Write the oil percentage, the ester lubricity package, and the water hardness. “MWF emulsifier” without those three numbers is not a specification.
Oil cut decides the emulsifier
Soluble oils hide a marginal emulsifier behind a high oil level. Semi-synthetics do not. The same HLB that makes a milky soluble oil can cream a 10–15% oil semi-synthetic, or the reverse if the package is too hydrophilic and lubricity washes off the tool.
Esteem ester and alkoxylate ranges are the usual building blocks: a low-HLB co-emulsifier for the oil phase and a higher-HLB alkoxylate for dilution stability. Lubricity esters are specified on the lubricant-additive pages, not as defoamers.
Hard water and tramp oil
Make-up hardness reacts with soaps and some anionics and throws a scum that looks like tramp oil. Identify it before you add more emulsifier. Tramp hydraulic oil has its own HLB and will shift the sump if the package has no rejection or absorption strategy.
Tell Esteem which strategy you want. A fluid that absorbs tramp oil stays stable and then fails lubricity. A fluid that rejects tramp oil needs a skimmer and a different emulsifier balance.
| Fluid | Emulsifier emphasis | Watch |
|---|---|---|
| Soluble oil | Lower HLB, milky emulsion | Cream on hard water |
| Semi-synthetic | Paired HLB, ester lubricity | Split or loss of film |
| Synthetic | Little or no oil emulsifier | Corrosion, not cream |
| Tramp-oil reject | Tighter HLB window | Skimmer duty |
The emulsion has to survive the sump
A semi-synthetic concentrate is a water-in-oil or oil-in-water package that inverts or dilutes into a fine emulsion at the machine. The emulsifier blend, often a nonionic alkoxylate plus an anionic such as a sulfonate or a phosphate ester, sets the droplet size. Small droplets look translucent and reject tramp oil more slowly. Large droplets look milky and split faster when hardness or temperature moves.
HLB is the first estimate, not the release specification. Required HLB depends on the base oil and on the lubricity ester. A blend that matches the oil in distilled water can still cream in 400 ppm hardness because the anionic has been salted out. Always confirm in the customer’s water.
Couplers, soaps, and reserve alkalinity
Coupling solvents keep the concentrate as one phase in the drum. They are not the emulsifier. Fatty-acid soaps add reserve alkalinity and some emulsification, and they also set the pH that protects ferrous metals. If the soap level is high, hard water makes scum. If it is low, the emulsion may be finer but the corrosion window shrinks.
Phosphate esters and alkanolamides show up as co-emulsifiers and as lubricity or corrosion partners. They change the salt tolerance. Adding them after the HLB has been set on a nonionic-only blend means the curve has to be rebuilt.
What “stable” has to mean on the purchase order
State the oil type, the ester lubricity package, the dilution, the water hardness, and the sump temperature. Ask for a concentrate that is one phase at the warehouse minimum temperature, and for a dilution that does not cream or oil out over the agreed standing test.
Tramp oil is a separate stress. A perfectly emulsified fresh dilution can still invert once hydraulic oil is sheared into the sump. The emulsifier that makes a tight fresh emulsion is not automatically the one that rejects tramp oil. Say which failure the plant actually sees.
How to Specify with Esteem
- State soluble oil, semi-synthetic, or full synthetic.
- Give the base-oil or ester level and the required lubricity test if you have one.
- Report make-up water hardness and expected tramp-oil ingress.
- Name the metals: steel, aluminium, yellow metals.
- Ask for an emulsifier pair, not a single HLB guess, when the concentrate must dilute in hard water.
Use lubricant additives and the metalworking lubricity article alongside this HLB note.