U.S. patent number 3,711,957 [Application Number 05/135,066] was granted by the patent office on 1973-01-23 for shrink tunnel.
Invention is credited to Herbert K. Carver, Jr..
United States Patent |
3,711,957 |
Carver, Jr. |
January 23, 1973 |
SHRINK TUNNEL
Abstract
A shrink tunnel, for shrinking plastic wrapping film about a
package as it moves along on a conveyor, has two blower-heater
units within its housing, one at each side of the conveyor. The
blower-heater units are so constructed and so positioned that each
delivers narrow vertical laminar streams of heated air diagonally
and slightly downwardly across the shrink zone in the tunnel and
across any package which is passing therethrough on the conveyor.
The heated streams of air projected from the two blower-heated
units flow in opposite directions, with the streams of air of one
blower-heater being located in vertical planes which are parallel
and laterally adjacent to the vertical planes of the streams of air
of the other. The heated streams of air projected from each
blower-heater are sucked into an intake duct of the other, are
re-heated, and projected back through the shrink zone and across
the package which may be passing therethrough. Heated air is thus
caused to flow back and forth and in so doing inpinges directly
upon all sides and upper surfaces of any film-wrapped package which
may be passing through the tunnel. The velocity at which the heated
air moves is not high, and as the air moves across the shrink zone
from the heater of one blower to the intake duct of the other, the
air which impinges upon the package tends to follow the contour of
the package as it is pulled on and into the intake duct of the
other blower.
Inventors: |
Carver, Jr.; Herbert K.
(Oakford, PA) |
Family
ID: |
22466370 |
Appl.
No.: |
05/135,066 |
Filed: |
April 19, 1971 |
Current U.S.
Class: |
34/487; 53/557;
34/223; 219/388; 392/379; 34/506 |
Current CPC
Class: |
B29C
35/04 (20130101); B65B 53/063 (20130101); B29C
35/045 (20130101) |
Current International
Class: |
B65B
53/06 (20060101); B65B 53/00 (20060101); B29C
35/04 (20060101); F26b 003/00 () |
Field of
Search: |
;34/31,33,34,223
;219/388 ;98/36 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3534393 |
October 1970 |
Bickham et al. |
|
Primary Examiner: Dority, Jr.; Carroll B.
Claims
What is claimed is:
1. A shrink tunnel for shrinking heat-shrinkable film about a
package which is passing therethrough, said shrink tunnel
comprising:
a. a housing;
b. a first blower-heater unit mounted within said housing at one
side of the path of movement of said package;
c. a second blower-heater unit mounted within said housing at the
other side of said path;
d. each of said first and second blower-heater units including a
blower, an intake duct for the blower, a motor drive for the
blower, a heater, and a duct leading from the blower to the
heater;
e. said heater being constructed to function as a discharge nozzle
and positioned to direct heated air diagonally laterally across the
path of movement of said package;
f. said heaters being so positioned and oriented relative to each
other that the heated air discharged from one of said heaters flows
in a plane which is laterally adjacent the plane of the heated air
discharged from other of said heaters;
g. each of said blowers having its intake duct located directly
opposite and in the plane of the direction of air flow from the
other of said blowers;
h. said input ducts of said blowers being so positioned and
oriented relative to said heaters that heated air discharged from
the heater of each one of said blower-heater units is sucked into
the intake duct of the other.
2. Apparatus according to claim 1 characterized in that each of the
heater units of said first and second blower-heater units
comprises:
a. a plurality of heater elements vertically disposed and laterally
spaced from each other;
b. partition elements between said heater elements and forming a
plurality of narrow vertical passages through which the air is
discharged in narrow vertical streams.
3. Apparatus according to claim 2 characterized in that:
a. said housing is provided with a mounting plate diagonally
positioned relative to the axis of said housing;
b. said blower-heater units are mounted on said plate, one at each
end thereof;
c. the blowers of said respective units being mounted on opposite
sides of said plate;
d. the intake ducts of said respective blowers being mounted on
opposite sides of said plate;
e. the intake duct of each blower being mounted on the opposite
side of said plate from the blower;
f. said plate being provided with openings providing communication
between the input duct and the blower.
