U.S. patent number 3,727,324 [Application Number 05/073,393] was granted by the patent office on 1973-04-17 for shrink tunnel for palletized loads.
This patent grant is currently assigned to Despatch Industries, Inc.. Invention is credited to Hans L. Melgaard.
United States Patent |
3,727,324 |
Melgaard |
April 17, 1973 |
SHRINK TUNNEL FOR PALLETIZED LOADS
Abstract
A shrink tunnel for shrinking a covering of plastic material
onto a palletized load including apparatus for generating a curtain
of air at entrance and exit of the tunnel to isolate a shrink zone
within the tunnel from an ambient environment and to provide
preheating and cooling of the plastic cover at entrance and exit,
respectively, as the load moves through the tunnel. The shrink zone
has a pair of stationary nozzles near the entrance of the tunnel
for directing heated air at the skirt of the plastic covering
adjacent the base of the palletized load to shrink the skirt to the
pallet. The remainder of the covering is thereafter shrunk onto the
load thereby protecting the load from the elements during shipment
or storage and binding it to the pallet for convenient
shipment.
Inventors: |
Melgaard; Hans L. (Mound,
MN) |
Assignee: |
Despatch Industries, Inc.
(Minneapolis, MN)
|
Family
ID: |
22113436 |
Appl.
No.: |
05/073,393 |
Filed: |
September 18, 1970 |
Current U.S.
Class: |
34/216; 34/66;
34/225; 34/233; 53/557 |
Current CPC
Class: |
B65B
53/063 (20130101) |
Current International
Class: |
B65B
53/06 (20060101); B65B 53/00 (20060101); F26b
019/00 () |
Field of
Search: |
;53/30,184
;34/66,242,216,219,225,230,232,233 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sprague; Kenneth W.
Assistant Examiner: Yeung; James C.
Claims
What is claimed is:
1. A shrink tunnel to shrink a plastic wrapper covering a
palletized load into a substantially tight fitting relationship
with the palletized load as the load moves along a path through the
tunnel comprising:
a tunnel housing including an entrance and exit;
apparatus for establishing a shrink zone within the tunnel housing,
the apparatus including means for raising the temperature of the
shrink zone to a temperature range adequate to shrink the plastic
wrapper into a substantially tight fitting relationship with the
palletized load as the load moves along the path through the shrink
zone;
apparatus for generating a combined air door and plastic wrapper
preheating zone adjacent the housing entrance, said generating
apparatus accepting heated air from the shrink zone and unheated
ambient air and combining them to obtain preheating air having a
temperature range less than that required to shrink the plastic
wrapper, said preheating air being conveyed to the entrance to
generate a curtain of air directed across and into the entrance to
thereby preheat a plastic wrapper entering the tunnel housing and
isolate the shrink zone from an ambient environment.
2. The combination according to claim 1 wherein said means for
raising the temperature in the shrink zone includes:
apparatus for heating and circulating air, the apparatus heating
the air to a predetermined temperature range adequate to shrink the
plastic wrapper onto the palletized load and circulating the
shrinking air through the housing to establish a shrink zone at a
distance from the entrance thereof containing an adequate volume of
shrinking air to shrink the plastic wrapper into a substantially
tight fitting relationship with the palletized load.
3. The combination according to claim 1 wherein the apparatus for
generating a combined air door and plastic wrapper preheating zone
further includes:
a preheating zone blower;
a preheating zone air return conveying said preheating air from the
tunnel housing to said preheating zone blower;
a plurality of preheating nozzles receiving said preheating air
from said preheating zone blower and located about the entrance for
emission of said preheating air to generate the curtain of air.
4. The combination according to claim 3 wherein an outlet duct
extending from the preheating zone blower to the said nozzles
supplies air to the nozzles, said outlet duct having a damper
therein adjacent the preheating zone blower to exhaust air from the
tunnel housing thereby causing ambient air to enter the housing at
a predetermined rate thereby controlling the temperature of said
preheating air.
5. The combination according to claim 3 wherein each preheating
nozzle has a longitudinally disposed slotted orifice and a pair of
lips adjoining the slotted orifice and separated thereby to direct
preheating air issuing therefrom across and into the tunnel
entrance to generate the curtain of air.
