INTRODUCING OF CHROMELESS PROTECTION TECHNOLOGY FOR HOT DIP GALVANIZED AND PLASTICIZED SHEET IN COLD MILL A.D. PLANT IN SKOPJE

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1 INTRODUCING OF CHROMELESS PROTECTION TECHNOLOGY FOR HOT DIP GALVANIZED AND PLASTICIZED SHEET IN COLD MILL A.D. PLANT IN SKOPJE Panovska Liljana, Arsovski Angel, Sekuloski Predrag AD Ladna Valavnica, 16 Makedonska Brigada N 0 18, 1000 Skopje, R. Macedonia Abstract: From the experiences of many well known companies, but also having on mind the legislative of the European Union about the direction which will take in the future, and using our own experiences we have come to a conclusion that the process of substitution compounds in which the chromium is found in a shape of its hexavalent ion, is an imperative, as for better environmental protection, so for accomplishing economic effects, and improvement of the products. In other words, we have in plan to make changes in the existing technology for pasivisation of the galvanized coils and the chemical preparation of the pre-painted coils before the process of applying primer, by ejecting chromate compounds in which chromium is hexavalent, and its substitution with non-harmful compounds. Also we predict substitution of the standard chromate primer with universal chromate-free primer. There are planned laboratory experiments in some of the institutes of the companies, which manufacture chemical products of this type (Henkel, BASF, Akzo Nobel and others) as well as semi-industrial and industrial trials at our plant In the frame of this project the focus will be in a direction of inventing pigments that do not contain strontium chromate, and who will provide best correlative characteristics in a function of the quality of the pre-painted product. Introducing a green label on the products will mean direct ecological influences (no need of expensive procedures for reduction and refining) on the environment Putting out of use the means, which contain hexavalent chromium gives benefits in the possibility of finding sophisticated buyers (manufacturers of householding products and their decoration) as well as more aggressive marketing appearance on the West European market. 1. SCIENTIFIC GROUNDS OF THE PROCESS OF CHEMICAL PROTECTION OF GALVANIZED AND PRE-PAINTED COIL The dominant technology for corrosive protection of galvanized products as well as final phases of chemical treatment of pre-painted coils on the use of chemicals which contain hexavalent chromium as basic element. Reasons for its massive use are based on the following: attractive-decorative surface, excellent adhesion of the color upon the metal surface, exceptional corrosive protection, economical effects. On the other side Cr6+ in the shape of compound of strontium may be found as a pigment in the process of manufacturing primer, the first layer of polish between the metal and the covering decorative color, which has the function to provide good adhesion among them. That is one of the most important characteristics for the quality of the pre-painted coil. Numerous advantages that offer Cr6+ for the mentioned processes bring a chain of dangers, as toxic and carcinogenic characteristics, which manifest very harmful on the human health. From these reasons the legislative of the EU is more and more determined on less usage of products which contain Cr6+. Therefore, leading chemical companies in the past years are focused on invention of substitute of Cr6+, which will not influence the product quality. One of the possible substitutes of Cr6+ in the process of pasivisation of galvanized coils is Cr3+ in the shape of dichromate of Na and K, which has not toxic and carcinogenic characteristics. As a salt has the following characteristics: possibility of various coloring, applicable, creates light coating, good conductivity and enables better corrosive resistance. Except these substitute of Cr6+ with Cr3+ there are actions of pasivisation of galvanized coils, which do not contain chromate at all. Those are different organic films, inorganic salts and oxides of Al, Ti, Proceedings of 3 rd BMC-2003-Ohnd, R Macedonia 375

2 V, Mo, W, Co, Ce, Zr, oxides of the type of silicates, phosphates, organ-metals, and so called multi steps, which are a combination of the pre-mentioned. Considering the chemical treatment of the pre-painted coils, although the efforts in invention of substitutes of Cr6+ are dating from the 70-ties, the instantaneous development has been reflected in the third generation of substitutes, silans. Silans are compounds, which do not contain heavy metals, and enable good adhesive power and exceptional anticorrosive protection. In this moment there are primers, which do not contain strontium chromate. The target of the project presents a strategy of the company for adding the sign "green product" of the galvanized and pre-painted coils through using the existing technical quantum in possession of the factory. Involving new procedures for chromate-free protection of galvanized products and using chromate-free primer_for pre-painted products of Cold Mill -Skopje leads to necessity of performing large research. Special advantage related to our competence from the region is the fact that only we will be able to manufacture this type of products. According to some internal analyzes the expectations are increasing the income from the production of galvanized and pre-painted coils up to 30%. 2. DESCRIPTION OF THE EXISTING TECHNOLOGY AND PERSPECTIVES FOR ITS SUBSTITUTION The existing technology for anticorrosive protection by the galvanized products as well as final phases of chemical treatment on pre-painted coils is based on the use of chemicals, which contain hexavalent chromium as basic element. Reasons for its mass use are based on the following: attractive-decorative surface of the galvanized coils excellent adhesion of the color upon the metal surface of the pre-painted coils exceptional corrosive protection economical effects A scheme of the coil coating line is given in fig. 1. PLANT DATA; Strip width max mm Strip thickness 0,4-1,5 mm Speed" max. 120m/min Capacity to/a EXIT SECTION ENTRY SECTION ROLLCOATERS PRIMER AND TOP COATI DIPPING SECTION SPRAYING SECTION STRIP CLEANING AND PRETREATMENT For anticorrosive protection of the galvanized coil in the moment is used chemical compound PASERITE 225-W (produced by Henkel) which contains hexavalent chromium. This resort is a concentrate, diluted with water till some defined concentration for use. This solution with nozzles is spread upon the galvanized coil over the small collector tank. For uniform spreading of the solution on 376 Proceedings of 3 rd BMC-2003-Ohrid, R. Macedonia

3 the surface of the coil are being used rubber, wiping rolls. Right after the solution has been spread upon the surface, with hot air galvanized coil is being dried on a temperature of 50C. The preparation of the coil on the pre-painting line is going in three phases: 1. Use of solution of alkali detergent - degreaser (RIDOLINE 72) 2. Rinsing with water 3. Alkali pasivisation with solution of GRANODINE Rinsing with water 5. Final pasivisation of the coil with DEOXYLYTE Drying the strip with air before applying the first layer of primer As first generation of the compounds that may substitute chromium, compounds are hydrofluotitanic, hydrofluocirconic or hydrofluosilitium acid on the base of polyakrili polymers. But, the experiences have shown that performances of these compounds are not consistent, and the products are unstable. Second generation of chromate-free compounds, are organic and inorganic polymers structurally bound with hydrofluotitanic and hydrofluocirconic components. On this way are obtained many stable products, with adhesion and corrosive protection comparable on the use of chromate protection. As a newest generation in the use of chromate-free protection are the silans. Silans are compounds, which do not contain heavy metals, and enable good adhesive power and exceptional anticorrosive protection. Siliconized Polyester! I High Durable Polymerl Chromate-free niversal Primej ipolyurethanel PVC-Plastisole Acrylates Electrogalvanized Steel I Hot-Dip Galvanized Steel Fig. 2 Compatibility of the chromate free universal primer Dry adhesion Coverage Wet adhesion Flexibility Corrosion Protection Universal Compatibility Compatibility to chromatefree pretreatment Fig. 3: Comparison of initial and new chromate-free universal primer Implementing chromate-free chemical preparation of the coil leads to a necessity of the use of chromate-free universal primer who is compatible with all top-finish technologies. Proceedings of 3 rd BMC-2003-Ohrid, R. Macedonia 377

4 INTRODUCING OF CHROMELESS PROTECTION TECHNOLOGY FOR.. Implementing chromate-free protection of the galvanized and pre-painted coils brings to a necessary expert collaboration with Henkel at first place (whose products we use in the moment). Henkel in its palette of products has announced production of this kind of products, which may be tested on our plants. Also for the use of chromate-free primer with chromate-free technology for anticorrosive protection we must collaborate with the companies: DUGA, BASF, Akzo Nobel ant others, in order to make an introduction on the domestic and European market as manufacturers of Eco-products. Literature: 1. "Replacing Hexavalent Chromium", Paul C.Wynn and Craig V.Bishop McGean UK, United Kingdom 2. "Replacement of Chromium (VI) in Passivitions on Zinc And Zinc Alloys", Patricia Preikschat, SurTec KmbH, D-6473 Zwingenberg 3. "Coating Clean, Coating Green, 36" ECCA Meeting 4. "Chromate-free Coil Coating" VOEST-ALPINE STAHL LDSfZ GmbH 378 Proceedings of 3 rd BMC-2003-Ohrid, R Macedonia

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