Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PLM ABj Malm~ PP 513
Proce~s ~or the production of a b:Lank for
containers and blank produced by the process.
The inYention relates to a tubular pre-moulding
of a thermoplastic, suit~ble ~or subsequent shaping to
give containers by a blow-moulding process9 and to a
process and e~uipment for producing the pre-moulding.
~ a tube, ~uture mouth parts and parts of adjacent neck
sections are moulded to pre-mouldings, from two blank
parts ~oined to one ano-ther~ by an axial stretch process
and a blow-mouldi~g process, the parts in the transition
between the two mouth parts being severed in order.to
form two separate blank parts which3 after closing at
one o~ the ends and subsequent reworking to produce the
requisite closi~g sur~aces at the respective ~ther ends,
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each alone ~orm a tubular pre-moulding.
: In a production process used for the manufacture
o~ containers from a thermoplastic, blanks normally
called pre-mouldings for containers are produced ~rom
severed parts o~ extruded long tubes o~ an ~morphous
thermoplastic. At one end, -the severed piec~s are
shaped in such a way that they form the future mouth part .
of the container, whils-t they are closed ~t the opposite
end.
- - -The present invention eliminates certain-dis-ad-
vantages co!nnected with the production process indicated
above, acco:rding to the known technologyO
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The inven-tion is sui-table especially for the
manufacture of containers from a thermoplas-tic of the
polyester or polyamide type. Exarnp]es of such materials
are polyethylene -terephthala-te, polyhexamethylene-
adipamide~ polycaprolactam 7 polyhexamethylene-sebacamide,
polyethylene 2,6- and 1,5-naphthalate, polytetramethylene
1,2-dihydroxybenzoate and copolymers of ethylene
terephthalate, ethylene isophthalate and similar
polymers. The description of the inv2ntion below
relates mainly to polyethylene terephthalate~ called
PET in the further text1 but -the invention is not
restricted only to the use of either this material or
~ne of the other materials already mentioned; instead,
it is also applicable to many other thermoplastics.
For a be-tter understanding of the existing
problem and of the invention, several characteristic
properties of the polyester polyethylene terephthalate
are described below. From the literature, for example
Properties of Polymers, by D.~. van Krevelen, ~lsevier
Scienti~ic Publishing Company, 19765 it is known that the
properties of the material change when amorphous poly-
ethylene terephthalate is oriented. Some of these
changes are shown in the dîagrams, ~igures 14.3 and 14.4
on pages 317 and 319 in the book "Properties of Polymers".
The symbols used in the discussion below correspond to
the symbols in the said book.
PET, like many other thermoplas-tics, can ~e
oriented ~by stretching the material. Normally this
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stretching takes place at a temperature above the glass
~ransition temperature Tg of -the material~ The
strength properties of the material are improved by
orienting. The literature shows that, in the case of
-~le thermoplastic PET~ an increase in the stretching
ratio ~9 that is to say the quotient of the length of
the stretshed material and -the length of the unstretched
material? also leads to an increase in the improvement
o~ the material properties. When the stretching ratio
J~ is increased from about 2 to a little ~ore than 3~
particularly large changes in the material properties
are obtained. The strength in the direction of orien-
tation is here markedly improved, whilst at the same time
the density ~ and likewlse the crys~tallinity Xc rises and
the glass transition temperature Tg is raised. It can
be seen ~rom the diagram on page 317 that, after stretch-
inglwith~ assuming the value of 3.1, the material with-
stands a force per unit area, which corresponds to ~ - 10
coupled ~ith a very small elongation, whilst the elonga-
tion atJ~_ 2.8 is substantially larger. In the
further text, the term "step" is sometimes used to
designate orlenting ~hich is obtained by
stretching, or a reduction in thickness by about 3 times~
and which leads to the marked improvements o~ the material
properties, indicated above.
The diagrams quoted above show changes which are
obtained on mono-axial orientation o~ the material.
In biaxial orientation, similar effects are obtained in
both directions of orien-tation. Orientation is
carried out as a rule by successive stretchings.
Improved material properties, corresponding to
those which are obtained by the "stepl' defined above, are
also obtained if an amorphous material is st~etched until
i~ flows and, before flo~ing, the material is at a tem
perature which is below the glass transition -tempera ~re
Tg~ In a rod being drawn~ a reduction of the diameter
o~ about ~ times results in the flow zone . On
drawing, the flow zone is continuously displaced into
-the amorphous material/ whilst at the same time the
material, which has already undergone the state of
flowing, absorbs the tensile forces of the test rod
w;thout an additional permanent stretching.
For bottles, defined external diameters of the
mouth with the associated thread are standardised and9 in
the technology known at present when using the moulding
process described as an introduction, this determines the
greatest diameter which is permissible in the blow-
moulded container body~ The reasons for this are
explained in more detail in the following text. ' In
order to obtain an arnorphous starting material for the
pieces o~ tube, which are to be shaped into pre mouldings,
the material must be cooled rapidly to below the glass
transition temperature Tg af-ter extruding - in the case
of extruded tubes from which the pieces of tube are
severed. In'the case of excessive wall thickness, the
materia'l does not possess adequate heat conductivity to
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enable the central sec-tions of -the wall to be cooled as
rapidly as required, so that the material located in the
centre becomes crystalline and opaque. For this
reason, viewed theoretically, the largest possible wall
thickness of the extruded tubes is less than about 9 mm.
In practice, however, wall thicknesses of less than 4 mm
are used as a rule. In fact, in blow-moulding of a
pre-moulding having wall material of excessive thickress9
problems arise due to the cooling of the material during
the actual blow-moulding step and before the material
reaches the wall of the mould. The blow-moulded con-
tainer is no longer clear as glass and, instead, contains
opaque ~hite sections. In blow-moulding, in order to
obtain containers having the requisite resistance against -
stresses and penetratlon of the container wall, the wall
thickness of the finished container must not fall below a
defined value. Moreover, a reduction of the~external
diameter of the tube during the shaping of the mouth part
of the pre-moulding is not possible in accordance with -
known technology. The result is that the desired
mouth diameter of the blow-moulded container is decisive
for the diameter of the pre-moulding and thus for the
maximum diameter of the blow-moulded container body.
If bottles of large capacity are required, these bottles
are extended, according to known technology, in the axial
direction after they have reached the maximum possible
diameter.--- In additiQn to the disadvantage of a certain
instability, the extension represents an unsatisfactory
utilisation of the quantity of material in he container
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body since the requisite quantity of ma-terial per unit
volume of storage capacity is greater than would be
necessary if both -the diameter and the length of the
container body were adapted -to -the actual volume required.
Moreover, the unnecessarily large surface of the con-
tainer leads to a corresponding increase in the overall
penetration of carbon dioxide during the storage of
beverages con-taining carbonic acid.
To utilise the ma-terial properties of -the material
in the best way7 it is desirable tha-t the diame-ter of
those parts of the pre-moulding which, after the blow-
moulding step, represent the ac-tual container body, is
given a value which has the result that the material in
the blow-moulded container body assumes the desired
orientation. In containers of PET it is desirable
that the material, in conjunction with blow-moulding5 is
biaxially stretched in such a way that the product o~ the
stretchings is about 9.
The above shows that, according to kn~wn tech-
nology, the quantity of material in the mouth part is not
deter~ined by the calculated stresses but by the maximum --
diameter of the container body. As a rule, this leads
to a considerable excess of material in the mouth part.
~ or example, in a PET bottle of 1 litre capacity,
the mouth part can, according to known -technology, contain
up to 25-3()% of the -total quantity of ma-terial. Dis-
regarding the~ unpleasant appearance of the oversizing of
-the mouth part, this fact also results in a waste of
ma-terial, which is of importance in the mass production
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o~ articles.
In the technology applied at present, the mouth
part and adjacent neck parts consist of unoriented
material, that is to say amorphous material. This
means that the material in the mouth part including
the adjacent neck parts has properties which differ
from those of the container body. In ~ontainers of,
for example9 PET, the material in the mouth part has a
glass transition temperature Tg of 71~C, whilst the
glass transition temperature of the material in the
container body is about 81C~ It follows from this
that the material in the mouth part softens at a lower
temperature than the material in the container body~
It is already known, by cold-forming of the mouth
part of the blank, to displace material downwards from
the mouth part into the sections of the blank, which
later represent the wall sections of the container body~
In this way, a certain matching of the quantity of
material in the mouth part to the future stresses is
achieved but, between the actual container body and the
mouth part, neck sections are formed in which the ma-
terial is stretched by a factor of less than 3. These
neck sections in the moulded container thus consist of
inadequately oriented material, whilst at the same time
the wall thickness is undesirably large. This method
is also known from Canadian Application ~o. 322,499,
filed February 28, 1979, inventor Kjell M. Jakobsen.
