DEVICE AND METHOD FOR COOLING A MOLD

Description

[0001] The invention relates to a device for cooling a casting mold. The device comprises an evaporation chamber formed in the casting mold. A first pump supplies a liquid to the evaporation chamber.

[0002] When producing castings, a liquid casting material is fed into a mold cavity. Within the mold cavity, the casting material cools and solidifies. The result is a casting with a shape that matches the mold cavity. The mold can be opened to remove the casting from the mold.

[0003] To specifically influence the cooling process, it is known to create an evaporation chamber in specific areas of the mold housing. A liquid that is fed to the evaporation chamber under high pressure can expand in the evaporation chamber, causing the liquid to evaporate. The amount of heat required for evaporation is extracted from the mold housing and indirectly from the casting material in the mold cavity, allowing the casting material in this section of the mold to be specifically cooled. This method for cooling a mold is also known as jet cooling.

[0004] When heat is removed from the mold by evaporating a liquid, this has the advantage that a defined temperature is established in the area surrounding the evaporation chamber due to the constant evaporation temperature. For example, if water is evaporated at atmospheric pressure, the temperature remains essentially constant at around 100 °C.

[0005] Patent EP 2 796 268 A1 presents a device for controlling the temperature of a mold, wherein a temperature control fluid circuit is configured to cool the mold by means of vacuum evaporative cooling. German Patent Application DE 1 758 140 A1 describes a method and a device for controlling the temperature of molds, wherein a circulating fluid is partially evaporated by a controllable vacuum. WO 2005 / 123357 A2 discloses a method for controlling the temperature of a casting mold.

[0006] The invention is based on the object of presenting a device and a method for cooling a casting mold, with which the cooling process can be specifically influenced. Based on the cited prior art, this object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0007] The device according to the invention is defined in claim 1 and the method according to the invention is defined in claim 10. Optional features are specified in the dependent claims.

[0008] In the device according to the invention, a second pump is provided to apply a pressure in the evaporation chamber that differs from atmospheric pressure. By adjusting the pressure in the evaporation chamber, the temperature at which the liquid evaporates can be influenced. By increasing the pressure in the evaporation chamber, the evaporation temperature can be increased, and by decreasing the pressure in the evaporation chamber, the evaporation temperature can be decreased. With a reduced evaporation temperature, the cooling process can be accelerated, which can be used to shorten the cycle time in the production of castings. With an increased evaporation temperature, the cooling process can be slowed, which allows a higher surface quality or an improved material structure to be achieved in certain castings.

[0009] The invention has recognized that it is advantageous to pressurize the liquid supplied to the evaporation chamber using the first pump. The cooling device according to the invention comprises a supply line that extends to the evaporation chamber. To enable targeted cooling, it is advantageous if the liquid does not evaporate in the supply line, but only when the liquid exits the supply line into the evaporation chamber. This can be achieved by placing the liquid in the supply line under increased pressure. The pressure under which the liquid in the supply line is therefore, according to the invention, higher than the pressure in the evaporation chamber.

[0010] A section of the supply line adjacent to the evaporation chamber can have a diameter that is smaller than the diameter of the supply line in a section further away from the evaporation chamber. The section of the supply line adjacent to the evaporation chamber represents a local constriction in the supply line and can open into the evaporation chamber. During operation of the device according to the invention, a pressure difference can exist across the local constriction. The pressure difference across the local constriction can amount to at least 2%, preferably at least 5%, more preferably at least 10% of the total pressure difference between the outlet of the first pump and the inlet of the second pump. The path along which the pressure difference is considered extends from the first pump via the local constriction and the evaporation chamber to the second pump.Preferably, the pressure difference across the local constriction is between 30% and 90% of the total pressure difference. This ensures that the liquid in the supply line up to the constriction maintains such a high pressure that it does not evaporate. The supply line can have a diameter of between 0.5 mm and 2 mm, preferably between 0.8 mm and 1.2 mm, in the section forming the local constriction, adjacent to the evaporation chamber. This applies to a supply line with a circular cross-section. For supply lines with a different cross-section, the cross-sectional area can be correspondingly large.

[0011] To prevent the liquid in the supply line from evaporating even when the temperature of the supply line is significantly above the evaporation temperature in the evaporation chamber, the liquid in the supply line can be subjected to a correspondingly high pressure. According to the invention, the pressure in the supply line is at least 5 bar, preferably at least 10 bar, and more preferably at least 20 bar higher than the pressure in the evaporation chamber. The first pump of the device according to the invention can be a liquid pump suitable for conveying the liquid through the supply line at such a pressure.

[0012] The device according to the invention comprises a drain line through which residual liquid, in the evaporated or liquid state, can be removed from the evaporation chamber. To prevent a sharp increase in pressure in the evaporation chamber during evaporation of the liquid, the drain line can have a larger cross-section than the supply line.

[0013] The second pump, which according to the invention adjusts the pressure in the evaporation chamber, is connected to the discharge line. This means that the pressure built up by the second pump is transferred to the evaporation chamber via the discharge line or a section of the discharge line.

[0014] The device according to the invention can be connected to a condenser in which evaporated liquid quantities from the evaporation chamber are recondensed. The condenser can comprise a heat exchanger for dissipating excess heat. Water, for example, can be used as the cooling medium for the condenser.

[0015] The condenser may comprise a tank whose lower portion is filled with liquid. The first pump may be connected to the lower portion of the tank. When the first pump is operating, liquid is drawn from the lower portion of the tank and pumped through the supply line to the evaporation chamber.

[0016] The second pump, which generates the desired pressure in the evaporation chamber, can be connected to the condenser tank above the liquid level. A negative or positive pressure generated by the second pump is transferred through the condenser tank and the drain line to the evaporation chamber. A pressure accumulator can be arranged between the second pump and the evaporation chamber so that the desired pressure in the evaporation chamber can be maintained even when the second pump is not operating.

[0017] A valve can be connected to the drain line, which, when open, establishes a connection between the drain line and atmospheric pressure. When the valve is open, pressure equalization occurs between the drain line and the environment, so that atmospheric pressure is established in the drain line. It may be useful to equalize to atmospheric pressure between two cycles in which the cooling liquid is evaporated in the evaporation chamber to prevent the evaporation of liquid during phases in which no cooling effect is desired.

[0018] The valve may be arranged at a suitable location between the evaporation chamber and the second pump, for example at the discharge line, at the condenser or at the pressure accumulator.

[0019] The cooling device according to the invention can be equipped with a gas connection through which a gas, in particular air, can be admitted into the evaporation chamber to blow out liquid residues from the evaporation chamber. The removal of liquid residues from the evaporation chamber can be carried out to create a defined initial situation for the next cooling process in which the evaporation chamber is filled exclusively with gas. The gas connection can, for example, be connected directly to the evaporation chamber or to a section of the supply line.

[0020] If the gas connection is open, the gas can enter the evaporation chamber under the influence of a pressure difference. If there is a negative pressure in the evaporation chamber, the pressure difference compared to atmospheric pressure can be sufficient to drive the gas. It is also possible that the gas is introduced into the gas connection at a positive pressure compared to atmospheric pressure. The liquid supply through the supply line is preferably interrupted while gas enters the evaporation chamber.

[0021] In one embodiment, the second pump is a vacuum pump designed to apply a pressure in the evaporation chamber that is less than atmospheric pressure. The absolute pressure in the evaporation chamber when the second pump is in operation can be, for example, between 50 mbar and 800 mbar, preferably between 100 mbar and 500 mbar. If the pressure in the evaporation chamber is reduced to, for example, 200 mbar, the water evaporates at just 70 °C.

[0022] The use of a vacuum pump is expedient if the cooling process is to be accelerated by the invention.

[0023] The use of a vacuum pump as a second pump is also advisable when the casting process takes place at mold temperatures below 100 °C. Evaporation of water at atmospheric pressure cannot then achieve a cooling effect. Mold temperatures below 100 °C are used, for example, in the injection molding of certain plastics, such as polyoxymethylene (POM), polyamide (PA), or polybutylene terephthalate (PBT).

[0024] In another embodiment, the second pump is a pressure relief pump designed to apply a pressure in the evaporation chamber that is greater than atmospheric pressure. The absolute pressure in the evaporation chamber when the second pump is operating can be, for example, between 5 bar and 15 bar. The use of a pressure relief pump as the second pump can be useful if the cooling process is to be slowed down by the invention.

[0025] If tool temperatures significantly above 100 °C are used, the mold is cooled very strongly locally when water is evaporated at atmospheric pressure in the evaporation chamber. Such strong local cooling can have undesirable effects on the structure of the material in the mold or lead to reduced surface quality. If the absolute pressure in the evaporation chamber is increased to a value of, for example, 10 bar, the water only evaporates at a temperature of around 200 °C. The material in the mold can thus be subjected to less abrupt cooling. A slower cooling process may be desirable, for example, when injection molding certain plastics. Examples of such plastics are polyacrylic acid (PAA), polyphthalamides (PPA), or polyphenylene sulfide (PPS).

[0026] The cooling device according to the invention can be designed to include a vacuum pump and a pressure pump. A changeover switch can be provided to switch between the vacuum pump and the pressure pump, allowing switching between the vacuum pump and the pressure pump depending on the desired cooling temperature in the evaporation chamber.

[0027] The mold of the device according to the invention can comprise a plurality of evaporation chambers. Liquid for evaporation can be supplied to the evaporation chambers synchronously or independently of one another.

