US3126301A - Molten salt spray process for descaling stainless steel - Google Patents

Molten salt spray process for descaling stainless steel Download PDF

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US3126301A
US3126301A US3126301DA US3126301A US 3126301 A US3126301 A US 3126301A US 3126301D A US3126301D A US 3126301DA US 3126301 A US3126301 A US 3126301A
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strip
steam
hot
oven
salt
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    • 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
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G3/00—Apparatus for cleaning or pickling metallic material
    • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
    • C23G3/023—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously by spraying
    • 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
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/28—Cleaning or pickling metallic material with solutions or molten salts with molten salts
    • 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
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G3/00—Apparatus for cleaning or pickling metallic material
    • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
    • C23G3/027—Associated apparatus, e.g. for pretreating or after-treating

Definitions

  • This operation is more than a cleaning operation; it is a process which conditions the stainless steel strip by oxidizing the scale, after which the thus oxidized scale may then be processed in accordance with the process of Patent No. 2,458,661 or any other process as, for example, through acid pickling, etc.
  • the immersion process also was not widely adopted for very high quality stainless steel, nor extremely light gauges of stainless steel (such as below .O"), particularly finished product Where on additonal cold rolling is used.
  • the stainless steel in strip form comes out of an annealing oven and into a spray oven or mufile or box where it is cleaned or oxidized by molten salt spray and then emerges into the customary treatments such as water rinsing, quenchng, dilute acid picklng, rinsing, and then rewinding.
  • the novelty here is the spray oven and what happens in the spray oven where molten salt spray is thrown onto the strip as it leaves the annealing furnace.
  • the spray muflle or oven under consideration comprises an enclosed spray zone which in practical structural form may be considered as a box into which the hot strip enters at one end from the annealing furnace and-from which the oxdized or cleaned strip emerges at the other end, thence passing into a rinsing zone which may be a rinsing bath or water spray.
  • the oxidizing oven or spray box as we may call it,
  • ice receives the hot steel strip from the annealing furnace and discharges it to the rinsirg bath.
  • the oxidizing oven there are no rolls to be engaged by the moving strip but the strip is moved freely under tension through the oven, entering a slot in one end and leaving through a slot in the other end and at no time in the oxidizing oven is the strip in contact with any rolls or supports'or guides;
  • the strip is not in contactwith metal rolls as it passes through the spray box. Hence there is no electrolytic or no galvanic action, as would be encountered in an immersion bath containing salt and metal rolls over which a metal strip passes.
  • the hot steel strip enters at a temperature of about 1000 F. and emerges at about the same temperature, there being no substantial drop in temperature of the strip until it enters the water rinse and quench. It is important to maintain the strip at substantially the same temperature all the Way through the oxidixing oven. As long as the strip is at high temperature, in the presence of a molten salt spray, the oxidizing action will take place without the formation of any solid particles that might otherwise abrade or scratch the strip.
  • the strip enters hot and is maintained at substantially the same tempera ture all the way through the oxidzing oven.
  • the oxidizing action is obtained by subjecting the strip and the atmosphere within the oven to a molten salt spray; such as Kolene #1, see Patent No. 2,458,661, for example, and the spray is formed by atomizing the molten salt, using large quantities of an inert gas such assuperheated steam at about 1000 F., which passes into nozzles, into which is fed in very tiny quantities and in small increments the molten salts which, at that point, is at a temperature of 1000 F.
  • the exact temperature is not critical, except that it exceed the melting point of the salt spray, about 550 F., a substantial range being permitted.
  • the interior of the oven is also maintained charged with an atmosphere of super-heated steam coming from different outlets from the steam super-heater.
  • some of the steam goes out through steam nozzles into the atmosphere for heating the atmosphere and filling it full of steam, and another part of the steam goes through the atomizing nozzles.
  • the pressure of 1000 F. steam is greater than the pressure of the atmosphere outside of the oven. It seems that when atmospheric air comes in contact with a heated steel surface, certain higher forms of oxides are promoted. Since it is a desire and intention, by the use of the molten salt spray process, to form no oxide or a form of oxide more easily soluble, it would appear that, since the pressure of steam does not allow atmosphere to' enter Y the oven, while the strip is hot, the lower forms of oxide formed in the presence of steam with the exclusion of air is more desirable, and this is another attribute of the molten salt spray process.
  • additional heating means may be employed to maintain the atmosphere at the desired temperature.
  • additional or auxiliary heating means may or may not be used in the actual operation from time to time, but is initially provided as equipment so that it is available when needed.
  • This additional means could comprise combustion burners for discharging large quantites of hot combustion vapors into a jacket around the oven, and such jacket is sealed from the oven so that no combustion vapors can enter the oven, and the oven is maintained free of any atmosphere except inert gas, such as steam.
  • the auxliary heating means could be electric heaters or any other type of heater, just so long as it beats from the outside and does not discharge any harmful vapors into the oven. If air or combustion vapors were to enter the oven, harm might result.
  • the air or vapors contain CO and because CO by reaction with the salt may form carbonates (CO and because these carbonates are solidified, there might result a plugging of the nozzles through which the molten salt is atomized and, also a marring of the strip by the solid particles.
  • the super-heated steam moves the atomized salt spray with very high velocity onto the strip and by so doing, concentrates the scouring and chemical action of the molten salt onto the strip and, thus, reduces possible wastage of molten salt. It is estimated that at least 90% of the molten salt is actually used in the reaction that takes place of the salt on the scale and converts it into ozides, and no more than is unused in the process.
  • the salt spray also has a scale loosening, scouring, or scrubbing action. Impinging on the strip, it facilitates oxidizing of the scale.
  • the condenser removes and exhausts the oven, which is constantly receiving a supply of fresh salt and fresh steam, and at least 90% of the salt enters into the chemical change.
  • the system operates in such a way that any scale or slndge formed is removed in the form of vapors Suspended in the steam and exhausted through the condenser and the exhaust system.
  • the dragout losses are extremely small here because instead of having a molten salt film of excess amounts on the strip, as is conventional with bath type processes, such excess molten salt film being needed to lubricate the strip as it passes over the rolls, here we use only as much salt as is absolutely necessary to create the desired reactions and, hence, the dragout loss is reduced to an absolute minimum.
  • the small amount of salt that is melted for use in the molten salt spray process hereof is always free of buildups of complex metallic impurities and metallic salts such as chrome oxides, iror oxides, nickel oxides, manganese oxides, titanium oxides and others, as might be found in immersion baths. While, to the best of our knowledge, no complete analysis has been made as to how the buildup of these metallic salts affects descaling in salt baths, we are reasonably sure they do have a deleterious eiect and that they impede the reaction.
  • the salt may be anhydrous. It might also contain some water; or it can be a concentrated solution which is heated, pressurized and superheated before it is sprayed onto the strip. In such case, fiashing off the water allows the salt to mpirge as usual on the metal in anhydrous form.
  • FIG. 1 shows diagrammatically one form of such apparatus in side view, with parts cut away for purposes of clarity.
  • FlG. 2 is a section on line 2-2 of FIG. 1.
  • the drawing shows an insulated steam box, mufile, or oven 10, supported on legs 11 and having entrance and exit slots 12-14.
  • the metal strip 20 being cleaned enters slot 12 after leaving an uncoiling means not shown and a pre-spray heating or annealing means 16, and leaves slot 14 on its way to rinsing means, acid treatment means, heating means, recoiling means, etc., also not shown.
  • the strip 20 is processed by the process of this application.
  • the box 10 is inclined as shown so that products formed or deposited in the box collect at a discharge point 22 from where they are removed by a suitable removal means, such as a condenser not shown, including an exhausting fan.
  • a suitable removal means such as a condenser not shown, including an exhausting fan.
  • Solid salt in the instance here shown is fed into hoppers 24 and passes into melting chambers 26 Where it is melted by steam admitted from outside the box 10 through a steam l-ine 27, a steam manifold 28, and pipe terminals 30.
  • siphon nozzles 32 which siphon the molten salt from chambers 26 and spray it onto strip 20 immediately after the strip leaves annealing means 16, as soon thereafter as possible.
  • the timing is such that when the strip reaches the salt spray nozzles, the strip is at a maximum annealed temperature; but by the time it leaves exit slot 14 and passes out of the steam atmosphere and into the room air atmosphere, it has cooled down to a point where it is not seriously affected by room air.
  • Additional steam nozzles or lines 34 admit steam into the box to spray live steam into the box to form a hot steam atmosphere therein at above atmospheric pressure.
  • a steam chest 36 supplied by lines 37 which ruaintains a live steam heated wall inside the box.
  • Example 1 A salt composition comprising 2 parts by weight of caustic soda, 1 part by weight sodium nitrate and 0.3 part by weight of sodium chloride are heated with steam at D F. to fusion, picked up as an atomized liquid, and sprayed in a high pressure blast upon both sides of a stainless 8-18 chromium nickel steel strip as it leaves an annealing oven maintained at 1500 F., the metal strip moving at a rate of about 1 ft. per minute and slowly cooling from the annealing temperature to the steam cleaning temperature. The strip is then sprayed with steam alone to clean off any adhering molten salts. The strip, as it leaves the steam cleaning chamber box 10, as described above, is finally quenched with a spray of steam at a temperature of 250' F.
  • Process for descaling hot sealed metal strip comprisirg continuously passing said hot scaled metal strip into, through and out of a confined molten salt spray descaling zone filled with hot inert gas under pressure, said zone having metal strip entrance and outward openings sealed by evolution of the inert gas under pressure, thereby inhibiting entrance of outside air, maintaining the surfaces of said strip out of contact with handling equipment while the hot strip is being cleaned in said zone, continuously spraying said strip With a hot molten descalng salt atomized and propelled as a spray by a hot inert carrier gas against the surface of said metal strip, said hot carrier gas being applied at a substantially raised pressure sufi'icient to propel said molten salt against the metallic surface as a spray and to supply a positive air inhibiting pressure within said zone around the strip as it enters and as it leaves said zone.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
US3126301D 1961-09-11 Molten salt spray process for descaling stainless steel Expired - Lifetime US3126301A (en)

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3424614A (en) * 1963-02-28 1969-01-28 Schloemann Ag Cleaning,particularly de-scaling,of metal articles
US3494793A (en) * 1965-05-12 1970-02-10 Dynamit Nobel Ag Reduction of hydride losses from molten baths containing hydrides
US3511250A (en) * 1968-07-25 1970-05-12 United States Steel Corp Descaling apparatus
US3715236A (en) * 1970-10-08 1973-02-06 Mitsubishi Heavy Ind Ltd Descaling method for steel
US4317685A (en) * 1980-06-06 1982-03-02 General Electric Company Method for removing a scale from a superalloy surface
US4439241A (en) * 1982-03-01 1984-03-27 United Technologies Corporation Cleaning process for internal passages of superalloy airfoils
US5272798A (en) * 1992-08-05 1993-12-28 Kolene Corporation Method and apparatus for descaling metal strip
WO1994003651A2 (fr) * 1992-08-05 1994-02-17 Kolene Corporation Procede, appareil et sel pour decalaminer une bande de metal
US6450183B1 (en) 1999-12-22 2002-09-17 Kolene Corporation Composition, apparatus, and method of conditioning scale on a metal surface
US6776359B2 (en) 2001-11-06 2004-08-17 Kolene Corporation Spray nozzle configuration

Citations (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1930601A (en) * 1931-02-12 1933-10-17 Frank P Townsend Metal coating apparatus
US2159297A (en) * 1932-06-26 1939-05-23 Strip Tin Plate Company Apparatus for coating metal
US2228836A (en) * 1936-05-25 1941-01-14 Gen Motors Corp Rust-proofing process
US2320329A (en) * 1942-08-06 1943-05-25 Metallizing Engineering Co Inc Spray metal coated, metal surfaced articles
US2447664A (en) * 1945-02-01 1948-08-24 Westinghouse Elec Elevator Co Electrostatic coating apparatus and method
US2458661A (en) * 1944-01-29 1949-01-11 J H Shoemaker Process of cleaning metal surfaces and compositions therefor
US2505530A (en) * 1948-04-16 1950-04-25 Aluminum Co Of America Metal spray coating mechanism
US2511797A (en) * 1950-06-13 Steam spraying
US2512743A (en) * 1946-04-01 1950-06-27 Rca Corp Jet sprayer actuated by supersonic waves
US2536208A (en) * 1942-12-22 1951-01-02 Western Electric Co Method of treating strands
US2635062A (en) * 1950-09-05 1953-04-14 Kolene Corp Apparatus and method for processing of steel strip continuously
US2674550A (en) * 1950-09-05 1954-04-06 Kolene Corp Apparatus and method for processing of steel strip continuously
US2717845A (en) * 1947-01-09 1955-09-13 Roy E Carter Metal descaling methods
US2762331A (en) * 1952-06-18 1956-09-11 United States Steel Corp Oil spray devices for electrostatic oiling machines
US3004879A (en) * 1958-11-03 1961-10-17 Dow Chemical Co Brightening and cleaning composition and treatment for magnesium and magnesium-base alloys
US3022203A (en) * 1955-11-02 1962-02-20 Nat Vulcanized Fibre Co Process for strip treatment

Patent Citations (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511797A (en) * 1950-06-13 Steam spraying
US1930601A (en) * 1931-02-12 1933-10-17 Frank P Townsend Metal coating apparatus
US2159297A (en) * 1932-06-26 1939-05-23 Strip Tin Plate Company Apparatus for coating metal
US2228836A (en) * 1936-05-25 1941-01-14 Gen Motors Corp Rust-proofing process
US2320329A (en) * 1942-08-06 1943-05-25 Metallizing Engineering Co Inc Spray metal coated, metal surfaced articles
US2536208A (en) * 1942-12-22 1951-01-02 Western Electric Co Method of treating strands
US2458661A (en) * 1944-01-29 1949-01-11 J H Shoemaker Process of cleaning metal surfaces and compositions therefor
US2447664A (en) * 1945-02-01 1948-08-24 Westinghouse Elec Elevator Co Electrostatic coating apparatus and method
US2512743A (en) * 1946-04-01 1950-06-27 Rca Corp Jet sprayer actuated by supersonic waves
US2717845A (en) * 1947-01-09 1955-09-13 Roy E Carter Metal descaling methods
US2505530A (en) * 1948-04-16 1950-04-25 Aluminum Co Of America Metal spray coating mechanism
US2635062A (en) * 1950-09-05 1953-04-14 Kolene Corp Apparatus and method for processing of steel strip continuously
US2674550A (en) * 1950-09-05 1954-04-06 Kolene Corp Apparatus and method for processing of steel strip continuously
US2762331A (en) * 1952-06-18 1956-09-11 United States Steel Corp Oil spray devices for electrostatic oiling machines
US3022203A (en) * 1955-11-02 1962-02-20 Nat Vulcanized Fibre Co Process for strip treatment
US3004879A (en) * 1958-11-03 1961-10-17 Dow Chemical Co Brightening and cleaning composition and treatment for magnesium and magnesium-base alloys

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3424614A (en) * 1963-02-28 1969-01-28 Schloemann Ag Cleaning,particularly de-scaling,of metal articles
US3494793A (en) * 1965-05-12 1970-02-10 Dynamit Nobel Ag Reduction of hydride losses from molten baths containing hydrides
US3511250A (en) * 1968-07-25 1970-05-12 United States Steel Corp Descaling apparatus
US3715236A (en) * 1970-10-08 1973-02-06 Mitsubishi Heavy Ind Ltd Descaling method for steel
US4317685A (en) * 1980-06-06 1982-03-02 General Electric Company Method for removing a scale from a superalloy surface
DE3121833A1 (de) * 1980-06-06 1982-03-04 General Electric Co., Schenectady, N.Y. "verfahren zum entfernen eines ueberzuges von einer oberflaeche"
US4439241A (en) * 1982-03-01 1984-03-27 United Technologies Corporation Cleaning process for internal passages of superalloy airfoils
US5272798A (en) * 1992-08-05 1993-12-28 Kolene Corporation Method and apparatus for descaling metal strip
WO1994003651A2 (fr) * 1992-08-05 1994-02-17 Kolene Corporation Procede, appareil et sel pour decalaminer une bande de metal
WO1994003651A3 (fr) * 1992-08-05 1994-08-18 Kolene Corp Procede, appareil et sel pour decalaminer une bande de metal
US5505786A (en) * 1992-08-05 1996-04-09 Kolene Corporation Method for treating surface oxides on a metal alloy strip
US6450183B1 (en) 1999-12-22 2002-09-17 Kolene Corporation Composition, apparatus, and method of conditioning scale on a metal surface
US6851434B2 (en) 1999-12-22 2005-02-08 John M. Cole Composition, apparatus, and method of conditioning scale on a metal surface
US6776359B2 (en) 2001-11-06 2004-08-17 Kolene Corporation Spray nozzle configuration

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BE631870A (fr)
GB964821A (en) 1964-07-22

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