IE84371B1 - A blow moulding process - Google Patents
A blow moulding process Download PDFInfo
- Publication number
- IE84371B1 IE84371B1 IE1995/0933A IE950933A IE84371B1 IE 84371 B1 IE84371 B1 IE 84371B1 IE 1995/0933 A IE1995/0933 A IE 1995/0933A IE 950933 A IE950933 A IE 950933A IE 84371 B1 IE84371 B1 IE 84371B1
- Authority
- IE
- Ireland
- Prior art keywords
- drum
- mould
- core
- cooling
- parison
- Prior art date
Links
- 238000000071 blow moulding Methods 0.000 title claims description 10
- 238000001816 cooling Methods 0.000 claims description 66
- 238000000034 method Methods 0.000 claims description 30
- 229920003023 plastic Polymers 0.000 claims description 29
- 239000004033 plastic Substances 0.000 claims description 29
- 239000000463 material Substances 0.000 claims description 28
- 238000000465 moulding Methods 0.000 claims description 17
- 239000000498 cooling water Substances 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- 238000007664 blowing Methods 0.000 claims description 4
- 230000001276 controlling effect Effects 0.000 claims description 4
- 238000002347 injection Methods 0.000 claims description 4
- 239000007924 injection Substances 0.000 claims description 4
- 238000007789 sealing Methods 0.000 claims description 4
- 230000000875 corresponding Effects 0.000 claims description 3
- 238000007599 discharging Methods 0.000 claims description 2
- 239000012530 fluid Substances 0.000 claims description 2
- 238000009826 distribution Methods 0.000 description 3
- 239000004615 ingredient Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000005755 formation reaction Methods 0.000 description 2
- 238000009966 trimming Methods 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
Description
"A Blow Moulding Process"
The invention relates to a blow moulding process.
The invention particularly relates to the blow moulding
of relatively large plastics drums, for example of a size
With the blow
relatively large
in the order of 120-220 litres capacity.
moulding of such drums, amounts of
plastics material have to be handled within the mould and
this presents problems in trying to achieve an even
distribution of plastics material within the mould and in
forming drum side walls of a desired thickness profile.
Further, relatively long cooling times are required once
the drum has been formed due to the large volume of
limits the
Also,
improper cooling can cause distortion of the drum as it
plastics material in the drum. This
production throughput of the moulding machine.
cools.
The present invention is directed towards providing a
blow moulding process for manufacturing a plastics drum
in an efficient manner which overcomes these problems.
According to the invention,
there is provided a blow
moulding process for manufacturing a plastics drum,
comprising the steps:-
forming a tubular parison by extruding plastics material
from an extruder accumulator head downwardly through a
die, the die having an annular outlet opening;
adjusting the width of the outlet opening for controlling
the thickness of the parison side wall;
locating a blow pin within a lower end of the parison;
clamping the lower end of the parison about the blow pin;
w 84371
closing a split mould about the parison in a controlled
manner by locating an associated pair of mould halves at
opposite sides of the parison, bringing the mould halves
together at a desired mould Closing speed in a number of
steps, incrementally reducing the mould closing speed for
each successive closing step;
injecting air at a preset pressure through the blow pin
into an interior of the parison, commencing air injection
during closing of the mould parts together, inflating the
parison against an inner wall of the mould to form the
drum;
opening the mould and discharging the drum from the mould;
delivering the drum to a drum cooler;
clamping the drum between. a pair of cooling plates by
engaging each end of the drum with the cooling plates;
circulating" a cooling" fluid through the cooling’ plates;
and
passing cooling air through the opening or openings for
circulating cooling air through the interior of the drum
at a preset air pressure.
