U.S. patent number 3,783,750 [Application Number 05/150,647] was granted by the patent office on 1974-01-08 for method and apparatus for forming packages of bags made from plastics material.
This patent grant is currently assigned to Verenigde Fabrieken Van L. J. Heijmeijer N.V.. Invention is credited to Carolus Lambertus Josephus Antonius Maria Heimeijer.
United States Patent |
3,783,750 |
Heimeijer |
January 8, 1974 |
METHOD AND APPARATUS FOR FORMING PACKAGES OF BAGS MADE FROM
PLASTICS MATERIAL
Abstract
A method and apparatus for forming a package of plastics bags,
wherein a web of flattened tubular bag material is intermittently
fed to welding and perforating stations where the web is
respectively welded transversely to define the bag bottoms and
perforated transversely to form scorelines along which the bags can
be separated for use. The intermittent web movement is converted to
continuous motion prior to coiling the leading length of web onto
rotary prongs of a winding head. The prongs are arranged in a
circle, the circle of prongs being contractable to facilitate
stripping of the coil. There are two alternately operable such
winding heads. While the prongs of one of the heads are not
rotating, they are projected longitudinally so that the web being
coiled on the other head passes through the circle defined by the
stationary prongs. Upon braking said other head and simultaneously
setting said one head into rotation, the coiled length is severed
from the rest of the web along one of the scorelines and the next
coil is formed on said one head.
Inventors: |
Heimeijer; Carolus Lambertus
Josephus Antonius Maria (Amsterdam, NL) |
Assignee: |
Verenigde Fabrieken Van L. J.
Heijmeijer N.V. (Amsterdam, NL)
|
Family
ID: |
19810277 |
Appl.
No.: |
05/150,647 |
Filed: |
June 7, 1971 |
Foreign Application Priority Data
Current U.S.
Class: |
493/196; 493/201;
242/524; 493/198; 493/209; 493/230; 242/526.1; 242/531.1;
242/532.6; 242/573.9 |
Current CPC
Class: |
B65B
25/146 (20130101); B31B 70/942 (20170801); B31B
2160/10 (20170801); B31B 70/946 (20170801); B31B
2155/001 (20170801); B31B 2155/00 (20170801); B31B
2155/0014 (20170801) |
Current International
Class: |
B31B
19/94 (20060101); B31B 19/00 (20060101); B65B
25/14 (20060101); B31b 001/00 (); B65h
019/20 () |
Field of
Search: |
;93/8R,32
;242/56A,25A,67.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Juhasz; Andrew R.
Assistant Examiner: Gilden; Leon
Attorney, Agent or Firm: Fleit, Gipple & Jacobson
Claims
I claim:
1. Apparatus for forming packages of plastic bags, wherein a
flattened tubular web of plastics material provided at intervals
with transverse weld seams defining the bases of the bags and with
adjacent transverse scorelines disposed between successive bags is
wound into a coil, the apparatus comprising first and second
winding heads each provided with a plurality of winding prongs on
which the web is wound, means for moving the prongs between a
spread-apart position, at which the prongs are at a maximum spacing
from one another, and a contracted position, means for axially
reciprocating the prongs between an extended operative position in
which the web can be wound thereon and a retracted inoperative
position in which the web can be positioned between the prongs, and
means for moving the prongs to the spread-apart position before the
prongs are moved to the operative position and to the contracted
position before the prongs are moved to the inoperative
position.
2. Apparatus according to claim 1, wherein both heads are disposed
symmetrically with respect to the plane of symmetry of a pair of
guide rolls which are disposed upstream of the heads and between
which the web is passed.
3. Apparatus according to claim 1, wherein the axes of the prongs
of each head are disposed on an imaginary cylindrical surface when
the prongs are in their spread-apart condition.
4. Apparatus according to claim 1, wherein the prongs of each head
are each fixed to one side of a cheek the other side of which
carries a pivot pin of which the axis is offset from the axis of
the associated prong, all the pivot pins of the prongs of each
winding head being mounted in a cylindrical housing with the axes
of the pins uniformly distributed on an imaginary cylindrical
surface.
5. Apparatus according to claim 4, wherein the housing of each head
is fixed to a hollow spindle which is parallel to the prongs and
rotatably carried by a slide plate which is reciprocatable in a
direction parallel to the length of the prongs and which is engaged
by an adjusting mechanism for periodically displacing the slide
plate between a first position in which the prongs assume their
operative position and a second position in which the prongs assume
their inoperative position, and vice versa.
6. Apparatus according to claim 5, wherein the slide plate of each
head carries a motor for intermittently driving the associated
hollow spindle.
7. Apparatus according to claim 5, wherein the hollow spindle is
provided with brake means.
8. Apparatus according to claim 5, wherein a mandrel is
longitudinally reciprocatable within the spindle between an
operative position and an inoperative position and is provided at
one end with a conical portion which, upon displacement of the
mandrel from its inoperative to its operative position co-operates
with guide faces on the cheeks to displace the prongs to their
spread-apart condition, and wherein a dog engages the other end of
the mandrel and is connected to an actuating rod which extends
parallel to the winding prongs and which is displaceable in a guide
block fixed to the slide plate and having a slot through which the
dog passes, the ends of the slots limiting displacement of the dog
relatively to the slide plate and of the mandrel relatively to the
spindle, the adjusting mechanism engaging the actuating rod.
9. Apparatus according to claim 8, wherein the mandrel is rotatable
relatively to the dog.
10. Apparatus according to claim 5, wherein displacement of the
slide plate to the position in which the prongs are in their
operative condition is limited by a stop.
11. Apparatus according to claim 4, wherein a rotatable stripping
ring extends about the prongs directly adjacent the cheeks in the
operative position of the prongs and is free from the prongs in the
inoperative position thereof.
12. Apparatus according to claim 7, wherein the stripping ring has
a central aperture communicating with radial slits for the passage
of the prongs.
13. Apparatus according to claim 8, wherein at least some of the
prongs are displaceable to their contracted condition under the
action of gravity when the mandrel is displaced from its operative
to its inoperative position.
14. Apparatus according to claim 1, including springs acting on the
prongs to bias same to their contracted condition.
15. Apparatus according to claim 1, wherein the two winding heads
co-operate with a change-over lever to which a second lever is
pivoted at its free end, the second lever carries
direction-changing rolls, the change-over lever is pivotable about
an axis disposed in the plane of symmetry of the two winding heads
and drive means are provided for periodically swinging the
change-over lever between two limiting positions.
16. Apparatus according to claim 15, wherein a sprocket which is
coaxial with the pivotal axis of the change-over lever is connected
by a chain to a second sprocket which is fixed to the second lever,
whereby during swinging of the change-over lever the second lever
pivots relatively to the change-over lever in a direction opposite
to the swinging movement of the change-over lever so that the
direction-changing rolls carried by the second lever guide the web
in the two limiting positions of the change-over lever in such a
way that the web passes through substantially the central medial
line of the set of prongs of the stationary winding head before
reaching the prongs of the rotating head.
17. Apparatus according to claim 2, wherein a pair of continuously
and uniformly driven supply rolls for the web is provided upstream
of the guide rolls.
18. Apparatus according to claim 17, wherein a compensating device
is provided between the pair of continuously driven supply rolls
and the pair of guide rolls, the compensating device comprising at
least one roll mounted on a fixed shaft and at least one roll
mounted on a shaft carried by a compensating lever which is
pivotable about a horizontal axis.
19. Apparatus according to claim 18, wherein the lowermost position
of the compensating lever is adjustable.
20. Apparatus according to claim 2, including a folding triangle
upstream of the guide rolls effective to fold the web about its
longitudinal centre line.
21. Apparatus according to claim 17, including welding means and a
scoreline applicator through which the web passes, a pair of
intermittently driven feed rolls for the web upstream of the
welding means, a pair of intermittently driven supply rolls for the
web downstream of the scoreline applicator moving in synchronism
with the feed rolls, the welding means and scoreline applicator
being operative durin the standstill periods of the intermittently
driven feed and supply rolls, and a transformer mechanism disposed
between the intermittently driven supply rolls and the continuously
driven supply rolls, wherein the transformer mechanism comprises at
least one roll mounted on a shaft carried by a pivotable
transformer lever and at least one roll mounted on a fixed shaft,
pivotal movement of the transformer lever being controlled by a
continuously driven cam roller.
22. Apparatus according to claim 21, wherein the cam roller is
fixed to a shaft driven by a chain from a sprocket which is mounted
on the same shaft as an eccentric roller, the shaft being
continuously driven and the eccentric roller controlling an
adjustable welding element of the welding means.