British Patent Specification 1,536,194 published
December 20, 1978 to Carnaud Total Interplastic has dis-
closed a method wherein a tubular blank9which is closed
at one end and which is provided at the other end with
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beading for flxing the blank in a downstream blowing
element, is injection-moulded and wherein the tubular
blank is blow-moulded after a certain reshaping to give
a container. Material in the tubular part of the
blank is expanded in the radial direction at a temper-
ature abo~e the ylass transition temperature Tg in or-
der thus to form the mouth part of the container. A
container formed in the manner described possesses a
mouth part and a neck section in which the material has
been exposed to only very slight stretching and hence
orienting, so that the disadvantages, already indica-
ted~ with respect to the mouth part of the known con-
tainers are also present in this container.
The invention described in British Patent Speci-
fication 1,536,194 also has the disadvantage that only
a part of the material content of the injection moulded
tubular blank is utilised when reshaping the blank to
give the finished container. It is obvious that the
losses of material, which occur in this process, rep-
resent an economic disadvantage in the mass production
of articles~
From Federal German Offenlegungsschrift DOS
2,540,930 published April 8 9 1976, a process is known
wherein a tubular blank of PET is reshaped to give a
; container and wherein the container wall consists of a
material which is stretched by a factor of, for example,
more than 1.5. ~he bottom part of the container con-
sists of an amorphous unoriented materi~l, whilst the
neck sections of the container consist of material which
has been oriented only to a slight extent. As a
result of heatin~ and crystallisation,
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caused thereby 9 the streng-th of -the material is impr3ved
in the unoriented ~ones which at the same time become
opaque. Furthermore~ a combination of the methods
indicated above results in an undesired oversizing of the
neck sectîons of the containers, whilst the latter at the
same time have poorer propertles than the material in -the
actual container body.
- The invention provides a blank which makes it
possible that, in a container formed from the blank, both
the mouth part and the neck sections and also the container
body consis-t of a material which is adapted -to the
occurring stresses and in which the material in the said
parts is oriented to a satisfactory extent in such a way
tha-t the material is stre-tched, at least in the axial
direction, by a factor of more than 3.
This results in the advantage of a raised glass
transition temperature Tg in all the said par1s of the
container. This means that all the sai~ parts will have
the same heat resistance, and this is a great advantage
compared with containers which are formed according to
the known technology and which, at least as far as con-
tainers with mainly clear and transparent materials are
concerned, have neck sections and mouth parts which-are
more sensitive to heat stresses than the actual container
body.
Moreover, the invention enables a container of
sm~l~rmouth diameter to be manufactured, the length and
diameter of the container body being matched to the
storage capacity of the container in such a way that the
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smallest possible quantity of material per unit volume of
storage space results.
In addition, the invention enables a cont.ainer of
any desired shape of the n~ck part to be formed from the
blank, the container material in the mouth part and in the
neck part also being oriented and having a crystallinity of
more than l~/ol this was achieved by stretching the material
to the requisite extent, for example in the case of con-
tai.ners of PET by stretching in the axial direction by a
Eactor of more than 3. According to known technology it was
hitherto not possible to obtain such a degree of orienting,
unless the mouth part and neck sections of the containers
wexe to consist of mainly unoriented material, in which case
the neck sections merge in the shortest possible distance
with oriented sections of the container body, where the wall
thickness has been reduced by a factor of at least 3. This
shaping represented an attem~t to reduce the size o~ that
zone in the neck part, which has mainly amorphous material
and low orientation and hence a low glass transition
temperature Tg.
In accordance with one aspect of the invention,
there is provided a tubular pre-moulding of a thermoplastic
material, the pre moulding having a mouth part with adjacent
neck sections at one end, a closure at the other end and a
tubular section between the two ends, and the closed end
and the tubular section of the pre-moulding consisting
mainly of amorphous unoriented material having a
crystallinity of less than 5%. The tubular pre-moulding of
the invention i.s characterized in that the rnouth part with
adjacent neck sections of the pre-moulding are oriented
mainly in the axial direction of the pre-moulding by
reducing the wall thickness by a factor corr@sponding to
the reduction of th.ickness obtained in a sheet of the
material monoaxially stretched into yielding, the crystal-
linity of the material in the mouth part and in the
adjacent neck sections being at most 5~/0~
According to a -further aspect of the invention,
there is provided in a tubular pre-moulding of a thermo-
plastic of polyester or polyamide type, the pre-moulding
having substantially uniform initial thickness and
comprising a mouth part with adjacent neck sections at
one end, a closure at the other end and a tubular section
between the two ends, the closed end and the tubular section
of the pre-moulding consisting mainly of amorphous unoriented
material having a crystallinity of less than 5%, the impro~e-
ment wherein the mouth part o-f the pre-moulding, with
adjacent neck sections, consists of material which is
oriented substantially by a reduction in the thickness of
the material while the remainder of the pre-moulding retains
its original thickness and, at least in the mouth part, the
material has a lower degree of orientation in the circum-
ferential direction of the pre-moulding as compared to the
axial direction. The crystallinity of the material in the
mouth part ;;s at most 50/0, the orientation of the mouth
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part and ad~acent neck sections of the pre-moulding by the
thickness reduction providing an increased glass transition
temperature Tg in the mouth part and neck sections which is
suhstantially equal to the glass transition temperature of
the tubular section when the amorphous material of the
tubular section is oriented by a subsequent blowing of the
pre~moulding to a container.
