Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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VACUUM SEALER FOR A BAG
FIELD OF THE INVENTION
THiS INVENTION relates to vacuum sealers.
BACKGROUND TO THE INVENTION
It is common practice to pack perishable goods in an evacuated bag of
synthetic plastics material. There are two widely used procedures for
evacuating and
then sealing a bag. In the first procedure the packed but open bag is placed
in a
chamber with its open mouth lying on an anvil. The lid of the chamber is
closed and
this brings a heatable sealer bar into close proximity with the upper face of
the bag.
The chamber is evacuated and hence the bag flattens. Once the pressure in the
chamber has fallen to a pre-set pressure, the sealer bar moves down towards
the anvil.
The bag is gripped between the anvil and the sealer bar and then current is
supplied to
a wire running along the sealer bar to weld the two walls of the bag together
along a
line adjacent the bag's mouth. The sealer bar moves away from the bag and
anvil, the
pressure in the chamber is allowed to rise to atmospheric and the lid is
opened so that
the evacuated and sealed bag can be removed from the chamber.
This procedure is initiated by pressing a start button once the lid is closed
and the procedure which follows is fully automatic.
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A disadvantage of this type of vacuum sealer is that the entire volume of
the chamber must be evacuated regardless of the volume of the bag.
The second common method employs a vacuum sealer which has an
anvil of resilient material and a sealer bar which can be lowered to grip the
mouth
region of the bag between itself and the anvil. A vacuum pipe passes between
the anvil
and sealer bar and enters the bag. Pneumatic cylinders press the sealer bar
against the
anvil and the sealer bar itself presses the part of the pipe which is between
the anvil
and sealer bar into the resilient material of the anvil. The air in the bag is
sucked out
through the pipe. Thereafter the pipe is withdrawn from the bag and from
between the
anvil and the sealer bar. The space left by the pipe as it withdraws is
immediately
closed-up by the material of the anvil which expands resiliently to fill the
space and
maintain the mouth of the bag sealed.
Power is then applied to the resistance wire of the sealer bar to weld the
two faces of the bag together and form the seal which closes the bag.
Unless care is taken to place the inlet end of the pipe close to the product
being packed, the bag can be sucked onto the pipe inlet end. Once the pipe
inlet end is
obstructed the time taken to evacuate the bag increases and a poor vacuum is
obtained, there usually being residual air left in the bag.
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in another form an internally ribbed bag is used, the ribbing being
intended to provide a series of channels which prevent the bag being sucked
closed
thereby inhibiting withdrawal of air from the bag. Such bags are expensive and
the
vacuum sealers that they operate with cannot be used on inexpensive bags
comprising
two juxtaposed films.
The present invention seeks to provide a vacuum sealer which does not
have the disadvantages set out above.
BRIEF DESCRIPTION OF THE INVENTION
According to one aspect of the present invention there is provided a
vacuum sealer which comprises a base plate onto which a bag of synthetic
plastics
material to be evacuated and sealed can be placed, a flexible flap which can
be
displaced from a position in which it lies on the base plate and a lifted
position in which
it is clear of the base plate, a heating element for forming a seal to close
the bag, and a
port through which a vacuum pump can be connected to the space between the
base
plate and the lowered flap.
According to a further aspect of the present invention there is provided a
vacuum sealer which comprises a base plate onto which a bag to be evacuated
and
sealed can be placed, a port in said base plate for connection to a source of
suction so
that air can be drawn from above the base plate through said port, a flexible
flap having
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a raised position in which it is clear of the base plate and a lowered
position in which it
lies on the base plate to confine a bag receiving space between itself and the
base
plate, elongate sealing means between the flap and the base plate for forming
an
elongate weld line across an evacuated bag to seal its mouth closed, and a
groove in
said base plate running transversely of said elongate means, said groove being
in
communication with said vacuum port. The base plate can have one or more
grooves in
it into which the lower film of a bag being evacuated is sucked thereby to
leave one or
more channels between said lower film and an upper film of the bag.
A separator in the form of a plate which is fixed along one edge can be
provided, the separator being spaced from and overlying the base plate whereby
a bag
can be positioned with one film of the bag above the separator and below the
flap, and
the other film of the bag between the separator and the base plate and
overlying the
groove.
Said sealing means is preferably an anvil carried on the underside of said
flap and an electrically conductive wire carried by said base.
In a specified form said wire is carried by a sealer bar which is in slot of
said base plate, said bar being secured to a diaphragm which divides a chamber
into
two compartments, an upper compartment communicating with said groove through
said slot and a lower compartment being connectable selectively to a source of
vacuum
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or to atmosphere.
In a preferred form the flap is fixed along one edge and has a stiffening
frame along its other edges.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show how the
same may be carried into effect, reference will now be made, by way of
example, to the
accompanying drawings in which:-
Figure 1 is a diagrammatic top plan view of a vacuum sealer;
Figure 2 is a side elevation of the vacuum sealer of Figure 1
Figure 3 is a cross section showing a detail of a modified form of a sealing
structure;
Figure 4 is a diagrammatic section taken at right angles to the section of
Figure
3;
Figure 5 illustrates the way in which a bag and a groove co-operate;
Figure 6 is a section similar to that of Figure 2 and showing a further form
of
vacuum sealer;
Figure 7 is a section illustrating a further form of vacuum sealer;
Figure 8 is a diagrammatic section illustrating another form of vacuum sealer;
Figure 9 is a diagrammatic top plan view of the base plate and separator of
the
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sealer of Figure 8;
Figures 10 and 11 show two ways in which the vacuum sealer of Figures 8 and 9
can be used; and
Figure 12 shows a modified form of separator.
DETAILED DESCRIPTION OF THE DRAWINGS
The vacuum sealer 10 illustrated in Figures 1 and 2 comprises a base
plate 12 which is rectangular in plan view and has a sealer bar 14 mounted on
the top
surface thereof. A port 16 is provided in the base plate 12, the port being
connected to
a vacuum pump (not shown) by a vacuum pipe (not shown). The power supply leads
to
the heating wire 18 of the sealer bar 14 pass through the base plate 12 from
below and
are diagrammatically shown at L.
Along the rear edge of the base plate 12 ( the right hand edge in Figure 2)
there is a fastening strip 20 which is secured to the base plate by a row of
fastening
elements 22. One edge of a rectangular flexible flap 24 of, for example,
Neoprene is
secured by the strip 20 and studs 22 to the base plate 12.
The flap 24 is large enough to cover the entire area of the top surface of
the base plate 12. An anvil 26 in the form of a "Teflon" strip is secured to
the underside
of the flap 24.
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In use the flap 24 is lifted away from the base plate 12 to the position
shown in dotted lines in Figure 2 to enable a packed bag B to be placed on the
base
plate. The bag B is closed along three sides and has an open mouth at M. The
bag is
placed so that the sealer bar 14 runs across the bag B parallel to, and
adjacent, the
open mouth M.
The flap 24 is then pulled back to a position in which it overlies the base
plate 12 and the bag B lying on it. Because the flap 24 is flexible it takes
up a position
in which it closely follows the contours of the bag and its contents and lies
against the
base plate around the bag. The r~iouth region of the bag is now trapped
between the
sealer bar 14 and strip 26.
The vacuum pump is then actuated and air is drawn out of the thin space
between the top face of the base plate and the flap. Because the flap has been
allowed to fall onto the base plate and the filled bag and takes up a closely
conforming
shape, the volume of air trapped between the flap and the base plate is small.
Thus
evacuation of what little air there is a quick procedure thereby speeding up
the cycle
time.
Once the bag has been evacuated the wire 18 has current supplied there
to heat it and form the seal. It will be understood that atmospheric pressure
presses
the strip 26 against the sealer bar and that the pneumatic cylinders
conventionally used
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for this purpose are not required.
At the end of the pre-set period during which the wire 18 is supplied with
current, the port 16 is opened to atmosphere to release the vacuum. The flap
24 can
then be lifted to enable the evacuated and sealed bag to be removed and the
next
cycle started.
Experimental work has shown that it is possible in some circumstances
for the mouth of the bag to be sucked closed at the beginning of air
evacuation thereby
trapping air in the bag and resulting in a poor vacuum. To avoid this a bar 28
can span
across the base plate between the flap 24 and the base plate. The bar 30, in
the upper
position illustrated, prevents the flap pressing down on the mouth region of
the bag and
closing it prematurely. Just before the end of the evacuation portion of the
sealing
cycle the bar 28 moves to the lower position illustrated in dotted lines in
Figure 2 and
the flap 24 is sucked down onto the bag.
In Figure 2 the flap 24 is shown as deforming to a curving shape when it is
in the lifted position (shown in dotted lines). This simple form can be used
if the flap and
base are relatively large compared with the dimensions of the bag. Even though
the
bag underneath the flap deforms it the edges of the flap still fall flat on
the base plate.
However, if the bag is relatively large compared with the flap and base plate,
then the
distortions caused by the bag can reach the edge of the flap as ridges. The
gap below
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the ridges prevent sealing taking place. To prevent this a frame 30 can be
provided.
This extends along the three sides of the flap 24 which are not connected to
the strip
20. The part of the frame 30 which is parallel to the strip 20 is shown on the
left hand
side of Figure 2.
In the sealing structure of Figures 3 and 4 the sealer bar 14 is secured to
one side of a diaphragm 32. The diaphragm 32 divides a chamber 34 into two
compartments 35.1 and 35.2. The compartment 35.1 communicates with the space
under the flap 24 and the compartment 35.2 is connected to the suction side of
the
pump. The heating wire 18 runs along the bar 14. The shape of the diaphragm is
such
that it adopts the illustrated position in which the sealer bar 14 is lowered
when the
pressures in the compartments 35.1, 35.2 are the same.
The base plate 12 is formed with at least one groove 36 which extends
the full width of the base plate from the port 16 to a position close to that
edge of the
base plate which is remote from strip 20. There can be a number of parallel
grooves
36.
In Figures 1 and 2 the anvil 26 is on the underside of the flap 24. In
Figures 3 and 4 the anvil 26.1 in the form of a strip is mounted on two
columns 38 (see
Figure 4), the columns 38 being in sockets 40 of the base plate. Springs 42
push the
columns 38 and anvil 26 upwardly.
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The base plate 12 has a thicker edge zone which provides a raised
platform 44. The bar 14 is in a slot 46 which opens through the top surface of
the
platform 44. The compartment 35.1 communicates with the groove through the
slot 46.
When the vacuum cycle starts, both compartments 34.1 and 34.2 are
evacuated. The diaphragm 32 holds the sealer bar 14 in the retracted position
shown.
At the end of the evacuation cycle the compartment 34.2 is connected to
atmosphere
so that the sealer bar 14 is pushed up against the underside of the bag.
Sealing then
takes place by feeding current to the wire 18 to heat it. The vacuum under the
flap 24
is then released.
If reference is made to Figure 5 this diagrammatically illustrates the
groove 36, a film F1 constituting the lower wall of the bag, and a film F2
constituting the
upper wall of the bag. Experimental work has shown that the lower film F1 is
sucked
into the groove 36 as diagrammatically illustrated. The film F1 stretches
somewhat and
shifts somewhat with respect to film F2. Because the flap 24 presses on film
F2, the
film F2 has less freedom of movement than film F1. Hence it tends not to
follow film F1
into the grooves) and thus one or more channels C remain which run to the
bottom of
the bag. Thus the bag films F1 and F2 do not suck into such close proximity as
to
close-off the bag leaving air trapped inside.
To enable bags of greater volume to be handled, the part of the base
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plate which is to the right of the platform 44 can be in the form of a
resiliently flexible
sheet. A filled bag placed on it creates a depression in the sheet in which
the bag lies.
Thus only a part of the bag protrudes above the level of the flexible sheet,
and this
reduces the size of the hump that must be created in the flap 24 when it is
lowered onto
the bag.
Turning now to Figure 6, the vacuum sealer illustrated comprises many
features which are also found in the sealers of Figures 1 to 5. Where
applicable the
same reference numerals have been used with the addition of the suffix ".1".
In this form there is a hinge 48 one leaf of which is mounted on the strip
20.1 and the other leaf of which is mounted on a plate 50. The sealing wire
18.1 is
mounted on the underside of the plate 50.
The flap 24.1 in this form does not overlie the entire bag but only extends
a short way beyond the free edge of the plate 50. The advantage of this form
is that the
contents of the bag can be seen, and collapse of the bag as it evacuates can
be
watched. The flap 24.1 extends the full width of the plate 12.1, or across
sufficient of
the width of the plate to cover the entire bag. If a visible bag is not a
required feature
then the flap 24.1 can extend over the whole area of the base plate.
The groove 26.1 ensures that a passageway into the bag is maintained
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open during evacuation there to ensure that the bag is totally evacuated. The
sequence
of operations is as described above in relation to Figures 1 and 2.
A gripping handle, shown diagrammatically at 52, can be provided for
lifting the plate 50 and hence the flap 24.1.
As the flap 24.1 does not extend over the filled part of the bag, it does not
require a frame around three of its edges.
The vacuum sealer of Figure 7 differs from that of Figure 6 in that the flap,
designated 24.2, covers the entire area of the base plate, designated 12.2,
and is
carried by a rectangular frame 54. In this form the plate 50.2 is fixed to the
strip 20.2
and not connected to it by a hinge. The frame is mounted so that it can pivot,
as shown
by the arrows A, to lift the flap 24.2 away from the base plate 12.2. The
frame 54 can
be fixed to the underside of a dome-like cover 56 which is provided purely for
aesthetic
purposes. It will be understood that only the space under the flap 24.2 is
evacuated and
not the space under the cover 56. The frame 54 ensures that all three
unattached
edges of the flap 24.2 lie flat on the base plate 12.2.
In Figures 8 and 9 parts which are also found in earlier Figures have been
designated with like reference numerals with the addition of the suffix ".3".
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In this form a separator 58 in the form of a thin plate having a castellated
edge (Figure 9) to provide fingers 60 is mounted on a strip 62 which is close
to the strip
20.3. Once the flap 24.3 has been lifted, the separator 58 is inserted into
the bag by
sliding the bag to the left as shown in Figure 8. This separates the bottom
film F1 from
the top film F2 and holds the mouth of the bag open. When vacuum is applied to
the
space under the flap 24.3 via the port 16.3, the film F1 is sucked into the
groove 28.3.
As will be seen from Figure 9, there are vacuum ports 62 in addition to the
port 16.3. Vacuum applied via these ports sucks the lower film F2 against the
base
plate 12.3 and prevents inadvertent movement of the bag.
As shown in Figures 8 and 9, the separator 58 is intended to be inserted
into the bag to separate the films F1 and F2 . However, experimental work has
shown
that even if both films F1, F2 of the bag are inserted below the separator
(see Figure
11 ) satisfactory evacuation and sealing occurs.
The flap 24.3 in Figures 8 and 9 does not require a frame as it does not
cover the filled part of the bag.
In the form of Figure 12 there is a protrusion 64 running from front to rear
on the separator 58. This protrusion 64 presses the film F2, or both films F1
and F2,
into the groove 28.3. The dimensions of the protrusion 64 are insufficient to
hold the
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films F1, F2 in face-to-face contact and close off the passageway leading into
the bag.
