GB2163983A

GB2163983A - Method of casting melt into a plurality of continuous casting moulds

Info

Publication number: GB2163983A
Application number: GB08521947A
Authority: GB
Inventors: Bernhard Tinnes; Heinz Kreuzberg
Original assignee: Metacon AG
Current assignee: Metacon AG
Priority date: 1984-09-05
Filing date: 1985-09-04
Publication date: 1986-03-12
Also published as: SE461258B; CS600085A3; SU1367846A3; DE3432611A1; ZA856821B; AT391643B; IT8521682A0; PL147451B1; PL254958A1; ATA252385A; CA1239523A; GB2163983B; IT1185654B; GB8521947D0; SE8504088D0; JPH0716774B2; ES546694A0; DE3432611C2; FR2569588B1; MX168192B

Abstract

A method of pouring a molten metal from an intermediate vessel (3) into a plurality of continuous casting moulds (A, B and C) through respective discharge valves (4) and withdrawing all the castings from the moulds with a common withdrawing unit (12, 13) includes opening all the valves (4) to initiate the pouring process, and monitoring the filling level (20) within each mould in a measuring zone (9). That mould whose filling level first reaches a first threshold level (21) has its associated valve (4) throttled and the withdrawing unit is switched on either when all the filling levels are substantially the same or when the first of the filling levels reaches a second threshold level (22) above the first threshold level, whichever occurs first. Each discharge valve is adjusted when the filling level in the associated mould reaches a desired level (8) above the second threshold level so as to maintain the filling level substantially at the desired level. Any mould in which the filling level has not reached the first threshold level (21) at the time the withdrawing unit is switched on has its associated valve (4) closed. <IMAGE>

Description

SPECIFICATION Method of casting melt into a plurality of continuous casting moulds The invention relates to a method of pouring a molten metal, in particular a steet melt, out of an intermediate vessel into a plurality of continuous casting moulds and is concerned with that type of such method in which the filling level in each mould is maintained within a measuring zone at a desired level by controlling respective discharge valves associated with the moulds and the resultant castings are withdrawn by a common withdrawing unit at the same speed.

Such a method is disclosed in European Patent No. 0019114 in which in order to facilitate the commencement of the pouring it is recommended that the filling levels or the devices which measure the filling levels in the moulds be given a very large height range in order to be able to compare the speed of rise of the filling levels in the moulds with one another. This comparison should give an early indication if the supply volumes to the moulds differ and actuate control devices which are of electromagnetic type or operate with gas nozzles and serve as discharge valves before reaching the desired filling level with the purpose of enabling an unimpeded commencement of pouring. There is however no information given as to how such a procedure is to be conducted.

It is an object of the present invention to provide an improved method of pouring a plurality of castings which are withdrawn at the same velocity in the initial phase which is both simple and has an improved operational reliability.

According to the present invention there is provided a method of pouring a molten metal from an intermediate vessel into a plurality of continuous casting moulds through respective discharge valves and withdrawing all the castings from the moulds with common withdrawing means at the same speed, which includes opening all the valves to initiate the pouring process, monitoring the filling level within each mould in a measuring zone, throttling the discharge valve associated with that mould whose filling level is the first to reach a first predetermined threshold level within the measuring zone, throttling the discharge valve associated with the or each mould whose filling level becomes equal to that of the said first mould, switching on the withdrawing means when all the filling levels are substantially the same or when the first of the filling levels reaches a second predetermined threshold level within the measuring zone above the first predetermined threshold level, and adjusting the throttling of each discharge valve when the filling level in the associated mould reaches a desired level within the measuring zone above the second predetermined threshold level so as to maintain the said fil!ing level substantially at the said desired level.

By use of the method in accordance with the invention the filling levels of all the moulds may be brought rapidly to a level at which the withdrawing means may be switched on and at which the filling levels may be readily brought up to and maintained at the desired level.

