Electric heating – Heating devices – Combined with pressure application means
Reexamination Certificate
2000-11-03
2003-12-02
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Combined with pressure application means
C219S543000, C219S388000, C156S583400, C156S583100
Reexamination Certificate
active
06657165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to machinery and processes for manufacturing spaced apart thermal seals in applications such as pouch-type bags in which metered quantities of substances, such as food stuffs, are sealed therein.
2. Description of the Prior Art
The Assignee of the present invention manufactures machinery for making thermally sealed pouch-type bags. Machines of this type are well known. A continuous web having the front and back sides of the bag printed thereon is folded in half and run over the outside periphery of a first sealing system to which the present invention relates in part. The sealing system has evenly spaced thermally actuated sealing elements mounted on the periphery of a rotating wheel which forms parallel spaced apart seals by melting a thermoplastic material coated on the inside of the web after the web has been folded in half. After the parallel seals are made by the sealing system, each bag in the web has been formed except for the closure of the top. After running across the sealing system, the continuous web with parallel spaced apart seals which define the opening of each bag is fed to a pouch filling station at which a metered quantity of substance, such as powered food, is placed inside the individual bags located along the continuous web as the bags at the pouch filling station rotate around the periphery thereof. After filling with the metered quantity of substance, the bags then pass to a second thermal sealing station which heat seals the top of each bag to close the food stuff or other material therein in a sanitary manner. Finally, the sealed bags, which are still part of the continuous web, pass to a cutting station at which a series of rotating knives cut the individual bags apart uniformly in the middle of the parallel spaced apart thermal seals which were formed by the first sealing system.
The Assignee of the present invention manufactures machines of the aforementioned type which operate at high processing speeds, such as up to 4000 linear inches per minute or higher, to make individual pouch-type bags from the moving web. High speed operation in machinery of this type is extremely important as a consequence of the economics of manufacturing products such as dry packaged foodstuffs. Any circumstance occurring during manufacturing of filled thermally sealed pouch-type bags which requires the line to be shut down has a serious effect on the productivity of the manufacturing operation.
Materials from which thermally sealed pouches are manufactured include paper, cellophane foil, metallized structures, polypropylene and other laminates of preprinted or unprinted stock.
In the prior art, two basic types of sealing systems, which typically operate with the axis of rotation of the sealing wheel of the sealing system being vertical, are known. These sealing systems are known as “drum” and “modular” sealing systems.
The drum style sealing system is a single piece of metal machined from a casting which has a calculated land diameter that is the heated surface contacting the moving web to form the spaced apart parallel seals. Drum style sealing systems have the disadvantage of not having an adjustable spacing between the parallel seals which define the width of the pouch-type bag. Behind each land and parallel thereto is a hole containing a tubular electric heater element. Drum style sealers work well once the substantial thermal mass of the machined casting has come up to operating temperature which is typically a temperature of 280° F. or above. The drum, as a consequence of its high thermal mass, will produce unacceptable seals if the continuously moving web has to be stopped for any reason. This high thermal energy of the drum at the point of contact of the lands with the web for a substantial period of time either causes the parallel seals to be destroyed because of the prolonged contact or the parallel seal grow to a greater width than desired which restricts the size of the bag. A reduced volume of the bag caused by wider seals either prevents the desired metered quantity of material from being placed inside the bag or worse, the spacing between the bags at the cutting station becomes out of synchronism with the spacing of the cutting knives causing severing of the web at spaced apart locations which do not correlate with the middle of the thermally formed seals which can cause the bags to have faulty seals or spill the contents thereof.
The modular sealing system is illustrated in FIG.
1
. The modular style sealing system
10
includes a wheel having a stationary lower circular plate
12
and an upper rotating annular ring
14
to which individual seal forming elements
16
are mounted by threaded type connectors
17
. The seal forming elements make peripheral contact with a continuous web
18
as illustrated in FIG.
2
. The wheel of the sealing system
10
is driven by rotating shaft
18
. Cooling air is blown from holes
19
. The individual seal forming elements
16
may be moved radially in slots
20
to permit adjustment of the spacing between the parallel seals
24
by loosening and tightening of the connectors
17
. Each of the sealing elements
16
, like the aforementioned drum style sealer wheel, has a tubular electric heating element (not illustrated) mounted in a longitudinally extending hole in each seal forming element
16
.
The modular style sealing system
10
is a substantial improvement over the drum style sealing system by permitting adjustability of the spacing between individual spaced apart seals
24
on the continuously moving web
18
. The overall thermal mass of the sealing elements
16
results in a substantial variation in the temperature along the longitudinal dimension thereof. The modular style sealing system typically operates with a temperature differential along the longitudinal dimension between the top and bottom of the individual sealing elements
16
of 30° to 40° F. and between 30° to 50° F. between different sealing elements
16
. In part, the difference in temperature along the longitudinal dimension of the sealing elements
16
during operation is caused by heat flow from the electrical heating element of the individual sealing elements
16
to the top rotating annular plate
14
during rotation and stoppage thereafter. In order to obtain a high quality seal across the length of a pouch-type bag, it is necessary to operate the modular sealing wheel at a temperature which, at its lowest point is a temperature such as 280° F., which can result in some of the individual sealing elements
16
operating at the center thereof, which are more thermally insulated than the top and bottom portions of the sealing wheel, at a temperature of at least 320° F.
As illustrated in
FIG. 2
, during normal operation, the continuous web
18
rolls across the periphery of the individual sealing elements
16
. The sealing elements
16
have precisely chosen spacings therebetween so that each peripherally outwardly facing surface
22
contacts the continuous web
18
at the same place as the web moves around the periphery of the wheel. The result of the precise registration during moving of the continuous web
18
in contact with the outer surfaces
22
of each sealing element
16
is the formation of a straight uniform width seal
24
even though there is the aforementioned temperature variation of 30° to 40° F. during operation between the center of the individual heating elements and the ends thereof. Because of the high speed rotation of the web across the sealing wheel
10
, there is a controlled short dwell time which produces uniformity in seal width, even though the aforementioned temperature variation exists.
However, if, for any reason the continuous movement of the web
18
has to be stopped, the higher operating temperature of the midpoint of the sealing elements
16
, which have substantial thermal mass, causes the individual surfaces
22
to contact the continuous web
18
sufficiently long to produce a seal
26
which grows in width toward the mi
Makutonin Boris E.
Oliverio Frank G.
Jeffery John A.
R. A. Jones & Co. Inc.
Wood Herron & Evans LLP
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