GB2109940A

GB2109940A - Method and apparatus for controlling the liquid metal level in a continuous casting mould

Info

Publication number: GB2109940A
Application number: GB08230944A
Authority: GB
Inventors: Manfred Beller; Hans Wiedemann
Original assignee: Wieland Werke AG
Current assignee: Wieland Werke AG
Priority date: 1981-11-23
Filing date: 1982-10-29
Publication date: 1983-06-08
Also published as: DE3146360A1; FR2516822B1; DE3146360C2; FR2516822A1

Abstract

A method of controlling a liquid metal level in a continuous casting mould (1) employs a pair of electrically conducting rods (4) which dip into the melt (2) and the electrical resistance of which is variable in dependence upon the depth of the melt, the resistance being measured for example by bridge 6. The rods are formed of a material which is resistant to the melt and signals from the probe are applied to processing circuitry (7,8) for controlling a slide valve (5) which is used to open and close an output port of a tundish (10) acting as a reservoir for the mould. The rods may be of high resistivity and connected at their lower end to form a U configured probe. <IMAGE>

Description

SPECIFICATION Method and apparatus for controlling the liquid metal level in a continuous casting mould The invention relates to a method and apparatus for controlling the liquid metal level in a continuous casting mould.

Because of the special environmental conditions (heat, dust, covering agents, metal splashes etc), an apparatus for controlling the liquid metal level mounted on a casting unit, must itself be robust and simple, both constructionally and with regard to handling. Additionally, it is required that the apparatus can be employed for all types of mould, and for all sizes of mould, as well as in the case of every alloy which has to be cast.

A known apparatus and method is disclosed in U.K. Patent Application No. 8039889 in which the level of the liquid metal surface is measured by an eddy-current technique utilising a loop located either above or in the melt. Using such a technique, it is necessary to use direct current.

The present invention seeks to provide a method and apparatus for controlling the liquid level in continuous casting moulds which is able to use either direct current or alternating current.

According to one aspect of this invention there is provided a method for controlling a liquid metal level in a continuous casting mould including the steps of detecting a change in the liquid metal level resulting from the change in the electrical resistance of two electrically conducting rods which dip into the melt but which are made of a material resistance to the melt and producing a measurement signal therefrom in a measuring system.

In a preferred embodiment of the invention, the change in resistance is measured by a direct-current resistant measuring bridge, or by an alternatingcurrent resistance measuring brdige, or is determined from a current/voltage measurement.

It is preferable to zero-balance the measuring system when the liquid metal surface is at the required level, and to use the measurement-signal, arising when the liquid metal surface departs from the required level, in order to effect control.

After further processing, the measurement-signal advantageously actuates, a stopper-valve or slidevalve in a tundish of the continuous casting mould.

According to a further aspect of this invention there is provided an apparatus for controlling a liquid metal level in a continuous casting mould including a probe formed by two electrically conducting rods which are arranged to dip into the melt in the continuous casting mould but which are made of a material resistant to the melt and a measurement system connected to the rods arranged to detect a change in the electrical resistance of said rods in dependence upon the level of melt in the mould.

The rods preferably possess a high resistivity, in order to measure as large a change in resistance as possible whenever a change in the liquid metal level occurs. These requirements are met, in particular, by rods manufactured from chromium-steel, graphite, or a cermet, it being possible for these rods, in addition, to be composed of material of any desired shape and size.

In one embodiment of the invention, the rods are connected, at the lower end, in a manner permitting conduction, so that the probe is designed in the shape of a "U". So as to hold the rods, and to reduce the resistance of the supply leads, it is convenient to fasten the rods to busbars, which may be manufactured from any desired, electrically conducting material such as copper, but if the intention is that the temperature-coefficient of the electrical resistance should be as low as possible, constantan or manganin may be used.

The invention will now be explained by way of example with reference to the accompanying drawings, in which: Figure 1(a) shows a vertical cross-section of a mould with a probe in accordance with the invention; Figure l fbJ shows a plan view of the mould shown in Figure 1(a); and Figure 2 shows a block circuit diagram of the measuring and control system.

In the Figures, like reference numerals denote like parts.

Figures 1 and 2 represent, diagrammatically, a continuous casting mould 1, containing a melt 2 having a liquid metal surface 2', into which two rods 4 dip. The rods 4 form a probe and are manufactured from an electrically conducting material having high resistivity which is resistant to the melt 2. The length, shape and cross-sectional area of the rods 4 can be selected to suit the requirements of the mould and material being cast, but in one embodiment the rods are connected at their lower end to form a U-shape.

The rods may be chromium steel, graphite or cermet. Copper busbars 3 hold the rods 4, and help to reduce the resistance of the supply leads. The rods 4 are connected, by other busbars 3, to a self-balancing direct-current resistance measuring bridge 6, (or alternatively to a seif-balancing alternating-current resistance measuring bridge 6). Following start-up ofthe casting unit, the bridge 6 automa ticallyzero-balances as soon as the level of the liquid metal surface 2' has reached the required height.

A change in the liquid metal level produces a measurement signal at the output terminal of the bridge 6 which is amplified in an evaluating unit 7 and, if alternating current is being used, is demodulated and filtered. The measurement signal, thus further processed, passes to a controller 8 which, with the aid of a motor 9, actuates a stopper-valve or a slide-valve 5 and thereby regulates the feeding of the metal 2, from a tundish 10, into the continuous casting mould 1 to thereby maintain a required melt level.

Round graphite bars, having a diameter of 10 mm and a length of 150 mm, can, for example, be used as the rods 4, while copper busbars, having a rectangu larcross-section, 20 mm by 15 mm and a length of 90 cm, can be used as the current busbars 3.

The resistance of the copper busbars 3 is only 0.1 mQ, while, in contrast, that of the graphite rods 3 is 31 mQ the change in resistance, of 2 mQ per cm change in liquid metal level, being readily measurable by means of a commercially available resistance measuring bridge 6.

Claims

1. A method for controlling a liquid metal level in a continuous casting mould includes the steps of detecting a change in the liquid metal level resulting from the change in the electrical resistance of two electrically conducting rods which dip into the melt but which are made of a material resistant to the melt and producing a measurement signal therefrom in a measuring system.

2. A method as claimed in Claim 1, wherein the change in resistance of the rods is measured by a direct-current resistance measuring bridge, or by an alternating-current resistant measuring bridge.

3. A method as claimed in Claim 1, wherein the change in resistance is determined from a currents voltage measurement.

4. A method as claimed in Claim 2 or 3, wherein the measuring system is zero-balanced when the liquid metal surface is at the required level and the measurement signal arising when the liquid metal surface departs from the required level is used to effect control.

5. A method as claimed in Claim 4, wherein after further processing, the measurement signal actuates a stopper-valve or a slide-valve in a tundish to thereby supply the mould.

6. An apparatus for controlling a liquid metal level in a continuous casting mould includes a probe formed by two electrically conducting rods which are arranged to dip into the melt in the continuous casting mould but which are made of a material resistant to the melt and a measurement system connected to the rods arranged to detect a change in the electrical resistance of said rods in dependence upon the level of melt in the mould.

7. An apparatus as claimed in Claim 6, wherein the rods possess a high resistivity.

8. An apparatus as claimed in Claim 6 or 7, wherein the rods are composed of chromium-steel, graphite, or a cermet.

9. An apparatus as claimed in any of Claims 6 to 8, wherein the rods are connected at their lower ends, in manner permitting conduction.

10. An apparatus as claimed in any of Claims 6 to 9, wherein the rods at their ends remote from the melt are fastened to busbars which are composed of electrically conducting material.

11. An apparatus as claimed in Claim 10, wherein the busbars are composed of copper, constantan, or manganin.

12. A method for controlling a liquid metal level in a continuous casting mould substantially as herein described with reference to and as illustrated in the accompanying drawings.

13. An apparatus for controlling a liquid metal level in a continuous casting mould substantially as herein described with reference to and as illustrated in the accompanying drawings.