Transverse flux induction heating unit

This relates to an induction heating unit which is particularly constructed for inducing electrical energy into the periphery of a metal foil barrier layer of a closure for a container to thereby heat the closure and heat bond the closure to the container. In lieu of the customary single turn coil, there is provided a multiple turn coil which is mounted in one of two opposing U-sections of a core. The U-sections may either be formed of ferrite or be of a laminated construction. First legs of the U-sections are utilized to clamp a closure to a container while there will be an air gap between the other opposed legs of the U-sections. Heating may be controlled by either varying the air gap or by varying the ratio of electrically conductive members with insulating spacers.

This invention relates in general to new and useful improvements in 
induction heating units, and more particularly to a transverse flux 
induction heating unit. 
Most particularly, this invention relates to an induction heating unit 
which is particularly adaptable for instantaneously heating a metal foil 
layer within a closure for a container so as to effect heat bonding of the 
closure to the container. 
It is known to induction heat a metal foil layer within a closure so as to 
heat bond the closure to a container utilizing a one turn induction 
heating coil. The strength of the induction field is determined by the 
ampere turns per inch. With a single turn induction coil, the amperes 
required to heat a closure in 0.1 seconds could be 2500 amperes or more. 
In accordance with this invention, it is proposed to utilize a multiple 
turn induction heating coil which will have a required number of turns to 
match the coil to a high frequency current generator. With such an 
arrangement and by cutting the lid at ninety degrees, a separate matching 
transformer is eliminated with the resultant circuit being more efficient 
and machine costs are reduced. 
In accordance with this invention, there are provided two U-sections which 
are arranged in stacked opposed relation with the multiple turn coil being 
located within one or both of the U-sections. The two stacked U-sections 
will have inner and outer legs arranged in opposed, generally aligned 
relation with one pair of legs forming means to clamp the workpiece to be 
heated and the other pair of legs being spaced apart. The amount of 
heating along any portion of the heating unit may be varied by varying the 
spacing between the other pair of legs. 
The U-sections, which form the core of the heating unit, can be formed of 
ferrite or more beneficially, may be of a laminated construction. When the 
core is of a laminated construction, a plurality of U-shaped members are 
provided, some of which are formed of electrically conductive magnetic 
material and others of which are formed of insulating material. By varying 
the ratio of the conducting members and the insualting members, the amount 
of heat produced along a selected portion of the heating unit may be 
varied. 
The heating unit is particularly adapted to the heating of a closure which 
is either of an outline including straight portions and a corner or has a 
projecting pull tab, or both. Due to the change in distribution of the 
heating currents induced into the metal foil layer of the closure at the 
corners, more heat is required at the corners. In addition, in the area of 
the pull tab, there is more metal foil to be heated with the result that 
more heat is required in the area of the pull tab. A heating unit as 
outlined above, may be beneficially adjusted or constructed to provide the 
desired heat in all areas of the closure whereby a uniform heating pattern 
may be obtained. 
With the above and other objects in view that will hereinafter appear, the 
nature of the invention will be more clearly understood by reference to 
the following detailed description, the appended claims, and the several 
views illustrated in the accompanying drawings.

