Title of Invention

IMPROVED RUBBER CLAD ROLLS FOR THE MANUFACTURE OF CONTINUOUS GALVANIZED STEEL SHEETS

Abstract

An improved rubber clad roll for continuous galvanizing lines (CGL) and planetary tandem continuous mill (PLTCM) comprising an optimum rubber covering composition suitable for the physical and chemical characteristics demanded by the service conditions of said rubber clad rolls while said rubber covering for alkali section rolls has a composition of: Sulphur 1.0 Zno 15 Stearic acid 1.5 2,2,4-trimethyl-l ,2,-dihydroquinoline 1.5 polymerized (HS/TQ) 2-mercapto benz (MB) 1.5 coumarone indene resin (C I Resin) 4.0 PF resin 10 high abrasion furnace black (HAF) 30 semi-reinforcing furnace black(SRF) 15 polyester resin (T 90) 3.0 di-n-octyl phthalate (DOP) 4.0 N-(cyclohexylthio) phthalimide (PVI) 0.5 N-cyclohexyl-2-benzothiazolesulphenamide 1.5 (CBS)

Full Text

FIELD OF APPLICATION The present invention relates to improved rubber clad rolls for the manufacture of continuous galvanized steel sheets. In particular, it relates to cladding rolls of cold rolling mill with improved rubber compound. BACKGROUND OF THE INVENTION During the production of galvanized sheets in a continuous galvanizing line the steel sheets are passed through acid (HCL) for pickling. In order to remove the carry over acid from the sheets, the rolls are passed through an alkali medium followed by passing through the squeeze rolls for absorbing the left over alkali. The steel sheet is then passed through chromate section followed by squeeze rolling. In the case of planetary tandem continuous mill (PLTCM) after pickling to eliminate the carry over acid the sheet is passed through a cleaning section followed by rolling with wringer rolls. Rubberized rolls are used extensively as squeeze rolls, wringer rolls for the production of galvanized steel sheet. These rolls have very short life and fail within a maximum period of 10 - 12 days under the production condition. This causes frequent shut down of the plant, to replace rolls and this hampers production of steel sheet. Apart from short service life, rubber covering used in Alkaline / chromate cleaning section used to fail due to (a) change in surface hardening, (b) surface cracks formation, (c) layer separation within rubber covering, (d) groove formation, (e) slippage and (f) cut. The objective should be to minimize and eliminate these failures. There was therefore, a need to develop better rubber compounds and manufacturing techniques to increase life of these rolls. SUMMARY OF THE INVENTION The main object of the present invention is to improve the quality of the rubberized rolls used in continuous galvanizing lines and planetary tandem continuous mills which will lead to increase in life of the rolls. This and other objectives of the present invention can be achieved by providing an optimum rubber covering composition suitable for the physical and chemical characteristics required for the rubber cladding. Understanding the service requirements wherein the rubber covered rolls are to perform is very important. This needed several measures to be taken like studying the exact working conditions through visits to the plant, going through the line working drawings and collecting informations / report from plant maintenance personnel. Based on the above, an outline was drawn as to the requirements of the rubber covering composition with respect to its various physical and chemical characteristics. The type and nature of failure that has taken place to various rolls supplied by existing sources were studied thoroughly. 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 mentioned study a refinement on the requirements of the properties to be attained in the rubber covering compositions has been proposed for the present invention. On this a series of rubber covering compositions were made and their various properties have been studied. After 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 selections were made. 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. The key point of the present invention lies in attaining a unique balance between the various physico-chemical properties demanded by the service conditions of the rubber rolls. Accordingly two approaches have been taken; one to improve the original properties of the rubber coverings and the other to maintain the attained properties with minimum change with time at the working conditions prevailing which may involve reaction with chemicals, higher temperatures, dynamic stress-strain cycle and cutting and abrasive conditions. For the planetary tandem continuous mill both NBR based and chloroprene based rubber coverings have been found to increase the life of the rolls. In Alkali sections of continuous galvanizing line, the blending of polymers with PF resins provided excellent resistance against chemical attack maintaining other physical properties such as cut and abrasion resistance etc. While in chromate section of continuous galvanizing line, the inclusion of epoxy resins provided not only increased cross - linking of the polymer but also improved the acid resistance property along with maintenance of physical properties which are so crucial in the cruel working conditions involved. Thus the present invention provides an improved rubber clad roll for continuous galvanizing lines (CGL) and planetary tandem continuous mill (PLTCM) comprising an optimum rubber covering composition suitable for the physical and chemical characteristics demanded by the service conditions of said rubber clad rolls. BREIF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention can now be described in detail with the help of the figures of the accompanying drawing in which Figure 1 shows separation of layers in the existing rubber cladding. Figure 2 shows formation of edge cuts and groove marks on the existing rubber rolls. Figure 3 shows groove formation and shallow surface cracks in rolls at chromating section. Figure 4 shows groove formation at edges in chromating section squeeze rolls. Figure 5 shows in line diagram form the continuous galvanizing line (CGL) where the present invention is applied. Figure 6 is a line diagram for planetary tandem continuous mill (PLTCM) where the present invention is applied. DESCRIPTION OF THE INVENTION Figures 1 and 2 respectively show the failure in existing rubber rolls by layer separation probably due to liquid penetration in pin hole and edge cuts with groove formation. In the chromating section the defects develop due to groove formation resulting in carry over with no edge cut problem. Shallow surface cracks develop which disappear after grinding. Hardness after service is 65-85 shore A. (Figure 3). Figure 4 shows the defects in chromating section squeeze rolls with problem of groove formation at edge resulting in carry over. A continuous galvanizing line shown in Figure 5 produces galvanized sheets for commercial market. Cold rolled strips in the thickness range of 0.80 mm to 9.18 mm are processed in this line for galvanizing. In the degreasing section the strip is first washed with 4 % NaOH solution and followed by hot water at 60 - 900° C to clean the strip surface for zinc coating. In degreasing section four pairs of rubber clad rolls are used to squeeze the degreasing medium from strip surface and prevent solution carry over inside the furnace. After degreasing the strip is baked inside a furnace and subsequently galvanized by hot dip galvanizing method. After galvanizing, the coated strip is quenched in water. Two pairs of rubber clad rolls are used to squeeze the water from the strip surface. After galvanizing the strip is passed through chromating section. Here the strip is treated with 2.5 - 3.5 % chromic acid at 60 - 900° C. In chromating section another four pairs of rubber clad rolls are used to squeeze the chromic acid solution before the strip goes to recoiler. Figure 6 shows the planetary tandem continuous mill (PLTCM). Input material for the PLTCM line is hot rolled coils of 2 to 6 mm thickness and 900 to 1580 mm width. Hot rolled coils are pickled in HCL and cold reduced to required thickness in this line. Area 1 as marked in Figure 6 contains the first critical set of rubber covered rolls in the line. These rolls are termed as wringer rolls. Number of rubber covered rolls are used in the pickling area marked as Area 2 in Figure 6. There are four numbers of pickling tanks and HCL concentration gradually increases from tank 1 to tank 4. After acid pickling and before water rinsing section, two pairs of rubber covered rolls are used for squeezing which are termed as steering wringer rolls. There are four tanks for water rinsing and six pairs of rubber covered rolls are used in the water rinsing section. Out of the six pairs, first four pairs are called squeeze rolls and the end two pairs of rolls are called as wringer rolls. After water rinsing the coil is hot air dried and goes for cold reduction in 5 strand tandem mill. The formulations for improved rubber flats provided by the present invention are shown in Tables 1 to 4. Table 1 shows the rubber formulation used in the present invention for the alkali section of the continuous galvanizing line. Table 2 shows the formulations used in the chromate section. The formulations used for the planetary tandem continuous mill (PLTCM) are shown in Tables 3 and 4. The formulation of Table 3 uses acrylo nitrile butadiene rubber (NBR) based compound. The formulation given in Table 4 uses a chloroprene based compound. Tables 5 and 6 show comparative evaluation of physico-chemical properties of existing rubber covering vis-a-vis those of the rubber coverings of present invention. The tables show wide variation in change in properties of existing rolls before and after use. At the same time the rubber rolls of the present invention reveal uniform change in properties before and after use of the rolls. The rolls developed by the present invention do not show any signs of major failure like surface crack, groove formation, edge cut, layer separation, slippage etc. Also there is no change in properties after continuous running. Moreover, extension of service life yields benefits in terms of (a) less breakdown time (b) reduction in frequency of shutdown, (c) uninterrupted production, (d) cost effectiveness due to less consumption of rubber rolls, (e) reduction of maintenance cost and (0 reduced rejection of rolls on the basis of quality. In the present invention the life of the rolls has been increased from 2 to 12 days to 35 days upto first grinding and 105 days after first grinding for alkali section of continuous galvanizing lines (CGL 1), 50 days upto first grinding and 120 days after first grinding for chromate section of continuous galvanizing line (CGL 1), and 90 days without any grinding for the wringer rolls of planetary tandem continuous mill (PLTCM). WE CLAIM ; 1. An improved rubber clad roll for continuous galvanizing lines (CGL) and planetary tandem continuous mill (PLTCM) comprising an optimum rubber covering composition suitable for the physical and chemical characteristics demanded by the service conditions of said rubber clad rolls wherein said rubber covering for alkali section rolls has a composition of: Sulphur 1.0 Zno 15 Stearic acid 1.5 2,2,4-trimethyl-1,2,-dihydroquinoline 1.5 polymerized (HS/TQ) 2-mercapto benz (MB) 1.5 coumarone indene resin (C I Resin) 4.0 PF resin 10 high abrasion furnace black (HAF) 30 semi-reinforcing furnace black(SRF) 15 polyester resin (T 90) 3.0 di-n-octyl phthalate (DOP) 4.0 N-(cyclohexylthio) phthalimide (PVI) 0.5 N-cyclohexyl-2-benzothiazolesulphenamide 1.5 (CBS) 2. The improved rubber clad roll as claimed in claim 1, wherein the rubber covering for said rolls for the alkali section of the CGL is acrylo nitrile butadiene (NBR) with polymers blended with PF resin. 3. The improved rubber clad rolls as claimed in claim 1, wherein the covering for rolls used in chromate section of the CGL are provided with epoxy resins. 4. The improved rubber clad rolls as claimed in claim 3, wherein said roll covering has the following composition: epoxy 10 nickel di-n-butyldithiocarbamate (NBC) 1 Semi-reinforcing furnace black (SRF) 30 coumarone indene resin (CI Resin) 3 dihydroquinoline polymerized (TQ) 2 poly ethylene glycol (PEG) 1 di-n-octyl phthalate (DOP) 8 spindle oil 6 Epoxidized vegetable oil (Ivamol) 4 dibenzthyiazyl disulphide (MBTS) 0.5 dipentamethylenethiuramhexasulphide 0.75 (Tetron A) N,N'-di-o-tolylguanidine (DOTG) 0.5 Sulphur 1 5. The improved rubber clad rolls as claimed in claim 1, wherein the covering for rolls used in PLTCM is based on acrylo nitrile butadiene rubber (NBR) having the following composition: Sulphur 1.0 ZnO 15 Stearic acid 1.5 2,2,4-trimethyl-l,2,-dihydroquinoline 1.5 polymerized (HS/TQ) 2-mercapto benz (MB) 1.5 coumarone indene resin (CI Resin) 4.0 high abrasion furnace black (HAF) 30 semi-reinforcing furnace black (SRF) 27 polyester resin (T 90) 3.0 di-n-octyl phthalate (DOP) 4.0 N-(cyclohexylthio) phthalimide (PVI) 0.5 N-cyclohexyl-2-benzothiazole 1.5 sulphenamide (CBS) 6. The improved rubber clad rolls as claimed in claim 1, wherein the covering for rolls used in PLTCM is based on chloroprene rubber (neoprene W) having the following composition : MgO 4 Stearic Acid 1.5 coumarone indene resin (CI Resin) 4 octylated diphenylamine (OCD) 1 intermediate super abrasion furnace black 40 ISAF (N220) N-(l,3 dimethyl butyl)'-N'-phenyl-p- 1 phenylene diamine (4020) Veg Oil 3 dibenzthyiazyl disulphide(MBTS) 1.3 ZnO 5 ethylene thiourea (NA-22) 0.7 7. An improved rubber clad roll for continuous galvanizing lines (CGL) and planetary tandem continuous mill (PLTCM), substantiall as substantially as herein described and illustrated in the accompanying drawings. An improved rubber clad roll for continuous galvanizing lines (CGL) and planetary tandem continuous mill (PLTCM) comprising an optimum rubber covering composition suitable for the physical and chemical characteristics demanded by the service conditions of said rubber clad rolls while said rubber covering for alkali section rolls has a composition of: Sulphur 1.0 Zno 15 Stearic acid 1.5 2,2,4-trimethyl-l ,2,-dihydroquinoline 1.5 polymerized (HS/TQ) 2-mercapto benz (MB) 1.5 coumarone indene resin (C I Resin) 4.0 PF resin 10 high abrasion furnace black (HAF) 30 semi-reinforcing furnace black(SRF) 15 polyester resin (T 90) 3.0 di-n-octyl phthalate (DOP) 4.0 N-(cyclohexylthio) phthalimide (PVI) 0.5 N-cyclohexyl-2-benzothiazolesulphenamide 1.5 (CBS)

Documents:

00485-kol-2006-abstract-1.1.pdf

00485-kol-2006-abstract.pdf

00485-kol-2006-claims.pdf

00485-kol-2006-correspondence others-1.1.pdf

00485-kol-2006-correspondence others.pdf

00485-kol-2006-correspondence-1.2.pdf

00485-kol-2006-description(complete).pdf

00485-kol-2006-description(provisional).pdf

00485-kol-2006-drawings-1.1.pdf

00485-kol-2006-drawings.pdf

00485-kol-2006-form-1-1.1.pdf

00485-kol-2006-form-1.pdf

00485-kol-2006-form-2-1.1.pdf

00485-kol-2006-form-2.pdf

00485-kol-2006-form-3.pdf

00485-kol-2006-form-5.pdf

00485-kol-2006-g.p.a.pdf

485-KOL-2006-ABSTRACT 1.1.pdf

485-KOL-2006-AMANDED CLAIMS.pdf

485-KOL-2006-CORRESPONDENCE 1.1.pdf

485-KOL-2006-CORRESPONDENCE.pdf

485-KOL-2006-DESCRIPTION (COMPLETE) 1.1.pdf

485-KOL-2006-DRAWINGS 1.1.pdf

485-KOL-2006-EXAMINATION REPORT REPLY RECIEVED.pdf

485-KOL-2006-EXAMINATION REPORT.pdf

485-KOL-2006-FORM 1-1.2.pdf

485-KOL-2006-FORM 18 1.1.pdf

485-kol-2006-form 18.pdf

485-KOL-2006-FORM 2-1.1.pdf

485-KOL-2006-FORM 3.pdf

485-KOL-2006-FORM 5.pdf

485-KOL-2006-GPA.pdf

485-KOL-2006-GRANTED-ABSTRACT.pdf

485-KOL-2006-GRANTED-CLAIMS.pdf

485-KOL-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

485-KOL-2006-GRANTED-DRAWINGS.pdf

485-KOL-2006-GRANTED-FORM 1.pdf

485-KOL-2006-GRANTED-FORM 2.pdf

485-KOL-2006-GRANTED-SPECIFICATION.pdf

485-KOL-2006-OTHERS.pdf

485-KOL-2006-REPLY TO EXAMINATION REPORT 1.1.pdf

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