DE1191657B - Descaling paste for iron, cast iron and steel - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C23g

German class: 48 d2 - 5/00

Number: 1191 657

File number: F 14078 VI b / 48 d2

Filing date: March 3, 1954

Opening day: April 22, 1965

As is well known, forms on the surface of iron and steel during rolling, forging or drawing When warm, a layer of scale that prevents paints and other protective coatings from adhering hindered on the base metal, so that there is a risk of destruction by corrosion. It is known, Descaling small objects or entire metal sheets chemically or electrochemically, by dipping the workpieces in acidic solutions. It is also known the solutions of acids or acid salts that cannot be oxidized or oxidized only slowly, hydrogen peroxide or compounds, which contain hydrogen peroxide to be added. In general, none of these processes occurs chemical or electrochemical dissolution of the scale, but that which lies under the scale Iron and iron oxide are attacked by the acids, and the hydrogen which is developed in the process lifts the scale off the surface of the steel so that it falls to the bottom of the container. It is also known to add inhibitors to such baths, which limits the attack on the steel.

For large objects that cannot be immersed in a bath, descaling can occur be done either mechanically by blowing sand or other granular material or by so-called natural descaling, by placing the objects under the action of the atmosphere long periods of time, the oxygen in the air and through the pores of the scale the humidity can penetrate and rust the iron under the tinder. Because the rust a takes up a much larger volume than the iron from which it was formed, the grate lifts the Scale off the surface. This method of natural descaling has the disadvantage that it takes a long time and the surface is relatively strong.

It is also known to take place in the treatment of metal surfaces, especially for derusting of immersion in liquids to use pastes that are inert from the treatment liquids Fillers are made and applied to the surface.

The invention relates to an acidic descaling paste for iron, cast iron and steel containing an oxidizing agent and inert mineral fillers, in which the disadvantages of known descaling agents are avoided, ie a paste which can be easily applied to any workpiece made of steel or iron and which Has the effect of quickly removing the scale layer from the surface, without descaling paste for iron, cast iron
and steel

Applicant:

Herbert Manfred Freud dit Jean Frasch,

Nanterre, Seine (France)

Representative:

Dr. H. Feder, patent attorney,

Düsseldorf 1, Pempelforter Str. 18

Named as inventor:

Herbert Manfred Freud dit Jean Frasch,

Nanterre, Seine (France)

Claimed priority:

France of March 5, 1953 (643 999),
of April 29, 1953 (52 114),
dated June 24, 1953 (650 521)

practically attacking the base metal. According to the invention, 1 kg of this descaling paste contains 0.2 to 1 gram equivalent of oxygen-releasing, water-soluble salts and a non-reducing acid or salts of such an acid, the remainder being water. The oxidizing anion can be chosen as desired, provided that it is reduced at normal temperature by the hydrogen released during the reaction. For example, the following anions are possible: CrO ₄ -, Cr ₂ O ₇ -, MnO ₄ -, MnO ₄ -, NO ₃ -, NO ₂ ", ClO ₃ -, ClO ₄ -. It is particularly advantageous to use anions, which change their color when they pass from the higher oxidation state into the reduced state, such as the anion Cr ₂ O ₇ , which is yellow-orange and ^{converts into the blue-green cation Cr ++} + during reduction, or the ion MnO ₄ " , which is dark purple and changes either into brown MnO., or into the pale pink colored cation Mn ⁺ +, or the anion MnO ₄ '-, which is green and yields _{brown MnO 2 on reduction.}

When such a colored paste is applied to the workpiece to be descaled, the in the Paste containing acid through the pores of the scale and attacks the underlying iron, causing Hydrogen is evolved, which by reducing the anions causes a significant change in the color of the paste. You can use this color change to see the

