CA1088457A - Treating metallic article in molten oxidizing salt before immersion in electrolyte - Google Patents
Treating metallic article in molten oxidizing salt before immersion in electrolyteInfo
- Publication number
- CA1088457A CA1088457A CA275,220A CA275220A CA1088457A CA 1088457 A CA1088457 A CA 1088457A CA 275220 A CA275220 A CA 275220A CA 1088457 A CA1088457 A CA 1088457A
- Authority
- CA
- Canada
- Prior art keywords
- electrolyte
- bath
- salt
- molten
- group
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
- C25F1/02—Pickling; Descaling
- C25F1/04—Pickling; Descaling in solution
- C25F1/06—Iron or steel
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Electrochemistry (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
METALLIC DESCALING SYSTEM
ABSTRACT OF THE DISCLOSURE
A process for descaling a metallic body, wherein the body is immersed in a bath of a molten oxidizing salt, and subsequently in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the chloride, sulfate and nitrate of an alkali metal or ammonium.
ABSTRACT OF THE DISCLOSURE
A process for descaling a metallic body, wherein the body is immersed in a bath of a molten oxidizing salt, and subsequently in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the chloride, sulfate and nitrate of an alkali metal or ammonium.
Description
The present invention relates to a metallic descalng process.
As anneals and other heat treatments are often carried out in oxidizing atmospheres, oxide scales are known to form on metallic surfaces.
To date, several methods of removing such scales are in commercial use.
These methods do, however, necessitate the use of hot mineral acid solutions. Typical methods are disclosed in United ~tates Patent Nos.
3, 043, 758 and 3, 260, 619.
Today it is becoming increasingly clear, that there is a need for a descaling process which requires little or no acid pic~ling. First of all, both the cost of using and of disposing of mineral acid~ has significantl~J
-~ increased. SecondlyJ with the continuing tightening of pollution laws, there is a distinct possibilit~ that the dumping of waste acid plcklina solutions ~0 will not be permitted at some time in the future. ~;hould this occur, metal producers would be forced to install ver~r costly acid regeneration or neutralization plants.
`'~
,, , . , ! , . . . . : . . ' ' ' ' ' ' ' ' ".' .. ' , . ' ' ' ' ''': , .' ' ' , .'' ,. . ", ~ . : ,' ' ' ' ,.',' ' ~' ~, ' " ' '' ,'' '.' ' '' , ,' `"",' ' ,, . ' .: ' ~ '' . . ' '' ' , :" ' ' ' ' " ' , ' ' ' :, .','' ,'' : :', ', ,, .' :. , . ' I The present invention provides a scale removal system which eliminates or minimizes the need for acid pickling. Appli-cants have found that such a desirable result could be achieved by immersing a scaled metallic body in a molten oxidizing salt and then in an electrolyte on the order of that disclosed in Patent No. 3,043,758. Such a process is contradictory to the teachings of Patent No. 3,043,758, as said patent does not hint at the use of a molten oxidizing salt; and to that of Patent No. 3,260,619, as said patent does not hint at the use of an electrolyte with 1~ .its moiten oxidizing salt.
It is accordingly an object of the present i:nvention to provide a metallic descaling process which eliminates or minimizes -the need for acid pickling.
The present invention provldes a process for descalincJ
metallic bodies. ~n its broadest sense, it comprises the steps of: immersing a metallic body in a bath of a molten oxidizi.ng : salt; and subsequently in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the . . chloride, sulfate and nitrate of an alkali metal or ammonium.
Said bath conditions the scale for subsequent remo~al.
Of the said baths in use, the most widely accep-ted contain a compound from the group consisting of sodium nitrate and potassium nitrate. ~hree typical salts are as follows:
: .
:
As anneals and other heat treatments are often carried out in oxidizing atmospheres, oxide scales are known to form on metallic surfaces.
To date, several methods of removing such scales are in commercial use.
These methods do, however, necessitate the use of hot mineral acid solutions. Typical methods are disclosed in United ~tates Patent Nos.
3, 043, 758 and 3, 260, 619.
Today it is becoming increasingly clear, that there is a need for a descaling process which requires little or no acid pic~ling. First of all, both the cost of using and of disposing of mineral acid~ has significantl~J
-~ increased. SecondlyJ with the continuing tightening of pollution laws, there is a distinct possibilit~ that the dumping of waste acid plcklina solutions ~0 will not be permitted at some time in the future. ~;hould this occur, metal producers would be forced to install ver~r costly acid regeneration or neutralization plants.
`'~
,, , . , ! , . . . . : . . ' ' ' ' ' ' ' ' ".' .. ' , . ' ' ' ' ''': , .' ' ' , .'' ,. . ", ~ . : ,' ' ' ' ,.',' ' ~' ~, ' " ' '' ,'' '.' ' '' , ,' `"",' ' ,, . ' .: ' ~ '' . . ' '' ' , :" ' ' ' ' " ' , ' ' ' :, .','' ,'' : :', ', ,, .' :. , . ' I The present invention provides a scale removal system which eliminates or minimizes the need for acid pickling. Appli-cants have found that such a desirable result could be achieved by immersing a scaled metallic body in a molten oxidizing salt and then in an electrolyte on the order of that disclosed in Patent No. 3,043,758. Such a process is contradictory to the teachings of Patent No. 3,043,758, as said patent does not hint at the use of a molten oxidizing salt; and to that of Patent No. 3,260,619, as said patent does not hint at the use of an electrolyte with 1~ .its moiten oxidizing salt.
It is accordingly an object of the present i:nvention to provide a metallic descaling process which eliminates or minimizes -the need for acid pickling.
The present invention provldes a process for descalincJ
metallic bodies. ~n its broadest sense, it comprises the steps of: immersing a metallic body in a bath of a molten oxidizi.ng : salt; and subsequently in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the . . chloride, sulfate and nitrate of an alkali metal or ammonium.
Said bath conditions the scale for subsequent remo~al.
Of the said baths in use, the most widely accep-ted contain a compound from the group consisting of sodium nitrate and potassium nitrate. ~hree typical salts are as follows:
: .
:
- 2 - ...
.~' .
~88~a57 A B C
62% NaOH 63~o ~aOH 62-89% NaOH
32%NaNO3 1~% KOH 11-38% NaNO3 6% NaC1 12% NaNO3 10% NaCl Immersion time in the molten salt is at least 2 seconds, and generally in excess of ~ seconds. Times are dependent upon the size of the ~netallic -body being descaled, as well as the type and thickness of the scale, and the temperature of the molten salt; and most significantly, upon the ~10 temperature of the metallic body. Metal at a temperatur~ of about 100F, .. ...
might require times approaching 30 ~econds, whereas metal at a higher temperature will require a shorter period e. g 5 seconds . F or purposes of the present invention, the term "heated body" refers to a metal article at a temperature of at least 100F. Unheated metal will generally require an immersion period of at least 30 seconds.
Subsequent to being immersed in the molten salt, the metal being treated is immersed in the electrolyte described hereinabove. Immersion time in the electrolyte is at least 4 seconds, and generall~ at least 10. As with the molten oxidizing salt, immersion times are dependent upon the size of the body being descaled, as well as the type and thickness of the scale, and the temperature of the electrolyte. With the electrolyte, times are also dependent upon the current density and upon the time the metal is anodic, Current densities are usually in excess of 0.1 amp per square inch.
Electrolyte temperatures are usually in the range of from 120 to 200~.
Current densities, temperatures and times are all, however, cLependent .
upon each other, as well as upon the other listed variables. To increase the effectiveness of the electrolyte, 0.1 to 50 grams per liter of a compound from the group consisting of fluorides, chlorides, perchlorates, chromates, nitrites, sulfites, nitrates and sulfates may be added.
Although the invention is believed to be adaptable to a number of metals, alloy steels presently appear to consitute the most significant embodiment thereof, For this reason, the following examples are directed to the removal of scale from stainless steel.
EXAMPLE I
Samples of mill annealed Type 304 ancl 309 stainless steel were exposed to scale conditioning in a molten oxidizing salt of the following chemistry:
62% NaOH 32% NaN03 6% NaCl and then, after rinsing, to a neutral sodium sulfate electrolyte, The solution concentration of sodium sulfate was between 15 and 20% by weight, The molten salt was maintained at a temperature of from 900 to 950F
whereas the electrolyte was maintained at a temperature of from lSO to 170F. Specifics as to metal gage, times, current densities and polarities are set forth hereinbelow in Table I, ' ~:
5~ ~
TABLE I
SALT XLECTROLYTE
Time of C urrent Ga~e Immersion Density Time of Immersion (seconds) Sample T~pe (inches) (seconds) (ame/sq.in~ Anode Cathode Anode A 304 0.030 60 1/2 9 9 9 B 304 0. 060 60 1/2 9 9 9 C 309 0. 018 60 1/2 18 1~3 18 D 304 0. 060 60 1/2 21 21 Zl E 304 0. 030 60 1/2 30 30 30 Samples removed from the electrolyte were cleaned and examined for residual scale at a magnification of 20~, The results of the examination appear hereinbelow in Table II. Also appearing in Table II are the results of a salt spray test. The samples were placed in a salt spray cabinet for seven days and subsequently examined for rust. Corrosion resistance of samples is somewhat impaired it' scale is not removed.
TABLE II
Salt Spray Sample Scale % l~/o Rust) B 0 0. 02 O O
D 0 0. 30 E 0 0, 05 ;~::
~ .
The results appearing hereinabo~e in Table TT clearly show that metallic surfaces can be effecti~ely descaled in accordance with the teachings of the present invention. Scale was not detected on the samples at a magnification of 20X, Moreover, salt spray results showed an ;5 insignificant rate of attack, if any.
A~dditional samples of annealed Type 304 and 309 stainless steels, at a temperature of approximately 600F, were exposed to scale conditioning in a molten oxidizing salt of the following chemistry:
62% NaOH 3Z~o NaNO3 6% NaCl ancl then, after rinsing, to a neutral sodium sulfate electro]yte. The solution concentration of sodium sulfate was between 15 and 20% by wei~ht.
The molten salt was maintained at a temperature of from 900 to 950F
whereas the electrolyte was maintained at a temperature of from 150 to 170F.
Specifics a9 to metal gage, times, current densities and polarities are set forth hereinbelow in Table III, :
TABLE III
SALT_ ELECTROLYTE
Time of Current GageImmersion Density Time of Inlmersion (seconds) Type (inches) ~seconds) (amp/sq. in. ) Anode Cathode Anode 304 0~ 060 5 1/4 20 20 20 309 0. 060 5 1/2 20 20 20 ~?~l~4S7 The treated steel was inspected and evaluated. No residual scale was evident, despite the short period of time in the molten oxidizing salt.
- The short period of time was possible as the steel was at an elevated temperature upon entering the molten oxidizing salt.
It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications ~ t~Q ~
t~ of the same. It is accordingly desired that in~construing~the breadth of the appended claims they shall not be li mited to the specific examples of the invention described herein.
' :
, ' .. .' ' ~ . . ';
.~' .
~88~a57 A B C
62% NaOH 63~o ~aOH 62-89% NaOH
32%NaNO3 1~% KOH 11-38% NaNO3 6% NaC1 12% NaNO3 10% NaCl Immersion time in the molten salt is at least 2 seconds, and generally in excess of ~ seconds. Times are dependent upon the size of the ~netallic -body being descaled, as well as the type and thickness of the scale, and the temperature of the molten salt; and most significantly, upon the ~10 temperature of the metallic body. Metal at a temperatur~ of about 100F, .. ...
might require times approaching 30 ~econds, whereas metal at a higher temperature will require a shorter period e. g 5 seconds . F or purposes of the present invention, the term "heated body" refers to a metal article at a temperature of at least 100F. Unheated metal will generally require an immersion period of at least 30 seconds.
Subsequent to being immersed in the molten salt, the metal being treated is immersed in the electrolyte described hereinabove. Immersion time in the electrolyte is at least 4 seconds, and generall~ at least 10. As with the molten oxidizing salt, immersion times are dependent upon the size of the body being descaled, as well as the type and thickness of the scale, and the temperature of the electrolyte. With the electrolyte, times are also dependent upon the current density and upon the time the metal is anodic, Current densities are usually in excess of 0.1 amp per square inch.
Electrolyte temperatures are usually in the range of from 120 to 200~.
Current densities, temperatures and times are all, however, cLependent .
upon each other, as well as upon the other listed variables. To increase the effectiveness of the electrolyte, 0.1 to 50 grams per liter of a compound from the group consisting of fluorides, chlorides, perchlorates, chromates, nitrites, sulfites, nitrates and sulfates may be added.
Although the invention is believed to be adaptable to a number of metals, alloy steels presently appear to consitute the most significant embodiment thereof, For this reason, the following examples are directed to the removal of scale from stainless steel.
EXAMPLE I
Samples of mill annealed Type 304 ancl 309 stainless steel were exposed to scale conditioning in a molten oxidizing salt of the following chemistry:
62% NaOH 32% NaN03 6% NaCl and then, after rinsing, to a neutral sodium sulfate electrolyte, The solution concentration of sodium sulfate was between 15 and 20% by weight, The molten salt was maintained at a temperature of from 900 to 950F
whereas the electrolyte was maintained at a temperature of from lSO to 170F. Specifics as to metal gage, times, current densities and polarities are set forth hereinbelow in Table I, ' ~:
5~ ~
TABLE I
SALT XLECTROLYTE
Time of C urrent Ga~e Immersion Density Time of Immersion (seconds) Sample T~pe (inches) (seconds) (ame/sq.in~ Anode Cathode Anode A 304 0.030 60 1/2 9 9 9 B 304 0. 060 60 1/2 9 9 9 C 309 0. 018 60 1/2 18 1~3 18 D 304 0. 060 60 1/2 21 21 Zl E 304 0. 030 60 1/2 30 30 30 Samples removed from the electrolyte were cleaned and examined for residual scale at a magnification of 20~, The results of the examination appear hereinbelow in Table II. Also appearing in Table II are the results of a salt spray test. The samples were placed in a salt spray cabinet for seven days and subsequently examined for rust. Corrosion resistance of samples is somewhat impaired it' scale is not removed.
TABLE II
Salt Spray Sample Scale % l~/o Rust) B 0 0. 02 O O
D 0 0. 30 E 0 0, 05 ;~::
~ .
The results appearing hereinabo~e in Table TT clearly show that metallic surfaces can be effecti~ely descaled in accordance with the teachings of the present invention. Scale was not detected on the samples at a magnification of 20X, Moreover, salt spray results showed an ;5 insignificant rate of attack, if any.
A~dditional samples of annealed Type 304 and 309 stainless steels, at a temperature of approximately 600F, were exposed to scale conditioning in a molten oxidizing salt of the following chemistry:
62% NaOH 3Z~o NaNO3 6% NaCl ancl then, after rinsing, to a neutral sodium sulfate electro]yte. The solution concentration of sodium sulfate was between 15 and 20% by wei~ht.
The molten salt was maintained at a temperature of from 900 to 950F
whereas the electrolyte was maintained at a temperature of from 150 to 170F.
Specifics a9 to metal gage, times, current densities and polarities are set forth hereinbelow in Table III, :
TABLE III
SALT_ ELECTROLYTE
Time of Current GageImmersion Density Time of Inlmersion (seconds) Type (inches) ~seconds) (amp/sq. in. ) Anode Cathode Anode 304 0~ 060 5 1/4 20 20 20 309 0. 060 5 1/2 20 20 20 ~?~l~4S7 The treated steel was inspected and evaluated. No residual scale was evident, despite the short period of time in the molten oxidizing salt.
- The short period of time was possible as the steel was at an elevated temperature upon entering the molten oxidizing salt.
It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications ~ t~Q ~
t~ of the same. It is accordingly desired that in~construing~the breadth of the appended claims they shall not be li mited to the specific examples of the invention described herein.
' :
, ' .. .' ' ~ . . ';
Claims (5)
1. A process for descaling a metallic body, which comprises the steps of: immersing said body in a bath of a molten oxidizing salt; maintaining said bath at a temperature above its melting point during said immersion; removing said body from said bath after scale on said body has been conditioned for subsequent removal; subsequently immersing said body in an electrolyte of an aqueous solution of at least one neutral salt from the group consisting of the chloride, sulfate and nitrate of an alkali metal or ammonium; passing an electric current through said body and electrolyte for a period of as least seconds; and removing said body from said electrolyte.
2. A process according to claim 1, wherein said bath contains a compound from the group consisting of potassium nitrate and sodium nitrate.
3. A process according to claim 1, wherein said electro-lyte contains from 0.1 to 50 grams per liter of a compound from the group consisting of fluorides, chlorides, perchlorates, chromates, nitrites, sufites, nitrates and sulfates.
4. A process according to claim 1, wherein the neutral salt is sodium sulfate.
5. A process a.ccording to claim 1, wherein said metallic body is an alloy steel.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US672,586 | 1976-04-01 | ||
| US05/672,586 US4026777A (en) | 1976-04-01 | 1976-04-01 | Metallic descaling system |
| US767,177 | 1977-02-09 | ||
| US05/767,177 US4066521A (en) | 1977-02-09 | 1977-02-09 | Metallic descaling system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088457A true CA1088457A (en) | 1980-10-28 |
Family
ID=27100786
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA275,220A Expired CA1088457A (en) | 1976-04-01 | 1977-03-31 | Treating metallic article in molten oxidizing salt before immersion in electrolyte |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5939518B2 (en) |
| AU (1) | AU505146B2 (en) |
| BR (1) | BR7701895A (en) |
| CA (1) | CA1088457A (en) |
| DE (1) | DE2714136C3 (en) |
| ES (1) | ES457467A1 (en) |
| FR (1) | FR2346466A1 (en) |
| GB (1) | GB1520705A (en) |
| IT (1) | IT1082692B (en) |
| MX (1) | MX147289A (en) |
| SE (1) | SE433950B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59157288A (en) * | 1983-02-25 | 1984-09-06 | Nippon Stainless Steel Co Ltd | Method for pickling stainless steel strip |
| JPS60121285A (en) * | 1983-12-02 | 1985-06-28 | Nisshin Steel Co Ltd | Molten salt composition for pretreating stainless steel before pickling |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE438799A (en) * | 1939-05-24 | |||
| FR1226856A (en) * | 1958-12-23 | 1960-08-16 | Alloy steels pickling process | |
| GB1082409A (en) * | 1963-12-04 | 1967-09-06 | Mitsubishi Heavy Ind Ltd | An electrolytic descaling solution |
| GB1082410A (en) * | 1963-12-26 | 1967-09-06 | Mitsubishi Heavy Ind Ltd | An electrolytic descaling method |
| US3260619A (en) * | 1965-02-04 | 1966-07-12 | Kolene Corp | Methods and compositions for cleaning metal |
| DE1496785A1 (en) * | 1966-12-10 | 1969-08-07 | Dynamit Nobel Ag | Process for removing metal powder and lower metal oxides from the surface of wire bundles pickled with sodium hydride |
| US3951681A (en) * | 1973-11-01 | 1976-04-20 | Kolene Corporation | Method for descaling ferrous metals |
-
1977
- 1977-03-22 GB GB11937/77A patent/GB1520705A/en not_active Expired
- 1977-03-23 AU AU23523/77A patent/AU505146B2/en not_active Expired
- 1977-03-24 SE SE7703405A patent/SE433950B/en unknown
- 1977-03-28 BR BR7701895A patent/BR7701895A/en unknown
- 1977-03-30 DE DE2714136A patent/DE2714136C3/en not_active Expired
- 1977-03-31 CA CA275,220A patent/CA1088457A/en not_active Expired
- 1977-03-31 JP JP52036897A patent/JPS5939518B2/en not_active Expired
- 1977-03-31 FR FR7709776A patent/FR2346466A1/en active Granted
- 1977-03-31 IT IT48766/77A patent/IT1082692B/en active
- 1977-03-31 MX MX168595A patent/MX147289A/en unknown
- 1977-04-01 ES ES457467A patent/ES457467A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU505146B2 (en) | 1979-11-08 |
| GB1520705A (en) | 1978-08-09 |
| IT1082692B (en) | 1985-05-21 |
| BR7701895A (en) | 1977-11-29 |
| DE2714136A1 (en) | 1977-10-20 |
| FR2346466B1 (en) | 1981-11-27 |
| SE7703405L (en) | 1977-10-02 |
| ES457467A1 (en) | 1978-08-16 |
| JPS5939518B2 (en) | 1984-09-25 |
| DE2714136B2 (en) | 1981-07-23 |
| MX147289A (en) | 1982-11-10 |
| SE433950B (en) | 1984-06-25 |
| FR2346466A1 (en) | 1977-10-28 |
| JPS52129635A (en) | 1977-10-31 |
| DE2714136C3 (en) | 1986-05-28 |
| AU2352377A (en) | 1978-09-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |