Product Knowledge

BIT 20% for Metalworking Fluids & Cutting Oils

Metalworking fluids and cutting oils are among the most microbiologically demanding applications for any industrial biocide, facing continuous bacterial challenge from recirculating water and tramp oil. This guide explains how BIT 20% is used to preserve these systems.

Published 2026-01-15Updated 2026-07-27By Vasudev Chemo Pharma Technical TeamReviewed by Vasudev Chemo Pharma Formulation & Regulatory Affairs Team, Industrial Chemistry, Biocide Formulation

Why Are Metalworking Fluids a Demanding Preservation Challenge?

Metalworking fluids recirculate for weeks or months, facing continuous fresh bacterial contamination from tramp oil, metal fines, and operator contact — unlike a sealed paint can used once. This is why they need higher and often supplemental biocide dosing.

Water-miscible metalworking fluids (soluble oils, semi-synthetics, and synthetics) are recirculated for weeks or months in CNC machining, cutting, and grinding operations, continuously exposed to fresh bacterial contamination from the workplace environment, tramp oil leaking from lubrication systems, metal fines, and operator contact. Left unprotected, these fluids rapidly develop bacterial slime, a characteristic foul odour (often from sulfate-reducing bacteria byproducts), reduced corrosion protection, dermatological irritation risk for operators, and emulsion instability as bacterial activity degrades emulsifier packages. Because these systems are diluted 5%-10% at the point of use, the biocide must be dosed into the concentrate at a level that remains effective after dilution.

What Dosage of BIT 20% Is Used in Metalworking Fluids?

BIT 20% is commonly dosed into metalworking fluid concentrates at 0.2%-0.5% on total concentrate weight — higher than paint or adhesive ranges — reflecting the more severe, continuous microbial challenge. This delivers low tens to low hundreds of ppm in the diluted working fluid.

BIT's documented stability at alkaline pH is particularly relevant here, since most metalworking fluid concentrates are formulated at pH 8.5-10.5 for ferrous metal corrosion protection. Because metalworking fluid systems are recirculated and topped up over extended periods rather than used once and discarded, many formulators pair BIT with periodic tank-side biocide treatments to manage bacterial populations that build up during in-use operation, in addition to the preservative dosed into the fresh concentrate.

Is BIT 20% Compatible With Amines and Other Metalworking Additives?

BIT 20% is generally reported as compatible with amine-based corrosion inhibitors used in metalworking fluids, unlike some formaldehyde-releasing biocides that can undergo unwanted side reactions with amines. Confirm through bench trials before full-scale use.

Metalworking fluid formulations commonly include amine-based corrosion inhibitors and pH buffers, emulsifiers, extreme-pressure additives, and biocide-boosting synergists. As with any new formulation, compatibility should be verified through bench trials — mix a sample batch, monitor for colour change, phase separation, or viscosity shift over several weeks of accelerated storage, and run a preservative efficacy challenge test using bacteria representative of the metalworking fluid environment, including sulfate-reducing bacteria where relevant.
BIT 20% dosage guidance for metalworking fluid systems
Fluid typeBIT 20% dosage in concentrateResulting active ppm after 5-10% dilution
Soluble oil0.2%-0.3%20-40 ppm
Semi-synthetic fluid0.3%-0.4%30-80 ppm
Full synthetic fluid0.3%-0.5%30-100 ppm

Frequently asked questions

Why do metalworking fluids need more biocide than paints or adhesives?+
Metalworking fluids are recirculated for weeks or months and face continuous fresh bacterial contamination, unlike a sealed paint can used once. This is why metalworking fluid concentrates are typically dosed with BIT 20% at 0.2%-0.5%, higher than typical paint or adhesive ranges.
Is BIT 20% stable in alkaline metalworking fluid concentrates?+
Yes. BIT is documented as stable across a wide pH range including the pH 8.5-10.5 range typical of metalworking fluid concentrates formulated for ferrous metal corrosion protection.
Can BIT 20% be used with amine-based corrosion inhibitors in metalworking fluids?+
BIT 20% is generally reported as compatible with amine-containing metalworking fluid formulations. Confirm compatibility through bench trials and accelerated storage testing for your specific formulation.
Does BIT 20% alone control bacteria throughout the working life of a metalworking fluid?+
BIT 20% dosed into the fresh concentrate provides ongoing baseline protection, but many operators also use periodic tank-side biocide treatments to manage bacterial populations that build up during extended in-use recirculation.

Sources

  1. Commission Implementing Regulation (EU) 2025/929 — BIT approved for product-type 13 (metalworking fluid preservative)