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New eco-process of superficial treatment of the metal wire products (MDPATC)
Date du début: 1 nov. 2010, Date de fin: 31 oct. 2013 PROJET  TERMINÉ 

Background Manufacturing of wire-rod products can have a high environmental impact because of the use of large quantities of water and acids, and the energy-intensive operations and emissions associated with the process of producing thick zinc coatings using hot-dip equipment. Objectives The objective of the MDPATC project was to demonstrate alternative technological approaches to reduce the environmental footprint of wire-rod products, and to improve raw material recycling opportunities during the manufacture of these products, which include nails, screws and arc-welded nets. The project focused on new descaling and scale-milling mechanical processes, and aimed to implement an innovative dry micro-layering treatment for descaling using mechanical and abrasive actions. The innovative treatment will be applied after the wires are drawn, using a microwave plasma surface technique that favours the subsequent hot deposition of high-performance Zn-Al-Mg based alloy. The overall aims of the project were to reduce raw material use, decrease acid and pickling bath use, reduce the production of pollutant zinc ash, increase the useful life of the manufactured products and make them more suitable for welding without affecting the protective surface coating. Results The MDPATC project demonstrated the technical viability of a new process to tackle the environmental problems related to the production of zinc-coated drawn wire, by acting on three specific phases of the production cycle: the wire rod drawing, the cleaning of the drawn wire and the final galvanising process. A new pre-treatment stage for surface cleaning and activation by microwave plasma was tested, which enabled reductions in the amount of zinc coating required. Iron-based particles recovered during the descaling process were separated and reused as pigments, or within metal processing plants. The project also utilised high-performance ternary alloys of Zn-Al-Mg at the dip-coating stage. Laboratory tests were first conducted to define the best conditions for descaling wire rods. The results were used to design a prototype system. The project team constructed a pilot plant to demonstrate the new process at the Calestano factory of the coordinating beneficiary, with the capacity to manufacture around 4 000 tonnes/year of iron-based wire-drawn products. This pilot plant line comprised equipment for the mechanical descaling of wire rods, microwave-induced plasma treatment, and a final dip-coating bath. The subsequent validation showed that the process reduced the main environmental impacts of the hot-dip galvanising process, including energy and water consumption levels; eliminated the production of waste (through the exploitation of metal waste produced in the descaling phase), air and vapour emissions, and the use of hazardous substances (e.g. hydrochloric acid and ammonium chloride); and reduced the use of materials, in particular zinc, in the galvanising process, and during the preparation of the wire rod. A final quantitative analysis by the project team showed that the process was both technically and economically feasible. Furthermore, the lower energy consumption of the plant and the low production of waste ensure the process is environmentally and economically beneficial. Environmental impact reductions were made during the wire surface preparation and zinc coating stages. The manufacture of wire-rod products with a lower environmental impact was achieved without any reduction in quality. The final results also demonstrated that the new process can be technically up-scaled to an industrial level. The analysis conducted by the project revealed that the production processes for wire-rod products is various and difficult to standardise. For this reason, companies need to hire experts if they wish to prepare specific environmental action plans. The project also found that companies must be sufficiently motivated to overcome initial reluctance to having their environmental performance improved, whilst the demonstrative action at pre-industrial scale can be a significant driving force to re-launch the wire-rod products industry. The Zn-Al-Mg alloy dip bath demonstrated in the project can be applied to any product undergoing a galvanising process, with significant reductions in the use of zinc and relevant emissions. Although not a toxic metal, if inhaled in its gaseous state zinc can cause several health problems in humans. In addition, due to the lack of availability in nature, zinc can have a high supply cost. The transfer of the technology to other processes will therefore lead to lower production costs and improved working conditions for employees in many metallurgical companies. The microwave plasma application system was specifically sized to treat metal wire, but the technology could be re-sizing to treat other products, with savings in terms of water and acid usage, and pollutant emissions. Project dissemination activities were targeted at expert groups and the general public, and included the production of reports and newsletters, a documentary film, a website, a scientific paper, and contributions at a project-organised seminar and at industry trade fairs. The main economic benefit is related to the reduction in use of zinc, a widely used metal of increasing cost. Zinc is not produced in Europe and, therefore, it must be imported from other parts of the world. Thus, a reduction in the use of zinc will result in lower production costs for companies and lower purchasing cost of final goods for consumers. This could increase the competitiveness of European companies operating in this sector, making them able to face product competition from emerging markets including India, China and Brazil. The project beneficiary calculated that if the new technique was implemented by all EU steel wire producers, it could valorise 2 000 tonnes of metallic waste (recycled during mechanical descaling) annually, reduce electric power consumption during descaling and hot-dip coating by 120 kWh/tonne, achieve water savings of around 25 000 m3/year, reduce acid sludge production by 2 500 tonnes/year, reduce the production of hydrochloric and sulphuric acid by 6 000 tonnes/year, reduce noxious vapour emissions, and reduce the amount of waste zinc ash produced during the coating process. Further information on the project can be found in the project's layman report (see "Read more" section).

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