Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02354593 2001-06-07
WO 00/35653 PCTIEP99I09785
METHOD AND MOLD CLOSING DEVICE FOR MOLDING PRESS.
FIELD OF THE INVENTION
The present invention relates to tie-bar less molding
machines, such as injection presses for plastics and metal
5. molten materials: more particularly concerns a method and a
device for tightly closing a mold positively using the
elastic features of the frame of the press in order to
generate thrusting actions to keep close the mold .members
during injection of the molten material into a shaped
10. cavity of a mold.
DDT!'1D TDT
Hydraulic, pneumatic, mechanical, electrical or different
type of actuators are generally known, and used in several
technical field in order to operate a movable member or to
I~~ exert thrusts on tools or machine members, by mechanical
connections.
In the case where forces with a substantially high value,
of the order of a few tonnes, tens or hundreds of tonnes
are required, the conventional actuators must be designed
20. and dimensioned such as to be heavy and extremely strong to
withstand the high forces generated by the reaction of the
tool or the machine; such problems particularly occurs in
the closure of a mold for plastics injection presses and
die-casting machines.
25. All this results in the use of very complex and costly
mechanical solutions which are subjected to several
drawbacks, such as a high degree of frictional forces
between the moving parts, which adversely affects the
efficiency and the performance of the molding press or die-
CONFIRMATION COPY
CA 02354593 2001-06-07
WO 00135653 FCT/EF99/09785
- 2 -
casting machine.
The molding and die-casting machines can be traditionally
classified in two main categories which comprise vertical-
stroke presses and horizontal-stroke presses, respectively,
5. of tie-rod or tie-rodless types the present invention is
particularly but not exclusively directed to improve the
mold-closure in tie-rodless presses.
In the injection molding of molten plastic or metal
material, a tie-rodless press typically comprises a base
1o. frame which extends in a longitudinal direction parallel to
the axis of a mold, provided with a stationary platen
rigidly connected to the base frame, for supporting a first
member of the mold, and a movable platen for supporting a
second mold member; the movable platen is suitably
15. connected to a drive unit which can be actuated so as to
firstly move and approach the movable mold member to the
stationary mold member, and secondly to tightly close the
mold by a thrust necessary for withstanding the high
internal pressures exerted by the molten material during
20, the injection.
In general, to prevent the two mold members from becoming
misaligned during the injection of the molten material,
causing a leakage at the high injection pressures, it is
necessary to exert clamping dawn forces for sealingly
closing the mold, which are very high i . a . of the order of
several tens, hundreds or thousands of tonnes, the reaction
of which must be fully withstood by the same closure
device. Presses of this kind are shown, for example, in US
5,297,925, US 5,332,385, WO 98/02291, WO 97/21529, WO
3o. 96/05041 or in EP-A-0,311,133 and EP-A-0,554,068.
In injection-molding machines or presses of the type
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 3 -
referred to, both of the vertical and of the horizontal
type, entirely conventional operating systems of hydraulic,
mechanical or electrical type are therefore used, having
several drawbacks in that they require closing actuators or
5~ toggle mechanisms which are extremely complex and bulky, in
order to approach the mold members and at the same time to
exert the high forces required for tightly clamping down
the mold, as well as to withstand the high reaction
stresses caused by the closure of the same mold.
10. Moreover, the conventional closing systems used hitherto,
in particular of the toggle-joint type, use of a large
amount of energy is required owing to the articulations or
joints structure which must be particularly strong and
complex in view of the high internal frictional forces to
15. be overcome and the high thrusts to be exerted on the mold.
There exists, moreover, an increasingly greater need to
facilitate the access to the working zone of a press for an
operator, both for maintenance operations and/or
replacement of the molds, as well as for automation
20. purposes of the working cycle, making the same press more
accessible for demolding.
In this connection, by way of an alternative to the
conventional presses described for example in US 4,545,757
or US 4,276,013 and US 4,773,845, tie-rodless presses, or
so-called C-shaped or open frame presses have been
varyingly proposed, said presses having to be designed with
a particularly strong frame to withstand the high forces
and reactions generated upon closing of the mold and during
the molding process.
30. Although this type of press allows for good accessibility
to the molding zone and its use is becoming increasingly
CA 02354593 2001-06-07
WO 00135653 PCT/EP99/09785
- 4 -
widespread, it nevertheless has certain limitations and
drawbacks mainly due to the intrinsic structure of the
frame and to the closing procedure of the mold.
In particular, with the open-frame presses of the
5. conventional type, it is not possible to exert high closing
forces while maintaining a simple and easily accessible
configuration of the press, since forces arising at the
closure tend to cause bending and distortion of the press
frame, causing in turn a misalignment between the two mold
io. support platens; in this type of press it is therefore
necessary to prevent or compensate for the deformations of
the frame.
In EP-A-0,726,131 therefore has been proposed to react or
compensate for the deformation of the press frame, and
15. misalignment of the mold members during the clamping down
of the mold, by means of a compression device comprising a
cylinder acting at the same time and in opposition to the
cylinder of the mold closing device, so as to restore the
parallelism condition between the movable platen and the
2p~ stationary platen, namely to correct or avoid misalignment
of the mold. As stated at column 5 line 37 onwards of EP
0.726.131, the compression system is merely used and
suggested, conjointly to the mold clamping down cylinder,
to compensate the deformation of the frame and maintain a
25. parallelism between the stationary and movable platens of
the press; therefore in EP 0.726.131 the compression system
is not suggested or used to positively cause the clamping
down of the mold. All this involves considerable
constructional and functional complications with consequent
30. increased costs, without however entirely overcoming the
drawbacks of said conventional press.
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
-- 5 -
OBJECTS OF THE INVENTION
There exists, therefore, the need to find new solutions
which allow for presses of simple design by the use of
hydraulic or different type of actuators to provide high
5. forces using an extremely small amount of energy.
Therefore the general object of the present invention is to
provide a method arid a . mold-closing device which are
suitable for solving the technical problems mentioned
above.
10. A further object of the invention is to provide a mold
closing device of the type mentioned above, which is
structurally simple and able to exert high clamping forces
for the mold, by using in a unique manner the same
structure of a press.
15. Another object of the present invention is to provide a
tie-rodless press both for plastic and for molten metal,
which makes use of a new closure for the mold, by means of
which the disadvantages previously referred to are
significantly reduced.
20. A further object of the present invention is to provide a
molding press or apparatus as defined above, provided with
a closing system for the mold, by means of which it is
possible retain an extremely simplified structure of the
same press, devoid of counteracting elements, while keeping
25. the mold members in an aligned and parallel condition.
Yet another object of the invention is to provide a molding
apparatus of the kind mentioned above comprising a mold
closing system of simplified constructional features, and
of comparatively low cost.
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
A further object of the invention is to provide an
injection molding apparatus both for plastics and metal, of
the tie-rodless type which, in addition to offering greater
constructional simplicity and ease of access to the working
5. zone, also allows a substantial reduction in energy
consumption, since the thrust for clamping down and
sealingly closing the mold is obtained by a fluid pressure
actuator of special design.
BRTEF DESCRIPTION OF THE INVENTION
10. These objects are achieved by means of a method according
to claim Z, and a mold closing device for a molding press
according to claim 2.
The innovative principle of the invention resides in the
generation of thrusts or pushing forces for closing mold
~.5. members of a mold disposed between thrust members or posts
of an elastically deformable structure, by providing an
expander between spaced apart abutting surfaces of the
deformable structure, and positively causing an elastic
deformation of the structure by the expander, at the
2o. closure of the mold, to generate oppositely directed
clamping forces by the thrust members to tightly close and
clamping down the mold.
Far the purpose of the present invention nclosure of a
mold" means a condition in which the two mold members,
25. after being approached and brought slightly in contact each
other, are clamped down and tightly urged against each
other, in a sealed condition, to allow injection of molten
of liquid materials preventing any leakage.
As stated above, unlike the molding apparatus of the known
30. type, where the bending or deflexion of the frame is
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
regarded as a negative phenomenon to be counteracted, the
novelty and originality of the present invention
substantially consists in positively using the elastic
bending or deflection or the machine frame, which is
5. deliberately caused so as to generate high thrust forces,
oppositely directed on the platens supporting the mold
members, to tightly close the mold; in this way any defect
in the parallel alignment of the mold members may be
automatically compensated for by controlling the deflection
lo. degree of the frame of the press.
