FIELD OF INVENTION
The present invention relates to industrial hydraulics. More particularly, the
present invention discloses hydraulic control circuit for electrode regulating
mechanism to arrest the upward drift of the hydraulic cylinders responsible for the
movement of the graphite electrodes in Ladle Heating Furnace (LHF).
BACKGROUND ART
The Continuous Casting Machine (CCM), houses Ladle Heating Furnace (LHF),
Argon Rinsing System (ARS), Caster Proper, Torch Cutting Machine (TCM) and
Slab Storage and Dispatch Yard.
Basically, a ladle heating furnace (LHF) is an electric arc furnace wherein the
furnace shell is replaced with the ladle and the ladle here in CCM-I is transferred
underneath the gantry by means of transfer car for refining process. LHF is used
for homogenizing and final adjustment of temperature and chemical analysis of
steel tapped from Converter before being sent to Casters for casting. LHF consist
of:
- Ladle Car
- Electrode arcing and heating mechanism
- Water cooled roof with dust collector system
- Alloying system
- Wire feeding machine.
The electrode masts with their electrode arms and the electrodes themselves,
required for reheating the liquid steel through electric power conduction, are
adjusted by means of the regulating (positioning) cylinders. As the cylinders have
plunger type design, hydraulic fluid is admitted at one end of it for upward
movement only, while the downward travel is actuated by its own weight driving
out the fluid from it.
3
The Ladle Heating Furnace of CCM, Rourkela Steel Plant was upgraded under
the CoE projects w.r.t to electrode regulation hydraulics. The old hydraulic
proportional direction control valves (Model Code: 4WRE 10 E-64-1X/24K4/M,
Make: Rexroth) were replaced by the state of the art valves with on board
electronics (Model code: 4WREE 10 V 75-2X/G24 K31/A1V, Make: Rexroth).
These valves ensured better regulation due to lesser valve overlap, but induced
creep in the regulating cylinders due to 3 % opening of the ports in the neutral
position. This created difficulty in positioning of the electrodes during non-arcing
periods, as the cylinders would creep to the topmost positions even in the valves
“OFF” state.
SUMMARY OF THE INVENTION
The basic objective of the invention is to ensure 100% stoppage and positioning
of electrode regulating cylinders at the neutral position of the proportional valves
either for maintenance activities, for cooling of the electrodes or for parking of the
same.
A further objective is to eliminate any safety hazard and equipment risk during
LHF electrodes’ contact clamp replacement as any upward creep in the
regulating cylinders at the time of dismantling/assembly of the contact clamps
can result in a serious mishap. With this invention, there is an appreciable
reduction in the replacement time of the contact clamps as repositioning of the
regulating cylinders required whenever the cylinders drift to the top most
positions, is eliminated, completely.
The invention involves fail safe load blocking and creep control of hydraulic
cylinders. Specifically, the entire hydraulic system has been used in the LHF
electrode regulating mechanism to arrest the upward drift of the 3 nos. hydraulic
cylinders responsible for the movement of the graphite electrodes. Such systems
can be used in other hydraulic applications, where drifting or creeping of
hydraulic cylinders need to be controlled.
Therefore such as herein described there is provided a hydraulic control circuit
for eliminating of upward creep in ladle heating furnace electrode regulating
hydraulic cylinders in arcing / non-arcing periods comprising of : at least one pilot
operated check valve and one solenoid operated DC valve connected in series
with existing check valve with pipe connections, fittings, sub-plates and hoses;
wherein the connected pilot valve opens in the normal direction, but closed in the
4
opposite direction without a pilot pressure and the solenoid valves open in the
reverse direction under the effect of a pilot pressure which allows the flow of
water / oil when the solenoid actuated DC valve is operated; and wherein the
furnace PLC logic for electrode lifting / lowering is modified to control the pilot
operated check valves.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig. 1 illustrates hydraulic circuit of the modified creep control system in
accordance with the present invention;
Fig. 2 illustrates Comparative study of the old and the new proportional valve in
use for LHF hydraulics for electrode regulating cylinders in accordance with the
present invention;
Fig. 3 illustrates the original hydraulic circuit diagram of the LHF system with the
connection points of the innovative creep control circuit, indicated by letter
bubbles;
Fig. 4 illustrates the applied modification in the LHF hydraulics for electrode
regulating cylinders in accordance with the present invention.
DETAILED DESCRIPTION
A unique, novel cost effective innovation is here disclosed to achieve accurate
positioning of electrode regulating cylinders during non-operational periods.
The mentioned development has been achieved after due close study of the
associated hydraulic and electrical systems’ circuitry and taking into
consideration the space constraint for installing such a complicated unit without
impinging on the existing electro-hydraulic system of the LHF. The various subunit
components are herein tabulated and explained:
TABLE 1
Sl.
No.
Component Description Position
(In Fig1)
Source
Of
Supply
No. of units
1 Direction Control
valves (spring off-set
solenoid operated)
with sub plates.
Model
code:4WE6D62/EG24N9K4
Make: REXROTH
1,2,3 External 3
2 Pilot operated check Model code:SL10PA2-4X 4,5,6 External 3
5
valves with sub
plates.
Make: REXROTH
3 Flexible HP hoses. DN 10 x 3000 mm
DN 20 x 2500 mm
7 to 12 Stock
Items
6
4 Seamless pipes
(MS)
O.D.= 10 mm,
Wall thickness = 1.5 mm
X1,X2,X3,
Y1,Y2,Y3
Internal 6
GENERAL DESCRIPTION OF DIFFERENT HYDRAULIC COMPONENTS
USED:
A direction control valve is used to steer the flow to selected direction in a
hydraulic system. It does this by changing the position of internal moving parts.
Herein, spring action automatically returns spool to normal offset position
as soon as shifter force is released (power to electrical solenoid actuator is
removed).
Pilot operated check valves are designed to permit free flow in one direction and
to block return flow, until opened by a pressure (pilot) signal. They can be used
to support vertical pistons which otherwise might drift due to leakage past the
directional valve spool.
Inter connections of the various elements in a hydraulic system is obtained
through piping/tubing and hosing. Hydraulic hoses are most convenient for
hydraulic lines where flexibility has to be accommodated.
WORKING OF THE HYDRAULIC CREEP CONTROL CIRCUIT:
In the mentioned invention, the creeping of regulating cylinders to the top-most
position during the “OFF stage” of the valves was overcome by introducing a
creep control hydraulic circuit developed in house. The circuit comprises of 3 nos
pilot operated check valves (Sl No: 2 of Table 1) and 3 nos. solenoid operated
DC valves (Sl No: 1 of Table 1), with pipe connections, fittings, sub-plates and
hoses. Each of the check valves is placed in series with the existing one, but in
the reverse flow direction. These valves are open in the normal direction, but
closed in the opposite direction without a pilot pressure. The valves open in the
reverse direction under the effect of a pilot pressure which is allowed to flow
when the solenoid actuated DC valves operate as shown in Fig 1. L, M, N, O, P,
Q are the connecting points of the modified system with the original hydraulic
6
circuitry and R is the pressure tapping point for the directional control valves
responsible for pilot pressure for operation of the check valves. (Ref. Fig.1 &
Fig.3).During non arcing periods/proportional valves in the neutral position, the
electrode regulating cylinders remain static as the flow of leakage oil is
completely shut off by the pilot operated check valves with no pilot pressure.
Creeping of the cylinders thus, has been eliminated completely. During arcing
periods, the regulation of the electrodes is not affected as the pilot operated
check valves remain open continuously with the solenoid valves energized
throughout the arcing cycle.
The mentioned development has been done in-house with minimum investment
to provide an easy to maintain/replace/repair system. It has been incorporated as
an “add-on” system thus not damaging the existing structural and circuitry of the
LHF hydraulics.
WORKING OF THE FURNACE PLC W.R.T TO ELECTRODE REGULATION :
The LHF electrode regulation at the time of arcing of the metal bath is executed
automatically with the help of programmable logic controllers interfaced with the
hydraulics of the system. The PLCs are programmed to regulate the electrodes
based on prescribed set points and voltage feedbacks of the transducers
(LVDTs) present on the new proportional valves. The low magnitude voltage
outputs generated by the LVDTs (Linear Variable Differential Transformers) are
amplified by the on board amplifier cards and fed to the PLCs, which then control
the solenoid excitation currents, varying the displacement magnitude and
direction of the proportional spools accordingly. This results in a change in
hydraulic oil flow to the electrode regulation cylinders, thereby effecting the
upward and downward displacement of the cylinders. At the time of stopping the
electrode movement, PLCs withdraw the power to the Proportional Valves,
causing the control spools of the valves to return to the neutral/centre positions,
shutting off the oil supply to the regulating cylinders.
Furnace PLC logic for electrode lifting/lowering has been modified to control the
new pilot operated check valves. Abrupt stopping of the electrode regulating
cylinders during lifting was observed after the modification, when the power to
solenoid operated DC valves was withdrawn. Subsequently, a delay of 3 seconds
has been introduced in the PLC logic (Power to solenoid operated DC valves
was withdrawn 3 seconds after lifting command was withdrawn), which resulted
in smooth stopping of the cylinders.
7
A closer analysis shows that after the due modification, LHF preparation time has
greatly reduced. Contact clamp replacement time reduced from 3 hrs to 2.5 hrs.
After the modification, specific consumption of Graphite electrodes reduced from
0.71Kg/TCS in Q2 (2015-16) to 0.63 Kg/TCS in Q3 (2015-16).Financial Savings
accrued/TCS = Rs 170*(0.71-0.63) = Rs 13.60 (Present cost of Graphite
electrode per ton = Rs1.70 lakhs).
As the leading hydraulic manufacturers incorporate such design modifications as
a proprietary item, outsourcing it to them would have incurred us Rs. 16 lakhs but
with just over Rs. 1.00 lakh spent on external procurement of the standard
proportional and check valves the mentioned innovation has been an efficient
functional cost-effective measure.
Although the foregoing description of the present invention has been shown and
described with reference to particular embodiments and applications thereof, it
has been presented for purposes of illustration and description and is not
intended to be exhaustive or to limit the invention to the particular embodiments
and applications disclosed. It will be apparent to those having ordinary skill in the
art that a number of changes, modifications, variations, or alterations to the
invention as described herein may be made, none of which depart from the spirit
or scope of the present invention. The particular embodiments and applications
were chosen and described to provide the best illustration of the principles of the
invention and its practical application to thereby enable one of ordinary skill in the
art to utilize the invention in various embodiments and with various modifications
as are suited to the particular use contemplated. All such changes, modifications,
variations, and alterations should therefore be seen as being within the scope of
the present invention as determined by the appended claims when interpreted in
accordance with the breadth to which they are fairly, legally, and equitably
entitled.

WE CLAIM:
1. A hydraulic control circuit for eliminating of upward creep in ladle heating furnace electrode regulating hydraulic cylinders in arcing/non arcing periods comprising of :
at least one pilot operated check valve and one solenoid operated DC valve connected in series with existing check valve with pipe connections, fittings, sub-plates and hoses;
wherein the connected pilot valve opens in the normal direction, but closed in the opposite direction without a pilot pressure and the solenoid valves open in the reverse direction under the effect of a pilot pressure which allows the flow of water / oil when the solenoid actuated DC valve is operated; and wherein the furnace PLC logic for electrode lifting / lowering is modified to control the pilot operated check valves.
