approximately 100 cubic feet of air per minute. 
     In operation, referring to FIG. 4, a container  130  having a foil liner  132  passes beneath sealing head  103 . As the container.  130  passes beneath sealing head  103 , a circuit including the power supply  152 , the transformer  118 , the capacitor  106  and the litz wire coil  108  cause a current to be induced in foil liner  132  heating and fusing it to the container  130 . A cap  136  can be used to position and press foil liner  132  against the top of container  130 . 
     Air is directed through slots ( 116   h  and  126   h ) formed within the ferrite core  120  to advantageously eliminate the need for thermally conductive materials disposed therein. This lowers the cost of producing the unit as well as reducing production time and overall weight of the unit. 
     Because air is channeled within the core  120  itself, through slots  116   h  and  126   h , operating temperatures can be easily controlled, thereby increasing the efficiency of the unit. Heat does not build up within the core  120  and even in the event of a power failure, air will naturally circulate through the core  120 , allowing some cooling to take place by convection. Units using thermally conductive materials disposed within the ferrite cores, store up more heat when deprived of a cooling air flow within the housing. The mounting plates ( 126  and  170 ) and heat sink  128  can be made of any thermally conductive metal, but aluminum is particularly well suited since it is lightweight, easily machined, relatively, inexpensive and conducts heat quite effectively, i.e., has a relatively high co-efficient of thermal conductivity. 
     The slots  126   h  in mounting plate  126  are shown as oblong in shape, but any shaped opening can be utilized as long as an air channel is formed allowing the air to circulate within ferrite core  120 . 
     The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching.