Does accepting an explosion-proof case require destructive testing?

Answer: Not at goods in. The four checks are non-destructive; destructive items belong to sampling.

Where does the 0.3 mm feeler figure come from?

Answer: From the residual gap: at 25 to 30 percent compression the seal leaves no path, and 0.3 mm is the largest gap an inspector can judge consistently.

Is 220 N per latch enough on an explosion-proof case?

Answer: It is the usual floor for a two-latch shell. A 28 kg load peaks at about three times static weight, so 440 N for the pair leaves margin.

Is three samples out of three hundred too few?

Answer: Sampling tests the mould, not the quantity. Three cases from different cavities, covering first, middle and last, expose spread; one failure doubles the sample.

How is the thirty percent rework figure reached?

Answer: Full replacement adds 42 CNY per unit plus seven days; over three hundred units that removes about thirty percent of margin. That is why the line moves to the dock.

Is concession risky on a failed explosion-proof case?

Answer: Shade, labels and missing accessories can be conceded; wall, joint gap and latch holding cannot. List concessions as unfit for pressure or drop duty.

Rework Adds Thirty Percent: Explosion-Proof Case Checks

Quick answer: The cost of accepting an explosion-proof case sits in rework, not in inspection fees. Four judgement lines on the acceptance sheet, covering wall, joint, latch holding and stacking, cut the rework rate on a batch of three hundred from one in five to under three percent.

Where Rework Cost Lands
Six Minutes at Goods In
Seal and Vent Face Three Moves
Stacking and Cold Sampling
Six Fields on the Record
Disposition Concess Repair Return
FAQ

1. Where Rework Cost Lands

Rework never costs the price of one case. A rejected unit drags freight both ways, unpacking, re-inspection, a fresh production slot and a late penalty onto the whole batch, so the unit price looks unchanged while the margin is gone.

Break rework into actions and the account opens up. Full replacement eats a production slot, re-taping seals is cheapest but means opening three hundred cases, and swapping latches sits in between.

Failed item	Rework action	Added cost per unit	Schedule impact
Wall below limit by 0.8 mm	batch replacement	42 CNY	7 days
0.3 mm feeler enters joint	re-tape seals	9 CNY	2 days
Latch holding under 220 N	add latches	6 CNY	1 day
Flat face past 3 mm	internal bracing	15 CNY	3 days

Only the first row pushes cost past thirty percent; the rest are priced for dock labour.

2. Six Minutes at Goods In

Six minutes per explosion-proof case, held by four judgement lines.

Explosion-Proof Case corner in charcoal texture, one large slotted latch centred, a second latch at the right edge, seam running across

Check	Instrument	Judgement line	Sampling
Side wall	caliper	5.8 mm minimum	3 cases, 4 points each
Lid joint	0.3 mm feeler	feeler must not enter	every case
Cavity	tape	within 2 mm of drawing	3 cases per batch
Latch holding	pull gauge	220 N minimum	3 cases, 2 latches each

Read wall at the middle of a flat face, never at the rim, the thickest part of a rotomoulded part, which biases every reading upward. Walk the feeler round the joint. Watch the 30 mm either side of the hinge. Take cavity length, width and depth, keeping the tape off the base ribs. Load each latch slowly before reading at hold. A case that overruns six minutes means an uncalibrated instrument or an unreadable drawing.

3. Seal and Vent Face Three Moves

Three moves settle seal and vent face.

Run a 0.3 mm feeler along the closed joint; 10 mm of penetration fails the case.
Take the vent face at 18 percent of side area, press the centre, require rebound within 1 second.
Hold seal compression at 25 to 30 percent; more kills rebound, less seals nothing.
Keep 100 mm clear in front of the vent face, with no liner, strap or nameplate.

The fourth item is usually treated as decoration: liners are fitted later, by people who do not know it has a job.

4. Stacking and Cold Sampling

Stacking is sampled, not performed on every unit: a 500 kg platform load on the closed case for 24 hours, with flat-face deformation above 3 mm failing it.

Explosion-Proof Case in worn grey standing under a wooden shelf, one latch in focus, tools and cartons blurred behind

The cold item is simpler: minus 25 C for 2 hours, then a corner-first drop from 0.9 m inside 90 seconds. No corner crack, no latch springing open. A platform scale with weights is the load, a chest freezer is the chamber, so the difficulty is sampling: cavities of one mould can differ by 0.4 mm of wall, and one case proves nothing.

5. Six Fields on the Record

The acceptance sheet is not for signing but for arguing later; drop one field and the judgement cannot stand.

Batch and cavity numbers, naming the cavities sampled.
Instrument ID and calibration date.
Measured values, not the words pass or fail.
Source of the judgement line, by drawing or clause.
Disposition, one of concession, repair or return.
Re-check date and signature, mandatory for repaired units.

Fill all six and a rework dispute has something to stand on.

6. Disposition Concess Repair Return

Three routes. Concession suits deviations with no structural meaning, such as shade; repair suits replaceable parts, such as latches and seals; return suits mould-level deviation in wall or cavity.

Concession needs a ceiling: past twenty percent of a batch, process capability is already short. Return needs a freight clause, since a full batch going back costs close to ten percent of goods value.

Conclusion

Acceptance earns its money by stopping rework at the dock rather than at the customer site. Four judgement lines, six minutes per case and six record fields are not complicated; doing them every time is. Put the lines in the contract, sample across cavities and route failures into three dispositions, and rework falls from one in five to under three percent. The more an explosion-proof case acceptance reads like a procedure, the more predictable its unit cost.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.