Level control system for continuous or semicontinuous metal casting equipment

Abstract: Level control system for controlling the metal level in continuous or semicontinuous casting equipment, for instance casting equipment for production of roll ingots or billets of aluminium. The casting equipment comprises a casting mould (3) with a upturned open filling hole (4) for melted metal and a supply gutter (7) or the like, with an outlet arranged above the filling hole, for transfer of the melted metal from a holde oven or the like. The metal level is arranged to be controlled by a PLC-unit (9) on the basis of a radar sensor (8) which is registering the level of the metal mirror, as the metal supply is controlled by a actuator driven (12) closing arrangement (13) on the basis of signals from the PLC-unit (9).

Description: The present invention relates to a level control system for controlling the metal level in continuous or semicontinuous casting equipment, for instance casting equipments for the production of billets or ingots of aluminium, which casting equipment comprises a casting mould with an upwardly open supply opening for melted metal and a supply gutter or the like, with an outlet arranged above the supply opening for transfer of the melted metal from a holding furnace or the like. When casting metal continuously or semicontinuously as mentioned above, a metal flow control system based on the use of floats is most commonly used today. This system possesses limited possibilities of controlling the metal level during the casting operation and no possibilities to control the metal supply during the start-up of the casting operation. Besides, the control for such a system is slow, which inter alia results in an uneven quality of the casted metal body. Especially when casting roll ingots, the metal supply at the starting phase and thereby the metal level in the casting mould is of very great importance since most of the problems which arise at later stage are caused by these initial conditions. DE-A-3346650 shows a device for controlling melt level in a casting mould, and to regulate the metal outflow from supply a gutter wherein is used an inductive sensor to detect the melt level. Further, US-A-4458530 and JP-A-54006013 reveal metal casting equipment wherein is used micro wave sensors for metal level detection. One major disadvantage with the above type of sensor is that they, due to their poor sensitivity, have to be provided directly above (very close to) the metal level. With the present invention is provided a level control system which gives an even and fast control of the metal supply in all the phases of the casting operation, which is dependable and easy to use and which can be pre-programmed in such a way that it at any time under the casting operation is obtained optimal casting conditions. This gives a number of advantages: Under casting with several casting moulds it will be possible to obtain the same metal amount and filling rate of all the casting moulds. The same filling rate from one cast to the other. Equal metal level in the moulds at the start-up, from one cast to the other. Even filling rate in the casting mould provides improved metal distribution against the casting shoe, which in turn improves the heat transfer from the cast material to the casting shoe and is the same from one cast to the other. This will also affect the shrinking tendency, and thereby secure that the cast material is in a stable position on the casting shoe. Less danger for solid contraction and crack initiation. Less danger for surface oxides which can initiate start cracks. Less danger for accidents. The invention is characterised in that the metal level is controlled by a PLC-unit on the basis of a signal from a radar sensor which is registering the level of the metal plane, as the metal supply is controlled by an actuator operated closing arrangement on the basis of signals from the PLC-unit as defined in independent claim 1. The dependent claims 2-6 define preferred embodiments of the invention. The invention will now be further described by means of examples and with reference to the attached drawing which schematically shows a part out cut section of a semicontinuous casting equipment 1 for the production of roll ingots, and a level control system 2 for controlling the metal level in the casting equipment. The casting equipment comprises briefly described, a casting mould 3 with an upwardly open supply opening 4 for melted metal, and in connection with the bottom side of the casting mould, on a vertical moveable support 5, provided casting shoe. The metal is arranged to be filled in the casting mould through a gutter or the like which is provided in connection with a holding furnace which can be tilted (not further shown). The level control system 2 comprises a radar sensor 8, a PLC (programmable logic control) 9, a hydraulic aggregate 10, a proportionality- or servo valve 11 and a hydraulic actuator 12. The radar sensor 8 which includes antennae (not further shown) is provided above the casting equipment, at a distance from this, and is arranged to measure the distance to the metal plane in the metal supply opening 4. Preferably, the radar sensor is provided at a sufficient distance from the casting equipment, for instance in the ceiling of the cast house where the control equipment is disposed. Thereby it will not be in the way during the casting operation or during the work with the casting equipment, for instance in connection with maintenance work of the casting equipment. Besides, with such distant positioning of the radar sensor, the sensor will be prevented from being damaged by the hot metal. The use of a radar sensor as a distance meter therefore represents an essential advantage of the invention. The radar sensor, i.e. the antennae, generates a modulated microwave signal and receives a reflected signal from the metal surface. The reflected signal is demodulated, filtered for unwanted reflections and analysed by a microprocessor in the sensor, which is turn releases an electrical signal to the PLC-unit 9 in accordance with the level for the metal plane. The accuracy of the measurement for the radar sensor is by testing found to be better than ± 0,5 mm. The metal through-put in the gutter 7 is regulated by a throttle valve 13 which reaches down into the gutter and which is moveable in the vertical direction by means of a hydraulic actuator 12. The actuator is constituted by a hydraulic piston/cylinder unit which is driven by hydraulic oil from a hydraulic aggregate 10. It has a built in electronic position device in the form of a sensor (not further shown) which gives off a signal to the PLC-unit in accordance with the position of the piston and thereby the throttle valves position in the gutter. The supply of the hydraulic fluid to the actuator 12 is regulated by a proportionality valve or servo valve 11 which receives electrical signals from the PLC-unit 9. The PLC-unit is the "brain" as such of the control system and can be programmed in such a way that the metal plane during the casting operation at any time is kept at the level which in desirable to obtain an optimal casting result. The control system in accordance with the invention works briefly as follows: When the casting process is starting, the throttle valve opens in the gutter by means of the actuator 12 such that liquid metal in desired amount can flow down into the supply opening 4 of the casting mould 3. The level of the metal plane in the casting mould is recorded by the radar sensor which continuously transmit signals to the PLC-unit in accordance herewith. From the beginning of and during the whole casting operation the PLC-unit transmits electrical signals to the servo valve 11 which in turn affects the hydraulic fluid supply to the actuator in such a way that this is controlling the position of the throttle valve in the gutter in accordance with the desirable metal flow. The hydraulic actuator continuously gives off signals regarding the position of the throttle valve in the gutter to the PLC-unit. As to the radar sensor, this can, in addition to be used for recording of the level of metal plane , also be used for recording of the position (height) of the casting shoe relative to the casting mould, ahead of the starting of the casting operation. This represent an other essential advantage of the invention which prevents water penetration in the shoe, damage of the equipment and prevents metal leakage. The invention as defined in the claims is not in any way limited by the example which is shown in the figure and described above. Thus an electrical driven actuator may be used instead of the hydraulic driven actuator. A hydraulic actuator is, however, preferred since it is less sensitive for high temperatures (heat). Further, a nozzle/needle arrangement where the actuator move a needle which reaches down into a nozzle orifice in the gutter, may be used instead of a closing arrangement in the form of a throttle valve 13. Besides, the PLC-unit in addition to controlling the level of the metal plane may, as an integrated function, be used to control the filling position of the holding furnace. This could be done utilising the PLC-unit to control a servo valve in a hydraulic system which could in turn control the tilting of the holding furnace in accordance with the necessary flow of metal in the gutter.