The stepped closure of the mould advantageously assists in
controlling expansion of the parison within the mould
while the forced cooling allows increased throughput and
ease of handling.
as mentioned above,
Advantageously, the cooling of the
drum downstream of the moulding machine allows early
removal of the drum from the moulding machine, the drum
cooled on the
Thus, the throughput of the
moulding machine can be increased. Further,
the drum during cooling thus
only being partially moulding machine
sufficient to allow handling.
the drum
ensuring
thus
cooler supports
proper cooling of the drum to a desired drum shape,
improving the quality of the drum produced. Maintaining a
preset pressure within the drum prevents the tendency of
the drum to buckle upon cooling.
In a
particularly preferred embodiment, the
includes the steps of standing the drum on a fixed bottom
process
cooling plate, engaging a top of the drum with. a top
cooling plate, moving the top cooling plate from a
retracted disengaged position to a drum engaging position
between the
through the
sealing one or Inore openings at a top of the drum for
for clamping the drum cooling plates,
circulating cooling water cooling plates,
sealing the drum, passing cooling air through said
openings for circulating cooling air through an interior
of the drum whilst maintaining a preset air pressure
within the drum. The circulation of cooling water through
the cooling" plates facilitates efficient cooling of the
top and bottom of the drum which contain the largest
amounts of material while at the same time, the cooling
air readily easily and efficiently cools the side wall of
the drum.
In a further embodiment, the process includes maintaining
the blow pin at a temperature in the range of S6f—8WC.
Preferably, the process includes maintaining the blow pin
at a temperature of 70W3. The heating of the blow pin has
been found to improve the formation of a neck around the
More usually, cooled,
blow pin. such blow pins are
however, such cooling can in some cases, particularly when
handling the relatively large volumes of plastics material
as in the present invention cause imperfections and
cracking in the neck portion which can prove difficult or
impossible to seal when a cap or cover is mounted on the
neck portion in use.
In another embodiment, the mould has a core for forming an
outwardly extending circumferential ring on the drum, the
core defining a shaped slot extending outwardly of an
inner side wall of the moulds the core having an. open
position forming an enlarged slot and a closed position of
reduced slot size corresponding to a desired ring shape,
the process including holding the core in an open position
while closing the nwuld, blowing plastics material into
the slot of the core, on attaining a preset desirable
pressure within the mould closing the core for forming the
captured plastics material into a desired ring shape, and
moving the core into the open position after completion of
blowing within the mould.
ha a particularly preferred embodiment, a pair of cores
are provided, namely, a top core and a bottom core spaced-
apart on the mould, the cores being closed at different
speeds for forming a pair of spaced-apart circumferential
Ideally, the
commencing closure of the cores
rings on the drum. process includes
at the same time and
closing the bottom core more slowly than the top core.
different
improved distribution of
The closing of the cores at speeds
advantageously facilitates an
plastics material within the mould for forming the desired
rings on an exterior of the drum.
The invention will be more clearly understood by the
following description of some embodiments thereof, given
by way of example only, with reference to the accompanying
drawings, in which -
Fig. 1 is a schematic flowchart illustrating a blow
moulding process according to the invention;
Fig. 2 is a perspective View of a drum formed by the
process;
Fig. 3 is a perspective view of another drum type
formed by the process;
Fig. 4 is a diagrammatic illustration of the
formation of a parison in the process;
Fig. 5 is a diagrammatic illustration. of a mould
closing about the parison according to the process;
Fig. 6 is a diagrammatic illustration showing the
mould in a fully closed position and the parison
inflated to form a drum within the mould;
Fig. 7 is a detail sectional elevational view of
portion of a mould used in the process shown in an
open position;
Fig. 8 is a detail View similar to Fig. 7 showing the
mould portion in a closed. position. for forming a
circumferential ring about the drum;
Fig. 9 is a detail view similar to Fig. 7 showing the
mould portion in an open position;
Fig. 10 is a detail sectional elevational view of
portion. of a drum formed according to the process
showing a circumferential ring on an exterior of the
drum;
Fig. 11 is a perspective view of drum cooling
apparatus used in the process;
Fig. 12 is a perspective View showing the drum
cooling apparatus in use cooling a drum according to
the process;
Fig. 13 is a partially sectioned elevational view of
a drum being cooled. in the apparatus of Fig. 11
according to the process; and
Fig. 14 is a perspective view of a cooling carousel
used in the process.
