Sizing a galvanizing kettle
Three inputs decide almost everything. Work through them here, or send them to us and we will do it.
Step 1 — Length and width, from your largest workpiece
Take the largest piece you need to dip. Add clearance to lower it in, withdraw it, and skim the surface with the work still in the bath. That sets the minimum internal length and width.
Do not size to your average piece. You will be asked to dip the exception, and a kettle is not something you can extend later.
Step 2 — Depth, from width
Depth is normally 1.3 to 2 times the width. — BG/T 1501-2015 §4.2.2 b)
Going deeper, within that range, is usually the better decision:
- More zinc means more thermal mass, so bath temperature swings less when you charge
- More wall area means lower heat input per m², which directly extends kettle life
- Deeper baths let dross settle well below the work, so it is not stirred back onto the coating
Step 3 — Zinc volume, from throughput
Zinc volume should be 30 – 40 × your maximum hourly throughput, including jigs. For wire galvanizing, 20 × is acceptable. — BG/T 1501-2015 §4.2.2 c)
This is the rule that gets broken most often, and it is the one that kills kettles. Under-size the bath relative to throughput and the only way to hold temperature is to raise heat input — which pushes the inner wall towards 480 °C, and above 480 °C the corrosion rate climbs steeply, peaking between 490 and 510 °C.
Step 4 — Wall thickness
| Wall | Use for |
|---|---|
| 40 mm | Small kettles |
| 50 mm | The normal choice |
| 60 mm | Very long kettles, or depth over 3 m |
Above 1.8 m depth, add one adjustable external support band. Above 2.5 m, two. Support points at 1.5–2.0 m intervals, with expansion clearance along the length.
The operating envelope you are sizing for
| Parameter | Value |
|---|---|
| Bath temperature | 445 – 460 °C |
| Inner wall temperature | Below 480 °C — 490–510 °C is the peak corrosion band |
| Wall-to-bath temperature difference | 30 – 50 °C normally; 15 – 20 °C during steady production |
| Furnace chamber temperature | Below 700 °C on oil or producer gas; below 650 °C on natural gas or electric |
| Permitted heat input at 445 °C | 31 kW/(m²·h) |
| Permitted heat input at 460 °C | 24 kW/(m²·h) |
| Resulting corrosion rate | 1.0 – 2.5 mm/year |
Note the direction of that relationship. A lower bath temperature permits a higher heat input. If your bath is well sized, running cooler lets you run harder.
Once you have the numbers
Take them to the product range to see which geometry fits your depth, and to the steel specification for what the wall is actually made of. If you are replacing an existing kettle rather than building new, replacement planning is the page you want.
Source: BG/T 1501-2015 — §4.2, §4.3, Appendix A.1.5, A.2.3, A.2.4, Table A.1.
Send us three numbers
Largest workpiece (L × W × H), required throughput in t/h, and how your furnace is heated. That is enough for a sized kettle, a wall thickness, a zinc volume, a weight and a lead time.