6. The combination according to claim 5 wherein one of the lips of
each preheating nozzle is moveable relative to the slotted orifice
to controllably obstruct the orifice and thereby vary the volume of
air passing through the orifice.
7. The combination according to claim 1 including:
a cooling zone blower;
a cooling zone air return located in the tunnel housing between the
shrink zone and the exit conveying air from within the tunnel
housing to the cooling zone blower; and
a plurality of cooling nozzles receiving the air from said cooling
zone blower, the nozzles located about the exit to expel the air
therefrom thereby generating a curtain of air adjacent the
exit.
8. A tunnel to shrink a plastic cover on a palletized load into a
tight fitting relationship with the load comprising:
a tunnel housing including an entrance and exit;
a conveyor moving the palletized load through the housing;
means heating and circulating shrinking air inside the housing to
establish a shrink zone in spaced relation to the entrance, the
temperature of the shrinking air being adequate to shrink the cover
into tight fitting relationship with the palletized load as the
load moves through the shrink zone;
second means for supplying an independent preheating zone of air
immediately adjacent the entrance and having a temperature
substantially less than the shrinking zone air;
said heating and circulating means also including a pair of
stationary shrink nozzles between the preheating zone and the
shrink zone, one nozzle being located on each side of said conveyor
adjacent the conveyor and on a vertical level with a pallet moving
therealong, the nozzles directing shrinking air substantially
horizontally across the housing and at the sides of the pallet as
the load passes through the preheating zone to thereby shrink the
skirt of the cover to tightly grip the pallet prior to the load
entering the shrink zone wherein the remainder of the cover is
shrunk onto the load.
9. The combination according to claim 8 wherein said second means
includes a plurality of entrance nozzles arranged to direct
preheating air against the top and sides of the palletized load,
said second means further including an air return spaced along the
tunnel housing from the entrance nozzles so the preheating air
flows along and preheats the top and sides of the palletized load,
and then enters the air return, the preheating zone extending along
the tunnel housing to said air return, the shrink nozzles being
disposed in the portion of the tunnel housing containing the
preheating zone to shrink the skirt of the cover onto the pallet
while preheating air continues to be applied to upper portions of
the cover.
Description
BACKGROUND OF THE INVENTION
Pallets are frequently used by manufactures in shipping their
products because pallets provide rigid, reliable platforms on which
loads can be stacked and bound. Transporting a loaded pallet is
simple, fast, and efficient since fork-lift trucks can easily lift
and transfer them from loaded vans or boxcars to their final use
area.
Traditionally loads have been bound to pallets by metal straps or
cords. Such retainers are adequate to hold the load on the pallet
but provide little protection from adverse weather and rough
handling during transit or storage. Accordingly, it is desired to
provide an apparatus which rapidly binds the load securely to the
pallet and provides protection for the load from weather and
handling at a minimum of cost.
The present invention comprises a shrink tunnel for palletized
loads. A loaded pallet is covered with a wrapper of shrinkable or
oriented plastic material and conveyed through the shrink tunnel to
shrink the material into a tight fitting relationship with the load
and pallet thereby protecting the load and binding it to the
pallet.
It is desirable to provide a preheating zone at the shrink tunnel
entrance to warm the plastic covering prior to its encountering the
high temperature shrink zone. The invention includes apparatus to
generate a curtain of preheating air at the tunnel entrance which
simultaneously preheats the plastic and isolates the shrink zone
from the ambient environment. Additional apparatus can be used to
generate a curtain of air at the exit of the tunnel to establish a
cooling zone to decrease the temperature of the plastic covering as
the load leaves the tunnel and further isolate the shrink zone from
the ambient environment.
Before the plastic cover is fully shrunk onto the palletized load,
the plastic covering should be shrunk tightly against the pallet
itself. If this step is not taken, the plastic covering as a whole
shrinks and the skirt of the covering recedes to a level above the
pallet making it difficult to thereafter anchor the load to the
pallet with the plastic covering. Accordingly, the invention
includes apparatus to shrink the plastic covering against the sides
of the pallet before shrinking the plastic covering against the
load.
SUMMARY OF THE INVENTION
The invention comprises a shrink tunnel for palletized loads which
shrinks a plastic covering against the palletized load to provide
protection for the load and bind it to the pallet. A loaded pallet
with a plastic covering thereover moves along a conveyor through
the shrink tunnel which includes a high temperature shrink zone.
The tunnel has apparatus for generating a curtain of air at
entrance and exit to respectively preheat and cool the plastic
covering as the palletized load passes therethrough. In addition
the curtain of air acts as an air door to isolate the shrink zone
from the ambient environment.
The shrink zone has apparatus for heating and circulating air at a
temperature adequate to shrink the plastic material into tight
fitting relationship with the load. The apparatus includes a pair
of stationary shrink nozzles near the entrance of the tunnel to
shrink the plastic material tightly against the sides of the pallet
before the remainder of the plastic material is shrunk tightly
against the load. The anchors the plastic material solidly to the
pallet and when the final shrinking of the plastic covering occurs
thereafter, the load is securely bound to the pallet. The plastic
covering provides protection against rough handling and adverse
weather.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictoral view of the shrink tunnel invention with the
outer tunnel wall partially cut away.
FIG. 2 is an enlarged sectional view taken along cutting plane 2--2
of FIG. 1 showing the conveyor system used with the invention.
FIG. 3 is a section side view of the shrink tunnel of FIG. 1 with a
palletized load entering the tunnel.
FIG. 4 is an enlarged sectional view of a preheating nozzle taken
along cutting plane 4--4 of FIG. 1.
FIG. 5 is an enlarged cross sectional view taken along cutting
plane 5--5 of FIG. 3 showing a stationary shrink nozzle.
DESCRIPTION AND OPERATION OF THE INVENTION
FIG. 1 shows a palletized load 10 about to enter a shrink tunnel
shown generally at 12. The palletized load 10, consisting of pallet
14 and load 16, has a bag-like wrapper or covering 18 of shrinkable
or oriented plastic material pulled downward over the load, the
covering being of sufficient length so the skirt 20 of the wrapper
covers the sides such as 22, of the pallet 10. The cover 18 may
consist of a length of tube stock polyethylene plastic, or other
shrinkable plastic like material, which is pulled over the
palletized load, the tube stock then being cut and sealed at the
top of the load to form a bag-like wrapper. Any loose folds of
plastic material can be folded against the load. The covering
selected should be sturdy enough to provide protection to the load;
polyethylene plastic with a thickness of approximately 5/1000 inch
is acceptable.
The palletized load 10 with its wrapper 18 is moved along a
conveyor system 24 which defines a path through the shrink tunnel.
Referring now to FIGS. 1 and 2 the conveyor has a pair of identical
tracks 26 and 28 with roller chain drives 32 and 34. Moving roller
chains 32 and 34 have a plurality of cross bars such as 36 attached
transversely to the chains at spaced intervals. The cross bars 36
engage the palletized load 10 to carry it along tracks 26 and
28.
Referring now to FIG. 1, the shrink tunnel 12 has a tunnel housing
40 which includes entrance 42 and exit 44. Approximately
intermediate between entrance and exit is an apparatus for
establishing a shrink zone within the tunnel housing. The shrink
zone apparatus includes apparatus for heating and circulating air
such as shrink zone heater 46, shrink zone blower 48, ducts 50, 52,
58, and 59, shrink nozzles 60 and 62, shrinking arch 56 and shrink
zone air return 54. Heater 46 warms air to a temperature range
adequate to shrink the plastic wrapper 18, and blower 48 forces the
shrinking air into ducts 50 and 52 leading to shrinking arch 56 and
into ducts 58 and 59 terminating at stationary shrink nozzles 60
and 62. The arch 56 and shrink nozzles 60 and 62 release shrinking
air to establish a shrinking zone of sufficient volume to shrink
the plastic wrapper 18 into a substantially tight fitting
relationship with the load. This temperature range varies with the
physical and chemical properties of the plastic material used, but
for polyethylene with a thickness of 5/1000 inch, it is
approximately 300-400.degree.F.
