EP0215153A1 - Low pressure casting device for the permanent mold casting - Google Patents

Abstract

In low-pressure casting installations for permanent-mould casting with a pouring furnace 1 and a casting machine 2, the casting pressure, which presses the metal out of the casting nozzle 6 of the furnace into the mould 5 and sinks during operation by dropping of the molten-bath level, is usually brought about by a displacement body plunging into the furnace or by frequent refilling with metal. In the process, sealing problems occur, and the melting in the molten metal bath is also problematic. The loss in time or effectiveness caused by frequent refilling with metal is not a point in its favour. The invention therefore works without a displacement body, with a pressure-gas control system which acts on the molten-bath level of the metering chamber of the furnace and is split up into a closed inlet- pressure circuit 3 on the furnace side and an open casting-pressure branch 4 which are separated by a diaphragm 9 in a diaphragm store 10. Furthermore, an electric pressure generator 25 is provided which, during a cycle comprising one or more fillings of the mould, transmits an output signal A1 with a uniform current value for the control of the inlet pressure and a further output signal A2 for the control of the casting pressure, the current value of which output signal A2 is equal to the current value of the signal for the inlet pressure plus a value increasing by an adjustable identical current sweep after every filling of the mould. After every cycle, an output signal is transmitted for the control of the inlet pressure, the current value of which output signal is one level step higher than the current value for the preceding cycle, while the size of the current sweeps of the signal for the casting pressure remains the same.

Description

The invention is directed to a low-pressure casting system predominantly for permanent mold casting, in which the casting is carried out by gas pressure on the bath level in the metering chamber of the casting furnace and in which the pressure increase required by the metal outlet from the casting nozzle into the mold does not increase with increasing emptying Metal refill or lowering of a displacement body, for example according to DE 21 28 425 A1, DE 29 50 597 A1, is achieved. In such a furnace, it is known to supply the pressure directly to the furnace via a signal converter and a volume amplifier. The signal converter gets a fixed prescribed after each casting Value for increasing the pressure, so that as the amount of metal in the furnace decreases, the pressure is increased. At the start of the casting cycle, a counter starts which, after a set number of castings, depressurises the furnace for refilling. If the furnace is not properly filled at the start of casting, the number of castings is no longer correct or the specified pressure increase is not sufficient to fill all molds properly. On the other hand, if the furnace is filled too high, metal may spurt out of the furnace.

It is also known from DE-OS 33 17 474 a low pressure casting process, in which the casting is also carried out by increasing the pressure in the metering chamber of the casting furnace, for which purpose the height of the bath level is measured in the pouring nozzle by a probe, the electrical signals of which are transmitted to an electronic one Computers are fed in, in which the pouring process is also stored and which increases the gas pressure in the storage chamber when the bath level drops below a desired value until the feedback from the probe indicates that the predetermined bath level has been reached. The pressure required for this is stored in the computer as the initial pressure and the programmed pressure increase for the casting in the computer is added to this starting point, while the initiation of the goat process and the casting time took place from an electronic control connected to the computer.

With this method, the same initial situation can always be created in the pouring nozzle, ie the bath level between the pouring operations can be brought to a predetermined level, but the system is too slow to be used for the filling a mold required a short time of about 3 to 8 seconds to achieve the necessary pressure increase. There are also maintenance problems due to the constant contact of the probe with the liquid metal.

Accordingly, the object of the invention was to develop a casting method which restores the same casting conditions after each casting and achieves the necessary pressure increase for the mold filling in the desired time and regardless of the filling level of the furnace.

The invention solves this problem with the means defined in the claims.

The invention is described below with reference to the drawings, of which FIG. 1 shows a gas pressure line diagram and FIG. 2 shows a current-pressure diagram.

The main parts of the low-pressure casting system according to the invention are a low-pressure casting furnace, generally designated 1, a mold casting machine, generally designated 2, and a compressed gas duct for the top furnace, which consist of an inlet-closed, generally designated 3 pre-pressure circuit and a generally designated 4 Casting pressure branch is composed.

The mold casting machine 2 takes over the function of handling the molds. The core is inserted in a first position, after which the carousel rotates in the direction of the casting furnace 1 into a second position in which the mold 5 is placed on the casting nozzle 6 of the furnace. The Placing the mold automatically increases the casting pressure by means of a magnetic valve and the metal flows into the mold 5. After the metal has solidified in the mold, the mold lifts off the furnace and the machine turns to a third position, in which the mold is opened and the casting is ejected. The casting machine then turns to a fourth position, in which the mold is immersed in a finishing bath.

The casting furnace 1 has, in addition to the casting nozzle 6, a metering chamber 7 and a filling chamber 8. Both chambers are equipped with pressure-tight lids to avoid pressure losses in the furnace.

A separating element for the upstream pressure circuit 3 opposite the casting pressure branch 4 is a membrane 9 in the membrane accumulator 10. In the closed circuit 3, therefore, for each casting, i.e. for each mold filling a pre-pressure which determines the bath level in the pouring nozzle 6, which also acts in the membrane reservoir on the underside of the membrane 9 and by applying the casting pressure to the top of the membrane, the pre-pressure is increased so that metal from the metering chamber 7 into the pouring nozzle 6 flows in and presses the metal in it into the mold 5.

The inlet pressure circuit 3, which is closed on the furnace side, can either be supplied via a separate pressure source, for example a nitrogen bottle 11, or via the gas network. For this purpose, the power line 12 splits in the factory into a pressure accumulator line 13, which leads to the pressure accumulator 14 and into an oven line 15 intended for supplying the upstream pressure circuit, which opens into the closed oven circuit 3.

In the upstream pressure circuit there are one or more solenoid valves 16a, 16b, 16c for the pressure build-up in the furnace feed line 17 and a solenoid valve 18 for the pressure reduction and an emergency valve 19 for the ventilation. A charging furnace for filling the casting furnace after it has been completely emptied is generally designated by 20. A plurality of solenoid valves 16 can be provided if molds of different shapes, different capacities or with different casting conditions are available for filling on a mold casting machine.

Between the pressure accumulator 14 and the membrane accumulator 10 there is a solenoid valve 21 "release casting pressure" and in the inlet pressure line 22 a solenoid valve 23 for releasing the inlet pressure. 24 is a vent valve.

An important component of the system according to the invention is an electrical pressure generator, generally designated 25, via which both the admission pressure and the casting pressure are controlled. Its task is to deliver two output currents in a low current range, e.g. from 4 to 20 mA after the presence of certain input signals according to a predetermined pattern, which is set depending on the number of castings in a cycle and the amount of metal for a mold filling and that is, according to the required pressures can be. For this purpose, the pressure generator has several inputs, namely an input for the release signal, without which no pressure may be built up, and for a signal “build up pressure” and “build up pressure”, both for setting the bath level after a furnace has been filled are determined by hand before the first mold filling. In addition, a "pour" signal and a "pour end" signal are received. The pressure generator also has two outputs, namely an output A1 "pre-pressure" and an output A2 "casting pressure". The setting is made by means of a first potentiometer F3, with which a positive current swing can be set, which is effective as long as the previous enable signal is present. Furthermore, a preselection switch F2 is provided for the operation, with which the number of current strokes set by the size of the potentiometer F3 can be set before the output values increase by the value set by the potentiometer F1. For example, if the selector switch F2 has a range from 0 to 9 and is set to 6, the same current stroke will occur six times in a cycle for 6 castings before a new cycle begins and the pressures (pre- and casting pressure) around the value be increased by F1.

A new cycle is initiated in that the aforementioned current stroke remains unchanged in its level, but assumes an increased level. This level jump can be set for operation with another potentiometer F1. After each cycle, there is a further level jump of the previously set height, as illustrated by the diagram in FIG. 2.

In addition, there are indicators and switches, buttons or the like in the pressure generator for the filling level of the furnace and malfunctions.

A current value is constantly present at the analog output A1 "pre-pressure" of the pressure generator, which is cyclically around that with the further potentiometer F1 set level jump increased; the current value of the "pre-pressure" output plus the current stroke set with potentiometer F3 is constantly present at the analog output A2 "casting pressure". For a casting cycle for a predetermined number of mold fillings, the same current value is present at the “pre-pressure” output, which current value only increases after the end of a cycle due to the abovementioned level jump. At the "casting pressure" output there is also the same current value for one cycle, which is composed of two constant variables, namely the current value for the admission pressure and the set current stroke.

Since the electrical currents of the pressure generator are converted into pneumatic signals in converters for the upstream pressure and for the casting pressure, the currents correspond to pressures in the gas lines.

Without prejudice to the setting of the aforementioned level jump, the absolute level of the current level can be increased or decreased gradually, for example in steps of 12.5% of the level jump, for the setting of the bath level by hand. This is done by means of inputs on the pressure generator with the functions "build up pressure" and "reduce pressure", which are controlled by two separate buttons. Each time you press one of these buttons, the values given above are increased or decreased.

The operation of the system according to the invention is as follows:

By opening the shut-off valve 26 at the factory, a compressed gas, usually compressed air, flows through a filter 27 into the pressure accumulator 14, the press air pressure is displayed on the manometer 28. By the volume amplifier 29 located behind the filter in the pressure storage line 13 and 30 in the pre-pressure supply line 22, the factory pressure is reduced depending on the electrical signal output by the pressure generator 25 via the electro-pneumatic transducers 31 and 32, with the casting pressure and via the volume amplifier 29 the volume booster 30 of the form can be set. The difference between the pre-pressure and the casting pressure is always constant and can be set manually on the pressure generator.

The casting pressure required for the mold filling is displayed on the manometer 33 in the casting pressure line 34 and the admission pressure required to achieve a constant bath level in the casting nozzle 6 is displayed on the manometer 35. When the solenoid valve 21 is actuated via a “casting” pushbutton on the pressure generator, the compressed air flows from the pressure accumulator 14 into the membrane accumulator 10. The influx of the compressed air causes the membrane to be deformed and thus a pressure on the gas volume in the closed furnace circuit 3, the casting pressure, exercised. The gas volume in the closed furnace circuit has a certain admission pressure, for example a maximum of 0.25 bar, and the casting pressure is applied to this gas volume via the speed control valves 36 and the opened solenoid valves 16, so that the metal is pressed into the mold.

The metal feed is set beforehand on the casting console using an electronic timer. After this time, the compressed air magnet valve 21 closed and thus the metal supply to the mold interrupted. The previously set holding or solidification time of the metal in the mold expires after a closing of the solenoid valve 21 via a second electronic time clock.

As already stated, the gas volume in the closed furnace circuit 3, that is to say that in the furnace space and membrane accumulator 10 and the feed and discharge lines between them, can either be via a special pre-pressure gas source, e.g. the nitrogen bottle 11 and the associated reducing valve 37 or via the furnace line 15 of the compressed air network can be set as a function of the electronically determined form in the pressure generator, for which purpose the shut-off valves 38 and 39 must be opened and closed accordingly.

After the set holding or solidification time, which delays the metal waste on the mold, the vent valve 24 in the compressed air-side casting pressure branch and the solenoid valve 18 in the furnace discharge line 40 is opened, via which the compressed air escapes from the diaphragm accumulator 10 into the free space and, on the other hand, that Metal in the pouring nozzle falls off. The solenoid valve 24 remains open until the manometer 41 indicates the pressure 0 bar. By closing the solenoid valve 24 and the solenoid valve 18 and simultaneously opening the solenoid valves 23 and 16, gas equalization takes place in the furnace chamber.

In order according to a predetermined number of mold fillings per cycle, which depends on the casting weight, and which is only one filling with a high casting weight If the bath level in the pouring nozzle is raised again, the pre-pressure is increased by the value Delta P after one cycle. This value is previously set via the potentiometer F1 as a level jump in the current value and a counter, so that after the set cast number has expired, the bath level is automatically adjusted for the following cycle via the analog output A1 "pre-pressure" on the pressure generator.

The overall control is protected by the safety pressure valve 42 on the compressed air side, which releases the compressed air flowing out of the pressure accumulator when a set pressure is exceeded. The control is also protected by the compressed air vent valve 24 and the furnace solenoid valve 19, which immediately release the pressure in the event of a power failure or actuation of an emergency button. This ensures that when metal escapes from the mold or pouring nozzle, the metal flow is interrupted immediately when the emergency button is pressed.

The maximum permissible pressure in the furnace is set by two contact pressure gauges 43 connected in parallel. When this maximum pressure is reached, the compressed gas escapes automatically and the furnace is depressurized.

If, after the cyclically repeated casting processes, the casting furnace 1 is empty, this is indicated by the contact manometer 43; all solenoid valves are de-energized and the casting furnace is depressurized. The pressure generator no longer receives an enable signal, which causes it to move to the start position returns and the oven can be refilled. 44 are filters in the furnace discharge line 40 for the pre-pressure gas flowing out of the furnace space.

Example: The potting furnace is half full and has a current value of 10 mA at output A1 "pre-pressure" of the pressure generator with a pre-pressure of 100 mbar. This means that a pressure of 100 mbar prevails in the filling chamber and the metering chamber of the casting furnace, while the casting nozzle is depressurized. The metal in the pouring nozzle is then at nozzle height. On the front panel of the pressure generator, set with the potentiometer F1 0.5 mA (corresponding to a pressure of 30 mbar), with the selector switch F2 2 (castings or current strokes per cycle) and with the potentiometer F3 3 mA (corresponding to 300 mbar).

The pressure generator continuously outputs 10 mA at output A1 "pre-pressure" and 13 mA at output A2 "casting pressure". The value of the "casting pressure" output is calculated in the pressure generator from the addition of the "pre-pressure" output and the set value of the potentiometer F3. In the converter 32, the signal "pre-pressure" with the current value 10 mA is converted into a pneumatic signal of 100 mbar. The volume amplifiers 30 amplify this signal at the output with the same value but larger volume, which specify the pressure in the furnace via the solenoid valve 23 and the solenoid valve 16. The output A2 "casting pressure" of the pressure generator gives the value 13 mA to the converter 31. There the electrical signal is converted into a pneumatic signal with 400 mbar. A pressure of 400 mbar is produced in the pressure accumulator 14 via the volume booster 29. The solenoid valve 21 is closed, the solenoid valve 24 opened. This means that the line between the solenoid valve 21 and the diaphragm accumulator 10 is depressurized, while it is filled with 100 mbar on the furnace side. At the start of casting, the mangle valves 29 and 24 close and at the same time the solenoid valve 21 opens. Nothing changes on the pressure generator. The air from the pressure accumulator 14 flows into the membrane accumulator 10, whereby the pressure in the furnace increases from 100 mbar to 400 mbar.

After the casting time has elapsed, the solenoid valve 21 closes and after the solidification time, the solenoid valve 16 closes and the solenoid valves 18 and 24 open. The air in the furnace escapes into the diaphragm accumulator via the solenoid valve 18; on the compressed air side, the line between the diaphragm accumulator 10 and the solenoid valve 21 is depressurized.

After actuation of the zero mbar contact on the contact manometer 41, the solenoid valves 19 and 24 close and the solenoid valves 29 and 16 are opened. Because the signals A1 = 10 mA and A2 = 13 mA are still present at the output of the pressure generator, the same pressure values are set in the furnace and in the pressure accumulator as before the casting process, 100 mbar and 400 mbar. The casting process is complete.

Because the preselection switch F2 has the value 2 on the front panel of the pressure generator, no pressure values are increased.

The next casting process is the same as the previous one. After the new casting process has ended, the pressure generator increases the values for the outputs A1 and A2 by the value of F1 = 0.5 mA, corresponding to 30 mbar. The value 13.5 mA is set at output A1. The new admission pressure for the furnace is 100 mbar + 30 mbar = 130 mbar. The new casting pressure for the furnace is 400 mbar + 30 mbar = 430 mbar. The difference between the admission pressure and the casting pressure therefore remains constant, namely 300 mbar or 3 mA as set with F3.

List of reference symbols

• 1 casting furnace (general)
• 2 mold casting machine (general)
• 3 pre-pressure circuit (general)
• 4 casting pressure branch (general)
• 5 mold
• 6 pouring nozzle
• 7 dosing chamber
• 8 filling chamber
• 9 membrane
• 10 membrane accumulators
• 11 nitrogen bottle
• 12 power cord
• 13 accumulator line
• 14 pressure accumulators
• 15 furnace pipe
• 16 solenoid valves (a to n)
• 17 furnace feed
• 18 solenoid valve
• 19 emergency valve
• 20 charging furnace
• 21 solenoid valve
• 22 inlet pressure line
• 23 solenoid valve
• 24 vent valve
• 25 pressure generator (general)
• 26 shut-off valve
• 27 filters
• 28 manometers
• 29 volume booster
• 30 volume boosters
• 31 transmitter
• 32 transmitters
• 33 manometers
• 34 casting pressure line
• 35 pressure gauges
• 36 speed control valve (a to n)
• 37 reducing valve
• 38 shut-off valve
• 39 shut-off valve
• 40 furnace discharge
• 41 manometers
• 42 Safety pressure relief valve
• 43 contact pressure gauges
• 44 filters

Claims (6)

1. Low-pressure casting plant, in particular for permanent mold casting with a filling chamber (8), a metering chamber (7) and one or more pouring nozzles (6) containing casting furnace (1) and one that moves the molds (5) into the casting position and other processing stations Casting machine (2) and a pressurized gas control acting on the bath level in the metering chamber, characterized in that the pressurized gas control is divided into a closed furnace-side pre-pressure circuit (3) and a casting pressure branch (4) which is separated by a membrane (9) are separated in a diaphragm accumulator (10) and that an electrical pressure generator (25) is provided for the pressure control, which during a cycle comprising one or more mold fillings has a first output signal (A1) with a constant current value for the control of the admission pressure and a outputs another output signal (A2) for the control of the casting pressure, the current value of which is equal to the current value of the signal for the upstream pressure plus a value which increases by an adjustable current stroke. 2. Low-pressure casting plant according to claim 1, characterized in that the pressure generator (25) emits an output signal (A1) after each cycle comprising one or more mold fillings for the control of the admission pressure, the current value of which is an adjustable level jump higher than the current value for the previous cycle. 3. Low-pressure casting system according to claims 1 and 2, characterized in that in the furnace feed line (17) of the closed admission pressure circuit (3) one or more solenoid valves (16) and before these speed control valves (36) and in the furnace discharge line (40) Solenoid valve (18) are switched for pressure reduction. 4. Low-pressure casting system according to claims 1 to 3, characterized in that in the pressure accumulator line (13) behind a volume booster (29) and in front of the membrane accumulator (10), a pressure accumulator (14) and between this and the membrane accumulator a solenoid valve (21 ) are arranged for the release of the casting pressure. 5. Low-pressure casting plant according to claims 1 to 4, characterized in that the supply of the upstream pressure circuit (3), controlled by shut-off valves (38, 39), optionally by a second compressed gas source, for example a gas bottle (11) or the power line (12 ) takes place and for this purpose the power line forks into a pressure storage line (13) for the build-up of the casting pressure and a furnace line (15) for the build-up of the pre-pressure. 6. Low-pressure casting system according to claims 1 to 5, characterized in that in the inlet pressure line (22) in the flow direction in front of the solenoid valves (16) one behind the other a volume booster (30), a inlet pressure gauge (35) and a solenoid valve (23) for the Release of the form are arranged.

Images