GB2193667A

GB2193667A - Continuous casting installations

Info

Publication number: GB2193667A
Application number: GB08717049A
Authority: GB
Inventors: Tetsuya Kohno
Original assignee: Mitsui Kinzoku Engineering Service Co Ltd
Current assignee: Mesco Inc
Priority date: 1986-08-14
Filing date: 1987-07-20
Publication date: 1988-02-17
Anticipated expiration: 2007-07-20
Also published as: GB2193667B; JPS6349346A; JPH0337820B2; GB8717049D0

Abstract

A continuous casting installation comprises a rotary drum (1) with a channel formed in its periphery, a steel belt (2) which contracts a portion of the periphery of the drum to define a casting space and a discharge spout (3), the width of whose downstream end is less than that of the channel, arranged to discharge molten metal into the channel upstream of the casting space. In use, the flow rate is such that a proportion of the molten metal flows backwardly in the gaps between the edges of the channel and the main flow of the metal (7) to form back fed portions (15). The position of the leading ends (15a) of the back fed portions (15) is monitored by an optical sensor and the speed of rotation of the drum or molten metal supply rate is altered by a controller to maintain the position of the leading ends (15a) substantially at a reference position (16). This ensures paper filling of the casting space. The installation is especially suitable for casting zinc. <IMAGE>

Description

SPECIFICATION Improvements in continuous casting installations The present invention relates to improvements in continuous casting installations and methods of operating such installations. The invention is particularly applicable to a casting installation and method for the casting of metal such as zinc.

Referring to Figures 3(a) and (b) of the accompanying drawings, there is illustrated a front elevation and plan view respectively of a known continuous casting installation.

Metal is melted in a melting furnace 5 and drawn up through a suction pump 8 for delivery to a molten metal feed tank 4. Molten metal 7 in the feed tank 4 is supplied through a spout or nozzle 3 to a channel la in the periphery of a rotating drum 1. The molten metal 7 flows in the direction of rotation of the drum 1, which is indicated by the arrow in figure 3(a), into a well or portion 9 of the channel 1 a in the periphery of the drum 1.

An endless steel belt 2, in close contact with the periphery of the drum 1, moves around spaced rollers at the same speed as the periphery of the drum. Thus, a mould cavity or space 10 is defined between the moving channel la and the belt 2.

The molten metal 7 in the well 9 passes into the space 10, where it is water cooled.

The molten metal thus solidifies in the form of a continuous cast plate 18 which is then drawn off from the lower part of the drum 1.

In such known continuous casting installations it is important that the space 10 is completely filled with molten metal to ensure the cast plate 18 has no discontinuities. Furthermore, from the points of view of safety and keeping the apparatus in good repair, it is important that the rate of supply of molten metal from the feed tank 4 matches the forming rate of the cast plate 18 to prevent over or under supply of the molten metal 7. To this end, known continuous casting installations are provided with a liquid level gauge 6.

The actuation of the suction pump 8 is thus controlled by the level gauge 6 to maintain a substantially constant head of molten metal 7 in the feed tank 4.

However, even if the head of molten metal 7 in the feed tank is maintained constant by the pump 8 under the control of the gauge 6, the rate of supply of the molten metal 7 can still be affected by the deposition of solidified metal on the inside of the spout 3 which reduces its flow cross-section and thus the flow rate through it. Furthermore, the casting rate of the metal is affected by changes in, for example, the rate of supply of cooling water, the cooling water temperature, the ambient air temperature etc. As a result, it is very difficult to maintain the feed rate of molten metal 7, as dictated by the head in the feed tank 4, equal to the solidification rate of the casting.

To ensure correct operation of the installation, therefore, the level of the molten metal 7 in the well 9 must be monitored visually by an operator who will adjust the speed of rotation of the drum accordingly.

Thus, control of the casting process relies ultimately on the manual intervention of the operator. Because of this, the operator must be in virtually constant attendance at the installation during a casting operation. During a long casting run, the operator will be prone to fatigue while carrying out the essentially mundane operating procedure and his judgement and ability to control the process correctly may become impaired.

The present invention has been made to overcome the foregoing deficiencies in the prior art and it is an object of the invention to provide an improved method and apparatus for continuous casting.

In order to achieve the above object, various studies have been made and it has been discovered that by slightly decreasing the inner width of the spout 3 as compared with the width of the channel 1a of the drum 1 so as to cause a backward movement of each side portion of the stream of the molten metal 7 tending to flow into the space 10 from the well 9 and controlling the rotation speed of drum 1 in relation to the rate of supply of the molten metal so as to maintain the forward end of each of the backward moving portions at a constant position, it is possible to maintain the space 10 full with molten metal 7 and also prevent the molten metal 7 from overflowing the well 9.

In accordance with the invention, there is provided a method of continuous casting comprising pouring a stream of molten metal of one width into a channel of a second, greater, width formed at the periphery of a rotating drum, which metal then flows into and fills a mould space defined between the channel and a metallic belt in contact with the periphery of the drum, the rate of pouring being such that a proportion of the poured stream flows backwards in the channel to form a back fed portion of molten metal on at least one side of the poured stream, deriving a signal indicative of the position of the end of the or each back fed portion and adjusting the speed of rotation of the drum or the rate of supply of the molten metal in accordance with the said signal.

Also in accordance with the invention there is provided a continuous casting installation comprising a drum having a channel formed in its outer periphery, a metallic band which is in contact with a portion of the outer periphery of the drum to define a casting space, means for rotating the drum in one direction, a molten metal discharge spout arranged to discharge molten metal in to the channel up stream of the casting space with respect to the said direction, the internal width of the discharge end of the spout being less than the width of the channel, sensing means arranged to monitor the presence of molten metal which has flowed backwards in the channel with respect to the said direction to form a back fed portion on one or both sides of the stream of molten metal from the spout and to derive a signal indicative of the position of the end of the or each back fed portion and control means responsive to the said signal to control the speed of rotation of the drum or the rate of supply of the molten metal.

The present invention can be put into practice in several ways, one of which will now be described by way of example with reference to Figures 1 and 2 of the accompanying drawings in which: Figure 1 is a schematic diagram illustrating part of a continuous casting installation according to the invention; and Figures 2 (a) and (b) show a side sectional view and plan view of the well portion of the continuous casting installation in Figure 1 respectively.

Referring- to Figures 2 (a) and (b) of the drawings, in which those components which are similar to components in Figure 3 are designated by the same numerals, molten metal 7 is transferred from a melting furnace (not shown) to a feed tank (not shown) by a suction pump (not shown). The molten metal 7 in the feed tank is supplied in a stream to a channel la in a drum 1 by means of a spout 3 extending from the feed tank.

The rotating drum 1 carries the molten metal 7 through a well portion 9 in the drum 1 and into a space defined between the channel la and one side of an endless steel belt 2 which is in close contact with a portion of the periphery of the drum 1. The steel belt is mounted to travel around spaced rollers at the same speed as the drum 1.

The inner width of the spout 3 is reduced slightly in relation to the width of the drum channel la so that, when the molten metal 7 is supplied to the well 9 of the drum 1 through the spout 3, a back-log in the form of a curved surface 14 in the profile of the molten metal is created by the steel belt 2 which serves as an obstacle to the passage of the upper surface of the molten metal 7. As a result, a back fed portion 15 is produced on each side of the molten metal 7. The back fed portions 15 constitute small pools of metal at the sides of the main flow of metal 7 which are fed from the downstream end and/or flow upstream with respect to the direction of flow of the metal 7 and the direction of movement of the drum 1.The position of the leading ends 15a, which are of course the trailing ends with respect to the directions of movement of the drum 1 and the main flow of the molten metal, of the back fed portions 12 extend back beside the oncoming stream of molten metal and vary with variations in the flow rate of the molten metal 7 and the drum speed. Thus, a predetermined reference point 16, i.e. a particular position of the leading ends 15a of the portion 15 can be set corresponding to the optimum condition in which the space defined between the steel belt 2 and the channel la of the drum 1 is thoroughly filled with the molten metal 7 without overflowing the drum channel la.

The amount of displacement of the leading ends 15a from the reference point 16 is detected and the rotation speed of the drum 1 is controlled in such a manner that the drum speed is decreased when the leading ends 15a are to the right of the reference point 16, as shown in the drawing, and the drum speed is increased when the leading ends 15a are to the left of the reference point 16. In this way, the molten metal 7 is cast smoothly and automatically. The reduced width of the flow of metal entering the space between the channel la and the belt 2 increases as it comes into contact with the belt 2 to fill the channel completely and form the cast plate.

Figure 1 illustrates the apparatus used to control the process automatically. An image sensor 11 detects the amount of displacement of the leading ends 15a from the reference point 16 in the well 9. The resulting position information signals are sent from the sensor 11 to a microcomputer 12. The microcomputer 12 computes the desired rotation speed of the drum 1 in accordance with the amount of displacement and the computed value is subjected to digital to analogue (D/A) conversion through a control unit 13 which transmits a control signal to a drum variable speed motor 1b to control its speed of rotation.

The image sensor 11 is a 2048-bit line sensor which measures the presence or absence of the molten metal in terms of a brightness difference in the sensed image. The measuring range 17 of the sensor 11 (see Figure 2(b)) is 100mm and the resolution is approximately 0.05mm/bit. The measured value is sent as an electric signal from the image sensor 11 to the microcomputer 12 which digitises it and performs averaging and/or image processing such as correction of the curved surface, to thereby compute the appropriate rotational speed of the drum 1 and send the computed value to the variable speed motor 1 b through the control unit 13.

From the foregoing description it will be seen that in accordance with the invention, by virtue of the fact that a continuous casting machine is provided with an image sensor, a microcomputer and a control unit to perform its automatic operation, the operator is not required to be in constant attendance at the installation while it is in operation in order to monitor it. Additionally, it is found that the product yield is improved, thereby making a great contribution to reduced production costs of the continuously cast metal.

The use of the image sensor for detecting the forward end position of each back fed portion of the molten metal allows the casting process to be monitored regardless of the effects of the molten metal temperature, the presence of scum on the molten metal, the molten metal surface level in the molten metal feed tank, etc. Also, the use of the microcomputer in combination with the image sensor makes it possible to control the rotation speed of the drum rapidly and accurately, thereby ensuring accurate and safe automatic operation of the installation.

In an alternative embodiment which is not illustrated the speed of the drum is maintained constant and the rate of supply of the molten metal is varied in response to the control signal. For this purpose a metallurgical valve of known type, eg a sliding gate valve or stopper valve, may be provided at the outlet of the metallurgical vessel. Moving the valve in the opening or closing or direction will vary the rate of supply of the molten metal and thus result in movement of the leading ends 15a of the back fed portions 15.

Claims

1. A method of continuously casting comprising pouring a stream of molten metal of one width into a channel of a second, greater, width formed at the periphery of a rotating drum, which metal then flows into and fills a mould space defined between the channel and a metallic belt in contact with the periphery of the drum, the rate of pouring being such that a proportion of the poured stream flows backwards in the channel to form a back fed portion of molten metal on at least one side of the poured stream, deriving a signal indicative of the position of the end of the or each back fed position and adjusting the speed of rotation of the drum or the rate of supply of the molten metal in accordance with the said signal.

2. A method as claimed in claim 1 in which the metallic belt constitutes an endless belt which is moved at the same iinear speed as the periphery of the drum.

3. A method as claimed in claim 1 or claim 2 in which the said signal is produced by an optical sensor.

4. A method as claimed in claims 1, 2 or 3, wherein the speed of rotation of the drum is controlled by a microprocessor.

5. A method as claimed in claim 4, wherein the output of the microprocessor is converted to an analogue signal by a digital-to-analogue converter.

6. A continuous casting installation comprising a drum having a channel formed in its outer periphery, a metallic band which is in contact with a portion of the outer periphery of the drum to define a casting space, means for rotating the drum in one direction, a molten metal discharge spout arranged to discharge molten metal into the channel upstream of the casting space with respect to the said direction, the internal width of the discharge end of the spout being less than the width of the channel, sensing means arranged to monitor the presence of molten metal which has flowed backwards in the channel with respect to the said direction to form a back fed portion on one or both sides of the stream of molten metal from the spout and to derive a signal indicative of the position of the end of the or each back fed portion and control means responsive to the said signal to control the speed of rotation of the drum or the rate of supply of the molten metal.

7. An installation as claimed in claim 6, in which the metallic band is an endless band mounted on rollers to move with the drum.

8. An installation as claimed in claim 6 or 7 wherein the spout is located centrally with respect to the width of the channel.

9. An installation as claimed in claims 6, 7 or 8 wherein the sensing means comprises an image sensor.

10. An installation as claimed in any of of claims 6 to 9 wherein the control means comprises a microprocessor.

11. An installation as claimed in claim 10 wherein the control means also comprises a digital to analogue converter.

12. A method of continuously casting a metal substantially as specifically herein described with reference to Figures 1, 2(a) and 2(b) of the accompanying drawings.

13. A continuous casting installation substantially as specifically described herein with reference to Figures 1, 2(a) and 2(b) of the accompanying drawings.