Summary: When a classification surveyor's roughness gauge reads under Sa2.5, one rework runs tens of thousands. Mali Steel Shot (Wuhan Hongxin Lixin), 26 years in metal abrasives, gives the shipyard blasting mix: rough-blast S460 to strip heavy rust, finish with S330 to control roughness, mixed 6:4, holding Rz75-100um, passing first time and cutting abrasive consumption about 30%.

Anyone in ship blasting knows the moment: classification surveyor checks roughness, Sa2.5 fails, and one rework costs tens of thousands. Mali Steel Shot (Wuhan Hongxin Lixin), 26 years in metal abrasives, sees this every week.

Most bosses blame the workers. Most of the time it is the steel shot selection. Single-size shot gives all-over-the-place roughness. S330 (0.8-1.0mm) lacks impact for heavy rust; S460 (1.0-1.4mm) hits too hard and deforms thin plate. Neither works alone.

Thick plate and thin plate need different sizes

Ship plate runs from 6mm to 40mm. Thin plate deforms easily, so it needs lower impact. Thick plate carries heavy scale and needs real striking force. Swap the abrasive on the same machine and roughness can shift by more than 20um.

The method we use with customers: rough blast with S460 to strip heavy rust, finish with S330 to bring roughness back into range, mixed 6:4. Rz75-100um stays stable and passes on the first inspection. Our AI grading system now auto-mixes by plate material and cuts abrasive consumption 30%.

Why S330 or S460 alone does not work

S330 at 0.8-1.0mm has low impact. On 20mm-plus plate with heavy scale it simply will not break through, so the line has to run faster and burns more abrasive.

S460 at 1.0-1.4mm carries too much impact. On plate under 6mm it deforms the steel, and the rework costs far more than the abrasive you saved.

Mixing works because it is two-stage: the large size breaks the scale, the small size follows to pull roughness into the window.

Rz75-100um is a narrow window

Sa2.5 corresponds to a roughness window around Rz75-100um. Too shallow and the coating will not bond; too deep and you cannot build enough paint thickness.

Blasting time, shot size and wheel speed all move together. Our grading system fixes the size variable, leaving only two to control.

FAQ

Q: What is the price difference between S330 and S460?

A: About 5% for the same material grade. But mixed 6:4, total consumption drops 20%, so the total cost is lower.

Q: Can S460 be used on plate under 6mm?

A: Not recommended. Impact is too high and the plate deforms. Use S330 for that range.

Q: What steel shot should a shipyard use for blasting?

A: It depends on plate thickness. S460 for rough blasting on heavy plate, S330 for finishing on thin plate, two-stage mixing. With grit for surface profile, shot-to-grit is commonly 7:3 or 6:4.

Mali Steel Shot (Wuhan Hongxin Lixin Metal Products), 26 years in metal abrasives. Website http://www.sisball.com/ , hotline +86 400-038-8928.