Note: Descriptions are shown in the official language in which they were submitted.
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NOZZLE PRESSING DEVICE OF AN INJECTION MOULDING MACHINE
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an injection moulding machine with an
injector unit
comprising a nozzle that can be displaced against a mould, and a nozzle
pressing device for
ensuring that the nozzle is held against the mould during the injection
process.
PRIOR ART
Injection moulding machines are widely used, and particularly for producing
plastic parts.
The injection moulding machines comprise in this regard essentially two
structural units,
namely the clamping apparatus for opening and closing a corresponding mould,
and an
injector unit for injecting flowable material into the mould.
The injector unit is usually displaceable relative to the mould, so that,
during the injection
process, it is essential that the nozzle through which the material being
injected leaves the
injector unit presses tightly against the mould, so that the injection
pressure can be maintained
on one hand and that no material to be injected is lost due to leakage between
the nozzle and
the mould on the other.
The prior art discloses nozzle pressing devices which ensure that the nozzle
presses securely
and firmly against the mould during the injection process, and in particular
also during post-
injection of material to be injected into the mould. Examples of this are
given in DE 42 32
533 Al and EP 1 364 765 Al. In the two apparatuses described therein, a drive
unit
comprising a spindle motor and a threaded spindle for moving the injector unit
towards the
mould has, between the spindle nut and the displaceable part of the injector
unit, which is
assigned to the displaceable spindle nut, a spring element in the form of a
spiral spring which
provides a nozzle press force through its elastic deformation.
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However, a drawback of these nozzle pressing apparatuses is that the nozzle
press force is
vulnerable to external influences and therefore cannot be adjusted with
sufficient precision, as
the spring element is arranged between moving parts. Moreover, the spring is
arranged offset
to the injection axis, as defined by the injection barrel and the nozzle, with
the result that
additional moments can arise on the injector unit that also affect precise and
defined contact
of a nozzle press force.
Furthermore, the arrangement of the spring is complicated and the use of coil
springs for the
intended purpose is unsatisfactory because, for reasons of stiffness, the coil
springs usually
have to be designed so as to have a relatively long spring displacement and
thus the time for
force build-up is also long.
DISCLOSURE OF THE INVENTION
OBJECT OF THE INVENTION
It is therefore an object of the present invention to create an injection
moulding machine or a
corresponding nozzle pressing device which avoids the disadvantages of the
prior art and, in
particular, facilitates precise and defined application of a nozzle press
force and which
maintains this nozzle press force, especially without further actuation of the
drive unit of the
injector unit. In this regard, the corresponding apparatus is to be of simple
construction and
easy and safe to use.
TECHNICAL SOLUTION
The invention proceeds from the recognition that the drive unit, which enables
the injector
unit comprising the nozzle to move relative to the mould, can be used simply
and effectively
to generate a nozzle press force. In this connection, it is assumed that the
drive unit is
designed to comprise two connection sides which are provided for connection to
the
components to be driven. Here, the components to be driven can be represented,
for example,
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by the injector unit on one hand and by the machine frame or the machine bed
of the injection
moulding machine on the other, with the injector unit moving relative to the
machine frame or
to the machine bed. By virtue of the relative movement of the connection sides
of the drive
unit, which are thus arranged on one hand on the displaceable injector unit
and on the other on
the stationary machine frame or machine bed, a spring force that can serve as
a nozzle press
force can be generated by interposing an elastically deformable spring
element.
This can be done advantageously as per the invention by providing the spring
element on the
machine frame or machine bed and connecting a connection side of the drive
unit to, or
supporting it in the spring element, such that the drive unit can cause the
spring element to
deform and thus a nozzle press force to be generated. Arranging the spring
element on the
machine frame or machine bed allows for optimal application of the opposite
force into the
machine frame or the machine bed and facilitates defined application of a
precise nozzle press
force, with all kinds of different spring elements lending themselves to this
use in respect of
type and design of spring element. In addition, arrangement of the spring
element is
simplified.
The drive unit can be a drive and a unit for generating a translatory motion,
wherein diverse
embodiments are conceivable. Examples include an actuator that facilitates
linear motion of a
drive rod, or a spindle motor with a motor-driven threaded spindle, which
cooperates with a
spindle nut. Rotation of the threaded spindle makes it possible to vary the
distance between
the spindle nut and spindle motor and so generate a corresponding translatory
movement.
Alternatively, in the case of a spindle drive, the spindle nut can be driven
instead of the
threaded spindle, with the result that the threaded spindle moves linearly
relative to the
spindle nut. In particular, a spindle drive with a small thread pitch can be
used, i.e. in
particular a spindle drive whose thread pitch is preferably chosen so as to be
small.
Furthermore, many diverse forms of drive unit for generating translatory
motion are
conceivable. For example, the actuator can be a hydraulic or pneumatic drive,
with a piston
rod executing the translatory motion.
The above-mentioned connection sides of the drive unit can thus be formed on
one hand by
the motor, i.e. the spindle motor, and on the other by the spindle nut or by
an actuator and an
actuating rod which can be moved linearly by it.
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Each connection side of the drive unit can be arranged on the elastic spring
element or is
effectively connected thereto. For example, in a spindle drive, either the
spindle nut or the
spindle motor can be fixed in place on the elastic spring element.
The further connection side of the drive unit can be located at any suitable
point on the
machine frame or machine bed, particularly on traverses of the machine frame
or on a
stationary platen.
The connection side of the drive unit can be connected direct to the spring
element or via
correspondingly rigid connecting elements. In particular, the connection side
of the drive unit
can be supported via a fixed bearing so as to be kinematically determinate.
The spring element can be configured as a rod or plate, for example in the
form of a leaf
spring or by a correspondingly configured part of the machine frame or machine
bed. It is
worthy of particular consideration to render traverses of a machine frame
transverse to the
injection direction appropriately elastic in order that they may act as spring
element. A
corresponding elastic configuration can be simply realized by manufacturing in
corresponding
spring steel.
A corresponding spring element can have short displacement, i.e. elastic
deformation, e.g.
maximum deflection, of less than or equal to 10 mm, especially in the range 1
to 3 mm, so
that short displacement and hence quick force build-up are ensured.
A corresponding spring element can be disposed not only in a simple manner on
the injection
moulding machine, but in particular can also be provided centrically with the
injection axis,
such that the spring element has a spring displacement running parallel or
concentrically with
the injection axis or in a plane that passes through the injection axis. In
particular, deflection
of the rod or plate in a direction opposite to the injection direction can be
provided as spring
displacement, such that the correspondingly generated nozzle press force
presses the nozzle
completely in the direction of the mould.
Accordingly, the spring element and/or the part of the connection side of the
drive unit
arranged thereon can be provided concentrically with the injection axis or
nozzle tip.
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However, the spring element and/or the part of the connection side of the
drive unit arranged
thereon can be arranged offset from the injection axis, in particular offset
in a direction which
is transverse to the injection axis, but which passes through the injection
axis.
For supporting the spring element on the machine frame or the machine bed, a
moment-free
support can be provided that avoids corresponding influences exerted by
additional force or
moment effects. Were the ends of a spring element, for example, to be rigidly
supported on
the machine frame or the machine bed, deformation of the spring element would
generate
additional forces on the support points that would hamper precise setting and
determination of
the resulting nozzle press force. This is avoided by a corresponding support
that permits
maximum mobility of the spring element in the support points. For example, a
support via
rotary joints can be provided on preferably bar-shaped connecting elements,
such that the
ends of the spring element can rotate freely via the rotary joints, with any
displacement of the
spring element or parts thereof as a result of deformation of the spring
element possibly being
at least partially compensated by elastic deformation of the bar-shaped
connecting elements.
In connection with the drive unit, a centring arrangement can be provided in
the region of the
spring element to ensure that the drive unit can continue to move unimpeded if
the spring
element undergoes elastic deformation.
The present invention can be used in particular on a tiebar-less injection
moulding machine,
such as is described for example in DE 10 2007 050 689 Al, because the machine
frame
concept presented therein permits a correspondingly simple arrangement of the
spring
element and direct application into the machine frame, via the spring element,
of the force
opposing the nozzle press force.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages, characteristics and features of the present invention are
apparent from the
following detailed description of embodiments using the enclosed drawings. The
drawings
show in purely schematic form in
Fig. 1 a perspective illustration of an inventive injection moulding machine;
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Fig. 2 a view of another embodiment of an inventive
injection moulding machine from below;
Fig. 3 a view of another embodiment of an inventive
injection moulding machine from below;
Fig. 4 a view of a fourth embodiment of an inventive
injection moulding machine from below;
Fig. 5 a view of an inventive injection moulding machine similar to that
of Figure 4 in the state of pressing the nozzle against a mould;
Fig. 6 a detailed view of the spring element from the injection moulding
machine as
per
Figures 4 or 5, and in
Fig. 7 a detailed view of the support of a spring element according to a
further
embodiment.
Figure 1 shows a perspective illustration of an inventive injection moulding
machine 1. Such
an injection moulding machine 1, is essentially well known and is described
for example in
detail in DE 10 2007 050 689 Al, whereby the disclosure of DE 10 2007 050 689
Al is fully
incorporated herein by reference.
The injection moulding machine 1 comprises a clamping unit 2 and an injector
unit 33. The
injector unit 33 comprises a displaceable injector unit 3, through which,
e.g., plasticised
polymer is injected via a nozzle into a mould where the plastic solidifies to
yield the
corresponding plastic injection-moulded product. The clamping unit 2 actuates
the mould
parts such that the mould opens and the finished plastic injection-moulded
product can be
removed from the mould. For the next injection operation, the mould is closed
accordingly by
means of the clamping unit 2. One part of the mould is arranged on the
displaceable clamping
unit 2, while the other part of the mould is arranged on a stationary platen
11, through which
the injector unit 3 comprising the nozzle is in contact with the mould for the
purpose of
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injecting the polymer into an opening in the mould. Figure 1 shows the
displaceable platen 12
which is arranged on the clamping unit 2 and on which a mould half can be
arranged. The
stationary platen 11 can be viewed as the separation between injector unit 33
and clamping
unit 2.
In accordance with the invention, the injection moulding machine 1 as shown in
Figure 1 has
a drive unit (not shown in Figure 1) which can move or displace the injector
unit 3 towards
the stationary platen 11.
In this connection, the drive unit comprising connection sides is on one hand
arranged on the
displaceable injector unit 3 and on the other is supported against a spring
element 10, which is
attached as a traverse on the side walls 5 and 6, which enclose the injector
unit 3.
In the illustrated embodiment of Figure 1, the injection moulding machine 1
comprises a
frame structure with the side walls 5, 6, 4, 7 between which are disposed
traverses 13, 14 and
31 and the intervening platen 11. The corresponding frame construction is
supported on a
machine bed 8, 9, which may have the same design of side walls and traverses.
In addition to the illustrated design of injection moulding machine 1 with
compact frame, in
which it is possible to largely dispense with tiebar arrangements for guiding
the displaceable
injector unit 3 and the corresponding displaceable components of the clamping
unit 2, an
inventive injection moulding machine can, however, also have the conventional
design of an
injection moulding machine with appropriate tiebar arrangements. The inventive
injection
moulding machines thus comprise tiebar-less injection moulding machines and
conventional
injection moulding machines with arrangements of tiebars.
As is clear from Figure 1, the spring element 10, which is used for generating
a nozzle press
force, can for example be configured as a traverse of the machine frame and
preferably be
arranged centrically with the injection axis 15, which passes centrally along
the injection
barrel and the nozzle in the injection direction.
Although Figure 1 does not show the drive unit for moving the injector unit 3,
it is easy to
imagine for example that, were the drive unit to be arranged between the rear
end 16 of the
injector unit 3 and the spring element 10, actuation of the drive unit so as
to increase the
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spacing of the connection sides generates a movement which moves the injector
unit 3 and the
spring element 10 away from each other until the nozzle of the injector unit 3
abuts the mould.
Provided that the drive unit continues to generate a drive force, the spring
element 10 then
becomes elastically tensioned, with the resultant spring force representing
the contact pressure
of the nozzle against the mould, said contact pressure being retained when the
movement of
the drive unit in the corresponding position is stopped. This press force
serves to press the
nozzle securely against the mould during the injection process and, in
particular, to ensure
that a post-injection process does not create gaps between the nozzle and the
mould through
which the material could escape.
Figure 2 shows a more detailed bottom view of further embodiment of an
inventive injection
moulding machine. In this connection, as also in the subsequent description of
the other
embodiments, the same reference numerals are used for identical or similar
components, with
a repeat description of similar or identical components in the following
embodiments being
eschewed.
Figure 2 shows the injector unit 3, which is displaceable along the injection
axis 15 via two
displaceable traverses 19 illustrated in Figure 2 , with slide elements 17
being provided on the
displaceable traverses 19, said slide elements being provided in corresponding
rail
arrangements 18 on the side walls 5 and 6 so as to constitute a linear
slideway for the injector
unit 3.
