WO2002100573A1 - Vacuum valve for a die casting machine - Google Patents

Abstract

In order to evacuate the moulding cavity of a die casting machine, at least one vacuum valve (30) is arranged between the moulding cavity and a suction channel (32) which is connected to the moulding cavity. Said vacuum valve (30) comprises a control rod (38) which can be displaced in the axial direction (x). A valve head is placed on the end of the control rod and can be placed against a valve seat (42) in a gas-permeable manner, in order to close the valve (30) by means of the displaceable control rod (38). A piston (44) is arranged on the other end of the control rod (38). Said piston protrudes into a gas-pressurised cylinder chamber (46) and can be displaced therein in a sliding manner in the axial direction (x). The end of the piston (44) opposite the cylinder chamber (46) can be subjected to a closing force acting on the valve head (40), by means of a spring element (58). The closing time can be reduced to less than 1 ms by means of the vacuum valve. The vacuum can be maintained longer during the casting process, causing less gas pockets to appear in the casting, and thus lower porosity.

Description

Vacuum valve for a die casting machine

The invention relates to a vacuum valve for evacuating the mold cavity of a die casting machine, in which at least one vacuum valve is arranged between the mold cavity and a suction channel connected to the mold cavity, the vacuum valve having a control rod which can be displaced in the axial direction and at one end of which a valve head is seated which can be placed gas-tight on a valve seat to close the valve by means of the displaceable control rod. Within the scope of the invention is also a die casting machine equipped with the vacuum valve according to the invention and the use of the die casting machine for the die casting of light metals.

In die casting machines with a suction device for venting the mold cavity, the last mold filling with liquid metal takes place in cooperation with the forced ventilation of the mold cavity within a few milliseconds. To achieve the highest possible negative pressure, it is therefore essential to close the suction channel that is required for the evacuation and is connected to the mold cavity as late as possible, i.e. just before the liquid metal would enter the vacuum system.

In the known die casting machines with a vacuum system, the problem is to control the vacuum valve seated in one half of the mold in dependence on the inflowing metal in such a way that on the one hand this valve remains open as long as possible in order to draw off as much gases and vapors from the mold cavity as possible, but that on the other hand, this valve can be closed in time so that liquid metal can in no way enter the vacuum system through this vacuum valve. The best possible extraction is advantageous because a high proportion of the oil vapors and crack products that are produced in the mold can also be extracted. In addition, be prevented that a bad vacuum creates air intakes in the casting, which lead to porosity and consequently to a loss of quality. This loss of quality manifests itself, for example, in a deterioration in mechanical properties and in a reduced weldability, especially when using laser welding processes.

DE-B-30 02 886 discloses a suction device in which a vacuum valve which can be actuated by a control pin and is arranged between a suction channel and the mold cavity is used, the control pin having an actuating insert which can be fastened to the die casting machine and is controlled by the actuation of a press piston can be coupled. The metal shot is triggered via a limit switch, the shot being triggered to inject the metal into the mold cavity actually only via a so-called timing element when the valve is completely closed.

In the die casting machines with vacuum system known from the prior art, the vacuum valve is still closed a few milliseconds before the mold is filled, i.e. the concentration of the residual gases in the mold cavity in the metal shot is still too high to practically exclude gas ingress in the casting.

The invention has for its object to provide a vacuum valve of the type mentioned and a die casting machine equipped with the vacuum valve, which make it possible to maintain a vacuum practically until the end of the mold filling.

One part of the task is to minimize the shutter speed of the vacuum valve, ie the time between the detection of the liquid metal injected into the mold cavity before the vacuum valve and the end of the closing movement of the valve, in order to be able to maintain the vacuum for as long as possible. A shutter speed of around 1 is aimed for ms.

Another subtask is to record the liquid metal flowing against the vacuum valve after the mold has been filled as quickly as possible.

In a vacuum valve of the type mentioned at the outset, the solution to the problem according to the invention is that a piston is arranged at the other end of the control rod, which projects into a cylinder chamber which can be pressurized with gas pressure and is slidably displaceable in the axial direction thereof, and that the piston on its End facing away from the cylinder space can be acted upon by a spring element with a closing force acting on the valve head.

A die casting machine according to the invention with a movable and a fixed mold half, a filling chamber, a press piston and a suction device provided for evacuating a mold cavity delimited by the two mold halves has at least one vacuum valve according to the invention.

The design of the closure system of the vacuum valve according to the invention enables a short actuation time in the order of magnitude of 1 ms, compared to an actuation time of approximately 10 ms or more in the valves with hydraulic actuation which are customary today.

The vacuum valve according to the invention closes by means of a spring force acting on the piston, wherein a counterforce which is greater than the closing force of the spring element when the valve is open is maintained until the closing movement is triggered by a gas pressure in the cylinder space. ^"

In addition to the shutter speed that can be calculated from the mechanical conditions and the closing force of the spring, it is very important for the closing movement of the vacuum valve that the gas pressure in the cylinder space be as rapid as possible can be broken down, ie the gas can escape from the cylinder space as quickly as possible.

Lockable first openings are provided for venting the cylinder space. These first openings are preferably arranged in the bottom of the cylinder space, these first openings being closed by a cover part having a second opening in a gas-tight manner at a first position of the cover part and open at a second position of the cover part by superimposing the first and second openings.

In a particularly preferred embodiment, the cover part is a rotatably mounted disk with bores or slots as the first openings.

The second openings in the cover part are expediently tapered. Under these conditions there is a small movement of the cover part, which leads to an overlap of the first and second openings, to the further automatic and sudden opening of the cylinder space by the initially flowing high-pressure gas, which leads to a conically tapering second Force components that act as openings already suffice.

To further optimize the outflow behavior of the gas, the first openings in the bottom of the cylinder space are preferably designed as Laval nozzles with an enlarged nozzle opening.

The cover part is operatively connected to a corresponding actuator in order to carry out a displacement or rotation to cover the first and second openings to trigger the closing process of the vacuum valve. This actuator can be any device that is suitable for transmitting a displacement or rotary movement to the cover part. A short response time is achieved in that the actuator comprises piezo elements, whereby to generate a sliding action acting on the cover part, a translational movement is converted into an angular movement.

In order to keep the response time of the vacuum valve as short as possible, the arrangement of a metal detector between the mold cavity and the vacuum valve is provided in a die casting machine according to the invention. This metal detector is used to generate a signal to close the vacuum valve as soon as the liquid metal is on the way from the mold cavity to the vacuum valve.

In a first embodiment of a die casting machine, a temperature sensor is provided. In a second variant, which responds considerably faster, the metal detector is a thermal radiation sensor.

The die casting machine according to the invention is suitable, inter alia, for die casting light metals, in particular aluminum and aluminum alloys.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments and from the drawing; this shows schematically in

Figure 1 is a partially sectioned view of a die casting machine.

2 is an enlarged, partially sectioned side view of the valve arrangement on the die casting machine of FIG. 1:

Fig. 3, 4 details of the valve assembly of Fig. 2;

5 shows the side view of an actuator with piezo elements;

6 shows a cross section through a thermal radiation sensor;

7 shows the end view of a combined metal detector with heat radiation and temperature sensors.

A die casting machine 10 shown in FIG. 1 for die casting of two For example, aluminum alloys each have a fixed mold half 14 and a movable mold half 16 which are clamped on a fixed machine plate 12a and on a movable machine plate 12b and which delimit a mold cavity 18 in the closed position. A filling chamber 20 extends into the fixed mold half 14, in which a plunger 22 is slidably arranged. The filling chamber 20 can be filled manually or automatically with liquid metal via an opening 24.

The mold cavity 18 is delimited on the side of the filling chamber 20 by a shaped gate 28 and on the opposite side by a vacuum run or mold exit channel 26. The mold cavity 18 is connected via the mold outlet channel 26 to a vacuum valve 30, which in turn is connected to a vacuum container 34 via a suction channel 32 and a shut-off valve 33 connected into the suction channel 32. The vacuum container 34 is evacuated by means of a vacuum pump 36.

The vacuum valve 30 shown in more detail in FIGS. 2 to 4 has a control rod 38, at one end of which a valve head 40 is seated which, when the valve is closed, rests gas-tight on a valve seat 42. At the end of the control rod 38 opposite the valve head 40, a piston 44 which is slidable in a cylinder space 46 is arranged. A pipe section 50 that can be connected to a pressure line, not shown, penetrates the base 48 and opens into the cylinder space 46.

The bottom 48 of the cylinder space 46 has first openings 52. In the cylinder space 46, a disc-shaped cover part 54 lies on the bottom 48, which has second openings 56, the number and arrangement of which correspond to the first openings 52. The pipe section 50 is rigidly connected to the disk-shaped cover part 54, so that the cover part 54 is rotated by rotating the pipe section 50. Depending on the position of the disk-shaped cover part 54, the first and the second openings 52, 56 are congruent, so that a continuous connection from the cylinder space 46 to the extension results in the atmosphere, or the first openings 52 are closed by the cover part 54.

As can be seen from FIG. 2, the first openings 52 are flared towards the outside of the valve and are designed as Laval nozzles. This enables gas to flow out of the cylinder chamber 46 at supersonic speed.

The second openings 56 in the disk-shaped cover part 54, which may have a circular cross-section 56a according to FIG. 3 or a slit-shaped cross-section 56b according to FIG. 4, are conically tapered towards the bottom 48 of the cylinder space 46. With this embodiment, a slight overlap of the first and the second openings 52, 56 is sufficient for the maximum passage opening from the cylinder space 46 against the outside of the vacuum valve 30 to be set automatically by the escaping gas.

On the side of the piston 44 opposite the cylinder space 46, a spring element 58 is arranged, with which a closing force for closing and keeping the vacuum valve 30 is generated.

FIG. 5 shows a possible actuator 60 for triggering the minimally required rotary movement of the disk-shaped cover part 54. The actuator 60 comprises piezo elements 62, 64 which are arranged and controlled in such a way that an angular movement of an actuating element 66 takes place. Such an actuator has a very short response and response time and is therefore suitable for initiating a rapid rotary movement.

The operation of the die casting machine 10 with the vacuum valve 30 is explained in more detail below with reference to FIGS. 1 and 2.

At the beginning of the die casting process, the two mold halves 14, 16 closed by moving the movable mold half 16 to the fixed mold half 14. Liquid metal is then introduced into the filling chamber 20 via the opening 24. The plunger 22 then moves into the filling chamber 20 and closes the opening 24. At this time, the shut-off valve 33 is opened when the vacuum valve 30 is open, so that the mold cavity 18 is evacuated via the suction channel 32 for the extraction of air and residual gases.

The liquid metal displaced by the plunger 22 has reached the mold gate 28 in front of the mold cavity 18 during the first filling phase described above. After this first slow filling phase, the second phase of fast mold filling begins, i.e. the actual metal shot. The mold cavity 18 is rapidly filled and the liquid metal flows into the mold outlet channel 26 adjoining the mold cavity 18, in which a metal speed of the order of 10 to 10 m / s is achieved.

After the liquid metal has entered the mold exit channel 26, the closing movement of the vacuum valve is triggered. Up to this point, the piston 44 is subjected to a gas pressure via the pipe section 50 and the cylinder space 46 that is greater than the closing force of the spring element 58. The first openings 52 in the base 48 of the cylinder space 46 are closed by the disk-shaped cover part 54. The entry of the liquid metal into the mold exit channel 26 is detected by a metal detector described in more detail below. A rotary movement of the disk-shaped cover part 54 is triggered via the actuator 60 via an electrical signal such that the first and second openings 52, 56 overlap. Due to the high gas pressure in the cylinder chamber 46, the outflowing gas causes the disk-shaped cover part 54 to rotate further until the first and second openings 52, 56 overlap to a maximum.