4. Apparatus according to claim 3 characterized in that adjustment
means are provided for adjusting the temperature of the heated air
discharged from said heaters.
5. Apparatus according to claim 2 characterized in that said
heaters are so positioned that said narrow vertical streams of air
are discharged from said heater passages diagonally and slightly
downward relative to the path of movement of said package.
6. Apparatus according to claim 2 characterized in that said heater
elements are helical coils.
7. Apparatus according to claim 2 characterized in that said heater
elements are connected electrically in series.
8. Apparatus according to claim 4 characterized in that said
adjustment means includes mechanical means for varying the velocity
of the air moving across the heater elements.
9. Apparatus according to claim 4 characterized in that said
adjustment means includes electronic means for varying the
effective voltage applied to said heaters.
10. Apparatus according to claim 3 characterized in that:
a. each of said heaters is positioned below its associated blower,
both being in the same vertical plane, and
b. the input duct of the one blower is in the same diagonal
vertical plane as the blower and heater of the other unit.
11. Apparatus according to claim 4 characterized in that said
adjustment means comprises:
a. mechanical means for varying the velocity of the air moving
across the heater elements; and
b. electronic means for varying the effective voltage applied to
said heaters.
12. The method of shrinking heat-shrinkable plastic film about a
package as it moves along a path, said method comprising:
a. projecting streams of heated air in laterally adjacent paths in
opposite directions diagonally across the path of said package;
b. creating a suction in planes common to the paths of each of the
projected streams;
c. sucking each of said streams toward the side of the package path
opposite that from which said stream was projected, and
d. re-projecting said sucked-in air back across the package path in
an air path laterally adjacent to its first-named path.
13. The method according to claim 12 characterized in that the
heated air stream is projected at a low velocity but sufficient to
enable the air stream to reach a point at which it is drawn by
suction toward the opposite side of the package path, whereby when
the heated air stream impinges upon a package the air stream tends
to follow the contour of the package.
14. The method according to claim 12 characterized in that the air
stream is heated immediately before it is projected across the
package path.
15. The method according to claim 14 characterized in that the
heated air streams are narrow vertical streams and that the moving
package is exposed to the heated air for but a short time
insufficient to cause the contents of the package to become hot.
Description
BACKGROUND OF THE INVENTION
The present invention relates to package wrapping and particularly
to apparatus and method for shrinking heat-shrinkable thermoplastic
film about the contents of a package. More particularly, the
invention relates to an improved shrink tunnel, and its method of
operation.
Shrink tunnels are well known in the prior art and numerous patents
have been granted relating thereto. Such shrink tunnels are usually
mounted over or in close relation to a conveyor on which are
carried the film-wrapped packages which are to be heat shrunk. As
the conveyor carries the film-wrapped package through the tunnel,
hot air generated by the tunnel apparatus comes into contact with
the thermoplastic film and causes the film to shrink about the
package and its contents. Many prior art shrink tunnels operate as
ovens, i.e., the package merely moves into and out of a heated zone
without direct impingement of heated air streams on the package. In
such shrink tunnels, heated air escapes from the tunnel each time a
package moves into and out of the tunnel through the entrance and
exit curtains.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a more
efficient apparatus and method for shrinking heat-shrinkable
thermoplastic film about a package as it passes along on a
conveyor.
Another object is to provide an improved form of shrink tunnel
which operates more efficiently, requires less power, and is more
economical to operate.
Another object is to provide a more efficient shrink tunnel which
is of short length so that the tunnel radiates less heat,
particularly into a cool or refrigerated area, thereby providing
efficiencies not only with respect to the operation of the tunnel
but also with respect to the operation of the refrigeration
system.
Another object is to provide an efficient tunnel having a shrink
zone of short length, whereby the contents of the package do not
become hot.
The foregoing objects are achieved, in accordance with the present
invention, by providing a short shrink tunnel having a shrink zone
in which laminar streams of heated air, generated within the
tunnel, are caused to flow back and forth across the moving package
in adjacent air paths, with little or no air excaping from the
tunnel.
More specifically, the new shrink tunnel has a blower-heater unit
on each side of the conveyor path. The units are so constructed and
so positioned that narrow vertical streams of laminar heated air
are directed diagonally, slightly downwardly, and in opposite
directions across the shrink zone in the tunnel through which the
packages are passing. The opposing streams of air are spaced
laterally from each other, with the air stream propelled at
relatively low velocity from one blower being sucked into the
intake duct and orifice of the other blower.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of a shrink tunnel according to
the present invention;
FIG. 2 is a top view, in section, looking down along the line 2--2
of FIG. 1;
FIG. 3 is an elevational view, in section, looking along the line
3--3 of FIG. 2;
FIG. 4 is an enlarged view of one of the heaters, looking along the
line 4--4 of FIG. 3;
FIG. 5 is a top view, in section, of the heater of FIG. 4 looking
down along the line 5--5 of FIG. 4;
FIG. 6 are a series of sequential diagrams to illustrate how the
diagonally directed narrow vertical streams of heated air impinge
upon all sides and upper surfaces of a flat rectangular package as
it passes through the shrink tunnel;
FIG. 7 illustrates a slight modification of the apparatus of FIGS.
1-6;
FIG. 8 is a wiring diagram of a presently preferred electrical
circuit for controlling the temperature of the heated air.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a view of the front end of a shrink tunnel 20 constructed
in accordance with the present invention. In FIG. 1, a film wrapped
package P, shown in phantom, is within the tunnel 20 having passed
through the split curtain 28 at the front or input end of the
tunnel. The package P is being carried along on a conveyor belt -10
which is supported on the conveyor frame 12. Shrink tunnel 20
includes a main housing 21 which is supported by suitable means on
the frame 12 astride the conveyor belt 10. In accordance with the
present invention, shrink tunnel 20 is provided with two
blower-heater units, 30 and 50, one at each side of the housing 21,
one on each side of the path of the conveyor 10.
Before describing the structure of shrink tunnel 20 of the present
invention, it will be helpful to describe the novel air flow, and
for this purpose reference will now be made to FIG. 6 which
consists of four diagrams identified as (a) to (d). In FIG. 6(a), a
package P, travelling in the direction indicated by the arrow, has
just entered into the shrink zone in the tunnel 20 and low velocity
streams of heated air from blower-heater 30 have impinged upon the
front edge and front portion of the package. In FIGS. 6(b) and
6(c), the package P is progressing more deeply into the shrink
zone, and its left portion is being impinged upon by streams of
heated air from blower-heater 50, while heated air streams from
blower-heater 30 are impinging upon the right portion of the
package. In FIG. 6(d), the package P has progressed beyond the air
streams from blower-heater 30, and the rear edge and rear portion
of the package is now being impinged upon by heated air streams
from blower-heater 50.
In FIGS. 6(a) through 6(d), the four solid arrow-headed lines from
each of the blower-heater units represent four narrow vertical
laminar streams of heated air emanating from the blower-heater
units 30 and 50, while the dashed lines represent the streams of
air from one blower being sucked into the orifice of the other
through the intake duct thereof. It will be observed that the
streams of air from the blowers are directed diagonally across the
path of the moving package.
In FIG. 6(a) through 6(d), the area of package P which is shown
shaded is the area which has been impinged upon by the heated air
streams from one or the other or both of the blower-heater units 30
and 50. The package P, in FIGS. 6(a) through 6(d), has been assumed
to be flat, as, for example, a package containing a tray having two
lamb chops therein. In such case, the air streams may sweep across
the flat package as indicated. However, when the package P is not
flat, as, for example, when it is peaked, or crowned, or contains
an irregular body of some heights, such as a chicken, the air
streams from each of the blowers will follow the contour of the
package and will be sucked into the input duct on the opposite side
of the tunnel.
It will be seen from FIG. 6, and from the foregoing description
that the entire surface (except only the bottom which is resting on
the conveyor belt) is impinged upon and shrunk by direct streams of
heated air as the package passes through the relative narrow shrink
zone in the tunnel.