Referring to the drawings,
blow
described.
a process and apparatus for
will be
Fig. 2 shows a drum 1 formed by the process.
moulding a cylindrical plastics drum
The drum 1 has a circular bottom wall 2 with an upstanding
cylindrical side wall 3 and a top wall 4. A. pair of
spaced—apart outwardly extending circumferential rings 5
are provided at an upper end and at a lower end of the
side wall 3.
section as can be seen in Fig. 10.
These rings 5 are generally" L-shaped in
A pair of openings are
provided in the top wall 4 defined by spaced—apart neck
portions 6 upstanding on the top wall 4. Each. neck
portion 6 is threaded for reception of a cap (not shown)
to seal the opening.
shows another drum 7
Fig. 3 formed according to the
process of the invention. The drum 7 has a bottom wall
and an upstanding side wall 8. An outwardly extending
circumferential ring 9 is provided at an upper end of the
side wall 8. A lid
upper end of the side wall 8 to seal the drum 7.
(not shown) is engageable with the
Ingredient materials for forming a plastics drum are
delivered from supply hoppers 10, 11 containing new
plastics material
blender 12.
which is
and dye material
Additionally,
a waste by-product
respectively to a
re~ground plastic material
of the
delivered to the blender 12 from a regrind material hopper
process is also
. The ingredient materials are mixed in the blender
typically in the ratio of about 70% new plastics material,
about 30% regrind. plastics material and about 0.4% dye
material.
The ingredient materials are delivered from the blender 12
to an extruder 14 of a blow moulding machine 16.
A tubular parison 18 is formed at the moulding machine 16
by extruding the plastics material from an accumulator
head of the extruder 14 downwardly through a die having an
annular outlet opening. The width of the annular outlet
opening can be adjusted during extrusion of the plastics
material for controlling the thickness of the parison side
wall to provide a desired thickness profile between. an
upper end 19 and a lower end 20 of the parison 18.
When fully extruded, the lower end 20 of the parison drops
over a pair of blow pins (not shown). The blow pins are
moved apart to spread the lower end 20 of the parison 18
and then the lower end 20 of the parison 18 is clamped
about the blow pins.
Referring to Figs. 4 to 6, a split mould 22 of the
moulding machine 16 has a pair of mould halves 23, 24.
The mould halves 23, 24 are closed from an initially open
position as shown in Fig. 4 to a closed position as shown
in Fig. 6. The split mould 22 is closed in a controlled
manner in a number of steps incrementally reducing the
mould closing speed for each successive closing step. For
the mould
initially" aligned with the parison 18, the
example, in the manufacture of a 210 litre drum,
halves are
mould halves being spaced 190 mm apart. In a first
the mould halves are closed to 70 mm at 100%
at 35%
closing step,
closing speed. Then in a second closing step,
mould closing speed, the gap between the mould halves is
reduced to 35 mm. Subsequently, in a third mould closing
step, the mould halves are closed to 16 mm at 12% mould
closing speed. Finally, in a fourth mould closing step,
the mould halves are brought together at 1% mould closing
speed.
As the mould 22 is being closed, air injection commences
for inflating the parison 18 within the mould 22. Air
injection takes place in a number of steps. A first pre-
blow of air at 4.5 bar pressure for 2.5 seconds is applied
After
a 0.1 second dwell time is
2.5 bar
parison
to the interior of the parison within the mould.
stopping the first pre-blow,
Then a
allowed. second pre—blow of air at
pressure for 4.8 seconds is applied to the
interior within the mould.
blow,
is carried out for 90 seconds.
After stopping the second pre-
a 5 second dwell time is allowed. Then a main blow
During the main blow, the
air pressure within. the parison. is cycled at intervals
between. 9 bar and :1 bar pressure. This advantageously
allows the air within the mould to be changed at intervals
to provide cooling of the drum formed within the mould.
