DE10346192B4 - Method for rust removal of molded parts and use of the method - Google Patents

Abstract

Method for rust removal of moldings having a non-alloyed ferrous metal surface, comprising the following steps:
Immersing the moldings in a first bath with an aqueous solution containing citric acid and no or at least one of the following acids: tartaric acid, lactic acid or glycolic acid, wherein the first bath contains at least 1% by weight acid, and therein intimate, deep pore contact the rusty surface is treated with the acid solution, the sparingly soluble Fe ³⁺ compounds going into solution;
- Transfer the dissolved Fe ³⁺ compounds into insoluble Fe ²⁺ compounds by adding a complex-forming inorganic salt in the first bath, so that form separate deposits from the moldings;
Immersing and rinsing the moldings in an alkaline second cleaning bath in which the parts are rinsed and residues of the acid are neutralized,
characterized in that
Tin sulfate is added to the first bath as the complex-forming inorganic salt, and
- That in the first bath, the weight ratio between citric acid and tin sulfate between ...

Description

• – Eintauchen der Formteile in ein erstes Bad mit einer wässrigen Lösung, enthaltend Citronensäure und keine oder wenigstens eine der folgenden Säuren: Weinsäure, Milchsäure oder Glycolsäure, wobei das erste Bad wenigstens 1 Gew.-% Säure enthält, und darin ein inniges, porentiefes Kontaktieren der rostigen Oberfläche mit der Säurelösung erfolgt, wobei insbesondere die schwerlöslichen Fe³⁺-Verbindungen in Lösung gehen;
• – Überführen der gelösten Fe³⁺-Verbindungen in unlösliche Fe²⁺-Verbindungen durch Zugabe eines anorganischen Salzes in das erste Bad, so dass sich von den Formteilen getrennte Ablagerungen bilden;
• – Eintauchen und Spülen der Formteile in einem alkalischen zweiten Reinigungsbad, in dem die Teile gespült und Reste der Säure neutralisiert werden.

The invention relates to a method for derusting moldings which have a non-alloyed iron metal surface, comprising the following steps:

• Immersing the moldings in a first bath with an aqueous solution containing citric acid and no or at least one of the following acids: tartaric acid, lactic acid or glycolic acid, wherein the first bath contains at least 1% by weight acid, and therein intimate, deep pore contact the rusty surface is carried out with the acid solution, in particular the sparingly soluble Fe ³⁺ compounds go into solution;
• - Transfer the dissolved Fe ³⁺ compounds into insoluble Fe ²⁺ compounds by adding an inorganic salt in the first bath, so that form separate deposits from the moldings;
• - Immersion and rinsing of the moldings in an alkaline second cleaning bath, in which the parts are rinsed and residues of the acid are neutralized.

Moldings, which have a non-alloyed, uncoated Fe-metal surface, corrode after a short while on their surface, when in contact with a moist, especially electrolyte-containing atmosphere come. On the surface Form Fe oxides of various compositions, called rust be designated. Such corrosion layers can be dense layer and conform to the shape of the parts manually inaccessible Are located.

Similar Problems arise for Sintered parts obtained by pressing and sintering of alloyed or be made of unalloyed iron metal powder. For example, gears, shafts or housing parts be sintered. Such parts generally have masses between 10 and 2000 grams. After pressing and sintering are in such Post-processing steps, such as tempering, mechanical processing, Trowalizing (sliding) and the like required at which often works with water. There sintered parts pores have, remains in these pores despite intensive drying a share of residual water.

In this residual water, but also in other undesirable components, such as hand sweat, bacteria and other microorganisms can develop and spread. Through metabolic processes acids are formed, so that rust develops in the form of sparingly soluble compounds on the iron substrate. The presence of electrolyte-containing liquids can also lead to corrosion. In particular, trivalent iron compounds such as Fe ₂ O ₃ or Fe (OH) _{3 are formed} .

there Corrosion often occurs due to poor antibacterial treatment only after the assembly of the moldings and leads to complaints. The parts have to expanded and usually scrapped, as a method for after-sustainable De-rusting of such moldings is not yet available.

It is known for pickling metals and rusting steel organic acids to use (Rituper, R .; "pickling of metals "; Eugene Leuze Verlag, Saulgau, 1993, pages 118-119, 149 to 150 and 192 to 201). Various accessories to the acid baths are also known, for example, peroxodisulfate, wherein in one such bath in particular cobalt and nickel oxides are removed should.

Citric acid has the advantage that they are inexpensive and physiologically largely available is safe to use. Instead of citric acid can also, at least in part, a citrate, in particular monoammonium citrate, be used. citric acid or citrates have the advantage that they are non-toxic and without danger potential easy to handle. The occurring rust types are very solved quickly.

Of the The first step of the method is therefore carried out in a first bath, in the rust-affected moldings in an aqueous acid solution, for example, solution of citric acid in a pH range preferably from about 2.5 to 5.

It the task arises, a method of the type mentioned for later Desoldering of sintered and other Fe-shaped parts of the beginning indicated type that causes no damage to the parts and easy to apply, in particular, by residual water resulting corrosion can be removed.

The Task is solved by that in the said method the first bath as complexing inorganic salt is added tin sulfate, and that in the first Bad the weight ratio between citric acid and tin sulfate is between 1: 1 to 1:20.

at Use of citric acid is - next to Water - im Bad the content of citric acid or to citrate between 1 and 25 wt .-%, preferably between 2 and 10 wt .-% and more preferably 5 ± 1 wt .-%. It should be at least for a quick rust solution a content of 1 wt .-% selected become. A concentration over 10 wt .-% usually brings no more acceleration, so that a concentration from 5 ± 1 Wt .-% probably represents the optimum.

In addition to citric acid, others can Acids, namely tartaric acid, lactic acid or glycolic acid, alone or mixed with each other, can be used.

It is also advantageous that the first bath a basic buffer solution, in particular an ammonium hydroxide solution, enclosed becomes.

In order to precipitate the Fe ³⁺ ions in solution, the reducing tin sulfate [Sn (SO ₄ )], which is added to the first bath together with the citric acid, has proved to be a reducing, water-soluble, complex-forming organic salt. In this case, preferably in the first bath, the weight ratio between citric acid and tin sulfate is between 1: 1 to 1:20, preferably between 1: 7.5 to 1:12. It leads to redox reactions in which Sn ^{2+ is} oxidized to Sn ⁴⁺ and the reaction ^partner Fe ^{2+ is} reduced to Fe ²⁺ . It comes to precipitation of granular, brownish iron-containing parts, probably a complex iron-tin citrate, which is easy to rinse off. Insoluble stannous citrates have been observed (see GMELIN, Handbook of Inorganic Chemistry, System Number 46, Tin, Part C2, p. 226).

The Reaction rate increases with the bath temperature. It still can work at reasonable time at room temperature (23 ° C); however, preferably above this temperature, i. H. at a Treatment temperature in the first bath between 40 ° C and 95 ° C, worked.

Farther should take the treatment and rinsing under mechanical agitation, d. H. especially under ultrasound, electromagnetic or piezo-mechanical excitation, with spin or the like. Also a vent of the Sintered parts in a vacuum chamber can be preceded by the introduction into the first bath.

The flush in the second bath is preferably carried out with the addition of wetting agents (surfactants).

Finally will after flushing In the second bath another treatment is performed in a third bath, in the parts are pasteurized at a high temperature (higher than 65 ° C) and / or treated with corrosion inhibitors and / or with biocides.

The Invention also relates to the use of the method described in the claims for derusting of ready-to-install sintered components.

The described and explained with reference to the following examples is suitable for rust removal of steel parts, ferrous components and other ferrometallic materials, in particular sintered moldings. This is of particular importance when appropriate assemblies made consist of several parts that have undesirable corrosion. Advantageously, can Components with hard to reach Recesses, holes, Holes, etc., are descaled by the method according to the invention. According to previous experience, assemblies, the components sintered components, ferrometallic parts and other components, including Camshafts or pipes, as a whole, are de-rusted without damage.

One embodiment one for execution The invention suitable apparatus is shown schematically in the drawing shown. With reference to the figure of the drawing, the invention in Examples explained.

example 1

The products to be de-rusted are gears produced in the sinter-forming process 1 used with a mass of about 2.4 kg and a diameter of 120 mm. The gears have been removed from existing gearboxes, as they had both visible on the outside and in their sinter pores rust. A chemical analysis showed that the "rust" was primarily Fe (OH) ₃ and Fe ₂ O _3. Residual water in the pores and hand sweat provided a breeding ground for bacteria, and metabolic processes of these microorganisms produced acids had formed, which had led to the unwanted iron rust formations.

In a first bath 2 becomes a solution three from water with 5 wt .-% citric acid and 0.5 wt .-% tin sulfate kept at a temperature of 40 ° C. The sintered moldings 1 Be careful in the solution three immersed so that they are not damaged. Using ultrasound transducers 4 Sound waves are generated in the bath, so that the penetration of the solution into the interstices and pores of the sintered moldings is facilitated.

To a processing time of about 15 minutes is due to the citric acid of watched "rust" on the sintered Moldings in a dissolved form been converted. The simultaneous presence of tin sulfate is reduced the iron (III) ions to iron (II) ions. It then formed a brownish Precipitate, easily washed off the sintered moldings could be.

In the second bath 5 the treated moldings were neutralized and rinsed. The water of the bath 5 was an alkaline solution of potassium hydroxide with nonionic surfactants (trade name P3-upon 5800, manufacturer Henkel and Cie. Prattel), wherein 5 wt .-% of the aforementioned alkaline solution were stirred. Subsequent treatment was at 40 ° C and for three minutes.

In a third bath 7 Pasteurization was carried out at 70 ° C to 80 ° C bath temperature. The bath liquid was added to addition a commercial corrosion protection concentrate based on mineral oil, with a share of 10 wt .-%. After an application time of about five minutes, the parts were removed. The concentration of the anticorrosive concentrate was chosen so that in addition to a sufficient protection of the parts they did not remain apparently oily on their surface. After treatment in the three baths 2 . 5 and 7 the parts were placed in a drying chamber 9 dried in a stream of hot air.

Example 2

Iron moldings, namely complex housing parts with an average mass of 1.7 kg, with clearly visible magnetite deposits (Fe ₂ O ₃ ) were in a bath 1 treated with 7.5 wt .-% citric acid, 1.5 wt .-% ammonium citrate and 0.8 wt .-% tin sulfate. The water temperature in the treatment was 50 ° C. The second and third bath 5 . 7 had the composition as in Example 1. The parts could be perfectly cleared of the coverings.

Example 3

in the first bath was for the rusting approximately 2.4 kg heavy wrought-iron camshafts instead citric acid an addition of 8% by weight of lactic acid used. The further steps and compositions correspond those of Example 1. Sufficient de-rusting has been achieved.

To The choice of concentrations should be noted that a high concentration the additives, so citric acid and / or stannous sulfate, rinsing out hinders the arrears; On the other hand, if the concentration is too low, no complete reaction occurs with the iron grate. Test approaches depending on the type and corrosion The molded parts are therefore required by expert judgment. The bath temperatures should be used to accelerate the reaction in the area from 40 ° C up to 70 ° C lie and about 80 ° C because of the risk of decomposition for the citric acid do not exceed.

Claims (14)

A process for rust removal of moldings having a non-alloyed ferrous metal surface, comprising the steps of: dipping the moldings in a first bath with an aqueous solution containing citric acid and no or at least one of the following acids: tartaric acid, lactic acid or glycolic acid; first bath containing at least 1 wt .-% acid, and therein an intimate, pore-deep contacting the rusty surface is carried out with the acid solution, wherein the sparingly soluble Fe ³⁺ compounds go into solution; - Transfer the dissolved Fe ³⁺ compounds into insoluble Fe ²⁺ compounds by adding a complex-forming inorganic salt in the first bath, so that form separate deposits from the moldings; Immersing and rinsing the moldings in an alkaline second cleaning bath in which the parts are rinsed and residues of the acid are neutralized, characterized in that tin sulphate is added to the first bath as the complex-forming inorganic salt, and that in the first bath the weight ratio between citric acid and tin sulfate is between 1: 1 to 1:20. Method according to claim 1, characterized in that that instead of the citric acid a citrate is used. Method according to claim 2, characterized in that that instead of the citric acid Monoammonium citrate is used. Method according to claim 1, characterized in that that when using citric acid, the citric acid content in the first Bath between 1 and 25 wt .-% is. Method according to claim 4, characterized in that that when using citric acid, the citric acid content in the first Bath between 2 and 10 wt .-% is. Method according to claim 5, characterized in that when citric acid is used, the citric acid content is 5 ± 1% by weight. is. Method according to Claims 1 to 6, characterized that the first bath a basic buffer solution is attached. Method according to claim 7, characterized in that that the ammonium hydroxide solution is added to the first bath as the basic buffer solution. Method according to one of the preceding claims, characterized characterized in that the treatment temperature in the first bath and in the second bath between 40 ° C and 95 ° C lies. Method according to one of the preceding Claims, characterized in that the treatment and rinsing operations are carried out under mechanical agitation. Method according to one of the preceding claims, characterized characterized in that the rinse in the second bath with addition of wetting agents. Method according to one of the preceding claims, characterized that after rinsing in the second bath, the moldings are pasteurized in a third bath become. Method according to claim 13, characterized in that that corrosion inhibitors and / or biocides are added to the third bath. Use of the method according to one of claims 1 to 13 for derusting of ready-to-install sintered components.