WCA March 2011

Consequently, the quality and productivity will appreciably improve for both the surface treatment plant, and the bolt manufacturing or cold extrusion plant. This paper was presented at Istanbul Cable & Wire ’09 and is reproduced here by kind permission of the IWMA.

Less frequent changes of oil in the bolt heading • machines, as no soap is carried over to contaminate the oil re-circulation system To conclude, both wire manufacturers and wire users benefit from the use of polymer coatings. This results in a competitive advantage for both parties. 5 Electrolytic phosphating – a heavy metal-free coating process If a conversion coating (zinc phosphating) is required, then the problems of disposal of the produced sludge and the heavy metals that contaminate the effluent stream must be addressed. The solution to this problem is a calcium phosphate coating applied electrolytically. 5.1 Electrolytic application of a calcium phosphate coating A calcium phosphate coating is also a conversion coating but it differs fundamentally from the conventional zinc phosphate coating used to date. The coating solution is free from heavy metals such as zinc or nickel and so, therefore, is the coating. The coating can best be described with the formulation CaHPO 4 . The principle of coating deposition on a conductive surface is illustrated in Figure 3 . Since the part acts as a cathode, pickling attack on the iron material does not occur. Without this pickling attack no phosphating sludge will form so this application process does not generate sludge. Figure 4 shows phosphated and drawn cold heading wire. It can be clearly seen that the calcium phosphate coats are white prior to forming. After forming, the wire exhibits a regular grey colour. 5.2 Benefits Free from heavy metals so the effluent becomes easier • to manage No sludge for disposal • Process temperature of approximately 25°C • Treatment time of 2–5 seconds allows for relatively • short plants Required coating weight of 5–15g/m² can be adjusted • via the current density (A/dm 2 ) Higher drawing speeds for wire, and lower pressing and • ejection forces in cold heading and cold extrusion No heavy metal-containing effluent in the de- • phosphating of fasteners prior to heat treatment 5.3 Outlook A future treatment process for cold heading wire and solid parts could combine the benefits of an electrolytic, heavy metal-free phosphating with those of a polymer coating. Figure 5 shows such a plant. This will contribute to reducing the treatment times for surface treatment from around one hour to less than one minute.

Jude Burke Chemetall UK – UK Fax : +44 1908 373939

Email : ukinfo@chemetall.com Website : www.chemetall.co.uk

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Wire & Cable ASIA – September/October 2007 Wir & Cable ASIA – March/April 11