FIELD OF THE INVENTION
The present invention relates to an improved rubber formulation for the rubber
clad squeeze rolls used in alkali cleaning section of cold rolling/continuous
galvanizing/polymer coating operation of steel sheet. These rubber clad squeeze
rolls can be used in normal or electrolytic cleaning in alkaline medium.
BACKGROUND OF THE INVENTION
During the pre-degreasing or degreasing of steel sheet after cold rolling or
before galvanizing or other functional coatings in continuous lines, the steel
sheets are passed through alkaline solution with or without electrolytic cleaning.
In order to remove the carried over cleaning solution from the sheet surface, the
steel sheet is passed along the squeeze rolls for absorbing the left over alkali.
The material being processed in the line has the following characteristics:
• Low or ultra low carbon steels after pickling and cold rolling with or
without annealing
• Input sheet thickness varies from 0.30 - 2.50 mm
• Sheet width varies from 900 - 1580 mm
• Output of these lines (coated or uncoated) are used mainly by auto and
white goods sector
The processing conditions are described below:
• Line speed - up to 500 meter per min (mpm)
• Line tension - up to 1.22Kg/sq mm at entry and 1.77Kg/sq mm at
processing section

• Line pressure - up to 3 bar acting on squeeze rolls
• Cleaning liquor - Alkaline solution with Concentration 0.8-3.0%
• Temperature - 60-80 °C
• Heated by - saturated steam/ steam coil
• Pressure at spray nozzles 2.5-3.5 bar
Rubber clad rolls are used extensively for squeezing to remove the left over alkali
solution along with holding or deflecting the sheets for the production of
uncoated or coated (galvanized and or functional coating) steel sheet. The
commercially available rolls have service life of 60 days or 120000 T production
at line speed up to 500 mpm, line pressure (acting on rolls) up to 3 bars with line
tension up to 1.77 Kg/sq mm.
The usual nature of failures observed at service in the commercial rolls includes
severe wear of roll surface, groove formation at edges, V-shaped cut at edges,
de-lamination between rubber - to - metal and between rubber - to - rubber.
Abrasive wear of Roll Covering (Ref: Fig 1) is a very common occurrence and
accounts for approximately 60% of premature failure of rolls. No surfaces are
true with respect to one another due to inherent surface roughness resulting in
intermittent contact instead of uniform contact between the adjacent surfaces. It
causes different radii of rotation resulting velocity differences along the axis of
roll and consequently driving / breaking share stresses are introduced leading to
abrasive wear. The rubber surface develops at first micro waviness perpendicular
to the direction of sliding which undergoes roll formation and eventual tearing of
rolled fragments caused by blunt asperities of the metal sheet surface. Again,
Micro cuts and serrations occur in the direction of sliding, more pronounced in
wet surface.

Groove formation at edges followed bv edge cuts (Ref: Fig 2 and 3):
As a rigid metal sheet is placed between two rubber covered rolls under
pressure, the rubber covering undergo a deformation. Since the rubber covering
is bonded to the metal core, the deformation is more at the edges of the metal
sheet where the rubber bulges out of the compression area thereby causing
stress concentration resulting more wear in comparison to the area in contact
with metal sheet surface. In a dynamic condition, this results in groove formation
at the edges. The groove formation at edges is basically again a wear
phenomenon which is severe at the edges of the metal sheet than at the surface
because of the above mentioned reason.
Groove formation occurs more with thicker metal sheets than with the thinner
ones because stress concentration at edges is more severe with thicker sheets in
comparison to thinner ones. Again, metal sheets have some unevenness of
thickness (whatever little it might be) and / or have some toughening or little
waviness at edges at some portions which impose additional abrasion / wear at
edges particularly with a fast moving metal sheet passing through counter-
rotating rubber covered rolls under pressure and with line tension, thereby
enhancing groove formation at edges.
Variation in sheet width results in the formation of several grooves at the edges.
The extreme condition of groove formation at edges is the edge cuts.
">" shaped cut mark (Ref: Fig 4) are always ">" shaped, i.e. cut is initiated from
middle portion of roll surface and propagates outwards. This is genuinely related
to maintenance of uniformity in line tension as any wavy edged metal sheet
moving under high line speed between two rubber rolls under pressure will
effectively act as a sharp blade.

De-lamination between rubber-to-metal and rubber-to-rubber (Ref: Fig 5):
Working condition of the squeeze rolls is severe as discussed earlier imposing not
only high compressive forces but also severe shear stress under a high shear
rate thereby demanding extremely good bonding between the rigid metal core to
highly deformable rubber covering as well as between the layers of rubber
covering.
Commercial rubber formulations tested in laboratory revealed following physical
properties:
Swelling Studies:
The swelling experiments were carried out following ASTM D 471-98. The
polymers were immersed in alkali/chromic acid at 90o 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.

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 (Punch press, Model P/44, MS
Instruments Company Inc., Stony Creek, New York) from the molded sheets with
ASTM D 412-80 Type C die along the grain direction, 90° angle specimens for
tear testing were 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 Zwick Universal Testing Machine (UTM) model 1445 (Zwick GmbH & Co,
Ulm, Germany) at crosshead speed of 500 mm/min at 25 + 2° C. The modulus
and tensile strength are reported in MPa and elongation at break in percentage.
The results were obtained directly from the printer of the computerized machine.
Tear strength of the vulcanized rubber was determined on un-nicked 90° angle
specimen (Die C) using Zwick UTM 1445 as per ASTM D 624-98 at room
temperature. Hardness of the samples was determined using Shore 'A'
Durometer (Shore Instrument and Manufacturing Co, Jamaica, New York, USA)

as per ASTM D 2240-98. Readings were taken after 15 s of the indentation when
firm contact was established with the specimen.

Service life of the commercial rolls is restricted to 60 days or 120.000 T
productions because
• Original rubber cover formulation is less resistant to hot alkaline solution
leading to high swelling index. Ingress of the working medium inside
rubber lead to blister formation at sub-surface and finally lead to
Delamination
• Change in hardness of the rubber cover within 60 days of service from 65-
70 shore A to 75-80 shore A thus making the roll ineffective for squeezing
out the liquid cleaning solution from the sheet surface leading to solution
carry over
• Increase in rubber cover hardness leads to slippage of the sheet while
passing through the rolls lead to surface marks due to abrasion

• Slippage of the strip/sheet on roll surface lead to > shaped cut marks on
the cover which further lower the service life of these rolls
To improve the service life of the squeeze rolls, rubber formulation is required to
have high modulus characteristics to take care of least deflection under high
pressure, high abrasion and cut resistant with minimum change in other physico-
chemical properties in hot alkali medium. It was taken care of in the new
formulation through proper choice of rubber, increasing cross linking density,
suitable choice of reinforcing agents and its loading amount.
SUMMARY OF THE INVENTION
According to the invention, there is provided Proper rubber formulation for clad
squeeze rollers used in metal cleaning section of a cold roll mill. These rolls
provided a service life of 1 year or 720000T of production level without any
maintenance requirement for the rolls. The optimum formulation has given 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 conditions.
">" Shaped cut marks at edges along with groove formation was avoided by
making the formulation highly abrasion and cut resistance. Additionally, the roll
dimensional parameter like high ratio of core diameter to roll covering thickness
of 20% require rubber compound with high modulus characteristics to take care
of least deflection under the condition of high line pressure of 3 bar.
Carboxyleted nitrile rubber (XNBR) was selected for much better modulus
characteristics and load deflection properties along with better tear and abrasion

resistance. However, since XNBR shows change in properties in alkaline medium,
the grade of XNBR with minimum carboxylic content was chosen. Additionally to
compensate for the changing characteristics in alkaline condition, phenol -
formaldehyde (PF) resin of resol type was added in the formulation.
The flowability and curing characteristics of the formulation in such that rolls can
be cladded with the developed formulation by using calendaring and hot
extrusion technique.
Brief description of the accompanying drawings
Figure 1 - Shows a photograph of a prior art rubber clad squeeze roll
emphasizing rubber abrasion from surface.
Figure 2 - Shows a photographic view of groove mark at edges of prior art
rubber clad squeeze rolls.
Figure 3 - Shows an edge cut developed on prior art rubber clad squeeze roll.
Figure 4- Shows shaped cut developed at edges of prior art rubber clad
squeeze rolls.
Figure 5 - Shows a condition of delamination of rubber in prior art rolls with
exposed metal surface.
DETAILED DESCRIPTION OF THE INVENTION
The development of the new rubber formulation involved studying both
mechanical and chemical aspects of the service condition including study of the

