Plastic injection moulding machine and method for operating a plastic injection moulding machine

Abstract

The invention relates to a plastic injection moulding machine comprising an injection moulding mould (15), a supply unit (17) for injecting a plastic material into a cavity (16) of the injection moulding mould (15) and comprising a cooling device (19, 24, 28, 32, 33) for the injection moulding mould (15). The injection moulding mould (15) has a mould core (18) projecting into the cavity (16) and provided with an evaporation chamber (28). A pressure source (26, 27) is connected to the evaporation chamber (28) for generating an overpressure in the evaporation chamber (28). The cooling device (19, 24, 28, 32, 33) comprises a high-pressure pump (30, 42) arranged upstream of the evaporation chamber (28) for conveying a fluid into the evaporation chamber (28), and an overflow valve (36) arranged downstream of the evaporation chamber (28) and with an opening pressure that is higher than the pressure generated by the pressure source (26, 27). A branching (45) is formed between the evaporation chamber (28) and the overflow valve (36), to which the pressure source (26, 27) is connected. A valve (34, 35) is arranged between the branching (45) and the pressure source (26, 27), which is open in a first state and closed in a second state. The invention also relates to a method for operating an injection moulding machine.

Description

[0001] Plastic injection molding machine and method for operating a plastic injection molding machine

[0002] The invention relates to a plastic injection molding machine and a method for operating a plastic injection molding machine.

[0003] In plastic injection molding machines, a plastic material in liquid or pasty form is injected into a cavity of an injection mold. The plastic material cools in the cavity of the injection mold and transforms into a solid state. The result is an injection-molded part that has a shape corresponding to the cavity. The injection mold can be opened to remove the injection-molded part from the mold.

[0004] In certain applications, the injection mold comprises a mold core that extends into the cavity of the injection mold. An evaporation chamber can be arranged within the mold core, in which a liquid is evaporated as the plastic material cools in order to extract heat from the plastic material in the vicinity of the mold core. It is known that the temperature at which the liquid evaporates can be influenced by adjusting the pressure in the evaporation chamber (WO 2019 / 158521 A1).

[0005] If there is excess pressure in the evaporation chamber, the liquid evaporates at a higher temperature, so less heat is extracted from the plastic material. A reduced cooling effect can be useful, for example, in applications where the structure of the plastic material would be adversely affected by excessively strong and rapid cooling. It has been shown that it is not easy to adjust the pressure conditions in the evaporation chamber so that the plastic material is cooled to an appropriate degree.

[0006] The invention is based on the object of presenting an injection molding machine and a method for operating an injection molding machine that avoids these disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0007] The plastic injection molding machine according to the invention comprises an injection mold, a feed unit for injecting a plastic material into a cavity of the injection mold, and a cooling device for the injection mold. The injection mold has a mold core which projects into the cavity and is provided with an evaporation chamber. A pressure source is connected to the evaporation chamber and is designed to generate an overpressure in the evaporation chamber. The cooling device comprises a high-pressure pump arranged upstream of the evaporation chamber for conveying a liquid into the evaporation chamber, and an overflow valve arranged downstream of the evaporation chamber. The opening pressure of the overflow valve is higher than the pressure generated by the pressure source.

[0008] The invention has recognized that the combination of the pressure source and the overflow valve makes it possible to create the desired pressure conditions for the evaporation process in the evaporation chamber. Starting from a state in which the pressure generated by the pressure source is present in the evaporation chamber, a pressure increase occurs as soon as liquid is pumped into the evaporation chamber by the high-pressure pump. The increased pressure spreads to the overflow valve, so that the overflow valve opens and the pressure in the evaporation chamber is limited by the opening pressure of the overflow valve. Defined pressure conditions therefore exist in the evaporation chamber, from which the temperature of the evaporation process results. In this way, the cooling effect can be set to a desired level, so that excessive cooling of the plastic material is avoided.

[0009] A high-pressure pump according to the invention is designed to pump the liquid toward the evaporation chamber at a pressure of at least 5 bar. One effect of the increased pressure in the evaporation chamber is to reduce the amount of liquid supplied to the evaporation chamber in a given operating state of the high-pressure pump.

[0010] The pressure generated by the pressure source in the evaporation chamber can be 0.5 bar to 10 bar, preferably 1 bar to 5 bar, higher than atmospheric pressure. If the liquid is water, the evaporation temperature at atmospheric pressure is 100 °C. The evaporation temperature increases to about 120 °C at a pressure of 2 bar and to about 133 °C at a pressure of 3 bar. The opening pressure of the overflow valve can be slightly higher than the pressure in the evaporation chamber, so that the overflow valve opens quickly after the pumping process begins. For example, the opening pressure of the overflow valve can be between 2% and 20% higher than the overpressure in the evaporation chamber generated by the pressure source. In an example where the pressure in the evaporation chamber is 2 bar higher than atmospheric pressure and the overflow valve opens at 2.2 bar, the opening pressure would be 10% higher than the pressure in the evaporation chamber.A relief valve is a valve that opens when the differential pressure across the relief valve is greater than a predetermined opening pressure, and closes when the differential pressure is less than the opening pressure. Atmospheric pressure can be present on the side of the relief valve facing away from the pressure chamber.

[0011] In one embodiment, a branch is formed between the evaporation chamber and the overflow valve, wherein the pressure source is connected to the branch. In other words, the branch arranged between the evaporation chamber and the valve can be designed such that the overflow valve is arranged in a first arm of the branch and the valve in a second arm of the branch. A valve can be arranged between the branch and the pressure source, which is open in a first state and closed in a second state. The valve can be opened in order to apply an overpressure in the evaporation chamber from the pressure source. The valve can be closed when an overpressure in the evaporation chamber is reduced via the overflow valve.The valve can be closed additionally or alternatively when gas and / or liquid is discharged from the evaporation chamber, bypassing the overflow valve. The disclosure also encompasses embodiments in which there is neither a valve nor a branch between the evaporation chamber and the pressure source.

[0012] The valve can be a valve arranged between the evaporation chamber and the pressure source, which counteracts backflow from the evaporation chamber into the pressure source. The valve can be designed as a check valve, which closes when the pressure on the side facing the evaporation chamber is higher than the pressure on the side facing the pressure source. A switchable valve, which is suitably controlled via control commands, is also possible. In this way, it can be ensured that a pressure increase triggered by the conveying process does not affect the pressure source.

[0013] The valve may be a check valve arranged between the evaporation chamber and the pressure source. The check valve may be designed to be switched between the first state and the second state by a control signal. The check valve may be opened to generate the overpressure in the evaporation chamber from the pressure source. The check valve may be closed to allow excess pressure to be released from the evaporation chamber without gas escaping from the pressure vessel via the same route.

[0014] In one embodiment, a check valve and a shut-off valve are connected in series between the branch and the pressure source, so that the gas passes through the check valve and the shut-off valve on its way from the pressure source into the evaporation chamber. If one of the two valves connected in series is closed, no gas can pass through. The effect of the valves connected in series can be combined in a switchable valve if, in addition to the switching processes described in connection with the shut-off valve, the switchable valve is controlled in such a way that the switchable valve closes, while the excess pressure from the evaporation chamber is reduced via the overflow valve.

[0015] The pressure source can comprise a source area in which an output pressure is present which is higher than the pressure to be applied in the evaporation chamber. The source area can be a pressure reservoir, for example, or a line under the corresponding pressure. A pressure reducer can be arranged between the source area and the evaporation chamber and is set to the pressure that is to be present in the evaporation chamber. Using such a pressure reducer, the pressure in the evaporation chamber can be set with the desired accuracy. The pressure reducer can be adjustable so that the pressure can be freely selected within the adjustment range of the pressure reducer. The pressure can be adjustable in steps or continuously. The adjustment range can cover the range from 1 bar to 5 bar, preferably the range from 0.5 bar to 7 bar. The information relates to the excess pressure by which the pressure is higher than atmospheric pressure.

[0016] The cooling device may comprise a central module from which the liquid is supplied to an outlet opening leading into the evaporation chamber. The liquid may be supplied through a liquid line extending between the central module and the outlet opening. The central module may comprise a high-pressure pump with which the liquid is conveyed to the outlet opening.

[0017] The mold core can extend from a proximal end adjoining the body of the injection mold to a distal end. The distal end can form a free end in the cavity. The advantages of the invention are particularly evident when the mold core is slim. A distal section of the mold core adjacent to the distal end preferably has a largest diameter of no more than 20 mm, preferably no more than 10 mm, more preferably no more than 7 mm. The largest diameter is generally not smaller than 3 mm. The section adjacent to the distal end can extend over at least 30%, preferably at least 50%, more preferably at least 70% of the length that the mold core projects into the cavity. The evaporation chamber can be arranged adjacent to the distal end of the mold core.A first channel can be formed within the mold core, through which the liquid is supplied to the evaporation chamber. The first channel forms a section of the liquid line between the central module and the outlet opening. A second channel can be formed within the mold core, through which the gas-liquid mixture is discharged from the evaporation chamber. The cross-sectional area of ​​the second channel can be larger than the cross-sectional area of ​​the first channel, preferably at least by a factor of two, more preferably at least by a factor of five, further preferably at least by a factor of ten. In one embodiment, the first channel extends inside the tube and the second channel inside the annular channel. The reverse design is also possible.

[0018] The tube can be designed as a capillary tube, within which the first channel extends. The capillary tube can comprise an outlet opening leading into the evaporation chamber. The diameter of the channel formed in the capillary tube can be, for example, between 0.5 mm and 2 mm, preferably between 0.8 mm and 1.2 mm. A section of the liquid line arranged between the inlet side of the capillary tube and the central module can have a diameter that is significantly larger than the diameter of the tube.

[0019] During a delivery phase, the high-pressure pump delivers liquid through the liquid line to the outlet opening. The liquid can be under a pressure that is significantly higher than the pressure generated in the evaporation chamber by the pressure source. For example, the pressure of the liquid can be at least 5 bar, preferably at least 10 bar, and more preferably at least 20 bar higher than the pressure in the evaporation chamber. In this way, the liquid can be prevented from evaporating before entering the evaporation chamber.

[0020] At the start of an injection molding machine cycle, the injection mold is closed so that the cavity forms a closed hollow space. During an injection phase, the plastic material is injected into the cavity in liquid or pasty form by the feed unit, filling the cavity with the plastic material. The injection phase can last a few seconds, for example between 0.2 s and 5 s. After the end of the injection phase, pressure continues to be exerted from the feed unit on the plastic material in the cavity during a post-press phase. The post-press phase ends when quantities of plastic material adjacent to the feed unit have hardened, so that the pressure no longer acts on quantities of plastic material further away from the feed unit. The length of the post-press phase can, for example, be between 2 s and 50 s.The time remaining for the plastic material to cure is referred to as the residual cooling time. The length of the residual cooling time can, for example, be between 2 seconds and 50 seconds. Once the plastic material has cured sufficiently, the injection mold can be opened and the molded part removed. This completes one working cycle of the injection molding machine, and the next working cycle can begin.

[0021] The delivery phase, in which liquid is pumped into the evaporation chamber by the high-pressure pump, begins after the start of the working cycle and ends before the end of the working cycle. The delivery phase preferably begins after the end of the injection phase. The delivery phase preferably ends before the injection mold is opened again. The high-pressure pump can be set up so that liquid is pumped into the evaporation chamber continuously between the start and end of the delivery phase. Interruptions in delivery would in principle be possible. However, this procedure would have the disadvantage that the cooling effect could not be adjusted very precisely because short delivery pulses are difficult to dose.

