WO1991001833A1

WO1991001833A1 - Process and device for controlling and regulating the mould filling rate and casting pressure of a low-pressure chill casting machine

Info

Publication number: WO1991001833A1
Application number: PCT/EP1990/001223
Authority: WO
Inventors: Georg Bilz; Hans Lämmermann; Alfred Dobner; Klaus Sterner; Klaus Riess
Original assignee: Alcan Deutschland Gmbh; Alcan International Limited
Priority date: 1989-07-26
Filing date: 1990-07-25
Publication date: 1991-02-21
Also published as: BR9007556A; CA2053922A1; MY106433A; ATE89773T1; JPH04506934A; EP0483191B1; DE59001574D1; EP0483191A1; PT94821A; ES2040600T3; KR920700811A; DE3924775C1; AU6043590A; DK0483191T3; DD295571A5

Abstract

The invention relates to a device and a process for controlling and regulating the mould filling rate and casting pressure of a low-pressure chill casting machine, preferably for casting aluminium. The furnace chamber containing the molten casting material can be hermetically sealed and communicates with the mould via a rising pipe connected to the mould. Gas pressure built up in a pressurized gasline forces the casting material from the furnace chamber into the mould. A contact probe (13) can be inserted to varying depths in a probe chamber (10) which extends downward into the furnace chamber (7) and which is open at its lower end (8) to admit the casting material. When contact is made, the contact probe sends a signal to a device (37) for controlling the flow of pressurized gas to the furnace chamber (7). When contact is made, the contact probe can be moved in the probe chamber (10) to a height which is not reached by the molten casting material during the casting process. In addition, a measurement device (36) for measuring the gas pressure in the furnace chamber (7) transmits the measured pressure in the form of a signal to the device (37) for controlling the flow of pressurized gas.

Description

Device and method for controlling and regulating the mold filling speed and the casting pressure of a low-pressure die casting machine

The invention relates to an apparatus and a method for controlling and regulating the mold filling speed and the casting pressure of a low-pressure mold casting machine, preferably for aluminum casting / its hermetically lockable furnace space or container which holds the liquid casting material and can be connected to the mold via a riser pipe leading to it which the casting material is pressed into the mold by means of gas pressure built up in the furnace chamber or container via a compressed gas supply line, with at least one contact probe in a height that can be changed in a probe chamber which projects into the furnace chamber or container from above and is open at its lower end for the entry of the casting material is arranged which gives a signal to a device for controlling the pressure gas inflow to the furnace chamber upon contact with the casting material rising due to the gas pressure in the probe pressure.

Such a control device using at least one contact probe is already known (DE-AS 28 08 588). In this known device a contact probe, which can also be moved in its height position, is used to control and regulate the gas pressure in the furnace chamber over the entire casting cycle. The contact probe ^' has two scanning needles with probe tips located at different heights. The pressure gas flow to the furnace chamber or container of the casting material is regulated so that the level of the casting material is held in the probe chamber integrated in the riser pipe between the lower and the upper probe tip of the contact probe, the height of the probe corresponding to the desired gas pressure in the furnace chamber or Container is set.

This known device has the disadvantage that the probe tips of the contact probe are in contact with or immersed in the liquid casting material several times or even continuously during each casting process, as a result of which the contact probe rapidly due to adhesion of residues and oxides of the casting material or through dissolution by the casting material loses its functional accuracy. In addition, due to the cyclically rising and falling melt in the probe space, there is a risk of growth due to crystallizing melt of the casting material, so that the latter. The room as well as the riser pipe must be heated up and kept functional by regular cleaning. _. ,

Devices for regulating the casting pressure in low-pressure die casting machines are also known (DE-AS 23 31 956), in which the gas pressure in the furnace space or in the container for the liquid casting material is set and controlled in a computer-controlled manner in accordance with a predetermined pressure / time curve. The pressurized gas is supplied through two pressurized gas feed lines with different flow cross sections. there several contact probes are provided, which are arranged immovably over the path of the rising height of the casting material and, via complicated pneumatic control elements, bring about partial or complete opening and closing of the two compressed gas supply lines and thus ensure a gas pressure which can be regulated within wide limits in accordance with the control specifications. With each casting cycle, these contact probes are immersed again in the liquid casting material which is pushed up to or beyond them, so that they have the same disadvantage as the probe in the first known device.

The invention is therefore based on the object, in a device and in a method of the type mentioned, to maintain the functionality of the contact probe unchanged over a large number of casting cycles and thus to eliminate disturbances in the regulation of the casting pressure, and to regulate the compressed gas supply introduced by the probe structurally as simple and reliable as possible. This is achieved according to the invention in that the contact probe upon contact with the casting material rising due to the gas pressure in the probe chamber, in which it gives a signal to a device for regulating the pressure gas flow to the furnace chamber or container, in which it receives the probe chamber in such a higher position which is not reached during the casting process by the level of the casting material, and that a measuring device is provided for measuring the gas pressure given in the upper region of the furnace space or container for the casting material, which measures the measured gas pressure in the form of a signal to the device Control of the compressed gas flow passes. The contact probe therefore only functions once during a casting cycle, and it indicates the contact entry to the device for controlling the pressure gas inflow, as a result of which the further control and regulation of the gas pressure in the furnace chamber or container over time after a predetermined time Program can be initiated. The gas pressure measured at that moment by the measuring device in the furnace chamber or container can be used as a reference pressure for the further control process. For the further control of the gas pressure in the furnace chamber, the gas pressure given in the furnace chamber or container can be continuously measured again with the provided pressure measuring device and the pressure gas flow to the furnace chamber or container can be regulated in accordance with the respectively measured actual pressures and the target pressures specified by the control.

The short contact between the contact probe and the casting material pushed up in the probe space, which is given only once during an entire casting cycle in the device according to the invention and this method, ensures that the contact probe is largely spared and kept free from incrustation by casting material.

The contact probe can be set in such a high position in the probe space that its scanning tip lies approximately at the height of the outlet opening of the riser tube which can be connected to the mold. This height corresponds approximately to the level of the casting material shortly before the mold starts to be filled, i.e. a level that is slightly below the mold cavity.

The probe chamber is expediently hermetically sealed with the exception of its lower opening for the entry of the casting material, so that a gas pressure can be built up above the casting material rising in this chamber, which prevents the casting material from rising up to the contact probe in its raised position with certainty. For this purpose, the upper part of the probe chamber can be connected to the furnace chamber or via a compressed gas compensation line provided with a shut-off valve Connect the container for the liquid casting material. This shut-off device can be a shuttle valve, which can be controlled in such a way that it opens the upper probe chamber to the outside air at the start of a casting cycle (vent position) when the contact probe comes into contact with the casting material that is pushed up in the probe chamber, closes the vent opening and opens the pressure compensation line to the furnace chamber and so that the gas pressure equalization between the probe chamber and the furnace chamber.

To regulate the gas pressure in the furnace chamber, the passage cross section of the compressed gas supply line can expediently be changed as a function of the gas pressure specified in the furnace chamber or container by the control program. In order to ensure the setting of the passage cross section and thus the amount of the compressed gas to be fed to the furnace chamber with the simplest possible control elements, in a preferred embodiment the compressed gas feed line is divided into a plurality of branch lines which are brought together again before they enter the furnace chamber or container and each have an unchangeable passage cross section, preferably in the form of a fixed orifice, for the compressed gas and a shut-off valve. The fixed orifices can have different through-openings and can be opened or closed individually or in any combination by the device for regulating the pressure gas inflow, as a result of which the pressure gas inflow required to the furnace or container, which is responsible for the rate of rise of the casting material in the riser pipe, can be precisely regulated. This simple control and regulation is cheap, technically unproblematic and least susceptible to malfunction. 1 of the drawing shows a particularly advantageous embodiment example of the control device according to the invention in a low-pressure casting system for aluminum casting, which is described in more detail below.

2 shows the gas pressure control possible in the course of a casting cycle with the device according to the invention in a pressure time diagram.

The casting plant shown in FIG. 1 consists of a metal melting furnace 1, into which a riser pipe 2 projects obliquely up to its bottom, which at its outer end has a connecting flange 3 for coupling to a connecting flange 4 with a casting opening and a mold 5 with mold cavity 6 Is provided. In the furnace chamber 7 also from above to close to its bottom a tubular body 9 open at its lower end 8, which delimits a probe chamber 10 in which an electrical contact probe by means of a pneumatically controlled or hydraulically controlled valve 11 by a drive cylinder 12 is arranged adjustable in height. This contact probe consists of a contact plate # 13 which sits on a guide rod 14 actuated by the drive cylinder 12. With 15 the level of the casting material located in the metal melting furnace 1, the metal melt, is indicated / which can be filled into the furnace space 7 through a closable inlet 16. The height of the probe 13 with the guide rod 14 can be adjusted and changed in the probe chamber 10 by the drive cylinder 12.

The probe chamber 10 receiving the probe 13 is, with the exception of its lower inlet opening 8 for the casting material and the junction with the furnace chamber 7 leading gas pressure compensation line 17 and a vent in the shuttle valve 18 hermetically sealed. In addition to the compressed gas compensation line 17, a compressed gas supply line 19 opens into the furnace chamber. This compressed gas supply line is in six branch lines 20 to

25 divided, which are merged before opening in the furnace chamber 7 and each an open-close control valve

26 have. The branch lines 20 to 24 are also provided with fixed orifices 27 to 31 which determine the passage of the gas volume and which have different passage cross sections. The lines 20 to 25 provided with the fixed orifices can be opened individually or in any combination via their control valves 26, so that the volume of pressurized gas required for the required climbing speed in the riser pipe 2 can be introduced into the furnace chamber 7 via the pressurized gas supply line 19 . The control valve 26 in the branch line 25 also serves, together with the throttle valve 32 also arranged in this branch line, for regulating the leakage compensation.

So that the compressed gas supply line 19 can also be used for venting the furnace chamber 7, a vent line 33 with a vent valve 34 is connected to this line. In the furnace chamber 7 also opens a gas pressure measuring line 35, which leads to a pressure transducer 36 designed as a pressure current transducer, which transmits the gas pressure registered by him via line 35 in the furnace chamber 7 via electrical signals to an electrical control device 37, which is used for control the valves 11, 18, 26 and 34 is set up.

The operation of the control device of this embodiment of the invention works as follows: First, the probe 13 is set at a height within the probe space 10, which corresponds approximately to the outlet opening of the riser pipe 2 in the area of its coupling flange 3. The shuttle valve 18 is switched so that the upper probe chamber is vented. Then, with the vent valve 34 closed, corresponding adjustment of the control valves 26 in the branch lines 20 to 25 of the pressurized gas feed lines 19 introduces pressurized gas into the furnace chamber 7, until the metal melt in the probe chamber 10 builds up to the lower edge of the contact probe 13 due to the gas pressure thus built up in the furnace chamber has been pushed up. The contact crossing between the pressed metal melt and the contact probe 13 is registered by the latter and "reported to the electrical control unit 37, which then initiates further control of the compressed gas flow via the line 19 into the furnace chamber according to a predetermined program. At the same time, the probe 13 is activated by the The drive cylinder 12 is raised to a height within the probe chamber 10, in which it remains out of contact with the cast material pushed up in the probe chamber during the entire subsequent casting process, and the shuttle valve 18 is switched over, so that the vent opening of the upper probe chamber is closed and the pressure gas compensation line 17 is opened , whereby the gas pressure in the furnace chamber 7 is transferred into the probe chamber 10 above the metal melt therein and the metal melt which has risen in this chamber is pushed back to the level of the melt in the furnace chamber 7.

In addition, the gas pressure given at this point in time in the furnace chamber 7 is measured by the measuring device and its measurement result is passed on electrically to the electrical control device 37, which is the height given at that moment of the gas pressure in the furnace chamber 7 is used as a reference variable for the further control of the casting pressure in the furnace chamber.

From this point in time, the further time control and regulation of the casting pressure and thus the rate of rise and height of the molten metal to be introduced through the riser pipe 2 into the mold cavity 6 of the mold 5 by controlling the volume flow of the pressurized gas to be introduced into the furnace chamber 7 via the compressed gas line 19 over time carried out according to a preprogrammed pressure-time curve 38, as can be seen from FIG. 2.

The numbers in the rectangles in FIG. 2 designate measuring points at which the pressure gas inflow and thus the further time course of the pressure rise in the furnace space undergoes a change in the course of a casting cycle. The first section of the curve between the measuring points 1 and 2 shows the increase in the gas pressure up to the point in time at which the metal melt has reached the contact probe 13 in the probe chamber 10 set at the level of the coupling flange 3 of the riser tube 2 (level line A). During this phase of the pressure increase in the furnace, all control valves 20 to 25 in the gas pressure supply line 19 are open. This pressure build-up phase is followed by the phase of the start of filling the mold cavity 6 in the mold 5, which is characterized by the curve section between the measuring points 2 and 3 of the pressure-time curve according to FIG. 2. The pressure increase per unit of time, as can be seen from FIG. 2, is somewhat less than in the previous pressure build-up phase. This is followed by the phase of the main mold filling, which is characterized by the curve section between the measuring points 3 and 4 in FIG. 2, followed by the phase of the end of the mold filling with an increased pressure rise according to the curve section between the measuring points 4 and 5, until the mold cavity 6 is completely filled (level line B). This phase is followed first by a renewed increase in pressure, the holding pressure phase, which is characterized by the curve section between measuring points 5 and 6, and then the phase of maintaining this holding pressure, which is used for feeding the feed, which is characterized by the curve section between measuring points 6 and 7. At the end of this holding pressure phase, the gas pressure in the furnace chamber 7 is reduced to zero by opening the vent valve 34, which is shown in FIG. 2 by the curve section between the measuring points 7 and 8. The liquid metal from the sprue and the riser pipe sinks back into the furnace.

Depending on the strength of the desired pressure build-up in the curve sections between measuring points 1 to 6, the control valves 26 are opened or closed in different combinations, as can be seen from the following example:

table

Control valves

Curve 1 2 3 4 5 section 1-2 + pressure build-up (metal rises up to the contact probe) Beginning of the mold filling Mold filling End of the mold filling Building the holding pressure Holding the holding pressure

Venting (pressure reduction to atmospheric pressure)

+ = Control valve open

- = control valve closed

The control valves remain in their set position in the individual phases of the casting cycle until the gas pressure in the furnace chamber 7, which is continuously measured by the measuring device 36, has reached the respective target pressure specified according to the control program.

To maintain the holding pressure for the duration of the above-mentioned make-up phase, the control and leakage loss valve 26 located in the branch line 25 is used, which according to the leaks determined by gas pressure measurement in the entire gas pressure system continuously allows a certain amount of compressed gas to flow into the furnace interior 7. The observation of the constancy of the gas pressure during the holding pressure phase can serve to register changes in the total leakage losses and to compensate for them by adjusting the loss compensation accordingly.

Claims

Claims:

Apparatus for controlling and regulating the mold filling speed and the casting pressure of a low-pressure mold casting machine, the hermetically lockable furnace chamber which receives the casting material is connected to the mold via a riser pipe leading to the latter, via which the casting material is pressed into the mold by means of gas pressure built up in the furnace chamber via a compressed gas supply line At least one contact probe is arranged to be changeable in its height in a probe chamber that projects into the furnace chamber from above and is open at its lower end for the entry of the casting material, which, when contact is made with the casting material that rises due to the gas pressure in the probe chamber, sends a signal to a device for controlling the pressure gas inflow to the furnace chamber, characterized in that the contact probe (13) can be moved up to such a height when contact occurs in the probe chamber (10) which receives it, during the casting process by the N level of the liquid casting material is not reached and that a measuring device (36) is provided for measuring the gas pressure given in the furnace chamber (7), which passes the measured pressure in the form of a signal to the device (37) for regulating the pressure gas inflow.

2. Device according to claim 1, characterized in that the contact probe (13) can be moved up and down by a pneumatically or hydraulically controlled drive cylinder (12).

3. Apparatus according to claim 1, characterized in that the contact probe (13) in the probe chamber (10) is adjustable at such an altitude that its scanning tip is approximately at the level of the outlet opening of the riser pipe (2) which can be connected to the mold (5).

4. The device according to claim 1, characterized in that the probe chamber has a closable vent opening in its upper region.

5. Apparatus according to claim 1 or 4, characterized in that the probe chamber (10) with the exception of its lower opening (8) for the entry of the casting material can be hermetically sealed.

6. The device according to claim 4, characterized in that the probe chamber (10) in its upper region via a lockable by a shuttle valve (18) pressure gas compensation line (17) with the furnace chamber (7) is in communication.

7. Apparatus according to claim 4 and 6, characterized in that the shuttle valve (18) is controllable so that it switches when the contact probe (13) contacts the cast material in the probe chamber (10) so that the vent of the probe chamber is closed and the pressure compensation line (17) is opened.

8. The device according to claim 1, characterized in that derv passage cross section of the compressed gas supply line (19) is variable depending on the gas pressure desired in the furnace chamber.

9. The device according to claim 8, characterized in that for setting the gas pressure desired in the furnace chamber (7), the compressed gas supply line (19) is divided into a plurality of branch lines (20 to 25) which are brought together again before the confluence with the furnace chamber and each have a fixed one Have passage cross-section (fixed orifice 27 to 31) for the compressed gas and a control valve (26) designed as an open-close valve.

10. The device according to claim 9, characterized in that the control valves can be controlled by a device (37) for controlling the pressure gas inflow.

11. The device according to claim 1, characterized in that a leakage valve (26, 32) is arranged in the compressed gas supply line (19) opening into the furnace chamber (7), which can be controlled as a function of the gas pressure losses given by leakage in the furnace environment.

12. A method for controlling the casting pressure of a low-pressure die casting system (metal casting system) with a device according to one or more of claims 1 to 11, characterized in that when the contact probe comes into contact with the casting material which is pushed up in the probe chamber, the gas pressure in the furnace chamber is measured and via an electrical signal as Reference pressure is used for the further control of the compressed gas flow to the furnace chamber.

13. The method according to claim 12, characterized in that after the contact of the contact probe with the cast material pushed up in the probe space, the gas pressure in the furnace space is measured continuously and the compressed gas flow to the furnace space is regulated in accordance with the target pressure specified in each case by the control program in the furnace space.