defective cladded rolls along with dimensional parameters of the rolls. In order to
achieve long service life in the prevailing mechanically and chemically aggressive
condition, long term studies under similar conditions of alkali concentration and
temperature were carried out.
A range of formulation with varying Carboxyleted nitrile rubber (XNBR) and other
ingredients content were developed and tested in laboratory for different
physical and chemical properties. Table 1 shows the formulations with different
ingredients that were tested for applicability. Table 2 shows the rheometric
graphs for them. Table 3 shows the laboratory swelling test results of them.
Table 4 shows the original physical properties and Table 5 shows the properties
after ageing in working medium at 90°C for 7 days.
Out of different combinations, the optimum formulation was selected based on
minimum change in hardness, tear and abrasion resistance with lowest % weight
and volume swell. This criteria was adopted to ensure the rubber clad maintain
original properties and surface condition in actual service condition. Co-efficient
of friction between rubber and metal is decreased due to change in surface
condition and physical properties. As a result, the rolls become sluggish and
move at a slower velocity than the speed of the sheet. It causes slippage
between roll surface and moving sheet. The relative slippage along with the
already prevailing differences in speed between entry and processing section of
the line with applied line tension further enhances the shear force on the cover
rubber resulting increased abrasion, developing groove and ultimately ">" cut
marks protruding outside at both the edges.
Along with minimum % swelling, the formulation is also required to be highly
abrasion and cut resistant. Additionally, high ratio between roll core diameter to
rubber cover thickness (20%) due to squeeze roll dimension, requires a

formulation with high modulus characteristics to take care of least deflection
under high pressure at line. The problem of abrasive wear of the rubber cover
was taken care of through proper choice of rubber and suitable reinforcing agent
providing high modulus characteristics. Groove formation and edge cut problem
was addressed by using suitable choice of abrasion resistant rubber with high
content of reinforcing fillers and high cross-linking density. The problem of ">"
shaped cut mark and de-lamination was also taken care of in the newly
developed rubber covering composition by using vulcanizing system. which
results in both ionic & covalent bonds and also by using suitable re-enforcing
fillers to modify the elastic modulus.
Accordingly, XNBR was chosen for its better modulus characteristics and load
deflection properties along with better tear and abrasion resistance. To improve
the alkali resistant properties of the XNBR based formulation, low carboxylic
content XNBR grade was used because with increase in carboxylic content, alkali
resistant properties of XNBR decrease. Phenol formaldehyde (PF) resin of resol
type which have excellent resistance against alkaline condition was also
incorporated in the formulation. PF resin is highly compatible with XNBR, being
both polar in nature.
The developed formulation makes a unique balance between mechanical and
chemical working conditions meeting the demand of life cycle for an extended
period of time along with the dimensional characteristics of rubber clad rolls in
particular. The flowability and curing characteristics of the formulation in such
that rolls can be cladded with the developed formulation by using calendaring
and hot extrusion technique.

Optimised Formulation was tested at plant by making rubber clad squeeze rolls.
Typical dimension of these rolls are as follows:
Core O/D: 250mm
Finished O/D: 300mm
Ratio between core O/D to rubber layer thickness: 20%
Table 2: Rheograph Data for the formulations
Temperature: 150°C; Chart motor: 30min; Range Scale: 100; Arc: 3°


Table 3: Change in properties after swelling test and swelling index for the
formulations

WE CLAIM
1. A rubber formulation for rubber clad squeeze rollers used in metal cleaning
section of a cold rolling mill, the rubber formulation consisting of:
100 parts by weight of a carboxylated nitrile rubber;
10 parts by weight of a resol type phenol formaldehyde resin;
2 parts by weight of a polymerised trihydro quinoline anti-oxidant;
1-3 parts by weight of Stearic acid;
1-1.5 parts by weight of Sulfur;
15-40 parts by weight of intermediate super abrasive furnace BLACK; and
1.20 -1.40 parts by weight of N-cyclohexyl- 2-benzothiazole sulphenamide
(CBS).
2. The rubber formulation as claimed in claim 1, wherein the carboxylated nitrile
rubber has carboxylation content of 1.40% and acrylonitrile content of 33%.
3. The rubber formulation as claimed in claim 1, comprising 5-15 parts by
weight of a poly butadiene rubber.
4. The rubber formulation as claimed in claim 1, comprising up to 5 parts by
weight of a cumarone-indene resin.
5. The rubber formulation as claimed in claim 1, comprising up to 1 parts by
weight of N-(l,3 dimethyl, butyl)'-N'-phenyl- phenylene diamine.
6. The rubber formulation as claimed in claim 1, comprising 24 parts by weight
of fast extruding furnace black, 0.70 parts by weight of Mastication agent
(Renacit), 1 parts by weight of a polyethylene wax (AC Polyethylene), 7 parts

by weight of condensation product of Anacardic Acid with Formaldehyde and
3 parts by weight of a low molecular weight Polyester Resin - RM - 5000.
7. The rubber formulation as claimed in claim 1, comprising 4-15 parts by
weight of VN3 Silica.
8. The rubber formulation as claimed in claim 1, comprising 4-24 parts by
weight of Di-n-Octyle Panthalate.
9. The rubber formulation as claimed in claim 1, comprising 7-7.5 parts by
weight of Zinc peroxide.
10. A rubber formulation for rubber clad squeeze rollers used in metal cleaning
section of a cold rolling mill, the rubber formulation consisting of:
100 parts by weight of a carboxylated nitrile rubber;
10 parts by weight of a resol type phenol formaldehyde resin;
5 parts by weight of a poly butadiene rubber;
2 parts by weight of a polymerised trihydro quinoline anti-oxidant;
1 parts by weight of N-(l,3 dimethyl, butyl)'-N'-phenyl- phenylene diamine;
1 parts by weight of Stearic acid;
1 parts by weight of Sulfur;
30 parts by weight of intermediate super abrasive furnace BLACK;
24 parts by weight of fast extruding furnace black;
24 parts by weight of Di-n- Octyle Panthalate;
7 parts by weight of Zinc peroxide;
0.70 parts by weight of Mastication agent (Renacit);
1 parts by weight of a polyethylene wax (AC Polyethylene);

7 parts by weight of condensation product of Anacardic Acid with
Formaldehyde;
3 parts by weight of a low molecular weight Polyester Resin - RM - 5000;
and
1.30 parts by weight of N-cyclohexyl- 2-benzothiazole sulphenamide
(CBS).
11. A rubber formulation for rubber clad squeeze rollers used in metal cleaning
section of a cold rolling mill, the rubber formulation consisting essentially of:
100 parts by weight of a carboxylated nitrile rubber; and
10 parts by weight of a resol type phenol formaldehyde resin.
wherein the carboxylated nitrile rubber has carboxylation content of 1.40%
and acrylonitrile content of 33%.
12. A rubber formulation as claimed in claims 1, 10 and 11, wherein the
formulation is used in high speed electro-cleaning lines with line speed up to
500 mpm.

ABSTRACT

The present invention is related to a new compounded carboxylated nitrile
rubber (XNBR) formulation for rubber clad squeeze rollers. These rubber clad
squeeze are used in alkali cleaning section of cold rolling/continuous
galvanizing/polymer coating operation of steel sheet.
The developed rubber clad rollers with the inventive compounded carboxyleted
nitrile rubber (XNBR) formulation can withstand high temperature with dynamic
stress strain workability at high line speed. The formulation provides improved
results with minimum change in hardness, % volume & weight swell, tear
strength and abrasion resistance. The disclosed formulation maintains original
physical and chemical properties including surface condition at the prevailing
mechanically brutal and chemically aggressive condition.