Hydraulic Casting Unit

Abstract

To provide a casting unit comprising a differential circuit and a pressure booster, which enables an optimal casting process with less device technology.SOLUTION: A liquid pressure type casting unit has a casting cylinder 10 formed as a differential cylinder, and a piston 11 of the casting cylinder defines a bottom space 14 on a bottom side, and an annular space 15 on a piston rod 12 side. Further, the casting unit is provided with a low voltage source 56 that can be connected to the bottom space particularly via a shutoff valve device 41. Furthermore, the casting unit is provided with a liquid pressure type booster 24 as a booster unit, and the booster is designed to support the advance movement of the casting cylinder during a pressure holding phase, especially to increase the pressure in the bottom space.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The invention relates to a hydraulic casting unit as defined in the preamble of patent claim 1.

[0002] The basic design of such a casting unit, which is used in a primary molding machine such as an injection molding machine, a die casting machine or a thixomolding machine, is disclosed, for example, in the publication DE 10 2017 220 836 A1, which is attributable to the applicant. According to this, the casting unit has a double-acting casting cylinder, the piston of which defines a bottom space on the piston bottom side and the end face of the casting cylinder on the piston rod side defines an annular space. In this known design, during the pre-filling and mould filling phases, the bottom space is first connected to a low-pressure accumulator, for example via a two-way, two-position seat valve designed as an active logic valve, the annular space of the casting cylinder being connected to the bottom space via a regulating valve, so that the pressure medium displaced from the contracting annular space during the pre-filling phase is fed to the expanding bottom space via said regulating valve in the differential or regenerative circuit. During the mold filling phase, the pressure medium connection to the tank can be opened via the tank-side regulating valve for injection, while the regulating valve between the piston space and the annular space can be closed. During the pressure holding phase, the bottom space is then connected to the high-pressure accumulator via another regulating valve, while the pressure medium connection to the low-pressure accumulator is closed via the active logic valve. During this pressure holding phase, the pressure medium connection between the annular space and the tank remains open via the tank-side regulating valve, so that the melt in the cavity is compressed under high pressure and any material shrinkage is compensated for.

[0003] The basic design of the active logic valve used in this casting unit is known from the publication DE 10 2005 035 170 C1.

[0004] The casting unit disclosed in the publication DE 10 2017 221 500 A1 is not provided with a differential or recuperation circuit. During the pre-filling and mould-filling phases, a low-pressure accumulator feeds the bottom space via an active logic valve, opening the outlet regulating valve, so that the piston of the casting cylinder advances at a predefined speed. During the transition from the pre-filling to the mould-filling phase, this outlet regulating valve is opened further, so that the piston is accelerated and advances at a comparatively high speed. The pressure medium displaced from the contracting annular space flows via the outlet regulating valve towards the outlet accumulator and then, when a predefined pressure is reached in the outlet accumulator, flows out via a check valve or a throttle towards the tank. This reduces the maximum volumetric flow rate to the tank and thus the associated vortexes. After the end of the pre-filling phase, the pressure intensifier (multiplier cylinder) is accelerated to introduce a pressure-holding phase, whereby a boost in the bottom space is created. In this case, the acceleration of the intensifier is achieved in that the annular space of the intensifier is connected via a regulating valve with a low-pressure accumulator or tank.

[0005] The object of the present invention is, in contrast, to provide a casting unit with a differential and a pressure booster, which allows an optimized casting process with minimal installation engineering expenditure.

[0006] This problem is solved by a casting unit having the features of claim 1.

[0007] Advantageous refinements of the invention are set forth in the subclaims.

[0008] The hydraulic casting unit according to the invention, preferably designed for use in an injection molding machine, die casting machine or thixomolding machine, has a casting cylinder configured as a differential cylinder, the piston of which defines a bottom space on the bottom side and an annular space on the piston rod side. Furthermore, a low pressure source is provided which can be connected to the bottom space, in particular via a shut-off valve device. Furthermore, a hydraulic pressure intensifier is provided as a boosting unit, which is designed to support the advancing movement of the casting cylinder during the pressure holding phase, in particular to increase the pressure in the bottom space. The casting unit further has a regulating valve device which connects the annular space of the casting cylinder to the bottom space via a first pressure medium flow path in the form of a recuperation circuit, in particular during the pre-filling phase, and which connects the annular space to a pressure medium reservoir, in particular a tank, via a second pressure medium flow path, in particular during the mould filling phase ("injection"), and which is designed to control the opening of a third pressure medium flow path which opens into the pressure space of the pressure intensifier, in particular during the pressure holding phase when the pressure intensifier is activated. According to the invention, the valve device is divided into three independently operable switching and proportional valves, of which a first switching and proportional valve is arranged in the first pressure medium flow path, a second switching and proportional valve in the second pressure medium flow path and a third switching and proportional valve in the third pressure medium flow path.

