Electroless
nickel plating of stainless steel parts (drive shafts, meshing parts, moving
parts, etc.) can improve the uniformity and self-lubricity of the plating,
which is better than chromium plating. However, electroless nickel plating on
stainless steel often results in unsatisfactory bonding between the plating
layer and the substrate due to poor pretreatment, which has become an urgent
problem in actual production.
The
original process: mechanical polishing → organic solvent degreasing →chemical
degreasing → hot water washing → electrochemical degreasing → hot water washing
→ cold water washing→ 0%HCl → cold water washing→ 20%HCl(50℃) → cold
water washing → flash plating Nickel →
electroless nickel plating.
Disadvantages
of the original process: the effect of using HCL alone to remove the oxide
scale is not good; the flash nickel plating of complicated shapes affects the
uniformity of electroless nickel plating due to poor coverage; the longer
process may cause the fresh surface of stainless steel to be re-oxidized. Film;
flash nickel plating solution is easy to pollute chemical nickel plating
solution, etc. To this end, someone improved the process.
Improved
process flow: the polishing and degreasing process is the same as the original
process → mixed acid removal film (25%HCl+8%HNO3+10%HF) → cold water washing →
activation (10%HCl+5%NH4F, 60℃)
→ hot water washing →
Electroless Nickel.
The
advantages of the improved process:
1. Use mixed acid to
remove the insoluble FeCrO4 oxide film, Si, SiO2 on the surface of the stainless
steel, and enhance the chemical activity of the surface of the substrate，
2. The process is
simplified to avoid the fresh surface of the stainless steel from being
re-oxidized，
3. The preheating
process of the substrate is increased , Eliminate the stress caused by the
temperature difference between the plating layer and the substrate. Therefore,
the electroless nickel plating has a good bonding force with the substrate, and
the plating speed is fast.
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