Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02354912 2001-08-08
4
- 1 -
BAG-FORMING MACHINE FOR MAKING
BAGS WITH CURVED BOTTOM WALLS
TECHNICAL FIELD
(0001 The present invention relates to a bag-forming
machine and method for making plastic bags having a curved
or roundish-like bottom wall and an open top end.
BACKGROUND ART
(0002 Bag-forming machines are well known in the art
for making plastic bags from a folded film sheet and wherein
the bags are packaged for future handling. Bag-forming
machines are also known wherein the bags are formed and then
filled with a product, closed and the filled bags are
conveyed to a packaging location.- Such bag-forming machines
usually form rectangular shaped bags which are heat-fused
along opposed parallel side edges thereof and with the
bottom edge being constituted by the folded film sheet. A
flap may also be formed adjacent to the open end to handle
the bags on wicket pins for filling such bags, and this is
also well known in the art.
SUMMARY OF INVENTION
(0003 It is a feature of the present invention to
provide a bag-forming machine for making plastic bags having
a curved or roundish-like bottom wall and an open top end.
(0004 Another feature of the present invention is to
provide a method of forming plastic bags having a curved or
roundish-like bottom wall and an open top end.
(0005 According to the above features, and from a
broad aspect of the present invention, there is provided a
bag-forming machine for making plastic bags having a curved
or roundish-like bottom wall and an open top end. The
machine comprises a bottom wall forming die having opposed
concavely curved seal-forming edges converging to a common
apex. Means is provided to heat the die. A film support
CA 02354912 2001-08-08
- 2 -
assembly is disposed under the die. Means is provided to
reciprocate the die over the film support assembly. The
folded film sheet is adapted to be displaced over a film
support surface of the film support assembly under the die.
The folded film sheet is oriented such that the die will
simultaneously slit and heat-fuse opposed film sheets of the
folded film sheet when stroked on the film sheet to form
opposed concavely curved seals extending from a longitudinal
folded edge of the folded film sheet and converging to an
apex at a location spaced on a transverse axis from the
longitudinal folded side edge. Means is provided to
evacuate a cut-out film portion of the folded film sheet
between the slit and heat-fused strokes of the die. The
folded film sheet with the opposed curved seals and cut-out
end portion is then fed to bag-forming means.
67 According to a further broad aspect of the
present invention, there is provided a method of forming
plastic bags each having a curved or roundish-like bottom
wall and an open top end. The method comprises the steps of
providing a bottom wall forming die having opposed concavely
curved seal-forming edges converging to a common apex. The
die is heated by heating means. A folded film sheet is fed
on a film support surface under the die. The die is
reciprocated over the folded film sheet in synchronism with
film feeding means whereby to simultaneously slit and heat-
fuse opposed film sheets of the folded film sheet when the
die is stroked on the folded film sheet to form opposed
concavely curved seals extending from a longitudinal folded
side edge of the folded film sheet and converging to an apex
at a location spaced on a transverse axis from the
longitudinal folded side edge. A cut-out film portion of
the folded film sheet is evacuated between the slit and
heat-fuse stroke of the die. The folded sheet with the
opposed curved seals and cut-out end portion is then fed to
bag-forming means.
CA 02354912 2001-08-08
a
- 3 -
BRIEF DESCRIPTION OF DRAWINGS
(000~~ A preferred embodiment of the present invention
will now be described in detail having reference to the
accompanying drawings, in which:
(0008 Figure 1 is a top view of the bag-forming
machine of the present invention for making curved or
roundish-like bottom walls in a folded film sheet;
(0009 Figure 2 is a side view of Figure 1, partly in
schematic;
(0010 Figure 3 is a rear view of Figure 2, partly in
schematic;
(ooll~ Figure 4 is an exploded view showing the
construction of the die and the film support assembly;
(0012 Figure 5 is a schematic top plan view showing a
folded film sheet in which curved bottom walls have been
formed and further illustrating associated devices to form a
bag with such roundish-like bottom wall; and
(0013 Figure 6 is a perspective view showing a bag
formed in accordance with the machine and method of the
present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
(0014 Referring now to the drawings, and more
particularly to Figures 1 to 4, there is shown generally at
the bottom wall forming section of a bag-forming machine,
which is more completely and schematically illustrated in
Figure 5. This bottom wall forming section 10 comprises a
bottom wall forming die 11, which is better illustrated in
Figure 4. As can be seen, the bottom wall forming die 11 is
a heat-conducting die plate 12, having opposed concavely
curved seal-forming edges 13 and 13'. These concavely
curved seal-forming edges converge to a common apex 14.
(ool5~ The die plate 12 has a flat rear wall 15 over
which is disposed a heat-producing resistive wire 16, which
is oriented in a serpentine fashion (not shown) whereby to
provide sufficient heat to the die plate 12. A heat-sensing
CA 02354912 2001-08-08
- 4 -
thermocouple 17 is conveniently secured to the die plate 12
and generate signals indicative of the temperature of the
die plate 12 whereby to control the temperature to provide
proper slitting and fusing of a folded film sheet 18
disposed thereunder on a film support assembly 19. A heat-
insulating material such as an insulating fabric 20 is
disposed over the resistive heating wire 16 and is
sandwiched between a connecting plate 21 and the die plate
12 by means of fastening bolts 22. The fastening bolts are
secured to a piston-actuated connecting plate 23 which is
spaced therefrom by the bolts 22. The insulating material
20 and connecting plate maintain the die plate 12 at a hot
temperature and isolated from the piston-actuated plate 23.
(0016 As shown in Figures 2 and 3, the piston-actuated
plate is connected to two in-line cylinders 24 and 25.
These cylinders have their piston rods 24' and 25'
respectively connected in line with the connecting plate 23.
Cylinder 24 is provided for the retracting or standby
position of the die assembly 11, while piston 25 provides
the reciprocating seal-slit stroke.
(001~~ With reference now to Figures 1, 2 and 4, there
will be described the construction and operation of the film
support assembly 19. That assembly comprises a film support
plate 26 having a Teflon (Registered Trademark) coating 27
thereover or TeflonTM sheet adhered to the upper surface
thereof. This film support plate 26 is also resiliently
mounted on resilient supports 28.
(0018 As can be seen from Figure 1, a vacuum port 29,
herein a round hole, is cut out from the support plate and
oriented spaced between the concavely curved seal-forming
edges 13 and 13' of the die. A vacuum conduit 30 is secured
to the port and connected to a suction device (not shown) at
a far end wherein to evacuate and collect cut-out film
portions 31 of the folded film sheet between the slit and
heat-fused strokes of the die. The vacuum port 29 also
extends to the top surface of the support plate 26 and
CA 02354912 2001-08-08
a
- 5 -
through the TeflonTM coating, whereby this port is situated
under the folded film sheet 18.
~0019~ A reciprocating plate valve 32 is disposed under
the film support plate 26 and connected to a reciprocating
piston 33 whereby to obstruct the vacuum port during heat-
fusing and slitting of the folded film sheet when the die is
stroked thereon and to open the port immediately thereafter
to evacuate the cut-out film portion. It is pointed out
that the frame assembly 34 may also be mounted on lockable
casters whereby the machine can be located in a bag-forming
line close other bag-forming devices.
~0020~ As shown in Figure 1, the folded film sheet 18
is herein shown as a J-folded film sheet with one of the
opposed film sheets, namely sheet 18', extending to form a
flap 35. This film sheet is advanced under the die in an
indexing fashion. The plate valve 32 is indexed in
synchronism with the pistons which~reciprocate the die, and
these operate at high speeds.
