Cost & maintenance
How to Calculate the Real Cost of a Sealing Bath
Sealer price per kilogram tells you almost nothing. Two products at the same price can differ by a factor of three in cost per square metre, because the number that drives consumption is the working concentration, not the drum price.
The model
Cost per square metre of treated surface can be broken into five parts:
| Component | How to estimate it |
|---|---|
| Make-up | Tank volume × concentration × product price, divided by the surface area treated before the bath is dumped or renewed. |
| Drag-out | Litres carried out per m² × concentration × price. Drag-out is usually 0.05–0.3 L/m² depending on part geometry, racking and drip time. |
| Energy | Only if the bath is heated: kW × hours × tariff, divided by monthly m². |
| Labour and filtration | Minutes per shift spent on pH adjustment, filter changes and bath checks, converted to cost. |
| Waste | Disposal cost of spent bath per m³, divided by the m² treated per bath life. |
Worked example (illustrative numbers)
Assume a 1,000 L bath, product at ¥30/kg (≈ ¥27/L), 2,000 m² treated per bath life, and a drag-out of 0.15 L/m². These figures are for method demonstration only — substitute your own.
| Item | 750 ml/L bath | 200 ml/L bath |
|---|---|---|
| Make-up per bath | 750 L × ¥27 = ¥20,250 | 200 L × ¥27 = ¥5,400 |
| Make-up cost per m² | ¥10.13 | ¥2.70 |
| Drag-out cost per m² | 0.15 × 0.75 × ¥27 = ¥3.04 | 0.15 × 0.20 × ¥27 = ¥0.81 |
| Chemical cost per m² | ≈ ¥13.2 | ≈ ¥3.5 |
| Heating (if 45 °C required) | adds energy all year | none if run at ambient |
Read this carefully. The table is not a claim about any specific product.
It shows that concentration dominates the cost equation, and that drag-out multiplies it. A plant
treating 2,000 m² per month is looking at a five-figure annual difference before energy is counted.
The hidden costs that never appear in a quotation
- Rejects. One batch of 96 h parts failing at 48 h can cost more than a year of chemical savings. Cost per m² is meaningless without a first-pass yield.
- Rework and replating. Stripping and replating doubles zinc consumption, labour and hydrogen risk on high-strength parts.
- Bath lifetime. A bath that accumulates zinc and iron quickly needs more frequent dumping, which changes the waste line of the model dramatically.
- Labour. A bath needing hourly pH checks does not just cost wages — it costs attention that would otherwise go to the line.
What to ask before switching
- Recommended working concentration range, and the film weight at the low and high end.
- Drag-out sensitivity: is there a recommended drip time or racking practice?
- Bath life: how is it monitored, and what triggers a dump?
- Does the product require heating, agitation or filtration — and what happens if any of them is skipped on a busy shift?
- Can I get the cost model in writing, with the assumptions stated?
Cost per m² is an engineering number, not a purchasing number. Ask your
process engineer to supply the surface area, drag-out and first-pass yield; without those three, any
comparison is a guess.