FIELD OF INVENTION
The present invention relates to measurement of the friction value between the
mould and the solidifying slab in a process of continuous casting of steel. More
particularly, the present invention relates to a condition monitoring system for
monitoring the friction level including the health of the oscillator in a continuous
steel casting process. The invention further relates to a method of measuring the
friction value between the mold and the solidifying slab in a system during the
process of continuous casting of steel.
BACKGROUND OF INVENTION
Continuous casting is a process whereby molten metal is solidified into a
"semifinished product" billet, bloom or slab. Prior to introduction of the
continuous casting process, molten steel used to be poured into stationary
moulds to form "ingots". However, "continuous casting" process achieves
improved yield, quality, productivity and cost efficiency. Presently, continuous
casting is the predominant process by which steel is produced in the world.
In an integrated steel industry continuous casting of steel plays a great role for
the productivity and quality of steel. During continuous casting operation of steel
slab, liquid steel is continuously poured in to a tubular mould at one end and at
the other end the solidified strand is withdrawn. The mould is continuously

cooled to solidify the steel. The mould is oscillated in a sinusoidal motion, so that
the liquid steel will not stick to the mould. Due to the interaction between the
mould and the steel, friction force between these two arises. Higher friction
value leads to poor surface quality and also indicator of abnormalities like sticker
during casting process. So it is very important to measure the friction value.
In the continuous casting process, illustrated in Figure 1, molten metal is poured
from a ladle (1) into a tundish (2) and then through a submerged entry nozzle
(3) into a mould cavity (4). The mould (4) is water-cooled so that enough heat is
extracted to solidify a shell (5) of sufficient thickness. The shell (5) is withdrawn
from the bottom of the mould (4) at a "casting speed" that matches the inflow of
metal, so that the process ideally operates at steady state. Below the mould (4),
water is sprayed to further extract heat from the strand surface, and the strand
(5) eventually becomes fully solid when it reaches the "'metallurgical length"'.
Solidification begins in the mould (4), and continues through the different zones
(6, 7) of cooling while the strand (5) is continuously withdrawn at the casting
speed. Finally, the solidified strand (5) is straightened, cut, and then discharged
for intermediate storage or hot charged for finished rolling.
To start a cast, the bottom of the mould (4) is sealed by a steel dummy bar (13).
This bar (13) prevents liquid metal from flowing out of the mould (4) and the
solidifying shell (5) until a fully solidified strand section (5) is obtained. The liquid

poured into the mould (4) is partially solidified in the mould (4), producing a
strand (5) with a solid outer shell and a liquid core. In this primary cooling area
(6), once the steel shell (5) has a sufficient thickness, the partially solidified
strand (5) will be withdrawn out of the mould (4) along with the dummy bar (13)
at the casting speed. Liquid metal continues to pour into the (4) mould to
replenish the withdrawn metal at an equal rate. Upon exiting the mould (4), the
strand (5) enters a roller containment section (14) and a secondary cooling
chamber (7) in which the solidifying strand (5) is sprayed with water, or a
combination of water and air to promote solidification. Once the strand (5) is
fully solidified and has passed through the straightener (14), the dummy bar is
disconnected, removed and stored.
The main function of the mould (4) is to establish a solid shell (5) sufficient in
strength to support its liquid core upon entry into the secondary spray cooling
zone (7). The mould (4) is basically an open-ended box structure, containing a
water-cooled inner lining fabricated from a high purity copper alloy. Mould
oscillation is necessary to minimize friction and sticking of the solidifying shell
(5), and avoid shell tearing, and liquid steel breakouts, which can wreak havoc
on equipment and machine downtime due to clean up and repairs. Friction
between the shell (5) and mould (4) is reduced through the use of mould
lubricants such as oils or powdered fluxes. Oscillation is achieved either
hydraulically or via motor-driven cams or levers which support and reciprocate
(or oscillate) the mould.

A prior patent EP 1043096 entitled "Process of measuring the frictional force
between the stand and the mould at continuous casting" which discloses a teaching of
a strand skin friction is determined from data collected for regulating continuous
casting mound oscillation. The friction between a strand skin and an oscillating
continuous casting mould is determined by recording the pressure between the two
chambers of all the regulated double-acting hydraulic cylinders used as oscillation
cylinders as well as the associated piston stroke positions with a predetermined
measurement frequency and using the data for calculating the frictional force at
instant.
A second prior patent EP 0885675 entitled "method and apparatus for
foreseeing a break out during continuous casting of steel with an oscillating method"
which discloses a teaching of a method included a continuous and comparative
measurement of operating parameters such as, for example, the temporal and spatial
temperature distribution in the copper mould plates, and an analysis of the measured
data. Two sets of measured data are combined with at least one further measurement
series and are subjected to on-line analysis. The apparatus includes a measurement
and analysis system with the following elements: a) at least one oscillations
acceleration sensor (10.1-10.4); b) a number of temperature sensors (11) in the
mould plates; c) a line camera (12) for detection of billet oscillation; d) a billet velocity
sensor (13); e) assessment units (20-22); f) a central computer unit (30); g) a unit
(31) for issuing an early warning signal.

OBJECTS OF INVENTION
It is therefore an object of the invention to propose a condition monitoring system for
monitoring the friction level including the health of an oscillator in a continuous steel
casting process which eliminates the disadvantages of prior art.
Another object of the invention is to propose a condition monitoring system for
monitoring the friction level including the health of an oscillator in a continuous steel
casting process which facilitates production of improved surface quality of the cast
steel.
A further object of the invention is to propose a method of measuring the friction
value between a mould and a solidifying slab including monitoring the machine
parameters in a process of continuous casting of steel.
SUMMARY OF THE INVENTION
The present invention is provided with a condition monitoring system for steel slab
caster for measuring the friction value between a mould and a solidifying slab
including monitoring the health of the oscillator in a process of continuous casting of
steel, the system comprising; a plurality of accelerometer (9) disposed at different
corners of a continuous casting mould table (8) to capture acceleration data, the
mould table (8) being operable

connected to a data acquisition device (10), the mould (4) being caused to oscillate in
a sinusoidal motion via an electrically operated rotating means leading to generation
of mechanical energy due to movement of liquid or solidifying steel between the
mould (4), the accelerations values in X, Y and Z directions in the form of converted
electric signals being outputted by the data acquisition device (10) both at casting and
no-casting conditions; characterized in that a process module incorporated in a
computer apparatus (11) for calculating the friction value generating due to
interaction between the mould (4) and the solidifying strand (5), and for analyzing the
collected data by adapting a Fast Fourier Transformation algorithm to identify any
abnormality in the machine parameters.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - schematic diagram of a continuous casting process
Figure 2 - schematic diagram of the condition monitoring system according to the
invention
Figure 3 - conceptually shows the principle of an accelerometer in a block diagram
Figure 4 - shows a flow chart illustrating the method of the invention.

DETAIL DESCRIPTION OF INVENTION
A condition monitoring system for steel slab caster is developed adapting
multiple sensors for monitoring the friction level, which has an improved effect
on slab surface quality. This system can simultaneously measure the friction
between the mould (4) and the solidifying slab (5) including monitoring the
health of the oscillator (4) for to identify abnormality during the operation. This
system adapts four numbers of Tri-Axial Accelerometers (9). Acceleration value is
collected in the X, Y and Z direction using the tri-axial accelerometers (9) which
are placed at the four corners of the continuous casting mould table (8). The
acceleration value is collected for both casting and no casting conditions of the
oscillator (4) using a data acquisition device (10). A process module is used for
post processing of data in a computer apparatus (11) connected to a power
source (12), to calculate the friction value and analyze the data collected from
accelerometers (9) for any abnormality in the machine health.
The inventive concept leading to the present invention constitutes that a
difference between the force during casting and the force during no casting with
the same frequency of oscillation gives the friction value which occurs due to the
interaction between the mould (4) and the solidifying strand (5). A FFT of the
collected data is carried-out in the 3 directions to find out if there is any defect in
the continuous casting machine for example problem with eccentric cam, worn of
bearing, non-sinusoidal nature of oscillation.

The new system is capable to measure the friction between the mould (4) and
the solidifying strand (5) efficiently. This will help in evaluating the performance
of different kind of lubricants based on the friction value obtained for them
during casting. This system also will help in monitoring any abnormal behaviour
of the casting machine.
As shown in Figure 3, the simplest model of an accelerometer is a mass-spring-
damper device (9) that is attached to an enclosing casing (4). The applied
acceleration of the casing causes the mass to move, and this motion can be used
to determine the magnitude of the acceleration. Due to the movement of the
mass the mechanical energy is converted into electrical signal from which the
acceleration is calculated. In a tri-axial accelerometer device at least, 3 no of
accelerometers are placed in the 3-axis of the space coordinate which can
calculate acceleration in 3 directions.
The specification of the accelerometers used for this system is given as under:


