FIELD OF THE INVENTION
The present invention relates to a pilot based directional control valve in tandem
mill. More particularly, the present invention is directed to providing modified pilot
system with separate fixture cooperating with 3 position, 4 way directional control
valve, double solenoid operated and spring centered along-with sub plate fitted
with seals and mounting bolts, for cold rolling mill hydraulic actuators actuated by
directional control valves. The modified pilot system for direction control valves for
actuators in cold rolling mill favoured achieving cost saving, productivity
enhancement, reduced downtime of plant, quality improvement, environment
friendliness and energy saving in operation.
BACKGROUND OF THE INVENTION
In the new millennium steel product manufacturers aim to become the preferred
choice of customers by supplying quality product and adhering to delivery schedules
along with high production level. Increasingly stringent requirements for shape and
thickness of strip can only be met through fine-tuning of electro-mechanical and
electro hydraulic systems.
Hydraulic valve stand actuate the cylinders. In Tandem cold Mill-1 hydraulic valve
stand of Russian make was commissioned in 1976.The pilots of the Directional
Control Valves have developed snag (internal leakages). The pilots are mounted
integrally with the Directional control Valves.
Applicants Steel Plant is a major plant engaged in producing flat products from the
range of 0.2mm to 16mm and is poised to augment its production from 4.0 Million
MT to 7.0 Million MT without capacity addition.
The Tandem Cold Mill no. 1 of Cold Rolling Mill receives the material from HOT STRIP
MILL after undergoing pickling operation to remove scales in Pickling Line-
l.Thickness of the strip is reduced in Tandem Mill no. 1. The Mill is 4 high 4 stands.
(It has 4 stands and each stand has 2 work rolls and 2 back up rolls). Force is
applied from the top on the rolls by setting the screw down mechanism. Inter stand
tension is also provided. With the help of load and strip tension thickness is reduced.

Cooling is through lubrication & emulsion system for the rolls emulsion (mixture of
dispersible oil & water) applied to the roll bite. Sheet is fed to the first stand by
changing direction of sheet through Deflector Roll. Apart from inter stand tension,
back tension exist between Uncoiler & stand no.1 and between stand no. 4 & Coiler.
Hydraulic actuators(cylinders) are used for the purpose of moving different machine
part. The hydraulic actuators are actuated by Russian make valve stands. There was
frequent malfunction problem of hydraulic valves. The Pilots of valves have
developed internal leakages. Pilots are mounted at the end of Directional Control
Valves.
In Russian units of cold rolling mill, hydraulic actuators are actuated by Russian
directional control valves which suffer from the following disadvantages and
limitations:
(1) Pilot not getting operated by solenoid force. We need to put load on solenoid
to support the solenoid prime moving force.
(2) Drives sometimes getting actuated by itself.
(3) Drive not actuated at all.
(4) Flow requirement from power unit was more causing mill to stop.
After detailed interactions and analysis it was found that pilot operating the main
directional control valves developed internal clearances and hence in case of:
Problem #1 : P was partially getting connected to T creating back pressure and
needing more force to operate pilot.
Problem #2 : P was partially getting connected to A giving pilot pressure to main
valve spool.
Problem # 3 : P and T line was completely through resulting zero pressure in a line
whenever required.

Problem #4 : was the result of all three problems. The requirement of fluids became
more due to internal by passing of the fluids resulting in hydraulic power pack
bottom level operating frequently and load on pumps.
There has been therefore a need in the existing directional control valve operation
for actuators in tandem mills in cold rolling mill to providing a modified and improved
pilot system to work in cooperation with the said directional control valve whereby
the above stated problems and limitations can be eliminated/avoided in a cost
effective manner, the pilot system would be capable of effectively operate the
direction control valves for timely actuation of actuators free of any internal
clearance causing failure of functioning or excess use of hydraulic fluid
consumption/waste etc.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to providing a modified and
improved pilot based directional control valves for effective operation of actuators in
tandem mill of the cold rolling mill in a reliable and cost effective manner.
A further object of the present invention is directed to providing a modified and
improved pilot based directional control valves for actuators in tandem mill of the
cold rolling mill adapted to ensure desired roll force and inter stand tension/back
tension for required accuracy of dimension of cold rolled products.
A still further object of the present invention directed to providing a modified and
improved pilot system for directional control valves for actuators in tandem mill of
the cold rolling mill which would avoid internal leakages of pilot and excess oil
consumption or waste.
A still further object of the present invention directed to providing a modified and
improved pilot system for directional control valves for actuators in tandem mill of
the cold rolling mill which would ensure reduction/elimination of off gauge coil
generation due to hydraulic tripping.

A still further object of the present invention directed to providing a modified and
improved pilot system for directional control valves for actuators in tandem mill of
the cold rolling mill to ensure enhanced productivity and cut down loss due to
downtime due to malfunctioning of the valves.
A still further object of the present invention directed to providing a modified and
improved pilot system for directional control valves for actuators in tandem mill of
the cold rolling mill to avoid oil loss from the system and reduced requirement of
running of pump on load and drive motor for pump, thus making the system
environment friendly and energy efficient.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a Pilot based directional
control valve for hydraulic actuators in tandem cold rolling mill, comprising
3 position, 4 way directional control valve, double solenoid operated with centre
poison A & B to T and P block, spring centered along-with sub plate;
both the ports of pilot provided as pilot line to the directional control valve;
end covers attached to said directional control valves adapted to house spring for
centering the spool and giving connection to the pilot line;
power supply.
A further aspect of the present invention is directed to a Pilot based directional
control valve for hydraulic actuators comprising end covers fixed after housing
spring and providing proper 'O' ring and operative connection to pilot lines.
A still further aspect of the present invention is directed to a Pilot based directional
control valve for hydraulic actuators wherein said power supply source comprising an
electrical circuit adapted to supply 24 volt needed for operation of solenoid of the
pilot.

The various features and advantages of the present invention is described in greater
details. with reference to the following accompanying non limiting illustrative
drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1(a): is the schematic view of the conventional system of directional control
valve showing 3 position, 4 way directional control valve PILOT operated with centre
poison A & B , T and P block, spring centered.
Figure 1(b): is the schematic view of the pilot 'A' according to the conventional
system of directional control valve showing 2 position,3 way directional control valve
with single solenoid operation.
Figure 2: is the photographic image of the complete unit of conventional directional
control valve with integrated pilot.
Figure 3: is the schematic view of the Pilot according to the present invention to be
used with existing direction control valves as new pilot for assembly on separate
fixture.
Figure 4: is the photographic image of the end cover of the directional control valves
for mounting of modified pilot according to the present invention.
Figure 5: is the photographic image of the complete unit of directional control valve
fitted with pilot system according to the present invention showing end covers fixed
after housing spring and giving proper 'O' ring and Pilot lines connected.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS.
The present invention relates to a modified and improved pilot based directional
control valves for actuators in tandem mill of the cold rolling mill. It is known that
pilot system is used in combination with directional control valves for desired
operation of hydraulic actuators in rolling mill stand for developing required roll gap,

roll force and interstand tension required for dimensional accuracy of the cold rolled
product.
Accompanying Figure 1(a) shows the schematic view of the conventional system of
directional control valve showing 3 position, 4 way directional control valve PILOT
operated with centre poison A & B , T and P block, spring centered and Figure 1(b)
shows schematic view of the pilot 'A' according to the conventional system of
directional control valve showing 2 position,3 way directional control valve with
single solenoid operation.
Accompanying Figure 2 is the photographic image of the complete unit of
conventional directional control valve with integrated pilot. It may be noted that in
the above conventional pilot system for directional control valves, there was frequent
malfunction problem of hydraulic valves. Pilots are mounted at the end of Directional
Control Valves. The pilots are mounted integrally with the Directional control Valves.
Although the main directional control valves were in good order, the Pilots of valves
have developed internal leakages and could not be repaired or replaced. Spares were
also not available. This resulted in a number problems like:
(1) Pilot not getting operated by solenoid force and needs additional load to be to
put on solenoid to support the solenoid prime moving force.
(2) Drives sometimes getting actuated by itself.
(3) Drive not actuated at all.
(4) Flow requirement from power unit was more causing mill to stop.
The present invention thus provides for a modified, efficient and cost effective pilot
system for directional control valves which avoids the limitations of the conventional
Russian make directional control valve with integrated pilot system and ensure
reliable operation of directional valves as well as the hydraulic actuators for tandem
cold rolling mill favouring higher plant availability, improved product quality, less oil
loss/less power consumption.

Accompanying Figure 3 shows the schematic view of the Pilot according to the
present invention to be used with existing directional control valves as new pilot
mounted with fabricated end plate assembled on separate fixture. Main directional
control valve was behaving normal. Thus only pilots needed to be changed. 3
position, 4 way directional control valve double solenoid operated with centre poison
A & B to T and P block, spring centered along-with sub plate fitted with seals and
mounting bolts.
From the drawing of the existing pilot end cover of the directional control valves has
been designed. Accompanying Figure 4 shows the photographic image of the end
cover/sub plate of the directional control valves for mounting of modified pilot
according to the present invention.
Accompanying Figure 5 shows the photographic image of the complete unit of
directional control valve fitted with pilot system according to the present invention
showing end covers fixed after housing spring and giving proper 'O' ring and Pilot
lines connected. New pilot which was available indigenously (Rexroth make along
with sub plate) was fixed on separate fixture. It was connected to pressure and drain
line of the existing use. Both the ports of pilot were utilized as pilot line to the
directional control valve. The end cover as designed was made from the plate in
house. It served two purposes (i) to house spring for centering the spool and (ii)
giving connection to the pilot line. End covers are fixed after housing spring and
giving proper 'O' ring. Pilot lines were then connected. In the new pilot system, the
pilot is made to operate with 24 volts instead of the original/ conventional pilot
being operated on 48 volts. The new pilots needed 24 volts .Necessary change was
done in electrical circuit.
The above described modified pilot valve with existing directional control valves were
tested and commissioned in a number of drives in tandem mill which ensured reliable
performance and satisfactory result improving plant productivity and enhanced
product quality with reduced downtime.
It is thus possible by way of the present invention to providing a pilot system for
directional control valve for actuators in tandem mill in cold rolling mills adapted to
ensure the following advantages:

1. Substantial cost saving by changing only pilot in each hydraulic panel to make
the directional control valves work satisfactorily.
2. Reduction in generation of off gauge coils leads to increased revenue earning.
3. Enhanced productivity and reduce downtime of cold rolling plant.
4. Reduced oil loss from pilots due to internal leakages.
5. Reduced oil pump load and motor running on load, saving energy costs.

We Claim:
1. A Pilot based directional control valve for hydraulic actuators in tandem cold
rolling mill, comprising
3 position, 4 way directional control valve, double solenoid operated with centre
poison A & B to T and P block, spring centered along-with sub plate;
both the ports of pilot provided as pilot line to the directional control valve;
end covers attached to said directional control valves adapted to house spring for
centering the spool and giving connection to the pilot line; and
power supply.
2. A Pilot based directional control valve for hydraulic actuators as claimed in claim 1
comprising end covers fixed after housing spring and providing proper 'O' ring and
operative connection to pilot lines.
3. A Pilot based directional control valve for hydraulic actuators as claimed in anyone
of claims 1 or 2 wherein said power supply source comprising an electrical circuit
adapted to supply 24 volt needed for operation of solenoid of the pilot.

ABSTRACT

The present invention relates to a pilot based directional control valve in tandem
mill. More particularly, the present invention is directed to providing modified pilot
system with separate fixture cooperating with 3 position, 4 way directional control
valve, double solenoid operated and spring centered along-with sub plate fitted
with seals and mounting bolts, for cold rolling mill hydraulic actuators actuated by
directional control valves. The modified pilot system for direction control valves for
actuators in cold rolling mill favoured achieving desired product quality, productivity
in cold rolling operation in cost effective and energy efficient manner.