Is case foam shedding a cut problem or a material problem?

Answer: Read the chips. Flakes over 0.5 mm with a whitened, fuzzy cut mean the blade; powder with a flat cut means the cells. When both appear, fix the blade first.

Is 3000 mm/min too fast for EVA?

Answer: Speed alone decides nothing; the edge does. A 0.05 mm edge runs clean at 3000, while a 0.2 mm edge sheds even at 2000, so change the blade before the number.

Does a hot wire end case foam shedding?

Answer: It closes the cut. At 320 ℃ the shed falls from 1.6 to 0.3 g/m², but foam at 78% closed cells still powders after 100 rubs.

How is the 0.8 g/m² line measured?

Answer: A 100 mm × 100 mm sample, a 200 g weight, 100 rubs and the median of three runs. A single run can swing 40% on rebound alone.

Which equipment needs the 0.1 g/m² limit?

Answer: Optical benches, vacuum chambers and cleanroom totes, where chips on a lens stop work and chips in a line force a teardown.

Case Foam Shedding: Cut or Material

Quick answer: Case foam shedding splits by chip shape: fuzzy white cut edges with 0.5 mm flakes mean the blade, while flat edges and fine powder mean the cells.

The fault tree: cut, density, regrind
Cut branch: 3000 mm/min and the blade
Material branch: 45 vs 70 kg/m³
Measuring the shed: 0.5 mm and 0.8 g/m²
Sealing: hot air, edge tape, tight rooms
FAQ

1. The fault tree: cut, density, regrind

A thin layer of white dust on black velvet, and a supplier saying foam is like that. The complaint is not one phenomenon but three: flakes, powder, and dust along the cut line only. Each leaves the tree by a different branch.

Chip shape decides the first branch. Flakes with fuzzy edges over 0.5 mm come from the cut; powder that clings to a lens comes from cell walls being rubbed down; dust along a single line means the edge was never sealed.

The second branch is the cut face itself. Only three faces shed: whitened and fuzzy, torn at the edge, or beaded with melted droplets. A clean knife cut and a smooth hot cut should not shed at all.

Cut face	Blade or heat state	Chip shape	Parameter to change
Whitened, fuzzy	Rounded blade	Flakes over 0.5 mm	New blade, edge back to 0.05 mm
Torn edge	Speed too high	Long slivers	Drop below 3000 mm/min
Beaded edge	Wire too hot	Hard beads	Wire down to 320 ℃
Stringy edge	Wire too cool	Fine threads	Wire up to 320 ℃

Static and humidity amplify what you measure: dry chips stick to windows and velvet, so condition samples at 45–55% RH for 2 h.

2. Cut branch: 3000 mm/min and the blade

A CNC knife at 3000 mm/min with a fresh 0.05 mm edge cuts EVA flat and clean. Let that edge round to 0.2 mm and the same speed presses a 0.1 mm white line along the cut, and the chips start there.

Case foam shedding sample bench, grey wheeled and black cases running to the far end of a white plinth, blue floor line

Speed and edge travel together. When the blade dulls, someone raises speed to 4000 mm/min to make it cut, which compresses the foam harder, crushes the cells at the edge and doubles the shed. Change the blade instead.

Two variables sit beside the blade: tip angle and stack height. A 30° tip cuts a narrow kerf with little crushing, a 45° tip holds up in thick board but crushes cells on both sides, and a three-layer stack sheds 40% more than a single layer because chips cannot escape.

A hot wire is the other route. At 320 ℃ it leaves a 0.1–0.2 mm melted bead that closes the cells, and almost nothing sheds. Below 180 ℃ the wire tears instead of melting, leaving strings and beads that fall off at a touch, with chips over 1 mm.

Read the face backwards and the process tells you what to do: flat and clean means a sharp blade, whitened means a dull one, round beads mean too much heat, strings mean too little. Four faces, four actions, no liner removal required.

3. Material branch: 45 vs 70 kg/m³

The same EVA at 45 kg/m³ and 70 kg/m³ differs in cell wall thickness. At 45 the walls are thin and an exposed cut face powders as soon as it is rubbed; at 70 the walls are thick, the same rub removes very little, and the cut is easier to keep flat.

Closed cell content is the second number. At 92% the cut section is mostly sealed bubbles and few chips come off; at 78% the cells interconnect and one rub produces a patch of powder. Two foams of similar density but 14 points apart in closed cells can differ twofold in shed.

Regrind is the third. A 30% regrind blend has uneven cells and density that wanders by ±6%, so one end of a sheet cuts well and the other sheds.

This branch is settled by weighing, not looking. Cut three 100 mm × 100 mm samples from one sheet, rub each 100 times the same way, and compare. A spread above 30% between the three means the sheet itself is uneven, so the case foam shedding comes from material rather than the blade.

Confirm the batch first. If all three samples sit above 1.2 g/m² the cells are open, and no blade or hotter wire will rescue it.

4. Measuring the shed: 0.5 mm and 0.8 g/m²

Shed is measurable. Take a 100 mm × 100 mm sample, 0.01 m², rub it 100 times near the cut with a 200 g weight wrapped in black velvet, collect the chips, weigh them and divide by area to get g/m².

Case foam shedding retest shelf wall, one orange case alone on top, black and dark grey cases below, sunlight squares on the floor

0.8 g/m² is the first threshold. Below it the dust is invisible; above it, a white layer shows on velvet within 10 min.

Weighing has one trap: chips cling to the velvet by static. Brush twice with an antistatic brush, or lose 0.005 g, which over 0.01 m² reads as 0.5 g/m² and pushes a borderline sample into failure.

Shed	Chip size mix	Verdict	Action
Under 0.3 g/m²	Mostly powder	Normal	Nothing
0.3–0.8 g/m²	Flakes under 20%	Borderline	Hot air seal
0.8–1.6 g/m²	Flakes 20–50%	Cut defect	New blade, lower speed
Above 1.6 g/m²	Flakes over 50%	Open-cell foam	Change batch

Run three tests and take the median. Foam rebounds, so the first rub reads high and the third low. Three results all above 0.9 g/m² mean the liner should not go into equipment that fears dust.

5. Sealing: hot air, edge tape, tight rooms

Hot air is the direct step: at 280 ℃ swept along the cut for 0.3 s the surface films over, the cells close, and the shed drops from 1.6 to 0.3 g/m².

Temperature and dwell both matter. Above 320 ℃ or longer than 0.6 s, the cut shrinks 0.3 mm and the size changes; below 240 ℃ the surface only shines and wipes off again.

Edge tape is the alternative. A 0.2 mm cloth or film over the cut covers the open cells and suits deep pockets that cannot take heat, at the cost of a larger corner radius that can foul the case wall.

Some equipment cannot tolerate any case foam shedding. Optical benches, vacuum chambers and cleanroom totes collect chips on lenses, on chamber walls and inside vacuum lines, so their threshold is 0.1 g/m² rather than 0.8.

For general tooling and outdoor transport, anything under 0.8 g/m² needs no treatment; sealing every liner gives away 0.3 mm of cut size for nothing.

Conclusion

Cut face	Density and closed cells	Verdict	Action
Flat, clean	70 kg/m³, 92% closed	Normal	Nothing
Flat, clean	45 kg/m³, 78% closed	Material	Change batch or foam
Whitened, fuzzy	Any	Cut	New blade at 0.05 mm
Beaded	Any	Wire too hot	Drop to 320 ℃
Stringy	Any	Wire too cool	Raise to 320 ℃

Work case foam shedding off this table: one face and one density reading give one action, with no loop of changing foam and then changing blades. Two thresholds do the rest. 0.8 g/m² covers general handling, 0.1 g/m² covers optics and vacuum, and the 0.5 mm sieve splits the branches, with flakes above 20% on the screen pointing to the cut and powder above 80% through it pointing to the cells. Used together, the three numbers close a complaint in 20 min without a lab visit.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.