EP0595686A1 - Process for pickling steel materials - Google Patents

Abstract

Process for pickling steel materials, especially continuously on a processing line, including an operation of pickling by means of an acidic solution and a water rinsing operation, characterised in that: - the pH of the rinsing water in contact with the said material is maintained at a value lower than 2.35 by adding to the rinsing water an appropriate quantity of at least one organic acid or an organic acid derivative until the material is passivated, or an acidic solution including, by weight: - from 5 to 35 % of maleic anhydride, - from 1.5 to 12.5 % of gluconic or glucoheptonic acid, - from 1 to 10 % of citric acid, the remainder consisting of water, is added to the rinsing water.

Description

The present invention relates to a process for pickling steel materials, in particular a process for continuous pickling on a treatment line, comprising a pickling operation proper and a rinsing operation.

The pickling process according to the invention can be implemented on metallic steel materials in an industrial environment, such as strips or sheets of steel before leaving the factory.

It is known to strip a steel material from passing it through a continuous or non-continuous treatment line, which puts said material in contact with an acid solution, by immersion or by spraying, then with rinsing water, also by immersion. or by sprinkling.

More particularly, it is known, in the case of pickling of steel strips by immersion, of passing said strip through successive tanks containing an aqueous solution of hydrochloric or sulfuric acid, the concentration of which varies from 350 g / l to 25 g / l according to the order of the tank in the pickling chain, and iron salts, then rinse the strip thus pickled by scrolling through tanks containing possibly demineralized water, in order to bring the pH of the residual solution on the sheet in the vicinity of neutrality.

However, it can be seen that in the event of a slowing down of the pickling line or a temporary stoppage thereof, it is formed on rinsing on the sheet of oxidation stains called rinsing stains, due to the oxidation of the salts of residual iron remained on the sheet despite rinsing and encrusted on the surface thereof.

• 100 g/l d'acide chlorhydrique ;
• 90 g/l d'ions ferreux sous forme Fe++ (FeCl₂),

le reste étant de l'eau déminéralisée, et la température de la solution dans les bacs étant maintenue à 85°C.Tests have been carried out by pickling a standard steel strip in pickling tanks containing a pickling solution having the following composition:

• 100 g / l hydrochloric acid;
• 90 g / l of ferrous ions in the form of Fe ++ (FeCl₂),

the rest being demineralized water, and the temperature of the solution in the tanks being maintained at 85 ° C.

It is noted that after two minutes of stopping the line, rinsing spots appear on the sheet, and after 6 minutes 30 seconds of stopping, the sheet has a multitude of rinsing spots.

However, the presence of these rinsing spots is detrimental to the quality of the product and leads to each stop, or even in the event of slowing of the pickling line, the scrapping of the pickled product.

The object of the present invention is to propose a process for pickling steel materials which makes it possible to avoid the appearance of oxidation stains (called rinsing stains) in the event of stopping or slowing down of the pickling line.

• l'on maintient le pH de l'eau de rinçage en contact avec ledit matériau à une valeur inférieure à 2,35 par addition à l'eau de rinçage d'une quantité appropriée d'au moins un acide organique ou un dérivé d'acide organique, jusqu'à passivation du matériau, ou
• l'on ajoute à l'eau de rinçage une solution acide comprenant, en poids :
  • . de 5 à 35% d'anhydride maléique,
  • . de 1,5 à 12,5% d'acide gluconique ou glucoheptonique,
  • . de 1 à 10% d'acide citrique, le reste étant constitué par de l'eau.

The subject of the present invention is a process for pickling steel materials, in particular continuously on a treatment line, comprising a pickling operation using an acid solution, and a water rinsing operation, characterized in that than :

• the pH of the rinsing water is kept in contact with said material at a value less than 2.35 by adding to the rinsing water an appropriate amount of at least one organic acid or a derivative of organic acid, until the material is passivated, or
• an acid solution is added to the rinsing water comprising, by weight:
  • . from 5 to 35% maleic anhydride,
  • . from 1.5 to 12.5% gluconic or glucoheptonic acid,
  • . from 1 to 10% citric acid, the rest being water.

Among the suitable organic acids, mention may be made of formic, acetic, malonic, succinic, tartaric, maleic, citric, glutaric, trioxyglutaric, gluconic, glucoheptonic, lactic, benzoic, citric, ethylenediaminetetraacetic, hydroxyethylenediaminetriacetic, diethylenetriaminepentaacetic acid the corresponding esters and anhydrides, and mixtures of said acids, esters and anhydrides.

Advantageously, a solution comprising a mixture of the corresponding acids or esters and anhydrides is added to the rinsing water.

• de 5 à 35% d'anhydride maléique,
• de 1,5 à 12,5% d'acide gluconique ou glucoheptonique,
• de 1 à 10% d'acide citrique, le reste étant constitué par de l'eau.

According to a preferred embodiment, the pH is maintained at a value lower than 2.35 by adding to the rinsing water a mixture comprising:

• from 5 to 35% maleic anhydride,
• from 1.5 to 12.5% gluconic or glucoheptonic acid,
• from 1 to 10% citric acid, the rest being water.

• 20% d'anhydride maléique,
• 7% d'acide gluconique ou glucoheptonique, et
• 5% d'acide citrique,

le reste étant constitué par de l'eau, le pH étant en outre avantageusement maintenu à une valeur inférieure à 2,35.Preferably, the acid solution added to the rinsing water comprises, by weight:

• 20% maleic anhydride,
• 7% gluconic or glucoheptonic acid, and
• 5% citric acid,

the remainder being constituted by water, the pH being advantageously maintained at a value lower than 2.35.

Advantageously, the acid solution is added to the rinsing water in a proportion of from 0.01% to 2% by weight, preferably 1% by weight.

• de 1 à 10%, de préférence 5%, en poids, d'un alcool, d'un amino-alcool ou d'un de leurs sels, avantageusement choisi parmi les alcools monovalents, divalents et polyvalents et les amino-alcools correspondants, et
• de 0,5 à 10%, de préférence 5%, en poids, d'un agent tensio-actif.

According to a particularly advantageous embodiment, the acid rinse solution also contains:

• from 1 to 10%, preferably 5%, by weight, of an alcohol, an amino alcohol or a salt thereof, advantageously chosen from monovalent, divalent and polyvalent alcohols and the corresponding amino alcohols, and
• from 0.5 to 10%, preferably 5%, by weight, of a surfactant.

As an example of preferred alcohols, mention may be made of glycerol, erythritol, ethylene glycol, diethylene glycol, ethanolamine, diethanolamine, triethanolamine, etc.

The surfactant can be of the nonionic, anionic, cationic and ampholytic type.

Among the nonionic surfactants, there may be mentioned the condensation products of ethylene oxide with various compounds with labile hydrogen, reactive with ethylene oxide, which have long hydrophobic chains (for example chains aliphatics of about 8 to 20 carbon atoms), these condensation products containing hydrophilic polyoxyethylene moieties, for example the condensation products of poly (ethylene oxide) with fatty acids, fatty alcohols, fatty amides, polyalcohols (for example sorbitan monostearate) and poly (propylene oxide) (for example the products of the Pluronic series).

Among the anionic surfactants, mention may be made of the water-soluble salts of monoglycerides of higher fatty acid monoglycerides, such as the sodium salt of monoglyceride monosulfate of hydrogenated coconut oil fatty acids, higher alkyl sulfates such as sodium lauryl sulfate, alkylarylsulfonates such as sodium dodecylbenzene sulfonate, higher alkyl sulfoacetates, higher fatty acid esters of 1,2-dihydroxypropane sulfonates, and substantially higher aliphatic acylamides saturated formed with lower aliphatic aminocarboxylic acids, such as those whose fatty acid, alkyl or acyl radicals have 12 to 16 carbon atoms, etc. Examples of the last mentioned amides are N-lauroylsarcosine, and the salts sodium, potassium and ethanolamine from N-lauroyl-, N-myristoyl- or N-palmitoyl-sarcosine.

Among the cationic surfactants, mention may be made of long chain quaternary ammonium salts, for example lauryltrimethylammonium chloride or cetyltrimethylammonium chloride.