[0028] The first pump and the second pump of the device according to the invention can be designed as separate structural units. It is also possible for the first pump and the second pump to be functional elements within a single pump unit.

[0029] The invention also relates to a plastic injection molding machine in which an injection mold is cooled by such a device.

[0030] The invention further relates to a method for cooling a mold, in which a liquid is supplied to an evaporation chamber formed in the mold in order to evaporate the liquid in the evaporation chamber. In this method, a pressure different from atmospheric pressure is applied in the evaporation chamber. The liquid in the supply line is placed under increased pressure so that the liquid does not evaporate in the supply line. The invention further relates to a method for producing a plastic injection-molded part, in which an injection mold is cooled according to this method.

[0031] The method can be further developed with additional features that are described in connection with the device according to the invention. The device can be further developed with additional features that are described in connection with the method according to the invention.

[0032] The invention is described below by way of example with reference to advantageous embodiments in the accompanying drawings. They show: Fig. 1: a schematic representation of a plastic injection molding machine according to the invention; Fig. 2: a detail of Fig. 1 in an enlarged view; Fig. 3: a schematic representation of an inventive device for cooling the casting mold.

[0033] One in Fig. 1 The plastic injection molding machine shown comprises an injection mold 14 in which a mold cavity 15 is formed. The injection mold 14 is shown in the open state, in which two halves of the injection mold 14 are spaced apart from each other. In the open state, an injection-molded part can be removed from the mold cavity 15 of the injection mold 14.

[0034] For the next injection molding process, the injection mold 14 is closed, in which the two halves of the injection mold 14 are tightly sealed. A plastic material in a liquid state is introduced into the mold cavity 15 by a forward movement of a piston screw 16. The process waits until the plastic material has hardened through cooling. The injection mold 14 is opened, and the finished injection-molded part is removed.

[0035] The injection mold 14 comprises a mold core 17 that protrudes into the mold cavity 15, defining a cylindrical recess in the injection-molded part. To ensure a good structure and surface quality of the injection-molded part in the area of ​​the cylindrical recess, the cooling process in this area should be precisely controlled.

[0036] The mold core 17 comprises, according to the enlarged illustration in Fig. 2 an evaporation chamber 18 in which a liquid is evaporated during the cooling process. A temperature corresponding to the evaporation temperature of the liquid is established in the evaporation chamber 18, so that the cooling of the plastic material in the mold cavity 15 occurs under defined conditions.

[0037] In the mold core 17, according to the enlarged illustration in Fig. 2 a supply line 19 is formed, which extends as a channel to the evaporation chamber 18. In a front section of the supply line 19, a capillary tube 20 is arranged, which has a diameter of approximately 1 mm.

[0038] A liquid, for example, water, is introduced under high pressure through the supply line 19 and the capillary tube 20 into the evaporation chamber 18. The pressure in the supply line 19 can be, for example, 15 bar. The pressure in the supply line 19 can drop above the capillary tube 20 between the transition from the supply line 19 into the capillary tube 20 and the mouth of the capillary tube 20 in the evaporation chamber 18. The temperature of the mold core 17 is higher than the evaporation temperature of the water, so that the water evaporates in the evaporation chamber 18.

[0039] The supply line 19 is according to Fig. 1 connected to a cooling device 22. The cooling device 22 comprises, according to the schematic representation in Fig. 3 a first pump 23, which is designed to pump the water under high pressure through the supply line 19 to the evaporation chamber 18. The vapor and liquid residues are removed from the evaporation chamber 18 through a discharge line 21 and returned to the cooling device 22.

[0040] A condenser 24 is formed in the cooling device 22, in which the steam is recondensed. The condensation heat is removed from the condenser 24 via a heat exchanger 25 connected to a cold water circuit 26. The water collects in a lower section of the condenser 24 and can be sucked in again by the pump 23.

[0041] A compressor 28 is also connected to the supply line 19 via a compressed air line 27. After completion of a cooling process and when the injection mold 14 is open, a burst of compressed air is passed through the supply line 19 to completely displace the vapor and liquid residues from the evaporation chamber 18, so that defined starting conditions are present for the next cooling process.

[0042] If atmospheric pressure is present in the evaporation chamber 18, the water evaporates at 100 °C. In the present embodiment, a tool temperature of 90 °C is used, so that no cooling effect can be achieved by evaporation at 100 °C.

[0043] The cooling device 22 of the injection molding machine according to the invention therefore comprises a pressure module 29 designed to specifically apply a specific pressure in the evaporation chamber 18 in order to influence the evaporation temperature. This can be done in two ways. By reducing the pressure in the evaporation chamber 18, the evaporation temperature can be reduced. A reduced evaporation temperature can accelerate the cooling process, which can be used to shorten the cycle time during the production of injection-molded parts. By increasing the pressure in the evaporation chamber 18, the evaporation temperature is raised, which can slow down the cooling process of the plastic material. With certain plastic materials, this can improve the surface quality.

