CLOSING UNIT FOR A SHAPING MACHINE

Abstract

A closing unit for a shaping machine includes mutually moveable mold mounting plates suitable for carrying mold tool portions, a first hydraulic cylinder adapted to apply a closing force to the mold mounting plates, a second hydraulic cylinder, and a pressure storage means connected to the first hydraulic cylinder and adapted to store a pressure prevailing in the at least one first hydraulic cylinder upon pressure relief as a storage means pressure. A hydraulic interconnection of the pressure storage means with the second hydraulic cylinder allows the storage pressure stored in the pressure storage means to be used for locking and/or unlocking the locking device.

Claims

1. A closing unit for a shaping machine comprising: mutually moveable mold mounting plates suitable for carrying mold tool portions, at least one first hydraulic cylinder adapted to apply a closing force to the mold mounting plates, at least one second hydraulic cylinder, a pressure storage means which is connected to the at least one first hydraulic cylinder and which is adapted to store a pressure prevailing in the at least one first hydraulic cylinder upon pressure relief as a storage means pressure, and a hydraulic interconnection of the pressure storage means with the at least one second hydraulic cylinder, by which interconnection the storage means pressure stored in the pressure storage means can be used for locking and/or unlocking the at least one locking device.

2. The closing unit as set forth in claim 1, further comprising at least one pull or push rod for transmission of the closing force from the at least one first hydraulic cylinder to the mold mounting plates and at least one locking device for locking the at least one pull or push rod relative to one of the mold mounting plates and/or relative to the at least one first hydraulic cylinder, wherein the at least one second hydraulic cylinder is adapted to lock and/or unlock the at least one locking device.

3. The closing unit as set forth in claim 2, wherein exclusively the storage means pressure stored in the pressure storage means is present as the pressure source for the at least one second hydraulic cylinder for unlocking and/or locking in cyclic mode.

4. The closing unit as set forth in claim 2, further comprising four pull rods which preferably pass through the mold mounting plates.

5. The closing unit as set forth in claim 4, further comprising four first hydraulic cylinders which are respectively associated with a pull rod and which are preferably arranged at a side of a mold mounting plate which is fixed relative to a machine frame, said side facing away from a mold mounting plate which is moveable relative to the machine frame.

6. The closing unit as set forth in claim 2, further comprising a central push rod associated with a single first hydraulic cylinder.

7. The closing unit as set forth in claim 1, further comprising a hydraulically driven core pull means and the at least one second hydraulic cylinder is adapted to drive the core pull means.

8. The closing unit as set forth in claim 1, wherein at least one pressure intensifier is connected hydraulically between the at least one first hydraulic cylinder and the pressure storage means.

9. The closing unit as set forth in claim 8, further comprising a plurality of stages of different pressure intensification and/or pressure reduction, wherein preferably there are provided a pressure-reduced stage, a direct stage and a pressure-intensified stage.

10. The closing unit as set forth in claim 9, wherein the plurality of stages of pressure intensification and/or pressure reduction are implemented by a pressure intensifier, the hydraulic circuitry of which can be selected by means of a switching valve.

11. The closing unit as set forth in claim 9, wherein the plurality of stages are embodied by a plurality of different pressure intensifiers.

12. The closing unit as set forth in claim 1, wherein the pressure storage means is in the form of a bladder storage means.

13. A shaping machine comprising a closing unit as set forth in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantages and details of the invention will be apparent from the Figures and the associated specific description. In the Figures:

[0033] FIG. 1 shows an embodiment of a hydraulic circuit according to the invention of a closing unit,

[0034] FIG. 2 shows a further embodiment of a hydraulic circuit according to the invention of a closing unit,

[0035] FIG. 3 shows graphs to illustrate the mode of operation of the hydraulic circuit of FIG. 2,

[0036] FIG. 4 shows a further embodiment of a hydraulic circuit according to the invention of a closing unit with pressure intensifiers,

[0037] FIG. 5 shows a further embodiment of the hydraulic circuit of a closing unit with a single pressure intensifier, and

[0038] FIG. 6 shows a side view of a shaping machine in the region of the closing unit in which the invention can be used.

DETAILED DESCRIPTION OF THE INVENTION

[0039] In accordance with the state of the art at the present time, in a hydraulic injection molding machine or a press, the build-up of closing force is achieved by the compression of hydraulic fluid (=pressure increase) in suitably large hydraulic cylinders (the at least one hydraulic cylinder 3). In a structural configuration of injection molding machines from the applicant (DUO-Machines) that is implemented for example by means of four large pressure cushion cylinders, wherein the transmission of force is effected by way of four pull rods 4 (also referred to as frame bars) and the at least one locking device 5. In this example there are provided four locking devicesone for each barat that mounting plate 2 which is moveable in relation to a machine frame and the other mounting plate 2. The oil volume required for producing the closing force is produced in that case from the short stroke necessary for overcoming the mechanical clearances, the compression volume of the hydraulic fluid, bar extension and plate flexing of the mold mounting plates 2.

[0040] In the reduction in closing force usually the hydraulic fluid which is under a high pressure is simply discharged to a tank in practice, in which case the stored energy of the compression volume of the fluid, the mechanical extension of the bars and plate flexing is lost without being used. Now the aim of the invention was to make it possible to better use that energy again, that is to say to a higher proportion thereof, than is proposed in the patent literature.

[0041] In the first embodiment shown in FIG. 1 for that purpose the hydraulic circuit in the reduction in closing force is initially of such a form that at any event in the first phase of pressure relief in the reduction of closing force (high-pressure phase) the fluid is not discharged to a tank, but a pressure storage means 7 in the form of a hydraulic accumulator (for example a bladder storage means) is loaded therewith up to a certain storage means pressure. The residual pressure of the closing force system can then be discharged for example to a tank in order to completely shut down the closing force. The pressure storage means which is charged in that way will be further used as a drive source for movements involving a lower need for pressure and amount, more specifically the at least one locking device for example of a pressure cushion machine.

[0042] The pressure storage means 7 is prestressed with a comparatively low gas pressure p.sub.0 (for example p.sub.0=40 bars). With a further pre-charge from a base pressure in the hydraulic system it is possible to provide a somewhat higher base pressure p.sub.1 (for example p.sub.1=50 bars) in the pressure storage means 7.

[0043] Here follows a brief operational sequence description of the build-up in closing force and reduction in closing force, in accordance with the embodiment shown in FIG. 1.

[0044] The first step is the build-up of closing force by way of the pump 12 and valve W1 in the pressure cushions (first hydraulic cylinder 3) by compression of the oil to for example about 250 bars.

[0045] In the reduction in closing force now in the first phase the valve W3 is switched and thus both the compressed oil and that volume of oil which occurs due to the relief stroke involved in bar extensions is fed from the pressure cushions (hydraulic cylinder 3) to the pressure storage means 7.

[0046] As the pressure storage means 7 is prestressed with a comparatively low gas pressure it is now charged to a pressure equalization state as between the pressure cushion chambers and the pressure p.sub.Akku in the pressure storage means 7.

[0047] Depending on the selected size of the pressure storage means 7 the pressure rise in the accumulator in the present embodiment is at about 10 bars. In other words, the compression volume of the pressure cushions by the reduction in pressure from 250 bars to 60 bars together with the stroke of bar stress relief and plate stress relief is now stored in the pressure storage means 7 at around 60 bars.

[0048] By way of the pressure sensors 13 (closing force) and 14 (p.sub.Akku) it is recognized the extent to which pressure equalization has occurred. Upon approximation of the two pressures (60 bars) the valves W2 and W3 are switched and the remaining closing pressure reduction can take place to the tank 15.

[0049] The stored energy of the pressure storage means 7 is now available by switching of the valve W4 at any time for other movements with a low level of pressure consumption (for example locking or core pull).

[0050] FIG. 2 shows a further example with locking cylinders as consumers, the relevant volumes (V1-V3) and the pressures also being shown.

[0051] By reference to FIG. 2 it will now be shown how the volume ratios of the at least one first hydraulic cylinder 3 (pressure cushion cylinder) and the at least one second hydraulic 6 (locking cylinder) can be implemented in order to be able to use the function according to the invention to the best possible degree. In that respect:

[0052] V.sub.1 denotes oil volume on the rod side pressure cushion cylinder+line volume

[0053] V.sub.2 denotes the maximum piston volume locking cylinder

[0054] V.sub.3 denotes maximum rod volume locking cylinder

[0055] V.sub.s change in volume due to bar extension and plate flexing

[0056] .sub.s denotes bar extension+plate flexing under closing force

[0057] .sub.V.sub.1 denotes compression volume in the pressure cushion under closing force

[0058] .sub.p.sub.v1 denotes pressure difference between maximum closing pressure and maximum accumulator charging pressure (storage means pressure)

[0059] K denotes compression module.

[0060] The following applies for the compression volume .sub.V.sub.1:

.sub.V.sub.1=V.sub.1*p.sub.v1/K

[0061] The total available volume V.sub.verf due to the reduction in pressure in the pressure cushions (first hydraulic cylinder 3) is composed of the compression volume .sub.V.sub.1 and the volume change V.sub.s due to the restoration of the bar extension and plate flexing:

V.sub.verf=.sub.V.sub.1+V.sub.s

[0062] In order to have stored sufficient hydraulic fluid for a cycle implementation in the pressure storage means 7 (to lock at least once and unlock once) V.sub.verf must be somewhat greater than the overall possible oil volume of the locking cylinders at the piston and rod side:

V.sub.verf>V.sub.2+V.sub.3

[0063] FIG. 3 finally shows an operational diagram involving the configurations of closing pressure in the pressure cushion (p.sub.v1), accumulator pressure (p.sub.Akku) and the associated switching positions of the relevant directional control valves W1 through W6 shown in FIG. 2 for a cycle which includes the actions closing force reduction/accumulator charging, unlocking and locking again.

[0064] Firstly the pressure p.sub.v1 in the at least one first hydraulic cylinder 3 under the closing force is at a maximum value p.sub.V1max. By opening of the valve W3, the pressure in the at least one first hydraulic cylinder 3 is reduced to a value p.sub.V1min and the pressure in the pressure storage means 7 rises to a storage means pressure p.sub.2. At that time, the valve W2 is opened and the valve W3 is closed. As a result the storage means pressure p.sub.2 in the pressure storage means 7 is stored and the residual pressure in the at least one first hydraulic cylinder 3 is discharged to the tank. By switching of the valves W5 for unlocking the at least one locking device 5 and W6 for the locking action that affords the possibility of opening the closing unit for example by a separate fast stroke, removing a produced molding and closing the closing unit again, before the closing force can be built up again in a next cycle, after locking has taken place.

[0065] In the pressure configuration graphs shown in FIG. 3, it can also be seen that it is precisely at the beginning of the reduction in closing force that there is a very high pressure excess available: about 250 bars in the pressure cushion (first hydraulic cylinder 3) and the minimal pressure in the pressure storage means 7 of about 50 bars. It is only at the close of the reduction in closing force that the pressures approximate (at about 60 bars) when the maximum charging of the pressure storage means 7 is reached.

[0066] Admittedly, that simple procedure provides that a part of the stored energy is recovered, but nonetheless there are high losses due to the great pressure difference at the beginning and by virtue of the fact that the last 60 bars cannot be used in this example.

[0067] A further improvement in that respect can be achieved with embodiments as shown in FIGS. 4 and 5. The above-described losses can be markedly reduced by the use of pressure intensifiers (shown in the form of piston-cylinder units 9).

