FIELD OF INVENTION
The present invention relates to a system for automatic
detection and control of leading edge of moving hot billets in
continuous casting plant. More particularly, the invention is
concerned about detection and control of leading edge of billets
in a continuous casting plant by means of IR sensors adapted for
measuring temperature of the billets above a threshold value so
as to give an output signal to a controller means for desirable
control of the movement of the billets.
BACKGROUND AND PRIOR ART
Conventionally, billets are casted in continuous casting systems
where in the sequence of operation, the ladle is raised on to a
turret that rotates the ladle to the casting position above the
tundish. Then the liquid steel flows out of the ladle into
tundish and water-cooled oscillating copper mold. The
solidification begins in the mould and continues through the
secondary cooling zone and strand guide. In this configuration
the billet is straightened and cut to desired length and then
discharged to take over bay. A cross pusher operating
perpendicularly to the cut to size billets is used to position
the billets to a defined position. Transfer mechanism takes over
the billets in turn over cooling bed area. Thus operation is
needed to position the billets accurately in a desired place to
maintain automatic operation of various sequence of material
transfer. The pusher operation has two modes one to slow it down
and the other is for accurate positioning of the billets at
final precise stop locations.
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At the locations of slow down and final stoppage, mechanical
limit switches were used to activate the operation of slow down
the cross pusher and final stoppage.
However, the disadvantages associated with the mechanical limit
switches are as follows:
The mechanical limit switches (11) were of contact type
(Reference is drawn to figure 1) and it was installed exactly
below the hot billets movement area and when the hot billets
(12) were hitting the mechanical limit switches (11) and the tie
rod attached to the system touching the contact of electrical
system and it was giving the output for further operation. But
due to hitting of hot billets and high temperature of that
particular zone the rod was bending very frequently and damage
of switches was very frequently. It was leading to the abrupt
stoppage of casting operation and as result increase in return
of running heat of caster and increase in down of caster.
Because when the cross pusher (13) is not operating due to the
limit switches failure, the continuous coming billets can not be
cleared from the area and we have to stop the caster. Area of
mechanical limit switches was very harsh and for replacement/
maintenance the temperature had to cool down and result decay
was occurring.
US6209619 discloses billet guiding system in a continuous
casting plant. This prior art teaches a measuring device for
detecting the pivoting movement of the support segment,
preferably a position sensor or an angle measuring device, is
provided which via a controller is coupled with an adjusting
device for adjusting the position of the support segment. The
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principle of measurement of position sensor is different from
the principle of measurement in the infra red sensor so it was
not known from the prior art that by sensing temperature of hot
billets within a specified range of temperature corresponding
relay signals can be provided to a controller means for
controlled movement of the hot billets.
US6279645 discloses a contact type sensor for high temperature
measurement as molten metal is of very high temperature. It was
not known from the prior art that by sensing temperature of hot
billets within a specified range of temperature corresponding
relay signals can be provided to a controller means for
controlled movement of the hot billets.
Thus there is a need to provide an improved system that prevents
limit switches from getting damaged frequently due to hitting of
red hot billets resulting in a non-availability of limit switch
signals to activate the sequence of operations.
The present inventors have surprisingly found that the drawbacks
/disadvantages of the conventional system as discussed
hereinabove can be overcome by providing non contact type
sensors based transportation control system for cross pushers
used in continuous casting plants. The inventors have found that
the movement of the pusher and therefore the billets can be
controlled by way of temperature sensing of hot billets and
sending corresponding output signals to control mechanism.
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OBJECTS OF THE INVENTION
Accordingly, one object of the present invention is to overcome
the disadvantages prevailing in the prior art and the existing
system as discussed above.
Another object of the present invention is to provide a control
system for detection and control of cross pusher movement in
continuous casting plants.
SUMMARY OF THE INVENTION
Accordingly, one aspect of the present invention relates to a
system for detection of leading edge of moving hot billets
thereafter controlling movement of said hot billets in a
continuous casting mill, said system comprising :
means for sensing temperature of said billets when the
temperature crosses a predetermined temperature threshold,
wherein distance of sensing means from hot billets being such
that temperatures of adjacent billets do not have effect on said
temperature threshold,
said means being operatively connected to interfacing means so
as to generate output signals corresponding to the temperature
sensed by the sensing means; and
means for receiving said output signals from the interfacing
means so as to control movement of the billets.
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DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a system to overcome the
drawbacks of the conventional mechanical limit switches. The
said system is developed for automatic detection of leading edge
of moving hot billets and control of transfer mechanism. The
system is installed in two casters wherein the system comprises
non contact infra red temperature switches along with power
supply and control units which are installed at the locations of
slow down and final stoppage at both casters.
The system of the present invention comprises means for sensing
temperature of the hot billets. The said means comprises IR
temperature switches which are connected to interfacing means
and power supply. Interfacing means includes relay unit and the
arrangement of the sensors and the relay unit is placed inside
the sensor protection box. The sensors are installed at the two
specified location for each caster for slow down and final
stoppage of cross pusher, which is pushing the packets of hot
billets. When the leading edge of the moving billets comes in
front of the sensor it sense the presence of material from the
specified distance and gives the relay output to PLC system and
the program in the PLC controls the automatic operation of slow
down, stoppage and finally backward movement of cross pusher
(Billet Transfer mechanism).
The sensor has a setting for temperature threshold, it is set
for 550°C. Whenever the temperature of the material goes above
550°C the sensor gives the relay output and the material is said
to be present. Normally the temperature of the hot billets is
more than 680°C, so when it comes in front of the sensor it gives
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the relay output and leading edge detection is done. In the
absence of the material or when the temperature is below 550°C,
the sensors will not give relay output.
Basically the sensor (IR temperature switches) requires 24V DC
power supplies for operation. The input supply to the power
supply unit is 230 V DC and it converts it to 24 V DC and gives
to the sensor for their operation. The relay contact unit with
NO (Normally Open) and NC (Normally Closed) contact is also
integrated with the power supply unit and when the sensor sense
the material it gives the signal to the relay unit and finally
the relay contact is obtained as output for integration with the
existing PLC.
The basic system design is based on the following requirements/
operation parameters:
Billets Sizes (mm x mm): 80x80,100x100, 125x125
Non Contact type system
Temperature range 35 Deg. C - 800 Deg. C
Distance from the object - 3.5 meters [Approx.]
The system components are as described Infrared Temperature
Switch:
Total four numbers of IR temperature switches were installed in
two casters.
The specification of the sensors:
Dimensions in mm : 25x125
Housing : Stainless steel
Protection : IP65
Power Supply : 24V DC (16...25V), 6 mA
Output : Transistor switch, 20V (max), 30
mA
Temp range : 500 ...1100 oC
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Emissivity, E : 1
Switch time : 1 ms
Repeatability : 0.3% of temperature value
Sighting : LED target light
Ambient temp. : 8 0 °C
Humidity : 95% RH, non-condensing
Power Supply
Four Numbers of Power supplies Unit were installed in two
Casters
Relay Circuit
Total four numbers of Relay circuits were installed in two
casters and the specification is
Input : Transistor Switch
Contact : 1 NO and 1 NC
Cooling Arrangement for Sensors:
MS Sheet : 6 mm
Asbestos Sheet : 6 mm
Valves : Two position for 25 NB Line
Pressure Gauge : 0-10 kg/ cm2 for Line size 25 NB
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates limit switches arrangement in the existing
systems.
Figure 2 illustrates a schematic diagram of the system of the
present invention.
Figure 3 illustrates cooling arrangement for sensor protection
in the present invention.
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Figure 4 illustrates field of view of the sensors in the present
invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 2 shows the arrangement of the system of the present
invention. The system comprises infrared temperature switch (21)
and electronic relay unit (not shown separately in the figure)
accommodated in sensor protection box (31) (reference is drawn
to figure 3). Relay output (Reo) is sent to the PLC (22). Al & A2
as shown in figure 2 are the slow down position and final stop
position of the billets (20).
Figure 3 shows cooling arrangement, which comprises a sensor
protection box (31) and sensor (21). Pressure gauge (32), valve
(33) and filter (34) are connected in a single line along the
air inlet line (Ain) to the sensor protection box (31). This
arrangement also comprises MS sheet (35) and asbestos sheet (36)
located between the sensor protection box (31) and billets (20).
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WE CLAIM
1. A system for detection of leading edge of moving hot
billets thereafter controlling movement of said hot billets
in a continuous casting mill, said system comprising:
means for sensing temperature of said billets when the
temperature crosses a predetermined temperature threshold,
wherein distance of sensing means from hot billets being
such that temperatures of adjacent billets do not have
effect on said temperature threshold,
said means being operatively connected to interfacing means
so as to generate output signals corresponding to the
temperature sensed by the sensing means; and
means for receiving said output signals from the
interfacing means so as to control movement of the billets.
2. System as claimed in claim 1 wherein means for sensing
temperature comprises infrared temperature switch.
3. System as claimed in claim 1 wherein the interfacing means
comprises relay unit.
4. System as claimed in claim 3 wherein the relay unit
comprises normally open and normally close contacts being
integrated to a power supply in a manner that instantaneous
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signals are received from the infra red temperature switch
on detection of billets.
5. System as claimed in claim 1 wherein means for receiving
output signal from interfacing means comprises a PLC.
6. System as claimed in claim 5 wherein the PLC is further
adapted to operate cooling arrangement.
7. System as claimed in any of the preceding claims wherein
the infrared temperature switch is adapted to sense
temperature of 550°C and above.
8. System as claimed in claim 7 wherein the infrared
temperature switch is adapted to sense temperature
preferably between 550°C to 1100°C.
9. A system for detection of leading edge of moving hot
billets thereafter controlling movement of said hot billets
in a continuous casting mill as herein described and
illustrated with reference to the accompanying figures.
Dated this the 30th day of January 2008

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The present invention relates to a system for detection of leading edge of moving hot billets (20) thereafter controlling movement of said hot billets in a continuous casting mill. The system comprises means for sensing temperature of the billets when the temperature crosses a
predetermined temperature threshold. Sensing means (21) are operatively connected to interfacing means generating output signals corresponding to the temperature sensed by
the sensing means (21). The system comprises Means for receiving said output signals from the interfacing means so as to control movement of the billets (20).