Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
  • C23C22/08—Orthophosphates
  • C23C22/22—Orthophosphates containing alkaline earth metal cations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
  • C23C22/08—Orthophosphates
  • C23C22/12—Orthophosphates containing zinc cations

Definitions

• This invention concerns the art of cold rolling ferrous strip stock continuously.
• the invention specificallyrelates to an improvement in the cold rolling process which enables easier production of cold rolled strip of superior flatness, smoothness and surface finish in comparison to heretofore known cold rolled strip.
• the present improve ment comprises a special processing of the strip after acid pickling and prior to cold rolling to facilitate the cold rolling operation.
• Present day cold rolling processing of steel strip stock comprises preparing the strip surface for cold rolling and then cold rolling in a reversing mill or a multiple stand mill.
• Low carbon steel, silicon steel or other steel strip, which emerges from a conventional hot rolling mill usually has some residual rolling scale and corrosion products on its surface.
• the preparation. for cold rolling normally includes processing the hot rolled strip to clean the surface by passing it through a pickle line of conventional form which may, for example, include in sequence one or more mineral acid dip stations, one or more water rinse stations and an oiling station. In certain instances where the scale is heavy, the pickleline may include mechanical abrading stations or alkali stations prior to the acid dip stations.
• the steel strip is continuously passed through these sequential stages and is recoiled after oiling to await the cold rolling operation.
• the rolling mill whether reversing or multiple stand, operates at speeds and under conditions which make it impossible to feed directly from the pickle line to the rolling line. Because of this necessary but variable length delay between the pickling of the strip and its rolling, the corroding of the pickled strip becomes an important problem. It is for this reason that most pickle lines include a final oiling station.
• the oiling step is highly undesirable from the dual standpoints that it drips. from the pickled coils, makes the working area slick, dirty and unsafe for workmen and that after cold rolling when the cold rolled strip is annealed the oil residue produces a surface coating of undesirable smut. It is one of the objects of this invention to provide a process which eliminates the necessity for oiling.
• the pickle line in order to produce sufficient pickled steel strip to keep a cold rolling rnil'l in continuous production, the pickle line must necessarily operate continuously and at relatively rapid speeds in order to be economic. Although actual speeds necessarily vary in difierent installations, pickle line speeds in the range of 150 feet/minute to 450 feet per minute are common.
• One of the difliculties in supplying a process for continuously forming a phosphate coating on the strip steel moving through a pickle line is to provide a solution which will form the necessary coating in the limited time which is available for contact of the strip surface with the phosphate coating solution. For example, if the pickle line moves at feet per minute a phosphate coating tank having a 25 foot length provides only about 10 seconds contact time for the strip.
• Another object is to supply means for providing a phosphate coating on moving ferrous strip stock having a minimum weight of 50 mg./ sq. ft. of surface area and a maximum weight of 1000 mg./ sq. ft., but which coating does not vary more than 200 mg./ sq. ft. from the average coating weight which is prevalent on the surface of the strip.
• Another object is to provide a phosphate coating which will enable the elimination of the use of a roughened surface roll such as a Pangbom roll in a reversing mill or in the last stand of a multiple stand mill and yet produce a cold rolled sheet of suitable surface condition to prevent sticking on annealing.
• Yet another object is to provide such a phosphate coating as to enable the annealing of sheets, without sticking, of such cold rolled strip in stacks that are higher than current practice and at temperatures up to about 1750 F.; to provide such a phosphate coating as to enable the subsequent stamping, in the hardened cold rolled condition of various parts such as. electric motor laminations, which after assembly may be annealed without sticking at temperatures as high as about 1750 F.
• One aspect of the present invention accomplishes the above and related objects by providing certain phosphate coating solutions and certain controlled conditions for their use.
• this invention provides processing steps which accomplish the objectives of this invention by controlling the time and conditions of contact of the strip by the phosphate coating solution. It is also contemplated by this invention to introduce an additional step of preliminary treatment after the acid pickling and prior to the phosphate coating to enable the formation of the desired coating.
• the method of this invention comprises the provision of aqueous acidic phosphate coating solutions which are capable of producing on the surface of a ferrous strip, normally pickled, a coating having a minimum weight of 50 mg./sq. ft. of surface area in not more than 10 seconds and a coating weight which does not vary more than 200 mg./sq. ft. from the average coating weight deposited in 10 seconds, the coating to have a maximum weight of 1000 mg. and preferably a maximum of 500 m./sq. ft.
• a phosphate coating which does not vary more than 200 mg./sq. ft.
• a substantially uniform phosphate coating is present on the ferrous strip, that strip is capable of being continuously cold rolled in a satisfactory manner.
• aqueous acidic zinc phosphate solutions containing zinc in an amount in a range of 0.05% to 1.5% and 0.4% to about 2.5% P and any of the conventional oxidizing agents known to be useable with such solutions, except chlorate, are suitable for this purpose when the contact time between the ferrous strip and the solution does not exceed 20 seconds.
• the proportion of oxidizing agent which should be present in order to achieve the minimum coating weight of 50 mg.'/ sq. ft. in seconds should fall within limits set forth bequinones, etc.
• Such solutions when operated at conventional strengths of between about 10 and 70 points and at conventional coating temperatures ranging from approximately 100'- F. to l F. depending upon the particular zinc concentration and oxidizing agent-being employed will produce the desired substantially uniform coating.
• the points of total acid refers to the number of ml. of 0.1 N NaOH required to neutralize a 10 ml. sample of the solution to a phenolphthalein endpoint.
• the solutions may opttionally contain the calicum ion in an amount in the range of about 0.012% to about 7.5% by weight.
• the presence of calcium in the coating solution apparently causes the production of somewhat finer grain coatings and these coatings have been found to give the maximum assistance in the rolling operation, i.e., in reducing the roll pressure required, the power required, and in producing the smoothest, flattest strip having the best surface finish.
• the ratio of calcium to zinc should be between 1 calcium to 4 zinc and 5 calcium to l zinc, or a ratio of calcium to zinc from 0.25:5 and preferably in the range of 0.6:4.
• the solutions may contain conventional oxidizing agents such as nitrate, nitrite, hydrogen peroxide and organic nitro compounds such as picric acid, m-nitrobenzene sulfonate and dinitrobenzene sulfonate, or bromates, iodates, t-butyl hydroperoxide, Nitrate and nitrite are the most desirable oxidizing agents for the purposes of this invention.
• oxidizing agents such as nitrate, nitrite, hydrogen peroxide and organic nitro compounds such as picric acid, m-nitrobenzene sulfonate and dinitrobenzene sulfonate, or bromates, iodates, t-butyl hydroperoxide, Nitrate and nitrite are the most desirable oxidizing agents for the purposes of this invention.
• nitrate is employed,- the ratio of nitrate to phosphate, N0,:P0 may satisfacto 'y extend from 0.5 :5.0.
• the ratio of NO,:P0 may satisfactorily extend from about 0.001 to about 0.05; for m-nitrobenzene sulfonate the ratio may extend from about 0.15 to about 3.0; for hydrogen peroxide the ratio may extend from about 0.002-0.0l and for dinitrobenzene sulfonate the ratio may extend from about 0.1-1.5.
• oxidizing agents such as bromates, methylene blue, iodates, picric acid, t-butyl hydro-peroxide, sulfites, hypochlorites, periodates, nitroguanidine, nitromethane, nitrourethane, nitraniline, nitrophenol, quinones, etc.
• the phosphate coating of this invention is beneficial in avoiding corrosion on the strip during the delay period prior to rolling and completely eliminates the need for the conventional oiling step. In certain instances, however, where the conditions which cause corrosion are worse than usual, it may be desirable and this invention contemplates the rinsing of the phosphate coated surface in an additional corrosion rinse such as a dilute aqueous solution of chromic acid, borax, sodium nitrite, soda ash, etc., in a conventional manner.
• an additional corrosion rinse such as a dilute aqueous solution of chromic acid, borax, sodium nitrite, soda ash, etc.