23. Apparatus according to claim 21, wherein the transformer lever
carries an adjustable clamping member engaging one end of an
actuating rod of which the other end is hinged to one end of a
pivotable lever, the other end of the pivotable lever carrying a
cam follower roller which co-operates with the cam roller.
Description
The invention relates to a method and apparatus for forming
packages of bags made from plastics material.
It is known to form a package of, say, 20 separate bags made from
plastics material such as polyethylene and sold for the purpose of
wrapping up garbage, by stacking the bags and then rolling up the
stack. Such packages are formed by hand and involve a
time-consuming and therefore costly operation. Also, in use it is
cumbersome to unroll the package, remove one of the bags and then
roll the package up again.
The invention aims to provide a method by which these disadvantages
can be avoided.
According to the invention, in a method of forming packages of
plastics bags a flattened tubular web of plastics material provided
at intervals with transverse weld seams defining the bases of the
bags and with adjacent transverse scorelines disposed between
successive bags is wound on winding prongs of a rotating first
winding head while passing between winding prongs of a stationary
second winding head spaced from the first head so that only one
scoreline of the web is located between the heads, the first head
is braked and the second head is simultaneously set into rotation
as soon as a predetermined number of bags has been wound on the
first head, whereby the web is severed along a scoreline between
the heads and starts to be wound on the second head, and the
severed length of web wound on the first head is thereupon stripped
from the prongs thereof and the web is passed between the prongs of
the first head.
By means of the invention, therefore, each package of bags is
formed mechanically. The withdrawal of one bag from the package is
particularly simple because the leading bag length need merely be
torn off along the preformed scorelines.
The invention also extends to an apparatus comprising first and
second winding heads each provided with a plurality of winding
prongs which are adapted to be displaced between a spread-apart
condition, at which they are at a maximum spacing from one another,
and a contracted condition and which are axially reciprocal between
a projected operative position and a retracted inoperative
position, and means for displacing the prongs to their spread-apart
condition before being moved to the operative position and to their
contracted condition before being moved to the inoperative
position.
The prongs of each head may each be fixed to one side of a cheek
the other side of which carries a pivot pin of which the axis is
offset from the axis of the associated prong, all the pivot pins of
the prongs of each winding head being mounted in a cylindrical
housing with the axes of the pins uniformly distributed on an
imaginary cylindrical surface. The housing of each head is
preferably fixed to a hollow spindle which is parallel to the
prongs and rotatably carried by a slide plate which is
reciprocatable in a direction parallel to the lengths of the prongs
and which is engaged by an adjusting mechanism for periodically
displacing the slide plate between a first position in which the
prongs assume their operative position and a second position in
which the prongs assume their inoperative position, and vice
versa.
A mandrel may be longitudinally reciprocal within the spindle
between an operative position and an inoperative position and may
be provided at one end with a conical portion which, upon
displacement of the mandrel from its inoperative to its operative
position co-operates with guide faces on the cheeks to displace the
prongs to their spread-apart condition. A dog engages the other end
of the mandrel and is connected to an actuating rod which extends
parallel to the winding prongs and which is displaceable in a guide
block fixed to the slide plate and having a slot through which the
dog passes, the ends of the slots limiting displacement of the dog
relatively to the slide plate and of the mandrel relatively to the
spindle, the adjusting mechanism engaging the actuating rod.
In order to alternate the feed of the web between the two winding
heads, the latter may co-operate with a change-over level to which
a second lever is pivoted at its free end, the change-over lever
being pivotable about an axis disposed in the plane of symmetry of
the two winding heads. The second lever carries direction-changing
rolls and drive means are provided for periodically swinging the
change-over lever between two limiting positions. A sprocket which
is coaxial with the pivotal axis of the change-over lever is
connected by a chain to a second sprocket which is fixed to the
second lever, whereby during swinging of the change-over lever the
second lever pivots relatively to the change-over lever in a
direction opposite to the swinging movement of the change-over
lever so that the direction-changing rolls carried by the second
lever guide the web in the two limiting positions of the
change-over lever in such a way that the web passes through
substantially the central medial line of the set of prongs of the
stationary winding head before reaching the prongs of the rotating
head.