Therefore, according to a first aspect of the invention, a
method has been provided for clamping and tightly closing a
mold comprising: movable and stationary mold members
disposed between thrust exerting shoulder members, on a
15. side of an elastically deformable structure of a press
frame; one of said mold member being movably supported from
an advanced and a retracted position in respect to the
other stationary member of the mold, the press frame
longitudinally extending in the direction of the thrust
20. axis of the mold, characterised by the steps of:
providing at least one thrust generating expander
between spaced apart abutting surfaces of a seat on at
least one side of the press frame;
approaching said movable mold member to the stationary
z5. mold member by an actuator; and
urging on the abutting surfaces of the press frame, to
cause an elastic deformation of the press frame, by the
same expander, to positively generate oppositely directed
thrust forces through the shoulder members on the both mold
members, to tightly clamp the mold.
CA 02354593 2001-06-07
WO 00135653 PCT/EP99109785
_ g _
According to another aspect of the invention, in a molding
press a mold-closing device has been provided, suitable for
generating high clamping forces along a thrust axis or the
center line of a mold provide between thrust exerting
5. members on a side ~of an elastically deformable frame
structure of a press, characterised by comprising:
at least one thrust generating expander
at least one seat having open side edges, for housing
said expander on at least one side of the press frame
10. said open side seat comprising spaced apart abutting
surfaces for the expander; and
control means to actuate said expander to urge against
both abutting surfaces with thrusting forces suitable for
positively causing an elastic deformation of press
15. structure to generate opposite thrusting forces by said
thrust members along said thrusting axis to tightly clamp
together both members of the mold.
According to another aspect of the invention, the expander
is in the form of a pressure-actuated expandable membrane,
20. having a pressure chamber connectable to a hydraulic
pressure source: the membrane may be provided by a
flattened tubular element sealingly welded to side support
bars having an inlet port for a pressurised fluid, and an
outlet port for venting air, or by facing steel sheets
25. suitably welded along their peripheral edges and/or to the
above mentioned side bars.
According to another aspect of the invention, the membrane
may comprise two parallely arranged facing plates which are
movable with respect to each other, to define a pressure
CA 02354593 2001-06-07
WO 00/35b53 PCT/EP99/09785
- 9 -
chamber closed by a peripheral seal.
According to a further aspect of the invention, the
expander is in the form of an elastically expandable flat
membrane, manufactured from a sheet-steel blank comprising
5. a rectangular or square central panel defining a first side
wall of the membrane,, and shaped panels on the-peripheral
sides inwardly foldable in respect to the central panel,
said central and peripheral panels being sealingly welded
along mating edges to form the other side wall of the
I0. membranes in this way the welds are provided on one side
wall of the membrane to adhere and be supported by the
facing thrust receiving or abutting surface of the seat
housing the membrane of the mold closing device.
According to a fourth aspect of the invention, the
15. expandable membrane comprises a flat plate on a side
defining a rigid wall, and an elastically flexible steel
sheet on the other side of the membrane, spaced apart and
suitably welded flush and along the peripheral edge of the
facing plate.
20. According to another aspect of the invention, a tie-barless
press for molding plastic or metal pieces has been
provided, of the type comprising:
an elongated frame having a longitudinal deflexion
axis, and a thrust exerting or shoulder member on each end
25. side thereof;
a stationary mold support platen fastened to a
shoulder member for supporting a first stationary member of
the mold;
a movable mold support platen for supporting a second
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/097$5
- 10 -
movable member of the mold, said first and second mold
members being axially aligned on said side of the press
frame; and
drive means to displace the movable platen to firstly
5~ approach the movable mold member to the stationary mold
member, and thrust generating means successively actuated
to the drive means for clamping and tightly closing the
mo 1 d,
characterized in that said thrust generating means
10. comprise:
at least one pressure-actuable expander between
abutting surfaces of a seat of the press frame, said
expander and said seat being constructed and positioned to
cause an elastic deformation of the press frame and
15. generate clamping forces on the sides of the mold members,
to close the mold; and
fluid pressure control means for connecting said
thrust generating expander to a fluid pressure source.