• the objects of this invention may be realized by adding a pretreatment step in the process following the acid pickling step and prior to the introduction of the strip into the phosphate coating solution. It has been found that by contacting the pickled strip with certain aqueous pretreatment solutions which are capable of activating the surface to make it more receptive to attack by acidic phosphate treating solutions, it is possible to greatly increase the initial coating producing capacity of zinc phosphate solutions on such surfaces so that the most desired coating weight may be obtained in the extremely limited treatment time which is available, for example, 3-8 seconds. It has been found to be satisfactory to employ as such a pretreatment soluoils,
• lion aqueous acidic solution of oxalic acid, an aqueous solution of disodium phosphate or tetra sodium pyrophosphate containing a small amount of titanium (e.g. up to 0.05% Ti) as a compound or zirconium as a compound; an aqueous solution of tetra sodium pyrophosphate; a mixture of tetra sodium pyrophosphate and meta phosphates in aqueous solution; a dialkali metal phosphate containing up to 0.05% of lead, tin or arsenic; and a mixture of tetrasodium pyrophosphate with disodium phosphate containing a small amount of a titanium or zircomum compound.
• suitable titanium compounds for this purpose are titanium chloride, titanium hydroxide, titanium nitride and titanium potassium oxalate.
• the desired coating weight of a substantially uniform phosphate coating can also be obtained by regulating the time of contact between the ferrous strip and the coating solution irrespective of the uncontrollable shutdowns or stoppages which may occur in the normal operation of the pickling line.
• This invention contemplates theprovision of mechanical means for removing the strip stock from the phosphate coating solution substantially simultaneously with any stoppage of the strip and immediately water rinsing the removed strip to free the surface of active phosphate coating solution.
• mechanical means for accomplishing this purpose will be apparent to those skilled in the art.
• Such a means may comprise roller means at the entering end of the phosphate coating tank and roller means at the exit end of the tank so adjusted as to cause the ferrous strip to be immersed well down into the phosphate coating solution during normal travel of the strip.
• the rolls may be suitably mounted on vertically moveable elements which are actuated to raise those rolls substantially simultaneously with the stoppage of horizontal motion of the strip so as to remove the strip from the solution.
• Water spray means mounted so as to be positioned above and below the strip, move into position after the strip has been raised item the solution to spray the surfaces and rinse the phosphate coating solution therefrom.
• the present invention contemplates the application of the phosphate coatiug solution by spraying as well as by immersion.
• conventional electrical interlocks may be provided which automatically shut off the spray upon strip stoppage and start the application of a water rinse from the spray or separate spray nozzles.
• the cold rolling can be done on a reversing or multiple stand mill by employing conventionally used lubricants during the rolling operation.
• Any of a number of satisfactory lubricants may be employed including oils, such as mineral oil, palm oil, rape seed oil, etc.
• Lubricants for this purpose are preferably used in aqueous form, either as a solution or emulsion. Dilute aqueous solutions consisting of, for example, 1% to 3% oil and the balance water, of a water soluble mineral oil, or a lard base oil together with a conventional emulsifying agent for such have been satisfactorily employed.
• aqueous base lubricant which has been used with unusual success is a mixture of lard oil and a fatty acid and has the following analysis: Fatty acid (calculated as oleic acid), l2.9% by weight, iodine number 36.9 and a saponification number of 32.4. A small amount of an emulsifying agent to make this mixed oil water soluble is added to a solution containing 1%2% of this mixed oil, balance water.
• Example I An aqueous acidic phosphate solution tank was installed as the last station in a strip steel sulfuric acid pickling line which comprised a sulfuric acid pickling station, a water rinse station and the phosphate crating solution station.
• An aqueous acidic zinc phosphate solution was prepared in the phosphate solution and analyzed to contain in percent w./v.: zinc 0.73, nitrate 2.07, PO 1.26, total acid 29.8, free acid 4.2.
• the number of free acid points refers to the number of ml. of 0.1 N NaOH required to neutralize a 10 ml. sample of the solution to a brom phenol blue endpoint.
• the solution also contained 0.008% N0 which was maintained at approximately that concentration during use.
• the solution showed freedom from the ferrous ion.
• the solution was maintained at a temperature of about 170 F.l F. and hot rolled low carbon steel strip was fedthrough the sulfuric acid pickle, water rinsed and thereafter introduced into the above solution and maintained in contact with the coating solution, measured times of 10 seconds, 20 seconds, 30 seconds. Samples of the processed strip stock were checked for the weight of coating formed on the surface in these time periods. After 10 seconds it was found that the strip had a coating weight of mg./sq. ft. of surface area, a weight of 275 mg./sq. ft. after 20 seconds and 385 mg./sq. ft. after 30 seconds.
• the strip emerging from the phosphate coating solution was coiled in the conventional manner.
• the coils were immediately rolled on a reversing rolling mill and in others a. time delay, measured in days, occurred before the rolling was done.
• the strip was passed through the Bliss rolling machine a'plurality of passes and in most cases was reduced from about 0.1 inch to 0.068" in one pass, to 0.05" in two passes, to 0.038 in three passes, to 0.029" in four passes and to 0.025 in five passes.
• the strip and the rolls were continuously flooded with an aqueous base lubricant of the type disclosed above in detail.
• no difficulty was experienced with the portions which received coating having less than 275 mgJsq. ft. coating weight which corresponds to the weight received after 20 seconds of treatment.
• Example 11 An aqueous acidic solution was prepared and upon analysis found to contain in percent w./v.: zinc 0.29,
• Example III An aqueous acidic solution was prepared and upon analysis found to contain in percent w./v.: zinc 0.19, nitrate 0.30, PO 1.38, iron 0, nitrite 0.006, calcium 0.14, free acid 1.5 and total acid 15.6.
• Example V An aqueous acidic solution was prepared and upon analysis found to contain in percent w./v.: zinc 0.35, nitrate 1.55, nitrite 0.006, P 0.84, iron 0, calcium 0.34, total acid 20.2 and free acid 2.7.
• Example VI An aqueous acidic solution was prepared and upon analysis found to contain in percent w./v.: zinc 0.21, nitrate 2.17, PO, 0.64, iron 0, calcium 0.53, nitrite 0.004, total acid 15.1, free acid 1.8.
• Example VIII An aqueous acidic solution suitable for operation at temperatures between about 110 F. and 135 F. by spraying was prepared and analyzed to contain in percent w./v.: zinc 0.11, nitrate 0.64, P0 0.76, iron 0, nitrite 0.006, total acid 10.6, free acid 0.5.
• Example IX An aqueous acidic solution was prepared and analyzed to contain in percent w./v.: zinc 0.12, PO, 0.46, iron 0, hydrogen peroxide 0.012, total acid 6.9 and free acid 0.4.
• Example X A tank was prepared to contain a 2% solution of oxalic acid in water. Hot rolled low carbon steel strip was fed through the sulfuric acid pickle line described in Example I, water rinsed and then fed into the oxalic acid solution maintained at room temperature so that the surface was in contact with the strip for thirty seconds. The strip was then rinsed for one minute in hot water and then processed directly into the phosphate coating solution of Example I. Portions of the strip corresponding to times of contact with the phosphate coating solution of seconds, seconds and 30 seconds were removed and analyzed for coating weight. After 10 seconds the coating weight was found to be 285 mg./sq. ft. of surface area, after 20 seconds 330 mg./sq.
• Example XI In a manner comparable to that set forth in Example X, another treatment solution consisting of a 1% solution of disodium phosphate in water and containing a small amount (between 0.005% and 0.05% Ti) of a titanium compound, believed to be titanium chloride, was prepared. Hot rolled low carbon steel strip which had been 8 preliminarily sulfuric acid pickled was immersed in this solution, maintained at 190 degrees for thirty seconds, removed from this solution and fed directly mto the phosphate coated solution of Example I. Samples ofthe strip representing phosphate coating solution contact times of 10 seconds, 20 seconds and 30 seconds were removed from the coil and analyzed for coating'weight. After 10 seconds the coating weight was found to 300 mg./sq. ft., 500 mg./sq. ft. after 20 seconds and 620 mg./sq. ft. after 30 seconds.
• Example XII Another intermediate treatment solution was prepared and used in a manner similar to that set forth in Example X.
• the solution was built up to contain in percent w./v. 0.87% tetra sodium pyrophosphate and 0.13% of disodium phosphate containing titanium (as described in Example XI). Withthe solution maintained at 160 F., the ship was contacted for one minute, hot water rinsed for one minute and then passed into the phosphate coating solution of Example I. In similar manner samples of the coils were analyzed for coating weights. After 10 seconds the coating weight was found to be 360 mg./sq. ft., 410 mg./sq. ft. after 20 seconds and 440 mg./sq. ft. after 30 seconds.
• a method for treating continuous ferrous strip stock which comprises the steps of pickling the strip, contacting the said pickled strip while the same is moving with an aqueous acidic zinc phosphate coating solution comprising as the essential coating producing ingredients zinc in an amount in the range of 0.05 1.5% by weight, 0.4 to about 2.5% P0 and an oxidizing agent other than chlorate in an amount suflicient to produce a coating weight of at least 50 mg. per square foot in not more than 10 seconds, and regulating the time of contact of said pickled strip with said solution so as to produce a coating which has a weight in the range of about 50 mg./ sq. ft. to about 1000 mg./sq. ft. and which varies frmn the average coating weight prevalent on said strip by not more than about 200 mg./sq. ft.
• a method for treating ferrous strip stock which comprises the steps of pickling the strip, contacting the pickled strip with an aqueous acidic zinc phosphate coating solution comprising as the essential coating producing ingredients zinc in an amount in the range of 0.05%- 1.5% by weight, 0.4 to about 2.5 P0 and an oxidizing agent other than chlorate in an amount sutficient to produce a coating weight of at least 50 mg. per square foot in not more than 10 seconds, controlling the time which said strip is in contact with said solution to not more than 20 seconds to thereby produce a coating which varies from the average coating weight prevalent on said strip by not more than about 200 mg./sq. ft., and thereafter continuously cold rolling said strip stock.
• aqueous acidic zinc phosphate coating solution comprising as the essential coating producing ingredients zinc in an amount in the range of 0.05%-1.5% by weight, 0.4 to about 2.5% P0 calcium in an amount in the range of about 0.12% to about 7.5% by weight and an oxidizing agent other than chlorate in an amount suflicient to produce a coating weight of at least 50 mg.
• P calcium in an amount in the range of about 0.12% to about 7.5% by weight
• an oxidizing agent selected from the group consisting of nitrate, nitrite, hydrogen peroxide, m-nitrobenzene sulfonate, dinitrobenzene sulfonate, bromate, iodate, t-butyl hydroperoxide, quinone, hypochlorite, periodate sulfite, methylene blue, nitroguanidine, nitromethane, nitrourethane, nitraniline and nitrophenol in an amount having an effect on the rate of coating equivalent to 2% to 12% nitrate, and regulating the concentration of said oxidizing agent in said solution and the time of contact of said strip with said solution so as to produce a coating having a minimum weight of 50 mg./sq. ft. and which is substantially uniform.
• a method for treating continuous ferrous strip stock which comprises the steps of pickling the strip, contactin 'the pickled strip wtih an aqueous solution capable of activating the surface to render it more receptive to the formation of a phosphate coating, contacting said strip with an aqueous acidic zinc phosphate coating solution comprising as the essential coating producing ingredients zinc in an amount in the range of 0.05%- 1.5% by weight, 0.4 to about 2.5% P0 and an oxidizing agent other than chlorate in an amount sufiicient to produce a coating weight of at least 50 mg./sq. ft.
• a method for treating continuous ferrous strip stock which comprises the steps of pickling the strip, contacting the pickled strip with an aqueous acidic zinc phosphate coating solution comprising as the essential coating producing ingredients zinc in an amount in the range of 0.05%-1.5% by weight, 0.4 to about 2.5% P0 and an oxidizing agent other than chlorate in an amount sufficient to produce a coating weight of at least 50 mg. per square foot in not more than 10 seconds, controlling the time which said strip is in contact with said solution to not more thm 20 seconds to thereby produce a coating which varies from the average coating weight prevalent on said strip by not more than about 200 mg./ sq. ft., continuously cold rolling said strip stock, and thereafter annealing said strip stock.
• a method for treating continuous ferrous strip stock which comprises the steps of pickling the strip, contacting the said pickled strip while the same is moving with an aqueous acidic'zinc phosphate coating solution comprising as the essential coating producing ingredients zinc in an amount in the range of 0.05% to 1.5% by weight, 0.4% to about 2.5 P0 and an oxidizing agent other than chlorate in an amount suflicient to produce a coating weight of at .least mg./sq. ft. in not more than 10 seconds, so as to produce a coating having a weight in the range of about 50 mg./sq. ft. to about 1000 mg./sq. ft. and varying from the average coating weight prevalent on said strip by not more than about 200 mg./ sq. ft., continuously cold rolling said strip stock and thereafter annealing said strip stock.

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• 1956
  • 1956-01-25 US US561354A patent/US2884351A/en not_active Expired - Lifetime
• 1957
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  • 1957-01-19 BE BE554334D patent/BE554334A/fr unknown
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