[0044] The printing module 29 comprises Fig. 3a vacuum pump 30 and a pressure pump 31, which can be switched between using a switch 32. The vacuum pump 30 and the pressure pump 31 are second pumps within the meaning of the invention. Pumps 30, 31 can be used to apply a pressure different from atmospheric pressure in a pressure vessel 33. To enable pressure equalization with atmospheric pressure, the pressure vessel 33 is connected to the environment via a valve 35.

[0045] The pressure from the pressure vessel 33 is transferred through an intermediate line 34, the interior of the condenser 24, and the discharge line 21 into the evaporation chamber 18. If the pressure vessel 33 is evacuated to an absolute pressure of, for example, 200 mbar using the vacuum pump 33, a pressure of 200 mbar is also present in the evaporation chamber 18. The water then evaporates at a temperature of just 70 °C, accelerating the cooling process. A shorter cooling process can contribute to shortening the cycle time in the production of injection-molded parts.

[0046] If overpressure is applied to the pressure vessel 33 using the overpressure pump 31, this pressure is also transferred to the evaporation chamber 18. Increased pressure in the evaporation chamber 18 leads to an increased evaporation temperature and thus to a slower cooling process. A slower cooling process can achieve an improved surface quality of the injection-molded part with certain plastic materials.

Claims

1. Device for cooling a casting mould (14), comprising a casting mould (14), in which a mould cavity (15) is formed, wherein an evaporation chamber (18) is formed in the casting mould (14), having a first pump (23) for supplying a liquid to the evaporation chamber (18), and having a second pump (30, 31) for applying a pressure in the evaporation chamber (18) which differs from atmospheric pressure, having an inlet line (19) which extends to the evaporation chamber (18), wherein the liquid in the inlet line (19) is put under an increased pressure, with the result that the liquid does not evaporate in the inlet line (19), wherein the first pump (23) is designed to deliver the liquid supplied to the evaporation chamber (18) in the inlet line (19) at a pressure which is at least 5 bar higher than the pressure in the evaporation chamber (18), and wherein a section of the inlet line (19) which is adjacent to the evaporation chamber (18) forms a local constriction in the inlet line (19), wherein an outlet line extends from the evaporation chamber, wherein the second pump is connected to the outlet line and wherein the device is designed such that the pressure built up by the second pump is transferred to the evaporation chamber via the outlet line or via a section of the outlet line.

2. Device according to Claim 1, characterized in that the inlet line (19) has a diameter of between 0.5 mm and 2 mm, preferably between 0.8 mm and 1.2 mm, in the section (20) forming the local constriction and adjacent to the evaporation chamber.

3. Device according to either of Claims 1 or 2, characterized in that the first pump is designed to deliver the liquid fed to the evaporation chamber (18) in the inlet line (19) at a pressure which is higher than the pressure in the evaporation chamber (18) by at least 10 bar, as a further preference by at least 20 bar.

4. Device according to any of Claims 1 to 3, characterized in that the outlet line (21) has a larger cross section than the inlet line (19).

5. Device according to any of Claims 1 to 4, characterized by a condenser (24) for condensing evaporated liquid quantities from the evaporation chamber (18).

6. Device according to any of Claims 1 to 5, characterized by a gas connection (27) for supplying a gas to the evaporation chamber (18).

7. Device according to any of Claims 1 to 6, characterized in that the second pump is a vacuum pump (30).

8. Device according to any of Claims 1 to 7, characterized in that the second pump is an excess pressure pump (31).

9. Plastics injection moulding machine having an injection mould (14) and having a device for cooling the injection mould (14), wherein the device for cooling is designed according to any of Claims 1 to 8.

10. Method for cooling a casting mould (14), in which a mould cavity (15) is formed in a casting mould (14), in which an evaporation chamber (18) is formed in the casting mould (14), in which a liquid is supplied to the evaporation chamber (18) through an inlet line (19) in order to evaporate the liquid in the evaporation chamber (18), in which residues of the liquid are discharged from the evaporation chamber (18) in the evaporated or the liquid state via an outlet line (21), and in which a pressure built up by a second pump is applied via the second pump in the evaporation chamber (18) via the outlet line (21) or a section of the outlet line (21), wherein a pressure which differs from atmospheric pressure is applied in the evaporation chamber, wherein the liquid in an inlet line (19) leading to the evaporation chamber (18) is put under an increased pressure, with the result that the liquid does not evaporate in the inlet line (19), wherein the pressure in the inlet line (19) is at least 5 bar higher than the pressure in the evaporation chamber (18) and wherein a section of the inlet line (19) which is adjacent to the evaporation chamber (18) forms a local constriction in the inlet line (19).

11. Method for producing a plastics injection mould component in which an injection mould (14) is cooled by the method according to Claim 10.