Reference is now made to FIGS. 2 and 3 for an understanding of the
structural features of the improved shrink tunnel of the present
invention. As seen in FIG. 2, mounted diagonally within the main
housing 21 of shrink tunnel 20 is a partition plate 22 which, as
seen in FIG. 3, extends downwardly from the top of the housing
about half way toward the base, leaving therebeneath an opening of
sufficient height and size for the packages P to pass through.
Supported on partition plate 22, at each end thereof, and on
opposite sides of the plate 22, are sub-housings 31 and 51,
respectively, for the blower-heaters 30 and 50, respectively. The
two blower-heaters, 30 and 50, one at each side of the tunnel
housing 21, are similar to each other, and it will be necessary to
describe but one of them in detail. Blower-heater 30 will be
described.
Supported externally on sub-housing 31 is a drive motor 32 having a
drive shaft 33 which projects through the wall of sub-housing 31
and into the interior thereof. Mounted for rotation on drive shaft
33 within sub-housing 31 is a support or backing plate 34 on which
are mounted in radial fashion the fan blades 35 of the blower 36 of
the blower-heater unit 30. A circular opening 23 is provided in
partition plate 22 in registry with the orifice of blower 36. Heat
insulating material, not shown, separates the body of motor 32 from
the blower sub-housing 31.
The sub-housing 31 of the blower 30 is so shaped, as seen in FIG.
3, to form a short duct portion 39 which curves downwardly to a
discharge or exit in which is mounted a heater unit 40. The heater
unit 40 is in the same vertical plane as the blower 36, i.e., the
heater unit 40 is directly below the blower 36, both being on the
same side of the vertical plane of partition 22. As will be
explained, heater 40 is so constructed, in accordance with the
present invention, that it not only heats the air immediately
before the air enters the shrink zone, it also functions as a
nozzle which converges the air from blower 36 into a plurality of
narrow vertical laminar streams which are projected into and
through the shrink zone.
The construction of heater unit 40 is illustrated in FIGS. 4 and 5
of the drawing. As there shown, heater unit 40 consists of four
heater elements 41, 42, 43 and 44, preferably helical coils with
large surface areas for greater heat transfer and lower watt
density, yet the turns of the coils are spaced far enough apart to
provide low resistance to the air stream. The heater coils 41-44
may be connected either in series or in parallel. The coils are
physically disposed vertically and in staggered relation, as seen
in FIGS. 4 and 5. Separators 45, preferably of electrical
insulation refractory material, are disposed between the heater
elements and also on the outward sides thereof, forming
therebetween four narrow vertical passages 48 through which the air
passes. It is in these passages 48 that the four heater elements
41-44 are vertically disposed. Material similar to that of the
separators 45 provides a base which is supported in a metal frame
47 secured to the housing 31 at the discharge or nozzle end
thereof.
Referring again to FIG. 2, supported on the diagonal partition
plate 22 on the rear or opposite side from blower-heater unit 30 is
an input duct 37 the bottom and sides of which may be perforated
for allowing passage of air therethrough while excluding from the
intake of the blower any foreign particles of a size which may
possibly cause damage.
The blower-heater 50 on the left side of the shrink tunnel housing
21 is identical, or at least similar, in construction to that just
described with respect to blower-heater 30, and corresponding parts
will be easily recognized in the drawing.
While the shrink tunnel 20 is in operation, air is sucked in
through the input duct 37 which is on the rear side of partition
22, then through the circular opening 23 in the partition plate 22,
and into the orifice of blower 36 on the front side of partition
plate 22. This air is then driven by the rotating fan blades 35
down through duct 39 and out through the heater 40, i.,e., through
the four slots or passages 48 in which the heater coils 41, 42, 43
and 44 are vertically disposed. As a result, four narrow vertical
laminar streams of heated air are projected at low velocity, in a
diagonal and slightly downward direction due to the position of
heater 40, across the conveyor belt 10, from right to left, on the
front side of partition plate 22 and across any package P which may
at that time be moving along on the belt within the shrink tunnel.