The invention will now be described with reference to the
accompanying drawings illustrating an apparatus for forming
packages of plastics bags. In the drawings:
FIG. 1 is a diagrammatic side elevation of the apparatus;
FIG. 2 is an enlarged part-sectional elevation of one of the
winding heads of the FIG. 1 apparatus, the prongs of the winding
head being shown in their spread-apart condition;
FIG. 3 is a view similar to FIG. 2 but showing the prongs in their
contracted condition;
FIG. 4 is a part-sectional front elevation of one of the winding
heads when its prongs are in the condition shown in FIG. 2;
FIG. 5 is a part-sectional front elevation of the other winding
head when its prongs are in the condition as shown in FIG. 3,
and
FIG. 6 is a front elevation of both winding heads and an associated
change-over lever.
The FIG. 1 apparatus is intended for making packages of bags of
plastics material such as polyethylene. A web 1 of the material is
supplied in tubular form by an extruder (not shown), passes as a
flattened tube through a printing machine (also not shown) and is
then led in the same flattened tubular form over a guide roll 2
between two intermittently driven feed rolls 3. The web then
reaches a welding apparatus 4 which, while the web is stationary,
applies a transverse weld seam to the web to define the base of
each bag. The welding apparatus 4 comprises a fixed welding element
5 and a vertically reciprocal welding element 6. The element 6 is
carried by a slide block 7 which is displaceable along vertical
guide bars 8 and which carries a cam follower roller 9 co-operating
with a continuously driven cam roller 10.
After the web has passed through the welding apparatus, it is led
over a number of guide rolls 11 past a photoelectric cell 12 which
scans the lengths of bags defined in the web material.
The web 1 then reaches a perforating apparatus 13 which, each time
the web is stationary, applies a transverse line of perforations
next to one of the transverse weld seams. Each line of perforations
constitutes a scoreline.
The web then travels over a guide roll 14 and through a pair of
supply rolls 15 which are intermittently driven in synchronism with
the feed rolls 3, whereafter the web reaches a transformer
mechanism 17 via a further guide roll 16. The transformer mechanism
serves to convert the intermittent movement of the web to
continuous motion before the web reaches a pair of continuously and
uniformly driven supply rolls 18. The mechanism 17 comprises two
rolls 19, 19' mounted on shafts carried by a transformer lever 20
which is pivotable about a shaft mounted in the frame of the
apparatus and two further rolls 21, 21' which are mounted on the
frame.
The lever 20 carries an adjustable clamping member 22 which is
pivotably engaged by the upper end of an actuating rod 23. The
lower end of the rod 23 is hinged to one end of a rocker arm 24 of
which the other end carries a cam follower roller 25 co-operating
with a cam roller 26. The roller 26 is fixed to a shaft which
carries a sprocket 27 driven by a chain 28 from a sprocket 29. The
sprocket 29 and the aforementioned eccentric roller 10 are mounted
on a continuously driven common shaft.
The configuration of the cam roller 26 and the adjustment of the
clamping member 22 on the lever 20 are such that the speed of the
web 1 after the latter has left the supply rolls 15 (which speed is
substantially sinusoidal from zero, when the rolls 15 are
stationary, to a maximum and then back to zero again) has a second
speed superimposed on it between the rolls 19 and 21' by reason of
the positive swinging of the transformer lever 20. This
superimposed speed has a constant value during the time when the
supply rolls 15 are stationary, the constant value being equal to
the peripheral speed of the continuously driven supply rolls 18. In
the interval between successive stationary periods of the supply
rolls 15, the superimposed speed follows a substantially sinusoidal
path which is a mirror image of the aforementioned substantially
sinusoidal speed of the web at the location of the supply rolls 15.
The superimposed speed therefore increases from a value a to a
maximum and then back to the value a again. As a result, the speed
of the web will be substantially uniform when it reaches the supply
rolls 18. Such conversion from intermittent to continuous movement
at a constant speed by means of positively swinging the transformer
lever 20 is of particular importance because a very low and
constant tension is produced in the web.
Experiments have shown that, if speed condensation were to be
carried out by means of freely rotatable rollers, inertia can give
rise to large fluctuations in the tension of the web 1, leading to
fractures along the preformed perforations and/or along the weld
seams which have not yet set, it being borne in mind that the web
material has a thickness of only about 30 to 60 microns. Further,
it has also been found impossible to form a freely hanging loop of
web material immediately upstream of the rolls 18 because there is
then a tendency for the web to move laterally out of alignment wth
the rolls 18 and to adhere to the rolls 18 under the action of a
high frequency and high voltage static charge to which the web was
subjected previously to facilitate printing.
The flattened tubular web leaves the supply rolls 18 and passes
over compensating rolls 30, 31', 30", 30'" and 31, 31', 31". The
purpose of these compensating rolls will be described hereinafter.
The rolls 30, 30', 30" and 30'" are mounted on shafts carried by
the frame of the apparatus while the rolls 31, 31' and 31" are
mounted on shafts carried by a compensating lever 32 whch is freely
pivotable on the frame and the lowermost position of which can be
adjusted by means of a set screw 33 projecting from a flange of the
frame.
After leaving the compensating rolls, the web 1 passes over guide
rolls 34 to a folding triangle 35 which folds the web double about
its longitudinal centre line, whereafter the folded web passes
through two guide rolls 36 to a winding device 37 which is
effective to form the folded web into coiled packages each of which
contains a predetermined number of bag lengths defined between
adjacent scorelines in the web. The winding device 37 comprises two
winding heads 38 which are mirror images of one another and which
are disposed symmetrically with respect to the perpendicular plane
of symmetry that passes through the guide rolls 36.
As more clearly shown in FIGS. 2 to 6, each winding head 38
comprises six winding prongs 39 each of which projects from one
side of a cheek 40, the opposite side of which carries a pivot pin
41 mounted in cylindrical housing 42. The axes of the pivot pins 41
are uniformly distributed along an imaginary cylindrical surface as
shown in FIGS. 4 and 5.
The cylindrical housing 42 is fixed to a flange 43 of a hollow
spindle 44 which extends parallel to the prongs 39 and is mounted
in bearings 45 and 46. These bearings permit the spindle to rotate
but prevent it from being displaced longitudinally. The bearings 45
and 46 are mounted on vertical plates 47 and 48 which upstand from
a slide plate 50 and are interconnected by a plate 49 at the
top.
The slide plate 50 carries two blocks 51 each of which carries a
laterally projecting guide roller 52 (see FIGS. 4 and 5). These
guide rollers 52 are adjustable along a respective horizontal guide
track 53 comprising an upper plate 54, a side plate 55 and a lower
plate 56 and supported by the frame by means of a U-beam 57. At the
side opposite the guide roll 52, each plate 47, 48 carries a guide
block 58 which is apertured to receive a horizontal guide shaft 59
carried by the frame. The guide shaft 59 and the guide track 53
extend parallel to the winding prongs 39.
Provided beneath the slide plate 50 there is a plate 60 from which
there is suspended an electric motor 61 which drives the associated
hollow spindle 44 by means of a chain 62 which engages a sprocket
63 on the spindle. Each plate 60 is carried by lugs 64 and, for the
purpose of keeping the chain 62 taut, the plate is hinged to one of
the lugs and connected to the other lug by means of a clamping bolt
65 and nuts 66.
The plate 48 carries one half of an electromagnetic brake 67 of
which the other half is mounted at the end of the hollow spindle
44. The brake serves to bring the spindle 44 to a quick
standstill.
A mandrel 68 passing through the spindle 44 is longitudinally
displaceable therein. One end of the mandrel is supported by two
thrust bearings 69 and an interposed dog 70. One of the thrust
bearings 69 is seated against a collar of the mandrel 68 while the
other bearing 69 is supported by an end ring 71 fixed to the
mandrel by a bolt 72.
The dog 70, which permits the mandrel 68 to rotate, is connected to
a horizontal actuating rod 73 which is displaceably mounted in a
guide block 74 fixed to the slide plate 50. The guide block 74 has
a slot 75 through which the dog 70 projects upwardly, the ends of
the slots 75 limiting displacement of the dog 70 relatively to the
block 74 and of the slide plate 50 and mandrel 68 relatively to the
spindle 44.
The actuating rod 73, which extends parallel to the prongs 39, is
periodically reciprocated between two limiting positions by means
of a drive (not shown). FIG. 2 illustrates one of the limiting
positions of the actuating rod 73. To reach this limiting position,
the rod 73 (and the dog 70 carried thereby) is first displaced
relatively to the block 74 until the dog 70 strikes the end of the
slot 75 in the block 74, the block 74 as well as the slide plate 50
still being stationary at this time. During this displacement of
the dog 70 the mandrel 68 is displaced relatively to the spindle 44
to an operative position at which a conical end portion 76 of the
mandrel co-operates with guide faces 77 of the cheeks 40 to turn
the cheeks about their pivot pins 41 and thereby bring the prongs
39 to a spread-apart condition at which they are spaced a maximum
distance from one another (FIGS. 2 and 4) and at which the axes of
the prongs are evenly distributed over an imaginary cylindrical
surface.
