Why does a heavy-duty protective case need three first-article samples?

Answer: One sample cannot show stability. Three reveal spread in wall, diagonals and latch effort; tight spread means the cavity is settled.

If pressure hold passes, is rain testing still needed?

Answer: Yes. Pressure hold measures gas differential; rain measures liquid ingress under spray. Splices and latch recesses can pass one and fail the other.

Why does a case fail after a drop when it looks intact?

Answer: The verdict follows function. Pressure hold repeats after the drop; a failure means the gasket or shell deformed invisibly.

Is sampling five cases per lot enough?

Answer: It is the baseline for lots up to 200; one failure doubles the sample to ten, a further failure rejects the lot.

Can a concession case be used for lifting?

Answer: No. Concessions apply to appearance only; lifting is structural, so any case used on a hook passes every item without waiver.

Heavy-Duty Protective Case Acceptance: Test Items and Verdicts

Quick answer: Acceptance of a heavy-duty protective case runs on two levels: a full first-article check and lot sampling. The first article proves the process is fixed; the lot proves it stays fixed. Every item needs a number and a verdict.

First-Article and Lot Inspection for a Heavy-Duty Protective Case
Wall Thickness and Dimension Measurement
Seal and Rain Testing
Drop and Stack Testing
Lifting Proof Load and Nonconformance
FAQ

1. First-Article and Lot Inspection for a Heavy-Duty Protective Case

A first article asks whether this mould, material and parameters can be frozen; a lot check asks whether the frozen process holds. Limits are shared, sample size is not.

Stage	Trigger	Sample	Verdict
First article	New mould, material or parameters	3 cases, all items	Pass all, then release
Lot	Each delivery lot	5 of up to 200	All 5 pass
Tightened	One lot failure	10 cases	Any failure, reject lot

When a first article fails, change the process rather than the limit: thin walls trace to hold pressure or melt temperature, oversize parts to cooling time. A failed lot is quarantined before judgement.

2. Wall Thickness and Dimension Measurement

Measure thickness by ultrasonic gauge at five points: four corners and the base centre. On a 6.0 mm nominal wall no reading may fall below 5.7 mm, and the spread must stay within 0.4 mm, which tracks fill and packing better than any single value.

Heavy-Duty Protective Case: corner close-up on a wooden bench, two stacked black cam latches clamping the lid edge, round valve seat, coiled cables behind

Internal dimensions carry plus or minus 2 mm, external plus or minus 3 mm. Diagonal difference on the closing face stays within 4 mm, and a 1.5 mm feeler gauge must not enter the closed joint.

3. Seal and Rain Testing

Start with pressure hold. Close an empty heavy-duty protective case, charge through the valve to 30 kPa and wait 5 minutes; a drop beyond 1 kPa fails. To locate a leak, cap the valve and repeat to rule out the disc, then brush soap solution along the joint.

Rain follows IPX5: a 6.3 mm nozzle delivers 12.5 L/min from 2.5 to 3 m, three minutes in each of four directions. Weigh absorbent paper inside before and after; a gain above 5 g fails.

Do not wipe the case before opening it; water marks show the leak path. Rain also precedes pressure hold, or residual moisture counts as loss.

4. Drop and Stack Testing

Drop from 1.2 m onto six faces, three edges and one corner, ten impacts per case at rated load. Latches must stay closed, no through-crack may appear, and pressure hold must still pass.

Heavy-Duty Protective Case: black case open on a warehouse bench, grey lid foam, six base compartments, metal brackets and a handheld gauge beside it

Test	Condition	Pass criteria
Drop	1.2 m, six faces, three edges, one corner	Latches closed, no through-crack, hold passes
Stack	Four times own weight, 24 hours	Top face under 2 mm, residual under 1 mm after 1 hour

Apply stack load at the lid centre, not uniformly: in a warehouse the load arrives through the four feet above.

5. Lifting Proof Load and Nonconformance

Lifting proof load is twice the rating held 5 minutes; the diagonal between lifting points may not change by over 0.5 mm after release. A dynamic check follows at 1.5 times the rating.

A rejected heavy-duty protective case is never patched and re-shipped: reinforcement changes local stiffness while the load path can no longer be verified.

Class	Typical defect	Disposition
A	Through-crack, cracked eye, hold drop over 3 kPa	Scrap, no repair release
B	Wall 5.7 to 5.4 mm, diagonal 4 to 6 mm	Repair, then full retest
C	Scratches, colour shift, wrong label	Concession or cosmetic rework

Verdicts carry a signature: Class A by the quality manager, B by the inspection lead, C by the inspector.

Conclusion

Acceptance of a heavy-duty protective case comes down to one line: the first article fixes the process, the lot guards consistency, every verdict is a number. Wall 5.7 mm, diagonal 4 mm, hold drop 1 kPa, drop 1.2 m, stack at four times weight, lifting at twice the rating. Sign, then dispose: scrap, repair and retest, or concession. These items make heavy-duty protective case acceptance repeatable.

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.