2. A hydraulic control circuit as claimed in claim 1, wherein the circuit comprises preferably of 3 no’s pilot operated check valves and 3 no’s. solenoid operated DC valves, with pipe connections, fittings, sub-plates and hoses.
3. A hydraulic control circuit as claimed in claim 1, wherein a delay of 3 seconds is introduced in the PLC logic i.e. (Power to solenoid operated DC valves is withdrawn 3 seconds after lifting command was withdrawn).
4. A hydraulic control circuit as claimed in claim 1, wherein during non-arcing periods the said valves are kept in the neutral position, the electrode regulating cylinders remain static as the flow of leakage oil is completely shut off by the pilot operated check valves with no pilot pressure.
5. A hydraulic control circuit as claimed in claim 1, wherein during arcing periods, the regulation of the electrodes is not affected as the pilot operated check valves remain open continuously with the solenoid valves energized throughout the arcing cycle.
Dated: this 15th September, 2016.
(N. K. Gupta)
Patent Agent,
Of NICHE,
For SAIL
To,
The Controller of Patents,
The Patent Office, Kolkata.
, Description:
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(Section 10 and rule 13)

TITLE
HYDRAULIC CONTROL CIRCUIT FOR ELIMINATION OF UPWARD CREEP IN LADLE HEATING FURNACE ELECTRODE REGULATING HYDRAULLIC CYLINDERS

APPLICANT
STEEL AUTHORITY OF INDIA LIMITED,
A GOVT. OF INDIA ENTERPRISE,
ROURKELA STEEL PLANT,
ROURKELA – 769011,
ORISSA, INDIA

The following specification particularly describes the nature of the
invention and the manner in which it is to be performed

HYDRAULIC CONTROL CIRCUIT FOR ELIMINATION OF UPWARD CREEP IN LADLE HEATING FURNACE ELECTRODE REGULATING HYDRAULLIC CYLINDERS

FIELD OF INVENTION
The present invention relates to industrial hydraulics. More particularly, the present invention discloses hydraulic control circuit for electrode regulating mechanism to arrest the upward drift of the hydraulic cylinders responsible for the movement of the graphite electrodes in Ladle Heating Furnace (LHF).
BACKGROUND ART
The Continuous Casting Machine (CCM), houses Ladle Heating Furnace (LHF), Argon Rinsing System (ARS), Caster Proper, Torch Cutting Machine (TCM) and Slab Storage and Dispatch Yard.
Basically, a ladle heating furnace (LHF) is an electric arc furnace wherein the furnace shell is replaced with the ladle and the ladle here in CCM-I is transferred underneath the gantry by means of transfer car for refining process. LHF is used for homogenizing and final adjustment of temperature and chemical analysis of steel tapped from Converter before being sent to Casters for casting. LHF consist of:
- Ladle Car
- Electrode arcing and heating mechanism
- Water cooled roof with dust collector system
- Alloying system
- Wire feeding machine.
The electrode masts with their electrode arms and the electrodes themselves, required for reheating the liquid steel through electric power conduction, are adjusted by means of the regulating (positioning) cylinders. As the cylinders have plunger type design, hydraulic fluid is admitted at one end of it for upward movement only, while the downward travel is actuated by its own weight driving out the fluid from it.
The Ladle Heating Furnace of CCM, Rourkela Steel Plant was upgraded under the CoE projects w.r.t to electrode regulation hydraulics. The old hydraulic proportional direction control valves (Model Code: 4WRE 10 E-64-1X/24K4/M, Make: Rexroth) were replaced by the state of the art valves with on board electronics (Model code: 4WREE 10 V 75-2X/G24 K31/A1V, Make: Rexroth). These valves ensured better regulation due to lesser valve overlap, but induced creep in the regulating cylinders due to 3 % opening of the ports in the neutral position. This created difficulty in positioning of the electrodes during non-arcing periods, as the cylinders would creep to the topmost positions even in the valves “OFF” state.
SUMMARY OF THE INVENTION
The basic objective of the invention is to ensure 100% stoppage and positioning of electrode regulating cylinders at the neutral position of the proportional valves either for maintenance activities, for cooling of the electrodes or for parking of the same.
A further objective is to eliminate any safety hazard and equipment risk during LHF electrodes’ contact clamp replacement as any upward creep in the regulating cylinders at the time of dismantling/assembly of the contact clamps can result in a serious mishap. With this invention, there is an appreciable reduction in the replacement time of the contact clamps as repositioning of the regulating cylinders required whenever the cylinders drift to the top most positions, is eliminated, completely.
The invention involves fail safe load blocking and creep control of hydraulic cylinders. Specifically, the entire hydraulic system has been used in the LHF electrode regulating mechanism to arrest the upward drift of the 3 nos. hydraulic cylinders responsible for the movement of the graphite electrodes. Such systems can be used in other hydraulic applications, where drifting or creeping of hydraulic cylinders need to be controlled.
Therefore such as herein described there is provided a hydraulic control circuit for eliminating of upward creep in ladle heating furnace electrode regulating hydraulic cylinders in arcing / non-arcing periods comprising of : at least one pilot operated check valve and one solenoid operated DC valve connected in series with existing check valve with pipe connections, fittings, sub-plates and hoses; wherein the connected pilot valve opens in the normal direction, but closed in the opposite direction without a pilot pressure and the solenoid valves open in the reverse direction under the effect of a pilot pressure which allows the flow of water / oil when the solenoid actuated DC valve is operated; and wherein the furnace PLC logic for electrode lifting / lowering is modified to control the pilot operated check valves.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig. 1 illustrates hydraulic circuit of the modified creep control system in accordance with the present invention;
Fig. 2 illustrates Comparative study of the old and the new proportional valve in use for LHF hydraulics for electrode regulating cylinders in accordance with the present invention;
Fig. 3 illustrates the original hydraulic circuit diagram of the LHF system with the connection points of the innovative creep control circuit, indicated by letter bubbles;
Fig. 4 illustrates the applied modification in the LHF hydraulics for electrode regulating cylinders in accordance with the present invention.
DETAILED DESCRIPTION
A unique, novel cost effective innovation is here disclosed to achieve accurate positioning of electrode regulating cylinders during non-operational periods.
The mentioned development has been achieved after due close study of the associated hydraulic and electrical systems’ circuitry and taking into consideration the space constraint for installing such a complicated unit without impinging on the existing electro-hydraulic system of the LHF. The various sub-unit components are herein tabulated and explained:
TABLE 1
Sl. No. Component Description Position(In Fig1) Source Of Supply No. of units
1 Direction Control valves (spring off-set solenoid operated) with sub plates. Model code:4WE6D62/EG24N9K4
Make: REXROTH 1,2,3 External 3
2 Pilot operated check valves with sub plates. Model code:SL10PA2-4X
Make: REXROTH 4,5,6 External 3
3
Flexible HP hoses. DN 10 x 3000 mm
DN 20 x 2500 mm 7 to 12 Stock Items 6

4 Seamless pipes (MS)
O.D.= 10 mm,
Wall thickness = 1.5 mm X1,X2,X3,Y1,Y2,Y3 Internal 6

GENERAL DESCRIPTION OF DIFFERENT HYDRAULIC COMPONENTS USED:
A direction control valve is used to steer the flow to selected direction in a hydraulic system. It does this by changing the position of internal moving parts. Herein, spring action automatically returns spool to normal offset position as soon as shifter force is released (power to electrical solenoid actuator is removed).
Pilot operated check valves are designed to permit free flow in one direction and to block return flow, until opened by a pressure (pilot) signal. They can be used to support vertical pistons which otherwise might drift due to leakage past the directional valve spool.
Inter connections of the various elements in a hydraulic system is obtained through piping/tubing and hosing. Hydraulic hoses are most convenient for hydraulic lines where flexibility has to be accommodated.
WORKING OF THE HYDRAULIC CREEP CONTROL CIRCUIT:
In the mentioned invention, the creeping of regulating cylinders to the top-most position during the “OFF stage” of the valves was overcome by introducing a creep control hydraulic circuit developed in house. The circuit comprises of 3 nos pilot operated check valves (Sl No: 2 of Table 1) and 3 nos. solenoid operated DC valves (Sl No: 1 of Table 1), with pipe connections, fittings, sub-plates and hoses. Each of the check valves is placed in series with the existing one, but in the reverse flow direction. These valves are open in the normal direction, but closed in the opposite direction without a pilot pressure. The valves open in the reverse direction under the effect of a pilot pressure which is allowed to flow when the solenoid actuated DC valves operate as shown in Fig 1. L, M, N, O, P, Q are the connecting points of the modified system with the original hydraulic circuitry and R is the pressure tapping point for the directional control valves responsible for pilot pressure for operation of the check valves. (Ref. Fig.1 & Fig.3).During non arcing periods/proportional valves in the neutral position, the electrode regulating cylinders remain static as the flow of leakage oil is completely shut off by the pilot operated check valves with no pilot pressure. Creeping of the cylinders thus, has been eliminated completely. During arcing periods, the regulation of the electrodes is not affected as the pilot operated check valves remain open continuously with the solenoid valves energized throughout the arcing cycle.
The mentioned development has been done in-house with minimum investment to provide an easy to maintain/replace/repair system. It has been incorporated as an “add-on” system thus not damaging the existing structural and circuitry of the LHF hydraulics.
WORKING OF THE FURNACE PLC W.R.T TO ELECTRODE REGULATION :
The LHF electrode regulation at the time of arcing of the metal bath is executed automatically with the help of programmable logic controllers interfaced with the hydraulics of the system. The PLCs are programmed to regulate the electrodes based on prescribed set points and voltage feedbacks of the transducers (LVDTs) present on the new proportional valves. The low magnitude voltage outputs generated by the LVDTs (Linear Variable Differential Transformers) are amplified by the on board amplifier cards and fed to the PLCs, which then control the solenoid excitation currents, varying the displacement magnitude and direction of the proportional spools accordingly. This results in a change in hydraulic oil flow to the electrode regulation cylinders, thereby effecting the upward and downward displacement of the cylinders. At the time of stopping the electrode movement, PLCs withdraw the power to the Proportional Valves, causing the control spools of the valves to return to the neutral/centre positions, shutting off the oil supply to the regulating cylinders.
Furnace PLC logic for electrode lifting/lowering has been modified to control the new pilot operated check valves. Abrupt stopping of the electrode regulating cylinders during lifting was observed after the modification, when the power to solenoid operated DC valves was withdrawn. Subsequently, a delay of 3 seconds has been introduced in the PLC logic (Power to solenoid operated DC valves was withdrawn 3 seconds after lifting command was withdrawn), which resulted in smooth stopping of the cylinders.
A closer analysis shows that after the due modification, LHF preparation time has greatly reduced. Contact clamp replacement time reduced from 3 hrs to 2.5 hrs. After the modification, specific consumption of Graphite electrodes reduced from 0.71Kg/TCS in Q2 (2015-16) to 0.63 Kg/TCS in Q3 (2015-16).Financial Savings accrued/TCS = Rs 170*(0.71-0.63) = Rs 13.60 (Present cost of Graphite electrode per ton = Rs1.70 lakhs).
As the leading hydraulic manufacturers incorporate such design modifications as a proprietary item, outsourcing it to them would have incurred us Rs. 16 lakhs but with just over Rs. 1.00 lakh spent on external procurement of the standard proportional and check valves the mentioned innovation has been an efficient functional cost-effective measure.
Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.