According to the invention, the tube of thermo-
plastic material is clamped in between two mutually separate
clamping devices. ~le material in the zone between the
two cla~ping devices is stretched in the axial direction
of the ~ube by shifting the clamping devices in the
direction away -from one another. When PET is used,
stretching by a factor of at least 3 takes place.
According to one embodiment of the invention, the
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material in -the tube is stretched, while -the material is
at a temperature above the glass transition tempera-ture
Tg, whereas in another embodimen-t -the material is stretched
in the cold state, which means that -the material is at a
temperature below the glass transition temperature Tg at
the beginning of the stretching step, On stretching
"in the cold state", the materia], is drawn until flow sets
in.
After stretching, at least the central sec-tions
of the drawn material are blow-moulded at a tempera-ture
above the glass transition temperature Tg against a mould,
in order to form, ~or example, threads and, in some cases
which may occur, parts of the adjacent neck sections,
while two future mouth parts are in adjacent positions.
Subsequently, the tube is severed at the transition
bet~een the two future mouth par-ts. Each of the two
severed blank parts -thus produced form a tubular pre-
moulding, after closing at one end and, if appropriate,
reworking at the other end in order to obtain the requi'red
closure surfaces.
In optional embodiments of the invention, the
material is heated before the axial stretching to a tem-
pera-ture above the glass transition temperature Tg 7 or
the stretching step is preceded by a blow-moulding step
in which the heated material is subjected to a certain
expansion in order to increase -the diameter of the zone.
; In another embodiment of the invention, the mouth
parts o~ the pre-mouldings are shaped by simultaneous
axial stretching, and blow-moulding for the purpose of a
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radial expansion o~ the hea-ted ma-teri.al.
In cer-tain application examples, the heated
ma-terial zone has a temperature profile such that one or
several annular zones are at a temperature which exceeds
the temperature of the adjacent material by 3-20C, pre-
ferably 10-15C. The actual drawing or stretching
step starts in the material zones of higher temperature.
In an application of the invention, wherein the
material in the tube is,at the start of axial stre-tching
of the malerial9at a tempera-ture which is less than the
glass transition temperature T~, the drawing or stretching
step is initiated, according to an optional embodiment of
the invention, with the aid of pressure forces. This
is achieved, for example, by means of a ring which sur-,
rolmds -the tube, the inner surface of thering being brought
into contact with the outer surface of the tube by reducing
the internal diameter of the ring.
On axial stretching of the material, the external
diameter of the tube is reduced. As a resul-t of the
invention, it is thus possible to produce a pre-moulding 7
the mouth part of which has an external diameter which is
less than the ~xternal diameter of the tube.
Equipment for carrying out the process comprises
a number of stretching and blow-moulding devices, which
are each provided with two clamping devices which are
loca-ted at a certain spacing from one another. The
clamping devices are provided for clamping a tube in, and
the two sets of clamping devices are arranged in suc'h a
way that they can be shifted towards one another or a~ay
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from one another. The con-tact surfaces of the
cla~ping devices with the tube are cooled. Appro-
priate devices are provided for heating the material in
the -tube between the said sets ofclamping devices, and
also the blow-moulds against which the heated.material is
blown. Moreover 9 the equipment comprises elements
for closing the two ends of the tube before b]ow-moulding
and also elements for applying an elevated pressure to
the closed cavity formed in this way. In certaln
illustrative embodiments, a cylindrical rod is also
fit-ted axially in the tube. Finally, an element for
severing the tube into -two preferably equal parts is
present~
In an embodiment of the invention, the clamping
devices are arranged in such a way that the tube can
rotate about its own axis. In -this way, hea-ting of
the material in the zone between the two sets of clamping
devices and also the se~ering of the tube into two eq~al
parts are facilitated,
In forming a blank, the tube is fixed between the
two clamping devices, after which the la-tter are shifted
in the direction away from one another, ir. certain .illus-
trative embodiments after the material between -the two
sets of clamping devices has first been heated to the
desired temperature pro~ile and, in certain application
case,s, with simultaneous radial expansion of the material
in the tube or after a first radial expansion o~ the
material in the tube has taken place. The length o~
displacement relative to the length of the part of the
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tube, the ma-terial of which is stretched, is selected in
the case of PET ln such a way that the material reaches
a crystallinity of at least 10% on axial orientationO
In some cases which may occur, the cylindrical rod is
introduced into the -tube before the material is stretched.
In certain application examples, the rod is heated. To
effect radial expansion, the two ends of the tube are
closed, the material between the two se-ts of clamping
devices is heated in some cases which may occur, and the
closed space in the tube is subjec-ted to pressure, the
heated material expanding in such a way -that it makes
contact with the mould surfaces, for example for the pur~
pose of moulding the mouth thread and adjacent neck
sections. When the material has cooled to a sufficient
extent to reach dimensional stability, the tube is severed
into two parts in the severing element. Each of the
two parts is closed at one end by reshaping and, if appro-
priate, reworked at the other end, that is to say the
mouth end, in order to produce t~e requisite closing sur-
faces. Thus, the pre-moulding is completed.
According to the process described above, each
drawing step with subsequent severing results in ~o blank
parts which, after a certain reworking and reshaping, each
form a blank. In this manner, no losses of material
arise in the production of pre-mouldings. Of course,
the stretched material formed during the drawing step can
be adaptecL in such a way that it is used for forming
exclusively one single future mouth part with adjacent
future neck sections. Due to the severing of parts of
33~
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the piece of tube 5 which can not be used for further
production of -the pre-moulding, however, this leads to
undesired losses of material, so that this embodiment of
the invention is only used in special cases~ for example
in the production of pre~mouldlngs which are intended for
containers having long mouth sections and neck sections.
Figure 1 shows, in perspective view, a stretching and
blow-moulding device having two sets of clamping
devices, and with the two sets of clamping
devices of the stretching device being in the
position for receiving a piece of tube,
Figure 2 shows, in perspective view, a s-tretching and
blow-moulding device, with the clamping devices
in the position for fixing a piece of tube,
Figure 3 shows a sectional view of the stretching and
. blow-moulding device during the heating of a
central part of a piece of tube,
Figure 4 shows a sectional view of a stretching and
blow-moulding device with the piece of tube
; fixed and drawn,
Figure 5 shows a sectional view of a stretching and
blow moulding device with the internal volume
of the piece of tube subjected to pressure in
order to form the mouth sections and adjacent
neck ecti ns
s o
Figure 6 shows a device for severing the piece of tube
into two separate blank parts,
Figure 7 shows, in diagrammatic view, a device for the
stepwise production of blank parts for pre-
~.
mouldlng s .
Figure 8 shows a sectional view of a stretching andblow-moulding device having a device for heating
an annular section in the piece of tube,
Figure 9 shows a sectional view of a stretching and
blow-moulding device during the cold-drawing
step of -the piece of tube,
Figure 10 shows a sectional vie~J of a stretching and
blow-moulding device af-ter the cold-drawing
step of the piece of tube has been carried out,
Figure 11 shows a sectional view of a stretching and
blow~moulding device with the length of the
: axially drawn zone increased,
Figure 12 shows a partial section through a stretching
and blow-mould.ing device according to Figure 11,
in which the internal volume of the piece of
tube has been subjected to pressure, and in
particular the forming of the neck sections
.- adjacen-t to the mouth part,
Figure 13 shows a completed tubular pre~moulding which
has been shaped from a blank part according to
Figure 5, and
Figure 14 shows a completed tubular pre-moulding whi.ch
has been shaped from a blank part according to
Figure 12.
Figures 1 and 2 show a frame on which two separate
sets of clamping devices 20 a-b and 21 a-b are located.
In principle, the two sets of clamping devices consist of
an upper clamping part 20a, 21a and a lower clamping par-t
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20b, 21bo In both sets o~ clamping ~evices, the upper
part can be shif-ted between an open position and a closed
position. In the closed position, the particular set
of clamping devices fixes one end of a tube 50 in each
case. The -two sets of cla~ping devices can be shifted
from their starting positions (Figure 1) towards one
another up to a smallest distance (Figure 2) which matches
the length of -the tube 50, and from there they can be
shifted back again into the particular starting position.
In the starting position, -the particular upper part assumes
the open position and remains in the latter until the two
sets of clamping devices have been shifted towards one
another up to the said smallest distance. Xn this
position, the particular upper parts assume the closed
position and thus cover a relatively large part of the
-tube 50, the latter being surrounded a-t the same time and
being fixed by the particular set of clamping devices.
While the upper parts are still in the closed position,
the two sets of clamping devices are subsequently shifted
back to the starting position. The shift of the upper
parts 20a, 21a of the two sets of clamping devices is
effected by means of drive mechanisms 25, 26, and a drive
mechanism Z4 is provided for shifting the two sets of
clamping devices towards one another. The two upper
par-ts slide in the grooves 22, 23 provided in the lower
parts, whilst the lower parts slide in grooves 13 a-b
provided in the frame 11.
A gripper 28 is provided for inserting the tube
50 into the clamping devices or removing it from the
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g
clamping devices. When the two se-ts of clamping
devices are at their smalles-t distance from one another,
a heating ele~ent consisting of the two heating jaws
29 a-b is brought into a position in which it can heat
the central sections of the tube 50. The motion of the
heating jaws is effected by means of a drive mechanism 33
-with a push-and-pull bar. A lead 31 for heating the,
heating jaws, for example by means of electric powera is
shown in the figures.
Adjoining one of the two sets of clamping devices,
a cylindrical forming and blo~ring mandrel 27 is provided.
This mandrel is moved by means of a drive mechanism 39
from and to a position in which the cylindrical part of
the mandrel protrudes a little into the opening of the
other set of clamping devices. The mandrel protrudes
into the said opening even when the two sets of clamping
devices are in their starting positions.
The external diameter of the mandrel and the
internal diameter of the tube 50 are matched in such a
way that the mandrel can be introduced into the tube.
Moreover, the mandrel is provided with a row o orifices
40 which lead to a cavity in the interior of the mandrel7
which cavity is connected to a line 32 for a pressure
medium.
A pressure medium is fed via the lines 30a, b,
c, e (the pressure line 30d is not shown in the ~igure)
to the individual drive mechanisms 24, 25, 26, 33 and 39.
In Figure 3, the two sets of clamping devices
20 a-b, 21 a-b are shown in the position for the smallest
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dis-tance between the sets. In addition, the figure
shows the said cavity 42 in the mandrel 27, a gasket 41
between one end of the -tube 50 and the set of clamping
devices 21 a-b and a gasket 34 between the other end of
the tube 50 and the set of clamping devices 20 a-b.
A gasket 35 between the mandrel 27 and the set of clamping
devices 20 a b can also be seen. An outlet valve 36
is located in the lower clarnping device 21b. In this
way, the closed space which can be sub~ected to pressure
through the orifices 40 is formed in the mandrel Z7.
Figure 4 shows -the two sets of clamping devices
shifted back into their starting positions9 while the
surrounded parts of -the tube 50 are still held firmly as
before. ~he Figure shows that the mandrel 27 continues to
projectinto the set ofclamping devices 21a-~ A central zone
51 of-the tube 50has beenstretched in the axial direction and
has a smaller wall thickne~s than the remainder of the tube.
In Figure 5, the central zone 51 has been blow~
moulded against the mould 57 a-b. The shaping surface
of the moul~ corresponds to the form of two mouth parts
52 a-b, facing one another, for containers which are tobe
formed ~rom the blanksand arein the process of manufacture.
Figure 6 shows the mandrel 27 in its starting
position. A severing disc 58 is located in the position
~or severing the tube 50, tha-t is to say at the transition
between the two moulded mouth parts 52 a-b.
Figure 7 shows a turntable 7 which rotates about
a bearing 12. Next to the turntable, a number o~
positions A-U is indicated. One frame 11 with the
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,
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associated set of clamping devices, drive mechanisms~
tubular mandrel, heating device and the like according to
Figures 1-2 is located on the turntable for each position.
In the positions, the particular working step is indicated
diagrammatically by the position of mandrel, heating JawS 9
sets of clamping devices and the like.
Figure 8 shows an embodiment of the invention,
which is adapted preferably for so-called cold-drawing of
the tube. An annular heating element 38 is located
b'etween the -two sets o~ clamping devices. By means of
this heating element, the central sections o~ the tube 50
are heated to an elevated ternperature over an annular
zone.
Figures9-10 rela-te to the cold-drawing of the
tube 50. In Figure 9, -the formation of a centrally
located drawn zone 53 has started, whilst in Figure 10
the entire centrally located dra~n zone 54 has been
formed.
Figures 11 and 12 relate to a variant of the
invention wherein the centrally located zone 51a of the
tube 50 is longer than in the previously described
embodiments of the invention. The figures show only
one of the two sets of clamping devices. Figure 11
shows the position after drawing of the tube has been
completed, whilst Figure 12 shows the central zone
51a (Fi~lre 11) after it has been blow-moulded against
an outer mould 59. The moulding surface of the outer
mould corresponds tothe shape of ~ro mutually facing
mouth parts (only one, 52a, is shown in the figure) and
, . .
parts of the adjacent luture neck section 60a of the
containers which are to be formed from the bianks and
are in the process o~ production. A zone 56, having
the largest diameter in the moulded future neck sections,
preferably has a diameter which is a-t least three times
the original diameter o~ the tube.
Figures 13 and 14 show comp~etPd tubular pre-
mouldings, the pre-moulding according to Figure 13 ha~7ing
been formed from a blank part shown in Figure 5 and a pre-
moulding according to Figure 14 having been formed from a
blank part shown in Figure 12. At one end 5 the pre-
mouldings have a mouth part 62a, b with adjacent neck
sections 63a, b. At the other end the pre-mouldings
have a closure 61a, b. A tubular section 64a, b can
be seen between the closure 6]a, b and the neck sections
63a, b.
In the production of a pre~moulding according to
the invention, a tube 50 is brought into the position
shown in Figure 1 with the aid of the gripper 28. The
t~ro sets of clamping devices 20 and 21 are shifted
towards one another with the aid of the drive meohanism
24 un-til the two ends o~ the tube are in ~ontact with
the gaskets 34 and 41. The upper clamping devices
are brough-t into their closed position with the aid of
the drive mechanisms 25, 26, the tube 50 being firmly held
at both its ends and at the same time being enclosed over
a relatively large part. This situation is shown in
Figure 2. As an alternative9 the mandrel 27 was
already in this phase brought beforehand into the position
~13~
_ ~2 -
which is shown in Figure 3. The heating jaws 29 are
brough-t into the heating position and remain in -this
position for such a perio~ as is necessary for heating
the materîal in the central sections of the tube to a
tempera-ture below the glass transi-tion temperature Tg.
The drîve element 24 now shifts the two sets of clamping
devices in the direction away from one another, the
central sec-tions of the -tube being stretched, with
simultaneous thinning of the tube wall, in such a way
that the tube is given the appearance shown in Figure 4.
Preferably9 stretching amounts to at least a factor of 3
and the reduction in thickness -thus also amounts to a
factor of 3. During the entire drawing step 9 the
mandrel 27 is located in the interior of the tubeg within
the stretched zone, and th~s prevents the stretched zone
~rom assuming an undesirably small diameter.
The closed space in the interior of the tube is
subjected to pressure, the material being expanded into
the zone concerned until it makes contact with the outer
mould 57. In this step, the future mouth parts and
parts of the adjacent neck sections in two blank parts
connected to one another are shaped to give pre-mouldings.
On con-tact wi-th the surfaces of the outer mould, the
material in the tube is cooled so that it becomes dimen-
sionally stable. With simultaneous retraction of the
mandrel 27 into its starting position, the outer mould is
opened and a severing disc 28 divides the tube at the
transition between the two future mouth parts. This
produces two separate blank parts ~hich are closed at one
end by reshaping and are provided with the requisi^te
closing sur~aces at the other end by reworking. In
this way, a tubular pre-moulding as shown in Figure 13
is sb-tained.
The design of the equipment for closing one end,
and likewise for the reworking, which may be necessary,
of the mouth part, is not sho~m in the figures, but this
can be in accordance with any technology already known
and used. Normally, closing is effected by heating
the material at one end of the tube up to a temperature
above the glass transition temperature Tg~ after whic'n the
end is forced in the axial direction against a substan- -
tially spherical shell which compresses the soft material
and closes the end. Subsequently, -the gripper 28 takes
the two blan~ parts formed out of the production equipment
after the two sets of clamping devices have released the
pre-mouldings~ Subsequently, the course of the pro-
cess described above is repeated~
According to a preferred embodiment of the inven-
tion, the production step described above is carried out
with the aid of the equipment shown in Figure 7. In
position A, th~ tube is fed to the ~lo sets of clamping
devices, in position B the two sets of clamping devices
are shifted in the direction towards one another, whilst
simultaneously the mandrel is introduced into the tube,
and in position C~E the central zone of the tube is heated 7
whilst in position F the heating process is interrupted.
In positions G-H t the central sections of the tube are
stretched, in position I the outer mo~lds move into the
,
,'I,S
_ 24 -
moulding position, in position J -the in-terior of -the
tube is subjected -to pressure and is f`ormed to give the
future mouth parts with the adjacent neck sections.
In position K, the outer moulds open, whilst in position
L the mandrel is retracted into its starting posi-tionO
Position M is a cooling position for stabi.l.ising the
form of the tube or, alternatively, is a reserve
position, whilst in position N the tube is severed into
two blank parts. In posi.tion 0, the two future mouth
parts are heated for reworking, if appropriate, and they
obtain their final form in position P. In position R,
the devices for reworking the mouth parts have assumed
again their starting position, and subsequently, in
position S, the blank parts have been shifted in the
direction to~ards one another in order to enable the
gripper to engage in position T and to enable the clamping
devices to open in position U, so that the mouldings
formed can be removed from the production equipment
according to Fi~ure 7. Advantageously, the gripper
device here transfers the blanks to devices for closing
one of their ends. Such devices can either be pro-
~ided independently of the equipment described in this
paragraph, or they can form part of this equipment.
In the latter case, this equipment mus-t be pro-
vided with a further number of posltions.
During cold-drawing of the cen-tral zone of the
tube, the m~terial is heated be~ore the drawing step with
the aid o~ an annular heating element 38 (Figure 8) over
an annular zone within the central zone. This hea-ting
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element is preferably designed to heat the central zone
as far as one of the sets o~ clamping devices. To
con-trol the direction of displacement during the flow
which sets in on drawing, the material is normally cooled
immediately next to -the heated annulus in that direction
in which it is intended tha-t the ~low step should not
propagate. In the embodiments in which the en-tire
material o~ the tube is to be drawn be~een the two sets
of jaws, the required cooling is obtained by the cooled
jaws. In other embodiments~ annular cooling devices
are used which~ in principle, are arranged in a manner
corresponding to the arrangement of the heating device 38
On warm-drawing of the central zone of the tube,
one or several annular heating elements are used in cer~
tain application examples in order to produce the desired
temperature profile in the central zone of the tube before
the latter is drawn. The annular heating elements here
frequently consist o~ zones o~ elevated te~perature in the
heating jaws 29.
On cold-drawing o~ the material in the central
zone of the tube, flow of the material sets in first in
the annular zone which has been heated by the annular
heating element 38. On further stretching of the cen-
tral zone of the -tube, the ~low zone of the material is
displaced in the direction of the other set of clamping
devices, compare Figure 9, so that 9 after completion of
the stretching step, a central drawn zone has formed~ the
appearance o~ which is shown in Figure 10. On cold-
drawing, the~ central zone has no tendency towards a
~ - "
reduction of -the internal diameter of the -tube 7 as long
as stretchlng is limited to about a factor of ~. In
this embodiment of the invention, it is thus not necessary
to cause the mandrel 27 to assume i-ts position in the tube
before the actual stretching step. Figures 11-12 show
an embodiment of the invention in which the stretched
central zone 51a has a greater length than in the embodi-
ments o~ the invention so far described. When the
in-terior of the tube is subjected to pressure, parts o~
adjacent neck sections are also formed, in addition to the
two future mouth parts 9 these neck sections being given a
greater diameter than that of the actual mouth part.
At this stage, it is preferable to allow the future neck
section to be shaped to such an extent that the greatest
rise in diameter is at least 3-fold. This has the
advantage that a relatively dimensionally stable neck
section is formed which, during the subsequent heating in
conjunction with the shaping of the remaining part of the
container, is affected only to a small extent. m e
appearance of a pre-moulding, which was formed from a
blank part par-tially shown in Figure 12, can be seen in
Figure lL~
In the above description, it was explained how
the blank parts are formed by severin~ the drawn and
shaped tube. In a preferred embodiment of the invention,
severing of the blank parts from one another is effected
with the aid of one or several severing discs which
revolve under pressure about the circumferential surface
o~ the tube formed at the.transition between the two
- æf~
future mouth par-ts.
It was assumed in the above descrip~tion that
hea-ting o~`the central material sections of the tube is
effected by heating jaws. To obtain the most uniform
heating of the ma-terial possible, the tube should pre-
ferably rotate relative to the heating element. To
make this pos.sible, the clamplng devices are modified,
if appropriate having cone-type bearings or having heating
jaws which revolve about the tube.
In the case where the central sec-tions of -the
tube are drawn at an initial -temperature which is below
the glass transition temperature Tg, -the material is
heated after the drawing step to a temperature above the
glass transition temperature Tg, af-ter which -the future
mouth part and parts of the adjacent neck sec-tions are
shaped.
In addition to the above descrlption, the inven-
tion is also comprised by the attached patent claimsO
