Note: Descriptions are shown in the official language in which they were submitted.
CA 02654106 2008-12-02
Process for the production of hollow bodies of thermoplastic material
The invention concerns a process for the production of hollow bodies
of thermoplastic material.
The invention concerns in particular a process for the extrusion blow
moulding of thermoplastic material to form integral hollow bodies, in
particular fuel tanks of plastic material for motor vehicles.
It is basically known for extrusion blow moulding of hollow bodies to
be effected by means of extrudates in web or band form. They can be
obtained for example by the extrusion of a tubular preform which was cut
up or divided into bands or webs. The extrusion of extrudates in web and
band form without implementing the roundabout route of using the tubular
form is also known. The preforms are either removed at the extruder by
means of a manipulator and fed to the tool or they are extruded directly
between the opened portions of a tool.
In the production of fuel tanks or other relatively large containers
which are provided with built-in fitment components and attachments, the
procedure involved is normally such that a tubular preform is extruded in a
hanging condition, in the form of a multi-layer extrudate, either
continuously or discontinuously, wherein after being expelled to the
predetermined length the extrudate is shaped directly within a tool formed
from two blow moulding mould halves. Expansion of the preform is effected
by the preform being subjected to the action of gas pressure within the
closed blow moulding mould.
If built-in fitment components such as for example surge
components, fuel pumps, senders, roll pots and the like are to be fitted in
the fuel tank, either they can be fitted by the plastic material being blow
moulded therearound in production of the hollow body or they can be
subsequently fitted into the finished container through assembly openings
on the container. The latter procedure is less desirable for various reasons.
More specifically, for emission reasons, openings and cut-out orifices in the
container wall should be as far as possible avoided or kept as small as
CA 02654106 2010-08-24
29513-26
2
possible. In addition the manual assembly expenditure on a fuel tank
produced in that way is comparatively high.
The operation of introducing such built-in fitment components is
found to be particularly difficult when the fuel tank is comparatively rugged
and irregular, that is to say it is of a complex spatial configuration.
Therefore, as an alternative to integral containers which are
produced by extrusion blow moulding, the possibility is known for producing
such containers, for example fuel tanks, from two injection-moulded or
deep-drawn half-shell portions. That procedure affords the advantage that
built-in fitment components can be fitted into the opened half-shell
portions. The two half-shell portions are then welded together to produce
the closed container. In that case the operation of assembling built-in
fitment components can be very substantially automated. A problem with
fuel tanks which are produced in that way is the weld seams at the
connecting locations of the half-shell portions. They represent potential
leakage locations on the container for gaseous hydrocarbons and require
additional devices for making the welded connections.
In principle there would also be the possibility of placing built-in
fitment components in the interior of a container when producing
containers by extrusion blow moulding of two or more preforms in web or
band form, by means of suitable manipulators. It will be noted however
that this is relatively complicated and expensive if the situation involves
introducing into the container fitment components which extend over the
overall cross-section of the container or which indeed are intended to join
the mutually oppositely disposed inside walls of the container together. In
that respect the procedure that presents itself for that purpose is to
assemble the containers from half-shell portions which are prefabricated,
for example injection-moulded or deep-drawn.
An object of some embodiments of the invention is therefore that of providing
a novel process for the production of hollow bodies of thermoplastic material
by
extrusion blow moulding of preforms in web or band form, in which built-in
fitment components can be placed in the container, at a particularly low
level of assembly complication and expenditure. In particular the invention
CA 02654106 2010-08-24
'29513-26
3
seeks to provide that the process minimises manual and machine finishing
working on a container provided with built-in fitment components.
An aspect of the invention relates to a process for the production of hollow
bodies of thermoplastic material, in particular by a process for the
production of fuel tanks of plastic material, in which preforms in web or
band form of plasticised plastic material are shaped in a multi-part tool
forming a mould cavity by expansion of the preforms and causing them to
bear against the internal contour of the mould cavity, wherein the process
-firstly includes the production of two mutually complementary intermediate
products in the form of shell portions, at least one respective built-in
fitment component is secured to the respective insides of the shell portions,
which face towards each other in the installation position, wherein at least
some built-in fitment components of mutually complementary shell portions
are respectively of mutually complementary configuration, in the sense that
they can be joined to provide an assembled component or to provide a
functional unit, and in addition the shell portions are assembled in such a
way that the mutually complementary built-in fitment components engage
into each other and/or come into operative connecting relationship with
each other.
Another aspect of the invention can be summarised to the effect that, in the
extrusion blow moulding of hollow bodies from bands or webs of a thermoplastic
extrudate, during the operation of shaping out the hollow body or during
the step of moulding the extrudates in web form, built-in fitment
components are fitted into the shell portions respectively forming
intermediate products, wherein the fitment components are so positioned
and are of such a nature that, when the shell portions are brought
together, the fitment components engage into each other and are brought
into operative connecting relationship with each other in such a way. that a
spatially complex arrangement of almost any configuration of fitment
components over the entire cross-section of the finished container is
possible.
CA 02654106 2010-08-24
= 29513-26
3a
Another aspect of the invention relates to a process for the
production of hollow bodies of thermoplastic material for the production of
fuel
tanks of plastic material, comprising the steps of: providing one or more
preforms
in web or band form of plasticised plastic material; providing a multi-part
tool
forming a mould cavity having an internal contour; shaping said one or more
preforms in said multi-part tool by expansion of said one or more preforms
thereby
causing said preforms to bear against the internal contour of the mould cavity
to
form two mutually complementary intermediate products in the form of shell
portions which face towards each other in the tool; providing built-in fitment
components capable of being secured to respective insides of the shell
portions,
wherein at least some of said built-in fitment components are respectively of
mutually complementary configuration; securing at least one of said built-in
fitment
components to each of the respective insides of the shell portions; assembling
the
shell portions such that said mutually complementary built-in fitment
components
at least one of engage into each other and come into operative connecting
relationship with each other, such that they can be joined to provide an
assembled
component or to provide a functional unit.
CA 02654106 2008-12-02
4
It is particularly desirable if the steps of producing and joining the
shell portions are effected in the first heat, that is to say without further
heating of the preforms.
In that way it is possible for example for bracing strut structures,
surge fitments or lines to be fitted into the container in a particularly
simple
manner, wherein the latter can extend over the entire cross-section of the
container. Bracing strut structures serve for example to counteract
deformation of the container because of an increased pressure or a reduced
pressure.
The container walls can also be joined together by way of bracing
strut structures, without the need for that purpose to produce wall-to-wall
welds by means of corresponding slider members in the tool.
The container can be equipped in that way exclusively by means of
additional built-in fitment components in the container. The design
configuration of the tools can turn out to be correspondingly simpler, for
example it is possible in that way to avoid the need for slider members.
Preferably the preforms are shaped in a multi-part mould tool which
includes at least two outer moulds and at least one central mould which
perform an opening and closing movement relative to each other, wherein
the outer moulds respectively form the sub-cavities which predetermine the
contours of the shell portions and the central mould is provided with at
least one component holder, in relation to which the fitment components
are placed or fixed at the insides of the shell portions, after the operation
of
shaping the shell portions.
In an embodiment of the invention it is provided that the central
mould is removed after placement of the built-in fitment components
between the outer moulds and then the outer moulds are closed against
each other in such a way that the shell portions and at least some of the
fitment components arranged therein come into operative connecting
relationship with each other.
By way of example bracing strut elements for stabilising the hollow
body can be used as the mutually complementary built-in fitment
CA 02654106 2008-12-02
components, the bracing strut elements latching together when the half-
shell portions are joined together.
Alternatively holding elements can be used as mutually
complementary built-in fitment components, which holding elements
5 respectively receive couplings of electric lines and fluid lines, wherein
the
arrangements respectively including a holding element and a line portion
with coupling are placed on the inside of the shell portions in such a way
that the couplings engage into each other when the shell portions are
joined together.
It is also possible to use surge fitment components, preferably in the
form of surge walls or surge wall arrangements which engage into each
other as mutually complementary built-in fitment components.
The invention is described hereinafter by means of two embodiments
by way of example with reference to the accompanying drawings in which:
Figures 1 to 12 show diagrammatic views of the individual steps in
the production process,
Figures 13 and 14 show diagrammatic views of mutually
complementary holding elements with couplings accommodated thereby
out of engagement and in operative connected relationship with each other,
and
Figures 15 and 16 show a tie anchor comprising two mutually
complementary elements which are brought into engagement with each
other when the mould is closed when the shell portions are brought
together.
Figures 1 to 12 diagrammatically show the tool identified by
reference 1 in cross-section during various phases in the process according
to the invention. The tool identified by reference 1 in the Figures is of a
three-part nature and comprises two outer moulds 2a, 2b and a central
mould 3. The outer moulds 2a, 2b are displaceable away from and towards
each other in the sense of an opening and closing movement. The central
mould 3 is displaceable with respect to the outer moulds 2a, 2b
transversely with respect to the opening and closing movement of the outer
moulds 2a, 2b. The moulds are each fixed in per se known manner to
CA 02654106 2008-12-02
6
respective known mould mounting plates which are not shown here for the
sake of simplicity. The mould mounting plates are slidable or displaceable
in a closing frame structure which is also not shown. An extrusion device
for producing preforms 8 in web or band form is also illustrated only by way
of indication, for reasons of simplification. By way of example, referring to
Figure 1, two suitable extrusion heads with wide-slot nozzles can be
arranged above the tool 1 outside the plane of the drawing, on the side
which is towards the person viewing the drawing. It is equally possible for a
preform in tube form to be divided up into two webs by suitable tools
during or immediately after extrusion and for those webs to be fed to the
tool 1 by means of a manipulator.
Arranged within the central mould 3 is a carrier 4 which, in the
illustrated embodiment, for the sake of simplicity, carries only two
displaceable component holders 5a, 5b which are displaceable with respect
to the carrier 4 by way of pneumatic cylinders 6. The use of hydraulic
cylinders is alternatively possible.
In the view shown in Figure 1 the central mould 3 is in the outwardly
displaced position, it can be displaced transversely with respect to the
opening and closing movement of the outer moulds 2a, 2b, the opening
and closing movement being indicated by arrows. In that position the
component holder 5a, 5b is fitted with built-in fitment components 7 (see
Figure 2). In a further step in the process the central mould 3 is moved
between the outer moulds 2a, 2b. Two preforms 8 in web form are then
respectively introduced between the central mould 3 and the outer moulds
2a, 2b which are in an open position relative to each other. As already
mentioned in the opening part of this specification, that can be effected by
extrusion from wide-slot nozzles arranged above the tool 1, that is to say
above the plane of the drawing in the Figures. As an alternative thereto it is
possible for the extruder or extruders to be arranged spatially remote from
the tool 1 and for the extrudates or preforms 8 to be transported between
the opened portions of the tool 1 by means of a suitable gripper.
For the production of a fuel tank it is provided for example that the
preforms 8 each comprise a six-layer co-extrudate with barrier layers for
CA 02654106 2008-12-02
7
hydrocarbons. A suitable barrier material is for example EVOH (ethylene
vinyl alcohol copolymer).
As soon as the preforms are arranged at the desired length between
the outer moulds 2a, 2b and the central mould 3 respectively the outer
moulds 2a, 2b are closed with respect to the central mould 3. The preforms
8 are then expanded by means of the action of gas under pressure in the
mould cavity (see Figure 6) so that they are each caused to bear against
the sub-cavities 9a, 9b of the tools 2a, 2b.
As can be seen in particular from Figure 7 the carrier 4 is of a two-
part configuration, wherein the two parts of the carrier 4 are moved away
from each other in a next step in the process, more specifically in the
direction of the outer moulds 2a, 2b respectively. The fitment components
7 which are arranged on the component holders 5a, 5b are finally pressed
against the inside wall of the shell portions 10a, 10b which are now
produced, by actuation of the pneumatic cylinders 6. There are various
possible ways of connecting the fitment components 7 to the inside wall,
which is still plastic, of the shell portions 10a, 10b. A force-locking
connection and/or a connection involving intimate joining of the materials
involved can be envisaged here. A connection by intimate joining of the
materials involved is achieved for example by welding the fitment
components 7 to the inside wall or also by glueing. As the process
according to the invention involves operating in a warmth or in a heat, that
is to say the preforms do not experience any further increase in
temperature after extrusion until the hollow body is finished, welding is the
operation that presents itself.
As can be seen in particular from Figure 7 the parts of the carrier 4
and the component holders 5a, 5b are positioned in the last phase of fixing
the fitment components 7 to the inside wall of the shell portions 10a, 2b, in
such a way that the component holders 5a, 5b with the fitment components
7 secured thereto project out of the respective separation plane 11
between the outer moulds 2a, 2b and the central mould 3. In the described
embodiment that separation plane 11 is actually illustrated as a plane, but
in principle the man skilled in the art also interprets the term 'separation
CA 02654106 2008-12-02
8
plane' as being a separating surface extending in a spatially complex
configuration between the portions of the tool.
After the parts of the carrier 4 and the component holders 5a, 5b
have been moved back into the starting position (Figure 8) the outer
moulds 2a, 2b are opened (Figure 9) and the central mould 3 is removed or
displaced between the outer moulds 2a, 2b so that the outer moulds 2a, 2b
can unimpededly perform a closing movement towards each other, as is
shown in Figure 11. When the outer moulds 2a, 2b are closed together on
the one hand the shell portions 10a, 2b are assembled to form the finished
article 12, while on the other hand the fitment components 7 respectively
arranged in the shell portions 10a, 2b are brought into operative connecting
relationship with each other. That can be effected in various ways, as will
be described hereinafter.
Finally Figure 12 shows removal of the finished article 12 from the
tool 1.
A possible configuration of the built-in fitment components 7 is
shown in Figures 13 and 14. Mutually complementary built-in fitment
components 7 illustrated there are in the form of holding elements 13a,
13b which are each placed on the inside wall of the respective shell portions
10a, 10b in accordance with the above-described procedure, wherein the
holding element 13a receives the coupling 14a and the holding element 13b
receives the plug 14b of a line connection. Both the coupling 14a and also
the plug 14b are arranged on the holding elements 13a, 13b in such a way
that the coupling 14a and the plug 14b are brought into engagement with
each other when the outer moulds 2a, 2b are brought together (Figures 10
and 11). It will be apparent to the man skilled in the art that for that
purpose it is necessary for the holding elements 13a, 13b or the fitment
components 7 to be placed in the shell portions 10a, 10b in such a way that
it is possible to produce an operatively connected relationship therebetween
when the outer moulds 2a, 2b are moved together. The parts which are to
be connected together must also have suitable tolerances, as will be clear
for example by reference to the embodiment shown in Figures 15 and 16.
CA 02654106 2008-12-02
9
The built-in fitment components 7 shown in Figure 15 represent a tie
anchor comprising a latching projection 15a and a sleeve-shaped latching
receiving means 15b. The latching projection 15a is provided with latching
protrusions 16a whereas the latching receiving means 15b has
corresponding latching openings 16b. In production of the hollow body the
two parts of the tie anchor are positioned or placed relative to each other
on the inside wall of the respective shell portions 10, 2b in such a way that
they are arranged in exactly opposite relationship. When the outer moulds
2a, 2b are closed against each other, the latching projection 15a engages
into the oppositely disposed latching receiving means 15b and the latching
protrusions 16a are locked in the latching openings 16b of a corresponding
configuration. In that way the shell portions 10a, 2b which represent the
mutually oppositely disposed walls of the finished container are non-
releasably braced together.
CA 02654106 2008-12-02
Reference numerals
1 tool
2a, 2b outer moulds
3 central mould
4 carrier
5a, 5b component holder
6 pneumatic cylinder
7 built-in fitment components
8 preforms
9a, 9b sub-cavities
10a, 10b shell portions
11 separation plane
12 article
13a, 13b holding elements
14a coupling
14b plug
15a latching projection
15b latching receiving means
16a latching protrusions
16b latching openings
