FIELD OF THE INVENTION
The present invention relates to a rubber formulation for application on rubber clad rolls
in an electrolytic cleaning line operating with alkaline medium after cold rolling
operation of steel sheets.
BACKGROUND OF THE INVENTION
Oil and dirt on the steel sheet surface percolating from a preceding cold rolling process
generates carbon soot during batch/continuous annealing under reducing condition.
Presence of the carbon soot causes blackening of the steel surface which is not
acceptable for subsequent processing for auto and white goods applications. Therefore,
it is mandatory to remove the oil and dirt before the annealing treatment. The removal
operation is carried out through cathodic and anodic cleaning of the steel sheet by an
electrochemical route in hot alkaline medium. The electrolytic cleaning treatment is
done by immersing the steel strip in hot alkaline solution using a bipolar process where
the strip acts as cathode or anode. Cathodic polarity favors removal of oily residues
through evolution of hydrogen and anodic polarity favors removal of metallic residues
through evolution of oxygen. Polarity is reversed after a stipulated time of operation for
cleaning the electrodes from the sticking residues. Fig 1 shows a typical process flow
diagram for such an operation.
The material being processed in the line has the following characteristics:
• Low or ultra low carbon steels after pickling and cold rolling without annealing
• Input sheet thickness varying from 0.30 - 2.50 mm;
• Sheet width varying from 900 -1580 mm; and
• Output of these lines are used mainly by auto and white goods sector.

The processing conditions are described below:
• Line speed - up to 600 mpm;
• Cleaning liquor - Alkaline solution;
• Concentration - 2.0-2.6%;
• Temperature - 65-75 °C;
• Heated by - Steam coil; and
• Line tension - up to 1.22Kg/sq mm at entry and 1.77Kg/sq mm at the processing
section.
According to the prior art process, the steel strip/sheet first passes through a pre-
degreasing/pre-cleaning section where the strip is cleaned by spraying hot alkali
through spray headers from top and bottom surface at a pressure. The second
treatment is done by a brushing unit and spray headers. The brushing action under
adjusted pressure takes place by rotating the brush rolls combined with spraying of hot
alkali. This step facilitates removal of major iron fines and dirt. After the alkaline
cleaning section and brushing machine, a deflector guides the strip into an electrolytic
cleaning tank. The rubber cladded sink rolls disposed inside the electrolytic cleaning
tank steers and guide the steel strip. Typically the residence time for the steel strip
inside the electrolytic cleaning tank is few seconds and corresponding electrolytic
contact time is fraction of a second. Therefore, a very high line speed (typically 600
mpm) is maintained. The next treatment consists of a brushing unit with hot DM water
and condensate to clean the loosened rust/oil particles from strip surface after
electrolysis. Subsequently, the strip is rinsed / washed with hot DM water with spray
headers, coated optionally with special material with spray headers and a set of
squeezer rolls, and finally dried to remove moisture by hot air blower.

Sink rolls inside the electrolytic cleaning tank performs the important role of steering,
balancing and providing support to the steel strip at high line speed and tension. These
rolls are typically 1000mm in diameter and much bigger than rubber clad squeeze rolls.
Sink rolls remain immersed in the cleaning liquid. Therefore, rubber covers of these rolls
need to be resistant to any chemical attack. Any change in surface characteristics for
example, color, glossiness, smoothness due to reactions with hot alkali affect the
coefficient of friction resulting in slippage of the sheet on roll surface contributing to
develop surface cuts on the cover rubber. Figures 3 and 4 shows the surface cuts
developed on the commercially available sink rolls after around 6 months of service.
Chemical attack to the rubber cover leads to a volume swell or a volume shrinkage due
to absorption of the working fluid. Chemical reaction with the compounding ingredients
of the rubber cover leads to micro porosity, leaching and volume change. Reaction with
base rubber material leads to substitution or addition and chain degradation. It also
causes the change in initial physical properties of the rubber cover which enhances the
chance of surface cut marks and further reduces the service life of these rolls.
Commercially available sink rolls are made from acrylo nitrile butadiene (NBR) based
rubber formulations. It was tested in laboratory and results are given below:
Swelling Studies:
The swelling experiments were carried out following ASTM D 471-98. The polymers
were immersed in alkali/chromic acid at 90° C in thermostatically controlled oil bath for
7 days. The results were reported in terms of percentage volume loss and weight loss
that is defined as follows: -


Wl = Initial un-swollen wt. of the polymer; W2 = swollen wt of the polymer.
% Volume swell [YW3-W4VfWl-W2)] = x 100
(W1-W2)
Wl = initial weight in air, W2 = initial weight in water, W3 = weight of the treated
rubber in air and W4 = weight of the treated rubber in water.

Physical property study:
Dumbbell shaped specimens were punched from the molded sheets with ASTM D 412-
80 Type C die along the grain direction for tensile testing. 90° angled specimens for
tear testing was cut across the grain direction. Tensile Properties like modulus, tensile
strength and elongation at break of the rubber compounds were determined according
to ASTM D 412-98 test method. The tests were carried out in a Universal Testing
Machine (UTM) at crosshead speed of 500 mm/min at 25 + 2° C. The modulus and
tensile strength were reported in MPa and elongation at break in percentage. The
results were obtained directly from the computerized machine.
Tear strength of the vulcanized rubber was determined on un-nicked 90° angle
specimen (Die C) using the UTM as per ASTM D 624-98 at room temperature. Hardness
of the samples was determined using a Durometer as per ASTM D 2240-98. Readings
were taken after 15 seconds of the indentation when firm contact was established with
the specimen.


Service life of the commercial rolls is restricted to 6 months because of the following
reasons :
• Original rubber cover formulation is less resistant to hot alkaline solution leading to
high swelling index.
• Change in hardness of the rubber cover leads to slippage of the sheet while passing
over the rolls lead to surface cut marks.
• Slippage of the strip/sheet on roll surface lead to cut marks on the cover which
further lowers the service life of these rolls.
In light of the above mentioned problems, there is a need of developing a rubber
formulation which is high resistant to alkaline medium. Further, rubber formulation
should show minimum variation in hardness and swelling properties with time.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a rubber formulation for
application on rubber clad rolls in an electrolytic cleaning line operating with alkaline
medium after cold rolling operation of steel sheets.

Another object of the invention is to propose a rubber formulation for application on
rubber clad rolls in an electrolytic cleaning line operating with alkaline medium after
cold rolling operation of steel sheets, which shows minimum variation in hardness and
swelling properties with passage of time.
Still another object of the invention is to propose a rubber formulation for application on
rubber clad rolls in an electrolytic cleaning line operating with alkaline medium after
cold rolling operation of steel sheets, which increases the service life of clad rolls.
A further object of the invention is to propose a rubber formulation for application on
rubber clad rolls in an electrolytic cleaning line operating with alkaline medium after
cold rolling operation of steel sheets, which is based on Acrylo Nitrile Butadiene rubber
(NBR).
A still further object of the invention is to propose a rubber formulation for application
on rubber clad rolls in an electrolytic cleaning line operating with alkaline medium after
cold rolling operation of steel sheets, which that can be processed to build clad rolls
using calendaring and hot extrusion techniques.
SUMMARY OF THE INVENTION
According to the invention, a rubber formulation is developed using Acrylo Nitrile
Butadiene rubber (NBR), resins and other ingredients such as curing agent, anti-
oxidants, pre vulcanization inhibitor, reinforcing agent etc. The rubber formulation of
the present invention comprises Acrylo Nitrile Butadiene rubber (NBR) and Cumarone
Indene resin. In one embodiment of the present invention, phenol formaldehyde resin
was also used along with Cumarone Indene resin, the phenol formaldehyde (PF) resin
having an excellent resistance against alkaline condition.

