Nuts & Bolts
It is often necessary to deposit metals over passive surfaces
of either stainless steel or previously applied nickel. To accomplish
this and achieve good adhesion, you must understand and use what
has become known as a "Woods Nickel Strike." Personally,
l like the use of such a bath over most ferrous substrates. The
all-chloride formulation makes this system very effective in removing
all types of scale, oxides and flash rust. When operating over
a ferrous substrate with an electroless nickel process, I find
the use of a Woods or modified Woods formulation indispensable.
First, the system removes any flash rust from the substrate and
keeps it out of the EN process and, second, the EN bath lasts
longer because the impurities from the cleaning process are not
brought along from the preparatory steps, with the parts. Last,
because the Woods strike removes all the flash rust from the parts,
l can make the cleaning and preparation steps much more severe
than I would ordinarily, and produce a chemically clean surface
for further processing.
A preferred formulation of an ali-chloride strike that l like
to use in the field is this:
This type of process will yield an active surface of passive parts
and will allow further processing with other finishes.
Typically, this solution is followed by a nickel coating. The
deposit from an all-chloride bath, at very low pH, is fine-grained
and smooth, but inherently very stressed, so that the thickness
of deposit derived from the Woods Nickel step should be very low.
The success of plating over passive surfaces depends greatly on
both the condition of the Woods Nickel Strike and the overall
preparation cycle. This is not to say that this is the only process
that will work, but to improve the success of such a process,
I have used this cycle with consistent results. A modification
of this process might be more dependable over some substrates: