What is alkaline cleaner?
An alkaline cleaner is a degreaser with a working pH above roughly 10, built on hydroxides, silicates, carbonates and phosphates. High alkalinity saponifies fatty soils and strips heavy machining oil from steel and cast iron — but it attacks aluminium, zinc and brass, which need a neutral cleaner instead.
- Working pH
- Above ~10
- Best on
- Steel, cast iron, forgings
- Avoid on
- Aluminium, zinc, brass, magnesium
Alkalinity is the heavy artillery of aqueous cleaning. On ferrous parts carrying forging scale, drawing compound, buffing paste or baked-on machining oil, nothing cheap works better. Silicates additionally passivate steel slightly, giving a small amount of in-bath corrosion protection.
The limit is metallurgical. Aluminium, zinc, magnesium and to a lesser extent brass and bronze are amphoteric or alkali-sensitive: above about pH 10 the cleaner etches them, dulling the surface, opening grain, and leaving a freshly reactive face that blooms into white rust within days.
Mixed-metal baskets are the trap. A line that cleans steel housings and aluminium covers in the same basket must run neutral chemistry, even though the steel would tolerate — and slightly prefer — alkaline.
