DE4204060C2 - Device for regulating the pressure in a container interior of a dosing furnace, a low pressure furnace or a metal pump - Google Patents

Description

The invention relates to a device for regulation of the pressure in a container interior of a dosing furnace, a low pressure furnace or a metal pump according to the preamble of the main claim.

In state-of-the-art casting plants, casting processes are automatically controlled and for a smooth process, a fast and accurate dosing of the molten metal is very important. It is known (H.-P. Bräuninger, R. Hann: Ge weight-dependent control of metal dosing during die casting. In: Gießerei 77 (1990) pp 75-78 and DE-PS 20 22 989) dosing processes from dosing furnaces via a pressure control and / or to carry out pressure control in which the pressure in the furnace chamber is detected and is controlled or regulated accordingly by the desired metering quantities. However, it has been shown that with known pressure control, the dosing accuracy is unsatisfactory, since the control is too slow and parameters that change during the dosing process cannot be detected or can only be recorded imprecisely. In addition, readjustments must be made if long-term changes occur; For example, if there is a decrease in the level in the furnace, an increasing pressure deviation occurs, which can only be remedied by readjusting.

From DE 37 08 826 A1 a control circuit for a Proportionally controlled, electro-hydraulically operated tes valve known, in which a closed rule circle depending on a signal deviation in one open control loop is switched.

In the publication "Border control with two circuits circuit "by G. Lausterer, Kandel in Automatisie tion technical practice atp, 30th year, issue 12/88, Page 586-588 describes a cascade control where a subordinate controller is an auxiliary control variable utes regulates, while a subordinate controller or Füh controller regulates the actual controlled variable.

Based on this state of the art, the Er find the task based on a generic To create a device for regulating the pressure even with different pressure conditions has fast and accurate control behavior, so that accurate and accurate over the life of the container Fast dosing possible without re-parameterization is.  

This object is achieved by the kenn Drawing features of the main claim solved. There through that a pressure cascade control with the help of a Proportional valve, the command variable from the Addition of the manipulated variable of a superimposed control reg lers and a tank pressure setpoint is provided, the master controller being a Reg with PI behavior and as input variables the actual pressure value from the furnace interior and the Receives pressure setpoint, is a very fast rain possible because of changes in pressure in the container For example, only the Pressure difference must be regulated. The master controller The manipulated variable also compensates for the pressure drop in the piping between the proportional valve and Furnace room, as well as offset, temperature and aging effects of the entire control loop.

The offset, temperature and aging effects arise hen in that the air temperature in foundries rature is between about 10 ° C and 50 ° C, and that the proportional valve is mounted on an oven, whose lid has a temperature of about 60 ° C.

The master controller, however, here control circuit 1 , can be placed in a control cabinet, which is also cooled with the help of a cooler system or a cooling unit and can be kept at a constant temperature.

In addition, a maximum absolute rule deviation (+/- 0.05%) over the entire pressure range given and the control parameters are not critical and long-term stable, so that no parameterization over the entire life of the oven is required.  

The control circuit has short response times (0.2-0.5 ms), which means that there is no overshoot when grinding a setpoint jump occurs. The control loop has a high degree of flexibility, since any adjustment the same proportional valve to different re gel routes with the help of the master controller without intervention into the proportional valve. Still is advantageous that the device according to the invention same control procedures for positive and negative Has setpoint jumps.

By the measure specified in the subclaims Men are advantageous further training and improvements possible.

An embodiment of the invention is in the Drawing shown and is in the following Description for a dosing oven explained. It demonstrate:

Fig. 1 is a schematic diagram of the inventive device for regulating the pressure and

Fig. 2 shows the schematic diagram of the master controller used in Fig. 1.

The device shown in Fig. 1 for regulating the pressure in a metering furnace has a Druckbe container 1 , which forms the furnace interior and in which the molten metal is received. Preferably, the pressure vessel 1 is under pressure, the interior filling level being taken into account when determining the pressure. For dosing, the pressure is briefly increased so that the liquid metal is pressed out of a pouring opening. The pressure vessel 1 is connected via a pipeline 2 to a pneumatic proportional valve 3 which is connected to a supply pressure source 4 and regulates the pressure supply into the pressure vessel 1 . In the pipe 2 at the output of the Proportionalven valve 3, a pressure sensor 5 is switched for the valve outlet pressure, which provides the information about the pressure P at the outlet of the valve 3 to the valve as a controlled variable.

The pipe 2 between the pneumatic valve 3 and the furnace serves to cool the hot furnace air (700 ° C - 900 ° C) and to repel the aggressive metal vapors. Otherwise the pneumatic valve would be destroyed immediately (normal air temperature of 50 ° C). The pipeline 2 but has a pressure drop to follow Ge.

Another pressure sensor 6 is arranged on or in the pressure vessel 1 , which detects the pressure in the interior of the furnace. The pressure sensor 6 is connected to an input of a PI master controller 7 , the other input of which receives the setpoint for the furnace interior pressure from an external setpoint. The block diagram of the master controller is shown in Fig. 2. It consists of an adder 8 , to which the actual pressure value and pressure setpoint is supplied, an amplifier 9 connected to the output of the adder 8 and an integrator 10 in parallel with it and a further adder 11 which amplifies the output signals of the amplifier 9 and of the integrator 10 receives. As can be seen, the master controller 7 is designed as a known PI controller.

The output of the master controller 7 is connected to an adder 12 , at the other input of which there is a scaling unit 13 , which is connected to the external setpoint specification and supplies the scaled setpoint value at its output. The adder 12 is connected to the proportional valve 3 and provides the guide size for the control loop present in the proportional valve 3 .

The device shown in FIG. 1 forms a pressure cascade control with a proportional valve 3 , the reference variable of which is formed from the addition of the manipulated variable of the master regulator 7 and the scaled setpoint of the furnace interior pressure. The proportional valve 3 works via the pneumatic pipeline 2 as a pressure regulator for the air volume of the pressure container 1 . Its electrical command variable is converted into a proportional pressure at its outlet with the aid of the valve-internal control circuit, this pressure being greater than the furnace interior pressure, since a pressure drop occurs in the pipeline 2 . So the following applies:

Valve outlet pressure = furnace interior pressure + pressure case,

whereby the pressure drop is not a firmly calculable quantity is because it depends on the volume flow and the pipe geometry depends. To have a very accurate furnace space To implement pressure control is the lead size, as already mentioned above, from two compos together, d. H.

Command variable = scaled setpoint + master controller manipulated variable.

The pressure variables are valve outlet pressure, furnace interior pressure, pressure drop the assigned electri variables reference variable, scaled setpoint, Master controller manipulated variable proportional, of which Master controller manipulated variable in addition to the pressure drop the temperature, offset and aging effects is also taken into account.

If in the furnace interior, ie in the pressure vessel, the pressure changes compared to the pressure setpoint, the master controller 7 delivers a manipulated variable that takes into account the difference between the target and actual value, where due to the design of the master controller as a PI controller rapid changes are also recorded. Since the reference variable for the proportional valve is made up of the scaled pressure setpoint and the manipulated variable corresponding to the difference between the pressure in the furnace chamber and the setpoint pressure, the pressure at the valve outlet is regulated so that it is higher than the furnace interior pressure, causing the pressure drop in the Piping between the valve and the furnace chamber as well as the offset, temperature and aging effects of the entire control loop can be compensated.

Usually, the commercially available fast but inexpensive proportional valves for higher pressures (0.2-10 bar) than in the furnace used in the invention are required (0-0.2 bar). In this low pressure range, proportional deviations in the normal application would occur (pipe 2 is not available and the pressure setpoint is given directly to the proportional valve) in the outlet pressure. The master controller 7 forces the proportional valve with a valve-internal control circuit to have a highly accurate proportionality, even in the pressure range for which it is not designed.

In the described process, the proportional valve is operated in the thermal limit range (ambient temperature around the furnace 30 ° -50 ° C). This results in aging that changes the internal parameterization over the years. This shift is also compensated for by the master controller 7 , which is protected in the control cabinet and retains its parameterization for about 10 years.

The device according to the invention can be used to implement pressure control with a very small and constant control deviation (+/- 0.75 mbar) over the entire pressure range ( 0 to 1 bar) and with a very short response time.

The invention was based on an example of a dosing oven described. Of course it is too applicable for other containers from which who dosed that should, for example for low pressure ovens or Metal pumps for conveying a molten metal.

Claims (3)

1. A device for controlling the pressure in a ter terraum a dosing furnace, a low-pressure furnace or a metal pump, with a pressure in the container interior pressure sensing pressure sensor and a control circuit for regulating the pressure in the interior of the container, characterized in that the control loop is designed as a cascade control loop A first control circuit forms a master controller ( 7 ) which has a PI control behavior and which receives the actual pressure value delivered by the pressure sensor ( 6 ) and a pressure setpoint and supplies a manipulated variable which, added to the pressure setpoint, the electrical command variable for a second control circuit present in a proportional valve ( 3 ), which is connected to a further pressure sensor ( 5 ) for the output pressure of the proportional valve ( 3 ), that between the proportional valve supplying a pressure proportional to the electrical command variable ( 3 ) and the inside of the container a pipe ( 2 ) for cooling the hot container interior air is provided, the further pressure sensor ( 5 ) in the pipe ( 2 ) to the container interior ( 1 ) at the outlet of the proportional valve ( 3 ). 2. Device according to claim 1, characterized in net that the first control loop is removed from the tank interior is arranged.   3. Apparatus according to claim 1 or 2, characterized in that the sum of the manipulated variable of the most control loop and a scaling unit ( 15 ) scaled pressure setpoint forms the guide variable for the second control loop.