Referring now to the drawings in detail, reference is first made to FIG. 3 
wherein there is illustrated a container 10 to which a closure 12 is to be 
heat bonded in sealed relationship with respect to the container 10. The 
container 10 is of a plastic material construction and may preferably be 
of a laminated construction so as to include a barrier layer. The 
container 10 is provided with a configuration so as to include a support 
flange 14 which extends entirely around the cavity 16 of the container. A 
peripheral portion only of the closure 12 rests on the support flange 14 
and it is this peripheral portion of the closure 12 which is to be heat 
bonded to the container 10 along the support flange 14. 
For an understanding of the utilization of the heating unit, a typical 
sectional view through the closure 12 is found in FIG. 4. It will be seen 
that the closure 12 is primarily of a plastic material construction and 
includes an outer structural plastic layer 18 and an inner plastic 
material bonding layer 20 with there being sandwiched between the layers 
18 and 20 a metal foil layer 22. The metal foil layer 22 is preferably in 
the form of aluminum foil and in a preferred embodiment of the closure, 
the aluminum foil will have a thickness on the order of 0.0018 inch. 
It is to be understood that the aluminum foil layer 22 only in the 
peripheral area of the closure 12 will be heated to a very high 
temperature in a very short time,for example, within 0.1 second. This heat 
will then be conducted to the layer 20 and from the container 10 so as to 
effect the heat bonding of the layer 20 to the outermost surface of the 
container 10 along the support flange 14. 
As is shown in FIG. 2, the closure 12 will preferably be provided with a 
pull tab 24 for facilitating the peeling of the closure 12 from the 
container 10 when it is desired to open the container 10. Inasmuch as the 
pull tab 24 will be of the same laminated construction as the closure 12, 
it will be seen that in the area of the pull tab 24, more heating will be 
required. 
Also, as is shown in FIG. 2, the container 10 may be of a rectangular 
outline or may have at least one corner. The current induced into the 
aluminum layer, has a tendency to shortcut the corners thereby requiring 
more heating at the corners. Furthermore, if the pull tab 24 is at one of 
the corners, then even more heat is required at that corner. 
In the past, the closure 12 has been heat bonded to the container 10 
utilizing a one turn induction coil with there being pieces of ferrite 
associated with that coil so as to vary the electrical energy induced into 
the metal foil layer 22 and thus the heating of the same. This results in 
a rather complex heating unit. Furthermore, because a single turn 
induction heating coil will not match the required high frequency 
generator, a matching transformer has been required. However, by utilizing 
a multiple turn coil, it has been found that the matching transformer can 
be eliminated with the circuit being more efficient and the ma chine cost 
being reduced. 
This invention particularly relates to a heating unit, generally identified 
by the numeral 26, which utilizes such a multiple turn coil generally 
identified by the numeral 28. 
The heating unit 26 also includes a core, generally identified by the 
numeral 30. The core 30 is of an outline in accordance with the 
configuration of the workpiece and in the case of a rectangular container, 
the core 30 would have the outline illustrated in FIG. 2. 
The core 30 is formed of two U-sections 32, 34 which are arranged in 
opposed relation. The lowermost U-section 34 includes an inner leg 36 and 
an outer leg 38 joined together by a base 40. In the illustrated form of 
the invention, the coil 28 is received in the lower U-section 34 and is 
potted therein. However, the coil may be in either or both of the 
U-sections 32, 34. 
The U-section 32 also includes an inner leg 42, an outer leg 44, and a top 
wall with each other while the legs 38 and 44 are generally aligned with 
each other. It is intended that the lid 12 be clamped to the support 
flange 14 and the container 10 by the legs 36, 42 as is shown in FIG. 3. 
On the other hand, if the workpiece was of a ring shape, then the 
workpiece would be clamped together by the legs 38, 44. 
With the arrangement shown in FIG. 3, there will be an air gap 48 between 
the legs 38, 44. This air gap may be varied with the thickness or height 
of the air gap 48 controlling the heat of the workpiece. 
At this time it is pointed out that the core 38 may be of two possible 
constructions. First of all, the U-sections 32, 34 may be formed of 
ferrite. Inasmuch as the heat requirements at the corners of the closure 
12 and also at the pull tab 24 will vary, then the thickness of the air 
gap 48 may be utilzed as the sole means of controlling the heating of the 
aluminum foil layer 22 about the periphery of the closure 12. The air gap 
48 is small for maximum heating and large for lesser heating. Thus, with 
respect to FIG. 2, where the pull tab 24 is located at a corner, the air 
gap 48 would be a minimum and along the straight sides and ends of the 
container, the air gap 48 would be a maximum. 
Although the U-sections 32, 34 may be formed of ferrite, in a preferred 
embodiment, they are of a laminated construction. As is schematically 
shown in FIG. 1, each of the U-sections 32, 34 is made up of a stack of 
U-shaped members, some of the members being formed of an electrical 
conductive material and being identified by the numeral 50 with others of 
the members being formed of an electrically insulated material and being 
identified by the numeral 52. For example, the members 50 may be stamped 
from sheet aluminum while the members 52 may be stamped from sheets of 
suitable plastic material. The members 50, 52 may be retained in alignment 
in accordance with the configuration of the U-sections 32, 34 in any 
desired manner. However, it is preferred that the members 50, 52 be 
mounted within any suitable support material, such as a potting material 
(not shown). 
It is to be understood that when the ratio of the members 50 to the members 
52 is relatively high and the members 50 are relatively close together, 
the spacer members 52 are increased thereby reducing the ratio of the 
members 50 to the members 52. 
It is to be understood that in addition to heat being controlled by the 
spacing of the members 50, heat can also be controlled by varying the air 
gap 48. Under the circumstances, along the straight portions of the lid 
12, the spacing of the members 50 will be a maximum. At the corners, the 
number of spacers 52 will be decreased so that the spacing of the members 
50 will decrease with the result that there will be greater heating as 
required at the corners. Finally, at the corner where the pull tab 24 is 
located, the ratio of the members 50 to the members 52 will be greatly 
increased to provide for the added heat requirement. 
Finally, with respect to FIG. 3, it will be seen that the multiple turn 
coil 28 will be connected by means of a suitable switch 54 to a high 
frequency generator 56. As pointed out above, the number of windings of 
the multiple turn coil 28 will be such as to match the generator 56 
thereby eliminating the requirement for the presently required matching 
transformer. Therefore, with the exception of the switch 54, the coil 28 
may be directly connected to the generator 56. 
Because the lines of flux through the U-sections 32, 34 cut the closure 12 
at ninety degrees, maximum efficiency can be obtained. This, combined with 
the elimination of the matching transformer, provides for a more efficient 
operation and a reduction in machine costs. 
Although only two preferred embodiments of the heating unit have been 
specifically illustrated and described herein, it is to be understood that 
minor variations may be made in the heating unit without departing from 
the spirit and scope of the invention as defined by the appended claims.