FIELD OF THE INVENTION:
The present invention is directed to a system for aligning ladle and tundish in bloom caster and in particular to a photosensor based system for aligning ladle and tundish in bloom caster which would be simple, low cost and at the same time, highly reliable and safe, for aligning of ladle and tundish at the continuous bloom caster. The system of alignment according to the invention also minimizes delay in said aligning time and ensures accuracy such that the liquid steel is poured at the center of tundish. The present system of alignment also avoids the accumulation of metal near the tundish wall. The system also avoid pouring of liquid steel over second stopper of tundish of 4 strand bloom caster.
BACKGROUND ART
It is well known in the art of continuous steel casting that the ladle carrying liquid steel need to be properly aligned with the tundish that acts as a distributor of liquid metal to the molds placed below it at the openings selectively located. The requirement of tundish is to allow for a residence time for the liquid metal after absorbing the impact of pouring to ensure uniform flow of metal into the mold at desired pouring temperature and improve the quality of casting. It is thus essential to place a new ladle full of liquid metal, in position on tundish with proper alignment after the previous one has been exhausted.
In conventional practice, the pulpit operator cannot see the position of the ladle for alignment with the tundish for safe pouring, due to obstruction created by metallic shield since it is hanged to ensure the safe working operation for four persons who are working very near to the mould and maintain desired level of liquid steel in mould. In conventional system, persons were standing on the shop floor just under the ladle for guiding or signaling to pulpit operator to facilitate positioning of ladle on tundish and as a result they met accident frequently due to spilling of hot liquid steel either due to-(i) as they need to stand under ladle while it is rotating or (ii) mismatch of positioning of the two or (iii) uncontrolled pouring from ladle. Moreover, in such conventional practice for matching of the ladle over the tundish by following human guidance from a distant location, much of time was required by the pulpit operator to align the ladle with tundish, causing loss of productivity, apart from loss due to accidents under unsafe working conditions.
Efforts have been made over a long period of time in the past, to resolve the difficulties in aligning the position of ladle with tundish at the time of pouring by deploying LASER based
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measurement or the Shaft Encoder but either type faced some limitation and could not produce desired result.
I. LASER based measuring system: these systems incorporated two types of control
for said aligning- (a) Time of flight based and (b) Reflecting surface/mirror. This
type of systems suffered from the limitations and inconsistent performance
arising due to error in aligning caused due to minor tilting of mirror/reflecting
plane due to vibration during alignment. Also, such system fails to perform
reliably due to dust deposition on lens surface. The system also has the
complexity and cost involvement needing nano second timer.
II. Shaft encoders: These devices are usually mounted on the free end of
motor/gear box/tacho generator for positioning aligning applications. But in case
of aligning of ladle with tundish, the motor/gearbox assembly used for
driving/rotating the ladle stand is completely covered in order to protect the
same from liquid metal spillage from the ladle, and thus prohibiting the use of
shaft encoders for the purpose of aligning.
There was therefore a persistent need in the art for developing a system for a low cost, safe and reliable aligning of the ladle with tundish in continuous bloom caster eliminating any hazardous human interface at shop floor, such that the productivity can be improved at the casting plant minimizing loss of productive time consumed during such alignment.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a system of proper aligning of ladle and tundish at the bloom caster, in a safe and reliable manner involving less time , cost and also avoiding any additional manpower at shop floor and importantly also making such process of alignment safe and user friendly.
A further object of the present invention is directed to a system for achieving said safe and reliable means for aligning the ladle and tundish at the bloom caster, which can be effectively and safely carried out from pulpit.
A further object of the present invention is directed to a system for achieving said safe and reliable means for aligning the ladle with the tundish at bloom caster by deploying effective indication means which would indicate to the operator in the pulpit the position of the ladle
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and favour its effective guidance from the pulpit for the desired alignment of the ladle with the tundish by the pulpit operator.
A further object of the present invention is directed to a system for achieving said safe and reliable means for aligning the ladle with the tundish by deploying multiple photosensors/phototransistors, for desired angular positional alignment of the ladle with tundish minimizing the time required for said aligning.
A still further object of the present invention is directed to a system for achieving said safe and reliable means for aligning the ladle with the tundish by deploying multiple photosensors/phototransistors, said desired proper aligning of ladle with tundish is achieved by adopting low cost photosensor and LED means to make such system cost effective.
A still further object of the present invention is directed to a system for achieving said safe and reliable means for aligning the ladle with the tundish having a safe and reliable and maintenance free working life of several years.
A still further object of the present invention is directed to a system for achieving said safe and reliable means for aligning the ladle with the tundish by selective deployment of multiple photosensors/ phototransistors and LEDs, adapted to provide the required accuracy in ladle alignment consistently over considerable period of time without any variation.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a system for aligning ladle and tundish in bloom caster comprising:
ladle stand having mounted thereon multiple photosensors alongwith corresponding individual light source (LEDs);
two rod means/metallic strips mounted on the moving part of the stand and maintained 180° apart from each other and adapted to cast shadow over respective photo sensors on movement of said moving part of the stand;
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said ladle stand operatively connected to motor means is rotated and in the process said rod means mounted on the moving part of the stand arm adapted such that the same comes in between the said individual light source (LEDs) and phototransistors to cast shadow whereby respective photo transistors emitter voltages change indicative of a change in signal;
ladle-align-indication unit provided with said change of signals generated by the photo transistors for effective guiding and precise alignment of the ladle.
A further aspect of the present invention is directed to the system of said aligning of the ladle with the tundish in bloom caster wherein said ladle-align-indication unit is located in the pulpit and provided with a display unit comprising of equal number of LEDs and below each LED respective angle -5°,-40,-30,-20,-10, +10, + 20, + 30,+40, + 50 are marked and provided before the pulpit operator for said ladle guiding.
A still further aspect of the present invention is directed to the system for aligning ladle and tundish in bloom caster wherein said all photo sensors and associated LEDs are put in oridinary wood piece.
A further aspect of the present invention is directed to a system for aligning ladle and tundish in bloom caster wherein in normal condition all the phototransistors are illuminated and the emitter photo transistor is adapted to receive 5 V supply through its collector and as soon as the strip casts a shadow over the respective photo transistors the emitter voltage goes to 0 volts indicative of the change in signal fed into said ladle-ahgn-indication-unit.
According to a further aspect of the present invention, the small voltage signals are sent to 100m (electrical distance) through multicore cable and the same voltages have been used to illuminating different LED in ladle-tundish-align-display unit located at pulpit. No amplifier, comparator or driving circuits have been used in the present system, although these are essential components in conventional photosensor circuits.
Another aspect of the present invention directed to said photosensor based low cost system for proper aligning of ladle with tundish such as to reduce the time required for said aligning
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in a safe and reliable manner directly from the pulpit, without any human interference at the location near to the ladle at shop floor.
Yet another aspect of the present invention directed to the system of aligning of the ladle and tundish involving multiple photosensors/ phototransistors and LEDs, such that the corresponding signals are displayed in said ladle-align-display unit located at the pulpit, for favored proper angular aligning of the ladle with the tundish by the pulpit operator accurately in lesser time.
A still further advantageous aspect of the present invention is directed to the system of proper aligning of ladle and tundish wherein the system having a maintenance free working life of at least 7-8 years, which is also the normal life for the photosensors/LEDs and said system is capable to provide the accuracy in ladle alignment consistently over considerable period of time without any variation.
The present invention and its objects and advantages are described in greater details with particular reference to the accompanying figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: is the illustration of the conventional method of aligning ladle and tundish by human involvement at shop floor where the operator at pulpit is obstructed from direct viewing of the ladle position vis-a-vis the present sensor based control from pulpit.
Figure 2: is the illustration of the conventional LASER based measurement system for aligning, using reflecting surface.
Figure 3: is the illustration of sensor stack arrangement comprising the photosensors and LEDs, used in the aligning system according to the present invention.
Figure 4: is the illustration of the angular sensor stack deployed to obtain preferred angular alignment of the ladle and tundish by operative obstruction of light from LEDs incident on the photosensors, by metal strips attached to the moving parts of rotating ladle stands, placed 180° apart.
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Figure 5: illustrates the calibration of the system for measuring angular shift of nozzle of ladle.
DETAILED DESCRIPTION OF THE FIGURES WITH REFERENCE TO ACCOMPANYING FIGURES
As detailed above ,the present invention relates to a low cost, safe and reliable system for appropriately aligning a new ladle filled with liquid steel with a tundish in less time, favoring desired rate of pouring into moulds enhancing productivity and avoiding accidents due to metal spill over. In conventional practice this aligning is either achieved by human interference by signaling/guiding from shop floor standing near the ladle stand, as illustrated in figure 1, for directing the operator at the pulpit for rotating the ladle stand through required angle by trial and error to obtain said alignment of the ladle with the tundish or some devices are tried out to eliminate said human interference that is prone to accidents due to liquid metal spill over during ladle handling/ metal pouring. The LASER based measuring system, using a reflecting/mirror surface to favour said guided by reflected Laser beam by a sensor stack to achieve favorable angular alignment of ladle with tundish, as has been illustrated in the accompanying figure 2, but such Laser based measuring system suffered from limitations as already described, making such system inaccurate and unreliable for the intended purpose. Moreover, the use of Shaft Encoder to control the rotational movement of the ladle stand drive motor could not be advantageously applied as this motor is essentially completely covered for protection from the likely spillage of liquid metal.
Reference is now invited to accompanying figure 3 and 4, wherein the system of aligning the ladle with tundish has been illustrated. The sensor stack for the purpose of aligning make use of selective numbers of photosensors and an equal number of LEDs from which light is emitted in normal operating condition such that the light ray is incident on the corresponding photosensor placed directly below it, maintaining selective gap. The angular sensor stack of the figure 4, indicates the positions of the sensors and the paired LEDs, located for achieving desired aligning of the ladle and the tundish by selectively controlling the rotation of the shaft of the ladle stand. The angular position change of the ladle is measured by means of the photosensors sensing the incident light and generating signals
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accordingly. Four sensors along with respective LEDs were put at the left hand side of sensor stack with a spacing of 500mm from the neighbouring sensors; another four sensors along with respective LEDs were put on the right hand side of the sensor stack with same spacing of 500mm in between successive four sensors. In the sensor stack, sensors were put at 10mm spacing. A calibration system for measurement of the angular position shift of the ladle stand arm, as illustrated in the figure 5, guides to determine the required locations at a specified locus(radii of curvature) for sensors and LEDs, measured from the center of shaft of ladle stand and with specified spacing in between the sensors, to favor desired accurate aligning of ladle with tundish. The objective of such a system of calibration is to ascertain the angular shift of nozzle of ladle. The respective distances(radius) of the angular arrangement of the photosensors stack and the nozzle of the ladle are lm and 5m and the spacing between the senors in stack is 10mm . The distance(radius) of the LEDs are at 980mm and rotating metal strip progressively obstructing the incident light from the LEDs is having radius of locus of 990mm from the center of shaft of the ladle stand. Thus for a range of error of l-10mm at the sensorstack stage is equivalent to an error at the nozzle stage amounting (5m/lm x 10mm = ) 50mm. Multiple photosensors along with individual light source (LEDs) have been mounted near to the ladle stand. All photosensors and associated LEDs are put in ordinary wood piece/strip. Thus, this is a novel aspect of the present invention that the conventional use of costly bakelite has been substituted with low cost wood strip to sustain the high surrounding temperature making the system less costly yet effective and reliable. Two metal strips/rods are mounted on the moving part of the stand and are attached 180° apart with each other. These strips/rods provide shadow over the respective photosensors during the locus of movement along with the rotating stand arm, progressively on the sensor stack comprising selective number of phototransistors. At the time of handling a new ladle with fresh liquid metal, the ladle stand which is coupled with lOOKw DC motor, is gradually rotated and the strips which are mounted on moving part of the stand arm come in between the LEDs and phototransistors and cast shadow. In normal condition, all the phototransistors are illuminated and emitter of the phototransistors receives 5volts supply through its collector terminal. As soon as the strips cast shadow over respective phototransistors, the emitter voltage goes to 0 volts. These change of signals are sent to the ladle-align-indication-unit which is located in pulpit, at a distance of 100 meters from the sensor stack. The display unit consists of equal number of LEDs as of the sensor stack and each LED representing a measured angle of rotation of the ladle stand which is marked just below the respective LED , such as -5°, -4°, -3°, -2°, -1°, 0°, 1°, 2°, 3°, 4°, 5°
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and that help the pulpit operator to control/stop the drive motor for ladle stand at the time proper alignment has been indicated on the display unit and read at the pulpit itself.
The present invention do not make use of any amplifier or comparator for the photosensor circuit; only combination of photosensor and LEDs have been used to generate signal voltage for useful display means favoring desired alignment. Multiple LEDs are used to illuminate respective photosensors and no focusing tube neither at LEDs side nor at the photosensor side is used. The rotating metal strips attached to the ladle stand arm that generates the shadow by obstructing light emitted from the LEDs and incident on the respective phototransistors, being positioned in between the stationary set of sensor stack and its illuminating LEDs, in such a way that it give proper indication in the pulpit in said LED based display unit displaying the angular positions to match with that of the tundish. The system ensures that the liquid steel is poured at the center of the tundish and avoids the accumulation/sticking of metal near the tundish wall and it also avoids pour over the 2nd stopper of tundish of 4 strands bloom caster; Thereby increasing the life of stopper, which is otherwise eroded quickly, say in 7-8 heats, while with new system its life has been increased to about 30 heats. The system of the present invention is capable to minimize time required for aligning of ladle and tundish in a safe and highly reliable manner. The normal operating life of such system is about 7-8 years, being same as that of the photosensors and the LEDs and the accuracy of the system in measurement/alignment is invariant over period of time.
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WE CLAIM
1. A system for aligning ladle and tundish in bloom caster comprising:
ladle stand having mounted thereon multiple photosensors alongwith corresponding individual light source (LEDs);
two rod means/metallic strips mounted on the moving part of the stand and maintained 180° apart from each other and adapted to cast shadow over respective photo sensors on movement of said moving part of the stand;
said ladle stand operatively connected to motor means is rotated and in the process said rod means mounted on the moving part of the stand arm adapted such that the same comes in between the said individual light source (LEDs) and phototransistors to cast shadow whereby respective photo transistors emitter voltages change indicative of a change in signal;
ladle-align-indication unit provided with said change of signals generated by the photo transistors for effective guiding and precise alignment of the ladle.
2. A system for aligning ladle and tundish in bloom caster as claimed in claim 1 wherein
said ladle-align-indication unit is located in the pulpit and provided with a display unit
comprising of equal number of LRDs and below each LED respective angle -5°,-4o,-
3o,-2o,-1o, + 1o,+2o,+3o,+4o,+5o are marked and provided before the pulpit operator
for said ladle guiding.
3. A system for aligning ladle and tundish in bloom caster as claimed in anyone of
claims 1 or 2 wherein said all photo sensors and associated LEDs are put in ordinary
wood piece.
4. A system for aligning ladle and tundish in bloom caster as claimed in anyone of
claims 1 to 3 wherein in normal condition all the phototransistors are illuminated and
the emitter photo transistor is adapted to receive 5 V supply through its collector and
as soon as the strip casts a shadow over the respective photo transistors the emitter
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voltage goes to 0 volts indicative of the change in signal fed into said ladle-align-indication-unit.
5. A system for aligning ladle and tundish in bloom caster as claimed in anyone of
claims 1 to 4 wherein the width of the rotating light shadower (metallic strip) is
maintained and hanged in between the stationary set of sensors stacks and
illuminating LEDs such as to provide proper indication in the pulpit for said LED
based ladle-aligning indication.
6. A system for aligning ladle and tundish in bloom caster and a method of ladle
aligning using the system for aligning ladle and tundish in bloom caster as claimed in
anyone of claims 1 to 5 substantially as herein described and illustrated with
reference to the accompanying figures.


Dated this 19th day of January, 2007.

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A photosensor based system that is simple, low cost and at the same time, highly reliable and safe, for aligning of ladle with tundish at continuous bloom casting. The system of alignment minimizes delay in said aligning time and ensures that liquid steel pours at the center of tundish. The angular position change during ladle change over is sensed by the photosensors receiving the incident light from LEDs and generating signals accordingly. Two rotating metal strips attached to the ladle stand arm generates shadow by obstructing light emitted from the LEDs and incident on the respective phototransistors, being positioned in between the stationary set of sensor stack and its illuminating LEDs, in such a way that it give proper indication in the pulpit in said LED based display unit displaying the angular positions to match with that of the tundish. The present system of alignment also avoids the accumulation of metal near the tundish wall.