Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present ~nvention relates to a method of ~orming
evacuated sealed packs, particularly packs containing
preserved foodstuffs.
~any vacuum packing methods are ~nown, and in general
these require relatively expensive equipment. The present
inve~tion is concerned with providing a method which can
be used in conjunction with existing for~-flll seal or
other bag ~illing machinery, without extensive modi~ication.
Thus, the present invention aims to be able to convert for
e~ample a normal, e~isting fill seal machine into a vacuum
packing machine at low cost.
Accordingly the invention provides a method of for~ing
an evacuated sealed pac~ comprising the steps o~ providing
an open ~outh bag containing the product to be packed,
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~- 15 inserting a steam injection nozzle into the mouth zone of
~ said bag, injecting steam via said nozzle into the bag so
-~ as to purge air from the interior of said bag, applying
tensile forces acrosC a lateral zone o~ the bag mouth so as
to laterally stretch the bag and flatten said bag mouth onto
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the nozzle, withdrawing the nozzle from the bag while
retaining lateral tensile forces in said lateral zone and
thereby allowing the flattened bag to progressively close
behind the nozzle, and sealing the closed evacuated bag.
The steam nozzle should have a flattened shape so that
the bag mouth can adequately flatten on to it and minimise
gas lea~age.
It will be recognised that the steam both purges the bag
of air and by virtue o~ condensation causes a vacuum to be
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produced in the bag. Also,the method involving stretching
in co~junction with use of a flattened nozzle enables the
nozzle to be removed from the bag without brea~ing the
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vacuum. Use of steam i9 ~nown for vacuum pac~ing, but
hitherto a satisfactory economical method o~ retaining the
vacuum and sealing has not been achieved.
Use of steam implies the introduction of a degree o~
moisture, and therefore it will be understood that the
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'~ invention is not applicable to the pac~ing o~ products
which would be a~fected by moisture, for example dried
: powdered materials. Alsoythe use of steam to flush and
purge out air from the bag can only be used where the
product to be packed is suitable for such air purging.
Thus,-where the product includes small air packets which
lS would resist the steam flushing the invention would ~ot
be suitable, for egample particulate materials li~e peas.
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: On the other hand, the invention is particularly applicable
' for pac~ing pieces of meat, or of other integral productswhich form a composite whole ~or example by the presence
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- 20 of a sauce or gravy.
The nozzle should be sufficiently flattened in shape so
-~ that when the bag mouth is ~lattened on to the nozzle the
bag mouth is virtually closed by this operation. In
practice while steam is still being injected into the bag it
is not necessary that fulI closing of the bag occars at this
stage, since the steam and purged air will be escaping under
slight over pressure and an effective one way valve is
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~ achieved. However at the next stage in the process as the
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nozzle is ta~en out of the bag, a per~ect closing is
achieved by the lateral stretching, and the vacuam is
retained.
Following formation of the vacuum it is preYerable to
~-~ retain the lateral stretching until a permanent seal has
been made on to the bag. Thig seal, usually a heat seal,
- is preferably effected over a fairly wide band (e.g. about
12 mm) in the mouth zone of the bag so as to ensure that an~
steam bubbles or prodact particles in the region of the
~;; seal zone are trapped.
. An embodiment of the invention will now be described by
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~ way of e~ample with reference to the ùiagrammatic drawings.
',J~ ' Figure 1 is a side elevation o~ a bag with an
injection nozzle located above it prior
to commencement of the processi
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Figure 2 is a plan view of the bag and nozzle in
the Figure l position;
Figure 3 is a side elevation of the bag after an
injection nozzle has been inserted therein;
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Figure 4 lS a plan view of the Figure 3 arrangement; and
Figare S is a graphical representation of the
. timing sequence.
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Referring to Figure l a bag 1, ~illed with a product to
~` 25 be packed for e~ample two pieces of preserved ~eat, is held
;~ between side grippers 2. Referring to Figure 2 it can be
seen that in this condition the bag mouth is open. Located
above the open mouth of the bag is a flattened divergent
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steam injection nozzle 3. The nozzle 3 is supported by means
permitting it to be inserted into and withdrawn from the mouth
of the bag 2. The nozzle is connected to a supply of
` pressurized steam. The nozzle has a flattened depth which is
less than the width of the open rnouth bag and its width is about
a third the length of the bag mouth opening, so that it can
readily enter into said bag.
The next stage of the process is that the nozzle is
inserted into the bag and steam is injected into the bag. Due
to the divergent shape of the injection nozzle, the steam,
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injected at a pressure of between 0.5 and 0.9 atm above atmos-
pheric, is able to be forced into the lower corners of the bay
and is thereby able to purge air out of the bag.
Referring to Figure 3, the grippers 2 are spring loaded
- 15 and are supported by means permitting them to be moved apart so
~ as to provide tensile forces across a lateral zone 4 of the bag
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. mouth, through which zone of the bag mouth the nozzle passes, so
; as to flatten the bag onto the nozzle and almost close the bag ~ -
(see Figure 4).
The spring loaded stretching across the zone 4 causes
the bag to form a one way valve which enables the purged air and
; steam to continue to pass out of the bag without further air
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~ being able to enter the bag. There are, in practice, slight gaps
- S at the corners of the nozzle as can be seen from Figure 4 but
, 25 the over pressure from the steam ensures that air and steam can
only flow outwards so that air cannot enter the bag.
' The next stage in the process is that steam pressu~e
is shut off and the steam injection nozzle is drawn out of
the bag while retaining the lateral stretching across the
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zone 4. .~9 the nozzle moves out o-f the bag the bag walls
-`~ in the laterally stretched zone 4 come together and
~¢` completely close the bag without loss of vacuu~.
~hereafter while retaining the lateral tension in the
zone 4, the bag i9 moved to a heat sealing station and
there a heat seal is placed just above the zone 4 so as
to provide an evacuated sealed pack.
In practice bags made of a heat sealable foil laminate
(12 micron polyester laminated with 9 micron aluminium and
r 10 70 micron modified high de~sity polyethylene) was used on
bags measuring 170 mm ~ 200 mm. Tension o-f 3 to 4 kg
laterally across the bag served to adequately seal the bag,
, and the nozzle of diver~ent shape had a width which was about
7 a third that ofthe open mouth of the bag i.e. 60 mm. Its
depth externally was 3 to 3~5 mm giving an internal depth
of 1 to 1A5 mm.
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Figure 5 shows the time sequence of the varioas
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operations schematically. In this Figure, on a linear
time scale, the function A represents the time o~ the nozzle
within the bag (the sloping parts at each end being
representative of entry and withdrawal); the funotion B
represents the time of steam flushing (about 1 to 1.5 seconds
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in practice); and the function C represents the timing of the
stretching of the baE moath, this commencing about 0.3 seconds
after the commencement of steam flushing.
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