X00217 Referring now to Figure 5, there is shown a bag-
forming machine and method incorporating therein the bottom
wall forming section 10. As herein shown, the folded film
sheet is oriented with its longitudinally folded edge 40
disposed along the free ends 41 of the opposed concavely
curved seal-forming edges 13 and 13'. V~7hen the hot die is
stroked down onto the folded film sheet 18, it will
simultaneously slit and heat-fuse opposed film sheets 18'
and 18 " to form opposed concavely curved seals 42 and 42'
extending from the longitudinal folded side edge 40 of the
folded film sheet 18 and converging to an apex 43 at a
location spaced on a transverse axis 44 from the
longitudinal folded edge 40. Simultaneously as the seals 42
and 42' are formed, the cut-out film portion 31 is detached
and evacuated as above-described.
~0022~ As shown in Figure 5, the indexing means may be
comprised by feed rolls 45 or feed roll assemblies which
contact the folded film sheet and move at a predetermined
CA 02354912 2001-08-08
- 6 -
length during each stroke of the die. The bag-forming means
also comprises an indexed vertical slit and seal die 46
disposed at an appropriate location spaced from the bottom
wall forming section 10 whereby to form a vertical seal 46
from the apex 43 of the opposed concavely curved sealed
edges 42 and 42' to a non-folded side edge 47 of the folded
film sheet 18 and thereby form a bag 48 to be detached from
the folded film sheet 18. The formed bag 48 has opposed
concavely curved seals 42 and 42' as herein illustrated,
which extend on opposed sides of a remaining central folded
edge section 49 of the folded film sheet whereby to form the
curved or roundish-like bottom wall 50, as better
illustrated in Figure 6, wherein a produce, herein~a lettuce
51, is disposed in this type of a bag.
(0023 The bag-forming machine, as illustrated in
Figure 5, is also provided with an indexed wicket pin hole
punch 52 to form two spaced-apart holes 53 in the flap 35
between the cut-out end portions 31 of the folded film
sheet 18.
(0024 The bag-forming machine illustrated in Figure 5
is further provided with a bag transport turret 54 to
position the formed bags 48 on a bag collector 55 in a
manner well known in the art whereby to form stacks of
formed bags.
(0025 As shown in Figure 6, the bag herein formed is
for the specific purpose of bagging lettuce or other produce
wherein it is important to aerate the produce when in the
bag and, for this purpose, a bag-perforating indexed
mechanism 56 is located at a convenient location along the
bag-forming line illustrated in Figure 5. At this station,
the folded film sheets are perforated by pins 57 in specific
regions of the folded film sheets wherein the bag is to be
formed.
(0026 Essentially, the method of forming plastic bags
48, having curved or roundish-like bottom walls 50 and an
open top end 58, as shown in Figure 6, comprises the steps
CA 02354912 2001-08-08
- 7 -
of providing a bottom wall forming die 11 having opposed
concavely curved seal-forming edges 13 and 13' converging to
a common apex 14. The die is heated by suitable heating
means such as the resistive heating wire 16. A folded film
sheet 18 is fed on a film support surface, herein a TeflonTM
coated surface 27, of a support plate 26 under the die 11.
The die is reciprocated on the folded film sheet in
synchronism with film feeding means whereby to
simultaneously slit and heat-fuse opposed film sheets of the
folded film sheet. The die is stroked onto the folded film
sheet to form opposed concavely curved seals 42 and 42'
extending from a longitudinal folded side edge 40 of the
folded film sheet 18 and converging to an apex 43 at a
location spaced on a transverse axis 44 from the
longitudinal folded side edge 40. The cut-out film portions
31 are evacuated between the slit and heat-fuse stroke of
the die. The folded film sheets with the opposed curved
seals and cut-out end portions are fed to a further bag-
forming station, as above-described and illustrated in
Figure 5.
(0027 It is within the ambit of the present invention
to cover any obvious modifications of the preferred
embodiment described herein, provided such modifications
fall within the scope of the appended claims.