The outflow of the gas from the cylinder space 46 is controlled by the the element 58 causes which pushes the piston 54 into the cylinder space 46. A sudden movement of the valve head 40 against the valve seat 42 takes place via the control rod 38, as a result of which the mold exit channel 26 is closed by the valve head 40 of the vacuum valve 30 within a very short time after the metal detector has responded.

1 shows a temperature sensor 68 in the form of a thermocouple as a metal detector. The temperature sensor 68 protrudes into the mold exit channel 26 or is part of the wall thereof. The temperature jump triggered by the metal flowing past the temperature sensor 68 is fed as an electrical voltage signal via an electrical cable 70 to an electronic control device (not shown in more detail). The signal is used to control the vacuum valve 30.

FIG. 6 shows an alternative embodiment of a metal detector in the form of a thermal radiation sensor 72. This has a housing 74 made of steel or ceramic, for example. A sapphire monocrystal fiber 78 with a diameter of, for example, 350 μm is arranged in the housing, one end of which ends at the end face 76 of the housing 74. At the other end of the sapphire monocrystalline fiber 78 there is an optical lens 80 which transmits the heat radiation absorbed by the sapphire monocrystalline fiber 78 when the liquid metal flows past the end face 76 onto a commercially available glass fiber cable 82 and feeds it as a signal to an electronic detector 84 which Signal to control the vacuum valve 30 is used.

In the variant of a metal detector system shown in FIG. 7, two temperature sensors 68 and a heat radiation sensor 72 or its sapphire monocrystalline fiber 78 end on the end face 76 of the housing 74. This arrangement with a plurality of metal detectors serves for security in the event of the failure of a single system. The housing 74 with the heat radiation sensor 72 is arranged within the die casting machine 10 such that the end face 76 protrudes into the mold exit channel 26 or is part of the wall thereof.

The following calculation example for a realistic valve arrangement shows that the closing time of a vacuum valve 30 according to the invention can be reduced to less than 1 ms. Assuming a mass M of 0.3 kg, a spring force P of 10 kN for the spring element 58 and a closing travel s of 6 mm for the valve head 40, this results from the formula

2 - s - m

a shutter speed of 0.6 ms. With a piston diameter D of 25 mm, a gas temperature To of 300 ° K and a critical area F * of the narrowest cross sections of the openings 52, 56 of 9 mm ² , the minimum outflow velocity t _{g of} the gas from the cylinder space 46 results according to the formula

π - D ² s

-y - •

4 ^■ F ^{* ■} iT ₀

where A is a constant dependent on the gas used, which is, for example, 0.030 for helium. If helium is used as the pressurized gas, a value of 0.57 ms results for the minimum outflow time t _{g of} the gas from the cylinder space 46 under the above-mentioned conditions, ie under the selected conditions the shutter speed of the vacuum valve 30 is 0.6 ms , With a closing force P of the spring element 58 of 10 kN, a gas pressure p of 22 MPa, for example, is sufficient to keep the vacuum valve 30 open.

Claims

claims 1. Vacuum valve for evacuating the mold cavity (18) of a die casting machine (10), in which at least one vacuum valve (30) is arranged between the mold cavity (18) and a suction channel (32) connected to the mold cavity, the vacuum valve (30 ) has a control rod (38) displaceable in the axial direction (x), at one end of which a valve head (40) is seated, which can be applied gas-tight to a valve seat (42) to close the valve (30) by means of the displaceable control rod (38), characterized in that At the other end of the control rod (38) a piston (44) is arranged, which protrudes into a cylinder chamber (46) which can be pressurized with gas pressure and is slidably displaceable in the axial direction (x), and that the piston (44) on its End facing away from the cylinder space (46) can be acted upon by a spring element (58) with a closing force acting on the valve head (40). 2. Vacuum valve according to claim 1, characterized in that closable first openings (52) are provided for venting the cylinder space (46). 3. Vacuum valve according to claim 2, characterized in that the first openings (52) in the bottom (48) of the cylinder space (46) are arranged, and that the first openings (52) of a gas-tight, the second openings (56) having cover part (54) closed in a first position of the cover part (54) and open in a second position of the cover part (54) by overlaying the first and second openings (52, 56). 4. Vacuum valve according to claim 3, characterized in that the cover part (54) is a rotatably mounted disc with bores (56a) or slots (56b) as second openings. 5. Vacuum valve according to claim 3 or 4, characterized in that the second openings (56) in the cover part (54) are tapered. 6. Vacuum valve according to one of claims 1 to 5, characterized in that the first openings (52) in the bottom (48) of the cylinder space (46) are designed as Laval nozzles with an enlarged nozzle opening. 7. Vacuum valve according to one of claims 3 to 6, characterized in that the cover part (54) is operatively connected to an actuator (60) for executing a displacement or rotation which coincides with the first and second openings (52, 56). 8. Vacuum valve according to claim 7, characterized in that the actuator (60) comprises piezo elements (62, 64), a translational movement being converted into an angular movement in order to generate a sliding movement acting on the cover part (54). 9. Die casting machine with a movable (16) and a fixed mold half (14), a filling chamber (20), a plunger (22) and for evacuating a mold cavity (18) provided by the two mold halves (14, 16) and a mold cavity (18) ), at least one vacuum valve (30) being arranged between the mold cavity (18) and a suction channel (32) which is connected to the mold cavity and is connected to the suction device (34), and wherein the vacuum valve (30) is arranged in the axial direction ( x) has a displaceable control rod (38), at one end of which a valve head (40) is seated, which for closing the valve (30) by means of the displaceable control rod (38) Valve seat (42) can be applied gastight, characterized in that At the other end of the control rod (38) a piston (44) is arranged, which protrudes into a cylinder chamber (46) which can be pressurized with gas pressure and is slidably displaceable in the axial direction (x), and that the piston (44) on its End facing away from the cylinder space (46) can be acted upon by a spring element (58) with a closing force acting on the valve head (40) 10. Die casting machine according to claim 9, characterized in that closable first openings (52) are provided for venting the cylinder space (46). 11. Die casting machine according to claim 10, characterized in that the first openings (52) in the bottom (48) of the cylinder space (46) are arranged, and that the first openings (52) of a gas-tight, the second openings lying on the bottom (48) (56) having cover part (54) closed in a first position of the cover part (54) and open in a second position of the cover part (54) by overlaying the first and second openings (52, 56). 12. Die casting machine according to claim 11, characterized in that the cover part (54) is a rotatably mounted disc with bores (56a) or slots (56b) as second openings. 13. Die casting machine according to claim 11 or 12, characterized in that the second openings (56) in the cover part (54) are tapered. 14. Die casting machine according to one of claims 9 to 13, characterized shows that the first openings (52) in the bottom (48) of the cylinder space (46) are designed as Laval nozzles with an enlarged nozzle opening. 15. Die-casting machine according to one of claims 11 to 14, characterized in that the cover part (54) is operatively connected to an actuator (60) for executing a displacement or rotation which coincides with the first and second openings (52, 56). 16. Die-casting machine according to claim 15, characterized in that the actuator (60) comprises piezo elements (62, 64), a translational movement being converted into an angular movement in order to generate a sliding movement acting on the cover part (54). 17. Die casting machine according to one of claims 9 to 16, characterized in that a temperature sensor (68) for generating a signal for closing the vacuum valve is arranged between the mold cavity (18) and the vacuum valve (30). 18. Die casting machine according to one of claims 9 to 16, characterized in that a heat radiation sensor (72) for generating a signal for closing the vacuum valve is arranged between the mold cavity (18) and the vacuum valve (30). 19. Use of a die casting machine according to one of claims 9 to 18 for die casting light metals, in particular aluminum and aluminum alloys.