[0068] By virtue of the effective area relationships the pressure intensifiers shown in FIGS. 4 and 5 generate pressure intensifications of 1:2 or pressure reductions of 2:1.

[0069] Here follows a brief operational sequence description of the reduction in closing force corresponding to the embodiment of FIG. 4.

[0070] A first stage S1, closing force reduction from 250 bars to 125 bars: valve W7 is activated and thus the charged pressure cushion (first hydraulic cylinder) is connected to the rod side of the pressure intensifier 9. That provides a pressure reduction of 2:1, whereby 125 bars are applied on the piston side of the pressure intensifier, that is to say the pressure storage means side. By virtue of the reduction in the pressure loss, at the same time a doubling of the volume of the hydraulic fluid to be stored in the pressure storage means 7 is achieved! Thus in the range of 250 bars to 125 bars double the volume is charged in the accumulator, than in the structures shown in FIG. 1 or FIG. 2.

[0071] Second stage S2, reduction in closing force from 125 bars to 60 bars: valve W3 is now activated and the accumulator is charged directly from the pressure cushion as in the embodiments of FIG. 1 or FIG. 2, until the pressure in the pressure cushion has fallen to 60 bars. The accumulator is selected to be of such a size that in the present embodiment only a pressure rise from 50 bars to about 57 bars was achieved up to that time.

[0072] Third stage S3, closing force reduction from 60 bars to 30 bars: valve W8 is now activated and thus a further reversed pressure intensifier cylinder 9 with a 1:2 pressure intensification is brought into play. For example therefore 60 bars in the pressure cushion is increased to 120 bars, thereby permitting further charging of the accumulator to 60 bars. That can be operated until only about 30 bars prevail in the pressure cushion (first hydraulic cylinder 3).

[0073] Fourth stage, closing force reduction of 30 bars: residual discharge of the pressure cushion to the tank is effected by way of the valve W2.

[0074] By virtue of that procedure the charge volume is doubled and the pressure losses reduced in the first stage S1 while in the third stage S3 the usable pressure of the pressure cushion (first hydraulic cylinder 3) is increased from 190 bars (250 minus 60 bars) to 220 bars (250 minus 30 bars). The number or design configuration of the pressure intensifiers, in particular pressure intensification and pressure reduction ratios, can be expanded and refined as desired.

[0075] FIG. 5 shows a further simplified variant in which it is possible to use a pressure intensifier 9 by virtue of a change-over switching valve 11 in both directions (first stage S1 and third stage S3). This has the advantage that it saves on a pressure intensifier 9 and in addition the pressure intensifier 9 after each cycle is automatically in the next starting position again.

[0076] FIG. 6 shows a side view of a shaping machine 10in this case an injection molding machinein the region of the closing unit 1, in which the invention can be used. It is possible to see the mold mounting plates 2, the first hydraulic cylinders 3 for applying the closing force, the pull or push rods 4 (in this case pull rods) as well as the locking device 5 driven by the second hydraulic cylinders 6.

[0077] By virtue of the side view only two portions of the first hydraulic cylinders 3 and the pull rods 4 respectively can be seen in FIG. 6, in which respect there are actually four respective portions. The situation is similar with the two second hydraulic cylinders 6 of the locking device 5, of which only one second hydraulic cylinder 6 is to be seen.

REFERENCE NUMERALS

[0078] 1 closing unit [0079] 2 mold mounting plates [0080] 3 at least one first hydraulic cylinder [0081] 4 at least one pull or push rod [0082] 5 at least one locking device [0083] 6 at least one second hydraulic cylinder [0084] 7 pressure storage means [0085] 8 interconnection [0086] 9 pressure intensifier [0087] 10 shaping machine [0088] 11 switching valve [0089] 12 pump [0090] 13 pressure sensor closing force [0091] 14 pressure sensor pressure storage means [0092] S1-S3 stages [0093] W1-W8 valves