Rust Inhibitors in Metalworking Fluids

Freshly machined steel surfaces are highly reactive. Between operations and during storage, residual moisture and oxygen cause flash rusting within hours.

Key Chemical Types

Amine carboxylates: Formed in-situ in alkaline metalworking fluids (pH 8.5–10). Diethanolamine oleate, triethanolamine stearate. Effective for ferrous metals.

Sulfonates: Oil-soluble sulfonates are the primary rust inhibitor in straight cutting oils. Calcium and sodium sulfonates are preferred replacements for barium types.

Triazoles (BTA, TTA): Benzotriazole (BTA) and tolyltriazole (TTA) are selective for copper and copper alloys (brass, bronze). They form a stable passivating film at 50–500 ppm. Essential in mixed-metal machining.

Ferrous vs Non-Ferrous Protection

Metal	Preferred Inhibitor	Concern
Steel	Sulfonates, amine carboxylates	Concentration threshold
Cast iron	Borate + sulfonate	Porosity penetration
Aluminium	Low-pH-stable carboxylates	Avoid strong alkali
Copper/Brass	BTA, TTA	Low dosage critical

HMEChem supplies rust inhibitor concentrates and triazole blends for water-soluble and straight metalworking fluids.