WO2006039922A2

WO2006039922A2 - Hydraulically actuated casting unit and method for controlling the same

Info

Publication number: WO2006039922A2
Application number: PCT/DE2005/001850
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: EP1836013A2; DE112005002528A5; WO2006039922A3; DE112005002528B4

Abstract

The invention relates to a hydraulically actuated casting unit comprising a casting cylinder, whose chamber, which is active in the extension direction, is supplied with a hydraulic medium via a volumetric-flow controller during a pre-filling phase. An annular chamber, which is active in the retraction direction, is connected to a hydraulic-medium sink via a butterfly-valve assembly, which determines the pressure in the annular chamber. The invention also relates to a method for controlling a casting unit of this type.

Description

description

Hydraulically actuated pouring unit and method for driving the same

The invention relates to a hydraulically operated casting unit according to the preamble of patent claim 1 and a method for driving such a casting unit.

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, with the molten or doughy molding material being introduced into a casting bushing in a first prefilling phase and then being displaced comparatively slowly in the direction of the gate 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. No. 5,622,217 shows a casting unit of a pressure casting machine in which pressure is applied to the molding composition by means of a casting cylinder. The casting cylinder is controlled via 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, mold 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 Ausfahrgeschwindig¬ speed of the casting cylinder is controlled on the drain side via a control valve, which opens a connection to the tank or.

For a high-quality casting process, it is necessary for the casting cylinder to move smoothly during the prefiltering phase and then to move at comparatively slow speed, so that the molding material is drawn in correspondingly "gently" and conveyed towards the cavity. For this purpose, when the low-pressure accumulator is first connected, a counterpressure must be built up on the outflow side of the casting cylinder, which prevents compression of the ring side when the pressure accumulator on the piston side is switched on. Hier¬ by a Anfahrrucken is avoided and the movement can be controlled by the amount of the returning Druck¬ targeted. The application of the Gegen¬ pressure on the ring side is possible in the known solutions only with great effort. Thus, for example, pre-compression pressure multipliers (multipliers) are used, with which the counter-pressure on the Stan¬ genseite is set. However, these require a considerable expenditure on equipment and it has been found that with such a solution the speed ability of the casting cylinder is not controllable with the required accuracy.

In contrast, the invention has the object zugrun¬ de to provide a hydraulically actuated casting unit and a Ver¬ drive to provide their control in which a jerk-free start with little device-technical effort is feasible.

This object is achieved by a hydraulically actuated casting unit having the features of patent claim 1 and a method having the features of patent claim 11.

According to the invention, a volume flow control of the pressure medium volume flow to the bottom side of the casting cylinder takes place, so that its extension speed and thus the acceleration of the melt in the direction of the mold gate are very precisely controlled. The backpressure in the annular space of the casting cylinder is adjusted via a throttle valve arrangement, which is arranged in the pressure medium flow path between the annular space and a tank or other pressure medium valley. Such an activation makes it possible to start the casting cylinder in the prefilling phase and in the transition to the mold filling phase without starting pressure, with the expenditure on device technology being minimal compared with the solutions described at the outset.

In a particularly preferred embodiment, the volume flow control of the pressure medium to the bottom side (cylinder space) follows the casting cylinder via a regulated variable displacement pump.

In a low-pressure line between a low-pressure accumulator and the cylinder chamber, a - preferably pre-controlled - low-pressure shut-off valve can be provided be. In its non-return function in the closing direction, this is acted upon by the pressure in the cylinder chamber and in the opening direction by the low pressure.

In a concept according to the invention, a comparatively low counterpressure is initially set during the startup and during the process of the casting cylinder in order to reduce the energy consumption and the pressure drop across the throttle valve arrangement in the pressure medium flow path between the annular space and the pressure medium sink is small to keep.

In a control concept according to the invention, the counter-pressure during the changeover to the mold filling phase is initially adjusted so that the LP shut-off valve is still kept closed against the pressure in the low-pressure accumulator. The pressurization of the casting cylinder with low pressure then takes place by rapidly controlling the throttle valve arrangement, so that the pressure in the annular space decreases correspondingly quickly and the LP shut-off valve opens the connection between the cylinder space of the casting cylinder and the low-pressure accumulator.

In an alternative control concept, the throttle valve arrangement is opened relatively quickly to initiation of the mold filling phase and the connection from the low-pressure accumulator to the cylinder space of the casting cylinder is simultaneously controlled via the LP shut-off valve. That is, in this variant, virtually the control of the throttle valve arrangement is switched from pressure to speed control. The throttle valve arrangement is already further opened during the transition from the pre-charge phase to the mold filling phase due to the lower pressure gradient than in the previously described concept and can thus be opened substantially more quickly. This variant also makes it possible to use the throttle valve arrangement instead of a servo pilot valve use a proportional pilot valve.

The throttle valve arrangement can be designed as a continuously adjustable seat valve with blocking position, which can be executed with or without fine control edge.

Other advantageous developments are the subject of further subclaims.

In the following, a preferred embodiment of the invention with reference to a schematic drawing erläu¬ tert. This single drawing shows a circuit diagram of a hydraulically operated casting unit.

In the single figure, the hydraulic circuit diagram ei¬ ner casting unit 1 of a die casting machine is shown. The casting unit 1 has a casting cylinder 2, the piston 4 actuates a guided in a casting sleeve, not shown casting piston. The molten molding material is introduced into this casting box 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 absorbed in the mold is compressed during the holding pressure phase and possible shrinkage is compensated.

The pressure medium supply of the casting cylinder 2 via a high pressure accumulator HD or a Niederdruck¬ memory ND and, as will be explained in more detail below, via a variable displacement pump 6, which also charges the high pressure accumulator HD and the low pressure accumulator ND.

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 flame retardant. 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 in the range required for die-casting machines can be applied up to 450 bar even in the case of HFC liquids.

The control of the casting cylinder via the control arrangement shown in Figure 1, which consists essentially of a directional control valve 10, a back pressure valve 12, a throttle valve 14, a LP shut-off valve 20, a high-pressure control valve 22, a directional seat switching valve 24, an LP loading valve 26th , an HP charging valve 28, an LP pressure relief valve 30 and an HP pressure relief valve 32.

Pressure medium is sucked from a tank T via the volume-flow-controlled variable displacement pump 6 and conveyed into a pressure line 34, which is connected to an input port A of the directional control valve 10 designed as a directional seated switching valve. This is biased by a spring in its illustrated locking position. By actuating the feedforward control of the directional control valve 10, this can be switched to a switching position in which a pressure medium flow from the input connection A to a working connection B is made possible and blocked in the opposite direction. This working port B is connected via a working line 36 to a bottom-side cylinder chamber 38 of the casting cylinder 2. This cylinder chamber 38 is connected via an LP line 40 to an input terminal A of the LP blocking valve 20, whose working connection B is connected by means of an LP storage line 42 is connected to the low-pressure accumulator ND.

From the LP line 40 branches off a line 44, in which the Wegesitzschaltventil 24 is arranged, which is biased by a spring assembly in its blocking position and in a passage position is bring¬ bar, in which the conduit 44 is connected to the tank T. in order, for example, to allow decompression of the cylinder space 38.

The LP shut-off valve 20 is designed as a pilot-operated logic valve, wherein a 2-way cartridge valve 46 is provided with a control cover (not shown) which carries a pilot valve 48, which is designed as a 4/2-way valve in the illustrated embodiment.

The cartridge valve 46 has a stepped piston, which is designed with a surface difference and which is biased by a spring against a seat. The Stufen¬ piston 50 is designed with a through hole, via which the pressure in the LP line 40 also in a spring chamber 54 of the cartridge valve 46 abuts. An annular end face 56 of the stepped piston 50, which is effective in the opening direction, can be acted upon by the pilot valve 48 with an opening pressure, which is tapped off via a pilot line 58 at a connection T of the pilot control valve 48. In the exemplary embodiment shown, this has a shut-off connection P and two working connections A, B, one working connection B via a tank line 60 to the tank T and the other working connection A via an LP control line 62 to the LP Memory line 42 is connected. In its spring-biased basic position, the connection T is connected to the connection B, so that the ring end face 56, which is effective in the opening direction, acts on the tank pressure. is beating. In the spring-biased basic position of the pilot valve 48, the cartridge valve 46 is locked by the force of the spring and acting in the closing direction pressure in the LP line 40.

By switching the pilot valve 48 to its switching position, the working port A is connected to the port T, so that the annular end face 50 is acted upon by the low pressure. The smaller Stirnflä¬ surface of the stepped piston 50 is acted upon by the pressure in the LP line 40, the the spring chamber 54 bounding the rearward larger end face is subjected to the same pressure, so that the ring end face 56 corresponding, acting in the closing direction surface difference with the pressure in the LP line 40 is acted upon. Accordingly, the cartridge valve 46 may be opened when the pressure in the LP conduit 40 and the pressure equivalent of the spring is less than or equal to the low pressure ND acting on the annular end surface 56. The basic structure of such installation valves 20 is known, so that it is possible to dispense with further embodiments with reference to spielsweise the data sheet RD 21 010 / 11.98 of the applicant.

In the switching position of the pilot valve 48, the cartridge valve 20 works for a pressure medium flow from B to A like a check valve. At high pressure in the LP line 40, the cartridge valve 20 is switched even when umge¬ switched pilot valve 48 in its blocking position. Instead of the ND check valve 20 shown in the figure, a check valve can also be used, as described in the applicant's application DE 10 2004 061 562.

From the pressure line 34 branches off an LP charging line 64, in which the designed as Wegesitzschaltventil ND Storage charging valve 26 is arranged. This is biased by a spring assembly in its illustrated blocking position and can be switched to a through position in which a flow of pressure medium from a port A to a port B allows and is locked in Gegen¬ direction, so that the ND charging line 64 via the ND Accumulator charging valve 26 is connected to a ND charging line 66 opening into the ND storage line 42. The pressure in the ND storage line and the ND charging channel 66 is limited via the LP pressure relief valve 30.

In the cylinder chamber 38 of the casting cylinder 2 further opens an HD memory line 68, in which the HD control valve 22 is arranged. This is designed as a continuously adjustable Wegesitzventil and can be proportionally aufsteuern from a locked position to open a connection between the HP storage line 68 and connected to the high-pressure accumulator HD HD channel 70, so that the bottom side of the casting cylinder 2 in the Nachdruckphase with High pressure can be acted upon. An annular space 71 of the casting cylinder 2 can be connected to the tank T via a drain line 72 and the continuously adjustable throttle valve 14. This has in principle the same structure as the high-pressure control valve 22 and is biased in its Darge presented locking position and can be proportionally adjusted via the pilot control to open the connection to the tank T and to regulate the pressure in the annular space 72 according to the set flow cross-section ,

From the pressure line 34 further branches off an HD charging line 74, which leads to a port A of the HD Spei¬ cherladeventils 28 whose other terminal B is connected by means of an HD charging channel 76 to the high-pressure accumulator HD. The high-pressure accumulator is protected by the HD pressure relief valve 32. The HD storage Deventil 28 has the same structure as the LP storage loading valve 26 and can be brought from a spring biased locking position in a passage position in which a pressure fluid flow for loading the high-pressure accumulator from the HD charging line 74 to the HD charging channel 76 is enabled.

The variable displacement pump 6 is designed so that the high-pressure accumulator can be charged up to 450 bar in the area required for die casting machines. In principle, however, a separate high-pressure pump for charging the high-pressure accumulator HD and a separate pump for charging the low-pressure accumulator ND could also be provided.

In the illustrated embodiment branches from the HD charging line 74 from a back pressure line 78, in which the back pressure valve 12 is arranged, the zip in the Prin¬ the same structure as the two aforementioned charging valves 26, 28 has. It is biased into a blocking position and can be a passage position um¬ switch, in which a flow of pressure medium from the HD charging line 74 to the annulus 72 is made possible, so that for example the piston 4 can be retracted.

For a better understanding of the function of the vorgesehe¬ nen circuit a casting cycle is explained.

Accordingly, the piston 4 of the casting cylinder 2 should initially travel relatively slowly during the prefilling phase and be accelerated without jerk to a comparatively low speed and then be moved at a constant low speed or in accordance with a speed profile. When switching to the mold filling phase, the piston is then accelerated in a short time (about 10 ms) almost to its maximum speed and then again be slowed down. In between, a track can be at a constant high speed. Subsequently, it is switched to the holding pressure phase, in which the piston travels only a comparatively small residual stroke, but at the same time is subjected to the maximum pressure (400-450 bar). 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 the casting cylinder is completely retracted and thus located at its stop. No counterhait pressure in the annular space 71 must be built up via the counter-pressure valve 12 in this solution, since the Ausfahrge¬ speed can be regulated via the controlled pump 6. In special operating conditions, however, it would be possible to pressurize the annular space before starting up via the opened counter-pressure valve 12 and the pump 6.

