Note: Descriptions are shown in the official language in which they were submitted.
,2~
-- 1 --
l~hi~ appl.ication is a division of application
Serial No. 35~,909 filed May 28, 1980.
The invention relates to a tubular pre-moulding
of a thermoplastic~ suitable for subsequent shaping to
give containers by a blow-moulding process,- and to a
process and e~uipment for producing the pre~moulding.
a tube9 ~uture mouth parts and parts o~ adjacent nec~
sections are moulded to pre-mouldings, from two blank
parts joined to one another, by an axial stretch process
and a blow-moulding process, the parts in the transition
between the two mouth parts being severed in order.to
form two separate blank parts which,.after closing at
~ one of the ends and subse~uent reworking to produce the
re~uisite closing surfaces at the respectiYe cther ends,
each alone form a tubular pre-mouldi~g.
In a production process used for the manu~acture
o~ contai~ers from a thPrmoplastic~ blanks n~rm~lly
called p~e-mouldings for containers are produced from
severed parts of extruded long tubes of an amorpnous
thermoplasticO At one endi the severed pieces are
shaped in such.a way that they ~orm the future mouth part .
vf the container, whilst they are closed at the opposite
end.
The present invention eliminates certain disad-
vantages connected with the production process indicated
above 3 according to the known technology~
-- 2 -- .
The invention is suitable especially for the
manufacture of containers from a thermoplastic of the
polyester or polyamide type. Examples of such materials
are polyethylene terephthalate 7 polyhexamethylene-
.
adipamide, polycaprolactam, polyhexamethylene--sebacamide,
polyethylene 2,6- and 1,5-naphthalate, polytetramethylene
l,?-dihydroxybenzoate and copolymers of ethylene
~erephthalate, e~hylene isophthalate and similar
po~ymers. The description of the invention below
relates mainly to polyethylene terephthal-ate, called
PET in ~he further text, but the invention ls not
restricted only to the use of either this material or
one of the other materials already mentioned; instead,
it is also applicable to many other thermoplastics.
For a better understandin~ of the existing
problem and of ~he invention, several cha~acteristic
properties of the polyester polyethylene terephthalate
are described below, Fro:m the literature, ~or example
Properties of Polymers, by D.W. van Krevelen, Elsevier
Scientific Publishing Company, 19769 lt is known that ~he
properties of the material change when amorphous poly-
ethylene terephthalate is oriented. Some o~ these
changes are shown in the diagrams, Figures 14.3 and 14.4
on pages 317 and 319 in the book "Properties of Polymersl'~
l~e symbols used in the discussion below correspond to
the symbols in the said book.
PET, like many other thermoplasti.cs 9 can be
oriented by stretc~ing the material. Normally this
stretching takes place at a temperature above the glass
transition temperature Tg of the material. The
s~rength properties of the material are improved by
orienting. The literature shows that, in the case of
the thermoplastic PET, an increase in the stretching
ratio~, that is to say the ~uotient of the length of
~he stretched material and the length of the unstretched
material, also leads to an increase in the improvement
of *he ~aterial properties. When the stretchlng ratio
,~ 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 7 whilst at the same time
the density ~ and likewise the crystallinity Xc rises and
the glass transition temperat~re Tg is raised. It can
be seen fr~m the diagram on p~ge 317 that, after stretch-
in~ ~ith~ assuming the ~alue of ~.1, the material with-
stands a force per unlt area, which corresponds to ~ = 10,
coupled with a very small elongation, whilst the elonga-
tion at.AL- 2.8 is substantially lar~er. In the
urther text~ the term "step" is sometimes used to
designate orienting which is obtained by
stretching, or a reduction in thickness by about 3 times,
and ~hich leads to the marked improvements o~ the material
properties, indica*ed above.
I~e diagrams quoted ab~ve show changes which are
obtained on mono-axial orientation of the material.
In biaxial orientation, similar effects are obtained in
~2~Z64
-- ,4 -- .
both directions of ori;entation. - Orientation is
carried out as a rule by successive stretchi~gs.
~ mproved material properties, corresponding to
those which are obtained by the "step" defined above, are
also obtained if an amorphous material is st~etched until
it flo~s and, before flowing, the material is at a tem-
perature which is below the glass transiti.on temperature
Tg. In a rod being dra.wn, a reduction of the diameter
of aboult ~ times results in the flow zone. On
drawing, the flow zone i.s c~nt]nuously displaced int~
the amorphous material~ whilst at the same time the
material, which has already undergone the state of
flowing, absorbs the tensile ~orces of the test rod
without an additional permanent stretching.
