Specify the metal, the soil, and the water hardness. A spray-washer low-foam surfactant is not automatically the soak-tank package.
Builder, chelate, surfactant
Caustic or silicate builds the alkalinity that saponifies some soils. The chelate holds calcium, magnesium, and some transition metals so the surfactant stays free. The surfactant wets oil and lifts pigment. Dropping any one of the three shows up as a different reject: etch, water spots, or oily film.
Esteem’s metal-complexing and chelant pages cover HEDTA versus glucoheptonate. Hard-surface and metal-cleaning surfactants sit on the metal hub. Ask for both when the bath is hard water and the parts are oiled.
What the trial should prove
Run a soil-loading series, not a single clean coupon. Record water-break, etch rate on aluminium if it is present, and foam after eight hours. A bright coupon at hour one can fail when soap builds.
If the next step is electroplating, say so. Cleaner films that are invisible on steel still poison a plate.
| Defect | Adjust first | Do not assume |
|---|---|---|
| Water spots / scale | Chelate and rinse | More surfactant foam |
| Oily film | Surfactant and temperature | Higher caustic only |
| Aluminium etch | Builder and inhibitor | A steel cleaner is universal |
| Spray foam-out | Low-foam surfactant | The soak formula can be sprayed |
Alkalinity, saponification, and the surfactant
An alkaline soak cleaner works in layers. Hydroxide or silicate saponifies some fats and raises the pH so mineral oil is easier to roll up. A nonionic or a low-foam alkoxylate adsorbs at the oil–water interface and finishes that roll-up. A phosphate ester can add wetting on a metal surface that a high-cloud-point nonionic wets poorly. None of those surfactants replaces the alkali, and the alkali does not replace them on a straight mineral oil.
Builders such as silicate, phosphate, or carbonate change buffering and soil suspension. Silicate also protects some soft metals by filming them. If the brief only says “alkaline cleaner,” the lab cannot tell whether the part is steel, aluminium, or a mixed rack.
Chelates and hard water
Calcium and magnesium turn fatty acids into insoluble soaps that redeposit as a grey film. A chelate or a complexing agent holds those ions so the soap stays soluble. The dose follows the water hardness and the soil, not a fixed percentage copied from a liquid laundry chart.
Too much chelate can strip protective ions or interfere with a later conversion coating. Too little, and the bath looks clean while the part fails a water-break test. Specify hardness, temperature, and whether a phosphate or zirconium coating follows the rinse.
Soak versus spray is a foam decision
A soak tank can tolerate more foam. A spray washer cannot. The same soil on the same metal may need a high-foam ether sulfate in a tank and an EO/PO or end-capped nonionic in a spray. Cloud point should sit near the operating temperature of a spray so the surfactant is surface-active without filling the cabinet with foam.
Oil loading ends the bath. A cleaner that starts at the right alkalinity drifts as saponified soil and dragged-in oil consume the alkali. Put alkalinity, chelate residual, and soil load on the control sheet, not only the initial make-up formula.
How to Specify with Esteem
- Name the alloy: steel, aluminium, zinc, or mixed.
- Describe the soil: drawing oil, coolant, pigment, or polishing compound.
- Give water hardness and whether the bath is regenerated or dumped.
- State temperature and whether foam is acceptable in a soak.
- Separate the chelate (HEDTA or glucoheptonate) from the surfactant on the request.
See metal complexing agents, hard-surface cleaners, and the chelant selection guide.