[0009] Due to this separate configuration, the regeneration process, the injection and the boosting pressure can be controlled or adjusted independently of one another, so that the casting process can be optimized and controlled or adjusted with minimal equipment engineering effort.

[0010] In the present invention, for the realization of the basic functions of the casting unit - pre-filling phase, regeneration, mould filling phase and pressure holding phase - three switching and proportional valves are provided which are simple in terms of device technology and can be operated independently of one another. The regeneration procedure of the casting cylinder allows the use of a smaller accumulator as low-pressure source. Due to the smaller pressure difference during the regeneration function, less cavitation and therefore less wear occurs. The use of a smaller first switching and proportional valve, which is also better separated during pre-filling, allows the movement of the casting cylinder to be performed with greater precision.

[0011] In one refinement, the primary piston of the intensifier defines with its larger end face acting in the increasing direction the pressure space of the intensifier and with its smaller end face acting in the opposite direction the counter-pressure space of the intensifier, in particular the annular space of the intensifier.

[0012] In one refinement, the counterpressure space of the intensifier can be fluidly connected via a third pressure medium flow channel with the pressure medium reservoir, whereby a controlled outflow during the pressure holding phase is achieved and whereby the intensifier can be activated.

[0013] In contrast to this, in one variant, in one refinement, the pressure space of the pressure intensifier can be fluidly connected to a pressure medium source via a third pressure medium flow path, so that the pressure intensifier can be flow-controlled and thus operated during the pressure holding phase.

[0014] The switching-proportional valve is preferably configured with a closed position, in which the respective pressure medium flow path is blocked or controlled to be closed.

[0015] In one refinement, a pressure relief channel is provided or can be formed which leads from the bottom space of the casting cylinder via a first and a second switching and proportional valve to the pressure medium tank, which can be opened or formed via the two switching and proportional valves, in particular as a function of the pressure detected in the bottom space or the pressure gradient over time.

[0016] In one refinement, at least one of the switching-proportional valves, at least the first and second switching-proportional valves, preferably all three switching-proportional valves, are configured as two-way switching-proportional valves, in particular as two-way, two-position flow control valves. Preferably, each switching-proportional valve or each two-way, two-position flow control valve is pilot-controlled, in particular electrohydraulically pilot-controlled.

[0017] In one refinement, at least two of the switching and proportional valves, preferably all, are configured identically, in particular identically, with respect to at least one characteristic. The use of identical, or even in extreme cases identical, switching and proportional valves represents a particularly advantageous arrangement from the standpoint of construction, procurement, manufacture, maintenance and operation, and especially from the standpoint of costs.

[0018] In this case, the term same configuration may relate to one or more characteristics of the switching and proportional valve, e.g. type, connection, number of connections, diameter of the connection, connection diagram, type of actuation, valve body, stroke, connection time, etc.

[0019] The term identical configuration can alternatively or additionally also relate to the nominal size. In this respect, it has proven to be advantageous if the first switching and proportional valve has a smaller nominal size than the second and third switching and proportional valves, since the pressure medium volume flow in the first pressure medium flow line is relatively small compared to the pressure medium volume flow in the second and third pressure medium flow lines.

[0020] In one refinement, pressure regulation in the bottom space is realized by means of a pressure relief channel and a first and a second switching and proportional valve. Advantageously, in this way pressure peaks or pressure overshoots in the bottom space can be regulated and / or reduced.

[0021] The pressure boost during the pressure holding phase is primarily achieved via the booster, by means of the third switching and proportional valve in the adjusting position, in particular by means of the outflow control or outflow regulation from the annular space of the booster and the open position of the second switching and proportional valve, i.e. by means of the pressure medium connection between the annular space of the casting cylinder and the tank.