Claims: Level control system for controlling of the metal level in continuous or semicontinuous casting equipment, for instance casting equipment for production of roll ingots or billets of aluminium, which casting equipment comprises a casting mould (3) with an upwardly open supply opening (4) for melted metal and a supply gutter (7) or the like, with an outlet arranged above the supply opening, for transfer of the melted metal from a holding furnace or the like, characterised by comprising a radar sensor (8) with antennae, provided at a remote distance above said casting equipment, to measure the distance to the molten metal plane in the metal supply opening (4) and to generate an electrical signal representative thereof, a programmable logic control (PLC) unit (9) in operable connection with said radar sensor, a closing/opening arrangement (13) at the outlet of the metal supply gutter (7) and an actuator (12) in operative connection with said PLC-unit for driving said closing arrangement (13), whereby in use the metal level is controlled by the PLC-unit (9) on the basis of said signal from the radar sensor (8) which is registering the level of the metal plane and whereby the metal supply is controlled by said actuator driven (12) closing arrangement (13) on the basis of signals from the PLC-unit (9). Level control system according to claim 1, characterised in that the actuator (12) is a hydraulic and is controlled by a proportionality valve or servo valve (11). Level control system according to claim 1, characterised in that the actuator (12) is electrically operated. Level control system according to claim 1-3, characterised in that the closing arrangement (13) is a throttle valve (14) which can be raised and lowered or revolved in the gutter (7). Level control system according to claim 1-3, characterised in that the closing arrangement (13) is a nozzle/needle arrangement. Level control system according to claim 1-5. characterised in that the PLC-unit (9) gives off signals to a servo valve (11) in a hydraulic system which control the filling of the holding furnace on the basis of the necessary metal flow of the gutter (7).

Inventors: ODEGARD MAGNE, SIVERTSEN JAN, ODEGARD, MAGNE, SIVERTSEN, JAN
Applicants: NORSK HYDRO AS, NORSK HYDRO ASA
Application year: 1995
Main classification: B22D2
IPC codes: B22D11, B22D2