It should be understood that the shown apparatus for heating and
circulating the air is but one means for raising the temperature of
the shrink zone to a shrinking temperature range and that other
means, such as radiant heating, are contemplated as usable with the
invention.
The shrink nozzles 60 and 62 are, of course, not the only apparatus
which can be used to shrink the skirt of the wrapper against the
sides of the pallet. Any means for heating the plastic material
adjacent the pallet to a shrinking temperature can be used to
anchor the skirt to the pallet.
As the palletized load with a plastic wrapper there-over moves
through housing 40 it encounters stationary shrink nozzles 60 and
62 before reaching shrinking arch 56. Shrink nozzles 60 and 62
direct shrinking air against the skirt 20 of the wrapper which
overlies the sides of the pallet 14 and shrinks the skirt 20
tightly against the pallet to anchor the wrapper thereto. Thus when
palletized load 10 reaches shrinking arch 56, the wrapper is
securely anchored to the pallet and as the air from shrinking arch
56 heats the plastic wrapper, it shrinks into a tight fitting
relationship with the load, binding it to the pallet.
The cross sectional configuration of a shrink nozzle 60 is shown in
FIG. 5. Lips 64 and 66 separated by slotted orifice 65 direct
shrinking air outward as shown by arrow 63, lip 64 being moveable
to control the quantity of air released in order to adapt the
shrink nozzle 60 to plastic materials having various thicknesses. A
lesser quantity of heated air is required to shrink a thin plastic
covering than is needed for a thicker covering. Nozzles 60 and 62
are elongated to extend longitudinally along the conveyor 24 to
provide continued heating of the wrapper shirk 20 to assure
shrinkage of the wrapper against the pallet.
Most of the shrinking air expelled from shrinking arch 56 or shrink
nozzles 60 and 62 circulates through the shrink zone and enters
shrink zone air return duct 54 which extends to the shrink zone
heater 46 and blower 48 which repeatedly heat and circulate the
air. Referring now to FIG. 3, the air return 54 is located below
the level of a pallet passing through the shrink zone. This
positioning creates a slight vacuum within the plastic wrapper 18
which minimizes billowing of the wrapper as it passes through the
tunnel. As will be further described hereafter a portion of the
shrinking air from the shrink zone is accepted by preheating zone
air return 76 to aid in establishing preheating zone.
The tunnel entrance 42 is provided with apparatus for generating a
combined air door and plastic wrapper preheating zone adjacent the
entrance. The generating apparatus is shown in FIG. 1 as including
preheating zone blower 70, outlet duct 72 exhaust duct 94, damper
92, preheating arch 74, preheating zone air return 76, and inlet
duct 78.
Preheating zone air return 76 accepts both shrinking air from the
shrink zone and ambient air entering from the entrance 42 and
combines them to obtain preheating air which has a temperature
range lower than that of the shrinking air. This preheating air
temperature range may be at approximately 200.degree.-250.degree.F
for 5/1000 inch polyethylene plastic. By manipulating damper 92 in
exhaust duct 94, a predetermined quantity of air is exhausted from
the shrink tunnel, thereby causing an essentially equal quantity of
ambient air to enter through entrance 42 and exit 44. Preheating
air is obtained by mixing the shrinking air with the ambient
air.
Blower 70 delivers the preheating air to the preheating arch 74
which includes a plurality of interconnected preheating nozzles
here shown as the three nozzles 80, 82, and 84; naturally, a
greater or lesser number of nozzles can be used. Preheating nozzles
80 and 84 have a length substantially equal to the height dimension
of the entrance; nozzle 82 has a length substantially equal to the
width of the entrance dimension.
FIG. 4 shows the cross sectional configuration of preheating nozzle
82 mounted adjacent wall 85 of the tunnel housing. Each preheating
nozzle has a longitudinally disposed slotted orifice 87 extending
substantially the length of the nozzle, and lips 88 and 90
adjoining the slotted orifice and separated thereby to direct
preheating air across and into the tunnel entrance 42.
Referring again to FIG. 4, the position of lip 90 of nozzle 82 can
be varied to control the volume of air expelled from the orifice in
order to balance the air flows from nozzles 80, 82, and 84 and
generate the curtain of preheating air. Operation of nozzles 80 and
84 is identical to that of nozzle 82. The three preheating nozzles
co-operate to generate a curtain of air at the entrance 42 which
establishes a preheating zone extending to return 76.
The flow pattern of the air issuing from preheating arch 74 is
indicated by flow arrows in FIGS. 1 and 3. The air flow of
preheating nozzles 80 and 84 is directed across and into the tunnel
entrance; the air flow of nozzle 82 is directed downward and into
the entrance. As a load passes through the arch 74 the air from the
arch flows along the load and into the return 76 as shown in FIG.
3. Preheating air emitted from preheating arch 74 heats the plastic
covering as the load passes through the arch and isolates the
shrink zone from the ambient environment outside the entrance
42.
Most air expelled from preheating nozzles 80, 82, and 84 enters
tunnel housing 40 and is drawn into preheating zone air return 76
and conveyed by duct 78 to the blower 70. Thus preheating air is
circulated and recirculated to generate a curtain of preheating air
at the entrance of the tunnel housing.
Referring again to FIG. 1, exit 44 has a cooling zone generated by
cooling arch 96 formed from a plurality of cooling nozzles, here
shown as three interconnected nozzles identical to preheating
nozzles 80, 82, and 84 of preheating arch 74. The cooling arch 96
receives its air supply through duct 97 extending from cooling zone
blower 98. A cooling zone air return 99 accepts air emitted from
the cooling arch 96 and returns it to the blower 98 for recycling.
Thus the cooling arch 96 with its blower 98 generates a curtain of
air at the exit which establishes a cooling zone for the plastic
wrapper and an air door which isolates the shrink zone from the
ambient environment outside the exit. A damper 100 exhausts a
predetermined amount of air out duct 101 in order to cause ambient
air to enter the exit at a predetermined rate. The mixing of shrink
zone air and ambient air permits one to obtain a supply of cooling
zone air having a temperature lower than the shrinking air. This
cooling zone air may be in the same temperature range as preheating
air.
Although the apparatus forming the cooling zone is not shown as
identical to that for generating the preheating zone, it should be
understood that the same identical structure could have been
used.
In operation, a palletized load 10 with a plastic covering 18
thereover is placed on conveyor system 24 which carries it through
the shrink tunnel 12. The palletized load enters preheating arch 74
and preheating air emitted from nozzles 80, 82, and 84 preheats the
plastic covering 18. As the load passes through entrance 42 the
preheating air flows about its periphery, rapidly warming the
plastic in preparation for its entering the shrink zone. The
nozzles 80, 82 and 84 establish a curtain of air which isolates the
shrink zone from the ambient environment. Most air from preheating
arch 74 is picked up by air return 76 by recycled.
As the plastic covering encounters stationary shrink nozzles 60 and
62 which as shown in FIG. 1 are disposed in the preheating zone to
shrink the skirt 20 onto the pallet while preheating air continues
to be applied to upper portions of the cover, shrinking air shrinks
the skirt 20 of the plastic cover into a tight fitting relationship
with the pallet. This anchors the skirt to the pallet and prevents
the plastic covering from shrinking upward and uncovering the lower
sides of the load in response to heat from the still to be
encountered shrinking arch 56. The remainder of the plastic
covering is shrunk into tight fitting relationship with the load as
the palletized load moves past the shrinking arch 56. It should be
understood that the shrinking arch 56 is not part of the invention
and can be replaced by any known equivalent structure.
As palletized load 10 leaves the shrink zone and passes through
exit 44 the plastic covering is cooled by air emitted from cooling
arch 96 which functions identically to preheating arch 74. The
cooling arch 96 reduces the temperature of the plastic wrapper 18
permitting earlier handling thereof, and also isolates the shrink
zone from the ambient environment.
While I have described a preferred embodiment of the present
invention, it should be understood that various changes,
adaptations and modifications may be made therein without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *