EP2245213B1 - Passivating means, surface treatment means, surface treatment spray means and method for treating metallic surfaces of work pieces or cast molds - Google Patents

Description

The present invention relates to a passivation agent for metallic surfaces of workpieces or molds with an aqueous phosphate solution with metal ions, a surface treatment agent and a surface treatment spray for cleaning and passivation of metallic surfaces of workpieces or molds with such a passivating agent and a method for treating metallic surfaces of workpieces or molds with such a surface treatment agent or surface treatment spray.

Molds used in low pressure, gravity, squeeze casting or die casting are usually made from hot work steels because their recrystallization and / or transformation temperatures are well above those of the molten light metal materials. In the casting operations, achieving smooth surfaces on the castings to be produced requires that the liquid melt, for example in the form of a light metal alloy, especially an aluminum alloy, not adhere to the surface of the casting mold. For this purpose, release agents or sizes are applied to the surfaces of the molds, which are intended to prevent adhesion of the molten metal to the mold.

Such a release agent which contains no toxic substances, for example, from DE 10 2005 042 475 A1 known. To ensure that the release agent or sizing on the tool surfaces must be previously cleaned and passivated if necessary.

The passivation creates a non-metallic protective layer on the metallic material, which should slow or prevent corrosion as much as possible. Of particular importance is the passivation by phosphating. This is a widely used method of surface technology in which a conversion layer of firmly adhering metal phosphates is formed by a chemical reaction between the metallic workpiece surface and an aqueous phosphate solution. The phosphating serves to protect against corrosion and forms a diffusion barrier. In addition, the adhesion can be improved, for example, subsequently applied sizing and reduce wear.

For phosphating both phosphate baths and phosphate spray systems are used. In either case, prior to phosphating, cleaning of the surface of the mold or workpiece is required.

The cleaning takes place for example by means of a high-pressure water jet, which is directed via a rotary nozzle with a pressure of 1750 to 3000 bar to the workpiece. The disadvantage of this, however, is that caused by the water contact of the cleaned workpiece corrosion and organic and inorganic residues from the jet water remain on the surface. However, the high pressures lead to high wear of the piston and valves of the blasting system and thus to increased costs.

For this reason, cleaning with lower pressures, for example, 200 bar are known. Although this reduces the wear, however, the cleaning effect decreases accordingly.

In addition, it is known to use in the cleaning of die casting granules, which are blasted under pressure on the workpiece. For this example, nutshells or glass beads are used. at In addition, steel, corundum or ceramics are used as granules for cleaning low-pressure casting molds or gravity molds. In addition to an additional increased mechanical wear of the surface, there is a partial inaccessibility at undercuts of the treated component. The result is dimensional inaccuracies in the subsequent casting operations and impurities on the mold surface by plating non-cyclic particles.

Furthermore, from the CN 1132802 A a rust removing agent for metals, which consists of a mixture of a fat solvent, a rust solvent such as phosphoric acid, a buffering agent, especially aluminum hydroxide, a phosphating agent consisting of zinc phosphate, potassium aluminum phosphate and gelatin as a thickening agent, and water.

When applying a size, for example, with waterglass binder after such cleaning, adhesion problems occur on the insufficiently cleaned and passivated surfaces for the above reasons, which lead to defects on the surface of the size after application. Particularly in the case of subsequent heat treatment, there is the danger of the sizing spalling off the treated surface or, in the case of casting molds in subsequent casting operations, the risk of intermetallic welding at the defects, so that the mold can no longer be separated cleanly from the cast workpiece.

There are also problems with the wetting of the insufficiently cleaned or corroded mold surfaces even when using known cooling / release agent systems for die casting molds. Again, this results in the casting process intermetallic compounds on the mold surface result.

To avoid these disadvantages, it is therefore necessary to post-purify the mold surface before passivation in order to obtain a metallurgically pure surface.

Known processes for purification and passivation are usually carried out in baths or by spray treatment.

In the bath treatment, after the blast treatment, first the mold or the workpiece is immersed in a pickling bath to remove organic residues and oxides at temperatures of 40-90 ° C by means of inorganic acids and suitable surfactants. Subsequently, a deep cleaning in the bath by means of ultrasound, whereupon the workpiece or the mold is immersed in another bath for rinsing and neutralizing. Thereafter, the workpiece must be dried and activated in a further process step in the bath, before the phosphating, for example, by means of zinc phosphate at 40 - 70 ° C or manganese phosphate at 70 - 90 ° C. Finally, the workpiece or the mold is neutralized and dried. Disadvantages of this process are the long necessary residence times in the baths, in particular in the case of large components such as diecasting tools. Accordingly, large amounts of energy are needed to achieve and maintain the necessary temperatures. Also, the bath care to maintain the necessary bath parameters is very expensive, since impurities arise between the individual bathrooms, which accumulating residues must be removed. Depending on the dimensions of the components and the size of the baths may need to be adjusted.

In the spray treatment, the high-pressure cleaning is followed by a pickling bath and then rinsing and neutralizing with a suitable spray solution. After subsequent drying and heating of the component, spray activation is carried out at elevated temperature before phosphating by means of a heated spray solution at 40-70 ° C for zinc phosphate and 70-90 ° C for manganese phosphate. Here too, the neutralization and drying of the workpiece or of the casting mold follows as further steps. As with the bath treatment, the energy expenditure for achieving the necessary temperatures is relatively high, even in the case of correspondingly large mass ratios, even during the spray treatment, so that the process is uneconomical becomes. In addition, there is a high logistical effort in the continuous process of the treated components.

Furthermore, the components treated with known passivating agents often have inadequate thermal shock resistance, which arises in particular from defects in the structure of the passivation layer.

To improve this will be in the DE-34 03 660 A1 describes a passivating agent which consists of an aqueous solution of aluminum hydrogen phosphate and organic polymers which form a film under the action of temperature. As organic polymers in this case acrylic or epoxy resins are used. When heated, however, these coatings lose their organic components. The disadvantage of this agent is, in particular, that defects occur during repeated casting, whereby welding can occur with a cast component. Furthermore, there is still insufficient thermal shock resistance.

It is therefore an object of the invention to provide a passivation agent, with which a long shelf life of the phosphate layer is achieved as possible without defects, and in a further development of the invention to provide a surface treatment agent and a surface treatment spray with such a passivation, with which the complex purification process can be simplified. In addition, it is an object of the invention to provide a correspondingly simplified method for the treatment of surfaces with such agents.

This object is achieved by a passivation agent, which according to the invention comprises a gelatin whose redox potential is adjusted so that the gold number of the gelatin is less than 50 μmol Au / g gelatin. While the phosphates cause in a known manner that formed with the base material iron phosphate in combination with the metallic ions of the phosphate system at the free lattice sites or grain boundaries in the treatment of steel components or molds Forming protective layer on the surface, which serves as corrosion protection and adhesion promoter for applied sizing, the gelatin acts in such an agent as a dispersant and equipotential bonding system and improves in a previously unknown manner, the diffusion barrier. The electrochemical reaction is influenced by the gelatin in such a way that the phosphating proceeds at room temperature. This significantly reduces the energy required for phosphating. It has been found that with these gelatins particularly good results can be achieved with regard to the adhesion of the passivation layer and the thermal shock resistance of a component treated therewith.

Preferably, the aqueous phosphate solution with the metal ions is an aqueous orthophosphate solution, wherein the orthophosphates consist of one or more of the compounds zinc phosphate, aluminum phosphate, manganese phosphate, titanium phosphate, calcium phosphate, boron phosphate or iron phosphate. These compounds have proven to be particularly effective at achieving phosphating in achieving smooth surfaces.

In a preferred embodiment, the passivating agent has the following composition: 0.1% by weight to 5% by weight gelatin, 5% by weight to 50% by weight orthophosphates and the remainder water. In such a composition, an optimal balance and equipotential bonding between the individual elements of the system, whereby particularly good results in the passivation are achieved with a small amount of the individual substances used.

The object of simplifying the cleaning and passivation processes known hitherto is additionally achieved by a surface treatment agent with such a passivating agent which additionally comprises nonionic surfactants, lactic acid and a citric acid monohydrate. Previous cleaning steps can be completely or at least partially dispensed with when using such a surface treatment agent, since even at room temperature rust and organic components such as fat, dirt, organic organics etc., are detached from the surface. The existing in the surface treatment agent Non-ionic surfactants reduce the surface tension and, in combination with the organic acids, infiltrate impurities on the surface, so that these impurities are dissolved or dissolved, so that a particularly good and largely defect-free connection of the phosphate system to the metallic surface can take place. The agent can be made by immersing the workpiece or the mold in a corresponding bath at room temperature.

• 0,1 bis 5 Gew.%, vorzugsweise 0,41 bis 1 Gew.% Gelatine
• 5 bis 50 Gew.%, vorzugsweise 5 bis 10 Gew. % Orthophosphate
• 0,5 bis 5 Gew.%, vorzugsweise 0,5 bis 2,5 Gew.% Milchsäure
• 0,5 bis 5 Gew.%, vorzugsweise 0,5 bis 2,5 Gew.% Zitronensäuremonohydrat
• 0,1 bis 3 Gew.%, vorzugsweise 0,5 bis 2 Gew.% nicht-ionische Tenside
• Rest destilliertes Wasser.