[0022] In one refinement, the pressure space of the intensifier can be connected for its acceleration via a shutoff valve or the like to a low-pressure source, in particular a hydraulic accumulator. In this case, a second pressure medium flow path leading from the annular space of the intensifier to a pressure medium reservoir / tank is controlled to be open via a third switching and proportional valve.

[0023] In one variant of the invention, the shut-off valve device is designed as a two-way, two-position active logic valve with a pilot valve, which shuts off or opens the pressure medium connection between the low-pressure accumulator and the bottom space of the casting cylinder and allows a very fast and reliable closing control during the pressure build-up during the dwelling phase, so that the mold filling phase can be ended very quickly and precisely.

[0024] In one alternative embodiment, the shut-off valve device is formed with a shut-off valve arranged downstream of the low pressure source instead of an active logic valve, in which case a check valve is arranged between the shut-off valve and the bottom space of the casting cylinder. The shut-off valve opens and closes the connection to the casting cylinder. The check valve closes the connection during pressure build-up during phase III or the pressure holding phase.

[0025] The outflow control or outflow regulation may alternatively take place via a valve which can be displaced by a servomotor.

[0026] In one refinement, for returning the casting cylinder and / or the intensifier and / or for applying preload to the casting cylinder and / or the intensifier, the casting unit has a hydraulic pump configured as a variable displacement pump or as a fixed displacement pump with a servomotor and a servo converter or as a variable displacement pump with a three-phase motor and a frequency converter or as a variable displacement pump with a three-phase motor.

[0027] In this case, by applying a preload to the annular space of the casting cylinder, start-up shocks when introducing the prefilling stage are avoided.

[0028] In one preferred refinement, the casting unit therefore comprises a device for applying a preload to the piston side and to the annular side of the casting cylinder and / or the intensifier.

[0029] The device for applying the preload is preferably formed by a hydraulic pump and a correspondingly arranged shut-off and preload valve.

[0030] In one refinement, the shut-off and preload valve is designed in such a way that a pressure connection of the hydraulic pump can be connected via the shut-off and preload valve to the annular space of the intensifier and / or to the annular space of the casting cylinder and / or to the bottom space of the casting cylinder, in which case pressure medium is fed into the annular space of the casting cylinder in order to preload or return the casting cylinder, in particular with the third switching and proportional valve closed.

[0031] In one refinement, the shut-off and pre-load valve is configured as a 4-way 3-position valve with at least a shut-off position, and furthermore has a first switching position in which the annular space of the booster and the annular space of the casting cylinder are connected to a pressure connection of the hydraulic pump, and in the first switching position the first pressure medium flow path is connectable or connected to a pressure medium reservoir, preferably via an openable check valve.

[0032] In one refinement, the shut-off and pre-load valve has a second switching position in which the bottom space of the casting cylinder is connected to a pressure connection of the hydraulic pump, and in the second switching position a pre-load conduit which in the first switching position can connect the annular space of the booster and the annular space of the casting cylinder to the pressure connection of the hydraulic pump is connected to the pressure medium tank.

[0033] In the following, one preferred embodiment of the invention is explained in more detail on the basis of a schematic drawing. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a diagram showing the principle of a casting unit. [Diagram 2] FIG. 2 shows a simplified hydraulic circuit of one embodiment of a casting unit.

[0035] In FIG. 1 the main mechanical components of a hydraulic casting unit 1 according to the invention of a die casting machine are shown.

[0036] According to this, the casting unit 1 has a casting cylinder 10 configured as a differential cylinder, whose piston 11 is correspondingly configured with a piston rod 12. Together with a housing 13 of the casting cylinder, the piston 11 defines a bottom space 14 on the bottom side and an annular space 15 through which the piston rod 12 passes. At the end of the piston rod 12 projecting from the housing 13, a casting piston 16 is attached which penetrates into an injection chamber 18 of a casting sleeve 17. In the casting sleeve 17, a filling opening 19 is located for the liquid or pasty molding material, hereinafter referred to as melt, which is to give rise to the workpiece to be molded. The casting sleeve 17 is attached to a mold 20, which generally consists of a movable mold half and a fixed mold half. The two mold halves define a mold cavity 21, also called a cavity, which is configured corresponding to the geometric shape of the workpiece to be processed. The injection chamber 18 opens into the mold cavity 21 via a pouring passage 22 .

[0037] Such a casting unit 1 is used to bring the melt into a mould 20, where high speeds are required for filling due to the rapid solidification process, and then high pressures are required to completely fill and compress the mould 20 and to accommodate the material shrinkage upon solidification.

[0038] In an embodiment according to the invention, shown in Fig. 2, a pressure intensifier 24 is arranged as a multiplier unit - also called multiplier cylinder - corresponding to the casting cylinder 10, which pressure intensifier 24 is formed, for example, as a differential cylinder. A primary piston 26 defines a pressure space 28 of the pressure intensifier at the bottom, a piston rod 30 passes through a counter-pressure space of the pressure intensifier in the form of an annular space 32. The construction of such a pressure intensifier 24 is known and therefore no further explanation is necessary.

[0039] The pressure medium supply of the illustrated casting unit 1 takes place via a hydraulic pump 34, which in the illustrated embodiment is designed as a fixed displacement pump and is driven by a speed-controlled electric motor 36, which is designed, for example, as a servomotor with a servo converter or as a three-phase motor with a frequency converter. The pressure connection of the hydraulic pump 34 is connected via a pump line to a shut-off and preload valve 42, which is designed as a 4-way, 3-position directional control valve. In its basic position, which is shown and is centered by a spring, or in an intermediate position, the shut-off and preload valve 42 shuts off the pressure medium connection between the hydraulic pump 34 and the bottom space 14. By means of two switching magnets and a hydraulic pilot control, two flow positions a, b can be switched, in which the shut-off and preload valve 42 together with the hydraulic pump 34 fulfills the function of a preloading device for the casting cylinder 10 and the pressure intensifier 24, as will be explained further below.

[0040] The annular space 15 of the casting cylinder is connectable to the bottom space 14 via a first pressure medium channel 23 and a first switching and proportional valve 27 arranged therein. In the illustrated embodiment, the first switching and proportional valve 27 is designed as an electrohydraulic pilot-controlled 2-way 2-position switching and proportional valve, known from the Applicant's portfolio as 2WRCE-4X, with a spring-loaded base or shut-off position, configured as a flow control valve. Upon initiation of the electrohydraulic pilot control, the opening cross section of the valve 27 is controlled to open in response to a control signal, and the annular space 15 is connected with the bottom space 14 for the recuperation procedure.

[0041] The annular space 15 of the casting cylinder 10 can furthermore be connected to the tank T via a second pressure medium flow channel 44, in which a second switching and proportional valve 46 is arranged. The second switching and proportional valve 46 corresponds to a valve type having the same design as the first switching and proportional valve 27, but with a larger nominal dimension, since the pressure medium volume flow through the second switching and proportional valve 46 is greater in the regeneration sequence than the pressure medium volume flow through the first switching and proportional valve 27. The second switching and proportional valve 46 is likewise designed as an electrohydraulic pilot-controlled 2-way, 2-position flow control valve, which in its basic position blocks the pressure medium connection to the tank T and, upon initiation of the electrohydraulic pilot control, opens the opening cross section to the tank T depending on a control signal.

[0042] The second pressure medium flow path 44 is fluidly connectable to a preload conduit 50 via a check valve 48 which opens into the second pressure medium flow path 44. The preload conduit 50 is blocked in the spring-preloaded basic position of the check valve 48.

[0043] The pump conduit 40 opens into the third pressure medium flow path 25 between the third switching and proportional valve 29 and the annular space 32 of the intensifier. In the pump conduit 40, between the branch of the pump conduit 40 and the preload conduit 50 and said opening, a check valve 70 is arranged, which opens into the annular space 32 of the intensifier. Both check valves 48, 70 are adapted to open when the pressure in the pump conduit 40 and in the preload conduit 50 is sufficient, so as to feed into the annular space 15 of the casting cylinder 10 and into the annular space 32 of the intensifier 24. In this way, the casting cylinder 10 and the intensifier 24 can be returned so that the counter pressure required for preloading them can be created in the respective annular spaces 15, 32. For this purpose, the shut-off and pressure valve 42 has a first switching position a, in which the pressure connection P of the hydraulic pump 34 is connected to the pump line 40 and to the pressure line 50, and the first pressure medium line 23 can be or is connected via an openable check valve 72 to the pressure medium tank T.

[0044] The pressure at the outlet of the hydraulic pump 34 itself may be limited, as is well known, via a pressure limiting valve opening to tank T.

[0045] In the present invention, the pressure intensifier 24 and the casting cylinder 10 are arranged in correspondence with a valve arrangement divided into three independently operable flow control valves 27, 46 and 29, each of which is configured as a constantly displaceable, electrohydraulic pilot controlled valve having two connections.

[0046] A pilot-controlled 2-way, 2-position integrated seat valve is formed as the active logic valve 41. The pilot control takes place via a pilot valve 52, which is formed as a 3-way, 2-position valve. The inlet connection A of the active logic valve 41 is connected via a low-pressure storage line 54 to a low-pressure accumulator 56. The active logic valve 41 may also be mounted inversely with respect to the connections A, B. The outlet connection B of the active logic valve 41 is connected to the bottom space 14 of the casting cylinder 10.

[0047] Since one possible configuration of the active logic valve 41 is known from the publications DE 102017220836 A1 and DE 102005035170 A1 cited in the introduction, only those elements which are important for the understanding of the invention will be described here, and in the rest reference is made to said prior art. According to this, the active logic valve 41 has a stepped main piston 60 which is preloaded against a valve seat 58 by a pressure exerted by the low-pressure accumulator ND via a switching pilot valve 52 on a surface A5 and which blocks the pressure medium connection between the connections A, B of the active logic valve 41 and thus between the low-pressure storage line 54 and the pressure line 59. The pressure line 59 opens into the bottom space 14 of the casting cylinder 10. The main piston 60 has an internal bore from the surface A5 to the surface A3, so that the pressure compensation of the surface A5 acting in a closing manner is ensured by the surface A3 acting in an opening manner. Via the control surface A4, the active logic valve 41 can be opened and closed precisely. In this case, in order to ensure the opening of the active logic valve 41, the surface A4 can be selected to be greater than the difference A5-A3 or the control pressure of the accumulator ND can be set correspondingly higher.

[0048] A tank line 62 is connected to the tank connection of the pilot valve 52, the inlet connection of which is connected via a line 64 to the control pressure or low pressure accumulator ND. By supplying current to the switching magnet of the pilot valve 52, the pilot valve 52 can be displaced against a spring force into a switching position in which the annular control space of the active logic valve 41 defined by the face A4 is connected to the low pressure accumulator ND, so that the main piston 60 is lifted from the valve seat 58 due to the pressure acting on the annular end face A4, thereby controlling the opening of the fluid connection between the connections A and B.

[0049] The active logic valve 41 is designed so that it can be flowed through with minimal pressure loss and, when appropriately controlled to open, closes very reproducibly in the shortest switching times via the pilot valve 52. To optimize the subsequent closing characteristics, the stroke of the active logic valve 41 can be limited. Due to this special design of the active logic valve 41, even in the case of large nominal dimensions, only a small control oil flow is required to open and close the active logic valve 41 quickly and reproducibly.

[0050] Furthermore, the operating reliability is increased by the active opening and closing of the active logic valve 41 by the pilot valve 52 and the reliable closing of the active logic valve 41 by the accumulator pressure. In this case, the active closing of the active logic valve 41 allows the closure conditions to be freely selected. This closure may take place, for example, depending on the pressure, the load force, the travel distance, the travel speed, etc.

[0051] 2, the low-pressure accumulator 56 can be connected to the pressure space 28 of the pressure intensifier via a 2-way, 2-position seat valve, hereinafter referred to as the accumulator shut-off valve 66, which is pilot-controlled by a pilot control valve 68. The control pressure medium for this purpose is generated by the low-pressure accumulator 56 itself. In the preloaded basic position of the pilot control valve 68, the return space of the accumulator shut-off valve 66, which acts in a closed manner, is supplied with the pressure of the low-pressure accumulator 56, and in the switching position with the tank pressure, so that the accumulator shut-off valve 66 connects the low-pressure accumulator 56 to the pressure space 28 of the pressure intensifier. In said switching position, the pressure intensifier 24 is thus tensioned in the support direction.

[0052] The manner in which the casting unit 1 shown in FIG. 2 functions during the initially described stages I to III will now be described.

