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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F3/00—Brightening metals by chemical means
  • C23F3/04—Heavy metals
  • C23F3/06—Heavy metals with acidic solutions

Definitions

• the present invention relates to a composition of a bath for the chemical polishing of steel surfaces, in particular stainless steel.
• Chemical polishing of metal surfaces is a well-known technique (Electrolytic and chemical polishing of metals - W.J.Mc.G.Tegart-Dunod -1960 - p.122 et seq.). This technique consists in treating the metal surfaces to be polished, with baths of mineral acids containing suitable additives, in particular viscosity regulators, surfactants and possibly brighteners.
• aqueous baths are generally used containing, in admixture, nitric acid, hydrochloric acid and optionally phosphoric acid.
• a composition of a bath for the chemical polishing of stainless steel surfaces comprising, in aqueous solution, a mixture phosphoric acid (145 to 580 g / 1), nitric acid (17 to 85 g / 1) and hydrochloric acid (16 to 80 g / l), a viscosity regulator chosen from water-soluble polymers, a surfactant and sulfosalicylic acid as a brightening agent.
• Polishing baths according to this known composition are very effective. Used at a temperature of the order of 70 to 100 ° C, they make it possible to obtain in a few minutes, generally in less than three minutes, an optimum polishing and polishing of stainless steel surfaces alloyed with chromium and nickel.
• a disadvantage of these known polishing baths lies in their high speed of action, which makes them unusable for certain applications, in particular for polishing the internal face of the walls of large tanks, such as boilers, autoclaves or crystallizers.
• the time required for filling and emptying such tanks being generally much greater than the duration of the optimum chemical polishing treatment, it indeed becomes impossible to obtain a uniform TIe polish . the wall, certain areas thereof being insufficiently polished, while others risk being corroded.
• the invention aims to remedy the aforementioned drawbacks, by providing a composition of a bath for the chemical polishing of steel surfaces, in particular stainless steel, which has a moderate speed of action while nevertheless ensuring that it is obtained of polishes comparable to those obtained with known polishing baths. It aims in particular to provide a composition of a polishing bath which, used at a temperature of the order of 20 to 100 ° C, requires several hours of treatment to impart optimum polish to surfaces made of stainless steel alloyed with chrome and nickel.
• the invention therefore relates to a bath for the chemical polishing of steel surfaces, comprising, in aqueous solution, a mixture phosphoric acid, hydrochloric acid and nitric acid, a viscosity regulator, a surfactant and sulfosalicylic acid as a brightening agent; according to the invention, the overall normality of the mixture of acids in the aqueous solution is between 1 and 6, the ratio between the normality of each acid in the mixture of acids and the overall normality of the latter is between 0, 05 and 0.80 for phosphoric acid, between 0.15 and 0.90 for hydrochloric acid and between 0.001 and 0.80 for nitric acid, the viscosity regulator is a cellulose ether whose content, expressed in g / 1 of aqueous solution, is between 0.3 and 0.7 times the overall normality of the mixture of acids, the surfactant is alkylpyridinium chloride, the content of which, expressed in g / 1 of aqueous solution, is between
• the respective contents of phosphoric, hydrochloric and nitric acids, cellulose ether, alkylpyridinium chloride and sulfosalicylic acid are chosen depending on the nature of the metal treated, the temperature of work and the desired duration for the polishing treatment.
• compositions which are very suitable for ensuring the chemical polishing of surfaces of stainless steel alloyed with chromium and nickel, in a time of between 2 and 24 hours are those for which the overall normality of the mixture of acids is between 1.5 and 3, the ratio between the normality of each acid in the mixture of acids and the overall normality of the latter being advantageously between 0.20 and 0.60 for phosphoric acid, between 0.25 and 0.75 for 1 hydrochloric acid and between 0.002 and 0.10, preferably 0.005 and 0.05, for nitric acid.
• the respective contents of cellulose ether, of alkylpyridinium chloride and of sulfosalicylic acid in the polishing bath according to the invention depend on its overall content of phosphoric, hydrochloric and nitric acids. According to the invention, it is generally advantageous that, in addition, the ratio between the weight of alkylpyridinium chloride and the weight of cellulose ether is between 0.5 and 1.5 and the ratio between the weight of chloride of alkylpyridinium and the weight of sulfosalicylic acid is between 1 and 3.
• Preferred compositions are those in which the weight of cellulose ether is equal to the weight of alkylpyridinium chloride and is twice the weight of sulfosalicylic acid.
• the cellulose ether used in the chemical polishing bath according to the invention must be soluble in water. Methylcellulose is particularly suitable.
• the alkylpyridinium chloride is preferably chosen from those derived from alkanes having from 10 to 18 carbon atoms. Cetylpyridinium chloride and laurylpyridinium chloride have been found to be particularly advantageous.
• a chemical polishing bath in accordance with the invention was used to polish the internal face of a stainless steel tank with a capacity of 27.5 m 3 and a diameter of 2.5 m, made of grade 316 stainless steel L, which is a steel alloyed with chromium (16.0 to 18.8%), nickel (10.0 to 14.0%) and molybdenum (2.0 to 3.0%) (Techniques de l ' Engineer - Metallurgy - Tome I - M.323-17 - March 1974).
• the polishing bath was introduced into the tank, at a rate of 5 1 per dm 2 of surface to be polished, and it was subjected to a stirring movement therein by means of a paddle stirrer, while maintaining its temperature at 45 ° C.
• the tank was drained and rinsed with carbonated water.
• the entire interior surface of the tank was found to be shiny and uniformly smooth to the touch, with no roughness or corroded area.
• Example 2 By way of comparison, a tank similar to that of Example 1 was subjected to mechanical polishing using an abrasive, the grain size of which corresponded to No. 270 of the ASTM series of standard sieves.
• the interior surface of the tank revealed a non-homogeneous polish. When touched, the surface still had significant roughness.
• a comparison of Examples 1 and 2 shows that the polishing bath according to the invention makes it possible to obtain very high quality polishes in high capacity stainless steel tanks, thanks to the application of a chemical polishing technique using slow action.

Landscapes

• 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)
• ing And Chemical Polishing (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Coating With Molten Metal (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=9225941

Family Applications (1)

Country Status (6)

Cited By (10)

Families Citing this family (2)

Citations (4)

• 1979
  • 1979-05-25 FR FR7913556A patent/FR2457315A1/fr active Granted
• 1980
  • 1980-05-14 AT AT80200451T patent/ATE3065T1/de not_active IP Right Cessation
  • 1980-05-14 EP EP80200451A patent/EP0019964B1/de not_active Expired
  • 1980-05-14 DE DE8080200451T patent/DE3062709D1/de not_active Expired
  • 1980-05-21 JP JP6766780A patent/JPS5629673A/ja active Granted
  • 1980-05-23 CA CA000352610A patent/CA1153675A/fr not_active Expired

Patent Citations (4)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events