Figure 4 describes the steps carried out by the process module embedded in the
computer apparatus (11).
Step 1: Acceleration data is read from the accelerometer (9) online
Casting speed data is read from operating table online
Matching the casting speed with the cold force data is read from COLD FORCE
(the force exerted with empty mould) look up table
Step 2: Oscillation frequency is calculated from the casting speed by multiplying
a constant A
Step 3: Fast Fourier Transformation (FFT) analysis of the acceleration data is
done and the Amplitude vs frequency plot is displayed
Step 4: Angular velocity (GO) is calculated from the frequency of oscillation as
Angular Velocity (ω) = 2nf
Step 5: Displacement (d) of the mould table (8) is calculated as
Displacement (d) = -a/Ω2

The displacement of mould with time is displayed
Step 6: HOT FORCE or the force on caster during casting is calculated by taking
the Root Mean Square (RMS) value of the acceleration.
Step 7: The friction value is calculated for the current casting speed by
subtracting the COLD FORCE from HOT FORCE and the friction with time is
displayed.
ADVANTAGES OF THE INVENTION:
1. On-line monitoring of mould oscillation is an important tool for the
performance of casting and also improving machine reliability.
2. Various parameters can be optimized using this system to lower the
friction level during casting.
3. Any abnormality situation like break-out can be known prior to its
happening by monitoring the friction level.
4. The friction force for different kind of lubricant can be assessed and the
best lubricant can be evaluated by this system.
5. This equipment is very useful as a preventive maintenance tool by
providing early warning about problems related to health of the machine.

WE CLAIM
1. A condition monitoring system for steel slab caster for measuring the friction
value between a mould and a solidifying slab including monitoring the health of
the oscillator in a process of continuous casting of steel, the system
comprising;
- a plurality of accelerometer (9) disposed at different corners of a
continuous casting mould table (8) to capture acceleration data, the
mould table (8) being operable connected to a data acquisition device
(10), the mould (4) being caused to oscillate in a sinusoidal motion via
an electrically operated rotating means leading to generation of
mechanical energy due to movement of liquid or solidifying steel
between the mould (4), the accelerations values in X, Y and Z directions
in the form of converted electric signals being outputted by the data
acquisition device (10) both at casting and no-casting conditions;
characterized in that a process module incorporated in a computer apparatus
(11) for calculating the friction value generating due to interaction between the
mould (4) and the solidifying strand (5), and for analyzing the collected data by
adapting a Fast Fourier Transformation algorithm to identify any abnormality in
the machine parameters.

2. A method of measuring the friction value between a mould and a
solidifying slab including monitoring the machine parameters in a process
of continuous casting of steel, comprising the steps of:
- providing a condition monitoring system as claimed in claim 1 being
operably disposed on a mould table of the casting machine;
- online reading of acceleration data and casting speed data
respectively from the accelerometers and the mould table (8);
- matching the casting speed in correspondence with the cold force
value displayed on the look-up table (8);
- calculating oscillation frequency from the acquired casting speed
data by multiplying a constant A;
- generating a graphical display of amplitude vs frequency data by
applying First Fourier Transformation algorithm;
- calculating the angular velocity (Ω) in the form of GO = 2nf from the
frequency of oscillation;
- calculating displacement of the mould table (8) in the form of (d) =
-a/ω2

- determining hot force on caster during casting by calculating Root Mean
Square (RMS) value of the acceleration data; and
- calculating the friction value by subtracting the cold force value from the
hot force value.
3. A condition monitoring system for steel slab caster for measuring the friction
value between a mould and a solidifying slab including monitoring the health of
the oscillations in a process of continuous casting of steel as substantially
described herein with reference to the accompanying drawings.

ABSTRACT

A CONDITION MONITORING SYSTEM FOR MEASURING THE FRICTION
VALUE BETWEEN A MOULD AND A SOLIDIFYING SLAB
A condition monitoring system for steel slab caster for measuring the friction value
between a mould and a solidifying slab including monitoring the health of the
oscillator in a process of continuous casting of steel, the system comprising; a
plurality of accelerometer (9) disposed at different corners of a continuous casting
mould table (8) to capture acceleration data, the mould table (8) being operable
connected to a data acquisition device (10), the mould (4) being caused to oscillate in
a sinusoidal motion via an electrically operated rotating means leading to generation
of mechanical energy due to movement of liquid or solidifying steel between the
mould (4), the accelerations values in X, Y and Z directions in the form of converted
electric signals being outputted by the data acquisition device (10) both at casting and
no-casting conditions; characterized in that a process module incorporated in a
computer apparatus (11) for calculating the friction value generating due to
interaction between the mould (4) and the solidifying strand (5), and for analyzing the
collected data by adapting a Fast Fourier Transformation algorithm to identify any
abnormality in the machine parameters.