EP0946314B1 - Metering oven - Google Patents

Abstract

The invention concerns a metering oven (1) with a vessel (12) for holding a liquid metal and with a device for detecting a liquid metal level in a vessel. A tubular probe (5) is connected to a gas source (10) for discharging a gas at a predetermined pressure from the gas source through the probe and out of its aperture. The probe is spatially associated in a fixed manner with the vessel such that pressures which can be detected by a pressure-measuring device (9) can be associated with different liquid metal levels inside the probe. At a given pressure threshold value, the pressure-measuring device can emit a signal for a given liquid metal level to be detected.

Description

The invention relates to a dosing furnace with a Vessel for holding liquid metal and a device for detecting a level of liquid metal in a vessel.

For dosing liquid metal from a dosing furnace must the metal column rising in the metering tube be recorded in their amount, as dependent the dosing quantity is calculated from this recording. It is also possible depending on the capture of the Height of the metal column taking into account others Parameters, for example different pressures, the height of the liquid level in the oven. From the US 4,220,319 is a sensor arrangement for dosing furnaces known in which the sensor from a vertical or Metal needle almost perpendicular to the metal surface exists when contacting the liquid metal surface emits a signal. To wear to reduce the sensor arrangement, the metal needle through an automated mechanical system swung away from the metal surface when making contact. This known arrangement has several Disadvantages, especially the mechanical swivel system very complex and expensive and despite the pivoting the wear on the metal needle is relative large. The needle can initially be in contact with liquid aluminum decomposes due to chemical processes become. In addition, the measurement result can Accumulation of aluminum or aluminum oxide on the Needle will be affected.

In practice is due to the wear explained above grinding, cleaning or the metal needle the replacement of the needle is necessary so that the scanning position not held for a long period of time can be. Furthermore, in practice there are none Adjustment aids are known which have a reproducible scanning enable. In particular, the scanning position in relation to the outlet edge of the metering tube of particular importance for dosing furnaces. The needle should be accurate for a well reproducible dosage the outlet position of the liquid metal at the outlet edge of the dosing tube (needle and outlet edge must sit at the same height). The capture is in practice not only by the above Maintenance and repair work on the Metal needle shifted but also through the exchange of the metering tube, the installation height of which directly Position of the outlet edge determined. Due large manufacturing tolerances in the refractory sector can the installation of a new dosing tube as well a new seal, etc. the outlet edge by up to Move 10 mm vertically.

With dosing furnaces, the scanning position is shifted in relation to the outlet edge by the above Measures of, for example, 5 mm a change of the dosed metal weight of typically 4%. A dosing accuracy of 1 to 2% is required. Due to poor access and the heat that prevails in the scanning area, in practice Do not readjust the needle, but it will Pressure or time parameters of the dosage or with us the dosage weight, which is known according to the integral method (Pressure over time) is determined, changed, to compensate for the falsification of the dosing weight. This has the disadvantage that founders who die Dosing parameters of different castings saved have corrections to these saved again and again Must make values since the sampling ratios and so that the dosage does not remain constant.

Another disadvantage of the metal needle shown above is (because of the necessary contact with liquid metal melt) due to the principle. A yourself on the surface of the molten metal after a very short time Time-training layer, for example from not conductive aluminum oxide, must first of the needle be breached. It comes as a result of the pressure of the Needle to bulge the metal surface below. On the one hand, this causes an inaccurate measurement result (the needle admits in one after the breakthrough low signal, i.e. it gets less Molten metal appears as actually present). It also happens after breaking through the oxide surface for an unnecessarily deep immersion of the needle into the molten metal, so that the above described Accelerated wear of the metal needle becomes.

DE-OS 44 20 712 is also a sensor arrangement to measure the level of liquid metal known in which the sensor made of electrically conductive There is ceramic and in the wall of the vessel or one Riser pipe is inserted flush.

The relevant prior art is JP-A-05099726 considered. This reveals one in the wall a tundish filled with molten metal, open to the inside of the tundish Pipe with the pipe opening below the top edge the molten metal is arranged. From the Gas is blown into the melt into the tube. The through the metal melt generated back pressure (by which the level of the molten metal can be concluded can) in the tube with a pressure measuring device detected.

For the measurement of an exact fill level, which the Would meet the requirements of a dosing furnace here, however, a complex pressure measuring device is necessary, which is also constantly calibrated at great expense should be.

The invention has for its object a metering oven with a vessel for holding liquid metal and a device for detecting a level to create liquid metal in a vessel, being the device has a predetermined high level Accuracy recorded.

This object is achieved by the characterizing Features of the main claim related solved with the features of the generic term.

The fact that the pressure measuring device as a pressure wave switch to capture a when closing the Probe opening occurring through liquid metal Pressure response wave within the probe and delivery of a corresponding signal is executed and the Probe into the wall of one provided in the vessel Riser is fixed, becomes a simple one Device for detecting the level of liquid Metal is provided that is inexpensive and still with certainty a certain one Level detected.

In contrast to the procedures mentioned in the introduction, which are based on electrical contacting is at for example, no grounding in the present device required. That on indirect measurement by means of a gas based (the "intermediary" of the Gases minimizes direct contact between the probe and molten metal, also show thin deposits no noticeable influence on the probe Flow conditions of the gas), wear-free and permanently installed scanning system also has the advantage that the sampling ratios remain constant. On the one hand, the height of the scanning position changes of the ceramic tube not (permanently installed), on the other not its position relative to the leading edge (permanently installed). That is, the sampling ratios remain constant even if the metering tube is higher or installed deeper in the dosing furnace. Moreover is a falsification of measured values by an im Over time, change in the electrical Conductivity (such as that mentioned above Sensor made of electrically conductive ceramic) excluded.

By the measures specified in the subclaims are advantageous further developments and improvements possible. The tube or the probe can be in the Wall or the riser pipe of a dosing furnace firmly inserted be, when passing the liquid level the desired signal is given on the riser becomes.

Preferably the probe is made of ceramic, this leads to the possibility of metal deposits on the probe is minimized (especially with the Material combination ceramic / aluminum). Should nevertheless thin deposits (e.g. due to the roughness of the probe), this leads to the invention Probe does not lead to a functional impairment, while with measuring systems based on electrical Contacting based, already thin deposits can cause a complete failure.

It is particularly advantageous to use ceramic Probe with an inner diameter of less than 2 mm to provide. Because of the surface tensions that arise, of liquid aluminum on the Ceramic, the probe then remains (even if there is no Gas flow) not through liquid aluminum locked.

Another advantageous embodiment provides that the pressure measuring device one in the pressure sensitivity adjustable pressure wave switch for Measurement of a pressure response wave from the probe escaping gas. The pressure response wave, when the probe reaches (or closes) through a mirror of liquid metal is created Example as a signal to close a feed valve used in the dosing furnace. The adjustability of the Pressure wave switch enables easy, too possible adjustment to the conditions during operation of the respective installation location.

An advantageous development provides that the Dosing furnace several devices for detecting a Level of liquid metal, each containing one Have a probe with an outlet opening. Lie these outlet openings (with respect to a resting one Level of the liquid metal) side by side, so is in the case of a moving surface of the liquid Metal level by appropriate averaging the pressures measured in the probes, are these outlet openings one above the other, is level determination possible within wide limits.

Fig. 1

schematisch einen Schnitt durch einen Dosierofen mit Steigrohr, und

Fig. 2

eine vergrößerte Teilansicht des Endes der in die steigrohrwand eingesetzten rohrförmigen Sonde.

An embodiment of the invention is shown in the drawing and is explained in more detail in the following description. Show it:

Fig. 1

schematically shows a section through a dosing furnace with a riser, and

Fig. 2

an enlarged partial view of the end of the tubular probe inserted into the riser wall.

1 shows a dosing furnace 1 with a vessel 12, in the liquid metal, for example aluminum, in a bath 2 is added. In the dosing oven 1 is a riser pipe 3 is used, which through the wall 4th of the dosing furnace 1 is led to the outside. About the Riser pipe 3, liquid metal is metered out. This can (according to a sensor device) through regulated pressurization inside the Vessel 12 is made to liquid metal through the To drive riser pipe 3 into a discharge pipe 13. The drain pipe 13 fills the molten metal, preferably Aluminum, for example in molds intended for this purpose. It is important that the amount of the vessel 12 expelled molten metal on the Volume of the molds is matched. For dosing it is necessary that the height of the metal column in the dosing furnace (or in the riser 3) exactly is detected, with a pneumatic for this detection Sensor device 6 is used.

The pneumatic sensor device has a Tube-trained probe 5, which is preferably made of Ceramic exists, and that according to FIG. 2 in the wall 7 of the riser pipe 3 is used. This is for example in the wall 7 designed as a stepped bore Bore 8 provided, being in the bore part with a larger diameter the end of the probe 5 from pressed into the riser wall 7 and / or glued on the outside and the smaller diameter of the Stepped bore 8 approximately the inner diameter of the Tube 5 corresponds. The probe 5 is via a pressure measuring device 9 connected to a gas source 10. The gas source supplies gas at a certain pressure to the probe 5, which from its front end and through the hole 8 flows out. If the metal mirror in the riser near the end of the probe the flow conditions at the end of the probe and there is a change in pressure in the probe. This Pressure change is determined by the pressure measuring device 9. So this is an indirect one Procedure for measuring the level, since the Water level not directly (e.g. by touching a provided contact element) must take place. Instead, the influence of a metal level to be measured to given flow conditions (one Gas coming from a gas source with a defined pressure flows out) determined. This influence can have a Pressure change of the outflowing gas in the probe 5 be determined. Are over this pressure change thus statements about the level of the liquid metal possible. A particularly clearly measurable change in pressure occurs when the open end of the probe 5 (or the hole 8) closed by the liquid metal becomes.

To accurately grasp the level of the liquid metal before the actual measurements Pressure curve when approaching or increasing the Level is measured and there is a pressure threshold determined at which the level a predetermined assignment to the end of the probe 5. The pressure measuring device 9 then indicates a corresponding signal its output 11 to the further evaluation control / regulating devices.

It becomes a so-called pressure wave switch used, the setting range about is between 0.5 and 5 mbar. Own these switches inside a membrane on which a contact is attached is. One side of the membrane stands with the Ambient pressure, which is the other side connected to the sampling tube or probe 5. Becomes now close the sampling tube 5 with a liquid, the pressure in the sampling tube 5 and so on one side of the membrane and this is against pressed a fixed contact so that the Contact on the membrane with the stationary in contact comes. This will result in a current flow when reached the pressure response threshold.

The adjustment of the pressure sensitivity is easy by adjusting the distance of the fixed Contact to the membrane with the help of a screw, which is provided with a scale. Depending on the position the screw is the fixed contact more or less far from the membrane contact, so that more or less pressure is applied to bring both contacts into contact.

Since it, for example during a metering process from the Vessel 12 or riser pipe 3 and the discharge pipe 13 in a mold to close the bore 8 or Probe 5 can provide protection against clogging to provide these openings. This is first by a back pressure caused by the gas source given, which ensures when the bore 8 is closed, that the probe does not fill with molten metal. Moreover can with a suitable choice of materials Probe or the surrounding or enclosing components (Riser pipe, a section of the wall of the vessel) the accumulation of molten metal largely prevented become. With the choice according to the invention Inner diameter of the probe 5 or as a connection hole 8 holes of less than 2 mm and a suitable material combination (ceramics for the parts of the metal which come into contact with the molten metal Probe 5 and the connection hole 8 containing Component, in this case the riser 3) is a Closure made difficult by molten metal. by virtue of that occurs with certain material pairings Surface tensions, for example between the ceramics and liquid aluminum, here is a closure even excluded. This is for the present Invention of vital importance, especially at On the basis of the fact that, for example in the form of casting, even the smallest voids are filled with molten metal become.

In another embodiment of the present Invention can use multiple detection devices of a level of liquid metal in one Dosing furnace can be provided. Any of these devices each has its own probe with an outlet opening on. Are these outlet openings (regarding a resting level of the liquid metal) side by side, so in the case of a moving one Surface of the liquid metal (e.g. during a filling process in the dosing furnace) the level by suitable Averaging can be recorded. So that are possible Incorrect measurements due to a moving metal level largely excluded. However, it is also possible, the above-mentioned outlet openings one above the other to be arranged so as to determine the level within wide limits.

Claims (7)

1. Metering oven (1) comprising a vessel (12) for holding liquid metal and a device for detecting a liquid metal level in a vessel, and a tubular probe (5) is connected to a gas source (10) for discharging a gas from the gas source through the probe and its outlet opening, and a pressure measuring device (9) is provided for detecting a pressure condition within the probe (5) in dependence of a counter-pressure caused by a liquid metal level, characterised in that the pressure measuring device (9) is designed as a pressure-wave switch for detection of a pressure response wave which develops when the probe opening is closed by liquid metal and which gives a respective signal, and the probe (5) is firmly inserted into the wall of a rise pipe (3) provided in the vessel (12).
2. Metering oven according to Claim 1, characterised in that the probe and/or the rise pipe (3) are made of ceramics or substantially of ceramics.
3. Metering oven according to one of Claims 1 or 2, characterised in that the probe (5) is pressed and/or glued into a bore (8).
4. Metering oven according to Claim 2 and/or Claim 3, characterised in that the outlet opening of the probe (5) and/or the bore (8) have an inside diameter of less than 5 mm, preferably less than 2 mm.
5. Metering oven according to one of the above claims, characterised in that the pressure-wave switch is adjustable as regards its pressure sensitivity.
6. Metering oven according to one of the above claims, characterised in that a first and a second device for detection of a metal level is provided which comprise a first and a second probe with a first and a second outlet opening.
7. Metering oven according to Claim 6, characterised in that the first outlet opening lies relative to an idle level of liquid metal above or alongside the second outlet opening.

Images