Clad rolls made using the rubber formulation of the present invention provide a service
life of 1 year (equivalent of 0.55 million ton of production). The optimum formulation
has shown best results with minimum change in hardness, % volume & weight swell,
tear strength and abrasion resistance. It ensured that the roll cover can maintain
original physical and chemical properties including surface condition at the prevailing
mechanically brutal and chemically aggressive condition. Surface cut marks at edges
along with groove formation was avoided by making the formulation highly abrasion
and cut resistance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 describes different process steps in an electrolytic cleaning line using prior art
clad rolls.
Fig 2 demonstrates surface cut marks on rubber cover of a sink roll according to prior
art.
Fig 3 demonstrates a closer view of the surface cut marks on the prior art rolls.
DETAILED DESCRIPTION OF THE INVENTION
A series of formulations were developed for clad rolls using Acrylo Nitrile Butadiene
rubber (NBR)/poly butadiene rubber, cumarone Indene resin, phenol formaldehyde
resin and other ingredients such as curing agents, anti-oxidants, pre vulcanization
inhibitor, reinforcing agents etc.

It is known that co-efficient of friction between rubber and metal decreases due to
change in surface condition and physical properties. As a result, the clad rolls become
sluggish and move at a slower velocity than the speed of the sheet. It causes a slippage
between a roll surface and a moving sheet. The relative slippage combined with already
prevailing differences in speed between an entry section and a processing section of the
cleaning line, surcharged with applied line tension, further enhances the sheer force on
the cover rubber resulting in increased abrasion, and developing cut marks on the
rubber surface. Hence, the formulation is to be applied on the rolls, need to be highly
abrasive and cut resistant. The rubber cover is made abrasion resistant through a
reinforcing agent providing high modulus characteristics. In an embodiment of the
invention, furnace black (different varieties), and silica are used as the re-enforcing
agent .The problem of surface cut is addressed by improving the tear strength of the
rubber with high content of reinforcing fillers and high cross- linking density. In an
embodiment of the invention, Di-n- Octyle Panthalate (DOP), N-cyclohexyl-2-
benzothiazolesulphenamide (CBS) are used as the reinforcing fillers. The problem of cut
mark is also taken care of by the inventive rubber covering composition by using
vulcanizing system which results in both ionic & covalent bonds and further using
reinforcing fillers to modify the elastic modulus. Table 1 below shows the formulations
with different ingredients that were tested for applicability.
The flow behavior and viscosity of the developed formulations were evaluated to study
the process-ability at higher scale of operation required to build rubber clad roll of at
least 1000 mm diameter for use in electrolytic cleaning line. Table 2 . below
demonstrates the rheograph data for the developed formulations obtained through
Oscillating Disc Rheometer complied with ASTM D 2084-95 standard.

The formulations were tested using applicable standards in the industry. Hardness of
the samples was determined using a Durometer Instrument as per ASTM D 2240-98.
Readings were taken after 15 seconds of the indentation when firm contact was
established with the specimen. The swelling experiments were earned out following
ASTM D 471-98. The developed formulations were immersed in alkali/chromic acid at
90° C in thermostatically controlled oil bath for 7 days. Table 3 below reports these
properties of the different formulations. Physical properties were determined by taking
dumbbell shaped specimens punched in a Punch Press from the molded sheets with
ASTM D 412-80 Type C die along the grain direction for tensile testing and 90° angled
specimens for tear testing across the grain direction. Tensile Properties for example
modulus, tensile strength and elongation at break of the rubber compounds were
determined according to ASTM D 412-98 test method. The tests were carried out in a
Universal Testing Machine (UTM) at crosshead speed of 500 mm/min at 25 ± 2°C. The
modulus and tensile strength were reported in MPa and elongation at break in
percentage. Tear strength of the vulcanized rubber was determined on un-nicked 90°
angle specimen (Die C) using the UTM as per ASTM D 624-98 at room temperature.
Physical properties before and after soaking in working medium are reported in Tables
4 and 5.

The formulations Nl, N3 and N9 showed significantly improved results in terms of swell
Index along with minimum change in hardness, tear and abrasion resistance after
swelling test in laboratory. This criteria was adopted to ensure that the rubber clad
maintain original properties and surface condition in actual service condition.
The developed formulation makes a unique balance between mechanical and chemical
working conditions and hence, meeting the demand of life cycle for an extended period
of time along with the dimensional characteristics of rubber clad rolls in particular. The
lability and curing characteristics of the formulation in such that rolls can be cladded
with the developed formulation by using calendaring or hot extrusion technique.

WE CLAIM:
1. A rubber formulation for application on rubber clad rolls used in an electrolytic
cleaning line of a cold rolling mill to steer the steel sheet inside a cleaning tank,
the rubber formulation comprising:
100 parts by weight of acrylo nitrile butadiene rubber (NBR);
15 -20 parts by weight of Zinc peroxide (ZnO);
1.5 parts by weight of Steraic acid;
1.5-3 parts by weight of N-cyclohexyl-2-benzothiazolesulphenamide
(CBS);
0-10 parts by weight of phenol formaldehyde resin (PF resin);
4 -5 parts by weight of Cumarone Indene (C.I) Resin;
15-100 parts by weight of a reinforcing carbon black;
0-2 parts by weight of an anti oxidant;
0-12 parts by weight Di-n-Octyle Panthalate (DOP);
0-5 parts by weight of Magnesium oxide (MgO);
1 -1.2 parts by weight of sulfur; and
0-1 parts by weight of a Pre vulcanization inhibitor.
2. The rubber formulation as claimed in claim 1, wherein the pre vulcanization inhibitor
is N-(cyclohexylthio) phthalimide.
3. The rubber formulation as claimed in claim 1, wherein the reinforcing carbon black is
selected from a group consisting of super abrasive furnace black (ISAF), semi
reinforcing furnace black (SRF), High Abrasion Furnace Black (HAF), fast extruding
furnace black (FEF), mineral thermal black (MT) and a combination thereof.

4. The rubber formulation as claimed in claim 1, wherein the rubber clad rollers are
immersed In the metal cleaning section partly or completely.
5. The rubber formulation as claimed in claim 1, wherein the anti oxidant is
polymerized tri-hydro quinoline.
6. The rubber formulation as claimed in claim 1, wherein the anti oxidant is N- (1,3
dimethyl, butyl)'-N'-phenyl-phenylene diamine (4020).
7. The rubber formulation as claimed in claim 1, wherein the cleaning medium is
alkaline in nature and maintained at a temperature range of 65 to 75 °C.
8. The rubber formulation as claimed in claim 1, wherein the formulation is used in
high speed electro-cleaning lines with line speed up to 600 mpm.
9. The rubber formulation as claimed in claim 1, wherein the rubber rollers are enabled
to withstand a line tension up to 1.22Kg/sq mm at the entry section and up to
1.77Kg/sq mm at the processing section.
10. The rubber formulation as claimed in 1, wherein the formulation is processed to
build clad rolls using calendaring and hot extrusion techniques.

11. The rubber formulation as claimed in 1, wherein clad rolls in the cleaning line are
having service life to process 0.55 million ton of steel sheet.
12. The rubber formulation as claimed in any of the preceding claims, wherein the clad
rolls are operable to steer the steel sheets/strips inside the cleaning tank of the
cleaning line.

ABSTRACT

The invention related to an improved compounded acrylo nitrile butadiene (NBR) rubber
formulation for rubber clad rollers is provided for high speed electrolytic cleaning lines.
These clad rolls are used to steer the steel sheet/strip inside the cleaning tank by
remaining partly or completely immersed in hot alkaline cleansing solution. The said
rubber clad rollers can sustain high temperature with dynamic stress strain workability
at high line speed, anti-chemical reactant, resistant to cut marks with minimum change
in hardness.