To initiate the Vorfüllphase the directional control valve 10 is switched to its switching position.

By suitably adjusting the volume flow via the controllable pump 6, the casting cylinder 2 is approached pressure-free in the inlet control, then accelerated and the melt is pushed with a velocity profile to the forming section. In the process in this Vorfüllphase the variable displacement pump 6 controls the speed. By suitable control of the throttle valve 14 in the course of the casting cylinder 2, the back pressure is regulated. In this case, according to the invention when starting the casting cylinder 2 and the method during the Vorfüllphase a comparatively low back pressure (for example 30-50 bar) set to reduce energy consumption and to keep the pressure drop at the throttle valve 14 small. Towards the end of the prefilling phase, according to a concept according to the invention, the pressure in the annular space 71 of the casting cylinder 2 is increased by reducing the opening cross-section of the throttle valve 14 in the drain line 72 such that a pressure in the cylinder chamber 38 which is somewhat higher than the pressure in the low-pressure accumulator ND (for example, 150 bar). After this Druckhόhung in the annular space 71, the pilot valve 48 is switched against the force of its spring, so that the annular end surface 56 is acted upon by low pressure. Since the pressure in Zylin¬ derraum 38 and thus in the LP line 40 is set slightly higher than the low pressure ND, the Einbauven¬ valve 20 is still closed by its non-return function, so that no jerking occurs by switching to low pressure. During the Formfüllphase (shot), the throttle valve 14 in the drain line 72 is relatively quickly opened (torn open) so that the pressure in the annular space 71 drops rapidly and also the pressure in the cylinder chamber 38 and the LP line 40 sags under the low pressure and the cartridge valve 46 opens, so that in the cylinder chamber 38 is applied low pressure and the casting cylinder 2 is accelerated and extends at high Geschwin¬ speed. Depending on the requirements of the control accuracy, the throttle valve 14 can be used with or without a fine control edge.

In an alternative control concept, the pressure in the cylinder chamber 38 for initiating the mold filling phase does not have to be increased slightly above the low pressure, as in the previously described variant. The jerk-free changeover is achieved in that the LP shut-off valve 20 is opened by switching the pilot valve 48 and at the same time the throttle valve 14 in the Ablauflei¬ device 72 is opened, so that practically with respect to the throttle valve 14 of a pressure in a Geschwin¬ digkeitsregelung is switched. Because the throttle valve 14 is already opened further during the transition from the prefilling phase to the mold filling phase due to the low pressure gradient than in the previously described control concept, it can be brought much more quickly into its opening position. In principle, instead of a servo pilot valve for the throttle valve 14, a simpler proportional pilot valve can be used.

In the mold filling phase, the mold is filled at high flow rate. In the subsequent post-pressure phase, the melt is compressed into the last cavity of the mold with high pressure and the material shrinkage is compensated. In this case, the high-pressure control valve 22 is opened and the LP 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 closing of the LP check valve 20 is assisted by the high pressure in the LP line.

The decompression in the cylinder chamber 68 and the retraction of the piston 4 is effected by opening the Wegesitzschaltven- tils 24 and the back pressure valve 12 - the caster is ready for the next cycle.

The charging of the two memories HD, ND is effected in each case by means of the variable displacement pump 6, wherein the high-pressure accumulator HD is charged with the high-pressure accumulator 28 and the low-pressure accumulator ND is charged with the low-pressure accumulator valve 26 in order to charge the high-pressure accumulator HD Return position is switched. The maximum pressure of the two memories HD, ND is limited by the associated pressure limiting valves 32 and 30, respectively.

With regard to the further details for the control of die casting machines, the sake of simplicity on the Priority applications of the present application verwie¬ Sen, the disclosure of which belongs to the description of the present application.

In the above-described embodiment according to the single figure, a variable displacement pump 6 is used to regulate the pressure medium volume flow to the casting cylinder in the prefilling phase and to fill the two memories HD, ND. Instead of such a control pump, the pressure medium volume flow can also be impressed in other ways. Furthermore, in principle, instead of the two memories HD, ND, pressure translators or the like can also be used.

Disclosed is a hydraulically actuated casting unit with a casting cylinder, the cylinder chamber in the extension direction is supplied with pressure medium during a Vorfüllphase via a volume flow control unit, wherein an effective in retraction annular space via a throttle valve arrangement verbun¬ with a pressure medium sink, wherein the throttle valve arrangement of the Pressure in the annulus is determined. Further disclosed is a method for driving such a casting unit.

LIST OF REFERENCE NUMBERS

1 pouring unit

2 casting cylinders

4 pistons

6 variable displacement pump

10 way valve

12 back pressure valve

14 Drosse1venti1

20 LP shut-off valve1

22 HD control1

24 directional seated switching valve

26 LP storage charge valve

28 HD storage charging valve

30 LP pressure relief valve1

32 HD pressure relief valve1

34 pressure line

36 work management

38 cylinder space

40 ND line

42 ND storage line

44 line

46 2-way cartridge valve

48 pilot valve

50 graduated piston

52 through hole

54 spring chamber

56 ring end face

58 pilot control line

60 tank line

62 ND control line

64 ND charging cable

66 ND charging channel

68 HD memory line

70 HD channel 71 annulus

72 Drain line 74 HD charging line 16 HD charging channel

78 back pressure line

Claims

claims

1. A hydraulically operated casting unit (1) with a casting cylinder (2) for pressurizing a molding compound, wherein an effective in the extension direction cylinder space (38) of the casting cylinder (2) during a Formfüllphase with a low pressure source (ND) and in a Nachdruckphase with a high pressure phase ( HD) is connectable and an effective in retraction annular space (71) of the casting cylinder (2) can be acted upon by a flow control unit (6) for setting a pressure medium volume flow to the effective in the direction of extension cylinder chamber (38) and with a throttle valve assembly (14) in the pressure medium flow path between the annular space (71) and a pressure medium sink (T) for setting a Gegenhaiterucks in the annular space (71).

2. casting unit according to claim 1, wherein the Volu¬ menstromregeleinheit a variable displacement pump (6).

3. casting unit according to claim 1 or 2, wherein in a the low-pressure accumulator (ND) with the cylinder chamber (38) connecting ND line (40, 42) an LP shut-off valve (20) is arranged.

4. casting unit according to claim 3, wherein the LP-check valve (20) is pilot-controlled.

5. casting unit according to one of the preceding patent claims, wherein the counter-holding pressure in the annular space (71) is increased approximately at the end of the pre-filling of a low Gegenhalte¬ pressure to a higher counter-holding pressure.

6. casting unit according to claim 5, wherein at the end of the Vorfüllphase the counter-pressure in the annular space (71) is adjustable such that the pressure in the cylinder chamber (38) is slightly above the low pressure, so that the LP shut-off valve (20) remains closed ge in its non-return function.

7. casting unit according to claim 5, wherein at the end of the Vorfüllphase the throttle valve assembly (14) open and about simultaneously via the LP shut-off valve (20), the connection between the low-pressure accumulator (ND) and the cylinder chamber (38) is aufsteuerbar.

8. casting unit according to one of the preceding patent claims, wherein the throttle valve assembly (14) is a continuously adjustable pilot operated poppet valve with blocking position.

9. casting unit according to claim 8, wherein the Dros¬ selventilanordnung is executed with Feinsteuerkerben.

10. casting unit according to claim 8 or 9, wherein the throttle valve assembly has a servo or Proportionalpilot- valve.

11. A method for controlling a casting unit according to one of the preceding claims, wherein an effective in the extension cylinder space (38) of a Gießzy¬ Linders (2) during a Formfüllphase with a Nieder¬ pressure source (ND) and during a Nachdruckphase with a high pressure source (HD) is connected and an effective in retraction annulus (71) of the casting cylinder (2) is acted upon with a Gegenhaeastruck, characterized in that during a Vorfüllphase the pressure medium flow to the cylinder chamber (38) and the back pressure in the annular space (71) are regulated.

12. The method according to claim 11, wherein the counter pressure in the annular space (71) is increased towards the end of the pre-filling phase.

13. The method according to claim 11, wherein at the end of the Vorfüllphase the pressure in the annular space (71) quickly verrin¬ siege and substantially simultaneously the cylinder space

(38) is subjected to low pressure.