FIELD OF THE INVENTION
The present invention relates to an oil based hydraulic system for roll balancing and
bending system in 5-stand Tandem Cold Rolling Mill(TCM) adapted to ensure desired
controlled steel strip shape of cold rolled products. More particularly, the present
invention is directed to providing an oil hydraulic system for roll bending and
balancing system involving oil hydraulic bending actuators for precise control on roll
gap contour during cold rolling defining desired strip crown and flatness avoiding
problems of leakages and/or failure of seals, valves or pumps. The oil based hydraulic
roll bending and balancing system of the invention thus facilitate operator to adjust
the gap according to the profile of input material and thermal camber of work roll so
as to correct the roll gap contour for controlling shape and flatness defects of the cold
rolled strip in a reliable manner. The system is adapted to reduce shape defects by
about 57% and delay due to roll changing by 50% and mill delay by 80% as
compared to conventional water hydraulic systems.
BACKGROUND ART
The Tandem Cold Mill(TCM-II) at applicants' Bokaro Steel Limited (BSL) was not
equipped with required gadgets for correcting the roll gap profile like Roll shifting, Roll
crossing and Differential roll cooling and thus leading to variety of symmetrical/
asymmetrical shape defects of CR strips. The mill was provided with water-based roll
bending system for the purpose of adjusting the roll gaps. Initially the work roll
bending and balancing was being operated with water hydraulics system in all the
Stands # 1,2,3,4 & 5 of TCM-II. The system was slow in response and also not
accurate and prone to maintenance due to frequent failures. This was resulting to
longer time requirement for roll changing due to low balance pressure, low
accumulator pressure, seal and valve failure in crown in system, malfunctioning of
loading valve leading to low mill availability.
From the point of view of product quality the strip profile, shape and flatness are all
important parameters. Shape of a strip is the manifest of the roll gap contour during
cold rolling and a composite parameter defining both strip crown and flatness. The
shape or flatness defects of CR strip develop due to mismatch of the profiles of the
incoming strip and the active roll gap resulting in a transverse stress distribution and
variation in elongation along the width of the strip. But, in a mill producing materials
with various grades, width and thickness, it is not possible to select a pre-determined
crown to match all the conditions.

The hydraulic systems of the mill comprised of both oil hydraulic and water hydraulic.
The oil hydraulic was used for operating entry and exit equipments of the mill, but in
the mill proper, water hydraulic was used as a medium to transmit power to the mill
roll bending and balancing systems and mill auxiliary equipments. The existing water
hydraulic system for roll bending and balancing was found to be unreliable and failure
prone to provide precise control of roll gap contour to generate desired CR strip
shape/profile.
Water hydraulics systems was applied for the following purposes :
On the basis of the operating mode, the system is categorized in two units -
(i)Balancing and Bending unit
(ii)Auxiliary drive unit
Auxiliary drives facilitate the feeding of strip to the mill and changing of rolls. The
bending cylinders are needed to create positive or the negative bending, as per
requirement, on the work rolls to counter the thermal crown developed on the roll
during rolling, to prevent the roll and the strip to go under plastic deformation as
asperities flatten under pressure and the area of the flattened asperities adjusts itself
to carry the load by plastic deformation and to create pressure on the boundary
lubrication, so that better shape can be achieved.
In the prior water-based hydraulic system, the following problems were faced which
occurred due to the failure of bending cylinders, pumps, and low pressure from the
system. The nature of failures included the following types:
(i) Failure of bending cylinders due to following three kind of failures:
a) damage of piston seal;
b) scuffing or scoring of cylinder and piston;
c) breakage of fixing bolts;
(ii) Failure of pumps and their gland seals;
(iii) Sudden drop of pressure in 200kg and 100 kg line due to external or internal
leakages of the auxiliary drive cylinders and valves;
(iv) Operating both roll bending system and the auxiliary drive units with the same
water hydraulic system causing excess loading of the pumps;
(v) Inconsistency of the oil concentration in the water fluid medium due to leakage.
The potential origins of the above nature of failures are as follows:
a) The probable reasons of damage of piston seals and leakages are -
i) Operating conditions - expiry of rated life, very high temperature, excessive load,
speed, vibration, high pressure etc.
ii) Low viscosity of fluid depends on temperature and pressure of fluid. Because of
the low viscosity of the water, the thermo physical properties of the mating
surface are affected adversely and the critical temperature of servo-vital film (oil
film) becomes very low. So, when the film raptures, the temperature rises at the
contact point and damages the seal.
iii) Chemical aggressiveness of fluid - The degree of swelling of oil resistant rubbers
mainly depends on the content of aromatic components in the fluid. An aggressive
fluid can destroy the rubber partially or completely. The sulphur or chlorine
containing substances in the fluid, which are activated by heat, cause a speeded
ageing of rubber.
iv) Physico-chemical process in the area of contact i.e., the distortions of the
geometry of the components due to wear or deformation leads to leakages.
v) Proper handling and maintenance.
vi) Physico-mechanical properties - Wear, largely induced by temperature, becomes
catastrophic. Other factors like pressure, speed, co-efficient of friction etc., affect
wear mainly through temperature changes. All these properties or factors are
greatly dependent on the nature of the fluid being sealed. Excessive pressure on
fluid increases the radial force, restricts the supply of lubricant to the contact
region, enlarges the part of the contact area where dry rubbing takes place, and
raises the friction force and contact temperature. These conditions result in
weakened tightness and shorter seal life. But also an insufficient force leads to
formation of a thicker film and makes for leakages.
b) Factors affecting Scuffing or Scorings of cylinders are as follows :
i) Roughness of mating surfaces and their material - a rough surface (2.5u to 1.25u)
holds the lubricant; however the normal and tangential forces applied to the seal
originate large deformation of the surface layer in the softer member. With the
increase in roughness, co-efficient of friction rises and disruption of fluid film is
possible.
ii) A very smooth surface (0.04u to 0.16u) is incapable of holding a low-viscous
lubricant. The "film starvation" at the contact area gives rise to higher shear
resistance and increased real area of contact causes the molecular component of
friction force to grow. Owing to low thermal conductivity of rubbers, these factors lead
to temperature rise in the contact zone during boundary friction and increase the co-
efficient of friction and wear rate.
iii) Physico-mechanical properties of lubricant like temperature, load, coefficient of
friction etc.
iv) Oil viscosity - the grade of oil is a major factor to hold back the development of
scuffing,
v) The growth in oil viscosity reduces contact heat evolution due to friction,
vi) Inadequate anti scuffing properties of oil - less additives
vii) Ingress of dirt, moisture or abrasive particles in the lubricant.
c) Frequent changing of pressure mode for thinner gauge rolling, frequent loading of
pumps because of leakages from joints and actuators, sudden drop of pressure in
200kg or 100kg system due to valve failures, low viscosity fluid - all these factors
leads to failure of the system.
There has been therefore a need in the art to developing a roll bending and balancing
system in Tandem cold mills in order to overcome the problems and limitations
experienced with the water-based hydraulic system for roll bending and balancing, by
providing an oil-based hydraulic system for roll balancing and bending in 5-Stand
TCM to have a better control on shape and flatness of the rolled strip through roll
force cylinder actuators in a reliable manner with faster response, free of any leakage
or pressure drop.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to providing an oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM, to have a
better control on shape and flatness of the rolled strip.
Another object of the present invention is directed to providing an oil-based hydraulic
system for roll balancing and bending system in 5-Stand TCM which enable reduction
in delays due to system failure and enable quicker roll changing time.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM which enable
to separate out bending systems and mill auxiliary drives into two different units.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM to facilitate
the operator to adjust the work roll gap/profile according to the profile of input
material and thermal camber of work roll in accurate and faster manner.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM ensure
improved quality of CR strip, less rejection, increased mill availability and higher
productivity.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM which is
capable of avoiding failure of pumps and their gland seals.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein
leakages from seals through clearance of seals is minimized by improving hydraulic
resistance by selection of working fluid/oil having high viscosity.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein the
system is adapted to avoid sudden drop of pressure in hydraulic lines due to cylinder
or valve failure.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein roll
force cylinder pistons are configured to minimize scuffing load.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein
surface roughness of the piston is maintained to reduce co-efficient of friction.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein
piston seal material is selected for higher heat resistance and low coefficient of
friction.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein
Maewest blocks are adapted to accommodate higher size bolts for higher load bearing
capacity.
A still further object of the present invention is directed to providing oil-based
hydraulic system for roll balancing and bending system in 5-Stand TCM wherein the
system would be adapted to correct the shape defects and reduce bad shape defect
by 57%, reduced mill delay by 80% and reduce delay on account of roll changing by
50%.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to an oil based hydraulic
system for roll bending and balancing in Tandem Cold Mill (TCM) comprising:
oil hydraulic bending actuators ;
variable volume pump controlled by pressure compensator adapted to maintain preset
pressure with the delivery pressure of the pump ranging from 0 to 320 bar, said
pump suction operatively connected to an oil tank;
pressure filter fitted at the discharge end of the pump ensuring desired filtration level
of the hydraulic oil to directional control valves in each valve stand ,
said valve stands being located closer to the application end of each stand of the mill
and comprising of said directional control valves, accumulators and pressure gauge
adapted to ensure steady and constant pressure to the hydraulic cylinders in the roll
chocks;
a pressure relief valve set;
providing for application of desired controlled hydraulic pressure as per desired shape
of the strip.
Another aspect of the present invention is directed to said oil based hydraulic system
for roll bending and balancing in Tandem Cold Mill (TCM) comprising a heat exchanger
in the return line for operative hydraulic circuit for cooling down the returned
hydraulic oil prior to the entry to the oil tank through desired filtration level.
According to a further aspect of the present invention is directed to said oil based
hydraulic system for roll bending and balancing in Tandem Cold Mill (TCM)
comprising:
a plurality of Hydraulic roll force cylinder actuators with piston selectively disposed in
all stands of TCM for roll bending and balancing connected through an operative
hydraulic circuit comprising,
variable volume pump controlled by a pressure compensator;
bladder type accumulator and pressure gauges for ensuing steady and constant
pressure to said hydraulic cylinders in the roll chocks;
directional control valves placed on each valve stand;
duplex type filters for filtration of hydraulic oil to desired level;
a heat exchanger preferably plate type for cooling of hydraulic oil;
a pressure relief valve to protect the system.
A still further aspect of the present invention is directed to said oil based hydraulic
system for roll bending and balancing in Tandem Cold Mill (TCM), wherein said
pressure compensator maintain the preset pressure by varying the volume of oil
discharged by positioning a wobbling plate on the drive shaft of the pump piston.
A still further aspect of the present invention is directed to said oil based hydraulic
system for roll bending and balancing in Tandem Cold Mill (TCM), wherein suction of
said pump is connected to an oil tank of 10m3 capacity.
A still further aspect of the present invention is directed to said oil based hydraulic
system for roll bending and balancing in Tandem Cold Mill (TCM), compriisng duplex
type filters comprising a duplex type pressure filter fitted in the discharge end of said
pump ensuring about 5µ filtration level of hydraulic oil to said directional control
valves and a duplex type return filter fitted in the return line of the hydraulic circuit
ensuring about 20µ filtration level of hydraulic oil returning to the oil tank.
A still further aspect of the present invention is directed to said oil based hydraulic
system for roll bending and balancing in Tandem Cold Mill (TCM), wherein said valve

stands comprise four of said directional control valves and are located closer to
application end of each rolling stand of the mill.
A still further aspect of the present invention is directed to said oil based hydraulic
system for roll bending and balancing in Tandem Cold Mill (TCM), wherein said roll
bending and balancing system is separated out from the auxiliary drives.
According to yet another aspect of the present invention is directed to said oil based
hydraulic system for roll bending and balancing in Tandem Cold Mill (TCM), wherein
said pressure relief valve is set at 0-100-200bar with on/off solenoid valve;
hydraulic fluid leakages reduced through the clearance by improving the hydraulic
resistance of the seals and wherein sealing effect is obtained by using high viscosity
of hydraulic oil/fluid, preferably about 46 cst With a sealing arrangement adapted to
ensure a seal performance factor (i=l-m/mp) which is more than 0, where m= actual
mass of leak substance, mp=permissible mass of leak substance;
said pistons are of larger size with chrome plating to minimize scuffing and with
surface roughness in the range of 0.17 micron to 0.24 micron for reduced coefficient
of friction;
material of rubber seals of said pistons are selected from nitrite poly acrylic or fluro-
elastomer rubber having high heat resistance and low coefficient of friction;
The objects and advantages of the present invention are described in greater details
with reference to the following non limiting illustrative accompanying drawings.
BRIEF DESCRIPTION OF THE ACOMPANYING DRAWINGS
Figure 1: is the schematic diagram for the arrangement of cylinders for Auxiliary
Drives of TCM showing the various components.
Figure 2: is the schematic diagram for the arrangement of cylinders for roll bending
and balancing operation.
Figure 3: is the schematic diagram of the work roll bending and balancing system with
oil hydraulic bending actuators according to the present invention showing the
actuations of different cylinders.

Figure 4: is the schematic illustration of the modified oil based hydraulic roll bending
and balancing system with valve stand for one Stand according to the present
invention.
Figure 5: is the schematic diagram of hydraulic arrangement of all valve stands for oil
hydraulic based roll bending and balancing system for the 5-stand TCM according to
the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
The present invention is directed to providing an oil-based hydraulic roll bending and
balancing system for last stands of the 5-stand Tandem Cold Rolling Mills in order to
precisely and reliably control the roll gap profile/contour for obtaining the desired
quality of the cold rolled steel strip in terms of shape and flatness. The oil hydraulic
system of the invention is further capable of preventing failure of bending cylinders,
failure of pumps and their glands or sudden drop of pressure in 200kg and 100kg line
due to leakages in auxiliary cylinders and valves.
The salient inventive aspects of the present invention may be summarized as follows:
-Designing of Oil-based hydraulic roll bending & balancing system for effective and
faster correction of roll gap contour for improved strip shape;
-Redesigning of roll force cylinder pistons to minimize scuffing load;
-Optimizing the surface roughness of the piston for reduced co-efficient of friction.
-Modification in Maewest blocks to accommodate higher size bolts for higher load
bearing capacity;
-Redesign of piston seal material for higher heat resistance and low coefficient of
friction.
-Retrofitting to existing mill logistics;
-Easy maintenance and trouble free operation with low investment;
As already indicated, the existing TCM mill comprised water hydraulics based system
to transmit power to the mill roll bending and balancing systems and mill auxiliary
systems Based on the mode of operation, such systems are categorized into (i)
balancing and bending unit and (ii) Auxiliary drive unit. Arrangement of cylinders for
auxiliary drives to facilitate the feeding of strip to the mill and changing of rolls are
illustrated schematically in the accompanying Figure 1. The arrangement of cylinders
to create positive or negative bending on the work rolls as per need to compensate
the thermal crown developed on the roll during rolling. Accompanying Figure 2
schematically illustrates the arrangement of cylinders for roll bending and balancing.
The existing water hydraulic system not being capable of precise control of work roll
gap contour/profile by controlling roll shifting, roll crossing, differential roll cooling
etc., developed various symmetrical/asymmetrical shape defects of rolled strips.
Oil-Hydraulic System:
The present invention provide for an oil hydraulic based roll bending and balancing
system for TCM wherein operator is facilitated to adjust the gap according to the
profile of input material and thermal camber of work roll, when producing materials of
various grades, widths and thicknesses, so as to correct the roll gap contour for
controlling shape and flatness defects of strips. Accompanying Figure 3 schematically
illustrates the work roll bending and balancing system with oil hydraulic bending
actuators according to the present invention showing the actuations of different
cylinders.
The system consists of variable volume pump controlled by a pressure compensator.
The pressure compensator will maintain the preset pressure by varying the volume of
oil discharged by positioning a wobbling plate on the drive shaft of the pump piston.
The delivery pressure of the pump ranges from 0 to 320bar. The pump suction is
connected to a 10m3 oil tank. Accompanying Figure 4 illustrates the modified oil
based hydraulic roll bending and balancing system according to the present invention.
A duplex type pressure filter is fitted in the discharge end of the pump ensuing 5µ
filtration level of hydraulic oil to the directional control valves placed in each valve
stand. These valve stands are located almost closer to application end of each Stand
of the mill. The valve stands comprises of four directional control valve, bladder type
accumulator and pressure gauges for ensuing steady and constant pressure to the
hydraulic cylinders in the roll chocks. The system is protected by a pressure relief
valve set at 0-100-200 bar with on/off solenoid valve. A plate type heat exchanger is
also incorporated in the return line of the hydraulic circuit for cooling down the
returned hydraulic oil prior to the entry to the oil tank. A duplex type return filter is
fitted in the return line of the hydraulic circuit ensuing 20µ filtration level of hydraulic
oil returning to the oil tank. Accompanying Figure 5 illustrates the hydraulic
arrangement of all valve stands for oil hydraulic based roll bending and balancing
system for the 5-stands TCM according to the present invention. The hydraulic
pressure is being controlled as per desired shape correction of the strip through visual
observation. The auxiliary drives are separated out from the modified system.

Leak Arresting:
Leakages reduced through improving the clearance of the seal by hydraulic
resistance. Proper sealing effect obtained by changing from low viscosity oil to high
viscosity hydraulic fluid.
Viscosity of water and hydraulic oil at 288°k & 1.0325x10*N/m2
Dynamic Kinematics
Centipoises est
Water 0.001x10* 1
Hydraulic oil 0.1x10* 46
Piston and seals:
Pistons are redesigned with larger size and chrome plating carried out to each pistons
to minimize scuffing. The surface roughness of the piston had been optimized at
0.17micron to 0.24 micron for reduced co-efficient of friction. Maewest blocks
modified for each stand to accommodate higher size bolts for higher load bearing
capacity.
Piston rubber seals are also redesigned with high heat resistance and low
coefficient of friction. Nitrite poly acrylic or fluro-elastomer rubber are used as seal
material. Hydraulic fluid leakages reduced through the clearance by improving the
hydraulic resistance of the seal. Seal performance factor ( i ) should be more than 0.
i = 1- m/mp;
where m = actual mass of leak substance
mp = permissible mass of leak substances
when m 0 and when m>mp, i< 0
Changing of hydraulic fluid from low viscosity oil to high viscosity oil had helped for
proper sealing. The oil film destruction minimized with the use of high viscosity oil.
Change to oil hydraulics from water hydraulics responds more positively to additives
and possesses better lubricating properties.
The system of the present invention thus achieved the following advantages by
implementing the above stated modifications and improvements in the oil based
hydraulic roll bending and balancing system for TCM:
-Correcting the edge waviness and center buckles on the cold rolled strip;
-Improvement in the strip shape of cold rolled strips by 20%;
-Reduced Customer complaint on account of bad shape by 50%;
-Delay on account of roll changing reduced by 50%;

-Delay in Hydraulic system reduced by 80%;
-Consumption of seal reduced by 50%;
-Reduction in leakages resulted in saving of hydraulic oil by 20%
-Financial impact of Rs 2.0 crore annual saving
It is thus possible by way of the present invention to providing an oil based hydraulic
roll bending and balancing system in TCM which would favour precise, accurate and
faster correction of roll gap contour for improved strip shape. The system enables the
operator to adjust and control of roll gap profile between work rolls in TCM such that
the desired strip shape and flatness is achieved eliminating shape defects of CR strips,
in a simple, cost effective and reliable manner. The system also ensures eliminating
frequent failure of roll adjusting cylinders due to leakage or seal damage. The system
delay and change over time of rolls are substantially minimized improving product
quality, mill availability and productivity in TCM.

We Claim:
1.An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) comprising:
oil hydraulic bending actuators ;
variable volume pump controlled by pressure compensator adapted to maintain preset
pressure with the delivery pressure of the pump ranging from 0 to 320 bar, said
pump suction operatively connected to an oil tank;
pressure filter fitted at the discharge end of the pump ensuring desired filtration level
of the hydraulic oil to directional control valves in each valve stand ,
said valve stands being located closer to the application end of each stand of the mill
and comprising of said directional control valve, accumulators and pressure gauges
adapted to ensure steady and constant pressure to the hydraulic cylinders in the roll
chocks;
a pressure relief valve set;
providing for application of desired controlled hydraulic pressure as per desired
shape of the strip.
2. An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in claim 1 comprising a heat exchanger in the return line for
operative hydraulic circuit for cooling down the returned hydraulic oil prior to the
entry to the oil tank through desired filtration level.
3. An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claims 1 or 2 in comprising:
a plurality of Hydraulic roll force cylinder actuators with piston selectively disposed in
all stands of TCM for roll bending and balancing connected through an operative
hydraulic circuit comprising,
variable volume pump controlled by a pressure compensator;
bladder type accumulator and pressure gauges for ensuing steady and constant
pressure to said hydraulic cylinders in the roll chocks;

directional control valves placed on each valve stand;
duplex type filters for filtration of hydraulic oil to desired level;
a heat exchanger preferably plate type for cooling of hydraulic oil;
a pressure relief valve to protect the system.
4. An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claims 1 to 3 , wherein said pressure compensator
maintain the preset pressure by varying the volume of oil discharged by positioning a
wobbling plate on the drive shaft of the pump piston.
5. An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claim 1 to 4, wherein suction of said pump is
connected to an oil tank of 10m3 capacity.
6. An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claims 1 to 5, compriisng duplex type filters comprising
a duplex type pressure filter fitted in the discharge end of said pump ensuring about
5µ filtration level of hydraulic oil to said directional control valves and a duplex type
return filter fitted in the return line of the hydraulic circuit ensuring about 20µ
filtration level of hydraulic oil returning to the oil tank.
7.An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claims 1 to 6, wherein said valve stands comprise four
of said directional control valves and are located closer to application end of each
rolling stand of the mill.
8.An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claims 1 to 7, wherein said roll bending and balancing
system is separated out from the auxiliary drives.
9. An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) as claimed in anyone of claims 1 to 8, wherein
said pressure relief valve is set at 0-100-200bar with on/off solenoid valve;
hydraulic fluid leakages reduced through the clearance by improving the hydraulic
resistance of the seals and wherein sealing effect is obtained by using high viscosity
of hydraulic oil/fluid, preferably about 46 cst With a sealing arrangement adapted to

ensure a seal performance factor (i=l-m/mp) which is more than 0, where m= actual
mass of leak substance, mp=permissible mass of leak substance;
said pistons are of larger size with chrome plating to minimize scuffing and with
surface roughness in the range of 0.17 micron to 0.24 micron for reduced coefficient
of friction;
material of rubber seals of said pistons are selected from nitrite poly acrylic or fluro-
elastomer rubber having high heat resistance and low coefficient of friction;
10.An oil based hydraulic system for roll bending and balancing in Tandem Cold Mill
(TCM) substantially as herein described with reference to the accompanying drawings.

The present invention relates to an oil based hydraulic system for roll balancing and
bending in 5-stand Tandem Cold Rolling Mill (TCM) adapted to ensure desired
controlled steel strip shape of cold rolled products, involving oil hydraulic bending
actuators connected in hydraulic circuit for precise control on roll gap contour during
cold rolling, ensuring desired strip shape and flatness avoiding problems of leakages
and/or failure of seals from valves or pumps etc. The system of the invention thus
facilitate operator to adjust the gap according to the profile of input material and
thermal camber of work roll to correct the roll gap contour for controlling shape and
flatness defects of the cold rolled strip in a faster and reliable manner. The system is
adapted to reduce shape defects by about 57% and delay due to roll changing by
50% and mill delay by 80% as compared to conventional water hydraulic systems.