According to a preferential embodiment of the invention,
20. the thrust generating expander is in the form of a double
walled expandable membrane having a pressure chamber,
fitted into a open seat of the press frame, or between
abutting surfaces transversally extending to the frame of
the press.
25. In all cases the expansion of the membrane should be such
as to cause a small displacement of the abutting surfaces
or of the force applying points, having the same order of
the admissible elastic deformations for the press frame,
for example of some millimetres, depending on the features
CA 02354593 2001-06-07
WO 00/35653 PCTIEP99/09785
_ Il _
and dimension of the press; the quantity of hydraulic fluid
to be supplied to the membrane being therefore entirely
negligible and the work necessary for generating the
thrusts for the clamping and the closure of the mold, being
5. very small or comparatively small in respect to the prior
know closing devices for malding presses.
Since the opposite thrusts for closing the mold are now
generated by the elastic deformation of the press frame,
after the two mold members have been approached using a
io. minimum amount of energy, it is no longer necessary to
design particularly strong and bulky closing devices as per
prior art molding presses, since the control means for
positioning of the movable platen, no longer has to
generate very high closing forces, as occurs in the
15. conventional presses, but must only be able to displace the
movable platen on respective guides and passively opposing
the reaction forces which arise at clamping of the mold.
BRIEF DESCRIPTION OF THE FIGURES
These and further features and advantages of the invention
20. will emerge more clearly from the description which follows
with reference to the examples of the accompanying drawings
in which:
Fig. 1 is a schematic view of a general thrust
generating device comprising an expandable membrane, to
25. explain the principle of the invention;
Fig. 2 is a cross-sectional view along the line 2-2 of
Figure 1;
Fig. 3 is a plan view of the membrane of the thrust
generating device according to Figure 1:
30. Fig. 4 is a cross-sectional view along the line 3-3 of
Figure 3;
Fig. ~ is a front view of a second embodiment of a
CA 02354593 2001-06-07
WO 00/35b53 PCT/EP99/09785
_ 12
membrane according to the invention;
Fig. 6 is a cross-sectional view along the line 6-6 of
Figure 5;
Fig. 7 is a front view of a third embodiment of a
membrane according to the invention;
Fig. 8 is a cross-sectional view along the line 8-8 of
Figure 7;
Fig. 9 is a top view of a fourth embodiment of a
membrane according to the invention
10. Fig. 10 is a cross-sectional view along the line 10-10
of Figure 9;
Fig. 11 shows an unfolded blank, which can be used to
obtain the membrane according to Figure 9;
Fig. 12 shows a cross-sectional view of a firth
15. embodiment of an expander membrane according to the
invention.
Fig. 13 is a cross-sectional view of a sixth
embodiment of an expander for the thrust generating device
according to the invention;
20. Fig. 14 shows a first embodiment of a tie-barless
molding press comprising a pressure actuable thrust
generating device according to the invention;
Fig. 15 shows a detail of the left side of a press
according to Figure 14, with a different arrangement of a
25. thrusting membrane;
Fig. 16 shows a further embodiment of a tie-barless
press according to the invention;
Fig. 17 is a top view of a tie-barless press
comprising a thrust. generating device according to the
30. invention.
Fig. 18 shows a sectional view according to line 18-18
of Fig. 17.
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99109785
- 13 -
DETAILED DESCRIPTION OF THE INVENTTON
With reference to Figures 1 to 4 we shall now describe the
general principles and a first preferred embodiment of the
thrust generating device according to the invention.
5. As shown in Figure l, a thrust generating device according
to the invention comprises a suitably shaped metal
structure 10 which may 'be elastically deformed by the
thrusting action of an expander 12 urging on abutting
surfaces of a seat 11, to deflect the same structure 10
10. according to a bending axis orizontally extending and
parallely arranged to the axis or center line of two mold
members A and B clamped between the shoulder members 10C
and lOD.
The frame 10 on the side opposite to the shoulder members
Z5. lOC, IOD, is provided with an elongated cavity 11 which
opens at the bottom and on both sides of the frame 10, to
provide an open side seat for housing an expander 12,
having side arranged thrusting surfaces urging against
corresponding spaced apart abutting surfaces of the seat 11
20. as shown .
The expander 12 may be of any type or shape, to positively
generate high clamping forces for a mold through an~elastic
deformation of the frame structure 10 caused by the
expander 12, without involving any substantial movement for
25. the same expander or part thereof.
Preferably the expander is in the form of a walled
pressure-actuable membrane having a pressure chamber 13 of
rectangular or square flat shape, and a small deep between
the side walls 14, 15, in respect to the width and length,
30. substantially corresponding to the deep or spacing between
CA 02354593 2001-06-07
WO 00/35653 PC'T/EP99109785
- 14 -
the abutting surfaces of the seat 11.
A first embodiment for the expandable membrane 12 is shown
in the example of Figures 2, 3 and 4; the membrane or
expander 12, is in the form of a flattened tubular element,
5. each end of which is fitted and welded into a corresponding
seat of a support member 16 and 17 such as a square rod, as
shown.
The rods 16 and 17 are provided with holes 28 to receive
fastening bolts for fixing the membrane l2 into the seat 11
10. of the elastic structure 10, such as the frame of a press,
as well as is provided with holes 19 and 20 opening into
the chamber 13 at both ends of the membrane 12. One of the
holes 19, 20, for example the hole 19 of the rod 16, can be
selectively connected and disconnected to a pressure fluid
15, source P, by a solenoid valve 22 or other pressure control
device. The hole 20 in the second rod is, on the other
hand, closed by a plug member 21, being used to vent air
from the chamber 13 of the membrane, when necessary.
Operation of the thrust generating device according to the
20. present invention is essentially as follows: when the
control valve 22 is operated to disconnect the chamber 13
of the membrane 12 from the pressure source P, no pressure
inside the said chamber 13 will exist, and no thrust will
be exerted by the membrane 12 against the abutting surfaces
25. of the seat 11; therefore, the elastic structure IO will
not be subject to any deformation or bending moment. In
these conditions, the thrusts S1 and S2 caused by the
membrane 12 will be zero.
Differently, when the chamber 13 of the membrane 12 is
30. connected by the control valve 22 to the source P of a
fluid under pressure, such as an oil pressure source to
CA 02354593 2001-06-07
WO 00!35653 PCT/EP99/09285
- 15 -
feed the chamber 13 of the membrane with a pressure which
may be of the order of tens or hundreds of atmospheres, or
higher depending on the thrusting forces S1 and S2 to be
produced, a very small quantity of oil under high pressure
5. will be fed into the chamber 13 depending by the small
volume of the chamber 13, which will tend to expand or to
spread out the side walls 14 and 15 pushing them with high
forces S1, S2 against the opposing surfaces inside the seat
11.
lo. Since the membrane 12 may extend over a large flat surface,
having a considerable thrusting area, compared to the small
deep of the seat 11, the two lower portions 10A and lOB in
which the cavity 11 divides the structure 10, will be
subjected to high thrusts S1 and S2 which are proportional
~.5~ to the hydraulic pressure inside the chamber I3 and the
surface area of the membrane; however, since the expansion
of the membrane 12 is extremely small or negligible, in
keeping with the maximum deformation permissible for the
frame structure 10, the oil quantity under pressure to be
20. supplied into the membrane 12 will also be minimal or
entirely negligible compared to conventional hydraulic
actuating systems.
The thrusts S1 and S2 of the membrane 12, owing to the
elastic deformation which the structure 10 undergoes, may
25. be positively used to generate opposing bending moments M1
and M2 in the structure 10, which cause the shoulder
members lOC and 10D of the frame structure 10 to exert
opposite thrusting forces S3, S4 against the opposite sides
of the pieces A and B such as the two mold members, to
30. clamp and keep the same mold tightly closed.
The novelty and the originality of the invention, compared
to conventional molding presses, therefore resides in the
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 16 -
fact of positively using the same capacity of the structure
of a press to be elastically deformed, by one or more
expanders, such as pressure actuable membranes connectable
to a pressure source, fitted into corresponding seats or
5. between opposite abutting surfaces of the structure of a
press, so as to generate even considerably high working
thrusts to clamp and keep close a mold, using a small
amount of energy which is required only in order to operate
the expander or to slightly expand the membrane by an
10. amount sufficient to elastically deform the structure of
the press. Moreover, since the membrane is wholly supported
on the two sides by internal opposing surfaces of the seat
or abutting surfaces of the press frame, the membrane may
have an extremely simple and lightweight structure even in
15. the case where high thrusts must be generated.
Figures 5 to 13 show further possible solutions for the
membrane 12.
In the case of Figures 5 and 6, the membrane 12 again
consists of a flattened tubular element having both ends 30
20. and 31 suitably welded together; a connector 32 is directly
welded to a longitudinal edge of the tubular membrane 12,
so as to allow the chamber 13 to be connected to a pressure
fluid source. In this case the connector 32 is coplanary
arranged to the chamber 13 and the side walls 14, I5 of the
25. same membrane 12.
Figures 7 and 8 show a third embodiment of the membrane 12;
in this case the side walls 14 and 15 of the membrane 12
consist of two spaced apart suitably shaped steel sheets,
which are welded peripherally along their edges 34; the
30. connector 33 in this case is welded to 'protrude from one
side wall of the membrane.
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 17 -
Figures 9 and 11 show a fourth embodiment of an elastically
expandable hydraulic membrane 40 for a thrust device
according to the invention.
The membrane 12 of figures 9 and 10 is provided starting
5. from a sheet-steel blank shown in Figure 11; the blank is
obtained from a sheet 40 of material suitably cut and
folded onto itself in the manner shown.
The blank comprises a rectangular central panel 41 defining
one side wall of the membrane 22, and four peripheral
io. panels 42, 43 and 44, 45 having complementary shaped edges
and suitably folded inwards towards the panel 41, so as to
form the second wall of the membrane 12 which is opposite
and parallel to the first one.
More precisely the blank comprises two peripheral panels
15. 42, 43 with a triangular shape, along the longitudinal
sides of the central panel 41, and two peripheral panels
44, 45 with a trapezoidal shape, along the cross sides, the
edges of which, after the peripheral panels have been
folded inside, met together and are joined by welding.
20. From Figure 11 it can also be noted that the peripheral
panels 42, 43, 44 and 45 are joined to the central panel 41
by narrow intermediate folding up strips 46, 47, 48 and 49
having a width corresponding to the thickness or deep of.
the membrane 12. References numbers 50 and 51 in Figure 9,
25. finally denote two connectors for supplying a pressurised
hydraulic fluid and for venting air inside the chamber 13
of the membrane 12.
Figure 12 of the accompanying drawings shows a cross-
sectional view of a fifth possible solution. In this case
30. an expander 12 is shown comprising a flat plate 53 defining
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 18 -
a rigid side wall, and a steel sheet 54 defining an
elastically flexible facing wall, the peripheral edges 55
of which are suitably folded and turned inside a seating to
be welded flush to the peripheral edges of the plate 53.
5. With reference to. Figs. 14 to 18 we shall now describe
hereinbelow the invention as applied to a tie-barless
injection press of the horizontal type; however, it is
understood that the invention is applicable in general to
any type of vertical or horizontal press, both for the
10. molding of plastic material and for the die-casting of
metallic material in molten state, namely for similar
applications where it is required to exert high thrusting
forces for closing a mold while maintaining an ample
accessibility to the working zone and a simplified
15. construction of mold closing device for a press.
Fig. 14 shows an injection-molding press of the horizontal
type, comprising a C-shaped base frame 60 having a
deflexion axis which extends in a longitudinal direction of
the press the frame 60 is provided on the upper side with
20. opposite shoulder members 61 and 62 which extend upwards
and are rigidly connected to the frame.
The shoulder member 61 is provided with a stationary
support platen for a first mold member 63 to co-operate
with a second mold member 64 fastened to movable support
25. platen 65 slidably guided along the frame 60 in any
suitable manner, for example by means of longitudinal rail
guides 66 which extend along the frame &0.
In Fig. 14 reference 67 indicates a three joint toggle
mechanism connected between the shoulder member 62 of the
30. frame 60 and the movable platen 65; the toggle mechanism 67
is actuated by a double-acting hydraulic cylinder 67' to
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 19 -
move the platen 65 between, a retracted position, with
respect to the stationary platen 61, in which the two mold
members 63 and 64 are spaced apart, in the open condition
of the mold, and an advanced position in which the movable
mold member 54 is simply brought alongside the stationary
mold member 63, making a light contact, so as to allow
subsequent sealed closing of the mold by means. of the
opposite thrusts produced by an elastic deformation of the
frame ~0, by the membranes 68, as previously described and
10. as clarified below.
As can be understood by figure 14, when the movable mold
member 64 has been approached to the stationary mold member
65, the toggle mechanism 67 is in an extended condition in
which the three joints are axially aligned, laying in a
15, plane containing the longitudinal axis center line of the
mold' 63', 64. Therefore no high frictional forces must be
overcame inside the joints during approaching of the mold
members and the same joints of the toggle mechanism does no
more require a strong and complex structure because the
20. toggle-joint mechanism 67, and the cylinder 67', must
merely perform the displacement of the movable platen 65
with the movable member 64 of the mold.
Furthermore, in the extended condition of the toggle
mechanism 67, the latter must only resist to the reaction
25. forces caused by the closure of the mold, in a steady
condition without involving any movement and frictional
forces.
In fig. 1 a toggle-joint control unit has been shown for
rapid approach of the movable mold member 64 to the
stationary mold member 63; instead of the said toggle-joint
unit, any other drive unit of the hydraulic, electric,
mechanical type, or their combination may be used, without
CA 02354593 2001-06-07
WO 00!35653 PCT/EP99109785
- 20 -
changing in any way the present invention.
As stated above, a mold closing device for a press
according to the invention comprises a first control means,
such as the toggle mechanism 67 for rapid approach of the
5. mold members 63, 64, lacking the movable mold-supporting
platen in the approached condition in respect to the
stationary platen of the press, and a second thrust
generating unit for tightly urging each other the mold
members in the closed condition of the mold, by means of an
io. elastic deformation of the press frame, positively caused
by one or more pressure actuated expanders.
In the example under consideration of fig. 14, the second
thrust unit for the closure of the mold, comprises two
pressure actuated membranes 68 of the type previously
15. referred to, housed in respective open seats 68'
symmetrically disposed in the C-shaped frame 60 of the
press, at the lower side which is opposite to the upper
side for the mold and the closure toggle mechanism; as
shown in the same figure 14, the membranes 68 are seated
20. and extending in planes which are orthogonal to the
longitudinal axes of the frame 60 and the mold members 63,
64; in this way it is possible to simultaneously exert
opposing thrust actions S1, S2 by both membranes 68 which
tend to open wide the two abutment surfaces of each seat
25. 68' to produce mutually opposing bending moments M1 and M2
in the frame 60, causing a bending and an elastic
deformation of the same frame.
Therefore, the bending and elastic deformation of the frame
60, according to the invention is advantageously and
positively used to cause simultaneously inwards rotation of
the shoulder members 61, 62 rigidly connected to or forming
part of the press frame, which rotation is opposed by the
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 21 -
approached mold members 63 and 64 which are therefore
pressed against each other; in this way high mold closing
forces are produced on both sides of the mold members, and
the mold is tightly kept in a sealed condition during the
5. injection of plastic or metal molten material.
As shown in fig. 14 the two thrusting membranes 68 are
connected to a fluid pressure source P by a fluid supply
circuit 69' and a control solenoid valve 69.
Summarising, according to the present invention, the use of
io. elastically expandable membranes 12, 68 and more generally
the use of pressure actuated thrust generating devices or
expanders for causing an elastic deformation of a frame 10
or 60 of a press, and the generation of opposite thrust
forces for closing a mold, is extremely advantageous for
15. the following reason: by positively exploiting the elastic
deformation phenomenon of the frame 10 or 60 of a press,
which is deliberately produced, it is possible to generate
the thrusts necessary for tightly closing the mold after
the mold members have been approached, simplifying greatly
20- the structure of the press and facilitating access to the
working zone thereof, while limiting as far as possible the
power consumption necessary for closing and keeping the
mold in a closed condition.
In fact, assuming that the front surfaces of the two mold
25. members 63 and 64 in figure 14 have been brought into
contact with each other by the first control unit provided
by the toggle mechanism 67, 67', the work required for
elastically deforming the frame 60 and closing the mold 63,
64, is very small or entirely negligible compared to that
30. required for a conventional press in which high frictional
forces have to be overcome, in view of the very small
displacement of the two thrust members 61, 62 and the small
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 22
quantity of pressure oil is to be fed into the thrust
membrane, compared to the pressure oil usually required by
the hydraulic cylinders of conventional presses. In fact,
whereas in a conventional press, the thrust for closing the
5, mold is generated by an axial action of the same control
unit which performs the sliding of the movable mold support
platen, tending to open the frame or move the two upright
ends of the press away from each other, causing a
misalignment of the two mold members which must be suitably
10. offset by using a greater amount of energy and a greater
closing force, according to the invention the elastic
deformation of the frame is positively .used to produce
bending moments inside the frame structure which tend to
cause the two shoulder members at both ends of the frame,
15. to move towards each other instead of spreading out, to
generate the closure forces for the mold. The two mold
members 18A, 18B or 63 and 64, are therefore pushed against
each other with the necessary forces to maintain a correct
alignment between them.
20. The energy required by the closure device according to the
invention, in order to produce and maintain the mold
closing thrusts, is therefore extremely reduced and solely
that required to elastically deform the frame structure 10
or 60 of the press, which is significantly less than that
25. required by conventional closing systems of a conventional
press. Therefore, the amount of energy used and the oil to
be supplied to the thrust membranes 12 or 68, for each
molding cycle, are very limited to that required for
generation of the pressure inside the membranes. Lastly,
30. because of the membrane are resting against the thrusting
surfaces on both sides of the seating, the structure of the
membrane may be extremely simplified in respect to an
hydraulic cylinder, saving costs.
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99109785
- 23 -
in fact, from calculations performed and from some tests
carried out, it has been established that the displacements
to which the press frame is subject at the various
application points of the forces, are of the order of a few
5. tenths of a millimetre for a frame having a length of
between 2 or 5 metres. which are well within the range of
the elastic deformation permissible for such a structure.
In the case of Fig. 14, the two thrusting membranes 68 are
positioned underneath and in planes substantially
io. transverse to the longitudinal axes of the mold members 63.,
64 and the same frame 60 of the press.
Other disposition of the thrusting membranes are possible,
as shown in the example of Fig. 15, in which only a left
hand side of the press frame 60 according to Fig. 14, is
~s. shown .
In the case of figure 15 use is made of a thrusting
membrane 68 which is identical to that of the preceding
example of figure 14, being arranged in a corresponding
seat 68 horizontally extending in a plane underneath and
2a- parallel to the longitudinal axis of the mold, at one end
62 of the frame 60.
In view of the arrangement of the membrane 68, in the case
of Fig. 15, oppositely directed thrusts S2 and S2 are
generated suitable for creating opposite bending moments
25. M3, M4 at the ends of the press frame 60, to cause an
elastic deformation of the frame 60 and closure of the mold
as described above; in general it is preferable to have a
symmetrical disposition of the thrusting membranes, even
though it is not entirely necessary.
30. Instead of the pressure expandable membranes 12, 60 it is
CA 02354593 2001-06-07
WO 00/35653 PCT/EP99/09785
- 24 -
possible to use any other type of hydraulic or mechanical
expander or thrust device in order to cause elastic
deformation of the press frame and generate the mold
closing thrusts, provided that they are suitable for the
5. intended purpose.
The same apply for the drive device for approaching the two
mold members; in the case of Fig. 16, differently from the
example of Figure 14, for~the displacement of the movable
platen 7, to approach mold members 73, 74, use is made of a
10. hydraulic control unit 77 for moving the platen 75 and the
mold member 74 towards and away from the stationary mold
member 73. However, in the example of Figure 16 as well,
the elastic bending or deflexion of the press frame 70 and
the thrusting by the shoulder members 71 and 72 is again
15. caused by the pressure actuated membranes 68. In this case
it will be necessary to envisage locking means 78 to lock
the rod 78 of the cylinder 37 so as to keep the movable
platen 75 locked in the advanced mold closing position, so
as to withstand the thrusts.
20. It is understood, however, that stated and shown has been
provided purely by way of illustration of the general
principles of the invention, which may be applied to any
type of press, different from that shown, either of
horizontal and vertical type for injection molding or for
25. any other suitable use, without thereby departing from that
which is claimed.
