FI83545B - FOERFARANDE FOER KEMISK POLERING AV YTOR AV ROSTFRITT STAOL SAMT VID FOERFARANDET ANVAENT BAD. - Google Patents

Abstract

Baths comprising, in aqueous solution, a mixture of hydrochloric acid, phosphoric acid, nitric acid and sulphosalicylic acid and at least one abietic compound.

Description

1 83545

The present invention relates to a composition for baths used in the chemical polishing of stainless steel surfaces.

Chemical polishing of metal surfaces is a well-known method (Polissage electrolytique et chimique des 10 metaux Electrolytic and chemical grinding of metals - W.J. Mc. G. TEGART - Dunod - 1960 - from page 122 onwards); it consists of treating the metal surfaces to be polished in oxidizing baths. When austenitic stainless steel is chemically polished, water-based baths containing a mixture of hydrochloric acid, phosphoric acid and nitric acid are generally used (U.S. Patent A 2,662,814). To improve the quality of the polishing, suitable additives such as surfactants, viscosity regulators and brighteners are usually added to the baths. Thus, U.S. Patent A-370,824 disclosed the composition of a bath for polishing stainless steel surfaces, wherein the aqueous solution contained a mixture of phosphoric acid, nitric acid and hydrochloric acid, a viscosity modifier selected from the group consisting of water-soluble polymers, and a surfactant.

These known polishing baths are characterized by the fact that they corrode metal very quickly. 30 Using these baths, the stainless steel surface usually cannot be polished for more than a few minutes, otherwise localized corrosion may occur. This high operating speed of the known baths is a disadvantage, since it makes it impossible to use certain applications, in particular the polishing of the internal surfaces of large partition tanks, such as steam boilers, autoclaves or crystallization basins. The time required for polishing and emptying these containers is generally considerably longer than the optimal time for chemical polishing treatment, whereby uniform polishing of the inner walls actually becomes impossible because certain areas do not become sufficiently polished while other areas are deeply corroded. The high operating speed of known polishing baths also makes it difficult to control polishing. Furthermore, the known baths are unsuitable for polishing surfaces in the vicinity of which it is difficult to renew the bath because of even drastic local changes in the composition of the bath. They are also not suitable for polishing equipment in which the surface area to be polished is very large in comparison with the volume of the bath used, for example heat exchangers in which the heat exchange surface area is very large.

EP Patent Publication B 19964 (Solvay & Co) discloses chemical polishing baths which have a very gentle function and which avoid the disadvantages described above. These baths consist of hydrochloric acid, phosphoric acid and nitric acid, sulfosalicylic acid, alkylpyridine chloride and methylcellulose mixed in the correct proportions. These have proven to be particularly useful for the gentle polishing of flat austenitic stainless steel surfaces, especially ASTM-304L or ASTM-316L of chromium and Nikke alloy grades.

New compositions of baths for gentle chemical polishing of stainless steel surfaces, in particular austenitic grades, have now been discovered which provide a better polishing result and also allow simultaneous polishing of different steel grades, which may be necessary, for example, in riveted, welded or bolted galvanized .

li 3 83545

The invention thus relates to baths for the chemical polishing of stainless steel surfaces which, in aqueous solution, contain hydrochloric acid, phosphoric acid and nitric acid and sulfosalicylic acid; according to the invention, these baths contain at least one soluble abietic compound in their aqueous solution.

In the bath of the invention, the abietic compound is a chemical compound having an abiethyl radical of the following general formula: 10 CH,

pA

C »3 A / k /

15 JlfjA

cl3 or a hydroabietyl or dehydroabietyl radical.

According to the invention, the abietal compound must be soluble in aqueous solution.

Useful abietal compounds in the baths of the invention include abietamines.

Particularly preferred abietamines for use in the baths of the invention are compounds of the following general formula:

RJN

30 X2 in which

R 1 is an abiethyl radical, a hydroabietyl radical or a dehydroxyethyl radical as described above, X 1 is a radical having at least one carbonyl group, and X 8 3445 X 2 is a hydrogen atom or a radical having at least one carbonyl group.

Examples of such abietamines which are well suited for the baths according to the invention are those in which at least one of the radicals Xx and X2 is a radical of the general formula -CH2-R2 wherein R2 is a linear or cyclic, substituted or unsubstituted, saturated or unsaturated alkyl radical which contains at least one carbonyl group. Most preferred of these compounds are those in which the -CH 2 group is attached to the carbonyl group of the R 2 residue via at least one carbon atom containing 15 hydrogen atoms. Such substituted abietamines and methods for their preparation are disclosed in GB Patent Publication A 734 665. Examples of such abietamines for use in the baths of the invention are those in which the R 2 alkyl-20 residue is acetonyl, 2-keto-butyl, 4-methyl-2-keto-pentene. -3-yl, 4-hydroxy-4-methyl-2-keto-pentyl, 2-keto-cyclopentyl, 4-hydroxy-2-ketopenten-3-yl, 2-ketocyclohexyl, 2,5-diketo -hexyl and 2-phenyl-2-keto-ethyl.

In the chemical polishing baths according to the invention, the concentrations of hydrochloric acid, phosphoric acid, nitric acid, sulfosalicylic acid and the abietic compound depend on the nature of the metal to be treated, the working temperature and the desired duration of the polishing treatment. Baths according to the invention which are well suited for the chemical polishing of chromium and / or Nikke-alloyed stainless steel surfaces in about 2-24 hours are those in which the aqueous solution contains, per liter, 1-6 moles of hydrochloric acid, 0.01-1 moles of phospho-35 silicic acid, 0.005 to 0.5 moles of nitric acid, 0.05 to 20 g of sulfosa-

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5,83545 lisylic acid and 0.001 and 3 g of the abietal compound. Particularly preferred baths are those in which the total molarity of the mixture of hydrochloric acid, phosphoric acid and nitric acid is 1 to 7, preferably 1.8 to 6, at a concentration of sulfosalicylic acid of 5, expressed in g / l of solution, 0.05 to 1.5 times the hydrochloric acid, the total normality of the mixture of phosphoric acid and nitric acid.

In one embodiment, the baths of the invention further comprise alcohol, ether or ether-alcohol in solution in an aqueous solution. The optimal amount of this additive in the aqueous solution of the bath depends on several parameters, in particular the said additive, the chosen abietal compound and the concentration of the ingredients of the bath. In practice, the concentration of this 15-like additive is preferably 0.001 to 10 g per liter of aqueous solution.

Provided that all other variables remain unchanged, the baths according to the embodiment of the present invention allow a very good surface polishing, in particular with good brightness.

The polishing baths according to the invention may additionally contain conventional additives used in known baths for the chemical polishing of metal surfaces, for example surfactants and viscosity regulators.

Baths according to the invention, developed in particular for the gentle polishing of austenitic stainless steel surfaces, contain per liter of aqueous bath solution: 2-5 moles of hydrochloric acid, 0.02-0.5 moles of phosphoric acid, 0.01-0.2 moles of nitric acid, 0.1 -10 g sulfosalicylic acid 0.010-2.5 g abietic substance, 0.002-5 g alcohol, ether or ether alcohol, 0.005-6 g surfactant.

6 83545

The great advantage of the polishing baths according to the invention, after the concentrations of the bath components have been selected, is their ability to perform polishing at a low speed, even often within an hour, whereby uniform polishing of large or hard-to-reach surfaces becomes possible. The baths are particularly well suited for polishing metal surfaces with a very large surface area compared to the possible volume of the bath. An example is an interesting application in which a metal surface is polished with an area (expressed in m2) of 1 to 10 times the volume of the polishing bath in contact with it (expressed in m3).

The baths according to the invention are suitable for polishing all austenitic stainless steel surfaces. A particularly preferred example is the polishing of austenitic copper and nickel alloyed stainless steel surfaces, especially those containing 12-26% chromium, 6-30% nickel and 0-6% molybdenum, such as steel grades 18/8 and 18/10/2, 5.

An interesting application for the baths according to the invention is the polishing of equipment containing different steels, in particular welded equipment, without local corrosion damage to the equipment. An example is the possibility of polishing welded equipment in which chromium and nickel alloy steel grade 18/8 (ASTM-304 and 304L) is combined with chromium, nickel and molybdenum alloy steel grade 18/10 / 2.5 (ASTM-316 and 316L ).

The invention also relates to a method for polishing a stainless steel surface, wherein the surface is brought into contact with a chemical polishing bath according to the invention.

In the method according to the invention, the polishing bath can be used at any temperature and pressure at which its components do not disintegrate. However, it has proven advantageous to use the bath at normal pressure above

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7,83545 at 25 ° C and below 100 ° C, with temperatures of 50-80 ° C being preferred.

Contacting the metal surface with the bath can be accomplished by any means, for example, by immersion.

In the method according to the invention, the time during which the surface to be sanded is in contact with the bath must be long enough to achieve effective surface polishing; however, it shall not exceed a critical value above which localized corrosion damage is possible. The optimal contact time depends on several parameters, such as the metal or surface-forming alloy to be polished, the shape of the surface and the initial roughness, the composition of the bath; the working temperature, the possible turbulence when the bath comes into contact with the surface, the surface area to be polished and the volume of the bath used; it must be determined in each case by routine laboratory determination.

In the preferred form of use of the method according to the invention, nitric acid is added to the bath after the metal surface has been brought into contact with the bath to regenerate the bath. Nitric acid addition can be performed continuously or intermittently. The addition is adjusted so that the nitric acid concentration of the bath 25 remains constant at an optimum value with respect to the gloss of the metal surface.

The value of the invention is proved by means of the application examples below.

Example 1 A stainless steel plate having an area of 21.50 cm 2, grade ASTM-304L (steel alloy with chromium 18.0-20.0% and nickel 8.0-12.0%) was immersed at 55 ° C; 500 cm3 bath per liter containing: 3 moles of hydrochloric acid, 35 0.15 moles of phosphoric acid, 0.01 moles of nitric acid _____ Γ e 83545 0.5 g of sulfosalicylic acid, 1 g of "RODINE 213" (Amchem Products Inc) (a mixture of substituted abietamines, isopropanol and surfactants).

5 The arithmetic mean starting roughness of the slab

Ra = 0.27 μm.

After 13 hours of treatment (the bath was shaken continuously), it was measured that the metal surface of the bath was corroded by an average of 20. The plate was then removed from the bath, washed with water and dried. The surface appeared smooth and shiny. Measured gloss (ASTM standard E430) and arithmetic mean roughness (Ra): gloss: 22%

Ra: 0.13 pm.

15 Example 2

The experiment described in Example 1 was repeated under the following conditions:

Stainless steel plate grade ASTM-316L (16.0-18.0% chromium, 10.0-14.0% nickel and 2.0-3.0% molybdenum 20 alloy)

Slab surface area: 50 cm2

Polishing bath composition (amounts per 1 1 bath): 2.7 moles of hydrochloric acid 25 0.2 moles of phosphoric acid 0.02 moles of nitric acid 1 g of sulfosalicylic acid 1 g of "RODINE 213" 2 g of "TRITON N101" (Rohm & Haas Co) 30 (surfactant mixture based on alkylaryl-polyether alcohols).

Bath temperature: 65 ° C. Bath volume: 1250 cm3 Processing time: 6 hours. The starting roughness of the plate was Ra = 0.28 μm. After the treatment, the following were measured: 35 corrosion depth: 22 μm gloss: 35% 983545 roughness Ra = 0.09 μm.

Example 3

The experiment described in Example 1 was repeated under the following conditions: 5 Hardened stainless steel plate grade ASTM-430 (16.0-18.0% chromium-containing alloy with nickel and carbon contents not exceeding 0.75% and 0.12%).

Slab surface area: 50 cm2.

Polishing bath composition (amounts per 1 l bath): 2.7 moles of hydrochloric acid 0.2 moles of phosphoric acid 0.02 moles of nitric acid 3 g of sulfosalicylic acid 15 1 g of "RODINE 213" (determined in Example 1) 2 g of "TRITON N101 "(determined in Example 2).

Bath temperature: 65 ° C. Bath volume: 500 cm3.

20 Processing time: 10 hours. The starting roughness of the plate was Ra = 0.70 μm. After treatment, the following were measured: etching depth: 25 μm gloss: 12% roughness R 2 = 0.22 μm.

25 Example 4

The experiment described in Example 1 was repeated under the following conditions:

Assembly with two rectangular stainless steel plates, welded together in the longitudinal direction: 30 one plate with an area of 30 cm2, steel grade ASTM-304L, the other plate with an area of 30 cm2, steel grade ASTM-316L.

Polishing bath composition (amounts per 1 1 bath); 4 moles of hydrochloric acid 35 0.1 moles of phosphoric acid 0.02 moles of nitric acid 10 83545 1 g of sulfosalicylic acid 1 g of the product "RODINE 213" 1.3 cm3 of a mixture of isopropanol and n-propanol. Bath temperature: 65 ° C. Bath volume: 1000 cm3.

5 Processing time: 10 hours.

The initial roughnesses of the plates in the assembly were as follows: ASTM-304L plate: Ra = 0.29 μm ASTM-316L plate: Ra = 0.28 μm.

10 After treatment, the assembly appeared smooth and shiny and showed no signs of corrosion. Corrosion depth, gloss and roughness were measured from both plates: ASTM-3041 plate: corrosion depth: 27 μm; Gloss: 21%, roughness Ra = 0.13 μm ASTM-316L plate: etching depth: 22 μm, gloss: 22%, roughness Ra = 0.11 μm.

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Claims (10)

1. A bath for chemical polishing of stainless steel surfaces comprising an aqueous solution of a mixture of hydrochloric acid, phosphoric acid and nitric acid and sulfosalicylic acid, characterized in that it contains at least one soluble compound with an aqueous solution. abietyl radical having the general formula ch3 ch3 or a hydroabietyl or dehydroabietyl radical. Bath according to claim 1, characterized in that the abietic compound is a substituted abietamine of the general formula. Xi R 1 is χ 2 where R 1 is an abietyl, hydroabietyl or dehydroabietyl radical X 2 is a radical containing at least one carbonyl group and X 2 is a hydrogen atom or a radical containing at least one carbonyl group. Bath according to claim 2, characterized in that at least one of the radicals X 1 and X 2 II is 83 545 is a radical of the general formula -ch 2 -r 2 where R 2 is a linear or cyclic, substituted or unsubstituted, saturated or unsaturated alkyl group containing at least one carbonyl group. 4. A bath according to claim 3, characterized in that in the radical -CH2-R2, the group -CH2- is bonded to a carbonyl group in the residue R2 by means of a carbon atom to which is attached at least one hydrogen atom. 5. A bath according to claim 4, characterized in that the alkyl group R 2 is selected from the following groups: acetonyl, 2-ketobutyl, 4-methyl-2-ketopenten-3-yl, 4-hydroxy-4-methyl-2- ketopentyl, 2-ketocyclopethnyl, 4-hydroxy-2-ketopenten-3-yl, 2-ketocyclohexyl, 2,5-diketo-hexyl and 2-phenyl-2-ketoethyl. 6. A bath according to any one of claims 1-5, characterized in that it further comprises an alcohol, an ether or an ether-alcohol dissolved in the aqueous solution. Bath according to claim 6, characterized in that it contains, per 1 aqueous solution, 2-5 moles of hydrochloric acid 0.02-5 moles of phosphoric acid 0.01-0.5 moles of nitric acid 0.1 - 10 g of sulfosalicylic acid, 0.1 - 2.5 g of an abiet compound 0.002 - 5 g of an alcohol, an ether or an ether alcohol and 0.005 - 6 g of a surfactant. A method of polishing a stainless steel surface by contacting the surface with a chemical polishing bath, characterized in that a bath according to any one of claims 1-7 is used. 83545 9. A method according to claim 8, characterized in that the bath has a temperature of 40-80 ° C. 10. A process according to claim 8 or 9, characterized in that, after the contact surface has been brought into contact with the bath, the same more nitric acid is added. Il