FIELD OF INVENTION
The present invention relates to building rubber covered rolls. More particularly,
it relates to an improved rubber cover building process on metal core.
BACKGROUND OF THE INVENTION
Rubber covered rolls are used extensively in paper, textile and steel industries.
With the advent of cold rolling, galvanizing and color coating technologies in
steel industries to produce thin gauge sheets being used in auto and white good
manufacturing sectors extensively, the use of rubber covered rolls has seen an
enormous increase in use. Most of the steel manufacturers are now going for
value added cold rolling, galvanizing and color coating technologies to meet the
increased demand from the auto and white good sectors. It has also resulted in
an increase in profit margin of the individual manufacturers and the industries
are going for the forward integration and value addition of their final product.
Rubber covered rolls are used extensively in the cold rolling, galvanizing and
color coating lines. Demand for the rubber covered rolls is also increasing with
the increase in production of the color coated, galvanized and cold rolled sheet
by different manufacturers.

Building the rubber cover on the metal core is mostly carried out through
calendaring process in spite of the basic drawbacks of the technology like
requirements of highly skilled labour, labour intensive,low productivity etc. On
the other hand, the available automated extruded rubber building technology has
not gained much popularity due to the initial high investment cost. The
commercially available extruded rubber building machines require sophisticated
control systems to produce quality rubber covered rolls which makes the
technology costly and unpopular.
Various methods are available for applying rubber coverings to the metal core.
1. Calendaring Technique: Calendared rubber sheet wrapping method is an
age-old system and is carried out manually or using a three roll building
machine. Sheet width availability is determined by the calendar roll width
and for most of the industrial roll coverings it becomes necessary to cut
and re-join sheets to make them wider. Again, the sheet thickness used
varies from 1.0 mm to 2.0 mm. Therefore, it requires putting multiple
layers of sheet one above another to attain the desired thickness of the
rubber cover above the metal core. Disadvantages associated with this
method are:
I. Requirement of an expensive calendar line
II. High sheet preparation cost
III. Poor adapatability to automation

IV. Less productivity
V. Labour intensive
VI. Quality depends on skill level of the labour
VII. High waste generation as the trimmed rubber cannot be reused
VIII. Requirement of undesirable solvents
IX. High rejection rate of the semi-finished/finished roll due to air
entrapment between different layers

2. Cross head roll covering technique: Cross head roll covering method
involves continuous all-round covering of rubber to a progressively fed
metal core in one single pass. This method is mostly limited to lower
metal core diameter rubber covered rolls of around 20 mm. This method
is generally used when rollers of large quantity of identical dimensions are
produced e.g. rollers used in off-set printing industry.
3. Extrusion technique: Extruded strip building technique is the only versatile
method which is not limited by roll diameter or quantity. Rolls of all
diameters and length can be conveniently covered with this technique.
General arrangement of the machine is shown in Fig.1 and the salient
features of the technique are listed below:
I. It can produce continuous rubber strip of varying sections
depending on the machine design by utilizing a cold feed rubber
extruder (Ref point 1 of Fig.l) with a variable speed drive.

II. Rubber strip is wrapped around the rotating metal core which is
held usually in a lathe machine (Ref point 3 of Fig.1). Variable
RPM adjustment facility of the lathe machine provides the
desired spin of the metal core.
III. Sequential covering of the metal core with the rubber strip is
accomplished by transverse and progressive movement of the
extruder mounting trolley at a variable speed as per
requirement.
IV. There is an auxiliary covering and pressing device mounted on
the traversing trolley to apply and press the rubber strip on the
rotating metal core. It also helps in stitching/joining of the
successive wraps of rubber strips. Pneumatic cylinder with
adjustable air pressure is used to accommodate different
diameters of rolls, different rubber compounding with different
stiffness and different thickness of the rubber strips. The device
comprises of a guide and tension compensating arrangement
for extruded strip consisting of (a) dancing roll (Ref point 2.1 of
Fig.l) for tension compensation, (b) series of guide rolls (Ref
point 2.2 of Fig.l) mounted on (c) lateral and longitudinal
carriage (Ref point 2.3 and 2.4 of Fig.l) and the application
head (Ref point 2.5 of Fig.l) connected to the pneumatic

cylinder which provides the necessary pressure on the strip for
covering the metal core.
The applied rubber covering thickness for such a method is determined by
I. Area of a single strip determined by multiplying width (varying from
20-60 mm) and thickness (varying from 2-12 mm) of the strip.
II. No. of building passes
III. Percentages of strip overlap with each other
Commonly used strip shapes are rectangular, parallelogram and trapezoidal.
Strip overlap is adjustable and is synchronized with the rotating speed of the
metal core. The rotational speed of the metal core for a particular traversing
speed of the extruder trolley is determined based on some dependent and
independent variables (as mentioned below) to keep the spin-traverse ratio
constant.
I. Metal core diameter which is an independent variable
II. Extrusion rate of the rubber strip which is a dependent variable
III. Strip overlap width which is an independent variable
Any variation in the spin-traverse ratio or variation in strip width overlap results
in voids and/or open seams between successive wrapped strips leading to
defective roll covering. To precisely control the process sophisticated control
systems are required which increases the cost of the equipment.

Hence there exists a need to improve the process of building rubber cover on
metal core.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an improved rubber cover
building process on metal core which eliminates the disadvantages of prior art
maintaining effectiveness and quality while making the equipment cost-effective
and user friendly.
Another object of the invention is to propose an improved rubber cover building
process on metal core which is capable of working on lower number of operating
variables keeping other variables fixed without affecting the final roll quality.
A still another object of the invention is to propose an improved rubber cover
building process on metal core which is capable of performing without
sophisticated control systems so that initial investment cost for the technology is
reduced by 60-70%.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows general arrangement of extruded strip roll building machine
Fig.2 - a photograph showing a developed extruder machine with proposed
modification
Fig.3 - shows a single pass angle build
Fig.4 - shows a single pass flat (25-50-75%) overlap
Fig.5 - shows a multipass flat, (0%) overlap
Fig.6 - shows a multipass flat, (50%) overlap
Fig.7 - shows a multipass flat (0-75%) overlap
Fig.8 - shows a rhombus shaped strip with dimension 7.5/40 mm against 15/40
mm having same strip overlap width of 20 mm
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Proper covering of the metal core by extruded rubber strips require simultaneous
synchronization of two different types of movements to ensure definite strip
overlapping.
I. Surface speed of the rotating metal core with the speed of the
extruded rubber strip

II. Traverse motion of the extruded strip with the requisite overlap in
order to have an axial covering through successive sequential
wrapping of the strip
Available extruder machines control the synchronized movements by controlling
both the independent and dependent variables through sophisticated control
systems and simultaneously using extruded strips of different dimensions
maintaining constant spin-traverse ratio. The patent proposes a lower number of
operating variables keeping the other variables fixed without affecting the final
roll quality and versatility of the automated extruder machine. Due to the
reduction in the number of operating variables the requirement for sophisticated
control systems can be avoided. Therefore, the initial investment cost for the
technology can be reduced by 60-70%.
The newly developed technology for which the patent is being applied was used
for making coverings of cold rolling mill rolls of an integrated steel plant.
Following significant improvements have been made in the proposed technology
over the existing one:
I. Reduction in the number of machine operating variables
II. Simultaneous usage of specific design of strip (rhombus shaped)
maintaining the versatility of the technique
III. More operator friendly
IV. Effective and less expensive

The improved process through the improvements made in the newly developed
machine over the existing commercially available extruded strip roll building
machines with sophisticated control systems are further explained below:
I. Metal core surface needs to match with the surface speed of the
extruded rubber strip for proper circumferential covering of the metal
core with the rubber strip.
In the commercially available machines, the surface speed of the metal
core is variable, whereas, in the newly developed machine the surface
speed of the rotating metal core is maintained constant (synchronized
with the speed of the extruded rubber strip). The surface speed of the
metal core is a function of the roll diameter (independent variable)
which is adjusted with the change in extruded rubber strip speed
irrespective of the independent variable like roll diameter e.g. for 9.0
mt/min extruded rubber strip speed, the spin of a roll with diameter
200 mm needs to be kept at 15 RPM and the same needs to be
adjusted to 10 RPM for a roll with diameter 300 mm to keep the final
surface speed of the metal core of both the rolls at 9.0 mt/min which
is equivalent to the extruded rubber strip speed. Fine tuning of the
extruded rubber strip speed is done through variable drive system of
the extruder screw only.
II. Traversing speed of the rubber strip needs to be synchronized with the
overlap width of the strip and RPM of the metal core for proper axial

covering of the metal core with the successive sequential wrapping of
the extruded rubber strip.
In the commercially available machines, the overlap width of the strip
is an independent variable, whereas, in the newly developed machine
the overlapping width of the rubber strip is made constant. Sidewise
sequential wrapping of strips can be controlled through regulating the
traversing speed (dependent variable) of the extruder mounting trolley
only and thus maintaining the constant spin/traverse rate.
Commercially available machines use different strip sections like
rectangular, parallelogram or trapezoidal. The flat overlap may be 0%
(butt joint), 25%, 50% or 75% (Fig 3 to 7). 0% overlap is used with
thin flat strip (approximately 1.5 to 2.0 mm thickness X 25 to 30 mm
width) and requires very precise spin-travel accuracy. Any gap
between successive strips would result in voids with consequent air
pocket/blister formation in the rubber covered roll. Excessive
overlapping would result in corrugated/ribbed surface of the covering
again leading to air entrapment between the layers resulting in
defective product. 25%-50%-75% overlap using parallelogram shaped
strip (width X length approximately 6X25 mm) are applied on the
metal core through inclined pressing roll only. Different percentages of
overlap are used to control cover thickness. Greater the strip overlap
higher is the rubber accumulation and it is controlled by adjusting the

spin to travel ratio through sophisticated and expensive control
systems handling several operational variables at a time.
The newly developed process utilizes rhombus shaped strip of fixed
width and fixed overlapping. Only difference made is in the height of
the rhombus shaped strip. It reduces the number of operating
variables and makes the control system simpler and user friendly e.g.
rhombus shaped strip of dimension 7.5/40 mm provides same
overlapping width of 20 mm as given a strip of 15/40 mm (Fig.8). It
provides the flexibility to the machine to develop different covering
thickness at same spin/traverse ratio.
This particular section where covering width and overlap width is
maintained at a ratio of 2:1 providing 67% covering width with 33%
overlapping has the essential advantage of giving a large strip to strip
joining surface area and +/- 5% variation in overlapping is easily
accommodated. It makes a better proposition to avoid any spiral void
formation which again could necessitate very precise spin/traverse
control.

WE CLAIM
1. An improved rubber cover building process on metal core
comprising the steps of:
maintaining the surface speed of the rotating metal core constant
irrespective of its diameter;
synchronizing the said surface speed of the rotating metal core
with the speed of the extruded rubber strip;
fine tuning the extruded rubber strip speed through variable drive
system of the extruder screw;
synchronizing traverse speed of the rubber strip with the overlap
width of the strip and rpm of the metal core;
maintaining the said overlap width constant;
controlling sidewise sequential wrapping of strips by regulating the
traversing speed of the extruder mounting trolley maintaining
spin/traverse rate constant; and
utilizing rhombus shaped strip of fixed width;
characterised in that different height of the rhombus shaped strip is
implemented to reduce number of operating variables and to
provide same overlapping width of the said strip.

2. An improved process as claimed in claim 1, wherein the said
process develops different covering thickness at same spin/traverse
ratio.
3. An improved process as claimed in claim 1, wherein the covering
width and overlapping width is maintained at a ratio of 2:1.
4. An improved process as claimed in claim 1, wherein 67% covering
width and 33% overlapping width provides a large strip to strip
joining surface area avoiding any spiral void formation.
5. An improved process as claimed in claim 1, wherein the particular
combination of strip shape along with the overlap area percentage
can accommodate at least +/- 5% tolerance without creating any
void at the seams as the thin edges of the rhombus shaped strip is
very easily smoothened by the pressing roll acting parallel to the
metal core.

An improved rubber cover building process on metal core comprises of maintaining the surface speed of the rotating metal core constant and
synchronizing it with the speed of the extruded rubber strip, fine tuning the extruded rubber strip speed, synchronizing the traverse speed of the rubber strip with the overlap width of the strip and rpm of the metal core maintaining the
overlap width constant. Then regulating the traverse speed of the extruder mounting trolley, the sidewise sequential wrapping of strips is controlled maintaining spin/traverse rate constant and a rhombus shaped strip of fixed
width is utilized with different height for different dimension of strip so that overlapping width of the strip remains same.