[0053] In order to prevent the occurrence of pressure waves that would cause a starting shock towards the casting cylinder 10 during the start-up of the pre-filling phase, the casting cylinder 10 is pre-pressurized before the opening of the active logic valve 41, also called the accumulator shut-off valve. This is done in such a way that when the casting cylinder 10 and the intensifier 24 return, the annular space 15 of the casting cylinder 10 and the annular space 32 of the intensifier 24 can be pre-pressurized to the maximum pump pressure via the hydraulic pump 34, the shut-off and pre-pressurization valve 42 moved to the first switching position a and the open check valves 48 and 70. In this procedure, the first switching and proportional valve 27, the second switching and proportional valve 46 and the third switching and proportional valve 29 are closed, so that a short circuit to the tank is prevented. The shut-off and pre-pressurization valve 42 is preferably designed with a non-return function.

[0054] In the next step, the melt shown in FIG. 1 is charged into the injection chamber 18 of the casting sleeve 17 via the charging opening 19, thus initiating the precharging phase I. For this, the hydraulic pump 34 is controlled via a ramp function, and the bottom space 14 of the casting cylinder 10 is charged to the value of the accumulator pressure of the low-pressure accumulator 56 via the second switching position b of the shut-off and preload valve 42. This causes the casting cylinder 10 to advance slightly at low speed and without a starting shock against the preload pressure in the annular space 15, until the fluid contained in the annular space 15 is compressed and the forces on the piston 11 are balanced. It is important in this case that this control ensures a shock-free adaptation of the pressure in the bottom space 14 of the casting cylinder 10 to the pressure in the low-pressure accumulator 56. Thereafter, via the active logic valve 41 (accumulator shutoff valve), the low pressure accumulator 56 can be connected to the bottom space 14 and via the accumulator shutoff valve 66, the low pressure accumulator 56 can be connected to the pressure space 28 of the pressure intensifier.

[0055] This procedure is not necessary if the pump 34 is able to generate a sufficiently high pressure. If a correspondingly high pre-pressure is applied to the annular space 15, the low-pressure accumulator 56 may also be switched into the piston space 14 via the active logic valve 41.

[0056] Depending on the customer's requirements, one common piston accumulator or dedicated piston accumulators for the casting cylinder and the intensifier may be used.

[0057] The first directional proportional valve 27 is then controlled by a pilot control, so that the pressure medium displaced from the annular space 15 is fed directly into the bottom space 14 in the form of a regenerative circuit. This makes it possible for the pouring cylinder 10 to be started and moved softly (without shocks and regeneratively controlled). This accelerates the melt and causes it to move towards the mould cavity 21 shown in FIG. 1. This continues until the melt reaches the mould gap and the prefilling phase I is finished.

[0058] Due to the recuperation procedure of the casting cylinder 10 in the pre-filling phase I, a comparatively small amount of pressure medium is taken from the low-pressure accumulator 56, so that the low-pressure accumulator 56 can be designed with a smaller volume than in a conventional design without the recuperation procedure. Furthermore, due to the smaller pressure drop caused by the differential circuit and the first switching and proportional valve 27 which is smaller by one or two nominal dimensions, a better analysis of the casting cylinder speed is possible, so that the casting cylinder 10 can be moved at a slower speed and with better repeatability.

[0059] A further advantage of the recovery procedure is that due to the relatively small pressure losses in the first switching and proportional valve 27 and the fact that the pressure medium flows out of the annular space 15 not against the tank pressure (0 bar) but against the pressure in the low-pressure accumulator 56, less cavitation and therefore less wear occurs on the valve 46, the piston 11 and the casing 13 of the casting cylinder 10 and the associated control blocks.

[0060] According to the invention, by controlling the first switching and proportional valve 27 and the second switching and proportional valve 46 connected in series thereto, the pressure in the bottom space 14 can be actively influenced in the sense of reducing or releasing the pressure, i.e., pressure overshoots in the bottom space 14 can be simply reduced in this way.

[0061] Furthermore, according to the invention, the pressure in the bottom space 14 can be influenced by means of a third switching and proportional valve 29 which can be operated completely independently of the first switching and proportional valve 27 and of the second switching and proportional valve 46. Due to said independent pressure medium channels 23, 44, 25 and valves 27, 46, 29, a more precise and more dynamic regulation of the pressure in the bottom space 14 results.

