Masking used for selective case hardening. Copper plating roughly 0.013 to 0.025 mm thick is the standard barrier against carbon, while ceramic or boron-based paints and tin-based pastes are brushed on for carburizing and nitriding. Threads, bores that will be machined later and weld zones are typical stop-off areas. Coverage must be complete and dry, because a pinhole leaves a hard spot right where machining or welding comes next.
Paint stop-off on the threads, they have to stay soft enough to chase after carburize.
Also heard as
- stopoff
- maskant
- copper stop-off
- anti-carb paint
Related terms
Carburizing
Diffusing carbon into the surface of low-carbon steel at high heat, then quenching for a hard case.
Nitriding
Diffusing nitrogen into steel below its critical temperature to form a hard case with no quench.
Case
The hardened outer layer of a case-hardened part, as opposed to its softer, tougher core.
Ion nitriding
Nitriding with a glow-discharge plasma in a vacuum vessel, which allows close control of the white layer.