Title of Invention	METHOD OF WET TEMPER ROLLING IN A SKIN PASS MILL AND APPARATUS FOR SAME
Abstract	The invention relates to a method of wet tamper rolling in a skin pass mill comprising applying an emulsion made of a temper fluid to annealed steel strips prior to and/or during the step of rolling. The emulsion carried by the strip from the step of rolling is wiped by mechanical wiping pads and the wiped strip to air dried.

Full Text

FIELD OF INVENTION The present invention related to a method for temper rolling of cold rolled steel and apparatus for carrying out such method. More particularly the invention relates to a method and apparently for wet temper rolling of cold rolled steel strips to obtain improved surface characteristics. BACKGROUND OF INVENTION : The basic purpose of temper rolling in to suppress the yield point extension characteristic of most low-carbon annealed steels so that the material may be subsequently formed without the formation of Luder's lines. The other reasons for temper rolling are : - to attain the required metallurgical properties like hardness, yield strength and elongation. - to provide improved strip surface finish in terms of RMS roughness value and the peak counts per inch for better paintability. - to provide desired degree of flatness/shape of cold rolled strips. - to attain desired degree of magnetic properties of electrical steel (low core loss and high permeability). - to break up spangles, eliminate curtains and correct flaws of galvanized, aluminates and other coated products. DRY TEMPER ROLLING The usually practiced temper rolling is known as dry temper rolling. Dry temper rolling is used extensively for flattening strip and correcting shape defects incurred during cold reduction process at Tandem Cold Mills. During 2 temper rolling, the amount of reduction is designed to be enough to eliminate yield-point extension and gross Luder's bands, the reduction is kept as low as possible (0.5 to 2.0%) so that excessive strengthening and loss of ductility do not occur. That is why, normally the temper mills are operated without lubricant i.e. dry temper rolling. The applicants have identified major shortcomings of dry temper rolling. In dry temper rolling the roll campaign life in shorter due to lack of lubrication and generates loose dusts and iron fines from the strip surface due to dry friction. These loosen dusts and debris from the strip surface are picked up by the work rolls and subsequently imprint on the strip surface resulting in poor surface quality and effects cleanliness of the steel strip. This problem is serious in nature and known as mill pick-up. In order to avoid mill pick-up and poor strip surface quality, the mill operator oftenly clean the work roll surface with expensive cleanser for improving strip surface quality and mill undergoes frequent stopping for cleaning of rolls. During dry temper rolling, the faster roll wear also takes place and affects the surface roughness of the rolled strip, resulting to gradual decrease in the RMS values and peak count values. The inventors have found that the shortcomings associated with the dry temper rolling may be alleviated by providing a wet temper rolling in a skin pass mill in which the annealed steel strips during and/or prior to the step of rolling is applied with an emulsion. Thus the present invention relates to a method of wet temper rolling in a skin pass mill comprising : applying an emulsion to the annealed steel strips prior to and/ or during the step of rolling. According to a preferred embodiment of the invention the method of wet temper rolling in a skin pass mill comprises the steps of 3 applying an emulsion to the annealed steel strips prior to and/or during the step of rolling ; wiping the emulsion carried by the strip from the step of rolling ; subjecting the wiped strip to air drying. According to a further preferred embodiment of the invention there is provided a method of wet temper roiling in a skin pass mill comprising: preparing a temper fluid emulsion of a base synthetic fluid ; applying the emulsion to the annealed steel strips prior to and/or during the step of rolling by means of emulsion spray headers located at the entry side of the mill stand ; wiping carry-over emulsions from the surface of the back up rolls by the use of a mechanical wiper pads ; subjecting the rolled strip to wiping by air blow-off system using air blow-off nozzles. The method according to the invention is carried out by the use of a specially designed apparatus comprising means for applying an emulsion to the annealed steel strips prior to and/or during the step of rolling. According a preferred aspect of the invention the apparatus comprises : means for preparing and storing the emulsion ; means for spraying the emulsion on the strip during rolling operation at the entry wide of the mill stand, said means comprising one or more 4 nozzles being provided for discharge of the emulsion on to the strip surface from a predetermined height and angle ; a wiper pad for wiping the carried away emulsion from the back up rolls ; air blow-off nozzles provided at a position before the coiling of the strip so as to arrest carry over of the emulsion, said air blow-off nozzles being air knife nozzles for delivering air knife curtain over the strip surface in the form of an divergent air spray at high velocity and high impact force. The invention will now be illustrated with reference to a specific working example in a typical apparatus which is also described with reference to accompanying drawings in which Fig. 1 shows a schematic diagram of the skin pass mill with arrangement for wet temper rolling ; Fig. 2 shows a diagram of the emulsion application header ; Fig. 3 shows a diagram of air wiper header; Fig. 4(a) and 4(b) shows front and side sectional views of the air wiping header; Fig. 5(a) to 5(c) shows configuration of the nozzles from different sides. The temper fluid used for wet temper rolling is an aqueous base synthetic 1 fluid which was having sufficient detergency property to wash away the iron fines and debris from the strip surface. The synthetic fluid is selected from synthetic esters. The incoming strip surface after batch annealed cold rolled strips have surface reflectance in the range of 50 to 60%. With the use of this temper fluid the strip surface reflectance has improved to 85 to 90%, whereas with the dry temper rolling the average strip surface reflectance was in the range of 70 to 80%. Beside this the wet tempered coil surface was found to be protected against corrosion for at least 10 to 15 days without application of rust preventive oil. 5 The emulsion was being prepared in the premix tank (1) of 3.0 M3 capacity (1.5 X 1.5 X 1.3 m) for easy handling of fluid (Di-Mineralized water and temper fluid) and maintenance. The different concentration level of emulsion were tried at the mill and it has been optimized at 3 to 3.5% concentration (by volume) which has given the desired property considering strip surface reflectance, wetting property and temporary surface protection against corrosion. Higher the concentration having better cleanliness property but not in direct proportional, but it involves high specific oil consumption and low cost benefit ratio as the fluid is costly. With the use of 3 to 3.5% concentration the specific consumption of fluid was maintained 0.3 lit/ton. The temper fluid and di-mineralized water are mixed in the premix tank of desired volume to maintain a concentration level of 3-3.5%. The pre-mix emulsion was then transferred to main tank (1) of capacity 3.0 M3. The emulsion was thoroughly agitated at a slow speed with an agitator (13) for maintaining the uniform concentration level, for at least 15 minutes. The emulsion was pumped to emulsion spray header (9) located at mill stand by the use of centrifugal pump and motor (2), through fine cartridge type filter (6) of 50 micron and pressure relief valve (3) for uniform emulsion pressure at 2.0 bar and constant flow-rate. The premix tank is also connected to an oil pressure gauge (4) and non return valve (5) a filter (6), diaphragm valve (7), gate valve (8) for transmitting the temper fluid to the mill stand. An emulsion spray header (9) is located at the entry side of the mill stand and the spray of emulsion takes place from both the sides (S1 & S2) of strip surface at a distance half a metre before the roll bite such that the emulsion washes away the loose iron fines and debris from the strip surface and also can have good wetting property with certain retain period for the high mill speed of 1200 to 1800 mpm. The impinge spray angle is maintained at 20 degree to the vertical towards the rolling direction in order to avoid the bouncing off the emulsion and smooth carry over of emulsion to the roll-nip. The spray header (9) consisting of 4 nos. flat jet nozzles (18) are interspaced at 6 400 mm with an off-set angle 15 degree such that each spray are not interfered by the adjacent spray and each spray are over-lapped by 25% of spray width. The nozzles (18) are being selected with flow rate of 2.5 1pm at 2 bar emulsion and can deliver spray width of 500 mm at a spray height of 250 mm. The spray angle of nozzle is optimized at 90 degree for lesser number of nozzle in use with higher spray width, which has resulted to uniform and full coverage strip width 1500 to 1800 mm and avoided chance of emulsion carry over with reduced specific oil consumption. The nozzle chocking phenomenon has been avoided with the use of higher bore size nozzle and higher degree of filtration. The mechanical wiper pads (11',11") for back-up rolls (17) are designed and retro-fitted to the mill stand in such a way that the wiper pads (11', 11") is always pressed to the back-up roll surface through high compression spring loading action. The material of wiper pads (11', 11") is used with Nitrite Rubber which is much softer and having cushioning effect and resistant chemically to the temper fluid solution and high abrasive strength. The wiper pads (11', 11") can be swivelled and locked as per the desired contact angle. The top wiper pad (11") is fitted to 60° to the vertical at the entry size where as the bottom wiper pad (11") is fitted at 60° to the vertical at the delivery side in order the avoid the emulsion splashing/carry-over at the exit side. The temper fluid emulsion is fed to the emulsion spray header by a needle valve (14) and diaphragm valve (7). The available compressed air is being made moist free through air dryer (12). The type of air dryer selected is heatless type for continuous and smooth operation and least maintenance and connected to the air blow-off system by gate valve (16) and air distributor valve (15). The requisite air volume calculated for wiping on both the surface of strip width 1850 mm was 700 m3/hr. On the basis of design requirement the air dryer installed of 750 m3/hr capacity with the pre-filter, twin drying tower with automatic change 7 over and after filter for getting a continuous air volume of 700 m3/hr (minimum) at a pressure of 5.0 bar. The air dryer (12) is installed at very close to mill stand and the discharge end such that the minimum pressure drop of 0.3 to 0.5 bar in allowed. The critical process parameter during wet temper rolling is the effective air wiping on both the strip surface for arresting emulsion carry-over completely from the strip surface prior to coiling. Special type of air knife nozzles (19). These nozzles (19) are having special configuration for delivering a perfectly air knife curtain over the strip surface. These nozzles (19) are fabricated from stainless steel and special designed for divergent spray with high velocity and impact force. Due to divergent type of spray less number of nozzles can be used with proper over lapping. The air wiping header (10) is made up of 80 NB seamless pipe and fitted with end trunion bracket (20) for adjustment of angle of impinging as per requirement. The headers (10) are placed on the both side of strip surface at a distance half a metre away from the roll bite. The impinging angle of spray was made 25 to 30 degree to the vertical for effective blowing off the carried emulsion from the strip surface with a spray height of 200 (max). The end connection of header (10) is fitted with quick-fix type coupling for ease dismantling and installation. The air blow-off header (10) consists of 11 no. of these specially designed nozzles (19) for wiping a strip width of 1850 mm. 7 of the nozzles are interspaced with 200 mm at the centre portion and rest 4 nozzles at the edges are interspaced with 100 mm. These nozzles are made off-set by 15° in order to avoid the interference of individual spray. The nozzles (19) are fitted with Chevron concept such that firstly the emulsion will be the arrested at the centre portion and gradually the arrested emulsion will be driven-off from the edges of the strip. The spray width of the nozzles is designed for 350 mm at a spray height of 200 mm. This design of air blow-off system has helped to 8 arrest emulsion carry-over completely and thus avoided the staining/rusting of strip surface after wet tempering. The specific designs of the mill shown in the drawing is a typical design and described with specific process parameters. Such illustrations are only for a clear understanding of the invention and not to limit the scope of the invention to the typical design or method. The invention covers several other designs and methods based on the same inventive concept. The major advantages of wet temper rolling invented by the applicant are as under: ? It provides a small amount of lubrication which helps to enhance roll life by 20%. ? It reduces the gradual decrease in strip surface roughness. ? It helped to increase the mill speed from 1000 to 1200 mpm leading to higher productivity. ? It avoided frequent stopping of mill for cleaning the work roll with cleanser. ? It reduces the mill load by 20%. ? It improved strip surface reflectance from-70% to over 90%. ? It also improved strip flatness and profile. As much no special machinery used for fabrication and erection of the wet skin pass system. 9 We claim: 1. A method of wet temper rolling in a skin pass mill comprising : applying temper fluid an emulsion being an oil water emulsion of an oil selected from synthetic esters to annealed steel strips prior to and/or during the step of rolling; wiping the emulsion carried by the strip after the step of rolling ; and subjecting the wiped strip to air drying. 2. A method as claimed in claim 1 wherein - the emulsion is applied to the annealed steel strips prior to and/or during the step of rolling by means of emulsion spray headers located at the entry side of the mill stand ; - emulsions are wiped from the surface of the back up rolls by the use of a mechanical wiper pads ; and -the rolled strip is subjected to wiping by air blow-off system using air blow-off nozzles. 3. An apparatus for carrying out the method of claim 1 in a skin pass mill comprising means for preparing and storing the emulsion ; means for spraying the emulsion on the strip during rolling operation at the entry side of the mill stand, said means comprising one or more nozzles being provided for discharge of the emulsion on to the strip surface from a predetermined height and angle ; means for wiping the carried away emulsion from the back up rolls ; air blow-off nozzles provided at a position before the coiling of the strip so as to arrest carry over of the emulsion, said air blow-off nozzles being air knife nozzles for delivering air knife curtain over the strip surface in the form of an divergent air spray at high velocity and high impact force. to 4. An apparatus as claimed in claim 3, wherein means for preparing the emulsion is a premix tank and is stored in a main tank. 5. An apparatus as claimed in claim 3, wherein the means for spraying the emulsion on the strip during rolling operation comprises a plurality of spray headers located at mill stand being in communication with a pump which pumps the emulsion to the spray headers through fine cartridge type filter and pressure relief valves for uniform emulsion pressure and constant flow rate. 6. An apparatus as claimed in claim 5, wherein the emulsion spray headers are located at the entry side of the mill stand on either side of the strip surface. 7. An apparatus as claimed in claim 3, wherein means for wiping the carried away emulsion from the back up rolls are mechanical wiper pads being adapted to be pressed to the back-up roll surface through high compression spring loading action. 8. An apparatus as claimed in claim 3, wherein air blow-off nozzles are heatless air drying type nozzles and being connected to a pre-filter and drying tower. 9. An apparatus as claimed in anyone of claims 3 to 8, optionally comprising an air blow-off system for wiping both the strip surface for arresting emulsion carry-over completely from the strip surface prior to coiling, 10.An apparatus as claimed in claim 9, wherein the nozzles used for air blow-off system are air knife nozzles for delivering an air knife curtain over the strip surface. Dated this 13 day of March 2000. The invention relates to a method of wet tamper rolling in a skin pass mill comprising applying an emulsion made of a temper fluid to annealed steel strips prior to and/or during the step of rolling. The emulsion carried by the strip from the step of rolling is wiped by mechanical wiping pads and the wiped strip to air dried.

Documents:

00152-cal-2000 abstract.pdf

00152-cal-2000 claims.pdf

00152-cal-2000 correspondence.pdf

00152-cal-2000 description(complete).pdf

00152-cal-2000 drawings.pdf

00152-cal-2000 form-1.pdf

00152-cal-2000 form-18.pdf

00152-cal-2000 form-2.pdf

00152-cal-2000 form-3.pdf

00152-cal-2000 pa.pdf

152-cal-2000-granted-abstract.pdf

152-cal-2000-granted-claims.pdf

152-cal-2000-granted-correspondence.pdf

152-cal-2000-granted-description (complete).pdf

152-cal-2000-granted-drawings.pdf

152-cal-2000-granted-examination report.pdf

152-cal-2000-granted-form 1.pdf

152-cal-2000-granted-form 19.pdf

152-cal-2000-granted-form 2.pdf

152-cal-2000-granted-form 3.pdf

152-cal-2000-granted-letter patent.pdf

152-cal-2000-granted-pa.pdf

152-cal-2000-granted-reply to examination report.pdf

152-cal-2000-granted-specification.pdf