Preferably, the surface treatment agent has the following composition:

• 0.1 to 5 wt.%, Preferably 0.41 to 1 wt.% Gelatin
• 5 to 50% by weight, preferably 5 to 10% by weight, of orthophosphates
• 0.5 to 5 wt.%, Preferably 0.5 to 2.5 wt.% Lactic acid
• 0.5 to 5 wt.%, Preferably 0.5 to 2.5 wt.% Citric acid monohydrate
• 0.1 to 3 wt.%, Preferably 0.5 to 2 wt.% Non-ionic surfactants
• Rest distilled water.

In this composition, particularly good results were achieved with respect to the thermal shock resistance of the coated component. Defects in the grid are completely eliminated, so that a long-lasting corrosion protection is achieved.

In a preferred embodiment, the surface treatment agent additionally comprises molybdenum disulfide and / or bismuth. Particularly advantageous is an added amount of 0.01 to 5 wt.%, Preferably 0.02 to 0.04 wt.% Molybdenum disulfide and / or 0.01 to 5 wt.%, Preferably 0.02 to 0.04 wt % Bismuth. The molybdenum sulfide or bismuth becomes chemically bound in the matrix of the surface upon passivation. As a result, the heat resistance and abrasion resistance of the mold or the workpiece can be further increased and the lubricating effect can be improved.

The above-described object is also achieved by a surface treatment spray in which the surface treatment agent according to the invention additionally comprises up to 60% by weight of a thickening agent. As a result, a sprayability, resulting in the elaborate Cleaning various baths can be dispensed with. Impurities of the surface treatment agent, such as may occur during treatment in baths are excluded.

The object of providing a simplified and more cost-effective compared to the prior art method is achieved by a method in which the workpiece or the mold is immersed in a bath of the surface treatment agent according to the invention or the surface treatment spray according to the invention on the surface of the workpiece or the Mold is sprayed on. This eliminates pre- and post-cleaning steps either completely or at least partially, so that the lead time in the production of corrosion-inhibiting layers can be significantly reduced. The surfaces treated in this way are cleaned absolutely residue-free and at the same time passivated, so that any further surface application can be applied uniformly and permanently. For example, release agents, sizes or lacquers can be applied to the surface cleaned and passivated in this way. The cleaning and passivation according to the invention thus increases the service life and the functionality of the workpieces and molds treated in this way.

It is advantageous then to heat the workpiece or the casting mold to 200.degree. The inorganic constituents, metallic ions and mineral elements of the gelatin are integrated from this temperature into the polymerizing chemical bond to the metal as a uniformly distributed nanosystem. The result is a solidification of the overall system by polycondensation.

In an advantageous continuation of the method for low-pressure casting, a size is applied to the cleaned and passivated surface of the casting mold after immersion in the surface treatment agent or after spraying the surface treatment spray agent. The sizing may be, for example, a sodium or potassium water glass sizing applied to the tool surface which makes the surface smoother and protects it from thermal stress.

Preferably, the size is applied at a mold temperature of 250 ° C. The heating required for the application of the size leads to the polycondensation of the phosphate system and its organic components. The gelatin of the surface treatment agent is incorporated into the chemical bonding of the metal with the phosphate system, whereby the adhesive strength is further increased. A separate heating of the surface treatment agent is therefore not necessary.

It is clear that it is possible by the described method with a passivation or surface treatment or surface treatment spray, to dispense with different process steps and to reduce the energy consumption. Nevertheless, the surfaces of the molds or the treated workpieces have improved adhesive strength, adhesion promoting ability and thermal shock resistance, which provides long-term protection against corrosion.

In the following, some methods according to the invention with surface treatment spraying agents according to the invention will be described with reference to embodiments for the surface treatment of molds and workpieces.

Embodiment 1

The workpiece used in the first embodiment was a non-prepurified, non-de-frosted and non-degreased test sheet of hot-work steel. To prepare a surface treatment agent according to the invention, 1% GELITA NOVOTEC (R) gelatin FP200 was dissolved in advance in 14% distilled water. For this purpose, the gelatin was first swollen at room temperature in distilled water for about twenty minutes and then dissolved at a temperature of 60 ° C. At this temperature, 0.03% molybdenum disulfide was dispersed in the medium. Thereafter, citric acid (0.7%), lactic acid (0.7%), phosphoric acid (1.4%) and an aqueous manganese phosphate solution of the type Brünofix GAM 5624 (36%) mixed and added to the suspension. The flowability of the surface-treating spray was adjusted with an Ardrox 6085 thickener containing almost equivalent amount of nonionic surfactant-containing thickener to prepare a surface-treating spray of the present invention.

The test panel was sprayed vertically standing with the surface treatment spray. After a short exposure time of 10 minutes, the plate was washed with water and dried. The sheet after cleaning had a closed black layer consisting of manganese phosphate and molybdenum disulfide. An additional heating of the sheet was not required. The sheet metal was largely free of defects, so that a high corrosion resistance was achieved.

Embodiment 2:

Here, a die casting mold was cleaned and passivated with a surface treatment spray of the invention. To prepare the surface treatment agent, 1% GELITA NOVOTEC (R) gelatin FP200 was pre-dissolved in 14% distilled water. For this purpose, the gelatin was first swollen at room temperature in distilled water for about twenty minutes and then dissolved at a temperature of 60 ° C. At this temperature, 0.03% molybdenum disulfide was dispersed in the medium. Then, citric acid (0.7%), lactic acid (0.7%), phosphoric acid (1.4%) and a Brünofix GAM 5624 aqueous manganese phosphate solution (36%) were mixed and added to the suspension. The flowability of the surface treatment spray of the invention was again adjusted with a nearly equivalent amount of a thickener of the Ardrox 6085 type, which in turn contains nonionic surfactants. This gave rise to a surface treatment spray according to the invention.

The mold was treated at room temperature by spraying the surface treatment spray. After a contact time of ten Minutes, the cleaning residues were washed off. Again, a uniform layer of manganese phosphate and molybdenum sulfide formed. Subsequently, the casting mold was tempered for four hours at 200 ° C. in the preheating phase and the leveling-out phase in the casting machine. It formed a closed layer of manganese phosphate and molybdenum disulfide

To test the thermal shock resistance, similarly coated test panels of the same material as the casting mold were heated at 800 ° C. for one hour and then quenched in water at room temperature. There were no defects on the phosphate layer. An extremely good adhesion of the layer to the casting mold has been demonstrated and thus an unusually good thermal shock resistance has been achieved.

Embodiment 3

In this experiment, a low pressure die was treated with a surface treatment spray according to the invention. Again, 1% GELITA NOVOTEC (R) Gelatin FP200 was pre-dissolved in 14% distilled water to prepare this surface treatment spray. For this purpose, the gelatin was first swollen again at room temperature in distilled water for about twenty minutes and then dissolved at a temperature of 60 ° C. Then, citric acid (0.7%), lactic acid (0.7%), phosphoric acid (1.4%) and Brünofix Z 5526 (36%), an aqueous zinc phosphate solution, were mixed and added to the suspension. The flowability of the surface treatment spray was also adjusted in this example with the Ardrox 6085 thickener containing almost equivalent amount of nonionic surfactants.

The mold was treated at room temperature by spraying the surface treatment spray. After a reaction time of ten minutes, the cleaning residues were washed off. The mold was then tempered for four hours at 250 ° C to apply a waterglass bound sizing.

Subsequently, a waterglass bound sizing was applied at 250 ° C mold temperature to investigate the adhesion promoter effect. After 86 casting operations without further use of sizing, the surface continued to be coated without defects. This results in an excellent effect of the surface treatment spray of the invention as a primer and diffusion barrier with very good corrosion protection. Usually, ie without the surface treatment agent according to the invention, components subjected to higher temperature, such as the cylinder capstans, must be post-straightened after every sixth casting.

Embodiment 4

In the fourth series of experiments, a squeeze-cast mold was sprayed with a surface treatment spray according to the invention. To prepare this detergent, 1% GELITA NOVOTEC (R) Gelatin FP200 was pre-dissolved in 14% distilled water. For this purpose, the gelatin was first swollen at room temperature in distilled water for about twenty minutes and then dissolved at a temperature of 60 ° C. At this temperature, 0.03% molybdenum disulfide was dispersed in the medium. Then, citric acid (0.7%), lactic acid (0.7%), phosphoric acid (1.4%) and a Brünofix GAM 5624 aqueous manganese phosphate solution (36%) were mixed and added to the suspension. The flowability of the surface treatment spray of the invention was again adjusted with a nearly equivalent amount of non-ionic surfactant-containing thickener of the Ardrox 6085 type.

The mold was treated at room temperature by spraying the cleaner. After a reaction time of ten minutes, the cleaning residues were washed off. The mold was tempered for four hours at 200 ° C in the preheating and balancing phase in the caster.

To test the thermal shock resistance, similarly coated test panels of the same material as the mold were heated for one hour heated to 800 ° C and then quenched in water at room temperature. There were no defects on the phosphate layer. An extremely good adhesion of the layer to the casting mold has been demonstrated and thus an unusually good thermal shock resistance has been achieved.

As a result, it should be noted that no caking occurred in the casting processes by the surface treatment spray, and no additional cooling or cooling release agents had to be used. The process for the treatment of the surfaces is greatly facilitated and the throughput times shortened accordingly. Treatment of the molds after each casting is no longer necessary.

It should be understood that the invention is not limited to the described embodiments. Thus, the same effects occur when using appropriately formulated surface treatment agents in cleaning and passivating the molds and workpieces in the dipping bath. Also, a pure passivation with a passivation agent according to the invention with previous cleaning is possible. Such a surface treatment leads to an increase in the effect of the metal phosphate layer as a primer and diffusion barrier. This is done in particular by the firm connection of the phosphate system to the metallic surface by the action of gelatin as a dispersant and equipotential bonding system and by the occupancy of defects.

Claims (12)

1. A passivating agent for metallic surfaces of workpieces or casting molds, comprising an aqueous phosphate solution with metal ions,
   characterized in that
   the passivating agent includes a gelatin, wherein a redox potential of the gelatin is set so that a gold number of the gelatin is smaller than 50 µmol Au/g of gelatin.
2. The passivating agent for metallic surfaces of workpieces or casting molds as recited in claim 1, characterized in that the aqueous phosphate solution with metal ions is an aqueous orthophosphate solution, wherein the orthophosphates comprise at least one of the compounds zinc phosphate, aluminum phosphate, manganese phosphate, titanium phosphate, calcium phosphate, boron phosphate and iron phosphate.
3. The passivating agent for metallic surfaces of workpieces or casting molds as recited in of one of the preceding claims, characterized in that the passivating agent is composed as follows:

   0.1% to 5% by weight of gelatin;

   5% to 50% by weight of orthophosphates; and

   water for the rest.
4. A surface treatment agent for cleaning and passivating metallic surfaces of workpieces or casting molds with a passivating agent as recited in one of claims 1 to 3, the surface treatment agent further comprising non-ionic surface-active agents, lactic acid and a citric acid monohydrate.
5. The surface treatment agent for cleaning and passivating metallic surfaces of workpieces or casting molds as recited in claim 4, characterized in that the surface treatment agent Is composed as follows:

   0.1 to 5% by weight, preferably 0.41 to 1% by weight of gelatin;

   5 to 50% by weight, preferably 5 to 10% by weight of orthophosphates;

   0.5 to 5% by weight, preferably 0.5 to 2.5% by weight of lactic acid;

   0.5 to 5% by weight, preferably 0.5 to 2.5% by weight of citric acid monohydrate;

   0.1 to 3% by weight, preferably 0.5 to 2% by weight of non-ionic surface-active agents; and

   distilled water for the rest.
6. The surface treatment agent for cleaning and passivating metallic surfaces of workpieces or casting molds as recited in claim 4 or 5, characterized in that the surface treatment agent further includes at least one of molybdenum disulfide and bismuth.
7. The surface treatment agent for cleaning and passivating metallic surfaces of workpieces or casting molds as recited in claim 6, characterized in that the surface treatment agent further includes at least one of 0.01 to 5% by weight, preferably 0.02 to 0.04% by weight, of molybdenum disulfide and 0.01 to 5% by weight, preferably 0.02 to 0.04% by weight, of bismuth.
8. A surface treatment spray agent for cleaning and passivating metallic surfaces of workpieces or casting molds, characterized in that the surface treatment spray agent includes the surface treatment agent as recited in one of claims 5 to 7 and up to 60% by weight of a thickening agent.
9. A method for treatment of metallic surfaces of workpieces or casting molds, characterized in that the workpiece or the casting mold is immersed into a bath of the surface treatment agent as recited in one of claims 5 to 7, or spraying the surface of the workpiece or the casting mold with the surface treatment spray agent as recited in claim 8.
10. The method for treatment of metallic surfaces of workpieces or casting molds as recited in claim 9, characterized in that the workpiece or the casting mold is subsequently heated to 200° C.
11. The method for treatment of metallic surfaces of low-pressure casting molds as recited in claim 10, characterized in that a facing is applied onto a cleaned and passivated surface of the casting mold after the immersing into the surface treatment agent or the spraying of the surface treatment spray agent.
12. The method for treatment of metallic surfaces of casting molds as recited in claim 11, characterized in that facing is applied at a temperature of the low-pressure casting mold of 250° C.