This air impinges upon and flow along the near sides and surfaces
of the film-wrapped package and is drawn in through the input duct
57 of blower 56. The air thus drawn in passes through the opening
24 in partition plate 22 and into the orifice of blower 56 on the
rear side of partition plate 22. This air is then projected by
blower 56 down through the duct 59, out through the heater unit 60
and across the conveyor belt 10 from left to right and impinges
upon the near sides and surfaces of the package P on the belt
within the shrink zone. In FIG. 2, the package P is moving in the
direction indicated by the arrow. Thus, FIG. 2 and the diagrams of
FIG. 6 correspond so far as orientation is concerned.
To summarize, the air in FIGS. 2 and 3 is sucked into the input
duct 37 on the rear side of partition plate 22 and through the
circular opening 23 in partition plate 22 into the orifice of
blower 36. The air is then propelled by blower 36 down through duct
39, out through the four slots 48 in heater 40 and across the
conveyor 10 and across any package P which may be thereon at that
time. This air is then sucked into the input duct 57 on the front
side of partition plate 22, through the circular opening 24 in
partition plate 22 and into the orifice of blower 56 on the rear
side of partition plate 22. This air is then propelled down through
duct 59 and out through the four slots in heater 60, across the
conveyor 10 and across the package P and is sucked back into input
duct 37, to complete the cycle. It will be understood that in the
foregoing summary the statement that the air flows "across the
package" is an abbreviated way of say that the air in crossing the
conveyor impinges upon the near side and top surfaces of any
package P that may be passing through the shrink zone. This air
follows the contour of the package surfaces and is drawn into the
input ducts and orifice of the other blower.
It will be seen that the air flow in the tunnel is back and forth,
with one stream flowing in one direction and the other stream
flowing in the opposite direction, with the two streams separated
laterally by a buffer zone and not interfering with each other. The
streams of air are projected by the blowers through the heaters at
relatively low velocity, just enough velocity to carry across and
be picked up by suction and drawn into the input duct and orifice
of the other blower. The principal function of curtains 28 and 29
is to obstruct environmental air from being sucked into the tunnel,
rather than to prevent heated air from escaping.
Several different means may be provided for adjusting the quantity
of heat applied to the package P. One such means is illustrated in
FIGS. 2 and 3. Another and preferred means of adjustment will be
described later. Or, a combination of both may be used.
In FIGS. 2 and 3, cover plates 70 and 80 are shown for adjustably
covering the openings 23 and 24 leading to the orifices of blowers
36 and 56, respectively. Cover plates 70 and 80 are shown to be
pivotally supported at 71 and 81, respectively, on partition plate
22, cover plate 70 being on the rear side and cover plate 80 on the
front side of partition plate 22. The cover plates 70 and 80 are
connected, by links 72 and 82 and pins 73 and 83 to a common
adjustment lever 90 which is pivotally mounted on stub shaft 91 and
movable between a "low" limit position shown in solid line, and a
"high" limit position shown in phantom.
The apparatus shown in FIGS. 2 and 3 and now being described may
preferably be so designed that (1) with the lever 90 in the "high"
position, which reduces the openings into the orifices of the
blowers 36 and 56, and with highest voltage applied to the heater
elements of heaters 40 and 60, the air intake to the blowers will
be sufficient to allow the heaters to operate without glowing while
yet heating the air to the highest level desired, and (2) with the
lever 90 in the "low" position which increases the openings into
the orifices of the blowers, and with lowest voltage applied, the
air is heated to the lowest level desired. It will be understood
that adjustment of the lever 90 to the "high" position, by
decreasing the area of blower intake, decreases decreases the
volume of air per unit of time passing through the heater, thereby
increasing the amount of heat imparted to such volume of air during
a given time interval.
While the adjustment means just described is one way of adjusting
the heat, the presently preferred method is illustrated in FIG. 8.
