DEVICE AND METHOD FOR COOLING A CASTING MOLD

Abstract

The invention relates to a device for cooling a casting mold (14), comprising an evaporation chamber (18) formed in the casting mold (14), a first pump (23) for supplying a liquid to the evaporation chamber (18), and a second pump (30, 31) for applying a pressure in the evaporation chamber (18), which differs from the atmospheric pressure. The invention also relates to a corresponding method. The invention allows the cooling of a casting mold to be controlled in a targeted manner. This can be helpful in particular in the injection molding of plastic parts.

Claims

1. A device for cooling a casting mold (14), having an evaporation chamber (18) formed in the casting mold (14), a first pump (23) for supplying a liquid to the evaporation chamber (18), and a second pump (30, 31) for applying a pressure in the evaporation chamber (18) which differs from atmospheric pressure, 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 at said increased pressure through the inlet line (19), 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).

2. The device as of claim 1, wherein the inlet line (19) has a diameter of between 0.5 mm and 2 mm in the section (20) which forms the local constriction and is adjacent to the evaporation chamber.

3. The device of claim 1, wherein 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 5 bar.

4. The device of claim 1, comprising an outlet line (21) which extends from the evaporation chamber (18).

5. The device of claim 4, wherein the outlet line (21) has a larger cross section than the inlet line (19).

6. The device of claim 4, wherein the second pump (30, 31) is connected to the outlet line.

7. The device of claim 1, comprising a condenser (24) for condensing evaporated liquid quantities from the evaporation chamber (18).

8. The device of claim 1, comprising a gas connection (27) for supplying a gas to the evaporation chamber (18).

9. The device of claim 1, wherein the second pump is a vacuum pump (30).

10. The device of claim 1, wherein the second pump is an excess pressure pump (31).

11. A plastics injection molding machine having an injection mold (14) and having a device for cooling the injection mold (14), wherein the device for cooling is designed in accordance with claim 1.

12. A method for cooling a casting mold (14), in which a liquid is supplied through an inlet line (19) to an evaporation chamber (18) formed in the casting mold (14) in order to evaporate the liquid in the evaporation chamber (18), and in which a pressure which differs from atmospheric pressure is applied in the evaporation chamber (18), wherein the liquid in an inlet line (19) leading to the evaporation chamber (18) is put under an in-creased pressure, with the result that the liquid does not evaporate in the inlet line (19), and a section of the inlet line (19) which is adjacent to the evaporation chamber (18) forms a local constriction in the inlet line (19).

13. A method for producing a plastics injection mold component in which an injection mold (14) is cooled by the method of claim 12.

14. The device of claim 1, wherein the inlet line (19) has a diameter of between 0.8 mm and 1.2 mm in the section (20) which forms the local constriction and is adjacent to the evaporation chamber.

15. The device of claim 1, wherein 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.

16. The device of claim 1, wherein 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 20 bar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention is described by way of example below by means of advantageous embodiments with reference to the attached drawings. In the drawings:

[0031] FIG. 1: shows a schematic illustration of a plastics injection molding machine according to the invention;

[0032] FIG. 2: shows a detail from FIG. 1 in an enlarged illustration;

[0033] FIG. 3: shows a schematic illustration of a device according to the invention for cooling the casting mold.

DETAILED DESCRIPTION

[0034] A plastics injection molding machine shown in FIG. 1 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. In the open state, an injection molding can be removed from the mold cavity 15 of the injection mold 14.

[0035] For the next injection molding process, the injection mold 14 is brought into a closed state, in which the two halves of the injection mold 14 end in leaktight contact with one another. By means of a forward movement of a reciprocating screw 16, a plastics material in a liquid state is introduced into the mold cavity 15. There is a pause until the plastics material has hardened by cooling down. The injection mold 14 is opened and the finished injection molding is removed.

[0036] The injection mold 14 comprises a mold core 17 which projects into the mold cavity 15 and which defines a cylindrical depression in the injection molding. For a good structure and surface quality of the injection molding in the region of the cylindrical depression, the cooling process should be selectively controlled in this region.

[0037] For this purpose, as illustrated in the enlarged illustration in FIG. 2, the mold core 17 comprises 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, with the result that the cooling of the plastics material in the mold cavity 15 takes place under defined conditions.

[0038] According to the enlarged illustration in FIG. 2, an inlet line 19 extending as a channel as far as the evaporation chamber 18 is formed in the mold core 17. Arranged in a forward section of the inlet line 19 is a capillary tube 20, which has a diameter of about 1 mm.

[0039] A liquid, e.g. water, is introduced at high pressure into the evaporation chamber 18 through the inlet line 19 and the capillary tube 20. The pressure in the inlet line 19 can be 15 bar, for example. The pressure in the inlet line 19 can drop across the capillary tube 20 between the transition from the inlet line 19 to the capillary tube 20 and the outlet 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, and therefore the water in the evaporation chamber 18 evaporates.

[0040] According to FIG. 1, the inlet line 19 is connected to a cooling device 22. According to the schematic illustration in FIG. 3, the cooling device 22 comprises a first pump 23, which is designed to pump the water at high pressure through the inlet line 19 to the evaporation chamber 18. The steam and liquid residues are discharged from the evaporation chamber 18 and fed back to the cooling device 22 through an outlet line 21.

[0041] A condenser 24, in which the steam is re-condensed, is formed in the cooling device 22. The heat of condensation is dissipated from the condenser 24 by means of a heat exchanger 25, which is connected to a cold water circuit 26. The water collects in a lower section of the condenser 24 and can be drawn in again by the pump 23.

[0042] A compressor 28 is furthermore connected to the inlet line 19 via a compressed air line 27. After the conclusion of a cooling process and when the injection mold 14 is open, a compressed air pulse is passed through the inlet line 19 in order to displace the steam and liquid residues completely from the evaporation chamber 18, ensuring defined starting conditions for the next cooling process.

[0043] If atmospheric pressure is present in the operation chamber 18, the water evaporates at 100 C. In the illustrative embodiment under consideration, work is carried out at a mold temperature of 90 C., and therefore no cooling effect can be achieved by evaporation at 100 C.

[0044] The cooling device 22 of the injection molding machine according to the invention therefore comprises a pressure module 29, which is designed to selectively apply a certain pressure in the evaporation chamber 18 in order to influence the evaporation temperature. This can take place in two directions. The evaporation temperature can be reduced by reducing the pressure in the evaporation chamber 18. By means of a reduced evaporation temperature, the cooling process can be accelerated, and this can be used to reduce the cycle time during the production of injection moldings. By increasing the pressure in the evaporation chamber 18, the evaporation temperature is increased, thereby enabling the cooling process of the plastics material to be slowed down. With certain plastics materials, it is thereby possible to improve the surface quality.

[0045] According to FIG. 3, the pressure module 29 comprises a vacuum pump 30 and an excess pressure pump 31, between which it is possible to switch by means of a changeover valve 32. The vacuum pump 30 and the excess pressure pump 31 are second pumps in the sense according to the invention. By means of the pumps 30, 31, it is possible to apply a pressure that differs from atmospheric pressure in a pressure vessel 33. In order to allow a pressure equalization with atmospheric pressure, the pressure vessel 33 is connected to the environment via a valve 35.

[0046] The pressure from the pressure vessel 33 is transmitted via an inter-mediate line 34, the interior of the condenser 24 and the outlet line 21 to the evaporation chamber 18. If the pressure vessel 33 is evacuated to an absolute pressure of 200 mbar, for example, by means of the vacuum pump 33, the pressure in the evaporation chamber 18 is also 200 mbar. The water then evaporates at a temperature of just 70 C., thus accelerating the cooling process. With a shorter cooling process, it is possible to contribute to a shortening of the cycle time during the production of injection moldings.

[0047] If an excess pressure is applied in the pressure vessel 33 by means of the excess pressure pump 31, this pressure is also transmitted to the evaporation chamber 18. An increased pressure in the evaporation chamber 18 leads to an increased evaporation temperature and thus to slowing down of the cooling process. With certain plastics materials, an improved surface quality of the injection molding can be achieved by a slower cooling process.