Among the ampholytic surfactants, there may be mentioned derivatives of aliphatic compounds or aliphatic derivatives of secondary and tertiary heterocyclic amines in which the aliphatic radical may be straight or branched chain, and in which one of the aliphatic substituents contains approximately 8 to 18 carbon atoms, while at least one other substituent contains an anionic group of solubilization in water, for example a carboxy-, sulfonate or sulfato group. Among the compounds of this category, mention will be made of sodium 3- (dodecylamino) propionate, sodium 3- (dodecylamino) propane-1-sulfonate, sodium 2- (dodecylamino) ethyl sulfate, 2- (dimethylamino ) sodium octadecanoate, disodium 3- (N-carboxymethyldodecylamino) -propane-1-sulfonate, disodium octadecyl-iminodiazetate, sodium 1-carboxymethyl-2-undecylimidazole and N, N-bis (2-hydroxyethyl) - 2-sulfato-3-dodecoxypropyl-amine sodium.

The rinsing operation is advantageously carried out by immersing the material to be treated in at least one rinsing cell, the acid rinsing solution being supplied in at least one of the rinsing cells, or by spraying the material, for example using spray bars.

The subject of the invention is also a acid rinse solution as defined above.

An example of a rinsing solution according to the invention will be given below.

Example:

• 20% d'anhydride maléique,
• 7% d'acide gluconique,
• 5% d'acide citrique,
• 5% diéthylèneglycol,
• 5% de dodécylbenzène-sulfonate de sodium,

le reste étant de l'eau déminéralisée.A solution consisting of:

• 20% maleic anhydride,
• 7% gluconic acid,
• 5% citric acid,
• 5% diethylene glycol,
• 5% sodium dodecylbenzene sulfonate,

the rest being demineralized water.

The characteristics and advantages of the invention will appear during the following description, for which reference will be made to the appended figure, representing a schematic view of an exemplary embodiment of a continuous pickling line for a strip of steel.

In the embodiment shown, the pickling line for a sheet metal strip 1 is made up of two units, a pickling unit 2, and a rinsing unit 3.

The pickling unit 2 consists of pickling tanks 4, containing a known acid pickling solution, for example an aqueous solution consisting of 50 g / l of hydrochloric acid and iron salts for the first tank of the line. pickling, and an aqueous solution consisting of 200 g / l of hydrochloric acid and iron salts in the last tank of the pickling line, the intermediate tanks containing solutions having intermediate concentrations.

Sheet 1 scrolls in successive tanks going from the first tank containing 50 g / l of hydrochloric acid in the last tank containing 200 g / l of hydrochloric acid, on rollers 5.

The rinsing unit 2 is made up of rinses for spraying rinsing water 6, sectorized, spraying the sheet 1 of rinsing water over its entire upper and lower surface.

In the exemplary embodiment shown, the pickling line comprises four rinsing cells, constituted by four spraying ramps 7a, 7b, 7c and 7d, the ramp 7a being that located immediately after the last pickling tank 4.

Under each sprayer boom 7a, 7b, 7c, 7d, there is a rinsing water recovery funnel, respectively 8a, 8b, 8c and 8d, and a water recovery tank, respectively 9a, 9b, 9c and 9d.

As a variant, the rinsing unit 2 can be of the same type as the pickling unit 1, that is to say comprise rinsing tanks in which the sheet 1 is immersed and scrolls.

Measurements of the pH of the rinsing water and / or of the concentration of the Fe³⁺ ions in the recovery tanks 9a, 9b, 9c, 9d, that is to say after passage of the sheet 1, were carried out.

These measurements made it possible to note that the pH in the first recovery tank 9a was less than 2, that is to say very acid, the pH in the tank 9b was close to 4, the pH in the tank 9c was close to 5, and in the bac 9d close to 6.

The tests have shown that, as long as the pH is less than 2.35, the iron ions contained in the solution do not precipitate in the form of ferric compounds of the ferric hydroxide type Fe (OH) ₃, but as soon as the pH is greater than 2.35, these iron ions precipitate as ferric compounds.

In view of the fact that part of the rinsing water remains on the sheet, this precipitation of residual ferric compounds on the sheet causes, in the event of the line stopping or slowing down, oxidation of said sheet, causing the rinse stain.

In addition, when the sheet is passivated, for example when it is established that the Fe³⁺ ions have been entrained in rinsing, it is protected, and the oxidation phenomenon is stopped.

The acid solution described in the above example was then added to the rinsing water of the spray boom 7b in a proportion of 1% by weight.

In this case, at the recovery tank 9b, the concentration of Fe³⁺ ions had increased significantly and the pH had decreased, the measurements carried out having given the following results: Rinsing tank N ° pH 9a 1.5 9b 2 9c 5 9d 6

It was found that the sheet was passivated and that the risk of oxidation had disappeared at the outlet of the second rinsing tank, and therefore it was not necessary to add the acid solution according to the invention to the rinsing water. 3rd and 4th rinsing tanks.

If the sheet had not been passivated at the leaving the second rinsing tank and / or if a risk of the appearance of the oxidation phenomenon remains, it would have been necessary to add the acid solution according to the invention also to the rinsing water of the third tank.

This risk of the appearance of the oxidation phenomenon can for example be evaluated in the following manner: the concentration of ferric ions in the recovery tank 9c is measured, the acid solution according to the invention is temporarily added to the water of rinsing of the third tank, and the concentration of ferric ions is again measured in the corresponding recovery tank 9c; a significant increase in this concentration indicates a risk of the appearance of the oxidation phenomenon.

The sheet 1 thus rinsed does not show any oxidation spots on the surface, even after the line has stopped for 8 minutes.

Claims (16)

Process for pickling steel materials, in particular continuously on a treatment line, comprising a pickling operation using an acid solution, and a rinsing operation with water, characterized in that: the pH of the rinsing water is kept in contact with said material at a value less than 2.35 by adding to the rinsing water an appropriate amount of at least one organic acid or a derivative d organic acid, until the material is passivated, or an acid solution is added to the rinsing water comprising, by weight: . from 5 to 35% maleic anhydride, . from 1.5 to 12.5% gluconic or glucoheptonic acid, . from 1 to 10% citric acid, the rest being water. Process according to Claim 1, characterized in that the pH of the rinsing water is kept in contact with said material at a value of less than 2.35 by adding to the rinsing water an appropriate amount of a mixture of organic acids or derivatives of organic acids. Process according to claim 1 or 2, characterized in that an acid solution is added to the rinsing water comprising, by weight: - from 5 to 35% of maleic anhydride, - from 1.5 to 12.5% gluconic or glucoheptonic acid, - from 1 to 10% citric acid, the rest being water. Process according to claim 3, characterized in that the acid solution comprises, by weight: - 20% maleic anhydride, - 7% gluconic or glucoheptonic acid, and - 5% citric acid,
the rest being water. Process according to Claim 1, characterized in that the acid solution is added to the rinsing water in a proportion of between 0.01% and 2%, by weight. Method according to claim 5, characterized in that the acid solution is added to the rinsing water in an amount of 1% by weight. Process according to any one of the preceding claims, characterized in that the acid solution also contains: - from 1 to 10%, by weight, of an alcohol, an amino alcohol, or a salt thereof, and - from 0.5 to 10%, by weight, of a surfactant. Process according to claim 7, characterized in that the acid solution contains: 5%, by weight, of an alcohol chosen from monovalent, divalent or polyvalent alcohols, the corresponding amino-alcohols, and their salts, and - 5%, by weight, of a surfactant. Process according to claim 7 or claim 8, characterized in that the alcohol or the amino alcohol is chosen from glycerol, erythritol, diethylene glycol, ethanolamine, diethanolamine and triethanolamine. Method according to any one of the preceding claims, characterized in that the rinsing operation is carried out by immersing the steel material in at least one rinsing cell, and the acid solution is added in at least one of said rinsing cells. Method according to one of claims 1 to 9, characterized in that the rinsing operation is made by sprinkling the material. Acid rinse solution for carrying out the process according to any one of the preceding claims, characterized in that it comprises: - from 5 to 35% of maleic anhydride, - from 1.5 to 12.5% gluconic or glucoheptonic acid, - from 1 to 10% citric acid, the rest being water. Acid rinse solution according to claim 12, characterized in that it comprises: - 20% maleic anhydride, - 7% gluconic or glucoheptonic acid, and - 5% citric acid,
the rest being water. Acid rinse solution according to claim 12 or claim 13, characterized in that it additionally contains: - from 1 to 10%, by weight, of an alcohol, an amino alcohol, or a salt thereof, and - from 0.5 to 10%, by weight, of a surfactant. Acid rinse solution according to claim 14, characterized in that the alcohol or the amino alcohol is chosen from glycerol, erythritol, ethylene glycol, diethylene glycol, ethanolamine, diethanolamine, and triethanolamine. Acid rinse solution according to claim 14 or claim 15, characterized in that it contains: 5%, by weight, of an alcohol chosen from divalent or polyvalent monovalent alcohols and amino alcohols, and - 5%, by weight, of a surfactant.

Images