Is immersion really required for a Shipping Case?

Yes. Spray proves a jet does not enter; immersion proves 1 m of head does not seep, and spray alone misses a gasket gap that opens in a flooded hold.

Does AQL 1.0 cover everything?

No. It suits dimensions and appearance; sealing and structure need two units per lot, since a proportional sample cannot catch a failure that appears once in hundreds.

Can a lot fail after the first article passed?

Yes. Production shortens the cycle and drifts mould temperature, so walls thin out. A 0.2 mm gap between unit five and the first article means stopping to check temperature and hold pressure.

Why stack at 1.8 times instead of the rating?

The rating covers static storage only; vibration and braking push the bottom unit close to double, so 1.8 times squeezes that margin out on the floor.

Can a rejected lot be sorted and used?

Only class C. Class A goes back whole, class B passes after a doubled sample, and sorting mixes good and bad units on one pallet with no way to trace which was out.

Shipping Case Acceptance Standards: Test Items and Limits

Quick answer: Run a Shipping Case acceptance in three gates: first article, lot sampling and release. Measure wall thickness at five points, immerse at 1 m for 30 minutes, stack at 1.8 times rated load for 24 hours, drop from 1.2 m and cycle the latches 5,000 times. Any result outside those limits rejects the lot.

The Three Gates of a Shipping Case Acceptance Standard
First Article and Lot Sampling
Measuring Dimensions and Wall Thickness
Immersion, Stacking and Drop Tests
Latch Cycling, Defect Classes and Records
FAQ

1. The Three Gates of a Shipping Case Acceptance Standard

Acceptance runs three gates, not one final inspection. The first article asks whether this mould and resin can start production, lot sampling asks whether the batch still matches it, and release asks whether every pallet was checked. Skip a gate and thin walls reach the customer.

The first article triggers on a new tool, a colour or resin change and after every mould repair: three units, two tested, one kept. Lot sampling at AQL 1.0 covers five units for appearance and dimensions plus two for immersion and stacking; release checks label and count on one unit per pallet.

2. First Article and Lot Sampling

Sample by cavity, shift and resin lot. A four-cavity tool needs one unit per cavity, because drawing only from cavity one never exposes sink on the other three. Take body and lid as a pair; the seam decides whether the case seals.

Shipping Case: a worn white case on a timber pallet rack, black scuff marks, white plastic crates behind, bolts and tape on the bench

Condition samples at 23 degrees Celsius plus or minus 2 for four hours. A fresh unit holds 40 to 50 degrees and reads 1 to 2 mm larger, so warm measurement passes dimensions that fail later.

3. Measuring Dimensions and Wall Thickness

Dimensions split into three groups: envelope, cavity and mating faces. Read the envelope 20 mm below the rim, the cavity 30 mm above the base, and the seam with a 0.2 mm feeler that must not enter.

Item	Tool	Point	Limit
Envelope	Tape and calliper	20 mm below rim	Plus or minus 3 mm
Cavity	Inside micrometer	30 mm above base	Plus or minus 2 mm
Wall	Ultrasonic gauge	Four corners, mid-long side	4.2 mm minimum
Seam gap	Feeler	Two points per side	0.2 mm will not enter

Wall thickness needs an ultrasonic gauge rather than a calliper, which only reaches the rim while the thin spot sits mid-wall. Five readings per unit, logged to 0.01 mm; a Shipping Case under 4.2 mm bulges by the third stacked layer.

4. Immersion, Stacking and Drop Tests

Test sealing by immersion, not spray: load 80 percent of rating, add absorbent paper, sink to 1 m for 30 minutes, then dry and open. At 1 m the pressure reaches roughly 10 kPa, enough to push water through a pinhole.

Shipping Case: grey-lidded plastic boxes stacked two high on steel shelving, latch handles aligned, warehouse daylight, timber pallets behind

Stack at 1.8 times rated load for 24 hours, then read base deflection one hour after unloading at 5 mm maximum. Drop from 1.2 m onto six faces, three edges and one corner, working the latches after each impact. Stack before dropping, so cracks open where transport puts them.

5. Latch Cycling, Defect Classes and Records

Cycle the latches 5,000 times at no more than 20 per minute, logging force every 500. A loss above 20 percent fails, because internal pressure then pops the latch open.

Sort failures into three classes: A rejects the lot, B doubles the sample, C passes with a note. Keep four records for three years: first article report, resin lot and trial sheet, inspection sheets, raw data.

Class	Typical defect	Action	Release
A	Leak at 1 m, base set over 5 mm	Reject lot	Retest after 100 percent check
B	Wall 4.0 to 4.2 mm, colour drift	Double sampling	Pass on retest
C	Label pad offset, flash	Accept with note	Record and fix next lot

Conclusion

A Shipping Case acceptance standard is not a certificate but a set of repeatable actions: where to sample, how long to cool, how many points to read, how often to drop, and what number forces a rejection. Write each action with its limit beside it, and the Shipping Case argument ends in a figure.

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.