WO2006039921A2

WO2006039921A2 - Hydraulically-operated casting unit

Info

Publication number: WO2006039921A2
Application number: PCT/DE2005/001849
Authority: WO
Inventors: Dirk Herold; Holger Engert
Original assignee: Bosch Rexroth Ag
Priority date: 2004-10-15
Filing date: 2005-10-17
Publication date: 2006-04-20
Also published as: WO2006039921A3; DE102005034202A1; DE112005002551B4; EP1809432A2; DE112005002551A5

Abstract

The invention relates to a hydraulically-operated casting unit, comprising a casting cylinder, the cylinder of which is effective in the extension direction and may be connected, during a form filling phase, to a low pressure reservoir and, in a pressure phase, to a high pressure reservoir, by means of a control valve arrangement. An annular chamber of the casting cylinder, acting in the withdrawal direction, may be pressurised before a pre-filling phase with a counter-pressure. According to the invention, said counter-pressure is applied by means of a high-pressure pump which may be connected directly to the annular chamber of the casting cylinder by means of a counter-pressure valve.

Description

description

Hydraulically operated casting unit

The invention relates to a hydraulically operated casting unit according to the preamble of patent claim 1.

Such casting units are used in die casting machines (cold chamber machines, hot chamber machines), tixomoulding, plastic injection molding machines or similar machines in which a molten or doughy molding material has to be introduced into a cavity of a mold.

The casting process can be subdivided into three main phases, wherein in a first prefilling phase the molten or doughy molding material is introduced into a casting bush and then displaced comparatively slowly in the direction of the cut of the mold. In this case, the molding mass movement should be done slowly and smoothly at low speed.

The filling of the cavity then takes place during the molding phase in which the molding compound is pressed into the mold at a comparatively high flow rate.

To complete the filling of the mold, to compress and to compensate for the shrinkage of the molding material during the solidification process is followed by a holding pressure phase, in which a relatively high pressure is built up. Following these three phases, the casting unit is then moved back to its starting position and is ready for the next shot. In US 5,622,217 a casting unit of a die-casting machine is shown in which the molding material is pressurized by means of a casting cylinder. The casting cylinder is actuated by a hydraulic control valve arrangement, via which a cylinder space effective in the extension direction of the casting cylinder during the first two phases (prefilling phase, filling phase) with the pressure in a low pressure accumulator and during the holding pressure phase with the Pressure in a high-pressure accumulator is connectable. The outward speed of the casting cylinder is controlled on the outlet side via a control valve which opens or closes a connection to the tank.

For a high-quality casting process, it is necessary for the casting cylinder to move smoothly during the mold filling phase and then to move at comparatively slow speed, so that the molding material is drawn in "gently" and conveyed towards the cavity.

It is important that the mold material is pushed pressure-free at low speed towards the mold during the pre-filling phase. For this purpose, when the low-pressure accumulator is first connected, a back pressure must be built up on the outflow side of the casting cylinder, which prevents compression of the ring side when connecting the low-pressure accumulator on the piston side. As a result, a starting pressure is avoided and the movement can be controlled selectively on the amount of the returning pressure medium. Since there is no load pressure at this stage (due to the filling of the mold), the entire piston force of the casting cylinder must be compensated on its ring side. This leads to high pressures and thus to a high pressure Pressure loss at the drain-side control valve, which must be designed to be relatively large due to the large pressure medium quantities that flow in particular during the Formfüllphase this valve and accordingly has a low resolution. The application of the back pressure, on the ring side is possible in the known solutions only with great effort. For example, pressure converters are used for precompression. However, these require considerable device complexity.

In contrast, the invention has for its object to provide a hydraulically actuated casting unit, in which a smooth start-up with low device complexity is feasible.

This object is achieved by a hydraulically actuated casting unit having the features of patent claim 1.

According to the invention, the hydraulically actuated pouring unit has a casting cylinder for pressurizing a molding compound, the cylinder chamber of which is effective in the extension direction can be connected to a low pressure source via a control valve arrangement during a mold filling phase and to a high pressure source during a holding pressure phase. An effective in retraction annular space of the casting cylinder is acted upon by a back pressure. According to the invention, the casting unit is provided with a high-pressure pump which can be connected directly to the annular space of the casting cylinder for applying the counter-holding pressure via a counterpressure valve. Ie. , According to the invention, the ring-side counter-pressure is applied before the start of the Formfüllphase directly via a high-pressure pump, which is preferably also used to charge a high-pressure accumulator. This allows the Counter-pressure with extremely low device complexity in the range of 0 bar to the maximum pressure (for example, 400 bar) are applied. The high-pressure pump is preferably pressure-controlled.

The setting of the counter-pressure during the Formfüllphase and the holding pressure phase via a throttle valve, via which the annulus is connectable to a tank.

The counter-pressure valve, via which the high-pressure pump can be connected to the annular space of the casting cylinder, is preferably designed as a seat valve with a blocking position and a passage position.

The continuously adjustable throttle valve is also preferably designed as a continuously adjustable seat valve.

The pressure medium connection of the cylinder space of the casting cylinder with a high-pressure accumulator is preferably carried out via a continuously adjustable high-pressure control valve.

The connection to a low-pressure accumulator can be blocked via a lockable LP shut-off valve, which is preferably designed as a pilot-operated logic valve.

To relieve the pressure and to initiate the return movement of a piston, the cylinder space of the casting cylinder can be connected via a directional seat switching valve to the tank. The charging of the low-pressure accumulator preferably takes place via a low-pressure pump.

In one embodiment, a continuously adjustable directional control valve is provided for controlling the casting cylinder movement.

Other advantageous developments of the invention are the subject of further subclaims.

In the following preferred embodiments of the invention will be explained in more detail with reference to schematic drawings. Show it: .

Fig. 1 is a circuit diagram of a hydraulically operated casting unit;

Fig. 2 is a partial view of the circuit diagram of FIG. 1 and

Fig. 3 is a circuit diagram of another embodiment of a casting unit according to the invention.

In.Fig. 1 shows the hydraulic circuit diagram of a casting unit 1 of a die casting machine. The casting unit 1 has a casting cylinder 2, the piston 4 of which actuates a casting piston guided in a casting bush (not shown). The molten molding material is introduced into this casting sleeve or filling chamber and then moved by axial advance of the casting piston in the direction of a mold so that it is filled with melt during the mold filling phase described above and the melt received in the mold is compressed during the post-pressure phase and any loss is compensated. The pressure medium supply of the casting cylinder 2 via a high-pressure accumulator HD or a Niederdruck¬ memory ND and - as nocli explained in more detail below - via a low-pressure pump 6 or a high-pressure pump 8, which also charges the high-pressure accumulator HD. The Aufla¬ the low-pressure accumulator ND via the Nieder¬ pressure pump 6 or its own low-pressure pump. 9

The pressure means normally used in such pressure casting machines, for example cold chamber machines, are HFC fluids which consist of a solution of polymers in water and are classified as having a low inflammability. These aqueous solutions cause problems, particularly with regard to the pumps, with regard to the shaft seal, so that they have an increased wear. In addition, cavitations may occur in such pressure media, which further increase the wear. The Applicant has developed a high-pressure pump, by means of which pressures of up to 450 bar can also be applied in the area required for die-casting machines, even in the case of HFC liquids.

The control of the casting cylinder via the control arrangement shown in FIG. 1, which consists essentially of a continuously adjustable directional control valve 10, a back pressure valve 12, a throttle valve 14, two lockable check valves 16, 18, a LP shut-off valve 20, an HP control valve 22nd and a Wegesitzschaltventil 24 whose interconnection will be explained with reference to FIGS. 1 and 2.

According to the enlarged illustration in FIG. 2, the continuously adjustable directional control valve 10 is designed with a pressure connection P, a tank connection T and two working connections A, B and can be transferred from its illustrated spring-biased basic position electrically operated pilot valves 26, 28 in positions (a) or (b). move. The axial displacement of a valve spool of the directional control valve 10 is detected via a displacement measuring device 30. The corresponding signal is forwarded to the control of the die casting machine.

The pressure port P of the directional control valve 10 is connected via a pressure line 32 to the LP pump 6. To the tank connection T, a tank T is connected via a tank line 34. The two working ports A, B are connected via working lines 36, 38 with input ports A of the check valves 16, 18. In the illustrated basic position of the directional valve, the pressure port P is shut off and the two working ports A, B are connected via throttles to the tank T. In the positions (a) of the working port B and thus the working lines 38 to the pressure port P and, the tank port T to the working port A is connected. When reversing the directional control valve 10 in the marked with (b) positions. the pressure port P connected to the working port A and the tank port T to the working port B. The positions (a) are activated in order to extend the piston 4 of the casting cylinder 2 in the pre-filling phase, the positions marked (b) are activated when the piston 4 is returned to its retracted position.

The two check valves 16, 18 have a substantially identical structure and are each designed as a pilot-operated logic valve, wherein a 2-way cartridge valve 40 and 42 are each provided with a control cover 44 and 46, on which a pilot valve 48 and 50 is arranged, which play in the illustrated Ausführungsbei¬ each designed as a 4/2-way valve. The installation valves 40, 42 each have a Stufen¬ piston 52, 54, wherein the area ratio of the Stufenkol¬ bens 54, ie the ratio between the smaller end face and the annular surface in the stepped piston 54 is substantially larger than the stepped piston 52. Both check valves are designed with damping pins. Since the basic structure of such check valves is known, can be dispensed with further embodiments with reference to, for example, the data sheet RD 21 010 / 11.98 of the Applicant.

The spring chambers 56, 58 of the cartridge valves 40, 42 are connected in the illustrated basic position of the pilot valves 48, 50 with a control port X of the control cover 44, 46. At this control terminal X is in each case the pressure of the LP pump 6, which is tapped via a control line 60 at the output of the pump 6. By energizing a solenoid of the pilot valves 48, 50 of the spring chamber 56, 58 pressure-relieved to the tank T, which is connected via a control terminal Y to the control cover 44, 46. That is, in the basic position of the pilot valves 48, 50, the intake valves 40, 42 are respectively locked by the pump pressure acting on the large closing surface. When pressure relief of the spring chambers 56, 58, a pressure medium flow in both directions is possible, wherein the required against the spring force opening pressure, however, is different in both flow directions due to the different area ratios.

1, the connection B of the installation valve 42 is connected via a return line 62 to an annular space 64 delimited by a piston rod 4 of the piston 4. The port B of the cartridge valve 40 is via a Supply line 66 connected to a bottom-side cylinder chamber 68 of the casting cylinder 2.

From the return line 62 branches a Tankzweiglei¬ device 70 (Fig. 1), in which the continuously adjustable throttle valve 14 is arranged. This is designed as a continuously adjustable Wegesitzventil and can be aufsteuern proportional from a locked position. The feed line 66 can also be connected to the tank T via a line 71 and the directional control valve 24. The Wegesitzschaltventil 24 is biased by a spring in, its closed position. By energizing an electromagnet, it can be brought into a passage position to reduce the pressure in the cylinder chamber 68.

According to FIG. 1, the cylinder space 68 of the casting cylinder 2 is connected via a pressure channel 72 to a port A of the LP shut-off valve 20. This is also designed as a pilot-operated logic valve and has a Ein¬ building valve 74 and a on a. Control cover 76 constructed pilot valve 78. The basic structure of this check valve 20 corresponds to that of the check valves 16, 18, so that only the differences will be discussed here. This difference essentially consists in the fact that in a spring chamber 80 the greater of the pressures is applied to the working port A of the pilot valve 78 or in the pressure channel 72. This greater pressure is selected via a shuttle valve 82, whose one input is connected to the working port A of the pilot valve 78 and the other input via a control port X and a control channel 84 to the pressure channel 72. At the pressure port P of the pilot valve 78, the pressure at the other terminal B of the cartridge valve 74 is applied. This pressure is tapped by a ND line 86, via which the low-pressure accumulator ND to the port B of Built-in valve is connected. In the case in which the pressure in the pressure channel 72 corresponds approximately to the low pressure and when switching the pilot valve 78 in its switching position, is in the spring chamber 80 of the low pressure, so that the cartridge valve 74 is locked. This locking takes place with even greater pressure when applied in the pressure channel 72 of the high pressure. By switching the directional control valve 78, the one input of the shuttle valve 82 is relieved via a port Y of the control cover 16 to the tank T, so that in the spring chamber 80, the pressure at the working port A of the cartridge valve 74 is present and this for a pressure medium flow from B to A as a Check valve works. At high pressure in the pressure channel 72, the cartridge valve 74 is switched even with switched pilot valve 78 in its blocking position. Instead of the LP shut-off valve 20 shown in FIG. 1, a check valve can also be used, as described in the applicant's application filed in parallel (DE 10 2004 061 562.4).

From the pressure channel 72 further branches off to Hoch¬ pressure accumulator HD leading HD line 88, in which the HP control valve 22 is arranged. This has in principle the same structure as the throttle valve 14. It thus has a blocking position, from which it is continuously adjustable in the direction of opening via a pilot control. The stroke of a piston of the two valves 14, 22 is detected in each case via a displacement measuring system and reported to the machine control.

The high-pressure accumulator HD is charged via the high-pressure pump 8. Its outlet is connected via a counter-pressure line 90 and the counter-pressure valve 12 to the annular space 64 of the casting cylinder 2. The back pressure valve 12 is an electrically operated switching valve, which is preferably designed as a seat valve and a Spring is biased in its locked position. By energizing the electromagnet, it can be brought into its illustrated passage position in which the output of the HP pump 8 is connected directly to the annulus. That is, in this solution, in contrast to the conventional solution, the structure of the back pressure is not connected to a pressure accumulator but directly via the high-pressure pump, which must, however, be designed so that it can also apply the required pressures (for example, up to 450 bar) ,

For a better understanding of the function of vorbe¬ written circuit a casting cycle is explained.

Accordingly, the piston 4 of the casting cylinder 2 during the Vorfüllphase first approach relatively slowly and be accelerated smoothly to a relatively low speed and then proceed at a constant low speed. When switching over to the mold filling phase, the piston should then be accelerated to its maximum speed in a short time (about 10 ms) and then decelerated again. In between, a track can be at a constant high speed. It is then switched to the holding pressure phase, in which the piston passes only a comparatively small residual stroke, but at the maximum pressure (400-450 bar) is applied. After complete filling and after expiration of the holding pressure phase, the piston is moved back to its original position.

It is assumed that the piston 4 of

Casting cylinder is fully retracted and thus is at its stop. The back pressure valve 12 is opened before the beginning of the Vorfüllphase and the pressure-controlled HP pump 8 controls in the annular space 64 of Casting cylinder 2 a counter-holding pressure, which is taking into account the area ratio of the piston 4 so high that even after the opening of the LP-check valve 20 and pressurization of the cylinder chamber 68 with low pressure of the piston 4 of the casting cylinder 2 remains at its stop.

To initiate the Vorfüllphase is the

Back pressure valve 12 is closed and the LP check valve 20 is opened, so that the low pressure is switched in the extension direction of the piston 4. The two pilot valves 48, 50 are switched so that the spring chambers 56, 58 of the two check valves 16, 18 are relieved of pressure and they can be opened against the force of relatively weak closing springs. In principle, the check valve 18 could remain closed. The continuously adjustable directional control valve 10 is then moved by controlling the pilot valve 28 in one of his (b) (Figure 2) designated working positions and then controls during the Vorfüllphase the initial acceleration and then the constant, slow movement of the piston 4 of the casting cylinder with its trailing edge , which determines the cross section of an outlet throttle. This control has a higher resolution than a control with the comparatively large throttle valve 14 and is therefore faster and more accurate. The additional check valve 18 should or may be closed in this phase. The annulus pressure 68 is independent of the setting of the continuously adjustable directional control valve 10. Assuming that the melt always opposes its displacement during this Vorfüllphase the same resistance, the load for the piston 4 is always the same. Outside of an acceleration or deceleration, the pressure in the annular space 68, taking into account the area ratio, is then equal to the low pressure minus the Load pressure. If, for example, the low pressure is 150 bar and the load pressure is 30 bar, the annular space pressure at a ratio of 2: 1 is 240 bar - the annulus pressure is thus independent of the opening of the throttle valve 14.

In this Vorfüllphase the melt is relatively slowly shifted to the mold gate and over the filling opening of the pouring can through the casting piston and closed.

In the subsequent Formfüllphase the mold is filled at a high flow rate. For this purpose, the directional control valve 10 and the check valve 16 (if necessary, the check valve 18) are closed and the throttle valve 14 relatively wide open, so that the piston 4 is accelerated, possibly driven a piece at a constant speed and then braked by suitable control of the throttle valve 14 becomes. The pressure in the annular space 64 is relatively low because of the necessary acceleration of the piston 4 and the increase of the load pressure.

In the subsequent repressurization phase, the melt is compressed into the last mold cavity with high pressure and the material shrinkage compensated. In this case, the high-pressure control valve 22 is opened and the NEJ shut-off valve 20 is closed as quickly as possible, so that the piston 4 is subjected to high pressure for recompressing the melt.

The precompression in the annular space 68 and the retraction of the piston 4 is carried out by opening the Wegesitzschaltventils 24 or by adjusting the continuously variable directional control valve 10 in one of his (b) marked positions - the casting machine is ready for the next cycle. In the above-described embodiment, the movement of the piston 4 during the Vorfüllphase (acceleration and slow movement) is controlled via the outflow edge of the continuously variable directional control valve 10. As shown in Figure 3, the above-described phases can be controlled without the continuously adjustable directional control valve 10. In the embodiment shown in Figure 3, the directional control valve 10 is not present, so that the LP pump 6 is connected directly via the working line 36 to the inlet port A of the check valve 16 and the tank T via the working line 38 to the inlet port A of the check valve 18 , Incidentally, the circuit of Figure 3 corresponds to the above-described embodiment, so that no further explanation is required.

Before the Vorfüllphase the back pressure is again built up, the piston 4 is at its stop and the back pressure valve 12 is opened. About the pressure-controllable HP pump 8 is controlled in the annular space 64 of the casting cylinder 2 as in the embodiment described above, the counter-pressure.

To initiate the Vorfüllphase is the

Back pressure valve 12 is closed and the LP check valve 20 is opened, so that the low pressure in the cylinder chamber 68 is applied. The throttle valve 14 is controlled so that it opens on a fine control notch and thus controls the initial acceleration and the subsequent constant, slow movement of the piston 4 of the casting cylinder 2. The annulus pressure is, as explained in the above-described embodiment, independent of the opening of the throttle valve fourteenth In the subsequent Formfüllphase the throttle valve 14 is opened wide and accelerated according to the piston 4 and possibly driven a piece at a constant speed and then braked. The pressure in the annular space 64 is low because of the necessary acceleration of the piston 4 and the increase of the load pressure (indeterminate).

In the subsequent repressurization phase, the HP control valve 22 is opened and the LP shutoff valve 20 is closed quickly, so that the melt is re-compressed by the high pressure in the annular space 68.

The decompression and the withdrawal of the piston 4 takes place in a suitable manner, for example via the Wegesitzschaltventil 24 and the two check valves 16, 18 or via a simple, not shown directional control valve in the position of the continuously variable directional control valve 10 of Figure 1.

In the embodiment shown in Figure 1, the continuously adjustable directional control valve 10 is executed in its working positions (a) with a crossing position. In principle, the directional control valve 10 could also be designed with a differential position.

As explained, the inventive concept is not limited to the application in die casting machines, but in general in all casting unit, for example a plastic injection molding machine used. The pumps 6, 9 or all 3 pumps 6, 9, 8 can be combined to form a pump.

Instead of the memory (HD, ND) and pressure intensifier or the like can be used. Disclosed is a hydraulically operated casting unit with a casting cylinder whose effective in the extension direction cylinder during a Formfüllphase via a control valve assembly with a low-pressure accumulator and in a Nachdruckphase with a high-pressure accumulator is connectable. An effective in the retraction annular space of the casting cylinder can be acted upon before a Vorfüllphase with a counter-holding pressure. This counter-pressure is inventively applied by a high-pressure pump, which is connected via a back pressure valve directly to the annulus of the casting cylinder.

LIST OF REFERENCE NUMBERS

1 pouring unit

2 casting cylinders

4 pistons

6 LP pump

8 HD pump

9 LP pump

10 way valve

12 counterpressure valve1

14 Drosse1venti1

16 check valve

18 check valve

20 LP shut-off valve1

22 HD control valve

24 directional seated switching valve

26 pilot valve

28 Pre-control valve

30 displacement measuring device

32 pressure line

34 tank line

36 work management

38 work management

40 2-way cartridge valve

42 2-way cartridge valve

44 control cover

46 control cover

48 pilot valve

50 pilot valve

52 cartridge valve (logic)

54 cartridge valve (logic)

56 spring chamber

58 spring chamber

60 ND control line

62 return line annulus

working line

Zy1inderkolbenraum

Tank branch line

management

pressure channel

Cartridge valve

control cover

pilot valve

spring chamber

Wechse1venti1

control channel

ND line

HD line

Against pressure line

Claims

claims

1. ^• Hydraulically operated casting unit (1) with a casting cylinder (2) for pressurizing a molding compound, wherein an effective in the extension direction cylinder space (68) of the casting cylinder (2) via a control valve assembly during a Formfüllphase with a low pressure source (ND) and in a Nachdruckphase with a high pressure source (HD) can be connected, wherein an effective in retraction annulus (64) of the casting cylinder

(2) can be acted upon by a counter-pressure, characterized in that the annular space (64) for applying the

Counter-pressure via a back pressure valve (12) with a

High-pressure pump (8) is connectable.

2. casting unit according to claim 1, with a high-pressure accumulator (HD), which via the high-pressure pump (8) is chargeable.

3. casting unit according to claim 2, wherein the high-pressure pump (8) is pressure-controlled.

4. casting unit according to one of the preceding claims, wherein the annular space (64) via a throttle valve (14) with a tank (T) is connectable.

5. Casting unit according to one of the preceding claims, wherein the counter-pressure valve (12) is a switching valve with a blocking and a passage position.

6. casting unit according to claim 4 or 5, wherein the throttle valve (14) is a steadily adjustable seat valve with a locking position.

7. Casting unit according to one of the preceding claims, wherein in a with the cylinder chamber (68) of the casting cylinder (2) connected to the HD line (88), a continuously adjustable Wegesitzventil (22) is arranged with a locking position and opening position.

8. casting unit according to one of the preceding claims, wherein in a LP line (86) to a low pressure accumulator (ND), a LP-check valve (20) is arranged.

9. casting unit according to claim 7, wherein the ND-check valve (20) is a pilot-operated logic valve.

10. casting unit according to one of the preceding

Claims, wherein the cylinder chamber (68) via a directional seat valve (24) with the tank (T) is connectable.

11. Casting unit according to one of the preceding claims, with a low-pressure pump (6) for charging the LP memory.

12. Casting unit according to one of the preceding claims, with a continuously adjustable directional control valve 10, for controlling the pressure medium volume flow in the Vorfüllphase. ,