As soon as the dog 70 has struck the end of the slot 75 in the
block 74, further displacement of the actuating rod 73 will also
cause the slide plate 50 to be displaced until the latter strikes a
stop 78 on the frame of the apparatus. At this time a stripping
ring 79 rotatably mounted on the frame will be disposed directly
adjacent the cheeks 40. The stripping ring 79 extends about the
prongs 39 and has a central opening 80 with radial slits for
receiving the prongs 39, the slits being sufficiently long to
enable the prongs 39 to assume their spread-apart condition.
In FIGS. 2 and 4 the prongs 39 of the respective winding head 38
are located in their projected operating position at which, as
hereinbefore described, they assume their spread-apart condition.
As soon as the rod 73 is moved in the opposite direction (out of
the position shown in FIG. 2), the dog 70 first of all traverses
the length of the slot 75 in the guide block 74 while the block 74
and the slide plate 50 remain stationary. This initial displacement
of the dog 70 causes the mandrel 68 to be retracted into the
spindle 44 to an inoperative position (FIG. 3), the conical end
portion 76 of the mandrel 68 thereby releasing the guide faces 77
of the cheeks 40 and allowing the cheeks which are at the top to
move under gravity about their pivot pins 41 so that the associated
prongs 39 assume a contracted condition. Such rotation of the
cheeks 40 can be assisted by means of springs (not shown) which
bias the prongs to their contracted condition, in which case all
the cheeks 40 and all the prongs 39 carried thereby will reach the
contracted condition of FIG. 5. However, it is believed that the
apparatus will function properly even without such springs, the
important feature being that at least some of the prongs assume the
contracted condition.
As soon as the dog 70 has reached the end of the slot 75, further
displacement of the actuating rod 73 will now cause the slide plate
50 to be carried along with the block, whereby the prongs 39 are
brought to their retracted inoperative position at which the prongs
have completely vacated the slots of the aperture 80 in the
stripping ring 79 to become released from the stripping ring. FIG.
3 illustrates an intermediate position of the winding head 38 at
which the prongs 39 are still partially engaged in the slots of the
aperture 80.
The two winding heads 38 are used alternately for the purpose of
forming a coiled package of bags from the folded web 1'. Use is
made of a change-over lever 81 (FIG. 6) which is pivoted to a
second lever 82 carrying direction-changing rolls 83 and 83'. The
lever 81 is pivoted to the frame of the apparatus by a shaft of
which the axis lies in the vertical plane of symmetry of the guide
rolls 36 and the two winding heads 38. This shaft is suitably
rotated to swing the lever 81 periodically between two limiting
positions which are shown in full lines and broken lines
respectively in FIG. 6.
The frame carries a sprocket 84 of which the rotational axis lies
in the same plane as the pivotal axis of the lever 81. A chain 85
extends about the sprocket 84 and about a second smaller sprocket
86 which is fixed to the lever 82. As the lever 81 is swung about
its pivotal axis, the lever 82 rotates relatively to the lever 81
in a direction opposite to the swinging movement of the lever 81
and through an angle which is greater than the angle through which
the lever 81 is swung.
The function of the winding mechanism 37 is as follows. In the
position shown in full lines in FIG. 6, the folded web 1' leaves
the guide rolls 36, sweeps past the direction-changing roll 83' and
over the direction-changing roll 83 and then passes substantially
along the central medial line of the set of prongs 39 of the
lefthand winding head 38 to reach the prongs 39 of the righthand
winding head 38. The prongs of both winding heads are in their
projected operative position in FIGS. 2 and 4, only the righthand
winding head 38 being driven by its motor 61 while the lefthand
head 38 is stationary. The spacing between the heads 38 is such
that only one scoreline of the web 1' will be located between the
two heads.
As soon as a predetermined number of bags has been coiled on the
prongs 39 of the righthand winding head 38 and a scoreline along
which the web is to be severed is located approximately halfway
between the winding heads at the point 87 indicated in FIG. 6, the
motor 61 of the lefthand winding head 38 is switched on with an
increased starting torque while the righthand winding head 38 is
simultaneously braked by means of the electromagnetic brake 67.
This causes the web 1' to tear along the scoreline between the
winding heads, whereupon the lefthand winding head 38 in FIG. 6
commences to coil the now leading length of web 1' passing through
the circle of prongs 39.