509 540/394

3 4

Observe the effect of the paste. The oxygen partial pressure which has an oxidizing effect is thus formed - when using a paste that contains the yellow-orange anions can be above or below an atmosphere of Cr ₂ O ₇ ions, depending on the porosity and the. In the case of low, less than one atmosphere thickness of the scale, more or less rapidly greening oxygen partial pressure, blue dots or spots are sufficient under certain circumstances , which gradually increase in the presence of only oxidizing anions until the entire surface of the paste is not anions always. But the paste may have taken on this color. The first points that appear to be a non-reducing mine in these cases indicate the places where the acid ralic acid with a pH value below 2.5, in particular, is able to penetrate the scale fastest. Sulfuric acid. In this case, since the hydrogen also reacts slowly with a slow change in color, the acid penetrating the scale can also diffuse through the paste to areas of the FeO layer between the metal and the scale where the scale is not yet completely penetrated With the formation of ferro- dration, it is advisable to wait a few more days after the color change with the sulfate and with the iron itself, with the formation of the entire surface, in order to obtain hydrogen and also ferrous sulfate. The ferrous to ensure that the paste is sulphate in all places through the oxidizing agent has worked enough to ferric sulphate, and only then the paste is removed and rust oxidizes, whereby the adhesion of the scale wash and then the washed surface of the to the Metal surface diminished and exposed to the scale atmosphere for the purpose of rust formation. is lifted. Any other can also

Some oxidizing agents, such as the hypochlorite mineral acid used with a pH value below 2.5 or the periodates, result in the reduction of water, with the exception of those acids which dissolve the anions, so that the paste continues to act as the paste contained oxidizing anion is capable. Other oxidizing agents, e.g. B. KMnO ₄ , for example HCl, HBr, H ₂ SO ₃ , give insoluble products in the reduction, through H ₃ PO ₂ , H ₃ PO ₃ . Practically and economically , however, the use of would be interrupted when the iron is passivated and the effect of the paste is most expedient. To avoid this , a water-soluble acid or a salt is added to the sulfuric acid in a concentration of 5 to 50%, based on the water contained in the paste. Because that removes this passivation. These salts can be the addition of a strong mineral acid as a result of the sulfates, acetates, pyrophosphates of metals, before lowering the pH value and the resulting increase in the oxygen partial pressure, for example the (NH ₄ ) ₂ SO ₄ or CH ₃ COONa. Weak acids, such as CH ₃ COOH, are advantageously used as acids for the shelf life and thus the shelf life of the paste. Strong acids in the paste are adversely affected. Strong acids such as H ₂ SO ₄ can also be used, expediently only at the moment they are used, but in such a weak concentration that they are added.

the self-destruction of the paste is avoided. The descaling effect can be improved or

Like solutions are achieved because of the oxygen partial 35 a greater descaling rate

pressure of oxidant metastable. If the paste is used as cations, alkali metals,

Oxygen partial pressure with the acidity of the paste - such as K or Na or ammonium contains, for example

pastes with a low pH value quickly become Na ₂ Cr ₂ O ₇ or KMnO ₄ .

destroyed. It is therefore advisable to use pastes when using the descaling paste according to the invention

Not to allow strong acids to be stored , but rather to act on the tinder for a longer period of time

the strong acids of the paste only when they are used. In the case of heavily scaled surfaces, leave

to add dung. expediently the paste for at least a week

As inert mineral fillers can be insoluble on the metal. Then it is washed off and

borrowed silicates or silica itself are exposed to the atmosphere for some time until the upper

the, for example, clay, kaolin, talc, bentonite 45 surface is completely covered by rust. The remains of the

or crushed clams. The filler should be fine scale and the rust can then be easily mechanically

crushed and wettable by water to remove a niche.

to obtain a spreadable paste that is roughly like a bis ρ ie 11
Apply oil paint to the surface to be treated

leaves. Crushed quartz and water of hydration 50 A solution is prepared from 600 g of water, 30 g of completely free silica are therefore less suitable. KMnO ₄ and 70 g (NHJ ₂ SO ₄ , which are used to form swellable colloidal fillers such as bentonite, slowly add 300 g of bentonite to a uniform gel , as such fillers are added. The pH of this paste is about 7, yours the same viscosity of the paste with different colors is red. This paste is applied to the to be determined proportions between liquid and solid- 55 can be achieved either with the aid of a gun or with a substance. For example, it is applied with a brush. After some time bentonite When added to a sulfuric acid solution, the paste becomes chestnut brown, which is a sign that , in order to obtain a certain viscosity, the KMnO ₄ requires a portion of its oxygen 35% bentonite and 65% acidic solution _{2 has} converted.
If, on the other hand, a gel made of bentonite is first made with 60. The paste is left to soak in water for about 10 to 14 days and only then does sulfuric acid take effect. After this time has elapsed, all of the KMnO _{4 has} set, so the same viscosity is reacted when used and the paste has no effect because of 25% bentonite and 75% acidic solution.

obtain. It is therefore possible, depending on the type of treatment, to remove the paste by washing

preparation of the paste, the same viscosity with a 65 and, if necessary, cleans with the metal brush to

a smaller amount of filler and a larger amount to remove the remains of the loosened scale.

to achieve the descaling promoting acid , or if the scale layer is thick and uniform,

adjust the viscosity of the paste at will. the method according to the invention is as follows

applied: The paste is applied to the scaled surface and left to act for a few days. That The shortest time the paste remains should be 48 hours, but it can be left for several months, without this accelerating or delaying the descaling. If the paste on shipbuilding sheets during its storage in the bin is applied, it can be left on it until the Sheet metal for their processing needs. But if the paste is applied to the ship's wall, for example When the ship is built, it is left on it for 5 to 6 days. After 8 days dry them. It must then be washed off with water, because it prevents the formation of rust, who blasts off the tinder.

After washing off the paste, the scale appears unchanged on the sheet metal, namely black and without traces of rust. In reality, however, the tinder is no longer so stuck and as compact as it was originally. You can see this easily if you use a painter's spatula or any blade, it is more or less easy to remove small pieces of scale solve what is impossible with the scale not yet treated with the paste.

The scale has cracked and its adhesion to the metal has decreased significantly, however is of the ferrous ferric salts, which are produced by the action of the oxidizing agent and the acid Paste on the iron and the ferro-oxide have arisen, not enough volume to be taken to exert a pressure on the scale which is sufficient to completely dissolve the scale. If but the paste is washed off with water, the oxygen in the air no longer finds an obstacle in its presence Passes through the pores of the scale up to the ferrous ferric salts, which it oxidizes to ferric salts, which in turn are hydrolyzed to rust under the action of the moisture in the air. The rust that one Much larger volume than the ferro-ferric salts takes up, loosens the semi-adherent scale.

The length of time the sheet will be exposed to the atmosphere after the paste has been removed must is 1 to 3 weeks, generally 15 days. Then the whole area is covered with powdery rust, which can be removed by simply brushing with the metal brush.

The slightest trace of rust that remains after brushing is preferably used, by carrying out a phosphating according to the known method in order to achieve better adhesion of the Colors to achieve.

Example II

A solution is prepared from 550 g of water, 40 g of potassium permanganate, 60 g of acetic acid and 50 g of sodium acetate, add 250 g of bentonite slowly with stirring to form a uniform gel and 50 g of kaolin added. The pH of this paste is around 4, its color is also red.

When this paste is used, too, the KMnO _{1 is} reduced to MnO ₂ , as in Example I. However, if the substances dissolved in the water of the paste penetrate through the pores of the scale, the red KMnO _{4 is} reduced to white manganese acetate.

The application is carried out as in Example I. The required exposure time also varies between two 15 days and one month, including exposure to air for rust formation.

Example III

A solution is prepared from 500 g of water, 80 g of concentrated sodium hypochlorite solution and 80 g Ammonium bisulfate, which is used to form a

ίο uniform gel while stirring slowly 240 g Bentonite and 100 g of silica are added. The pH of this solution is around 6 and its color is straw yellow.

When using this paste, the straw yellow NaClO loses oxygen and turns colorless NaCl over. The method of application and the duration of action of this paste are the same as in Example I and II.

Example IV

A solution is prepared from 450 g of water, 170 g of H ₂ SO ₄ at 66 ° Baume and 30 g of Na ₂ Cr ₂ O ₇ , to which 350 g of bentonite are slowly added with stirring to form a uniform gel.

During the preparation, the addition of sulfuric acid to the water causes warming 40 ° C. The gel obtained at this temperature is relatively liquid, but thickens when Cooling down. It is yellow in color.

The gel obtained in this way is applied to the surface to be descaled either by means of a pistol or by means of applied with a brush. Blue-green dots appear after just a few minutes, the gradually enlarge and multiply, depending on the porosity and thickness of the scale, up to they cover the whole surface.

When you determine the pH of the paste, immediately after the whole area turns green-blue has colored, this is still below 2, which means that not all of the acid has passed through the pores of the scale and reacted.

However, if you keep the sheet 3 to 4 days after the complete color change, the action continues leaves the paste, which has then turned green, and checks the pH of the paste again, so shows found that it has risen practically uniformly to about 4, which means that all of the acid is in reaction stepped. The paste can then be washed off. After washing off, the scale adheres on the metal is greatly reduced and the scale can be removed by scratching. Because this treatment however, it is tedious and costly, it is preferable that the washed sheet is kept for 10 to 15 days Exposed to atmosphere. After a few hours, red rust appears and covers the entire surface. As soon as this rust is strong enough, it is removed with a metal brush or with a painter's spatula replaced in whole pieces. After this treatment can either be done immediately or after prior phosphating paint can be applied.

Example V

A very thick gel is first prepared from 350 g of water and 35 g of bentonite. This will then by adding a solution of 190 g of water, 160 g of sulfuric acid from 66 ° Baume and 20 g of potassium permanganate made more fluid.

The suspension obtained in this way is thickened again by adding 200 g of bentonite and 45 g of kaolin to restore it to the gel.

The gel formed in this way has a dark purple color and is applied to the scaled surface. The change in color of the paste is expressed by a change from dark purple to pink or a very light brown.

The type of application, the duration of the action and the exposure to the atmosphere in order to achieve the desired rust formation correspond exactly to the previous examples.

Claims (10)

Patent claims: 1. Acid, an oxidizing agent and inert mineral fillers containing descaling paste for iron, cast iron and steel, characterized in that 1 kg of paste 0.2 to 1 gram equivalent oxygen-releasing, water-soluble salts and a non- reducing acid or salts contains such acid, the remainder being water. 2. Descaling paste according to claim 1, characterized in that the oxygen abge bende, water-soluble salt contains anions which change color on transition to the reduced state. 3. Descaling paste according to claim 1 or 2, characterized in that the inert filler is a water-insoluble silicate, in particular Ben tonite or silica which is not completely free of water of hydration. 4. Descaling paste according to one of claims 1 to 3, characterized in that it additionally contains a mineral acid when using oxygen-releasing, water-soluble salts which result in water-insoluble compounds when the anion is reduced. 5. Descaling paste according to claim 4, characterized in that the pH of the additional acid is below 2.5. 6. Descaling paste according to claim 5, characterized in that the additional acid Is sulfuric acid. 7. Descaling paste according to one of claims 1 to 6, characterized in that the Oxygen-releasing, water-soluble salt containing alkali metals or ammonium as cations. 8. Method of descaling articles made of iron, cast iron or steel using the descaling paste according to one of claims 1 to 7, characterized in that the paste is brought into action until a pH value of about 4 has been established. 9. Method of descaling articles made of iron, cast iron or steel using the descaling paste according to one of claims 1 to 7, characterized in that after complete reduction of the oxidizing anions of the water-soluble salt Paste washed off, the washed surface of the object of exposure to the atmosphere is suspended until rust forms and then the scale residues and the rust are removed mechanically will. 10. A method for using the descaling paste according to claim 4, 5 or 6, characterized characterized in that the acid is added to the paste only at the moment of its use. 3ο Considered publications: German patent specifications No. 466 077, 523 505,
740432, 742477; Swiss Patent No. 273 080;
French Patent No. 941433;
U.S. Patents Nos. 2,158,992, 2,368,955,
431728, 2,538,702, 2,564,549; Otto Vogel: "Handbuch der Metallbeizerei", 1951, Vol. I, pp. 267, 268, 274; Vol. II, pp. 150, 418; Magazine "Metalloberfläche", 1953, Issue B, pp. B 37 and B 38; "Chemisches Zentralblatt", 1951/11, p. 1960;
Presentation on Swedish patent specification 128 052.