Method for closure heating

A method and appaatus for curing a gasket material on a cap, the apparatus having a microwave transmitter, associated wavegide and a device for moving multiple caps through the waveguide. A plastic material is applied to the cap so as to form a gasket. The cap is then moved through the waveguide where microwave energy is absorbed by plastic material. The plastic material then heats from room temperature to a predetermined curing temperature in the waveguide. The cap is then removed and allowed to cool back to room temperature so that the gasket material will harden.

BACKGROUND OF THE INVENTION 
This invention relates to microwave energy curing of material and more 
particularly to hardening gasket material for closures used, together with 
a jar, to ensure package and material integrity within the jar. 
It is known in the art that perishable material, such as food, is preserved 
in jars by using a closure comprising a cap and cap gasket to enclose the 
perishables within the jar. More specifically, during processing, food is 
placed in a jar. The air within the jar is then evacuated. Next a cap, 
with a cap gasket, is screwed onto the jar. Caps are typically made from a 
hardened plastic such as polypropylene. Hardened plastic caps do not seal 
to glass jars well enough to prevent the outside air from re-entering into 
the jar. Accordingly, in some applications, a cap gasket material that 
does seal to the jar is implanted in a groove formed on the inside of the 
top of the cap. When such a cap is placed on the jar, the cap gasket 
material will mold to the shape of the jar. 
One such cap gasket material is a combination of a vinyl chloride polymer 
such as PVC powder and a plasticizer that is a member of the phthalate 
family, such cap gasket material comes in a liquid form. The cap gasket 
material is first placed in the groove and is then cured by being heated 
to a 340.degree. F. temperature. After such heating, the cap is cooled to 
room temperature, more specifically a closure of such type is constructed 
by the following steps (more detail of this process is explained in U.S. 
Pat. No. 4,309,744): First, the liquid cap gasket material is injected 
into a groove on the inside of the top of the cap. Second, the cap and cap 
gasket are pre-heated in a conventional heating oven to 300.degree. F. 
Third, the cap gasket, which absorbs microwave energy, and cap are then 
placed in a 10 kilowatt multi-mode industrial microwave oven and heated 
until the cap gasket material reaches a curing temperature of 340.degree. 
F. The cap itself is essentially transparent to microwave energy. Thus, 
the cap itself remains relatively cool because it does not absorb 
microwave energy. After the cap gasket material reaches curing temperature 
by the absorption of microwave energy, the closure is then removed from 
the microwave oven and allowed to cool, at which time the cap gasket 
material will harden. 
The purpose of the pre-heating step is to prevent temperature gradients 
from developing within the cap gasket material. That is, if the cap and 
cap gasket material were inserted into the multi-mode oven at room 
temperature, as the gasket material absorbed energy to reach 340.degree. 
F., the cap, being non-absorptive to the energy, would act as a heat sink 
for the energy absorbed by the gasket material. Thus, the portion of the 
gasket material on, or adjacent to, the cap would be cooler relative to 
the portion of the gasket material furthest from contact with the cap. 
Thus, a temperature gradient would be developed across the gasket 
material. Temperature gradients may cause uneven hardening in the cap 
gasket material. Further, if the temperature in the cap gasket material 
becomes too hot, it may scorch, which results in the cap gasket material 
turning brown. If the temperature in the cap gasket material does not 
reach 340.degree. F., the cap gasket material will not cure and 
accordingly will remain liquid. If the closure is heated too long, the cap 
may melt and become distorted. 
It is desirable, however, to eliminate the pre-heat step. One drawback of 
preheating is that the preheat oven requires a large amount of floor 
space. Further, preheating is an additional process step. Another drawback 
of preheating is that caps side walls may have a thin cross-sectional area 
that will deform if pre-heated. 
Another drawback in using a multi-mode oven is that because it may not 
always be known how many closures are in process at any given time and 
because as closures absorb a percentage of the surrounding microwave 
energy, the requisite processing time may vary from load size to load 
size. This variation complicates the microwave oven processing procedure 
by requiring heating parameters to be constantly changed with load 
variations. 
When processing many closures simultaneously, a large amount of floor space 
may be required to accomplish preheating. A multi-mode microwave oven may 
require 100-200 square feet of floor space. However, in a production 
environment, available floor space is typically very limited. 
Finally, continuously processing closures having a height greater than 
11/2" in a multi-mode microwave oven may not readily be accomplished 
without requiring elaborate choking structures to reduce leakage of 
microwave energy. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an improved method and 
apparatus for processing closures. 
It is also an object of the present invention to provide a method for 
uniformly curing cap gasket material. 
It is further an object of the present invention to provide an apparatus 
that continuously cures the cap gasket material for many closures 
simultaneously. 
Another object of the present invention is to provide an apparatus to 
process closures in a microwave or radio frequency oven without requiring 
a pre-heating of caps and gasket material. 
An additional object of the invention is to provide a microwave heating 
apparatus that processes closures of various heights without requiring 
elaborate leakage supression chokes. 
A further object of the present invention is to provide an apparatus for 
curing cap gasket material with reduced floor space requirements. 
These and other objects are accomplished by an apparatus for curing a 
closure coupling a cap and a gasket material disposed thereon comprising: 
a single mode radio frequency waveguide; means for transmitting radio 
energy into the waveguide; and, means introducing cap and gasket material 
therein into the waveguide at room temperature for moving the cap and 
gasket material through the waveguide to selectively heat the cap gasket 
material to a predetermined curing temperature and for removing the cap 
and gasket material therein from the waveguide to return the gasket 
material to room temperature and cure the gasket material. By having a 
single mode radio frequency waveguide, a uniform radio frequency field 
develops within the waveguide so that the temperature of gasket material 
on the cap is relatively uniform when heated from room temperature to the 
curing temperature when passed through the waveguide. 
It is a preferred embodiment that the apparatus include a waveguide 
termination structure having impedance match the output impedance of the 
waveguide so that the termination structure absorbs substantially all of 
the microwave energy transmitted into the waveguide and not absorbed by 
the gasket material. 
It is a further feature of the invention that the closures be rotated while 
moving through the waveguide. The rotation will uniformly cure the gasket 
material on the cap. It is additionally preferable that the waveguide be 
substantially vertically positioned so that the apparatus will reduce the 
amount of floor space required to heat gasket material by having the caps 
move vertically rather than horizontally. It is additionally preferable 
that the microwave or radio frequency energy have a preset operating 
wavelength and that the waveguide have a first and second opening wherein 
the caps are introduced into the waveguide through the first opening and 
removed from the waveguide through the second opening. The size of the 
openings are preferably less than 1/2 of the preset operating wavelength 
so that the apparatus will allow closures to enter and exit through the 
waveguide without elaborate choking structures. 
The apparatus also comprises means for moving the cap into the first 
aperture, by a belt extended through the waveguide to transport closures 
into the waveguide without interfering with the transmission of microwave 
or radio frequency energy into the waveguide. 
In accordance with an additional feature of the invention, the apparatus 
includes means for introducing a predetermined amount of microwave power 
into the waveguide. This amount of such power is several orders of 
magnitude greater than the amount of energy expected to be absorbed by the 
maximum amount of closures being processed in the waveguide at a 
predetermined processing interval. Thus, if the load is varied from the 
maximum load, the processing time need not be varied. 
The invention may also be practiced by the method of curing plastic 
material comprising the step of positioning the plastic material at room 
temperature into a single mode waveguide energized with radio frequency 
energy so as to heat the plastic material to a predetermined curing 
temperature. It may be preferable that the method include the step of 
removing the heated plastic material from the waveguide to return the 
plastic material to room temperature. 
The invention may further be practiced by the method of curing gasket 
material on a cap to make a closure comprising the step of positioning the 
cap with the gasket material at room temperature into a single mode 
waveguide energized with radio frequency or microwave frequency energy so 
as to heat the gasket material to a predetermined curing temperature. It 
may be preferable that the method further comprise the step of removing 
the heated gasket material from the waveguide to return the temperature of 
the gasket material to room temperature to cure the gasket material. 
Alternately, the method may comprise the steps of moving the cap through 
the waveguide when the gasket material is heated and rotating the cap as 
it moves through the waveguide.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown an apparatus 9 for curing a closure 
made up of a cap and gasket material, such apparatus 9 includes a 
microwave frequency transmitter 10 (300 MHz-300 GHz) or any radio 
frequency (approximately 20 KHz-300 GHz) transmitter connected to a 
waveguide structure 11. Waveguide structure 11 has a straight waveguide 
section 12 attached to the lower portion 14 of a vertical main, 
rectangular cross-section waveguide section 16. Attached at the upper 
portion 18 of the vertical main waveguide section 16 is a straight 
waveguide section 20 having a water load 21 at its far end. Within main 
waveguide section 16 is single mode waveguide cavity 23. 
Referring to FIG. 2, there is shown a closure 22 having a cap 24 with a 
gasket material 26 typically embedded within a groove 28 formed on the 
cap's end panel 30. Caps 24 can vary in height and shape and ordinarily 
have a ridge 32 and a skirt 33. Cap 24 will preferably have a height of 
less than 4 inches and a diameter also less than 4 inches. The cap 24 is 
typically made from a hardened plastic, such as polypropylene material. 
The gasket material 26 is also made from a plastic material such as 
Polyvinyl Chloride (PVC) powder and another plastic material that 
plasticizes PVC and may be a member of the phthalate family. Gasket 
material 26 is highly absorptive of microwave energy (i.e. it has material 
properties that absorb microwave energy and cause it to heat up in a 
microwave field) relative to the microwave energy absorptivity of the cap 
material (which has a small conductivity and is essentially transparent to 
microwave energy). The gasket material 26 thermal conductivity may be 
increased by mixing in with it a filler material such as alumina. 
Referring to FIGS. 1 and 3, there is shown a vertical main waveguide 
section 16 preferably constructed with a WR 975 guide tubing having a 
total length of approximately 8.0 feet. WR 975 guide has a width dimension 
that is twice its height dimension. The vertical main waveguide section 16 
is constructed to operate in a TE.sub.l0 mode. Disposed on the opposite 
side of vertical main waveguide section 16 across from straight waveguide 
section 12 is feed inlet section 34. Across main waveguide section 16 from 
feed inlet section 34 is chain outlet section 36. The floor of both feed 
inlet section 34 and chain outlet section 36 is disposed below the level 
where straight waveguide section 12 mates with main waveguide section 16. 
Across from straight waveguide section 20, connected to main waveguide 
section 16, is feed outlet section 38. The height of feed outlet section 
38, feed inlet section 34 and chain outlet section 36 are less than 1/2 
wavelength of the free space operating wavelength of the microwave energy 
used by the apparatus 9 to prevent microwave energy from leaking out of 
feed inlet section 34, chain outlet section 36 and feed outlet section 38. 
As is well known, microwave energy will not propagate through openings 
having a width and height less than 1/2 its wavelength. Hence, since the 
free space operating wavelength is approximately 13" inches, this feed 
structure allows 4" caps to pass into main waveguide section 16 without 
requiring complicated choking structures. The distance between feed inlet 
section 34 and feed outlet section 38 is approximately 6.5 feet. 
Referring to FIGS. 1, 3 and 4, on the floor of lower portion 14 of main 
waveguide section 16 is bottom guide structure 75. The top surface 77 
(FIG. 3) of bottom guide structure 75 is located 1/2 wavelength below the 
center of straight waveguide section 12 resulting in the guide structure 
75 appearing as a short circuit. Microwave energy from straight waveguide 
section 12 propagates up main waveguide section 16 and is not reflected 
back into straight waveguide section 12. Bottom guide structure 75 
supports guide shafts 66 and 68 and drive screws 46 and 48. 
Referring to FIGS. 1 and 3, a conveyer belt 40 runs through vertical main 
waveguide section 16 via feed inlet section 34 and chain outlet section 
36. Conveyer belt 40 transports closures 22b (FIG. 1) and 22c (FIG. 3) 
into main waveguide section 16. Closure 22d is then transported upwards by 
a pair of drive screws 46 (FIG. 1) and 48. Closures 22a are deposited onto 
conveyer belt 40 through conveyer 42. It is recognized by placing feed 
inlet section 34 and chain outlet section 36 below the level of straight 
waveguide section 12, a conveyer belt 40 can extend through main waveguide 
section 16 and downward without having to also extend through straight 
waveguide section 12. Extending a conveyer belt through straight waveguide 
section 12 can complicate its construction. Referring to FIG. 1, connected 
to straight waveguide section 12 is blower 50. Blower 50 moves cool air 
into straight waveguide section 12 and through main waveguide section 16 
to keep the air temperature within cavity 23 cool. This cool air prevents 
drive screws 46 and 48 from melting. 
Located at the top of vertical main waveguide section 16 is a guide 
structure 52 which holds the drive screws 46 and 48 in place during 
operation. The bottom surface 53 (FIG. 3) of guide structure 52 is located 
at approximately 1/2 wavelength above the center of straight waveguide 
section 20 resulting in guide structure 52 operating as a short circuit. 
Accordingly, the microwave energy within cavity 23 propagates into 
straight waveguide section 20 and does not reflect back in main waveguide 
section 16. Disposed directly below guide structure 52 is feed outlet 
section 38. Feed outlet section 38 has a maximum height dimension of less 
than 1/2 wavelength. 
Referring to FIG. 3, within feed outlet section 38 is a ramp 54 sloped at 
an angle such that closure 22e slides down and out of main waveguide 
section 16 after closure processing. Across from feed outlet section 38 is 
a nozzle 58 which forces out closures 56 onto ramp with air pressure. 
Referring to FIG. 2, during closure processing operation, gasket material 
26 in liquid form is injected into the groove 28. 
Referring to FIG. 1, the closure 22 moves at room temperature onto a series 
of belts 42 and 40 into the waveguide section 16. Next closure 22c moves 
through the main waveguide section 16. Microwave frequency energy couples 
into main waveguide section 16, wherein gasket material 26 is heated to a 
predetermined curing temperature, as noted previously the microwave 
absorptivity of the gasket material 26 is greater than that of the cap 24 
material. Accordingly, the gasket material 26 heats up faster than the cap 
24 in the microwave field. The cap 24 heats primarily by conduction from 
the gasket material 26. The gasket material 26 heats to the predetermined 
curing temperature. After reaching such temperature, the closure 22c (FIG. 
3) then moves out of the main waveguide section 16 down ramp 54 onto other 
belts 60 where the closure 22g is cooled to room temperature and is 
transferred for further processing. More details of this curing operation 
will be explained later. 
Disposed across from feed outlet section 38 below air blower 58 is straight 
waveguide section 20. Within straight waveguide section 20 is water load 
21 which absorbs substantially all of the microwave energy that is 
propagated into main waveguide section 16 from transmitter 10 except for 
that portion absorbed by the gasket material. The length of straight 
waveguide section 20 may contain inductive posts or tuning stubs (not 
shown) to ensure minimal reflection from water load 21. 
When microwave energy from transmitter 10 propagates through main waveguide 
section 16, substantially all of the microwave energy is absorbed by water 
load 21. More particularly, much less than 1% of the total power available 
in main waveguide section 16 is absorbed in any individual closure such as 
closure 22d. For example, when closure 22 moves through main waveguide 
section 16 with no other closures in process, that closure moves through a 
microwave field having 100% of the available power available when it first 
entered main waveguide. That closure also has 100% of the available power 
available when it leaves main waveguide. Hence, the average power that a 
closure is exposed to is 100%. As a closure absorbs much less than 1% 
(approximately 0.1% for a 50KW field) of the average total power and is 
moved through the waveguide in approximately 30 seconds, the closure will 
absorb approximately 1500 joules. 
Thus, when a closure moves through main waveguide section 16 in 30 seconds 
with the maximum number of closures in process (approximately 60), that 
closure moves through a microwave field having 100% of the available power 
when it first enters main waveguide section 16. Sixty closures will absorb 
6% of the total power in the main waveguide. Hence, a closure moves 
through a field having 94% of the available power just before it leaves 
main waveguide. The average power that a closure is exposed to is 97%. 
Accordingly, a closure in a fully loaded system moving through apparatus 9 
within 30 seconds will absorb 1455 joules, only 3% less than a system with 
only one closure in process. It is recognized by having a substantial 
percentage of microwave energy being absorbed by water load 21, the number 
of closures within main waveguide section 16 at any given time with a 
fixed time interval will have little effect on the curing and final 
temperature of the gasket material 26. In other words, having 1 closure or 
60 closures within waveguide during a 30 second microwave exposure will 
have little effect on the finished closure and its gasket material. 
It is preferable that the transmitter 10 transmit between 30 and 50 
kilowatts of power at 915 MHz to be able to cure gasket material at a rate 
of 120 closures per minute; however, more or less power may be used if the 
main waveguide section 16 is modified slightly, as will be explained 
later. It is also preferable that a WR 975 type waveguide be used for 915 
MHz transmitter frequency. The length of the main waveguide section 16 is 
constructed to ensure maximum throughput and that each closure remain in 
the waveguide for the minimum time (see FIG. 6). 
The feed inlet section 34 and feed outlet section 38 preferably have a 
height dimension of less than 41/2 inches. It is recognized that this 
height dimension is dependent on the microwave transmitter frequency. By 
having the maximum height dimension of feed inlet section 34 and chain 
outlet section 36 less than 1/2 wavelength, no special choking structure 
around feed inlet section 34 or chain outlet section 36 is required. 
In FIG. 5, there is shown a drive system 64 which transports a closure 22d 
through the vertical main waveguide section 16. The drive system 64 
includes a left drive screw 48 and a right drive screw 46. The drive 
system 64 also includes a pair of closure guides 66 and 68 which are held 
in place with mounting screws 70 and 72. Each drive screw 46 and 48 has a 
helical lip 74 (FIGS. 3, 4 and 5) which rotates around drive screws 46 and 
48. The spacing between lips 74 is preferably 1-2 inches. 
Referring to FIGS. 3 and 4, located on the bottom of waveguide section 16 
is bottom guide structure 75. Bottom guide structure 75 supports drive 
screws 46 and 48. Closures 22 contain caps 24 that have a ridge 32 which 
is held in place with lips 74. Optionally, cap 24 may be supported on lips 
with end panel 30. These caps 24 also have a skirt 33 having an outer 
diameter less than the ridge 32 outer diameter so that the closure 22 can 
hang between more than one pair of lips. Lip 74 supports closures (not 
shown) having taller walls. If taller closures are used, the processing 
rate must be reduced. 
Referring to FIG. 5, the drive screws 46 and 48 rotate counter-clockwise 
which results in the closure 22d turning clockwise while being pushed 
upward. It is recognized by turning the closure while moving it through 
the main waveguide section 16, more uniform curing occurs within the 
gasket material 26. It is also recognized by not turning the closure 22d, 
the gasket material 26 (FIG. 2) may scorch. 
Referring to FIG. 4, the left drive screw 48 and right drive screw 46 are 
turned by a belt 78 connected to a motor (not shown) that is located below 
the main waveguide section 16. It is preferable that the left drive screw 
48 and right drive screw 46 are connected at their bottom to prevent 
slippage. It is also preferable that left and right drive screws 48 and 46 
have one of their lips 74 properly aligned when the closure 22d is moved 
upward. 
Referring to FIG. 3, various conveyer systems are preferably used to place 
a closure into the main waveguide section 16. At the bottom of the main 
waveguide section 16 running through feed inlet section 34 and feed inlet 
section 36 is conveyer belt 40 which is formed with a microwave 
transparent chain 80. Chain 80 is placed over a gearing mechanism 82 that 
is connected to motor (not shown) to move closures. Conveyer 42 places 
closure 22a onto belt 40. Belt 40 moves closures 22c into main waveguide 
section 16. Closure 22d then moves through main waveguide section 16, 
wherein closure 22d gasket material (not shown) is cured. Closure 22e 
containing cured gasket material moves onto ramp 54. Below ramp 54 is 
conveyer 60 which moves closure 22g to another step for further 
processing. 
Referring to FIGS. 3 and 4, during operation, the closure's 22 path is as 
follows: First, the liquid gasket material 26 is injected into the cap 24. 
The closure 22 is then put on conveyer 42 at room temperature. The 
conveyer 42 then deposits the closure 22a onto conveyer 40. Conveyer 40 
moves closure 22c through feed inlet section 34 and into vertical main 
waveguide section 16. The closure 22c is stopped from going through the 
main waveguide section 16 by closure guide 68. The left and right drive 
screws 46 and 48 rotate, resulting in the closure 22d rising upward. It is 
noted that as the closure 22d rises upward, it is held in place with 
closure guide 66 and closure guide 68, and rotates in a counter-clockwise 
direction (see FIG. 5). Further, as the closure 22d moves upward through 
vertical main waveguide section 16, the gasket material 26 temperature 
rises, as does the temperature of the cap 24 until the gasket material 26 
exceeds the curing temperature. At that time, the closure 22e will reach 
the top of vertical main waveguide section 16. A blower, or alternately a 
tapping device, or equivalent, moves the closure 22e onto ramp 54 and then 
downward onto belt 60 to return the gasket material to room temperature. 
The gasket material will harden when cooled to room temperature. The 
closure 22g then moves to the next step in the process. 
