Title of Invention

A CONTROL SYSTEM FOR CONTINUOUS MEASUREMENT OF LIQUID STEEL LEVEL IN A MOVABLE TUNDISH

Abstract A control system for continuous measurement of liquid steel level in a movable tundish for feeding liquid metal in a continuous casting mould comprising: a level measurement laser sensor (6) for sensing the free metal level in the tundish (3) and sending the generated signal to be processed in a processor (16); a distance meter sensor (8) focused on the upper surface of the shell of the tundish (3) to locate the instantaneous position of the vertically movable tundish (3) connected to the caster through a submerged entry nozzle (4) and sending the generated signal to a processor (16); a converter (14) for converting the current signals received from said level measurement sensor (6) and distance meter sensor (8) into voltage signals; and a processor (16) with a display unit (18) coupled to the converter for receiving the voltage signals wherein the level of the liquid steel in the tundish is measured on prior knowledge of inclination of both the sensors from vertical and maximum vertical movement (h) of the tundish obtained by carrying out calibration of the two sensors (6 and 8) through mathematical relationships.
Full Text The present invention relates to a continuous measurement of liquid steel level in
a movable tundish for feeding liquid metal in a continuous casting mould.
Liquid steel, after tapping from BOF is carried in ladles to the secondary
metallurgical units like basic oxygen furnace (BOF), Online purging (OLP), ladle
furnace (LF) and Rheinstahl-Heraeus (RH) for refinement. Thereafter the ladle is
transferred to casters.
Liquid steel from the ladle is teemed through a refractory shroud into an
intermediate refractory lined container, known as tundish, which in turn feeds
the liquid steel into the continuous casting moulds through submerged entry
nozzles.
The metal level in the tundish is required to be operated, at a healthy position so
that suction of tundish slag into the mould can be minimized. Maintaining the
liquid steel level in the tundish will also maximize inclusion floatation.
Furthermore, the tundish is moved in a vertical plane in order to safeguard the
submerged entry nozzles against the preferential wearing at the interface.
For measuring the level of liquid steel in the tundish, usually load cells are used
which determine the weight of metal in the tundish. Such load cell based
weighing system gives an indirect estimate of the level of liquid steel in the
tundish.

The load cell based system of indicating the level of liquid
steel in tundish, however requires regular calibration. Such
calibration procedures are time consuming and requires great deal
of attention.The system also needs regular maintenance.
The main object of the present invention therefore, is to provide
a continuous level control system for measuring with greater
accuracy the liquid level in the tundish without the need for
frequent calibration.
Another object of the present invention is to provide a
continuous level control system that is robust in construction
and needs very little maintenance.
These and other objects are achieved by using a distance meter
sensor and a level measurement sensor for measuring the free
metal level in the tundish. The distance meter sensor can be a
laser distance meter manufacured by Leica,Switzerland. For the
level measurement sensor a high temperature ievel measurement
sensor manufactured by Riegl laser measurement system can be
used.
The optical unit in the high temperature level measurement laser
sensor device senses the free metal level in the tundish and
sends the signal to the level sensor electronic circuitry of the
device.

The laser distance meter is focussed on the upper surface of the
tundish shell for locating the instantaneous position of the
tundish in the vertical plane.
The above mentioned two sensors generate current signals in
milli-amperes which can be converted to voltage signals with the
help of a signal converter.
The two signals from the two sensors in conjunction dynamically
provide the instantaneous metal level in the tundish. For this,
the voltage signals from the level measurement and distance meter
sensors are processed in a processor with a built in analog to
digital converter. The liquid metal level in the tundish can then
be displayed in a display unit connected to the signal processor.
The invention thus provides a continuous level control system for
measuring the liquid steel level in a tundish, comprising a ladle
with a ladle nozzle shroud, an intermediate container or tundish
for receiving liquid steel from the ladle, said tundish being
provided with a submerged entry nozzle and movable in a vertical
plane through a distance characterized in that said system is
provided with a level measurement sensor for sensing the free

metal level in the tundish and generating a signal, a distance
meter sensor for focussing on the upper surface of the tundish to
locate the instantaneous position of the tundish in the vertical
plane, a converter for converting the current signals received
from said level measurement sensor and distance meter sensor into
voltage signals and a processor coupled to said converter for
receiving said voltage signals and calculating therefrom the
level of liquid steel in said tundish.
The invention will now be described in detail with the help of
the accompanying drawings, where :
Figure 1 shows the weight of steel in a tundish as a function
of metal fill height of the tundish,
Figure 2 shows schematically the layout of a continuous casting
facility,
Figure 3 shows in block diagram form the layout of the system
of present invention,
Figure 4 shows schematically the calibration layout of the
present invention.
As shown in Figure 2, in a typical casting facility, liquid steel
from the steel ladle 1 is teemed through a refracting ladle
nozzle shroud 2 into an intermediate container 3. This

intermediate container 3 is refractory lined and is known as
tundish. This tundish 3 in turn feeds the liquid steel through a
submerged entry nozzle 4 into the continuous casting moulds S.
The tundish is moved in a vertical plane through distance H for
safeguarding the submerged entry nozzles 4 against wear at the
interface,
The level control system comprises a level measurement laser
sensor 6, as shown in Figure 3. This level measurement laser
sensor 6 is provided with high temperature level sensor
electronics and an optical unit. The electronics may be LD90-3100
HT-GF and the optical unit MK 56 in a Riegl Laser Measurement
Systems, GmbH make laser sensor and their details are not shown
in Figure 3.
The optical unit of the level measurement laser sensor 6 senses
the free metal level in the tundish 3 and sends a signal to the
high temperature level sensor electronics.
A distance meter sensor 8 is focussed on the upper surface of
the shell of the tundish 3, to locate the instantaneous position
of the tundish 3 in the vertical plane. The distance meter sensor
8.

can be a Leica Switzerland make laser distance meter. The two
signals generated by the level management laser sensor 6 and
laser distance meter S are current signals of 4 to 20 milli
amperes. These are converted to voltage signals with the helpof a
converter 14 before being fed to a processor 16.
The processor 16 is provided with a built-in analog to digital
(A/D) converter (not shown) for receiving the signals from the
level measurement sensor 6 and distance meter sensor 8, now
converted into voltage signals.
The processor 16 for calculating and displaying in a visual
display unit 18 the metal level of tundish 3 can be a Motorola
68000 processor. The tundish level calculations require prior
knowledge of inclinations (from vertical) of both the sensors,
which is obtained by carrying out calibration of the two sensors.
The calibration layout is schematically shown in Figure 4. The
maximum vertical movement (h) of the tundish is known. The two
sensors inclinations can be estimated by using the following
formulae:


Where,
8 = Level measurement laser sensor's inclination from the
R
vertical
B = Laser distance-meter sensor's inclination from the
L
vertical
RT - Level measurement laser sensor's reading of the bottom of
B
the tundish when it is at its lower most position in
the vertical plane.
RT = Level measurement laser sensor's reading of the bottom of
T
the tundish when it is at its upper most position in
the vertical plane
LT = Laser distance measurement reading of the upper surface of
B
the tundish when it is at its lower most position in
the vertical plane
LT = Laser distance measurment reading of the upper surface of
T
the tundish when it is at its upper most position in
the vertical plane.
In order to obtain the height of steel filled in the tundish
fallowing formula is used :
RTT x cose +(cosθL x(Dist.Meas Reading- LTT)-(LevelDistRead,xcosθR)
From the three dimensional structural drawing of the tundish
volume of steel at different selected fill heights of metal can be

obtained. Knowing the density of liquid steel volume is converted to weight unit.
A piecewise non-linear regression is then carried out between the height of metal
and the corresponding calculated tundish weight. Table 1 shows the result of the
regression for a tundish used for slab casting.


WE CLAIM
1. A control system for continuous measurement of liquid steel level in a
movable tundish for feeding liquid metal in a continuous casting mould
comprising:
- a level measurement laser sensor (6) for sensing the free metal
level in the tundish (3) and sending the generated signal to be
processed in a processor (16);
- a distance meter sensor (8) focused on the upper surface of the
shell of the tundish (3) to locate the instantaneous position of the
vertically movable tundish (3) connected to the caster through a
submerged entry nozzle (4) and sending the generated signal to a
processor (16);
- a converter (14) for converting the current signals received from
said level measurement sensor (6) and distance meter sensor (8)
into voltage signals; and

a processor (16) with a display unit (18) coupled to the converter
for receiving the voltage signals wherein the level of the liquid steel
in the tundish is measured on prior knowledge of inclination of both
the sensors from vertical and maximum vertical movement (h) of
the tundish obtained by carrying out calibration of the two sensors
(6 and 8) through the equations

Where,
θR = Level measurement laser sensor's inclination from the vertical
θL = Laser distance-meter sensor's inclination from the vertical
RTB = Level measurement laser sensor's reading of the bottom of the
tundish when it is at its lower most position in the vertical plane.
RTT = Level measurement laser sensor's reading of the bottom of the
tundish when it is at its upper most position in the vertical plane.

LTB Laser distance measurement reading of the upper surface of the
tundish when it is at its lower most position in the vertical plane.
LTT Laser distance measurement reading of the upper surface of the
tundish when it is at its upper most position in the vertical plane.
2. The system as claimed in claim 1, wherein said processor 16 is connected
to a visual display unit 18 for displaying a calculated level of liquid steel in
the tundish.
3. The system as claimed in the preceding claims wherein said high
temperature level laser sensor comprises high temperature level sensor
electronics LD90-3100 HT-GF for sending a signal generated by said laser
sensor 6.
4. A control system as claimed in claim 1 wherein the height of steel filled in
the tundish being measured by the equation
RTTx COSΘR + (cosθLx (Dist.Meas Reading - LTT) - (LevelDistRead xcosθR)

5. A control system as claimed in claim 1 wherein the weight of tundish is
measured from the obtained metal level in the tundish from the three
dimensional structural drawing of the tundish at different selected fill
heights of metal and the obtained volume of the liquid metal is converted
to weight unit from the density of liquid steel and on carrying out a
piecewise non-linear regression between the height of metal and
corresponding calculated tundish weight to generate a regression
equation
h = 7 x 10-6 h2 + 0.004 h - 0.0086
where h is height of liquid steel from the bottom of the tundish.
Dated this 30th day August 2002

A control system for continuous measurement of liquid steel level in a movable
tundish for feeding liquid metal in a continuous casting mould comprising: a level
measurement laser sensor (6) for sensing the free metal level in the tundish (3)
and sending the generated signal to be processed in a processor (16); a distance
meter sensor (8) focused on the upper surface of the shell of the tundish (3) to
locate the instantaneous position of the vertically movable tundish (3) connected
to the caster through a submerged entry nozzle (4) and sending the generated
signal to a processor (16); a converter (14) for converting the current signals
received from said level measurement sensor (6) and distance meter sensor (8)
into voltage signals; and a processor (16) with a display unit (18) coupled to the
converter for receiving the voltage signals wherein the level of the liquid steel in
the tundish is measured on prior knowledge of inclination of both the sensors
from vertical and maximum vertical movement (h) of the tundish obtained by
carrying out calibration of the two sensors (6 and 8) through mathematical
relationships.

Documents:

510-cal-2002-granted-abstract.pdf

510-cal-2002-granted-claims.pdf

510-cal-2002-granted-correspondence.pdf

510-cal-2002-granted-description (complete).pdf

510-cal-2002-granted-drawings.pdf

510-cal-2002-granted-examination report.pdf

510-cal-2002-granted-form 1.pdf

510-cal-2002-granted-form 13.pdf

510-cal-2002-granted-form 18.pdf

510-cal-2002-granted-form 2.pdf

510-cal-2002-granted-form 3.pdf

510-cal-2002-granted-gpa.pdf

510-cal-2002-granted-pa.pdf

510-cal-2002-granted-reply to examination report.pdf

510-cal-2002-granted-specification.pdf


Patent Number 226920
Indian Patent Application Number 510/CAL/2002
PG Journal Number 01/2009
Publication Date 02-Jan-2009
Grant Date 30-Dec-2008
Date of Filing 30-Aug-2002
Name of Patentee TATA STEEL LIMITED
Applicant Address RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR
Inventors:
# Inventor's Name Inventor's Address
1 KUMAR ANUP TATA STEEL LIMITED RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR 831 001
2 JATLA SSVS TATA STEEL LIMITED RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR 831 001
PCT International Classification Number B 22 D 11/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA