A PHOTOSENSOR BASED LENGTH MEASURING SYSTEM FOR CUTTING A
CONTINUOUSLY CAST BLOOM AND THE METHOD THEREOF
Description
FIELD OF THE INVENTION
The present invention relates to a very low cost photo-sensor based bloom length
measuring system for cutting the bloom accurately into pieces of desired length at the
continuous casting unit, with a view to minimizing the generation of scrap in the
finishing mill of the steel plant (for example, the Rail Mill). Also, the present invention
relates to a new concept that involves sensing hot as well as cold blooms using
multiple sensors for measurement of length with minimum error and give a reliable
and consistent performance over a long period of time.
BACKGROUND OF THE INVENTION
Continuous casting is a known process for producing steel blooms, slabs and billets.
The molten steel is cast into blooms by pouring the molten steel through a mould and
cooling the steel as the steel exits from the mold to form a continuous solid strand.
The steel strand travels vertically beneath the mold and bends along an accurate
path defined by guide rollers, and finally it is straightened. As the bloom moves
horizontally, it is cut into pieces of desired length by means of a gas cutting torch.
KOBE STEEL LTD in a Japanese Patent specification JP2001096348 discloses a
strand cutting process for obtaining bloom which reducing the production amount of
cut off loss, and moreover, collecting a single quality of billets uniformized to the
upper limit value of a cut-off planning. In the collection of a plurality of blooms by
cutting strands which are cast with a continuous casting facility, there the planned
length (a) of an overall bloom, is compared with a qualitative length L of strand using

the compound command information where a billet cut-off command information,
which is used in the next booming process, to a bloom cut-off command information,
and the remainder of molten metal or a lack amount of molten metal is found. By
adding or reducing the number of billets of one bloom depending on the remainder of
molten metal or the lack amount of molten metal, the amount of molten metal is
adjusted to become less than one bloom, which are distributed equally into each
uncut bloom in the upper limit value limit of bloom.
REPUBLIC ENGINEERED STEELS INC (US) and others in a PCT patent
specification WO9806052 discloses a continuous steel caster to cut length
optimization to minimize the amount of scrap steel in cutting a steel strand into
blooms with a traveling torch cut-off station. The steel strand is cut to produce at least
one bloom having a determined cut length. The length for a next-to-last bloom is
determined such that it is within a predetermined range of cut lengths and such that
the bloom may be cut into a number of billets each within a predetermined range of
lengths. The length for a last bloom is also determined such that it is within a
predetermined range of cut lengths and such that the bloom may be cut into a
number of billets each having a length within a range of lengths.
NIPPON STEEL CORP; TAIHEI KOGYO KK; DAIHO GIKEN in a Japanese Patent
specification JP59019071 discloses the gas cutting of billets or like with fully
automated and unmanned operation and to improve the efficiency of cutting, by
providing a moving device for the billet, etc. in the position where a welding machine
for welding small billets and an automatic gas cutter are provided.
IPU LTD (BS) in an US specification US4202707 discloses a method and apparatus
for flame cutting steel slabs or the like in strip casting apparatus employs a flame
cutting machine which moves at the strip casting speed during the flame cutting. A
control device so adapts the flame cutting speed to the casting speed automatically,
taking into account any temporary delay in the cutting operation, that until the

termination of the flame cutting a definite predetermined distance of accompaniment
is maintained.
Drawbacks of other measuring systems:
(I) Contact type: Prior to the present invention, a contact type metallic chain / rod
charged with 48 volts electric supply hanged at a specific distance w.r.t. the rest initial
position of the gas cutting torch. On arrival of the bloom, the hanging metallic rod
made contact and a relay coil got energized and subsequently actuated the gripper,
and cutting started across the bloom.
Drawbacks:
i. Very frequently metallic rod used to get damaged, especially at the starting of the
casting due to the bend in the bloom.
ii. Metallic rod was also getting damaged if the gap between two successive blooms
was less than 100 mm.
iii. Due to the scale layer / carbon particles over the bloom, many a times it was
observed that there was discontinuity in the electrical circuit.
iv. At least 0.5 m gap is needed to distinguish between two successive blooms, but
such a wide gap is not available.
(II a) Drawback of Laser based measuring system (Flight time based)
- A minor tilting of reflecting plane of vibrating bloom during rolling on roller table.
- Dust on lens causes system failure.
- Needs continuous adjustment.
- Object should be visible from laser source but there is hardly any gap between two
successive blooms.
- It needs at least 0.5 m gap between two successive blooms.

(II b) Drawback of Laser based measuring system (Doppler Shift based)

At the cast bloom moves at a low speed, desired variation in the width of fringes
(dark and bright bands) does not take place. Secondly, the bloom does not have a
reflective surface.
(III) Drawback of Shaft Encoders
It needs continuous calibration because of the decay in the diameter of idle roll in
which shaft encoder is coupled.
- Slippage in between rolls and bloom.
- Loose coupling generates higher order harmonics
- Needs high temperature sustained Greece for bearing.
- Failure of coupling
- Needs continuous cooling
(IV) Drawback of CCD camera: It needs a clear view of the object but due to the
presence of other equipments in the vicinity an obstruction is created. Therefore , a
complete view of the object is not possible with a CCD camera. The CCD camera is
not a suitable measuring device to measure the dimensions of bloom at CCS
because of wide degree of fluctuation in the surface temperature of bloom.
The disadvantages of the prior art are overcome by the present invention. Therefore,
it is an object of the present invention to provide photo-sensor based bloom length
measuring system, which can accurately measure the bloom length at continuous
casting unit for minimizing the generation of scrap in the Rail Mill of the steel plant.
Further objects of the invention may become apparent from the following description,
given by example.

SUMMARY OF THE PRESENT INVENTION
Various embodiments of the present invention can significantly improve upon
existing systems and methods. In some exemplary embodiments of the present
invention, one or more of the above mentioned / or other problems with existing
systems can be overcome.
In the continuous caster of Bhilai Steel Plant (India), molten steel is cast into a
rectangular shape object (called bloom; dimension 300 mm x 340 mm cross section)
at a height of 15 meters, in four narrowly spaced bloom strands. After passing
through accelerated water spray cooling system, the molten steel gets solidified and
the stream of bloom is gradually dragged and rolled down to the ground level, where
it is cut one after other into small pieces (say 5.6m long for 52 kg/mm2 tensile
strength and other orders viz. 4.4 m etc) by means of flame of gas cutting torch
which is installed on a trolley. During cutting, the velocity of gas cutting torch is
synchronized with bloom velocity by means of gripper mechanism, which grips the
bloom and forces trolley to move. After cutting the bloom, the gripper mechanism is
released from the bloom and the gas cutting trolley returns to its initial position and is
ready to grip and cut the incoming stream of bloom. These small pieces of bloom (5.5
m to 5.6 m) are sent to rail mail to rolling into 84m long rail.
Therefore, according to the present invention, there is provided a photosensor based
system for measuring and cutting of bloom in continuous casting in steel plants
comprises of a lighting unit preferably a bulb (halogen);_a sensor stack; a LED based
bloom length display unit; a gas cutting trolley position-sensing unit; a control circuit
to actuate gripper mechanism wherein during the cutting operation the velocity of gas
cutting torch is synchronized with bloom velocity by means of gripper mechanism,
which grips the bloom and forces trolley to move and after cutting the bloom, the
gripper mechanism gets released from the bloom and the gas cutting trolley returns
to the initial position.

Moreover, according to the present invention, there is provided a method for
measuring and cutting of bloom in continuous casting in steel plants comprising the
steps of sensing the advancement in the bloom position using the sensor stack;
displaying the bloom position in LED based bloom length display unit; sensing of
the trolley position for any dislocation from "zero reference" position and
subsequently cutting of the bloom wherein during the cutting operation the velocity of
gas cutting torch is synchronized with bloom velocity by means of gripper
mechanism, which grips the bloom and forces trolley to move and after cutting the
bloom, the gripper mechanism gets released from the bloom and the gas cutting
trolley returns to the initial position..

Therefore the principle object of the present invention is to provide for a measuring
apparatus and control system for cutting a continuously cast bloom at desired length
as it moves horizontally after leaving the guide rollers, at the completion of
solidification process.
Another object of the present invention is to minimize the generation of rail-scrap
material by cutting a strand of bloom accurately to get pieces of desired length and
make the cutting operation highly reliable.
Yet another object of the present invention is to provide a system as well as the
device that is contact less and is maintenance free and gives consistency in the
accuracy in bloom length measurement over a large period of time.
According to other embodiments, a system is configured to detect / distinguish the
two successive blooms with a gap of 5mm (1st bloom which is already cut and is
resting on rollers and another which is to be cut)
In accordance with one embodiment of the present invention, the system is able to
select bloom length by means of selector switches.
In accordance with another embodiment of the present invention, the system is able
to counteract the bloom length error due to bouncing of trolley by displaying its initial
position (reference zero position)
In accordance with still another embodiment of the present invention, the Sensor unit
does not get damaged since it is away from the bloom line.