For bottles~ defined external diameters of the
mouth with the associated thread are standardised and, 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
e~plained in more detail in the following text. In
order to obtain an amorphous starting material ~or -the
pieces ~f tube, which are to be shaped into pre-mouldings,
the material must be cooled rapidly to below the glass
transition temperature Tg after extruding - in the case
o~ extruded tubes ~rom which the pieces of tube are
severed In the case of excessive wall thickness, the
mater.ia'l does no~t possess adequate heat conductivity tD
52
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enable the central sections of the wall ~o 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 thickress,
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 white sections. In blow-moulding, in order to
obtain con~ainers 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 o* the tube during the shaping of the mouih part
of the pre-moulding is not-possible in accordance with
known technology. The result is that the desired
mouth diameter o~ the blow-moulded container is decisive
~or the diameter o~ 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.- I-n additiQn to the disadvantage of a certain
instability, the extension represents an unsatisfactory
utilisation of the quantity of material in the container
~ ~ 52~
body since the requisite quantity of mate~ial 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 s-torage of
beverages containing carbonic acid.
. To utilise the material properties of the material
in the best way, it is desirable that the diameter of
those parts of the pre~moulding which, af-ter the blow-
moulding step, represent the actual container body, is
given a value which has the result that the material în
the blow-moulded container body assumes the desired
orientation. In containers of PET it is desirable
:~ that the.material, in oonjunct:ion with blow moulding, 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
determined 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.
For example, in a PET bottle of 1 litre capacity,
the mouth part can, according to known technology, contain
up to 25-30% of the total quantity of material. Dis-
regarding the lmpleasant appearance of the oversizing o~
the mouth part; this fact also results in a waste o~
material, which is of importance in the mass production
~25~2
7 --
o~ articles.
In the technology applied at present, the mouth
part and ad~acent neck partsconsist of unoriented material,
t~at is to say amorphous material. This means that the
material in the mouth part including the adjacen~ neck
parts has properties which differ from those of the c~n-
tainer body. In containers of, for example, PET, *he
material in the mouth part has a glass transition tem-
perature Tg of 71C, whilst the glass transition tempera-
ture 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-~orming of the mouth
part of the blank, t~ displace material downwards from the
mouth par~ in*o the sections of the blan~, which laier
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 material is stre~ched
by a factor of less than 30 These neck sections in the
moulded container thus consist of inadequately oriented
material, whilst a-t the same time the wall thickness is
undesirably large. This metho~ is also ~nown 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
disclosed a method wherein a tubular blanX, which is closed
at one end and which is provided at the other end with
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beading for fixing t,he 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 temperature
above the glass ~ransition temperature Tg in order thus to
fo~m the mouth part of the containerl A container
formed in the manner described possesses a mouth part and
a neck section in which the material has beeM exposed to
only very slight stretching and hence orienting, so that
the disadvantages, already indicated, with respect to the
mouth part of the known containers are also present in
this container..
The invention describecl in-Bri~tish Patent Specifica-
tion 1,536,194 also has the di~advantage that only a part of
the material content of the injection-moulded tubular blank
is utilised when reshapln~ the blank to give the ~inished
container. It is obvious that the losses of materia~ ich
occur in t~i~ proce~s, represent an economic disadvantage in
th~ mass production of articles.
From Federa~ German O~fenlegungsschrift DOS
2,540,930, publishea April 8, 1976, a process i5 known where-
in 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~ample, more than 1.5. The bottom
part of the container consists of an amorphous unoriented
ma-terial, whilst the neck sections o~ the container con-
sist of material which has been oriented only to a s~ight
extent. As a result of heating and crystallisation,
.
caused thereby, the strength l~f the material is improved
in the unoriented zones which at the same time become
opaque. Furthermore, a cornbination of the methods
indicated above results in an undesired oversizing of the
neck sections o~ the containers, whilst the latter at the
same time have poorer properties than the material in the
actual container body.
- The invention provides a blank which makes it
possible that 9 i~ a container ~ormed from the blank, both
the mouth part and the neck sections and also the container
body consist 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
that the material is stretched, at least in the axial
direction, by a factor of more than 3.
This results in the advantage of a raised glass
transition temperatuL~e Tg in all the said parts of the
container. This means -~hat,all thesaid 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~lermout~ diameter to be manufactured, the length and
diameter of the container body being matched to the
storage capacity o~ the co,ntainer in suoh a way that the
~.~05;~6~
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smallest possible quantity of material per unit volume of
storage space results.
In addition~ the invention enables a container of
any desired shape of the neck 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~/o; this was achieved by stretching the material
to the requisite extent, for example in the case of con-
tainers of PET by stretching in the axial direction by a
factor 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
were to consist of mainly unoriented material, in which case
the neck sections merge in the shortest possible distance
with oriented sections of the contalner body, where the wall
thickness has been reduced by a factor of at least 3. This
shaping represented an attempt to reduce the size of 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 tukular 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 arnorphous unoriented material having a
~s~
crystallinity of less than 5%. The tubular pre-moulding of
the invention is characterized in that the mouth pa.rt 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 corresponding to
the reduction of thickness obtained in a sheet of the
rnaterial monoaxially stretched into yielding, the crystal-
.linity of the material in the mouth part and in the
adjacent neck secti.ons being at most 5~/0.
According to a further aspect of-the invention,
there is provided in a tubular pre-moulding o-f 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 closecl end and the tubular section
of the pre-moulding consisting mainly of amorphous unoriented
material having a crystallinity of less than 5%, the improve-
ment wherein the mouth part of 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 dlrection of the pre-moulding as compared to the
axial direction. The crystallinity of the material in the
mouth part is at most 5~/0, the orientation of the mouth
~ ~r~5~
-part and adjacent neck section~ of the pre-moulding by the
thicknes~ reduction providing an increased glass transition
temperature Tg in the mouth part and neck sections which is
substantially equal to the glass transition temperature of
the tubular section when the amorphous material of the
tubular section is oriented by a subsequerlt blowing of the
pre-moulding to a container.
According to the invention, the tube of thermo-
plastic material is cl~nped in between two rnutually separate
clamping devices~ The material in the zone between the
two clamping devices is stretched in the axial direction
; of the tube by shifting the clamping devices in the
direction a~ay from one another. When PET is used,
~tretching by a factor of at least 3 taXes place.
According to one embodiment of the inventionO the
.
.
s~
- 13 -
material in the tube is stretched, while-the material is
at a ~emperature above the glass transition temperature
Tg, whereas in another embodiment the'mater~al is stretched
in the cold state9 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 material is drawn until flow sets
in.
After stretching~ at least the central sections
of the drawn material are blow-mouIded at a temperature
above the glass transition temperature Tg against a mould,
in order to form, for example, thre~ds and, in some cases
which ma~ occur, parts of'the adjacent neck sections,
while two future mouth parts are in adjacent posiiions.
Subsequently, the tube is severed at the transition
between the~two ~uture mouth parts. Each of the two
severed blank parts thus produoed ~orm a tubular pre-
moulding~ after closing at one end and, if appropriate,
reworking at the other end in order to obtain the re~ui'red
closure surfaces.
Tn optional embodiments o~ the invention, the
material is heated before the axi~l stretching to a tem-
perature above the glass transition -temperature Tg, 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 o~ the invention, the mouth
parts of the pre-mouldings are shaped'by simultaneous
axial stretching, and blow-moulding for the purpose of a
\
- ~2f~2~
radial expansion of the heated ma-terial
In certain application examples, the heated
,,
material zone has a temperature profile such that one or
several annular zones are at a tempèrature which exceeds
the temperature of the adjacent material by 3-20C, pre-
ferably 10-15C. The actual drawing or stretchi~g
step starts in the material zones o~ higher temperature.
In an application of the invention, wherein the
material in the tube is,at the start of axial stretching
of the ma~eria~ at a temperature which is less than the
glass transition temperature Tg, the drawing or stretching
step is initiated~ according to an optional embodiment of
the invention, with the aid of press~re forces This
is achievecl, for example, by means o~ a ring which sur-
rounds the tube, the inner surface of therin~ being brough~
in~o contact with the outer sur~ace o~ the tube by reducing
the internal diameter of the ring.
On axial stretching of the material, the external
diame~er o~ the tube is reduced. As a resu7t o~ the
invention, it is thus possible to produce a pre-moulding 9
,
the mouth part o~ which has an external diameter ~rhich is
less than the ~xternal diameter of the tube.
Equipment ~or carrying out the process comprises
a number o~ stretching and blow-moulding devices, which
are each provided with two clamping devices which are
located at a certain spacing from one another. The
clamping devices are provided for clamping a tube in, and
the two sets o~ clamping devices are arranged in such a
way that they can be shifted towards one another or a~ay
-
,. , 1~, .
~2~52~
15 -
from one another. The contact 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, the equipment comprises elements
for closing the t~o ends of the tube before blow-moulding
and also elements for applying an elevated pressure to
the.closed cavity formed in this way. In certain
illustrative emboaiments, a cylindrical rod is also
fitted axially in the tube. Finally, an element for
severing the tube into two preferably equal parts is
present.
In an embodiment o~ the invention, the clamping
devices are arranged in such a way that the tube can
ro-tate about its own axis. In this way, heating o.~ '
the material in the zone between the two sets of clamping
devices and also the severing of the tube in-to two eq~al --
parts are facilitated.
In forming a blank, the tube is fixed between the
~wo clamping devices, after which the latter are shi~ted
in the direction away from one another, in certai~ illus-
trative embodiments after the material between the two
sets vf clamping devices has first been heated to the
desired temperature profile and, in certain application
cases, with simultaneous radial expansion of the material
in the tube or'a~ter a first radial,expansion of the
material in the tube has taken place. The length of
displacement relative to the length o~ the part of the
3 Zf.~l-5
- 16 -
tube, the material D~ which is stretched, is selected in
-the case of PET in such a way that the material reaches
a crystallinity o~ at least 10% on axial orientation.
-- . .
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
e~fect radial expansion, the two ends o~ the tube are-
closed~ the material between the two sets of clamping
. . .
--devices is heated in some cases which may occur, and the
closed space in the tube is subjected to pressure, the
heated material expanding in such a way tha-t it makes
contact with the mould surfaces, for example for the pur-
pose of moulding the mou-th thread and adjacent neck
sections. When the material has cooled to a sufficient
extent to reach dimensional stability, the tube is severed
into ~wo parts in the severin~g element. Each o~ the
two parts is closed at one end by reshaping and, if appro-
priate, reworked at the other end, that is ~o say t~e
mouth end, in order to produce the requisite closing sur-
faces. Thus, the pre-moulding is completed.
According to the process described above, each
drawing step with subsequent severing results in t~o blank
parts which, after a certain reworking and reshaping, each
form a blank. In this manner, no losses of material
arise in the produc-tion of pre-mouldings. Of course~
the stretched material formed during the drawirlg step can
be adapted in such a way that it is used ~or forming
exclusiv~ely one single future mouth part with adjacent
future neck sectior3s. Due to the severing of parts of
~-2re5~6~
17 -
the piece of tube 9 which can not be used for further
production of the pre-moulding, however, this leads to
undesired losses of material,.so that this em~odiment of
the invention is only used in special cases, for example
in the production of pre-mouldings which are.intended for
containers having long mouth sectîons and neck sections.
Figure 1 shows, irl perspective view, a stretching and
blow moulding device having ~wo 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 stretching and
blow-moulding device, with the clamping devices
in the position for fixing a piece o~ tube,
.Figure 3 shows a sectional view of the stretching and
. blow-moulding device during the heating o~ a
central part of a piece of tube,
Figure 4 shows a sectlonal view o~ a stretching and
blow-moulding device with the piece of tube
fixed and drawn,
Figure 5-shows-a sectional view of a stretchin~ and
blow-moulding device with the internal volume
of the piece o~ tube subjected to pressure in
order ~o for.m the mouth sections and adjacent
neck sections,
Figure 6 shows a device for severing the piece of tube
-into two separate blank par-ts,
Figure 7 shows, in diagrammatic ~îew, a device for the
ste~ise production o~ blank parts for pre-
- mouldings.
Figure 8 shows a section~l view of a stretching and
blow-m~ulding device having a device for heating
an annular section in the piece o~ tube,
Figure 9 s~ows a sèctional view of a stretching and
blow-moulding device during the cold-arawing
step of the piece of tube,
Figure 10 shows a sectional view o~ a stretching and
blow-moulding device after the cold-drawing
step o~ the piece of tube has been carried out,
Figure 11 shows a sectional view o~ 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-moulding devi.ce according t~ Figure 119
. in which the internal volume o~ the piece-of
. tube has bee~ subjected to pressure, and in
particular the forming of the neck sections
adjacent to the mouth part,
Fi,~ure 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 which
has been shaped from a blank part according to
Figure 12.
Figures 1 and 2 show a frame on which ~wo separate
sets o.~ clamping devices 20 a-b and 21 a-b are located.
In principle, the two sets of clamping devices consist ~f
an upper clamping part 20a, 21a and a lower clamping part
:,, .
S~:6~
-- 19 _
20b, 21b. In both sets o~ clamping devices, the upper
part can be shifted between a~ open position and a closed
positio~. In the closed position; the particular set
of clamping devices fixes one end of a tube 50 in each
case~ The two sets of clamping 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
shi~ted 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 distanoe7 In 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 at the same time and
being fixed by the particular set of-clampin~ devices.
While the upper parts are still in the closed position,
the two sets o~ clamping devices are subsequently shiftèd
back to t~e starting position. The shift of the upper
parts 20a~ 21a of the ~wo sets of clamping devices is
e~ected by means o~ drive mechanisms 25, 26, and a drive
mechanism 24 is provided for shi~ting the two se-ts of
clc~mping devices towards one another. The two upper
parts slide in the grooves 22, 23 provided in the lower
parts, whilst the lower parts slide in grooves 13 a-b
provided in the frc~me 11.
A gripper 28 is provided for inserting the tube
50 into the clamping devices or removing i-t from the
2~
.
2~
clamping device When the two sets-o~ clamping
devices are at their smallest distance ~rom one anoth-r,
a heating element consisting o~ the ~wo heating jaws -
29 a-b is brought into a position in which it can heat
the central sections of the tube 50. The motion o~ the
heating jaws i5 ef~ected 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 power, i~
shown in the figures.
Adjoining one o~ the tWQ sets of clamping devices~
a cylindrical forming and blowing 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 mar~drel 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 ma~ched in such a
way that the mandrel can be introduced into the tube.
Moreover, the mandrel is provided with a row of orifices
40 whlch lead to a cavity in the interior of the mandrel,
which cavity is connected to a line 32 ~or a pressure
medium.
A pressure medium is fed via the lines 30a, b7
c, e (the pressure line 30d is not shown in the figure~
to the individual drive mechanisms 24 9 25, 26, 33 and 39.
In Figure 3, the two sets of clamping devices-
20 a-b? ~1 a-b are shown in the position for the smallest
.
.
~ ~2~3~;~6~
_ 21 -
distance between the sets. In addition, the figure
shows the said cavity 42 in the mandrel 27, a gasket 41-
between one end o~ the tube-50 and the set of clamping
devices ~1 a-b and a gasket 34 between the other end of
.
the tube 50 and the set of clamping devices 20 a-b.
A gaske-t 35 between the mandrel 27 and the set of clamping
devices 20 a-b can also be seen. hn outlet valve 36
is located in the lower clamping device 21b. In this
I way, the closed space-which can be subjected to pressure
j through the ori~ices 40 is ~ormed in the mandrel 27.3 Figure 4 shows the two sets of clamping devices
shifted back into their starting positions, while the
', surrounded parts o~ the tube 50 are still held ~irmly as
before. The Figure shows that the mandrel 27 continues to
projectinto the set ofclamping devices21a-~ A central zone
51o~the tube 50has been stretched inthe axialdirectionand
hasasmaller wall thickness than theremaindero~ the tube.
In Figure 5~ the central zone 51 has been blow-
moulded against the mould 57 a-b. The shaping surface
of the mould corresponds to the ~orm of two mouth parts
52 a b, facing one ano-ther, ~or containers which are tobe
formed fromthe blanksand arein the processof manufacture.
~igure 6 shows -the mandrel 27 in its starting
position. A severing disc 58 is located in the position
for severing the tube 50, that is to say at the transition
be~ween the two moulded mouth parts 52 a-b.
Figure 7 shows a turntable 7 which ro-tates about
a bearing 12. Next to the turntable, a number o~
positions A-U is indicated. One frame 11 with the
.
526~
- 22 -
associated set of c~amping devices, drive mechanisms,
tubular mandrel, heating device and the like according to
^ Figures 1-2 is looated on the'turntable-for each position.
In the positions,'-the particular working step is indicated
'' diagra~atically'by the position of mandrel7'heating jaws,
sets of clamping de~ices and the like~
! Figure 8 shows an embodiment of the invention,
1 which is adapted ~referably ~or so-calle~ cold-drawing o~
31 ,the tube. An annular heating element 38 is located
between the two sets of clamping devices~ By means o~
this heating element, the central sections of the tube 50
are heated to an elevated temperature over an annular
zone.
~igures9-10 relate to the cold-drawing of the
' tube 50. In ~i,gure 9, the formation of a centrally
located drawn zone 53 has started, whilst in Figure 1
the entire centrally located dra~m zone 54 has been
formed~ ~
'Figures 11 and-12 relate to a variant of the
invention wherein the centrally iocated zone 51a of the'
tube 50 is longer than in the previously described
embodiments o~ the invention. The Iigures show only
one of the two sets of clamping devices. Figure 11
sh~ws the position after drawing of the tube has been
completed 9 whilst Figure 12 shows the central zone
51a (~igure 11) .after it has been bl.ow-moulded against
an outer mould 59. The moulding surface of the outer
mould corresponds tothe shapeof t~o mutually facing
mouth parts (only one, 52a, is shown in the figure) and
,~ .
2~
-- 23 --
parts of the adjacent future neck section 60a of the
containers which are to be ~ormed from the blanks and
are in ~he process of production. A zone 56, having
the~largest diameter in the moulded ~uture neck sections,
preferably has a diameter which is at least three times
the original diameter of the tube.
Figures 13 and 14 show comp~eted tubular pre-
mouldings, the pre-moulding according to Figure 13 h~.~ring
been formed ~rom a blank part shown in Figure 5 and a pre-
moulding according to F.igure 14:having been formed from a.
blank par-t sho~n in Figure 12. At one end, 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 61a, b and the neck sections
63a, b~ - .
In the production of a pre-moulding according to
the invention, a iube 50 is brought into the position
sho~m in Figure 1 with the aid of the gripper 28. me -
two sets of slamping devices 20 and Zl are shi~ted
towards one another with the aid o~ the drive mechanism
24 until the ~wo ends o~ the tube are in contac~ with
the gaskets 34 and 410 The upper clamping devices
are brought into their closed position with the aid o~
the drive mechanisms 25, 26, the tube 50 being ~irmly held
at both its ends and at the same time being enclosed over
a relatively large part. This situation is shown in-
Fi~ure 2. As an alternative, the mandrel 27 was
already in this phase brought beforehand into the position
3 2~52~91
- 24 -
which is shown in Figure 3. ~he heating jaws 29 are .brought into the heating position and remain in this
position for such a perio~ as-is necessary for heating -
. .
the material in-the c`entral sections of the tube to a
temperature below the glass transition temperature Tg.
~le drive element 24 now shifts the two sets o~ clamping
devices in the direction away from one another, the
central sections of the tube being stretched, with
simultaneous thinning o~ the tube wall, in such a way
that the tube is given the appearance shown in Figure 4.
Preferably, stretohing amounts to at least a factor.of 3,
and the reduction in thickness thus also amoun~s to a
factor of 3. During the entire drawing step, the
mandrel 27 is located in the interior of the tube, within
the stretched zone~ and thls preven LS the stretched zone
from ass~ming 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 t~e 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 contact with ~he surfaces o~ 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 star-ting position, the outer mould is
opened and a severing disc Z8 divides the tube at the
transition be-t~een the two future mouth parts. This
prGduces two separate blank parts ~hich are closed at one
., .
~L2~5~6~
:
- 25 -
end by reshaping and are provided with the requisite
closing surfaces at the other end by reworking. In
this way, a tu~ular pre-moulding as shown in Figure 13
is obtained.
The design of the equipment for closing one end~,
and likewise for the reworking, which may be necessary,
of the mouth part, is not shown in the figures, but this
can be in ~ccordance with any technology already known-
and used. Normally, closing is effected by ~eating
t~e material at one end of the tube up to a temperature
above the glass transition temperature Tg. after which the
end is ~orced 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 blank parts ~ormed 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 re;oeated.
According to a preferred embodiment o~ the inven-
tio~, the production step described above is carried out
with t~e aid of thP equipment shown in Figure 7. In
positioD A; th~ tube is fed to the two sets o~ clamping
devices, in positio~ ~ the two sets o~ clamping devices
are shifted in the direction to~Jards one another, whilst
simultaneously the mandrel is introduced into the tube,
and in pusition C-E the central zone o~ the tube is heated,
whilst in position ~ the heating process is`interrupted.
In positions G-H, the central sections o~ the tube are
stretched, in position I the outer mo~lds move into -the
- . ,
---` 3 ~526~
- 26 -
moulding position, in position J the interior of the
tube is subJected to pressure and'is formed to give the
future mouth parts with the adjacent nec~ sections.
In position K, the outer moulds open, whilst in position
' L the mandrel is retracted into its starting position.
j .Position M is a cooling position for s-tabilising the
~o~m of the tube or, alternative-ly, is a reserve
position, whilst in position N the ~ube is severed into
~wo blank parts. In position 0, the two future mouth
parts are heated for reworking, if appropriate, and they
obtain their final form in position P. In posi~ion ~,
the devices ~or reworking the mouth parts have assumed
again their starting position, and subsequently, in
position S, the blank parts have been shifted in the
direction tow~rds one another in order to enable the
gripper to engage in position T and to enable ihe clamping
;'~ devices to open in position U, so tha~ the mouldings
~ormed can'be removed from -the prsduction equipment
according to Figure 7. Advantageously9 the gri~per
device here transfers the blanks to de~ices ~r closing
one of their ends. Such deviGes can either be pro-
vided independently o~ the equipment described in this
paragraph, or they can form par~ o~ this equipment.
In the iatter case, this equipment must be pro-
vided with a fur-ther number o~ positions.
During cold drawing of the central zone of the
tubel the material is'heated before the drawing step with
the aid of an annular heating element 38 (Figure 8) over
an annular zone within the central zone. This'heating
' ' ' .
s~
- 27 -
element is preferably designed to heat the central zone
as far as one of the sets of clamping devices. To
.
con~rol the directlon o~ displacement during the flow
which sets in on drawing, the material is normally cooled
i~mediately nex~ to the heated annulus.in that direc-tion
in which it is intended that the flow step should not.--
propagate. In the embodiments in which the entire
material of the tube is to be d.rawn bet~een the two sets
of jaws, the r.equired cooling is obtained by the cooled
ja~sO In other ëmbodiments, 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 t~ produce the desired
temperature pro~ile in the central zone o~ the tube before
the latter is drawn~ The annular heating elements here
~requently consist ~ zones o~ ele~a-ted temperature in the
heating jaws 29.
On cold-drawlng o~ the material in the central
zone of the tube~ flow of the material sets in fir~t in
the annular zone which has been hea-ted by the annular
heating element 38. On further stretching of -~he cen-
: tral zone o~ the tube, the flow zone o~ the material is
displaced in the direction of the o-ther set of clamping
devices, compare Figure 9, so -that, after completion of
~e stretching step, a central drawn zone has formed 9 t~e
appearance o~ whlch is shown in Figure 10. On cold-
drawing~ the cent.ral zone has no -tendency to~ards a
- . .
. . .
~ 2d~5~
- 28 -
! reduction of the internal diameter of -the tube 9 as long
as stretching is~limited to about a factor o~-3. In
~his embodiment of the invention, it is t'hus not'necessary
' to cause the mandrel 27 to assume its 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
: . .
interior of the tube is subjected to pressure~ parts of
.
ad jacent neck sections are also ~ormed, in addition to the
two future mouth parts, 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, durirlg t~e subsequent heating in
conjunction with the shaping o~ the remaining part o~ the
container, is a~fected only to a small extent. ~he
appearance cf a pre-moulding, which was formed from a
blank part partially shown in Figure 12, can be seen in
~igure 14. ~ '
I~ the above'description, i* was explained how
the blank parts are formed by severing the drawn and
shaped tube. In a preferred embodiment o~ the invention,
severing of the blank parts from one another is effectea
with the aid of one or several severing discs which -
revolve under pressure about the circumferential surface
of the tube formed at the transi-tion be~ween the two
5~
-29 -
~uture mouth parts.
It was assumed in the above descrip~ion that
heating of the-central material sections of the tube is
e~ected-by heating jaws.- To obtain the most uniform
heating o~ the material possible, the tube should pre- -
ferably rotate relative to the heating element. To
make this possible, the clamping devices are modified,
i~ appropriate having cone-type bearings or having heating
-jaws which revol~e about the t~lbe.
In the case where the central sections 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, after whi~h the future
mouth par-t and parts o~ the adjacent neck sections are
shaped.
I~ addition to the abo~e description, the inven-
tion is also comprised ~y the attached patent`claims.
~ ' , ' ' ` .