It is preferred that the method including closing the discharge valve associated with any mould in which the filling level has not reached the first predetermined threshold level at the time when the withdrawing means is started. This preferred step ensures that the melt cannot run straight out of a mould before a satisfactory casting skin has formed since this would damage parts of the installation, for instance a secondary cooling unit, and prevent the removal from the installation of intact castings.

It is preferred that the first and second predetermined threshold levels and the desired level are situated substantially 10%, 70% and 85% respectively, of the way up the measuring zone. It will however be appreciated that these figures may be varied to suit the particular operational requirements.

Further features and details of the invention will be apparent from the following description of certain specific embodiments which is given by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammaic view of a multiple continuous casting installation at the beginning of pouring; and Figures 2 to 4 diagrammatically illustrate different possible operational sequences during the beginning of pouring.

Figure 1 shows a casting ladle 1 from which steel melt is supplied via a controllable discharge valve 2 to an intermediate vessel 3 which for its part has three discharge valves in the form of sliding gate valves 4 which control the supply of the melt through respective pouring tubes 5 into three continuous casting moulds A, B and C into which the free ends of the pouring tubes extend. Each sliding gate valve is mechanically connected to a positioning member 6 whose operational position at any time is detected by a position sensor 7.

The liquid or filling level in each mould is detected within a measuring zone 9 by a respective level measuring device comprising a transmitter 10 and a receiver 11. The desired filling level of each mould is set to be about 85% of the way up the measuring zones. In normal operation, the position of each sliding gate valve is controlled in dependence on whether the actual liquid level in the associated mould is above or below the desired level.

Downstream of the moulds is a secondary cooling device which is not illustrated for the sake of simplicity and a withdrawing unit common to all the castings 18 which includes drive rolls 12, a drive motor 13, a drive controller 14 and a withdrawing velocity sensor 15. The latter supplies signals indicative of the withdrawing velocity both to the drive controller 14 and to a processor 16 which also receives and processes signals from the position sensors 7 indicative of the degree of opening of the sliding gate valves 4 and signals from the receivers 11 indicative of the actual filling levels in the moulds. The data obtained is fed to a control computer 17 integrated in the processor 16 which gives appropriate controi commands to the positioning members 6 of the sliding gate valves 4 and to the controller 14 of the withdrawing unit.The withdrawing velocity is set as a constant, i.e. the castings 18 formed in the moulds are withdrawn by the common withdrawing unit at a constant velocity, which means that the filling levels in the moulds are controlled only from the supply side by means of the sliding gate valves 4. For this purpose the sliding gate valves 4 are maintained in normal pouring operation in throttled positions in order to enable the flow through them to be increased as well as decreased.

At the commencement of pouring the withdrawing drive 13 is switched off and cold castings 18 are introduced into the moulds. The pouring begins by opening the sliding gate valves 4 which are fully or only partly opened in dependence on the format of the castings to be cast. The melt rises to levels 20 above the cold casting heads 19 in the moulds. These levels 20 are, however seldom at the same level.

In particular, the flow passages may have differing cross-sectional areas which result in differing discharge rates from the pouring tubes 5 because constrictions occur in the discharge or flow passages of the intermediate vessel 3 and the sliding gate valves 4, for instance by "bear" formation as a consequence of solidification of melt on regions of the passage wall which are not sufficiently hot.

Also the viscosity of the melt may be increased by being cooled when flowing a greater distance in the intermediate vessel.

An equalisation of the different filling levels 20 is effected by throttling that sliding gate valve 4 in whose associated mould the filling level first reaches a threshold level 21 which is approximately 10% of the way up the measuring zone 9.

When the filling levels of the other moulds b-ecome equal to that in the first said mould their valves 4 are also throttled so that the associated filling levels rise at the same rate as that in the first said mould. The filling levels are monitored by the measuring devices 10, 11 which control the sliding gate valves 4 by means of the processor 16 and the control computer 17. The equalisation of the filling levels 20 in the moulds is also monitored and when this is complete the control computer 17 switches on the withdrawing drive motor 13.The filling levels then oscillate about and finally settle down at the desired filling level 8, If all the filling levels do not become equal, or if only two of them become equal, the control signal to switch on the withdrawing drive motor 13 is issued at the latest at a further threshold level 22 situated within the measuring zone 9 below the desired filling level 8 when the first filling level 20 reaches it At the same time those sliding gate valves 4 associated with moulds in which the filling level 20 is still below the threshold level 21 receive closing commands and are closed.

In Figures 2 to 4 the pouring is -continued until the desired filling level 8 has been achieved.

It may be seen from Figure 2 that the threshold level 21 was exceeded first by the liquid level in the mould A in time At, then by the level in the mould B in time Bt and finally by the level C in time Ct. The sliding gate valve 4 of the mould A is moved into a predetermined throttled position at the threshold level 21 and this gives the levels in the moulds B and C the opportunity to catch up, which occurs at points 30 and 31 respectively. At the points 30 and 31 the valves 4 associated with the moulds B and C respectively are throttled. At point 31 all three filling levels are thus at the same level and the withdrawing drive motor 13 is switched on, conveniently with 70% of its normal velocity.As soon as the withdrawing drive is switched on the filling levels in the three moulds rise together, but more slowly, and move up a line 32 of reduced gradient until at time t the desirec filling level 8 is reached whereafter the filling levels are maintained susbtantially at the desired level In the embodiment of Figure 3 the filling levels A20 and C20 become equal at the point 33 but the level C20 does not catch them up even after all the filling levels have passed the threshold level 21.

After the point 33 the two filling levels C20 and A20 rise together until they reach the second threshold level 22, at which the withdrawing drive unit 13 is switched on. The levels C20 and A20 then reach and remain at the desired filling level 8.

The rate of rise of the level B20 decreases at the point 34, i.e. at the time when the withdrawing drive unit is switched on and then reaches the desired level 8 after a pouring time t.

The beginning of pouring follows a similar course in the embodiment of Figure 4 in which the filling levels B20 and A20 pass through the threshold level 21 at times Bt and At, at which the valves 4 associated with the mould B is throttled. The two levels then become equal at the point 35, at which the valve associated with the mould A is throttled, and thereafter rise together to the second threshold level 22 and then to the desired filling level 8 in time t. At the time at which the withdrawing- drive unit 13 is switched on by the levels B20 and A20 having reached the threshold level 22 the filling level C20 has not risen above the critical threshold level 21 but has remained actually below the bottom end of the measuring zone 9 as a result of which the sliding gate valve C4 has been automatically closed, in the present case after time Ct.

With the monitoring of the filling levels described above continuous casting installations with a withdrawing unit for simultaneously producing a plurality of castings can be brought up to the desired filling levels in an operationally safe manner.

Claims

1. A method of pouring a molten metal from an intermediate vessel into a plurality of continuous casting moulds through respective discharge valves and withdrawing all the castings from the moulds with common withdrawing means at-the same speed, which includes opening all the valves to initiate the pouring process, monitoring the filling level within each mould in a measuring zone, throttling the discharge valve associated with that mould whose filling level is the first to reach a first predetermined threshold level within the measuring zone, throttling the discharge valve associated with the or each mould whose filling level becomes equal to that of the said first mould, switching on the withdrawing means when all the filling levels are substantially the same or when the first of the filling levels reaches a second predetermined threshold level within the measuring zone above the first predetermined threshold level, and adjusting the throttling of each discharge valve when the filling level in the associated mould reaches a desired level within the measuring zone above the second predetermined threshold level so as to maintain the said filling level substantially at the said desired level.

2. A method as claimed in claim 1 which includes closing the discharge valve associated with any mould in which the filling level has not reached the first predetermined threshold level at the time when the withdrawing means has started.

3. A method as claimed in claim 1 or claim 2 in which the first and second predetermined threshold levels and the desired level are situated substantially 10%, 70% and 85%, respectively, of the way up the measuring zone.

4. A method of pouring a molten metal from an intermediate vessel into a plurality of continuous casting moulds substantially as specifically herein described with reference to Figure 1 and any one of Figures 2 to 4.