Note: Descriptions are shown in the official language in which they were submitted.
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The present lnvention relates to machines ~or blow
molding hollow articles ~rom a tubular parison of plastic material
del~ivered by an extruder, In such machines an extruder delivers,
sually continuously, a tube of plastic material~ termed a parison
at a high temperature. A section o~ this tube as it emerges is
enclosed between the two halves of a mold, within which the tube
is blown to confo~m to the walls of the mold so as to produce a
shaped article. ~
In machines of this character o~ the particular type
10; j termed discontinuous parison machines, cutting ~eans are provided
¦for cuttin~ the parison which however operate only once ~or each
hollo~l article produced~ cutting the parison to lengths suf~lcient
¦for manufacture of the desired hollol~r bodies. In contrast, in
machines of this character o~ the part~cular type called contin-
uous parison machines there is no such cutting means. Instead,
successive lengths of the continuously emerging parison are seized
i ¦between the halves of a succession of mold hal~ pairs ~rhich may be
i mounted for example on a turntable, the rlm of which moves past
the extrusion head~ The mold halves close one after another on
lengths of the hollow piastic raterial, which is cut Olr by the
~nolds themselves as they close on the plastic material.
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A similar mounting for the mold half palrs may
also be employed in discontinuous parison machines
With either type of machine, steps must be taken to
dispose of the tubular plastic material which continues to
emerge from the extruder in the event of stoppage of the
molding process and consequent interruption in the motion
of the molds, for example in the event of a malfunction of
the molding and blowing apparatus proper.
Hitherto, such elimination was manually effected or
was effected automatically by conveyor means which detach the
hot plastic tube without chopping or grinding it and which
then carry it outside the machine to cool.
The introduction of such automatic means eliminates
the danger to the operator of introducing his hands into the
machine, but it does not provide a satisfactory solution
since the hot plastic material as extruded cools so slowly
that, at least in the case of certain materials it is not
possible to prevent decomposition or Eurther chemical change
Z therein. The result is the evolution of noxious gases such
as hydrogen chloride and carbonization of part of the plastic
material which renders it substantially useless and incapable
of being recycled to the extruder.
According to the present invention, and in order to
av~oid these shortcomings, there is provided driving means
connected to the cutting means for moving the cutting means
through the parison repeatedly during interruption of the
normal operation to sever the parison into fragments having
a length, as measured along the path, which is a small fraction
of the length received by the molds during the normal operation.
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By means of the invention therefore, the unwanted and
unblown, unmolded parison is recovered in short lengths or
fragments, e.g. of the order of one centimeter in length, which
cool rapidly and without change in the nature the plastic
material thereof. These fragments can after grinding be
recycled into the extruder.
The cutting device may comprise for example two blades
disposed on opposite sides of the parison and suhjected to
oppositely phased reciprocating translatory motions toward
and away from the axis of the extruder head, these blades coming
substantially into contact with each other in the vicini-ty of
that axis, somewhat in the manner of a pair of shears.
In another embodiment of the invention the cutting
device or the parison may include a single blade subjected
to a reciprocating translatory motion transversely of the axis
of the extruder head, moving back and forth through that axis.
It is also possible to use as a cutting device a blade
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pivotably mounted about an axis and subjected to a continuous
rotating motion or to a reciprocating arcuate motion through
the axis of the extruder.
In al~ these embodiments the parison cutting device is
permanently disposed at a fixed position on the blow-moldin~
machine, with the blade or blades thereof, when stationary, in
a retracted position outside the path of the parison from the
extruder so as to permit the parison to pass into the ~olds in
normal operation. The blade is set into motion across the axis
of the extruder, i.e. across that path, as soon as a variation
or malfunction in the operation of the machine makes it desirable
to withdraw the parison and to cut it into small pieces.
The fragments of the parison may advantageously be
recovered in a trough which delivers them onto a conveyor, either
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a belt conveyor or a pneumatic conveyor for delivery to a
grinding device or to a storage vessel.
~rief Description of the Drawings
The invention will now be further described in terms of
a presently preferred exemplary embodiment thereof and with
reference to the accompanying drawings in which the figures
of drawings are a perspective view of a blow molding machine
including a parison cutting device in accordance with the
invention and a wiring diagram for the cutting device.
Detailed Descri tion of Preferred E~boaiment
P
In the drawing, the extruder 5 of the blow molding
machine and the parison cutting or chopping device are shown
in full lines whereas the remainder o~ the blow moldin~ machine
is schematically indicated in chain lines. The blow molding
- machine includes an extruder S and a plurality of openable
and closeable pairs of mold halves 13. The pairs of mold halves
are mounted on suitable blowing mechanism 13a, well-known in
the art, which moves them cyclically in a closed path past the
extruder 5, opening the halves of each pair prior to arrival
at a position adjacent the extruder to eject a molded article
and then to receive a length of parison from the extruder, and
closing them thereafter or the blowing of the new parison.
The chopping device includes a base plate 1 on which is
mounted a motor 2. The motor is equipped with a variable ratio
speed reducer which, through an angle drive 2a and a trans-
mission including a link 2b and a bell crank 2c, imposes recipro-
cating motion on a blade carrier 3 having a blade 3a mounted
therein. The elements 2b, 2c, 3 and 3a are mounted beneath
the plate 1 and therefore appear in phantom in the drawing.
When the machine is in operation, the extruder head 5
continuously delivers a tubular parison which passes through an
opening 4 provided in the base plate 1 into the path of the
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blade 3 when the parison chopping device is in operation, and
into the path of the pairs 13 of mold halves, as previously
described when the chopping device is not in operation.
Below the base plate 1 is disposed a trough 7 supported
from blocks 7a which are slideably movable on rods 7b between a
retracted position for the troughl which permits the parison
to pass during normal operation of the machine into the path
of the molds 13, and an advanced position, the one shown in
the figure. In this advanced position, to which the trough is
set upon activation of the parison cutting or chopping device,
the fragments into which the emerging parison is chopped by~
the blade 3 will fall into the trouyh.
Passage of the trough 7 from its retracted ~o its
advanced position is automatically effected for example by
operation of the rod 6a from an electropneumatic actuating
cylinder 6 when the parison chopping device is set into operation.
To insure that the chopped fragments of parison material
produced by the knife 3 fall into the trough, there is provided
a set of nozzles 8 which produce jets of air directed into the
interior of the trough. These air jets operate not only to send
the parison fragments into the trough but also to chill them,
thereby avoiding decomposition or other chemical change of the
plastic material thereof.
At the other end of the trough the parison fragments
- fall onto a conveyor generally indicated at 9 havin~ an endless
belt 11. At the end of the conveyor remote from the trough,
the parison fragments fall into a grinder 10 or any suitable
form of storage vessel.
The conveyor 9 may advantageously include an electronic
detector 12 (for instance 16FSl of HONEYWELL) which detects
the presence of foreign matter, in ~act of metallic particles,
which might damage the blades of the grinding device 10 or
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otherwise pollute the plastic material to be recycled. This
electronic detector may control operation of a gate 12a which,
when shifted to the dash-line position shown therefore in the
lateral wall lla of the conveyor, interrupts the passage of
the parison fragments toward the grinder. These fragments
then fall to the outside of the conveyor.
Operation of the parison chopping device is automatically
terminated when the two following conditions are fulfilled:
l. When, on start-up, the blowing device 13a, bearing
the molds 13, reach operating speed, and
2. When, on start-up, a pair of mold halves moving
toward the extruder has reached a position such that
a suitable and not excessive length of parison will
be extruded during the time required for that pair
of mold halves to reach the position of the extruder.
Satisfaction of the first condition is detected by a revolution
counter 14 which energizes a relay at a settled speed value.
Satisfaction of the second condition is detected by the motion
of a metallic element 15a fixed to each mold carrier past a
detector switch 15 suitab]y adjusted in position on the machine
frame ~not shown) with respect to the extruder. These detectors
are coupled to the control circuit for the motor 2. A switch
16 is provided at the out-shaft of 2a to insure that the
motor 2 is de-energized just as blade 3a comes to rest in its
retracted position, leaving the opening 4 clear. The trough
7 is simultaneously shifted to the left, in the figure, out of
the path of the parison; jets of nozzles 8 and conveyor 9 are
then stopped.
On the wiring diagram of figure 2 are shown:
relay M controlling for starting and braking the motor 2 of the
chopping device 3 and its sr~7itches ml to m4; relay C for
starting (and stopping) the conveyor 9, and its swi-tch cl; electro-
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valve N controlling nozzles 8; electrovalve T controlling thecylinder 6 for advance (and return) of thè trough 7; switch
15 acted on by element 15a when the molds 13 are in a convenient
position; switch 16 acted on by the driving mechanism of the
chopping device 3 when blade 3a is in its retracted position;
relay S of the revolution counter 14 of the blowing device
13a, and its switches sl to S3; relay MM for manual control
of relay M of the motor 2, with its hand-contactor mm and its
s~itches mml to mm3; relay CM for manual control of relay C
of the conveyor 9, with its hand-contactor cm and its switches
cm1, cm2; safety contactor STOP. All switches are shown at
rest. Their temporizations are indicated through an arrow,
with the delay given in seconds.
The device wo~ks as will be explained below:
As long as hand-contactors mm and cm are open, as usual, and the
blowing device 13a moves normally, switches mml and mm3 remain
open, mm2 is closed; cml is closed and cm2 is open.
Relay S is excited by the revolution counter 14; s~, s2, S3 thus
are open. Switches 15 and 16 close periodically but, as long as
memory-switch ml is open, re}ay M is not energized. Switches m2,
m3, m4 are open; thus relays C, N, T are not energized and the
whole device is at rest.
Appropriate sensors (not shown) cause the blowing device 13a to
stop when a malfunction appears, such as a failure o~ the blowing,
a bad stripping of a molded article etc... As soon as blowing
device 13 is stopped, or if it is merely slowed down, the revolution
counter 14 ceases exciting relay S, thus switches sl to s3 close,
relay C is energized, conveyor 9 starts and authorization switch
Cl closes: M in turn is energized and the chopping device 3 enters
into operation; switches ml and m2 become closed; switches m3 and
m4 become closed, thus N and T are energized and the whole device
beyins working. As soon as the malfunction is settled and the
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blowing device 13a turns again at its normal speed, S becomes
excited, switches sl to s3 become opened; relay M keeps on
being excited through switch ml and both switches 15 and 16,
but, when the element 15a of a mold passes in the convenient
position in front of switch 15, the latter becomes opened; then,
as soon as the blade 3a of the chopping device 3 comes to its
back position thus opening switch 16, supply of relay M is cut,
and the chopping device 3 stops. Then switches ml to m~ open
again; relays C, N, and T cease to be energizea and the device
1~ becomes at rest.
It may easily be seen that the operator can, at will, start the
conveyor 9 by means of the hand-contactor cm, through relay CM,
switch cm2 and relay C.
In the same way, he can put the chopping device 3 into operation
by means of the contactor mm, through its relay MM, switch mm3
and relay M, even if the speed of the blowing device 13a is
at the settled value. Energization of relay M causes also relays
C, N and T to be energi3ed.
When contactor mm is released by the operator, switch mm3 again
opens, but switch m~l keeps closed during a sufficient time,
that allows a further mold to pass in front of detector 15. After
releasing of switch mml, the opening of switches 15 and 16 cuts
the supply o relay M, that causes the whole device to stop as
explained hereabove.
Action on safety contactor STOP puts the whole device at rest
as soon as blade 3a is in its retracted position.
On a discontinuous parison machine there may be added
to the parison cutting device a specialized form of cutter but
it is in general possible to use, for chopping the parison in
accordance with the invention, the cutting blade or blades
which are already provided on condition that they be provided
with an auxiliary control in accordance with the invention so as
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to drive them at a much higher than their normal speed, the
latter of which of course corresponds to the rate of passage
of the molds across the path of the parison as it emerges from
the extruder.
While the invention has been described hereinabove in
terms of a number of presently preferred embodiments thereof,
the invention itself is not limited thereto but rather compre-
hends all modifications of and departures from those e~bodiments
properly falling within the spirit and scope of the appended
claims.
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