Cutting and metalworking fluid is the second-largest industrial lubricant category in India after engine oil, with consumption tied directly to the auto-component, capital goods and machined-parts manufacturing base. Four very different chemistry families — neat sulphurised cutting oil, soluble oil emulsion, semi-synthetic and fully synthetic — each suit different machining operations. The formulator must balance emulsifier stability, EP performance, biocide protection, hard water tolerance, tramp-oil rejection, foam and operator-skin compatibility. This guide covers the four categories, the chemistry, treat rates and the practical realities of formulating for the Indian machining shop floor.
| Component | Function | Typical % (m/m) | Notes |
|---|---|---|---|
| Mineral oil — Group I SN150 / SN500 | Lubrication base, viscosity, oiliness | 55–70% | Lower aromatic content preferred for skin compatibility |
| Petroleum sulphonate (sodium / calcium) | Primary anionic emulsifier; corrosion inhibitor | 8–15% | 500–600 TBN sulphonate; provides hard-water tolerance up to ~200 ppm |
| Ethoxylated nonyl phenol or fatty alcohol (NPE / AE) | Non-ionic emulsifier; HLB modifier | 3–7% | NPE being phased out for EU markets; replaced by AE |
| Fatty acid (tall oil or oleic) | Co-emulsifier; saponification with amine for self-emulsification | 1.5–4% | Saponified in-line with ethanolamine |
| Monoethanolamine / triethanolamine | pH buffer; saponification base; corrosion inhibitor | 1–3% | Working pH target 8.8–9.5 |
| Sulphurised triglyceride / olefin (EP) | Extreme pressure additive for heavy machining | 2–6% | Active sulphur 1–2% (5–15% S in additive) |
| Coupling agent (glycol ether or alcohol) | Phase compatibility; cold storage stability | 2–5% | 2-butoxyethanol or DPM common |
| Biocide (formaldehyde-releaser or isothiazolinone) | Bacterial / fungal control | 0.10–0.30% | Bactericide for sump liquid + fungicide for headspace |
| Silicone defoamer | Foam suppression | 100–500 ppm | 10% silicone emulsion |
| EDTA / chelating agent | Hard water tolerance enhancement | 0.2–0.6% | Sequesters Ca / Mg ions |
| Boric acid / amine-borate | Cast iron rust prevention; pH stabilisation | 0.5–1.5% | Avoid in pregnant operator workplace |
The concentrate above is diluted 1:20–1:40 by the end-user (workshop) with water in the cutting fluid sump. The concentrate is typically supplied in 25 L jerry can or 200 L drum. Indian aftermarket workshops add concentrate manually based on refractometer (Brix) reading — target Brix 4–7 corresponding to 5–8% concentrate.
| Component | Function | Typical % (m/m) | Notes |
|---|---|---|---|
| Mineral oil (Group II preferred) | Lubrication base for boundary film | 12–25% | Lower content than soluble; Group II for cleaner skin profile |
| Synthetic ester (TMP / PE oleate) | Bio-based lubricity boost | 3–8% | Improves machining performance at low concentration |
| Synthetic emulsifier (alkanolamide, ethoxylated alcohol) | Micro-emulsion formation | 10–18% | HLB-balanced for translucent emulsion at 0.1–1 µm droplet |
| Polyalkylene glycol (PAG) lubricant | Water-soluble lubricity contribution | 3–6% | Inverse-cloud-point behaviour helps lubricity at temperature |
| Alkanolamine (MEA / TEA / MIPA) | pH buffer; corrosion inhibitor; reserve alkalinity | 5–10% | Higher amine content for longer sump life |
| Carboxylate corrosion inhibitor | Ferrous protection without ash | 3–6% | 2-EHA or dodecanedioic acid common |
| EP additive (sulphur or phosphate ester) | Extreme pressure | 1–3% | Water-stable; phosphate esters preferred for stainless |
| Biocide | Microbial control | 0.10–0.25% | Same families as soluble |
| Defoamer | Foam control | 100–500 ppm | Critical at low dilution |
| Water | Carrier; balances ionic strength | 35–50% | Demineralised preferred for concentrate manufacture |
| Property | Test Method | Soluble Target | Semi-Synthetic Target | Synthetic Target |
|---|---|---|---|---|
| Appearance (5% in 200 ppm water) | Visual | Milky white | Translucent | Clear |
| Emulsion pH (5% working) | pH meter | 8.8–9.3 | 9.0–9.5 | 9.0–9.5 |
| Refractive index factor | Brix refractometer | 1.2–1.5 | 1.0–1.2 | 0.8–1.0 |
| Foam (after 5 min stirring, IS 1448 P-67) | Stirring test | <30 ml @ 1 min | <20 ml @ 1 min | <20 ml @ 1 min |
| Corrosion (chip / filter paper test) | IP 287 / IS 1115 | No corrosion 4% | No corrosion 3% | No corrosion 3% |
| Hard water stability (5%, 400 ppm) | Visual | Stable 24 hr | Stable 72 hr | Stable 7 days |
| Tramp oil rejection (5% hydraulic added) | Separation | Separates in 2 hr | Separates in 1 hr | Separates in 30 min |
| Sulphate ash (active sulphur) | D874 | 1.0–3.0% | 0.5–1.5% | <0.5% |
| Falex pin-and-vee EP load | ASTM D2670 | 200–600 lbf | 150–500 lbf | 100–350 lbf |
| Microbial baseline (TVC) | Dip slide | <10³ CFU/ml | <10³ CFU/ml | <10³ CFU/ml |
| Patch corrosion (cast iron) | IP 287 | Pass at 5% | Pass at 4% | Pass at 4% |
ISO 6743-7 classifies metalworking fluids in four families: (1) Neat / straight cutting oil — mineral oil with sulphurised / chlorinated EP, used undiluted for heavy gear cutting and broaching. (2) Soluble oil — mineral oil emulsified with anionic / non-ionic emulsifiers, diluted 1:20 to 1:40 with water for milky white coolant. (3) Semi-synthetic — 10–30% mineral oil emulsified with synthetic surfactants in water concentrate, dilutes translucent. (4) Fully synthetic — no mineral oil, water-soluble synthetic lubricant in water, dilutes clear.
Soluble oil is diluted 1:20 (5% concentrate) for light machining, 1:10 (10%) for heavy machining and grinding. Semi-synthetic typically 1:25–1:40 (2.5–4%). Fully synthetic 1:50 (2%) for grinding to 1:20 (5%) for tapping. Neat cutting oils are used undiluted at 100% concentration.
Hard water shifts the dilution ratio upward — to maintain stable emulsion in 300 ppm hardness water, increase concentrate by 1–2 percentage points.
Two main biocide families: (1) Formaldehyde-releasing biocides — triazines, hexahydrotriazines, oxazolidines — release controlled formaldehyde for broad-spectrum bacterial and fungal control. (2) Isothiazolinone biocides — methylisothiazolinone (MIT), chloromethylisothiazolinone (CMIT) — non-formaldehyde alternative for plants with formaldehyde-restriction policies.
Typical treat rate 0.05–0.3% in concentrate. Bactericide for liquid phase + fungicide for headspace is the practical combination.
For neat cutting oil, sulphurised lard / sperm oil substitutes, sulphurised olefins (5–15% S) and chlorinated paraffins (40–55% Cl) are the workhorse EP additives. For soluble and semi-synthetic, water-stable EP additives — sulphurised triglyceride emulsions, phosphate esters, and overbased calcium sulphonate — are used.
Chlorinated paraffin use is declining due to short-chain chlorinated paraffin (SCCP) regulatory restrictions; OECD members increasingly require medium-chain or long-chain MCCP / LCCP.
Hard water (300+ ppm CaCO&sub3;, common in many Indian industrial centres) destabilises ionic emulsifiers — calcium and magnesium ions react with anionic emulsifiers to form insoluble soaps. To improve hard water tolerance, the emulsifier system shifts toward non-ionic emulsifiers (ethoxylated alcohols, sorbitan esters) and EDTA-type chelating agents are added.
Semi-synthetic and fully synthetic formulations naturally have better hard water tolerance than traditional soluble oil.
Tramp oil is hydraulic oil and slideway lubricant that leaks into the cutting fluid sump from machine seals and gaskets. Tramp oil dramatically degrades cutting fluid life — it feeds anaerobic bacteria, smothers the emulsion, and causes operator skin problems. A good cutting fluid formulation must 'reject' tramp oil — the tramp oil floats on the cutting fluid surface where it can be skimmed off.
Tramp-oil rejection is tested by adding 5% hydraulic oil and observing whether it separates within 1 hour.
Working pH 8.8–9.3 for soluble oil and 9.0–9.5 for semi-synthetic and synthetic. pH below 8.5 invites bacterial growth (most bacteria prefer 6–8); pH above 10 causes operator skin irritation and aluminium etching. The reserve alkalinity from the amine buffer holds pH stable through sump life despite incoming acidic contamination from atmosphere and microbial metabolism.
In Europe, formaldehyde-releaser biocides are being progressively restricted under REACH and the Biocidal Products Regulation. In India, no such restriction yet, but multinational OEM-supply customers (especially auto components selling into EU OEMs) increasingly demand non-formaldehyde formulations. Isothiazolinone-only biocide systems are the standard alternative — we formulate both options depending on the client's end-customer requirements.
Share your target machining segment (CNC turning, grinding, gear cutting, tapping, aluminium), category (soluble / semi-syn / synthetic / neat) and customer profile. We respond within one business day with a formulation plan and BOM.