After the main blow, air is vented from the mould. The
mould is opened and a drum 1 formed within the mould is
at which excess
discharged to a trimming station 26
plastics material is cut away from the drum 1. The waste
plastics material is passed through a grinder 27 and
returned to the regrind hopper 13 for re—use.
station, the drum 1 is
Downstream of the trimming
delivered to a drum cooling apparatus 50 which is
described later.
During moulding, a pair of spaced-apart L—shaped support
rings 5 are preferably formed around a circumference of
the drum 1 projecting outwardly from an exterior surface
of the drum.
a pair of spaced-apart support rings 5 on an exterior of
Figures 7 to 9 show the sequence for forming
the drum 1. The mould. 22 has a pair of spaced—apart
cores, namely a top core 30 and a bottom core 31 spaced-
apart on the mould 22.
shaped slot 32, 33 extending outwardly of an inner side
wall 34 of the mould 22.
position (as shown in Fig. 7) forming an enlarged slot 32,
33 and a slot
corresponding to a desired ring shape as shown in Fig. 8.
Each core 30, 31 defines an L-
Each core 30, 31 has an open
closed position of reduced size
Initially the cores 30, 31 are held in an open position
After the mould. 22 has been
fully closed at a preset internal pressure,
while closing the mould.
the top core
It will be noted that both
31 commence closure at the same time,
and bottom core 31 close.
cores 30, however,
the bottom core 31 closes more slowly than the top core
. The top core 30 has a closing time of approximately
2.75 seconds, while the bottom core has a closing time of
Thus,
bottom core 31 is approximately 1.5 times that of the top
approximately 4.1 seconds. the closing time for the
core 30. This closure differential advantageously assists
in the even distribution. of plastics material into the
slots 32, 33.
slots 32,
In the closed position shown in Fig. 8, the
33 shape the plastics material into a desired
ring shape. Upon subsequent opening of the cores as shown
in Fig. 9, an L-shaped ring 5 thus formed can be released
from the core 30, 31.
Fig. 10 shows the desired L-shaped profile of the ring 5
which is achieved according to the method.
the drum 1 is
11). The
cooling apparatus 50 has a support frame 51 with a fixed
Downstream of the moulding machine 16,
delivered to a cooling apparatus 50 (Fig.
bottom cooling plate 52 and an associated top cooling
plate 53 spaced—apart above the bottom cooling plate 52
and movably mounted on the frame for vertical movement by
means of a ram 54. An upstanding arcuate drum locating
band 55 is mounted at a rear of the bottom cooling plate
52. Each of the cooling plates 52, 53 are connected to a
cooling water supply (not shown) for circulating cooling
water through the plates 52, 53 for cooling a top wall 2
and a bottom wall 3 of a drum 1 placed in the cooling
apparatus 50 as shown in Fig. 10. Openings in a top of
the drum 1 are closed by sealing discs 60, 61, each
63 on the frame 51 for
movement between a retracted disengaged position and a
carried by an associated ram 62,
drum engaging position as shown in Fig. 12. Air pipes 65,
are connected. to each disc 60, 61 for circulating
cooling air through the drum 1 whilst maintaining a preset
It will be noted that in
the drum 25 is supported between
air pressure within the drum 1.
the cooling apparatus 50,
the cooling plates 52, 53 which support the drum in a
desired alignment during cooling of the drum to form high
quality" drums of a uniform shape. By" pressurising an
interior of the drum during cooling, this prevents the
tendency of the top wall 2 of the drum 1 to collapse or
buckle during cooling which weakens the drum.
Advantageously, the cooling apparatus 50 allows the drum
to be removed earlier from the moulding machine 16 without
the need for fully cooling the drum on the moulding
machine 16. Thus, advantageously a greater throughput of
drums can be achieved with the moulding machine.
Referring to Fig. 14, there is shown a cooling carousel 70
used in the process. The cooling carousel 70 essentially
has a plurality of the cooling apparatus 50 previously
Parts similar
to 13 are
described with reference to Figs. 11 to 13.
to those described with reference to Figs.
assigned the same reference numerals. The carousel cooler
70 has a central post 71 about which a support frame 72 is
rotatably mounted. A plurality of cooling stations are
_ 11 _
provided by spaced-apart pairs of bottom cooling plates 52
and associated top cooling plates 53 arranged on the frame
72.
In use, drums 1 received from the moulding machine 16 are
53 and the
previously
The frame 72
through one
When the
cooled drum 1 is returned to the loading station, it is
mounted between a pair of cooling plates 52,
cooling of the drum 1 is carried out as
described with reference to Figs. 11 to 13.
of the
revolution in the time taken to cool a drum 1.
carousel cooler 70 is rotated
unloaded and a fresh drum 1 from the moulding machine 16
is mounted on the carousel cooler 70.
embodiments
both
limited to the
which may be
The invention is not
hereinbefore described varied in
construction and detail.
Claims (1)
1. A blow moulding process for manufacturing a plastics drum, comprising the steps:- tubular material from an extruder accumulator head downwardly forming a parison by extruding plastics through a die, the die having an annular outlet opening; width of the outlet controlling the thickness of the parison side wall; adjusting the opening for locating a blow pin within a lower end of the parison; clamping the lower end of the parison about the blow pin; closing a split mould about the parison in a controlled manner by locating an associated pair of mould halves at opposite sides of the parison, bringing the mould halves together at a desired mould closing speed in a number of steps, incrementally reducing the mould closing speed for each successive closing step; injecting air at a preset pressure through the blow pin into an interior of the parison, commencing air injection during closing of the mould parts together, inflating the parison against an inner wall of the mould to form the drum; opening the mould and discharging the drum from the mould; delivering the drum to a drum cooler; clamping the drum between a pair of cooling plates by engaging each end of the drum with the cooling plates; sealing one or more openings at a top of the drum to seal the interior of the drum; circulating a cooling fluid through the cooling plates; and passing cooling air through the openings for circulating cooling air through the interior of the drum at a preset air pressure. A process as claimed in claim 1 which includes the steps of standing the drum on a fixed bottom cooling plate, engaging a top of the drum with a top cooling plate, moving the top cooling plate from a retracted disengaged position to a drum engaging position for clamping the drum between. the cooling plates, and circulating cooling water through the cooling plates. A. process as claimed in any’ preceding claim which includes maintaining the blow pin at a temperature in the range of 50°C-80°C during moulding of the drum. A process as claimed in claim 3 which includes maintaining the blow pin at a temperature of 70°C. A process as claimed in any preceding claim wherein the mould has a core for forming an outwardly extending circumferential ring on the drum, the core defining a shaped slot extending outwardly of an inner side wall of the mould, the core having an open position forming an enlarged slot and a closed position of reduced slot size corresponding to a desired ring shape. A process as claimed in claim 5, the process including holding the core in an open position while closing the mould, blowing plastics material into the slot of the core, on attaining a preset desirable within the forming the captured plastics material into a desired pressure mould closing the core for ring shape, and moving the core into the open position after completion of blowing within the mould. A process as claimed in claim 5 or 6 wherein a pair of cores are provided, namely, a top core and a bottom core spaced-apart on the mould, the cores being closed at different speeds for forming a pair of spaCed—apart circumferential rings on the drum. which commencing closure of the cores at the same time and A process as claimed in claim 7 includes closing the bottom core more slowly than the top core . A blow moulding process substantially as hereinbefore described with reference to the accompanying drawings. A. plastics drum whenever formed. by the process as claimed in any preceding claim. Apparatus substantially as hereinbefore described for forming a plastics drum according to the process as claimed in any of claims 1 to 10.
Publications (1)
Publication Number | Publication Date |
---|---|
IE84371B1 true IE84371B1 (en) | 2006-10-04 |
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