[0022] Compared to a condition in which atmospheric pressure prevails in the evaporation chamber, the cooling effect is reduced by the inventive overpressure in the evaporation chamber. This is due, on the one hand, to the fact that the evaporation temperature increases with rising pressure. On the other hand, the pressure difference compared to the pressure applied by the high-pressure pump decreases, which results in a reduction in the amount of liquid entering the evaporation chamber.

[0023] Assuming that the amount of escaping liquid and the duration of the cooling phase are essentially predetermined, the pressure in the evaporation chamber is the key variable with which the cooling process can be influenced. According to the invention, the pressure in the evaporation chamber is set so that, on the one hand, the cycle time for a working cycle of the injection molding machine can be kept as short as possible, while, on the other hand, excessive cooling of the plastic material in the area around the mold core is avoided. The appropriate pressure value is determined for each application based on these criteria.

[0024] For precise adjustment of the cooling effect, it is advantageous if the initial conditions are known at the beginning of a pumping phase. For example, if the liquid line between the central module and the outlet opening is completely filled with liquid, the liquid will flow into the evaporation chamber without delay as soon as the liquid in the central module is pressurized.

[0025] In order to prevent the liquid from being forced through the liquid line back towards the central module under the pressure applied by the pressure source, a second valve can be arranged in the liquid line. The second valve can be open during the delivery phase. The second valve can be closed outside of the delivery phase if there is excess pressure in the evaporation chamber. The second valve can be designed as a second check valve which closes when the pressure on the side facing the evaporation chamber is higher than the pressure on the side facing the central module. It is also possible for the second valve to be a switchable valve which is controlled in a suitable manner using control signals.

[0026] A second branch can be formed in the liquid line between the outlet opening and the central module so that a section of the liquid line lying between the second branch and the outlet opening can be blown out. A gas line, the other end of which is fed from the central module, can be connected to the branch. The evaporation chamber can be blown out via the gas line between the end of a first conveying phase and the beginning of a subsequent conveying phase so that defined initial conditions are present for the next conveying process. The defined initial conditions include the section of the liquid line lying between the second branch and the outlet opening not being filled with liquid.

[0027] The second valve can be arranged between the outlet opening and the branch. If the second valve is arranged between the branch and the central module, a third valve can be provided in the gas line in order to prevent a backflow of the gas towards the central module there too if there is excess pressure in the evaporation chamber. The third valve can be designed as a third check valve. It is advantageous if the second valve is arranged close to the conveyor core. The section of the liquid line between the central module and the second valve is preferably larger, more preferably at least twice as large, more preferably at least three times as large as the section of the liquid line between the second valve and the outlet opening.

[0028] After a delivery process, the pressure in the evaporation chamber may be higher than the pressure previously generated by the pressure source. It may be advantageous to release the pressure from the evaporation chamber before the next delivery process. For this purpose, a second shut-off valve may be provided through which the gas-liquid mixture can escape from the evaporation chamber, bypassing the overflow valve. The second shut-off valve may be designed so that it can be switched between an open state and a closed state by control signals.

[0029] The cooling device can comprise a return line extending between the evaporation chamber and the central module. The overflow valve can be arranged in the return line so that quantities of the gas-liquid mixture passing through the overflow valve are returned to the central module. The second check valve can be connected in parallel to the overflow valve within the return line. The central module can comprise a condenser in which the liquid is recovered so that it can be used by the central module for a further conveying process. The first branch, via which the pressure source is connected to the return line, can be arranged between the evaporation chamber and the overflow valve. A first check valve can be arranged between the first branch and the pressure source to prevent the pressure from escaping from the pressure source when the second check valve is open.The first shut-off valve can be controlled so that it is in a closed state when the second shut-off valve is open.

[0030] The plastic injection molding machine can comprise a control unit. The control unit can be designed to control the interaction of the components during a working cycle of the plastic injection molding machine. For this purpose, the control unit can provide control signals that trigger one or more of the following steps. The steps can be carried out in the order specified below or in a different order. The control unit can control an actuator with which the injection mold is brought into a closed state. The control unit can open a first shut-off valve arranged between the pressure source and the evaporation chamber so that the evaporation chamber is pressurized from the pressure source. The control unit can control the feed unit so that a plastic material is injected into the cavity of the injection mold in an injection phase.The control unit can control the feed unit so that pressure is exerted on the plastic material in the cavity in a post-pressure phase following the injection phase. The control unit can control the high-pressure pump so that liquid is continuously pumped into the evaporation chamber in a delivery phase. The control unit can control the central module so that the delivery process is ended before the injection mold is opened. The control unit can control the actuator of the injection mold so that the injection mold is opened. The control unit can close the first shut-off valve arranged between the pressure source and the evaporation chamber. The control unit can open a second shut-off valve which bypasses the overflow valve so that the excess pressure in the evaporation chamber can dissipate.The control unit can control the central module so that the evaporation chamber is blown out with a gas burst. The control unit can control the second shut-off valve so that it closes. The control unit can control the first shut-off valve so that it opens. The control unit can control the injection molding machine so that a work cycle of this type is performed multiple times.

[0031] The control unit does not need to be a single structural unit. It is also possible, for example, for the injection molding process to be controlled by a first control module and the cooling device to be controlled by a second control module. This can be a master-slave configuration, with the first control module acting as the master and the second control module acting as the slave.

[0032] The invention also relates to a method for operating a plastic injection molding machine. The plastic injection molding machine comprises an injection mold. The injection mold has a mold core which projects into the cavity of the injection mold and is provided with an evaporation chamber. A feed unit is used to inject a plastic material into the cavity. In the evaporation chamber, an overpressure is applied from a pressure source. To cool the plastic material in the cavity, a liquid is conveyed into the pressurized evaporation chamber. A pressure increase in the evaporation chamber resulting from the conveying process and from evaporation of the liquid is reduced via an overflow valve whose opening pressure is higher than the overpressure applied in the evaporation chamber.The pressure in the evaporation chamber can be applied while a valve located between the pressure source and the evaporation chamber is open. The pressure in the evaporation chamber can be released while the valve is closed.

[0033] The disclosure includes further developments of the method with features described in connection with the plastic injection molding machine according to the invention. The disclosure includes further developments of the plastic injection molding machine described in connection with the method according to the invention.

[0034] The invention is described below by way of example with reference to the accompanying drawings using advantageous embodiments. They show:

[0035] Fig. 1: a schematic representation of an injection molding machine according to the invention;

[0036] Fig. 2: the mold core of the injection molding machine from Fig. 1 in an enlarged view;

[0037] Fig. 3: a representation of the pressure source from Fig. 1;

[0038] Fig. 4-7: further details of the injection molding machine from Fig.

[0039] 1.

[0040] An injection molding machine shown in Fig. 1 comprises a frame 14 which supports an injection mold 15 consisting of two mold halves 11, 12. In Fig. 1, the injection mold 15 is shown in the open state. To close the injection mold 15, the two mold halves 11, 12 are moved towards one another so that a completely enclosed cavity 16 is formed inside the injection mold 15. A mold core 18 connected to the first mold half 11 projects into the cavity 16. The injection molding machine comprises actuators (not shown) with which one or both mold halves 11, 12 can be moved in a suitable manner relative to the frame 14.

[0041] After the injection mold 15 has been closed, a piston screw 13 of a feed unit 17 is started in order to inject a plastic material in a liquid state into the interior of the injection mold 15 so that the cavity 16 is completely filled with the plastic material. In an immediately subsequent post-pressing phase, the piston screw maintains the pressure acting on the plastic material until the plastic material has hardened in an area 40 between the feed unit 17 and the cavity 16. In a subsequent residual cooling phase, the plastic material in the cavity 16 hardens completely without any further pressure being exerted from the outside. After the plastic material has completely hardened, the injection mold 15 is opened. An injection molded part whose shape corresponds to the cavity 16 is removed from the injection mold 15. The injection-molded part has a recess that corresponds to the mold core 18 .

[0042] According to the invention, heat is specifically extracted from the plastic material in the vicinity of the mold core 18 during curing. A blind bore is formed inside the mold core 18 and extends almost to the distal end of the mold core 18, see Fig. 2. The end of the bore forms an evaporation chamber 28 arranged inside the mold core 18. A capillary tube 30 extends in the center of the bore, and an outlet opening 43 leading into the evaporation chamber 28 is formed at its distal end. A proximal end of the capillary tube 30 is connected to a supply line 32. An annular return channel is formed between the capillary tube 30 and the wall 29 of the mold core 18 and is connected to a return line 33. The supply line 32 and the return line 33 are connected to a central module 19, which together with the evaporation chamber 28 and other components forms a cooling device of the injection molding machine.The central module 19 comprises a high-pressure pump 42 which is connected to the other end of the supply line 32. The high-pressure pump 42 is designed, in a delivery phase, to deliver water towards the capillary tube 30 under a high pressure which may, for example, be 20 bar higher than atmospheric pressure. The water exits the outlet opening 43 of the capillary tube 30 as a fine jet and is distributed in the evaporation chamber 28. The temperature in the evaporation chamber 28 and in the distal region of the annular return channel is so high that the liquid evaporates. The evaporation process extracts heat from the plastic material in the vicinity of the mold core 18.

[0043] If the evaporation process were to take place at atmospheric pressure, the plastic material would be cooled too much. In the injection molding machine according to the invention, the pressure in the evaporation chamber 28 is therefore higher than atmospheric pressure. This has a twofold effect. Firstly, as the pressure increases, the evaporation temperature increases, whereby the temperature difference compared to the plastic material decreases. Secondly, the amount of liquid emerging from the capillary tube 30 is reduced. Both of these effects result in less heat being extracted from the plastic material.

[0044] In order to be able to apply the desired pressure in the evaporation chamber 28, a pressure source 27 is connected to a branch 45 in the return line 33 via an adjustable pressure reducer 26 and a first valve combination 25. The first valve combination 25 comprises, as shown in Fig. 3, a check valve 34 and a switchable shut-off valve 35, which, when open, provides a free passage between the return line 33 and the check valve 34 and, when closed, closes the passage.

[0045] In the pressure source 27, which can be, for example, a pressure accumulator or a pressurized line, there is a pressure PI which is reduced to a lower pressure P2 by the adjustable pressure reducer 26. The pressure P2 set by the pressure reducer 26 spreads, when the shut-off valve 35 is open, via the return line 33 to the evaporation chamber 28, provided that a pressure lower than the pressure P2 is present in the return line 33 and the evaporation chamber 28. Conversely, if the pressure in the return line 33 is higher than the pressure P2 set by the pressure reducer 26, the check valve 34 closes and no pressure equalization takes place.

[0046] At the start of a working cycle of the injection molding machine, atmospheric pressure prevails in the evaporation chamber 28. After the shut-off valve 35 opens, the pressure P2 spreads into the evaporation chamber 28. When the plastic material begins to harden after the plastic material has been injected into the cavity 16 of the injection mold 18, this is accompanied by active cooling, with water being pumped into the evaporation chamber using the high-pressure pump 42. The pressure P2 is set so that the pumping phase can extend without interruption over the entire duration of the curing, i.e. from the start of the post-pressing phase to the end of the residual cooling phase, without the structure of the plastic material being damaged by excessive cooling.

[0047] During the conveying process, the pressure in the evaporation chamber increases because the pressure at which the liquid is conveyed into the evaporation chamber is higher than the pressure P2 present in the evaporation chamber. The evaporation process is accompanied by an expansion, which also causes a pressure increase in the evaporation chamber 28. The increased pressure spreads through the return line 33 and causes the check valve 34 of the first valve combination 25 to close. A second valve combination 24 is arranged in the return line 33 and, according to Fig. 4, comprises an overflow valve 36 and a switchable shut-off valve 37 connected in parallel. The shut-off valve 37 is closed. The overflow valve 36 has an opening pressure which is slightly higher than the pressure P2 set by the pressure reducer 26, so that the overflow valve 36 opens quickly when the pressure increases from the evaporation chamber 28.Even during the delivery phase, the pressure in the evaporation chamber 28 does not increase significantly.

[0048] After the end of the pumping phase, the second shut-off valve 37 is opened and the first shut-off valve 35 is closed, so that pressure equalization to atmospheric pressure takes place via the return line 33. The water-gas mixture is then returned from the evaporation chamber to the central module 19. Any water contained in the mixture is condensed in the central module 19 and can be reused in a subsequent pumping phase.

[0049] The supply line 32 arranged between the central module 19 and the evaporation chamber 18 comprises a branch 46 to which a compressed air line 22 is connected. After the pressure in the evaporation chamber 28 has been equalized to atmospheric pressure, a burst of compressed air can be directed from the central module 19 into the compressed air line 22. This burst spreads through the capillary tube 33 to the evaporation chamber 28 so that any liquid residues remaining there are blown out through the return line 33. In this way, defined initial conditions can be created for the subsequent working cycle of the injection molding machine, if desired. A second check valve 38 is arranged in the supply line 32 so that the burst of compressed air from the compressed air line 22 cannot spread in the direction of the central module 19, see Fig. 6.Conversely, a third check valve 39 is arranged in the compressed air line 22 in order to prevent an undesired backflow towards the central module 19 during the delivery phase, see Fig. 7.

[0050] A fourth check valve 21 is arranged in the supply line 32 adjacent to the mold core 18, see Fig. 5. The fourth check valve 21 becomes effective when, at the beginning of a working cycle of the injection molding machine, the pressure equalization between the pressure P2 of the pressure reducer and the evaporation chamber 28 is carried out. The pressure P2, which is higher than atmospheric pressure, only spreads as far as the fourth check valve 21. In this way, the liquid can penetrate more easily to the evaporation chamber 28 in the subsequent conveying phase.

[0051] The injection molding machine includes a control unit 41 that controls the interaction of the components. At the start of a working cycle of the injection molding machine, the injection mold 15 is closed and the first shut-off valve 35 is opened so that the pressure in the evaporation chamber rises from atmospheric pressure to the pressure P2 set by the pressure reducer 26. The feed unit 17 is activated to fill the cavity 16 of the injection mold 15 with plastic material. The pressure exerted by the feed unit 17 is maintained during the subsequent post-pressing phase. The high-pressure pump 42 is controlled so that water is pumped into the evaporation chamber 28 during the post-pressing phase and the subsequent residual cooling phase. At the end of the residual cooling phase, the high-pressure pump 42 is deactivated. The injection mold 15 is opened so that the injection-molded part can be removed. In parallel, the first shut-off valve 35 is closed and the second

[0052] The check valve 37 is opened to equalize the pressure in the evaporation chamber 28 to atmospheric pressure via the central module 19. A compressed air blast emitted by the central module 19 creates defined initial conditions for the subsequent working cycle of the injection molding machine.

Claims

Patent claims Plastic injection molding machine with an injection mold (15), a feed unit (17) for injecting a plastic material into a cavity (16) of the injection mold (15) and with a cooling device (19, 24, 28, 32, 33) for the injection mold (15), wherein the injection mold (15) has a mold core (18) projecting into the cavity (16) and provided with an evaporation chamber (28), with a pressure source (26, 27) connected to the evaporation chamber (28) for generating an overpressure in the evaporation chamber (28), wherein the cooling device (19, 24, 28, 32, 33) has a high-pressure pump (30, 42) arranged upstream of the evaporation chamber (28) for conveying a liquid into the evaporation chamber (28) and a downstream of the evaporation chamber (28) arranged overflow valve (36), the opening pressure of which is higher than the pressure generated by the pressure source (26, 27), wherein a branch (45) is formed between the evaporation chamber (28) and the overflow valve (36), to which the pressure source (26, 27), and wherein a valve (34, 35) is arranged between the branch (45) and the pressure source (26, 27), which valve is open in a first state and closed in a second state. Plastic injection molding machine according to claim 1, wherein the pressure generated in the evaporation chamber (28) by the pressure source (26, 27) is 0.5 bar to 10 bar, preferably 1 bar to 5 bar, higher than atmospheric pressure. Plastic injection molding machine according to claim 1 or 2, wherein the valve (34) counteracts a backflow from the evaporation chamber (28) into the pressure source (26, 27).

4. Plastic injection molding machine according to claim 3, wherein the valve (34) is designed as a check valve (34).

5. Plastic injection molding machine according to one of claims 1 to 3, wherein the valve (35) is designed as a switchable valve (35).

6. Plastic injection molding machine according to claim 1 or 2, wherein a check valve (34) and a switchable valve (35) are connected in series between the branch (45) and the pressure source (26, 27).

7. Plastic injection molding machine according to one of claims 1 to 6, wherein the cooling device (19, 24, 28, 32, 33) comprises a central module (19) from which the liquid is fed to an outlet opening (43) opening into the evaporation chamber (28).

8. Plastic injection molding machine according to one of claims 1 to 7, wherein a distal portion of the mold core (18) has a largest diameter of not more than 20 mm, preferably not more than 10 mm, more preferably not more than 7 mm.

9. Plastic injection molding machine according to one of claims 1 to 8, wherein the liquid is supplied to the evaporation chamber (28) through a capillary tube (30).

10. Plastic injection molding machine according to one of claims 1 to 9, wherein the liquid is conveyed into the evaporation chamber (28) in a conveying phase, wherein the conveying phase begins after the start of a working cycle of the injection molding machine and ends before the end of the working cycle of the injection molding machine. A plastic injection molding machine according to claim 10, wherein liquid is continuously pumped into the evaporation chamber (28) during the delivery phase. A plastic injection molding machine according to claim 10 or 11, wherein a second valve (21) is arranged in a liquid line (32) between the high-pressure pump (30, 42) and the evaporation chamber (28), which second valve is open during the delivery phase and closed outside of the delivery phase when an overpressure is present in the evaporation chamber (28). A plastic injection molding machine according to one of claims 10 to 12, wherein a second shut-off valve (37) is connected in parallel to the overflow valve (36) so that pressure can be released from the evaporation chamber (28) after the conclusion of a delivery phase. Plastic injection molding machine according to one of claims 1 to 13, comprising a control unit (41) which is designed to control the interaction of the components during a working cycle of the plastic injection molding machine.Method for operating a plastic injection molding machine which has an injection mold (15) with a mold core (18) projecting into the cavity (16) of the injection mold (15) and provided with an evaporation chamber (28), wherein a plastic material is injected into the cavity (16) by means of a feed unit (17), wherein an overpressure is applied in the evaporation chamber (28) from a pressure source (26, 27) while a valve (34, 35) arranged between the pressure source (26, 27) and the evaporation chamber (28) is open, wherein for cooling the plastic material in the cavity (16) a liquid is introduced into. the evaporation chamber (28) which is under overpressure is conveyed and wherein, while the valve (34, 35) is closed, a pressure increase in the evaporation chamber (28) resulting from the conveying process and from evaporation of the liquid is reduced via an overflow valve (36) whose opening pressure is higher than the overpressure applied in the evaporation chamber (28).

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