| Steel coils destined for use in the production of deep-drawn pressings for the automotive industry require corrosion protection before leaving the mill to preserve surface quality.
The level of protection offered will depend on the specification of the fluid but also upon its application. Coating thickness may not be consistent, and fluid may be displaced as the material is coiled. The fluid must be washed off before the steel is processed because particulate matter can become embedded in the oil film; this could create blemishes in the finished part. A fresh coating of lubricant must then be applied prior to pressing to aid forming.
This is clearly a wasteful procedure. The washing cycle and second application of lubricant are non-value adding processes, presenting an opportunity for cost reduction.
Castrol, working with steel suppliers and OEMs, is developing dry film lubrication systems to offer an alternative to existing methods.
Castrol surface treatment specialist Dirk Liese said: “Dry film lubricants are inherently more stable and therefore produce a more even and durable coating that isn’t affected during handling, storage and transit. More importantly, when coils and blanks are delivered to the customer, they can be fed directly into the pressing process. With no need for a pre-wash or a re-application of lubricant to aid deep draw pressing, the dry film system eliminates a complete pre-press process!”
According to Castrol, the existing spray equipment can be modified to dispense dry film lubricants. Liese explained: “Dry film, which is solid in its natural state, has a melting point of 45–50°C, and wet lubrication spray processes are currently operating at 60°C. So the equipment changes needed to use existing spray booths are mainly focused on the installation of heaters to maintain the dry film in a liquid form between the storage tank and the spray heads. When the dry film lubricant hits the steel it cools and reverts to its solid state to provide a completely uniform and consistent coating that won’t run off the surface.”
Trials of Castrol Iloform PN 950 DF have yielded multi-stage pressed parts that have then completed adhesive and welding processes without any additional washing, de-greasing or lubrication operations.
Audi, BMW, Daimler/Chrysler, Ford and GM/Opel are currently trying the dry film system.
At present dry film lubrication will only be used for internal panels. Exterior panels require the highest quality surface finish and this is determined in part by the effectiveness of the lubricant. Castrol believe that dry film technology could be developed to suit, and therefore become the universally accepted pressing lubrication system.
There is also potential for dry film coating of aluminium, which currently uses water-based pre-press lubricant, which requires a drying stage before the material can be formed.
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