Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B27/00—Other grinding machines or devices
  • B24B27/033—Other grinding machines or devices for grinding a surface for cleaning purposes, e.g. for descaling or for grinding off flaws in the surface
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D13/00—Wheels having flexibly-acting working parts, e.g. buffing wheels; Mountings therefor
  • B24D13/02—Wheels having flexibly-acting working parts, e.g. buffing wheels; Mountings therefor acting by their periphery
  • B24D13/10—Wheels having flexibly-acting working parts, e.g. buffing wheels; Mountings therefor acting by their periphery comprising assemblies of brushes
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0242—Flattening; Dressing; Flexing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/02—Rolling special iron alloys, e.g. stainless steel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the object of the present invention is to economically produce a scale-free, smooth or directional surface finish on stainless steel coils after continuous line annealing.
• Cold-rolled stainless steel sheet is used in contact with food, chemicals and pharmaceuticals because of its resistance to corrosion and oxidation.
• the initial surface finish of the item made from stainless steel remains permanently and it is important that this finish be aesthetically pleasing, cleanable, and not detrimental to corrosion resistance.
• a brushed finish, called #3 or #4 polish is often used. This surface finish is generally produced on cold-rolled material which has been annealed and pickled by any of numerous schemes to remove oxides from the surface.
• the polish finish is then achieved by abrading the surface.
• Impregnated-abrasive brushes have become readily available only within the past 15 years employing hard materials such as SiC and A1 2 0 3 . New and stronger resin fibers have been recently formulated that have led to longer wear and broader acceptance and use of this abrasive technology.
• Polishing generally takes place after annealing, pickling and temper passing. Polishing may be performed in continuous coil form or in cut-to- length sheet form by abrading the surface with belts which have been coated with an abrasive mineral.
• the abrasion imparts a directional decorative finish which is used in many exposed applications where appearance of the stainless steel is of prime importance. This processing is costly and may result in polishing related defects during subsequent processing operations if the abrasive residues are not completely removed after polishing.
• Abrasive coated belts also experience rapid wear as compared to relatively thick, impregnated-abrasive brushes.
• Two United States Patents disclose brushing, abrading or grinding rolled steel to remove scale. United States Patent No.
• 5,131,126 discloses a method for removing oxide scale from a hot-rolled stainless steel strip including the steps of applying a solution of alkaline earth metal chloride to the surface of an oxide scale layer formed on a hot-rolled stainless steel strip, allowing the solution to penetrate into the oxide layer, annealing the strip and descaling the strip with brushes.
• Practice of this method is not directed to the descaling of cold-rolled steel, it involves use of a chemical bath and the surface finish of the end product is not suitable for consumer use.
• United States Patent No. 2,318,432 discloses removal of scale from hot-rolled steel where the ho -rolled steel sheet is first run through a scale breaker including staggered bending rollers which loosen the scale by progressively subjecting the sheet to sharp bends in opposite directions. The sheet is then brushed to remqve the scale. It is notable that the surface finish of the end product of this method is only suitable for cold rolling. To prepare a product suitable for delivery to a customer, the product must later be cold-rolled, annealed and again pickled.
• a key objective of the proposed invention is to develop a commercial process wherein an attractive, scale- free, smooth or directional polished surface finish can be produced on annealed stainless steels in such a way that pickling can be avoided entirely.
• a passivating step may be employed after this processing to further improve corrosion resistance, if desired.
• Impregnated-abrasive materials can effectively remove annealing oxides from the surface of the steel following annealing and thereby eliminate a costly, dangerous and hazardous effluent- producing pickling process.
• a second key objective of the present invention is to consolidate processing of cold-rolled stainless steel into a single manufacturing line.
• Conventional lines using a pickling step require transfer of the steel coil to a high speed temper mill where the steel is flattened; it is then leveled and cut to length and polished as individual sheets or polished in coil and then cut into sheets.
• the high speed tempering step may be avoided and the tension-leveling step may be inserted after annealing but before brushing to ensure a superior finish upon brushing. Elimination of the high speed tempering step allows consolidation of the cold-rolled stainless steel production process into one continuous line, saving energy and production costs.
• the cut-to- length facility can then be in line with the annealing and brushing operation.
• a method for descaling and polishing flat cold- rolled metal strip which has been previously annealed comprising the steps of annealing the strip and abrasively removing the oxide using thick, mineral-impregnated brushes or materials.
• the surface may be subsequently passivated to restore full corrosion resistance.
• the present invention is also directed to a manufacturing line for carrying out the steps of the method described above.
• a method for improving productivity of an existing conventional mill for producing cold-rolled stainless steel, having one or more pickling tanks wherein the mill may be converted to include an abrasive brushing station, eliminating the pickling steps.
• the mill may be further converted to include a tension leveler, a slitter and a shear in the same line as the annealing furnace and the abrasive rollers.
• FIG. 1 shows a schematic diagram of a conventional processing of cold-rolled stainless steel
• Fig. 2 shows a schematic of the present invention
• Fig. 3 shows a graph of the surface roughness of the trial samples after abrading both annealed and 2D finished cold-rolled stainless steel
• Fig. 4 shows a graph of the gloss measurements of the trial samples after abrading both annealed and 2D finished cold-rolled stainless steel.
• the stainless steel is annealed in a continuous annealing line at 1500 to 2200°F. These lines typically subject the strip to several treatments after annealing to remove the oxide generated in the annealing furnace.
• Traditional methods for removing the oxide are by pickling, or treatment with strong acids, such as hydrofluoric or sulfuric acid, to remove the oxides.
• the pickling step also removes impurities, such as sulfides, that can result in pitting of the stainless steel.
• a conventional pickling process is shown in Fig. 1. In Fig.
• a coil 10 of steel is unrolled and a steel strip is consecutively passed through an annealing furnace 18, a molten salt bath 20, a first rinse 21, a first strong acid bath 22, a second rinse 23, a second strong acid bath 24, a third rinse 25, a weak acid bath 26, a fourth rinse 27, a first temper pass 28, an abrasive belt polisher 29 and a second temper pass 30.
• the pickling treatment or treatments (A) are replaced by an abrading treatment as shown in Fig. 2.
• annealed and unpickled surfaces may be cleaned and/or conditioned using an impregnated-abrasive brush 40 on a continuous annealing or processing line 10 by abrading the sheet/strip surface.
• the present invention differs from the past conventional practice in that both the scale removal and the application of a directional decorative finish may be imparted to the stainless steel surface after the continuous line annealing operation but without the use of costly pickling solutions and/or abrasives after pickling.
• the abrasive brush 40 roller or wheel contains hard, mineral abrasives which are impregnated within the brush fibers. This yields a very abrasive yet flexible contact patch with the steel surface.
• the roughness, reflectivity and surface finish are controlled by the brush arrangement, roll speed, contact pressure and the size of the abrasive particles in the brush 40.
• the relative surface speed of the brush 40 to the steel surface is 1400 to 4000 feet per minute, most preferably, 2400 feet per minute.
• the pressure, or power consumption of the brush 40, not including drive train losses, is preferably .25 to 2.5 hp per inch of brush width, most preferably .66 hp per inch.
• This abrasive brush 40, wheel or belt has enough flexibility to contour with the steel surface and is sufficiently abrasive to remove any oxide scale layers or provide a distinctive, directional polish-type finish, depending on the grit of the abrasive employed.
• Impregnated-abrasive brushes readily available only within the past several years, now offer significant cost savings over standard abrasive belts which are coated with an abrasive mineral.
• One such brush is a Scotch-Brite ® #36 grit A1 2 0 3 9A Extra Coarse Wheel, produced by 3M of Minnesota.
• the impregnated-abrasive brush Since the impregnated-abrasive brush has mineral contained within the fibers, a more consistent finish is generated during the surface conditioning action. As the impregnated brush wears, "new" abrasive is continuously being exposed to the steel surface which improves product consistency and promotes much longer wear life compared to standard belts coated with an abrasive. The life of such rolls is quite long, and the operation of the continuous line thus need not be regularly interrupted to replace the rolls.
• the brushes 40 and/or surface of the steel strip 12 are preferably wet during the abrasion process.
• the wetting may be accomplished through either spraying with a wetting solution or submerging the brushes and steel during the abrasion process.
• the surface of pickled materials can be conditioned to match the polishing finish produced using conventional coated abrasive belts, i.e., #3 and #4 polished finishes.
• the surface roughness and gloss produced by varying the number of passes of the abrasive brushes is set forth in Table 1, below, presented in conjunction with Example 2.
• Surface roughness is a very important indicator of the quality of finish of the steel .
• experimental data shows that a #3 finish has an average surface roughness (Ra) of 22 micro inches with a range of 8-38 micro inches.
• the Kool Line ® finish was shown to have an average surface roughness of 22 with a range of 17-32 micro inches.
• surface roughness readings of the abraded annealed, but not pickled steel strip were comparable to these readings for steel prepared by standard finishing processes.
• a tension-leveling device 42 preferably but not necessarily inserted after the anneal furnace 18 step and before the abrasive brushes 40, can provide excellent flatness for uniform brush contact. This also obviates the need for subsequent temper mill flattening.
• the strip may then be conveniently passed through a passivating bath 44 and a subsequent passivating wash 45 which restores full corrosion resistance to the abraded surface.
• a passivating bath 44 and a subsequent passivating wash 45 which restores full corrosion resistance to the abraded surface.
• impurities will remain. Retention of these impurities, such as sulfides, in the surface of the steel will often result in pitting. "Passivating" the strip with an acid, such as nitric acid, will remove impurities. After passivation, the coil of strip may then be discharged from the continuous line.
• the steps of slitting the strip and shearing the strip to length can also be performed on the same processing line as the annealing, brushing and passivating steps.
• the strip can be passivated and subsequently slit in a slitter 46 to a desired width and then cut to length in a shear 48.
• the slitting step does not necessarily have to follow the passivating step although it is preferable that it does so.
• annealing and pickling, temper mill flat passing, polishing and slitting and re-temper passing are separate steps that are carried out at different speeds. These steps are usually followed by the low speed steps of roller leveling and cutting the coil to length.
• the present invention removes the need for separate lines having different processing speeds, allowing production of a finished product, finished and cut to size, from a single line.
• the combination of all steps into one line removes the need for multiple coilings and uncoilings of the strip and transport of the strip to other lines, resulting in lower production costs and energy usage, reduced floor space and less opportunity for damage of the sheets .
• the present invention is also directed to increasing the productivity of an existing line used for the preparation of cold-rolled stainless steel.
• one or more pickling steps (A) are used to prepare cold-rolled stainless steel according to conventional processes. These pickling steps are eliminated through practice of the present invention.
• An existing mill having a line for manufacturing cold-rolled stainless steel may be modified by eliminating the pickling tank(s) (A) and installing an abrasive brush 40 to replace the pickling tanks (A) .
• the brush 40 is preferably installed into an existing pickling tank along with a water source for wetting the brushes. Further modifications to an existing conventional line preferably include installing a tension leveler 42 before the brushes 40, installing a slitter 46 after the annealing furnace 18 and installing a shear 48 at the end of the processing line.
• EXAMPLE 1 A small-scale pilot trial was conducted on narrow 304 2D finished strips in light of promising preliminary results achieved using alumina/Sic brushes on the same substrate on a 52" wide line. On this small processing line, brush loading, abrasive wheel types and brush rotational speeds could be readily manipulated and controlled. A trial, "best practice", using an alumina impregnated wheel, #36 grit, and .25 Hp/inch of width brush loading, yielded an acceptable polished finish on top of the pickled 2D surface in just one pass. Based on these favorable findings, it was decided to apply this processing to 304 annealed but not pickled material, thereby eliminating the costly and hazardous pickling processing altogether. This trial is presented below in Example 2.
• EXAMPLE 2 The original trials involved abrasive polishing of a 304 strip which had a 2D surface finish. This strip was abraded with various mineral wheels and produced good results in terms of surface roughness characteristics as compared to standard Kool Line ® (employing hydrogen annealing, no pickling and temper rolling with an embossed set of work rolls) and polished finishes. Based on the success of the trial outlined in Example 1 above, it was decided to abrade an annealed but not pickled 304 strip.
• the pilot line includes a single head abrasive wheel. Power was supplied by a vari ble-speed 15 HP motor. All line conditions remained constant during the trial and matched the "best practice" as shown in Example 1. The alumina wheel and all equipment were unchanged from the original trials. A brush oscillator was used at all times. All surface polishing was conducted wet using 60°F ta D water.
• the roughness of the annealed but not pickled material did not appear to change appreciably after the second and third passes with the coarse #36A wheel as shown in Fig. 3.
• the roughness of the second trial coil (Bl) prepared with the #36A wheel, decreased from over 20 micro inches to less than 10 micro inches af er conditioning with the very fine 7AVF wheel .
• Gloss values during the trial were obtained using 3M's BYK Gardner Glossmeter and are illustrated in Fig. 4. Gloss values for the annealed but not pickled starting substrate were only 19 in the transverse direction before surface abrading. The gloss increased to 65 after one pass with a coarse #36A wheel and then to 110 when a coarse #36A wheel was followed by a fine 7AVF wheel, as shown in Fig. 4. A sample of 304 2D material was also measured for comparative purposes. The 2D finish had a high gloss reading of 138 in the as-received condition and the gloss decreased to 62 following one pass with a #36A coarse wheel. Visual observations were made during the trial .
• the #36A wheel produced a uniform and visually clean surface in just one pass when applied over the 304 annealed but not pickled substrate.
• Surface Ra values were in the 20 to 30 micro inch range using the #36A wheel over the 304 annealed but not pickled substrate, comparable to Kool Line ® and #3 polish finishes. Roughness values can be reduced using the Scotch-Brite ® process by applying smoother grit finish wheels to the annealed but not pickled substrate.
• the trial began by determining the minimum power requirements needed to drive the wheel and belt grinder's spindle without contacting the surface of the coil, at both operating speeds of 900 rpm and 1,800 rpm (Table 2, set up 1 and 2) .
• the contact roll position was then placed at the two o'clock position, or 1.75" offset towards the entry end of the unit .
• the belt grinder processing variables as listed in Table 3 were initially arranged as noted in setup 3 by the belt grinder operator. During the first pass the wheel pressure and contact roll wrap angles were adjusted as documented in setups 3 and 12. At the conclusion of setup 12, it was visually observed that all of the unpickled substrate had been removed, and the coil exhibited a uniform surface appearance except for some heavy chatter.
• setup 13 was used to process the coil and the surface roughness was checked.
• the Ra was 23 micro inches, the same as the average for #3 Polish.
• setups 14 through 25 were tried, but these set ups increased the chatter.
• Setup 13 was determined to be the best for removing the annealed unpickled substrate while producing a uniform finish.
• the belt grinder was then changed back to setup 13 and the remainder of the coil was processed.
• Tests were cut and an additional surface roughness test was taken (Ra 22 micro inches) . Since the surface roughness and appearance were virtually the same as with setup 13 , the process was proven to be capable of being duplicated on a consistent basis.
• Setup 13 was then used to apply a second pass to both sides of the coil .
• Results of this process are shown in Table 3 setup 27. Surface roughness results were taken and shown to be Ra 16 to 21. The most important aspect of adding a second pass to the coil was that the chatter was dramatically reduced. To try to further reduce the surface chatter a third pass was applied to just one side of the coil using the same processing parameters as originally used in setup 13. Tests were taken after the third pass . Surface roughness tests showed the coil to have an Ra of 12 to 15 micro inches . Tests received from the head end of the second pass still exhibited some remnant chatter, but tests from the tail end of the third pass had no chatter.
• Wear rate of the 3M Scotch-Brite ® wheel was also measured.
• the wheel which was originally used on the belt grinder at 9.75" diameter had been reduced to 9.63" while processing the coil #7996245. During this time frame it was calculated that 12,000 linear feet was passed through the belt grinder. The total wheel loss was calculated to have been 91.3 in 3 . This measurement was then translated into wear life per linear foot of processed coil.
• Total wear usage of 3M Scotch-Brite ® wheel in terms of total line as footage: 3,730 in 3 /0.007306 in 3 /ft 510,539 ft.
• the above information was then applied to the average processing rates for a cold anneal and pickle unit to achieve an approximate cost per ton in incorporating this type of system into a cold anneal and pickle line.
• the costs involved in using the brushes (wheels) of the present invention were low and the wear rate of the brushes is long enough for substantially continuous operation of the line.

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• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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• 1997
  • 1997-12-29 EP EP97954639A patent/EP0923420A1/en not_active Withdrawn
  • 1997-12-29 AU AU59040/98A patent/AU5904098A/en not_active Abandoned
  • 1997-12-29 WO PCT/US1997/024048 patent/WO1998029205A1/en not_active Application Discontinuation

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