DIN Electroplated coatings – Zinc coatings on iron or steel – Terms, testing and corrosion resistance (Foreign Standard) This standard only applies in . Buy DIN () Electroplated Coatings – Zinc Coatings On Iron Or Steel – Terms, Testing And Corrosion Resistance from SAI Global. Buy DIN ELECTROPLATED COATINGS – ZINC COATINGS ON IRON OR STEEL – TERMS, TESTING AND CORROSION.
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The present invention relates to chromium VI -free chromate according to claim 1, a method for their preparation according to claim 4, a concentrate according to claim 7, a passivation bath according to claim 11, a method for passivating according to claim 17 and a passivation layer according to claim 21st.
Metallic materials, in particular iron and steel, galvanized or cadmium plated to protect them from corrosive environmental influences. The corrosion protection of the zinc based on the fact that it is still less noble than the base metal dun therefore initially draws the corrosive attack exclusively to itself, it acts as a sacrificial layer.
The base metal of the zinc-plated component remains intact, while there is still continuously covered with zinc, and the mechanical functionality is maintained over longer periods of time than in the case of parts. The corrosive attack on the zinc layer in turn cin be greatly retarded by applying a chromate treatment, and thus also the base metal corrosion is even further delayed than by mere zinc plating.
Further, the optical deterioration of a component is delayed by environmental influences by a chromate treatment – the corrosion products of zinc, the so-called white rust, have a disruptive effect on the appearance of a component. The advantages of an applied chromate are so important that almost any galvanically zinc-plated surface is additionally chromated.
The prior art has four named according to their colors chromating that a galvanized 509961 with the corresponding aqueous chromate coating can be applied in dim case by treatment dipping, spraying, rolling.
Furthermore, yellow and green chromations for aluminum are known which are prepared in an analogous manner. The 509661 is up to 80 nm thick, pale blue in the color xin their own, and has depending on the layer thickness of a golden, reddish, bluish, greenish or yellow iridescent color generated by light refraction. Very thin chromate almost no intrinsic color are referred to as colorless Group A.
The chromate coating can be made in both cases, both hexavalent and trivalent di and mixtures of both, moreover conducting salts and mineral acids. Es gibt fluoridhaltige und fluoridfreie Varianten. There is fluoride and fluoride-free variants.
The corrosion protection of intact blue chromatings amounts to h in the salt spray cabinet according to DIN SS until the first occurrence of corrosion products. The yellow chromate layer is dln 0. The chromate 50691 consists of water-dissolved hexavalent chromate, conducting salts and mineral acids substantially. Application of the chromate is done at room temperature. The corrosion protection of intact yellow chromates amounts to h in the salt spray cabinet according to DIN SS until the first occurrence of corrosion products.
The minimum requirement for the process group C according to DIN Chapter 10 Table 3 is 72 h for barrel plating and rack plating for 96 h. The typical Olivchromatierungsschicht is up to 1. The chromate coating consists essentially of water-dissolved hexavalent chromate, conducting salts and mineral acids, in particular phosphates or phosphoric acid and may also contain formates.
The corrosion protection of intact olive chromatings amounts to h in the salt spray cabinet according to DIN SS until the first occurrence of corrosion products. The minimum requirement for the process group D according to DIN Chapter 10 Table 3 is 72 h for barrel plating and rack plating for h.
Die Schwarzchromatierungsschicht ist im Grunde eine Gelb- oder Olivchromatierung, in die kolloidales Silber als Pigment eingelagert ist.
The Schwarzchromatierungsschicht is fundamentally a yellow or olive chromating, is inserted as a pigment in the colloidal silver. The chromating have the same composition as yellow or olive chromatings approximately and additionally contain silver ions. The corrosion protection of unmarred black zinc amounts to h in the salt spray cabinet according to DIN SS until the first occurrence of corrosion products.
The minimum requirement for the process group E according to DIN Chapter 10 Table 3 is 24 h for barrel plating, and 48 h on racks. Schwarzchromatierungen auf Zinklegierungen liegen erheblich oberhalb der genannten Werte.
Black chromations zinc alloys are significantly above the recited values. The chromate coating consists of water-dissolved hexavalent chromate, conducting salts and mineral acids, and in particular of phosphates and silicofluorides substantially.
Accordingly, the chromate contained with said requests to the Cor rosionsschutz even these extremely toxic and carcinogenic chromium VI – compounds, which are also not completely immobilized in the layer. Chromate coating with chromium VI compounds is problematic with regard to safety at work.
The use of zinc and chromium VI compounds prepared chromating such. As the widespread yellow chromates such. Therefore, it is object of the present invention to provide a chromium VI -free, thick chromate film with a high chromium content on zinc, cadmium or aluminum are available. The solution of this object is achieved with respect to a layer by the features of claims 1 and 21, process technology by the features of claims 4 and 17, and with respect to a composition useful for carrying out the method according to the invention by the features of claims 7 and The sub-claims represent preferred embodiments of the present invention.
Further advantages and features of the present invention will become apparent from the description of exemplary embodiments and based on theoretical considerations that are not binding on the one hand and on the other hand have been made having regard to the present invention by the inventors.
It was carried out the following experiment: Kleine Stahlteile wurden elektrolytisch glanzverzinkt ca. Die Tauchzeit betrug 30 s. Immersion time was 30 seconds. The parts were then rinsed with water and dried in air stream.
Surprisingly, it was found in the corrosion test in the salt spray cabinet according to DIN SS, that the formed chromate film having a corrosion protection until the first occurrence of corrosion products according to DIN Chapter 10, in particular chapter The novel greenish chromate layer had a thickness of about nm was formed on chromium VI free paths and was shown to chromium VI free.
The production method according to Example 1 for the new greenish chromium VI -free chromate is not very economical for conventional plants because of the relatively high temperature of the process solution. Further theoretical reflections on chromium VI -free chromate coating and further trials finally resulted in economical production conditions. Chromating of zinc is accomplished by the formation of a so-called conversion coating on the zinc surface, the zinc surface that chemically reacts with the chromating solution and is converted into a chromate layer.
DIN – European Standards
The formation of conversion layers is a dynamic process beyond the chemical equilibrium. To describe the underlying processes one must therefore use of chemical kinetics. With the specially established kinetic model starting points for the optimization of the present invention could win. The conversion layer formation in a chromating solution on the basis of chromium III can be based on two reaction equations describe: ZnCrO m 2 taken into account that reaction I by the growing vin layer is increasingly slowed down.
Der Term tanh p 2. The term tanh p 2. The tanh function ensures a smooth transition from 0 to 1, which can be set with p. The differential equation system is solved numerically by means of dn. As a result of 500961 layer thickness profile and the concentration developments over time were obtained.
In Figure 1, the layer don profiles for different values of the rate constants are shown j k. For good corrosion protection, the passive layer should be thick and at the same time as compact as possible. The faster the initial dissolution of zinc rate constant k 1 and the faster the dissolved zinc with the chromium III precipitates rate constant k 2the thicker the chromate layer. A low pH favors the dissolution of zinc, but also provides for increased redissolution of the layer.
The reaction I and the forward reaction II must take place as soon as possible, the reverse reaction II must remain slow. For this, there are the following approaches: Chromium III complexes generally have slow kinetics. Durch Einsatz geeigneter Liganden sollte sich die Reaktionsgeschwindigkeit beschleunigen lassen. By using appropriate ligands, the reaction rate should be accelerated.
Further, these transition metal cations can act as catalysts in the ligand exchange on chromium III. There were conducted series of experiments. Die Ansatzpunkte a und b sind dem Fachmann bekannt. The starting points a and b are known in the art.
Beschleunigung der Hinreaktion II. Wohingegen die Fluoridkomplexe kinetisch sehr stabil sind. Whereas the fluoride complexes are kinetically very stable. Electrolytically bright zinc 15 m steel parts were immersed in an aqueous chromating solution: Die Tauchzeit betrug 60 s. Immersion time was 60 seconds.
After rinsing and drying SS a corrosion protection of h until first attack according to DIN was found in the salt spray cabinet according to DIN. Malonic acid is a don of an on chromium III enables faster ligand replacement kinetics than the fluoride from Example 1.
Electrolytically bright zinc 15 microns consisting of steel parts were immersed in an aqueous chromating solution: Cobalt is an element that, according to the model concept catalyze the ligand exchange and could reduce by incorporation of kinetically stable oxides in the chromate layer the reverse reaction II further, so that the chromate film should be thicker overall.
On this point, the condition laid down in the present invention model concept is supported ddin the practice.
The corrosion protection could be significantly increased simply by adding cobalt in the chromate again compared to Example 3. Further advantageous ligand arising from the list according to claim 6 and 8. The new greenish chrome VI free chromate is dn depending on the production temperature between and nm thick, pale green in color and the natural red-green iridescent. The chromate coating consists of trivalent chromates, moreover conducting salts and mineral acids.
The corrosion protection of intact greenish chrome VI free chromating amounts depending on the production temperature to h in the salt spray cabinet according to DIN SS until the first occurrence of corrosion products. So that the new chromate meets the minimum requirements for protection 550961 corrosion for the methods C and D according to DIN Chapter 10, Table 3 and without chromium VI neither in the preparation nor in the product.
In aluminum etching pretreated aluminum parts were immersed in an aqueous chromating solution: Die Passivschicht war grau.
Niedax Galvanik GmbH
The passive layer was gray. In our industrial society galvanized and chromated metal surfaces are omnipresent. So far, a good corrosion protection only on the basis of toxic chromium VI was reached. The Chromiting is a novel method based on non-toxic chromium III compounds and is intended as a more environmentally friendly replacement of the yellow and olive chromatings.
Chromated zinc coatings are easy to prepare, relatively inexpensive, available in several colors and change neither diameter nor shape of the coated parts significantly.
Trotz dieser Vorteile ist nicht nur die Automobilindustrie dabei, Zink durch andere Beschichtungen zu ersetzen oder zumindest nach praktikablen Alternativen zu suchen. Despite these advantages is not only the automotive industry to replace zinc by other coatings or to search at least for viable alternatives.