[0062] As soon as the melt reaches the mold gap, the actual mold filling process (phase II) is initiated. If the mold filling (injection) takes place at a low mold filling force, a regenerative procedure is then followed. Correspondingly, when the melt reaches the mold gap, the first switching and proportional valve 27 is displaced, for example with a jump function, into a position in which the pressure medium connection between the annular space 15 and the base space 14 is largely open, so that the melt is injected into the mold 20 at a high injection speed (up to 10 m / s). In this case, the process continues regeneratively, i.e. the pressure medium displaced from the annular space 15 is supplied to the expanding base space 14.

[0063] Such a recovery procedure has the advantage that, even in phase II, less pressure medium has to be drawn from the low-pressure accumulator 56 than in the case of conventional arrangements.

[0064] If the injection takes place at a relatively high mould filling force, the first switching and proportional valve 27 is brought, for example with a jump function, into its closed position at the time when the melt reaches the mould gap, so that the pressure medium connection between the annular space 15 and the bottom space 14 is interrupted. In parallel, the second switching and proportional valve 46 is opened in the process, for example with a jump function, to a defined opening cross section towards the tank T. This results in the melt being injected into the mould cavity 21 at a high injection speed, but not regeneratively in this case, as opposed to the procedure in the case of low mould filling forces, so that the maximum force of the casting cylinder 10 can be utilized.

[0065] In principle, a mixed configuration is also conceivable in which the first switching and proportional valve 27 is displaced into its shut-off position only during phase II as a function of the load force.

[0066] Phase II can also be carried out completely regeneratively, provided that the load force required in phase II can also be achieved in the regenerative circuit. In this case, it is envisaged that the second switching and proportional valve 46 can be replaced by a fast switching valve in order to relieve the annular space 15 in phase III.

[0067] After the mould cavity 21 is completely filled, the transition takes place in phase III. For this purpose, at the end of the mould filling phase II, the third switching and proportional valve 29 is controlled by a pilot control in the direction of opening the connection between the intensifier annular space 32 and the tank T. At the same time, the second switching and proportional valve 46 is opened. The release of pressure into the intensifier annular space 32 accelerates the primary piston 26, which correspondingly creates a high pressure in the bottom space 14, which presses against the piston 11 and recompresses the melt. Once the desired holding pressure has been reached, the second switching and proportional valve 46 is again switched back to the closing direction via the pressure control device. If the second switching and proportional valve 46 does not close quickly enough, the pressure overshoot in the bottom space 14 can be reduced by controlling the opening of the pressure relief path, i.e. the switching and proportional valves 27 and 46 leading to the tank T.

[0068] By using the first two-way proportional valve 27 for both pressure control in the bottom space 14 and regenerative control, instead of a three-way proportional valve (50% connection between A and T, 50% connection between A and P), a first proportional valve 27 with at least one nominal size smaller than the three-way proportional valve can be used (A and T 100%). As a result of the smaller nominal size, improved thrust is produced.

[0069] The described casting unit has the advantage over conventional configurations that, due to a recuperation procedure of the casting cylinder 10, the pressure medium displaced from the annular space 15 can be fed directly to the bottom space 14 of the casting cylinder 10 via the first switching and proportional valve 27. Another feature consists in the active closing of the active logic valve 41 at the end of phase II.

[0070] The active logic valve may also be replaced by a shutoff valve and an external check valve.

[0071] The casting cylinder of the disclosed casting unit may be moved in a regenerative manner in the pre-filling phase via a first flow regulating valve, which also serves to regulate the pressure in the bottom space of the casting cylinder. Via a second flow regulating valve, the casting cylinder may be moved in a regulated manner with or without regeneration in the mold filling phase. Furthermore, a booster unit formed as a pressure booster is connected in the pressure holding phase via a third flow regulating valve. The pressure in the bottom space can also be regulated via the third flow regulating valve. All of the flow regulating valves can be operated independently of one another. Together, these flow regulating valves allow a very precise and dynamic regulation of the pressure in the bottom space, which is an improved arrangement compared to an arrangement using a three-way flow regulating valve.

Claims

1. A hydraulic casting unit of a molding machine, in particular an injection molding machine, die casting machine or thixomolding machine, a casting cylinder (10) formed as a differential cylinder, with a piston (11) defining a bottom space (14) on the bottom side and an annular space (15) on the piston rod side; a low pressure source (56) connectable to the bottom space (14) for the advancing movement of the casting cylinder (10); a hydraulic intensifier (24) configured to increase the pressure in the bottom space (14) during a pressure holding phase; a regulating valve device which is fluidly connectable between the annular space (15) via a first pressure medium flow path (23) and to the bottom space (14) and to a pressure medium tank (T) via a second pressure medium flow path (44) and which is capable of controllably opening or forming a third pressure medium flow path (25) which opens into the annular space (32) of the pressure intensifier (24) for operating the pressure intensifier (24); a hydraulic pump (34) for applying a pre-pressure to the casting cylinder (10) and / or the pressure booster (24); a shut-off and preload valve (42) configured to connect a pressure connection of the hydraulic pump (34) to the annular space (32) of the pressure intensifier (24) and / or to the annular space (15) of the casting cylinder (10) and / or to the bottom space (14) of the casting cylinder (10); In a hydraulic casting unit comprising: the regulating valve device is divided into three independently operable switching and proportional valves (27, 46, 29), of which a first switching and proportional valve (27) is arranged in the first pressure medium flow path (23), a second switching and proportional valve (46) is arranged in the second pressure medium flow path (44) and a third switching and proportional valve (29) is arranged in the third pressure medium flow path (25), the shut-off and pre-loading valve (42) is configured as a four-way three-position valve, in which the annular space (32) of the pressure booster (24) and the annular space (15) of the casting cylinder (10) are connected to a pressure connection (P) of the hydraulic pump (34), and the first pressure medium flow path (23) is preferably configured as a four-way three-position valve having a first switching position (a) which is connectable or connected to the pressure medium tank (T) via an openable check valve (72), 13. A hydraulic casting unit comprising: a pressure supply valve (42) for supplying pressure to said hydraulic pump (34) through said bottom space (14) and a pressure supply line (50) for connecting said bottom space (14) and said bottom space (14) to said pressure connection (P) of said hydraulic pump (34) through said pressure supply line (50) which is capable of connecting said annular space (32) of said booster (24) and said annular space (15) of said casting cylinder (10) to said pressure connection (P) of said hydraulic pump (34) in said first switching position (a), said pressure supply line (50) being connected to said pressure medium tank (T).

2. 2. The casting unit according to claim 1, wherein the primary piston (26) of the pressure intensifier (24) defines with its larger end face acting in the increasing direction a pressure space (28) of the pressure intensifier (24) and with its smaller end face acting in the opposite direction defines the annular space (32) of the pressure intensifier (24), and via the third pressure medium flow path (25) the annular space (32) of the pressure intensifier (24) is fluidly connected to the pressure medium tank (T).

3. 3. The pouring unit according to claim 1, further comprising a pressure relief channel which can be generated from the bottom space (14) via the first switching and proportional valve (27) and the second switching and proportional valve (46) to the pressure medium tank (T), in particular as a function of the pressure or the pressure gradient detected in the bottom space (14).

4. 4. The casting unit according to claim 1, wherein at least one of the switching and proportional valves (27, 29, 46) is preferably designed as an electrohydraulic pilot-controlled two-way two-position switching flow control valve.

5. 5. The casting unit according to claim 1, wherein at least the second switching and proportional valve (46) and the third switching and proportional valve (29) or at least two of the first to third switching and proportional valves (27, 29, 46), preferably all of the switching and proportional valves (27, 29, 46), are formed in the same configuration.

6. The casting unit of claim 2, wherein the pressure space (28) of the pressure intensifier (24) is connectable to a low pressure source (56) via an accumulator shutoff valve (66).

7. A casting unit as described in any one of claims 1 to 6, wherein the bottom space (14) of the casting cylinder (10) is connectable to a low pressure source (56) via a two-way, two-position switching active logic valve (41).

8. A casting unit as described in any one of claims 1 to 7, wherein the hydraulic pump (34) is formed as a variable displacement pump or as a fixed displacement pump with a servo motor and a servo converter or as a variable displacement pump with a three-phase motor and a frequency converter or as a variable displacement pump with a three-phase motor.

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