FIELD OF APPLICATION
The present invention relates to a rubber formulation for rubber covering rolls used in steel industry, particularly in alkaline cleaning and chromate treatment operations.
BACKGROUND OF THE INVENTION
The existing rubber covering rolls used in alkaline cleaning operation in steel industry has a short service life of only 10 to 12 days. During this period, the rolls develop a change in surface hardness and separation of layers within the rubber covering is observed. The rolls also develop edge cuts and cut marks with groove formation.
Similar problems are also encountered with rubber covering rolls used in the chromate operation. Formation of surface cracks and slippages are also observed.

Existing formulations used for rubber covering rolls in the absence of balanced properties result in the defects and associated low service life.
There was therefore, a need to develop a rubber formulation for rubber covering rolls used in the steel industry which can overcome the problems encountered with known rubber covering rolls.
SUMMARY OF THE INVENTION
The main object of the present invention therefore, is to provide a rubber formulation having a unique blend of compounding ingredients to give balance of properties required to extend the service life of the rubber covering used in alkaline cleaning and chromate operations in steel industry.
Developing an appropriate formulation involves understanding of the service requirements wherein the rubber covered rolls are to perform.

This needed several measures to be taken like studying the exact working conditions:
(a) Through visits to the plant.
(b) Going through the line working drawings and
(c) Collecting informations / reports from plant maintenance personnel.
Based on the above, an outline can be drawn as to the requirements of the rubber covering composition with respect to its various physical and chemical characteristics.
Studying thoroughly the type and nature of failure that has taken place to various rolls supplied by existing sources. The study involved (a) visual observations (b) photographic study of surface characteristics (c) measurement of various physical and chemical characteristics such as dimensions, hardness, surface topography and acetone extraction comparisons of samples of rubber coverings between working portions and non-working portions. The study also

involved examining the characteristics of failed portions to ascertain mode of failure as to whether the same is due to chemical attack, or due to heat build-up, or fatigue failure or abrasive or cutting type of failure or is due to construction or manufacturing faults like de-laminations or interfacial failure. As in many instances the nature of failure revealed that the same is due to the combined effect of various facts, further analysis had to be done to find out the predominant one involved.
Based on the above, a refinement on the requirements of the properties to be attained in the rubber covering compositions for the present invention was on the basis of the above a series of rubber covering compositions was made and their various properties were studied.
Followed by screening of the results of such compositions, several rubber formulations have been selected which were then subjected to simulated environments and based on the comparative evaluation results a few have been short listed.

A fine tuning of the selected formulations have been carried out so that those laboratory developed formulations are transferred to usable and process-able ones to real plant conditions. Such fine tuned compositions again have undergone simulated service tests and finally have been used in actual roll manufacturing.
Thus the present invention provides a rubber formulation for rubber covering rolls used in steel industry comprising: compounding ingredients for giving a balance of properties required for extending the service life of said rubber covering in alkaline cleaning and chromate operations.
A rubber composition using concentrated PF iresin a balance of properties can be provided for improving the service life in the alkaline section. In the chromate section an epoxy resin can be incorporated in the polymer.

In one embodiment of the present invention the composition of the rubber formulation based on NBR for use in alkali section comprises:
NBR - 100, Sulphur - 1, ZnO - 15, Steraic Acid - 1.5, HS/TQ - 1.5, MB - 1.5, CI Resin - 4, PF Resin - 10, HAF - 30, SRF - 15, T 90 - 3, DOP - 4, PVI - 0.5, CBS -1.5.
In another embodiment of the present invention the composition of the rubber formulation based on Hypalon for chromate section comprises:
Hypalon - 100, epoxy - 10, NBC - 1, SRF - 30, CI Resin - 3, TQ - 2, PEG -1, DOP - 8, Spindle Oil - 6, Ivamol - 4, MBTS - 0.5, Tetron A - 0.75, DOTG - 0.5, Sulphur -1.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of the figures of the accompanying drawings in which:
Figures la
and b show defects in rolls - edge cuts - groove marks.
Figure 2 shows degreasing Section (Alkali and hot water rinsing).

Figure 3 shows degreasing Area Section.
Figures 4a, b
4c and d show defects in rolls at Allkali Rinsing Area edge cuts - groove marks, layer separation probably liquid penetration in pin hole -manufacturing problem, mechanical damage - difficult to explain.
Figure 5 shows defects in rolls - edge cuts.
Figure 6 shows defects in rolls at water rinsing area -edge cuts - cut marks on roll surface.
Figure 7 shows no cut or edge mark observed after 34 days of use
Serverity of groove formation after 34 days of use is negligible.
Figure 8 shows rolls have not been taken out and continued for run till further
Very fine groove formation at both ends after use of 34 days Rolls being re-grinded and rre-installed
Figure 9 shows at hot rinsing section the alkali sediment is
covered on the roll and due to this slippage is occurring. Very fine groove formation at both ends after use of 34 days. Rolls being re-grinded and re-installed.

DETAILED DESCRIPTION
The present invention can now be described with the help of photographs of the rubber covering rolls.
For the rubber covering rolls for the alkaline section nital and neoprene rubber are exclusively used. For the chromate section ESP rubber is used. The edge cuts and groove marks developed in existing rubber covering rolls are shown in
Figures l(a) and l(b). Figures 2 and 3 show the alkali section where neoprene based rubber covering rolls are being used. The development of edge cuts and groove marks are shown in Figure 4(b). Layer separation, possibly because of liquid penetration through pin holes, is shown in Figure 4(c). Other mechanical defects developed during use can be seen in Figure 4(d).
Figures 5 and 6 show in enlarged view the development of edge cuts and cut marks in the rubber covering rolls.
Table 1 and Table 2 show the data on the existing roll life in the alkali section and Table 3 gives the data sheet for the chronnate section.

In order to meet the conflicting demands of the working environments, different formulations were tried. A special rubber covering composition with unique blend of compounding ingredients providing balance of properties was developed for each of the two areas of operation.
The composition of the formulations of the present invention for the two operations are shown below.
COMPOSITION FOR ALKALI SECTION

As shown in Figure 7, no cut or edge mark was observed after 34 days of use. The severity of groove formation after 34 days of use was negligible. After taking out for continued run beyond 34 days, rolls were regrinded for removing very fine formation of grooves at the two ends, as shown in Figure 8.
At the hot rinsing section, occurrence of slippage was observed due to alkali sediment covering the roll. After use for 34 days very fine groove formation was observed and the roll was regrinded and reinstalled (Figure 9).
Thus, by using concentrated PF resin in the rubber composition for the alkaline section and by incorporation epoxy resin the polymer for the chromate section a balance of properties can be provided resulting in improved surface life.
The extension of service life of the rubber covering rolls will also yield other benefits like shorter breakdown time, reduced shutdown frequency, uninterrupted production and reduction in cost due to reduced consumption of rubber rolls. Reduction in maintenance cost and rejections on account of quality may be considered as other benefits accruing from the present invention.

WE CLAIM;
1. A rubber formulation for rubber covering rolls used in steel industry wherein
said formulation is based on hypalon for use in chromate section comprising:
Hypalon - 100, epoxy - 10, Nickel-di-n-butylldithicarbamate-1, Semi-reinforced
Furnace Black - 30, Coumarone indene Resin-3, TQ - 2, Polyethylene glycol-1,
Dloctyl pthalate-8, Spindle Oil - 6, Epoxidized vegetable oil - 4, Dibenzthiazyl
disulphide - 0.5, Dipentamethylenethiuramhexasuphide - 0.75, N,NDi-O-
Tolyguanidine - 0.5, Sulphur -1, for giving a balance of properties required for
extending the service life of said rubber covering in chromate operations.
2. The rubber as claimed in claim 1, wherein an epoxy resin Is incorporated in
the polymer for using the rubber covering in chromate section for balance of
properties to obtain improved service life.
3. A rubber formulation for rubber covering rolls used in steel industry,
substantially as herein described and illustrated in the accompanying drawings.

The main object of the present invention therefore, is to provide a rubber formulation having a unique blend of compounding ingredients to give balance of properties required to extend the service life of the rubber covering used in alkaline cleaning and chromate operations in steel industry.
Developing an appropriate formulation involves understanding of the service requirements wherein the rubber covered rolls are to perform.
This needed several measures to be taken like studying the exact working conditions:
(a) Through visits to the plant.
(b) Going through the line working drawings and
(c) Collecting informations / reports from plant maintenance personnel.
Based on the above, an outline can be drawn as to the requirements of the rubber covering composition with respect to its various physical and chemical characteristics.
Studying thoroughly the type and nature of failure that has taken place to various rolls supplied by existing sources. The study involved (a) visual observations (b) photographic study of surface characteristics (c) measurement of various physical and chemical characteristics such as dimensions, hardness, surface topography and acetone extraction comparisons of samples of rubber coverings between working portions and non-working portions. The study also involved examining the characteristics of failed portions to ascertain mode of failure as to whether the same is due to chemical attack, or due to heat build-up, or fatigue failure or abrasive or cutting type of failure or is due to construction or manufacturing faults like de-laminations or interfacial failure. As in many instances the nature of failure revealed that the same is due to the combined effect of various facts, further analysis had to be done to find out the predominant one involved.
Based on the above, a refinement on the requirements of the properties to be attained in the rubber covering compositions for the present invention was on the basis of the above a series of rubber covering compositions was made and their various properties were studied.
Followed by screening of the results of such compositions, several rubber formulations have been selected which were then subjected to simulated environments and based on the comparative evaluation results a few have been short listed.
A fine tuning of the selected formulations have been carried out so that those laboratory developed formulations are transferred to usable and process-able ones to real plant conditions. Such fine tuned compositions again have undergone simulated service tests and finally have been used in actual roll manufacturing.
Thus the present invention provides a rubber formulation for rubber covering rolls used in steel industry comprising: compounding ingredients for giving a balance of properties required for extending the service life of said rubber covering in alkaline cleaning and chromate operations.
A rubber composition using concentrated PF iresin a balance of properties can be provided for improving the service life in the alkaline section. In the chromate section an epoxy resin can be incorporated in the polymer.