The present invention refers to a process of electrolytic galvanizing, thick layer passivation and subsequent treatment in order to enhance anti-corrosive protection, wherein said process comprises a pretreatment and, respectively, cleaning of products to be protected against corrosion, galvanizing in an alkaline media and final treatment.

A process of electrolytic galvanizing of the aforementioned kind has been disclosed by the publication of a patent application No. EP 1 199 376 A1. In said document is disclosed a Zn coated steel material, a Zn coated steel sheet and a painted steel sheet that are excellent in corrosion resistance and can be applied to various purposes, such as for home electrical appliances and building materials, and a process for production thereof. In spite of the known process meets the requirements set by the users, it also comprises certain disadvantages as demonstrated particularly in a relative high power consumption and, as result, in use of relatively aggressive medium. In addition, the layer thickness of the anti-corrosive protection on products exceeds 20 µm and are thus useless in the environment with very demanding and up to extremely demanding climatic load.

It is the object of the present invention to create a process of electrolytic galvanizing with an enhanced anti-corrosive protection which remedies the drawbacks of the known solutions.

A process of electrolytic galvanizing with an enhanced anti-corrosive protection according to the invention comprises a pretreatment, wherein organic impurities, rust, dross and similar is removed from the surface of a product to be protected. Said pretreatment is carried out in alkaline solutions comprising sodium metasilicate, sodium hydroxide, sodium carbonate, and in acidic water solutions comprising sodium hydroxide and sodium carbonate. By means of said pretreatment the surface of a product to be protected is prepared for the next process step.

Further step of the process of electrolytic galvanizing with an enhanced anti-corrosive protection according to the invention comprises galvanization being carried out in an alkaline cyanide-free media. It is provided for according to the invention that the alkalinity of said cyanide-free media is as high as possible. Said alkaline cyanide-free media comprises silicic acid, sodium salt comprising sodium silicate, components of a water polymer solution comprising nitrogen, a solution of trition trisodium salt and triazine, and a polymer solution comprising methanol and formaldehyde.
Between the steps of the pretreatment and galvanization processes of washing by means of a flow system, cascade system and spraying system, respectively, are carried out alternately after each operation.

Furthermore, the process of electrolytic galvanizing with an enhanced anti-corrosive protection according to the invention comprises a step of final treatment, wherein a thick layer passivation based on chromium III compounds and cobalt compounds represents the primary layer on the zinc coating applied by means of galvanization to the product to be protected. Said product to be protected is treated in a working bath at the temperature in the range between about 19 °C and about 30 °C, preferably in the range between about 21 °C and about 28 °C. Said working bath comprises a pH value in the range between about 2,0 and about 3,0, preferably in the range between about 2,3 and about 2,7. Afterwards, said product is flushed by means of a pure water, preferably by means of demineralized and deionized water. The previous step is followed by sinking said product for the first time period into a polymer dispersion of silicate and polyurethane in water. It is provided for according to the invention, that the ratio between the silicate and the polyurethane in said polymer dispersion in water amounts to approximately 10 : 1. Said first time period lies in the range between 40 seconds and 80 seconds, preferably between 50 seconds and 70 seconds. Further, it is provided for according to the invention, that said polymer dispersion in water comprises a pH value in the range between about 8,0 and about 11,0, preferably in the range between about 8,5 and about 10,5.

In the continuation of the process, said product to be protected is removed for the second time period from said polymer dispersion of silicate and polyurethane in water. It is provided for according to the invention that said second time period lies in the range of about 10 seconds.

The removal of said product from said polymer dispersion of silicate and polyurethane in water is followed by a re-immersion for the third time of period of said product to be protected into said polymer dispersion of silicate and polyurethane in water. Said third time period lies in the range between 15 seconds and 50 seconds, preferably between 20 seconds and 40 seconds.

It appeared as preferred according to the present invention that said polymer dispersion of silicate and polyurethane in water must be continuously stirred during the process.
The above disclosed process step is followed by draining and/or removing of the surplus of said polymer dispersion in water off the product to be protected being followed by drying. The drying is carried out during the fourth time period by means of a hot air in closed or partially closed drying chambers in the temperature range between about 50 °C and about 90 °C, preferably in the temperature range between about 60 °C and about 80 °C. According to the invention, it is provided for that said forth time period ranges between 6 minutes and 15 minutes, preferably between 8 minutes and 12 minutes.

The above disclosed process of electrolytic galvanizing with an enhanced anti-corrosive protection according to the invention is carried out entirely at relatively low temperatures, thus having significant advantages over the present solutions. Thus, the process of low-temperature thick layer passivation features substantial energy savings since it is carried out at the room temperature. In addition, less aggressive media having smaller content of Zn²⁺ and Fe²⁺ ions is used during the process, resulting in waste waters comprising no nano particles.

By means of the disclosed process according to the invention, the anti-corrosion protection increases on products intended for building hardware and other sectors where high anti-corrosion protection on zinc coating is required. The layer of the anti-corrosion protection is equally distributed over the entire surface of the product to be protected. By means of the process according to the invention, an outstanding anti-corrosion protection is obtained where the thickness of an average layer of the anti-corrosion protection lies in the thickness range of 10 µm without reducing the anti-corrosion protection of products being used in extreme climate conditions.