The severed and coiled length of web is stripped from the prongs 39
during the hereinbefore described longitudinal displacement of the
prongs to their inoperative position at which they are disengaged
from the stripping ring 79, the latter holding the coil of web
while the prongs are being withdrawn. The coiled package of bags
will now no longer be seated on a core and can be pressed flat and
packaged to a very compact form, especially since the web 1' is
already folded double.
At the same time as the righthand winding head 38 of FIG. 6 was
braked, the change-over lever 81 is swung clockwise from the
position shown in full lines to that shown in broken lines. At the
same time the lever 82 carrying the direction-changing rolls 83,
83' is also pivoted but in an anti-clockwise direction. The rolls
83, 83' thereby disengage and then re-engage the web 1', the latter
now sweeping past the roll 83 and passing about the roll 83'.
As soon as the change-over lever 81 has reached the position shown
in broken lines in FIG. 6, the actuating rod 73 of the righthand
head 38 is displaced in the aforedescribed manner so that the
prongs 39 thereof reach their spread-apart extended position. In so
doing, the web 1' will become positioned between the prongs 39 of
the righthand winding head 38, namely, substantially along the
central medial line of the set of prongs. The longitudinal folding
line in the web 1' is preferably located at the edge of the web
facing the winding heads so that there will be no danger of the
prongs entering between the two layers of the web.
As already mentioned, as the righthand winding head 38 is braked,
the motor 61 of the lefthand winding head starts to turn at an
increased torque to commence coiling of the web on the lefthand
winding head. The accelerated rotation of the lefthand winding head
may last for several seconds, the additional lengths of web
required during this acceleration being obtained by reason of the
compensating lever 32 (FIG. 1), which is normally in its lowermost
position bounded by the set screw 33, swinging upwardly so that the
distance between the rollers 30, 30', 30", 30'" on the frame and
the rollers 31, 31', 31" on the compensating lever is decreased. As
soon as the increased starting torque of the motor 61 of the
lefthand winding head 38 has caused the latter to turn at a speed
which is higher than the normal coiling speed (equivalent to the
peripheral speed of the supply rolls 18), the motor 61 is then so
controlled that it turns its winding head at a lower than normal
speed until it turns at a normal coiling speed at which time the
compensating lever 32 has just reached its lower limiting position
as determined by the set screw 33.
The use of a compensating lever 32 which, in contrast with the
transformer lever 20, is not positively pivoted but takes place
solely under the influence of gravity and the force exerted by the
web 1 on the rollers 31, 31', 31" is made possible by the fact that
this section of the web is not subjected to very large speed
differences.
By correctly adjusting the setting of the set screw 33 it is
further possible to ensure that at the time one of the winding
heads 38 is braked and the other winding head is set into rotation
one of the scorelines will be located roughly at the position 87
indicated in FIG. 6 so that this will be the line along which the
web is severed.
It will be evident that, after the predetermined number of bags has
been coiled on the prongs 39 of the lefthand winding head 38 in
FIG. 6, the hereinbefore procedure will be repeated in that the
lefthand winding head 38 is braked and the motor 61 of the
righthand winding head 38 is started with an increased torque to
tear the web between the heads and commence coiling on the prongs
of the righthand winding head, the completed package being stripped
from the prongs of the lefthand head by retracting the prongs.
As will be evident from FIG. 6, the two end positions of the
change-over lever 81, the second lever 82 and the two
direction-changing rolls 83 are not symmetrical with respect to the
vertical plane of symmetry of the two winding heads 38. The reason
for this is that the direction of rotation of both winding heads is
the same, the folded web 1' being coiled from below the set of
prongs of the righthand winding head but from above in the case of
the lefthand winding head. To ensure that the folded web will
always pass substantially along a diameter of the set of stationary
winding prongs on its passage towards the rotating prongs, the
aforementioned asymmetric arrangement is therefore necessary.
The hereinbefore described apparatus has been particularly
developed for the manufacture of packages of polyethylene bags for
wrapping up garbage, the predetermined number of bags in each
package being determined by the electrical equipment of the
apparatus and the leading bag length being separable from the rest
of the package along a scoreline. However, it will be evident that
the apparatus is also suitable for forming packages of bags for
other purposes, the folding trignale 35 of FIG. 1 being omitted if
small bags are involved.
* * * * *