It is recognized that with the disclosed embodiment, 120 closures per 
minute may be processed. It is noted that other embodiments may also be 
constructed having wider distances between lips, taller main waveguides, 
different waveguide shapes with a corresponding microwave frequency (other 
than 915 MHZ) to change the processing rate, maximum cap heights or cap 
shape. It is also recognized that the closure 22 is moved through 
waveguide structure 11 at a rate to prevent gradients and scorching from 
developing in the gasket material 26. The closure 22 moves through main 
waveguide section 16 at a fast enough rate so that the cap 24 does not 
heat by conduction from the gasket 26 to such an extreme temperature that 
closure 22 becomes distorted. 
The preferred embodiment has a water load termination 21 which absorbs 
substantially all of the microwave energy generated by the transmitter 10. 
However, it may also be preferable that the water load 21 (or other load) 
be located within the transmitter and the far end of the vertical main 
waveguide be constructed so as to reflect all of the microwave energy 
transmitted into the main waveguide section 16. This approach will permit 
each closure to absorb twice the power as a non-reflecting waveguide; 
however, the variation in the power going to each closure 22 will be more 
susceptible to non-uniformities in main waveguide section 16 due to 
varying numbers of closures in the vertical main waveguide section 16. If 
this approach is taken, a three port microwave circulator would be located 
in the transmitter. The load would be coupled to one port of the 
circulator, the microwave source would be coupled to the second port and 
the waveguide applicator would be coupled to the third port. 
It may also be preferable that another approach be taken having one or more 
waveguides connected to the first waveguide structure 11. These waveguide 
structures would be substantially identical and would be connected so that 
several waveguide structures may process caps simultaneously. This 
additional waveguide structure will be positioned such that the microwave 
energy from the first waveguide structure enters the additional waveguide 
structure through the location where the water load 21 is located on the 
shown embodiment (FIG. 1). At the location of where transmitter 10 is 
located on the first waveguide structure on the additional waveguide 
structure would be a water load which would absorb substantially of the 
microwave energy flowing through first and additional waveguide 
structures. The advantage of this approach is that twice or more caps may 
be processed simultaneously using the same transmitter 10. 
Referring to FIG. 6, there is shown a plot of the temperature differential 
(.DELTA.T) from the top to bottom of gasketing material 26 within a 
closure 22 as a function of the constant power process time using a gasket 
material having either standard degree of thermal conductivity, (line 94) 
or higher degree as by adding alumina powder (line 92). The process times 
given were for gasket material 26 having a thickness of 1/32 inches, 
reaching curing temperature (approximately 425.degree. F.) from room 
temperature (80.degree. F.). The process time is a function of the 
dielectric absorptivity of the gasket material 26, the heat transfer 
characteristics of cap 24 and the surface cooling rate of the gasket 
material 26 due to surrounding air. 
Line 96 is the threshold where the temperature differential (.DELTA.T) 
between the top and bottom of the gasket material 26 is too high. The high 
temperature differential may cause scorching in the gasket material 26. 
Below line 98 is the region where the gasket material temperature 
differential (.DELTA.T) is acceptable. In this region, the gasket material 
26 will cure evenly. Therefore, standard gasket material, the desired 
process time is 50 seconds (line 94) and for high conductivity gasket 
material, the process time will be approximately 30 seconds (line 92). 
Between line 96 and line 98 is the region where the gasket material 26 
temperature differential (.DELTA.T) at curing temperature is marginal. In 
this region, a few of the processed closure's 22 gasket material 26 will 
have scorchings as well as a few of the closure's gasket material may not 
be cured. The processing time for a closure 22 to fall in this region is 
either less than 0.25 seconds or greater than 25 seconds for standard 
conductivity gasket material (line 94) and greater than 13 seconds for 
high conductivity gasket material (line 92). Accordingly, the closure may 
be processed in as quick as 13 seconds for high conductivity gasket 
material and as quick as 25 seconds for standard conductivity gasket 
material. 
Accordingly, the closures should be transported through the main waveguide 
section 16 at a rate that will result in the gasket material reaching 
curing temperature with minimal scorching or distortion. It is recognized 
that moving a closure 22 through the main waveguide section 16 in 30 
seconds under constant power will cure gasket material 26 with the 
acceptable limits. This rate will allow 120 one inch closures to be 
processed in one minute. 
This concludes the Description of the Preferred Embodiments. A reading of 
those skilled in the art will bring to mind many modifications and 
alternatives without departing from the spirit and scope of the invention. 
Accordingly, it is intended that the invention only be limited by the 
following claims.