The injector unit 3 has a nozzle 25 which projects through the stationary
platen 11 and makes
contact with the injection opening of the mould 30.
For the purpose of moving the injector unit 3 along the rail arrangements 18,
provision is
made for a drive unit comprising a drive 20, a drive rod 21 and a fastening
element 22 for the
drive rod 21 on the injector unit 3.
When the drive 20 pushes the drive rod 21 in the direction of the mould 30,
the injector unit 3
comprising the nozzle 25 moves in the direction of the mould 30 until the
nozzle 25 makes
contact with the mould. Further generation of driving force by the drive 20
causes the drive
rod to move further and the spring element 10 deflects elastically until the
spring force
matches the driving force of the drive unit. If the drive rod 21 is then
immobilized in this
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position, the spring force of the elastic spring element is retained, such
that the spring force
presses the nozzle 25 against the mould 30. Accordingly, a simple but
effective nozzle
pressing device is created.
In particular, the drive 20, the drive rod 21 and the fastening element 22 and
the spring
element 10 can be arranged centrically, in particular concentrically, with the
injection axis 15,
such that, when the nozzle press force is exerted due to the elastic
deformation of the spring
element 10, the nozzle is pressed straight onto the mould 30. The avoidance of
moments
during application of the nozzle press force makes for extremely precise
setting of the nozzle
press force. However, it is also possible to arrange the drive unit and/or the
spring element 10
offset from the injection axis 15.
The drive 20 can be formed by any suitable drive that enables linear movement
of the injector
unit 3. This could, for example, be any actuator which can move the drive rod
21 back and
forth.
In particular, however, the drive can be a spindle motor which drives a
threaded spindle, as
shown in the embodiment of Figure 3. Accordingly, the embodiment of Figure 3
differs from
that of Figure 2 only in that, instead of a drive 20 in the form of an
actuator, a spindle motor
20' is provided, which drives a threaded spindle 21' which cooperates with a
spindle nut 23.
The spindle nut 23 is arranged on the fastening element 22 so as to rotate,
said spindle nut in
turn being firmly connected to the displaceable injector unit 3. Actuation of
the threaded
spindle 21' via the spindle motor 20' screws the threaded spindle 21' into or
out of the
spindle nut 23 to displace the injector unit 3 along the injection axis 15 in
order that the
nozzle 25 may be brought into or out of contact with the mould 30.
In the same manner as in Figure 2, further actuation of the threaded spindle
21 after the nozzle
25 is in contact with the mould 30 bends the spring element 10 such that the
elastic spring
force generates a nozzle press force which counteracts the injection pressure
during injection
moulding or the holding pressure during post-injection and thus ensures that
the nozzle makes
firm contact with the mould.
As is again evident from Figure 3, the spindle motor 20' comprising the
threaded spindle 21'
is arranged centrically with the injection axis 15 in order that the
corresponding forces, i.e. the
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spring force generated by the spring element 10, may be transmitted
centrically onto the
injector unit 3 and thus onto the nozzle 25. In addition to a completely
concentric arrangement
of the spindle motor 20' of the threaded spindle 21' and the spindle nut 23
with the injection
axis 15 or the nozzle 25, it is also possible to choose a centric arrangement
in which the
respective components are offset in one direction.
Figure 4 shows a further inventive injection moulding machine, which differs
from the
embodiments of Figures 2 and 3 in that the spring element 10' is formed as a
separate
component and is not formed by a traverse of the machine frame. Accordingly, a
special
arrangement of the spring element 10' is provided on the machine frame, said
arrangement
being discussed in detail later.
In addition, the embodiment of Figure 4 differs from those of Figures 2 and 3
in that the drive
or spindle motor 20' is not fixed in place on the machine frame or arranged on
the machine
bed, but rather is arranged on the displaceable injector unit 3, such that it
can move along with
this.
Through the arrangement of the spindle motor 20' on the traverse 19 of the
displaceable
injector unit 3, the spindle nut 23 acting in cooperation with the threaded
spindle 21' is fixed
in place on the spring element 10', which is connected to the machine frame
via a support. By
means of the drive of the threaded spindle 21', the injector unit 3, to which
the spindle motor
20' is firmly attached, is moved back and forth along the rail arrangements 18
via the thread
of the threaded spindle 21' acting in cooperation with the spindle nut 23. As
soon as the
nozzle 25 makes contact with the mould 30 and the spindle motor 20' is moved
further so that
the injector unit 3 is displaced in the direction of the mould 30, the spring
element 10' comes
under load and deflects due to elastic deformation. This elastic deformation
in turn provides
the nozzle press force with which the nozzle 25 is pressed against the mould
30.
This is illustrated in Figure 5, which shows the deflected spring element 10'.
Figure 6 shows the arrangement of the spring element 10' on the traverse 50 of
the machine
frame in greater detail. Alternatively, the spring element could be arranged
on the stationary
platen.
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Firmly arranged in place via screw connections on the traverse 50 are two
retaining elements
41, which have a bar extending from a square base, and an articulated head 46.
The spring
element 10' in each case is accommodated on an articulated head 46 via a
rotary joint 40.
Arranged in the middle of the spring element is the threaded nut 23, with an
opening provided
in the spring element 10' through which the threaded spindle 21' is guided.
The threaded
spindle 21' is in engagement with the spindle nut 23, such that the threaded
spindle 21' can
move back and forth relative to the spindle nut 23 and spring element 10'.
Correspondingly, also provided in the traverse 50 is an opening through which
the threaded
spindle 21' may be guided.
For the purpose of guiding the threaded spindle 21', a centring unit 42 is
arranged on the
traverse 50, said unit having a plain bearing bushing 43, which cooperates
with a centring pin
44 arranged on the spring element 10'. The centring pin 44 is movably
accommodated in the
plain bearing bushing 43 such that the centring pin 44 can be axially
displaced in the plain
bearing bushing 43. The centring pin 44 has a bore through which the threaded
spindle 21'
can be guided. In other embodiments, in which the threaded spindle need not
move through
the centring unit, such as when the spindle motor is arranged on the spring
element or an
actuator is mounted to the injector unit 3 and actuates a piston rod which is
attached to the
spring element, the bore in the centring pin can be dispensed with. However,
even in such a
case, a corresponding centring unit can be provided to guide the spring
element during
deflection.
The plain bearing bushing 43, together with the centring unit 42, makes it
possible, in the
event of deflection of the spring element 10', for the threaded spindle 21' to
be accurately
guided through the bore 44, such that no influences due to jamming and the
like can occur.
Moreover, the bearing of the spring element 10' on the rotary joints 40 and
the retaining
elements 41 ensure that a precise and defined nozzle press force can be
provided through the
deformation of the spring element 10', without any impairment arising due to
additional
resulting moments or forces. Arranging the spring element 10' via a rotary
joint 40 and the
articulated head 46 of the retaining element 41 ensures that the respective
ends of the spring
element 10' can freely rotate about an axis perpendicular to the plane of
Figure 6, such that
the bearing does not introduce bending moments onto the spring element 10'. In
addition, the
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thin bar 47 of the retaining element 41 permits displacement of the rotary
joint 40 towards the
threaded spindle 21' through corresponding elastic deformation of the bar 47,
so that no
significant additional forces or moments are applied as a result.
Correspondingly, a fixed
connection, instead of a loose support, can be provided between the spring
element and the
traverse, e.g. with pushing elements, a fact which simplifies the
construction.
Whereas, in the embodiment of Figure 6, the retaining elements 41 are arranged
directly on a
traverse 50 of the machine frame, Figure 7 shows an embodiment in which the
retaining
elements 41 are arranged on the side walls 5 of the machine frame via angle
elements 48.
Here, too, just as in the previous embodiments, it is ensured that the force
acting on the
counter-support in the form of the support arrangement for the elastic spring
element 10 or
10' is applied direct into the machine frame, which acts as a compact and
stable frame for the
entire injection moulding machine.
Although the present invention, as already stated above, can also be used in
connection with
other injection moulding machines which have a tiebar structure, use in the
case of a tiebar-
less injection moulding machine having the compact and stable machine frame
construction,
as shown for example in Figure 1, is particularly preferred, as this ensures
optimum
application of the force of the nozzle press force or the corresponding
opposing force into the
machine frame. Nevertheless, the advantages of the invention can also be used
in other types
of injection moulding machines having tiebars if the drive unit with a
connection side, i.e. the
spindle nut or a spindle motor, is arranged on a machine bed via a spring
element.
Although the present invention has been described in detail with reference to
the
embodiments, it is self-evident to a person skilled in the art that the
invention is not limited to
these embodiments, but rather that modifications involving the omission of
individual
characteristics are possible, or that other types of combinations of the
presented characteristics
can be made without departing from the scope of the appended claims. The
invention
comprises in particular all combinations of individual characteristics
presented.
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