EW January 2011

technical article

New technology for lubricating cold extrusion materials and cold heading wire By Jude Burke, Chemetall PLC, UK

Abstract It is increasingly difficult to deal with the contamination of wastewater from zinc phosphate or zinc-calcium phosphate coatings. This paper describes a conversion coating process involving the electro- lytic deposition of a calcium phosphate carrier coat. The process is efficient, free from heavy metals and sludge, and well suited to wire drawing, cold heading and extrusion. The paper highlights the cost savings, environmental benefits and productivity improvements that can be achieved by a combination of calcium phosphating with a polymer coating.

1.1 Explanations regarding the state of the art Initially the parts are pickled, rinsed and activated. An alternative to pickling is mechanical descaling. This is followed by a zinc phosphate conversion coating, which is obtained by means of a chemical reaction. For many manufacturing processes a conversion coating is essential to achieve high quality, cost effective large-scale production. The parts being processed are again rinsed, neutralised and finally a lubricant is applied. The lubricants are water-soluble soaps that react with the conversion coat or, alternatively molybdenum disulphide (MoS 2 ) dispersions. The complete process sequence takes between 60 and 90 minutes. It is worth noting that the quality of the phosphate, and the subsequent performance results, are a reflection on how much care has been taken in the early process stages.

Conventional coatings used are zinc phosphate or zinc-calcium phosphate. However, it is becoming increasingly diffi- cult to deal with the sludge and heavy metal contamination of wastewater from these processes. The answer to these problems is given in this paper, which describes a conversion coating based on the electrolytic deposition of a calcium phosphate carrier coating. This process is highly efficient and free from heavy metals and sludge. The con- version coating is eminently suitable for wire drawing, cold heading and cold extrusion. This paper highlights the cost savings, environmental benefits and productivity improvements that can be achieved by using a combination of calcium phosphating with a polymer coating. 1 State of the art The diagram below illustrates what is currently described as the state of the art process sequence.

Synopsis

The for drawing cold heading wire and for cold extrusion processes are soaps. In addition, molybdenum disulphide dispersions are used for cold extrusion processes. These lubricants currently used

lubricants are increasingly being replaced by ultra thin polymer technology, which offers benefits such as improved tool life, extension of the interval between oil changes in cold heading machinery and allowing the fabrication of parts with complex geometry. These polymer coatings are applied on top of conventional coatings as use on bare steel is restricted to a very few specific cases.

Figure 1 ▼ ▼ : State of the art workflow

Conversion coating

Activation

Rinsing

Neutrali- sation

Lubrica- tion

Rinsing

Pickling

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EuroWire – January 2011