In the circuit of FIG. 8, when the ON-OFF switch 91 is closed, the
blower motors 32 and 52 are connected across the power line L1-L2,
and so is pilot light 92. In FIG. 8, the four heater coils 41-44
are represented by a single resistance element identified as 41-44,
and similarly, the other four heater coils 61-64 are represented by
a second single resistance element identified as 61-64. These two
resistance elements, representing the two sets of heater coils
41-44 and 61-64 are connected across the line L1-L2 in series with
a Triac power control module 93. A control rheostat 94 controls the
angle at which the Triac is triggered to start conducting on each
half cycle of the input supply voltage. Thus, the power output of
the heater elements is infinitely variable from zero wattage to
maximum wattage. The power output is essentially constant in
relation to time. The heater elements conduct a portion of each
half cycle of the input supply voltage and produce an average power
output.
In some cases, it may be desirable to be able to control both the
wattage output of the heater element and the velocity of the heated
air. In such cases, both the electrical adjustment of FIG. 8 and
the mechanical adjustment of FIG. 3, may be employed.
FIG. 7 represents slight modifications with respect to the shrink
tunnel 20 and conveyor. In the description of the shrink tunnel of
FIGS. 1-6, the conveyor belt 10 has been assumed to be impervious
to air. Thus, in FIGS. 1-6, the conveyor belt itself prevents loss
of air downwardly, and the only air that is lost during operation
is that which is due to the opening of the front and rear curtains
28 and 29 when the packages P pass through. In some instances, the
conveyor may not be an air impervious belt, but may, for example,
be a mesh, or a roller type of conveyor. A roller conveyor 110 is
illustrated in FIG. 7. In such case, a deflector plate 112 may be
mounted in frame 12 below the roller conveyor under the shrink
tunnel to deflect air back into the housing of the shrink tunnel.
In such case, heated air will impinge upon and shrink the film on
the bottom of the package.
A second modification which is illustrated in FIG. 7 concerns the
length of the split curtains. In FIGS. 1-6, the curtains 28 and 29
are assumed to be full length, as shown in FIG. 1. In some
installations, because of the short length of the tunnel, the
curtains may be shortened to allow high packages to pass through
the shrink zone without having the curtains draped across the top
of the package.
Due to the high efficiency of the new tunnel apparatus described
herein, considerably less power is required. A high percentage of
air is re-circulated and only a small percentage is lost. This
results from the blow-out-and-suck-in feature, and to the recasting
of the air back and forth in laminar fashion across the path of the
package. In optimum operation, the air does not move any faster
than is necessary to maintain the laminar characteristics. The
slower the movement of the laminar air, the better the heating. In
the tunnel device of the present application, the tunnel may be
only 10 inches long; the shrink zone even shorter. Thus, the
exposure time of the package to the high temperature is short. The
contents of the package do not get hot, but a sufficient number of
heated molecules impinge upon the film within the short period of
time to impart sufficient heat to the film to accomplish
satisfactory shrinking.
As indicated previously herein, the fact that the new tunnel has
lower heat losses to the environmental atmosphere, due to less
heated air escaping through the curtains and to less heat radiation
from the tunnel housing, contributes not only to a more efficient
shrink tunnel, but also, in those cases where the shrink tunnel is
operating in an air conditioned or refrigerated atmosphere, to a
more efficient refrigeration system.
Also, as previously indicated, the method of operating tee shrink
tunnel involves moving the air through the narrow passages of the
heaters at a relatively low velocity, just enough to cause the air
streams to reach the suction of the intake on the opposite side.
The slow moving air retains its laminar characteristics, and
follows the contour of the package on its way to the intake duct. A
further desirable effect is that the large surface heater elements
are in longer contact with the slow moving air and are able to heat
more molecules of air. Thus, the heater elements may be operated at
lower temperature and yet provide sufficient heated air to shrink
the film, while the contents of the package do not get hot. A
further advantage is that, in comparison with prior art oven-type
shrink tunnels which are ordinarily thermostatically controlled,
and which have an ON-OFF temperature range which requires time to
attain, the temperature of the heated air of the shrink tunnel of
the present invention responds very quickly to the adjustment
controls. This quick response is particularly advantageous, for
example, where the operator is changing from one type of packaged
item to another which requires more (or less) heat, as there is
little or no delay waiting for the new temperature.
* * * * *