In accordance with another exemplary embodiment of the present invention, the
yield is increased by measuring and controlling the product length accurately wherein
no calibration is required.
Besides improving the yield, the system has uplifted the working condition by
relieving the workers from excessive heat, dust and also from accident from fatigue
operations involved in different process since the operators need not go in the vicinity
of the hot bloom.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
a) Fig 1 is a schematic illustration of the location of the light sources and the
sensors for the cutting bloom at desired length.
b) Fig 2 is the schematic illustration of radiation of different light sources and the
sensitivity of Ge / Si photosensor.
c) Fig 3 is the schematic illustration of the length of the sensor stack.
d) Fig 4 is the more detailed view of the electronic circuit for the photosensor
processing.
e) Fig 5 is the schematic illustration of the dimensions of the display unit.
DETAILED DESCRIPTION
As per one of the objects of the present invention, the method for sensing the bloom
measurement is disclosed hereinafter. For minimizing the generation of Rail-scrap
due to inaccurate bloom size, a very low cost photo-sensor based bloom length
measuring system has been designed, developed and tried in two of the four strands.
Factors such as irregular coating of casting powder, formation of scale layers over
bloom surface and fluctuation in casting speed say (0 mm to 30 mm per second)
cause a wide variation in the bloom temperature and it is not possible to sense it by
any photo sensor reliably. A bloom whose surface temperature varies ranging from

450° C to ,1100°C is sensed by method of light interruption (as shown in Fig 1). For
this purpose a reference uninterrupted high intensity light source of halogen (wave
length 6000 A°- 6800 A0) is focused over luminous hot-bloom (wave length < 5000
A°) while shadow of luminous hot bloom is sensed by silicon phototransistors. The
luminosity of halogen light and response of Silicon and Germanium phototransistors
have been shown in Fig-2. Error due to diffraction (of the order of micrometer) does
not put a kind of impact on accuracy in measurement (of the order of mm).
The measurement range of the bloom depends upon the factors such as the variation
in the initial position of trolley (gas cutting torch) due to bouncing wherein the
required least count in measurement and measuring range decide the quantity of
sensors.
t
It has been observed that the problem in the use of such system is of sensing the
bloom at desired length with respect to gas cutting torch ("zero reference" point of the
measuring scale). Due to bouncing, initial position of the trolley deviates and
generates error in the bloom length
The present system can accurately measure and subsequently cut the bloom into
pieces of desired size in continuous casting unit for minimizing the generation of Rail-
scrap in the Rail mill of the steel plant. Blooms are cut one after other into small
pieces by means of gas cutting torch, which is installed in a trolley. During cutting the
velocity of gas cutting torch is synchronized with bloom velocity by means of gripper
mechanism, which grips the bloom and forces trolley to move. After cutting the
bloom, the gripper mechanism gets released from the bloom and the gas cutting
trolley returns to the initial position and is ready to grip arid cut incoming stream of
blooms.

The system consists of the following units.
a) lighting unit preferably a bulb (halogen)
b) sensor stack
c) LED based bloom length display unit.
d) gas cutting trolley position sensing unit.
(b) Sensor stack: The sensor-stack is installed in such a way so that its mid point
coincides with the centre point of the range (variation in the bloom length) w.r.t. gas-
cutting torch. A bulb (halogen) whose luminosity is higher than luminosity of hot
bloom is put to one side of bloom while a sensor stack consisting of 23 numbers of
phototransistors has been put on other side of the bloom. The internal surface of the
tube is coated with black unm'ated (rough / not shining paint) in order to reduce the
internal reflection of light. The bulb should be focused on the photo sensors. The bulb
is put in a concave reflecting mirror in order to strengthening the light beam.
The phototransistors are put in tubes (Fig-3) and their photoelectric current is sent
through 0.2 sq mm heat resistant cable to electronic processing unit in which weak
signal of photosensors are further amplified. Comparator circuit clips the photo
voltage, which is due to surrounding light (Fig-4). The output current of comparator
I.C. LM324 operational amplifier illuminates the LEDs (light emitting diodes). On
arrival of bloom before respective photosensor channel (tube), its shadow is
displayed by means of glowing the LED's, which are installed before operator in
pulpit. Photosensor type is 14 LF 32 Silicon phototransistors configured in darlington
pair with inbuilt convex lens.
(c) LED based bloom length display unit: Array of light emitting diodes (LED) is
used to indicate the bloom length and put before operator (Fig-5). There are 23 nos
LED (alternate colours Green/red) have been put in the display unit. Below each
LED the measured bloom length is written say 4.4 m, 5.450 m, -- 5.7 m. Each LED is
incorporated with length selecting switch for selecting the desired bloom length for
cutting.

(6) Gas Cutting trolley Position sensing: For sensing the deviation of trolley from
its initial position, a sensor stack consists of 10 photo sensors which are kept at a
interval of 12.5 mm from one side of the shadow provider (a metallic strip is projected
from the trolley) while a bunch of LED are used as alight source is kept on other side.
If any deviation of trolley from its initial position is observed from the glowing of LED's
of display unit immediately operator takes corrective action by selecting the
corresponding selection switch (Fig-5).
The herein described system works satisfactorily even if a minute gap of the order of
5 mm exists between two blooms. The sensor does not get damaged since it is
placed away from the bloom. The multiple photosensors are provided to select any
bloom length by means of selector switches. Moreover the error due to bouncing of
trolley is displayed before the operator thereby he can take immediate action for
selecting the bloom length for compensating the error due to initial reference position.
The system has uplifted the working condition by relieving the workers from
excessive heat, dust and accident, fatigue operations involved in different process
since the operators need not go in the vicinity of the hot bloom. Variation in bloom
length and trolley position (gas cutting torch) position decides the measuring range
and number of sensors to be used, for setting the desired least count in
measurement.
In this invention system and method for measuring and cutting of bloom in continuous
casting in steel plants has been evolved. Tracking the bloom at hot saw of rail mill
has given following advantages:-
- Bloom length has been measured to the accuracy of 0 to +25 mm in the range of
4.5 m to 5.8 m, and the range can be changed.
- Average bloom length reduced from 5.660 to 5.525m
- One Extra bloom getting produced per strand from same metal in every Shift
- Monetary benefit: 83 Lakhs per strand. Thereby 1.66 crore in two strands.

The above-described embodiments of the invention are intended to be examples of the
present invention. Numerous modifications changes and improvements within the scope
of the invention will occur to the reader. Those of skill in the art may effect alterations
and modifications thereto, without departing from the scope of the invention, which is
defined solely by the claims appended hereto.

We Claim:-
1. A photosensor based system for measuring and cutting of bloom in continuous
casting in steel plants comprises of:
- a lighting unit preferably a bulb (halogen);
- a sensor stack;
- a LED based bloom length display unit;
- a gas cutting trolley position-sensing unit;
- a control circuit to actuate gripper mechanism wherein during the cutting
operation the velocity of gas cutting torch is synchronized with bloom velocity by
means of gripper mechanism, which grips the bloom and forces trolley to move and
after cutting the bloom, the gripper mechanism gets released from the bloom and the
gas cutting trolley returns to the initial position.

2. The system as claimed in claim 1, wherein the luminosity of the halogen bulb is
greater as compared to hot bloom.
3. The system as claimed in claim 1, wherein sensor stack comprises of
phototransistors encased in small tubes.
4. The system as claimed in claim 1, wherein the sensor stack comprises of
phototransistors depending on the accuracy of the measurement desired.
5. The system as claimed in claim 1, wherein the sensor stack comprises of an
amplifier circuitry, which amplifies the weak signals of phototransistors.
6. The system as claimed in claim 1, wherein the sensor stack includes a
comparator circuit, which eliminates the photo voltage due to background light.
7. The system as claimed in claim 4, wherein the phototransistors are configured in
darlington pair with inbuilt convex lens.

8. The system as claimed in claim 1, wherein the LED based bloorrnength display
unit comprises of a plurality of LED's.
9. The system as claimed in claim 8, wherein each LED is incorporated with a
length-selecting switch for selecting the desired bloom length for cutting.
10. The system as claimed in claim 1, wherein the Gas cutting trolley position
sensing unit comprises of a sensor stack consisting of plurality of sensors, which are
positioned at an appropriate interval (such as 12.5 mm) from one side.
11. The system as claimed in claim 10, wherein the sensor stack comprises a bunch
of LED's used as a light source to illuminate the photosensors and a shadow
provider over one of the photosensor in the said stack.
12. A method for measuring and cutting of bloom in continuous casting in steel plants
comprising the steps of: -

- sensing the advancement in the bloom position using the sensor stack;
- displaying the bloom position in LED based bloom length display unit;
- sensing of the trolley position for any dislocation from "zero reference" position
and subsequently cutting of the bloom wherein during the cutting operation the
velocity of gas cutting torch is synchronized with bloom velocity by means of gripper
mechanism, which grips the bloom and forces trolley to move and after cutting the
bloom, the gripper mechanism gets released from the bloom and the gas cutting
trolley returns to the initial position.

A PHOTOSENSOR BASED LENGTH MEASURING SYSTEM FOR CUTTING A
CONTINUOUSLY CAST BLOOM AND THE METHOD THEREOF

ABSTRACT

The present invention relates to a photosensor based system for measuring and
cutting of bloom in continuous casting in steel plants comprises of a lighting unit
preferably a bulb (halogen);_a sensor stack; a LED based bloom length display unit; a
gas cutting trolley position-sensing unit; a control circuit to actuate gripper
mechanism wherein during the cutting operation the velocity of gas cutting torch is
synchronized with bloom velocity by means of gripper mechanism, which grips the
bloom and forces trolley to move and after cutting the bloom, the gripper mechanism
gets released from the bloom and the gas cutting trolley returns to the initial position,
and a method thereof.