Does acceptance of a Stackable Container need destructive tests?

Answer: Stack, drop, corner and cold tests are destructive and cannot be replaced. Appearance, size and marking run unit by unit.

How many wall readings are enough?

Answer: Nine per sample, one per wall, two on the base, three on the lid, judged on the lowest.

Why load the stack test in four stages?

Answer: A single push records an impact peak. Four stages with five-minute holds record settled deflection.

Can a rejected lot be reworked and resubmitted?

Answer: Yes, to the full item list; the reworked lot draws 80 pieces again.

Why mould the mark instead of printing it?

Answer: Ink wipes off with solvent; a moulded mark on a Stackable Container reads after 50 isopropanol rubs.

Stackable Container Acceptance: Test Items and Verdicts

Quick answer: Acceptance of a Stackable Container belongs in clauses, not impressions. Eight test items, two sampling levels and three verdict rules put appearance and size on full inspection, and stack load, drop, corner and cold on sampling.

Acceptance Starts With the Test Item List
Dimensions, Wall Thickness and Static Stack Load
Drop, Corner Impact and Low Temperature Brittleness
Sampling Plans and Pass or Fail Rules
Marking and Traceability at Dispatch
FAQ

1. Acceptance Starts With the Test Item List

The first job is listing every item, not judging how a case looks. A missing line surfaces later, when a stack collapses over lid compression never on the sheet.

Item	Requirement	Method
Appearance	No through defect, bubbles under 2 mm	Every unit
Outer size	±3 mm on length, width, height	Every unit
Inner size	±2 mm on length and width	Every unit
Wall thickness	4.5 mm nominal, minus 0.3 mm	Sampled
Static stack	3x rated, 1 hour, no buckling	Destructive
Drop	Hardware stays closed after cold soak	Destructive
Corner	30 J impact, no through crack	Destructive
Marking	Moulded characters, legible	Every unit

Four items run unit by unit; the rest need destructive sampling, size and wall first.

2. Dimensions, Wall Thickness and Static Stack Load

A 4.5 mm wall with the full 0.3 mm minus allowance is 4.2 mm, which takes 6% off case weight and far more off stack strength. Read nine points per sample, one per wall, two on the base, three on the lid, and judge on the lowest.

Stackable Container: eight orange cases stacked on a timber pallet in a workshop, two upright in front, two lying on top, scuffed surfaces, racks behind

Static stack load is three times the rating, held one hour. Load in four stages of five minutes, reading lid deflection at each step; a single push records a peak, not a settled shape. At three times rated the lid may deflect 1.5% of body height, with residual set under 1.5% after 30 minutes of release.

Condition samples 24 hours at 23 °C ± 2 °C, with weights spread on 10 mm rubber pads.

3. Drop, Corner Impact and Low Temperature Brittleness

The drop sequence is five faces, three edges and one corner from 1.2 m onto a 50 mm steel plate. Samples condition at -18 °C for four hours, and the first drop lands within 30 seconds.

Corner strength uses a 30 J pendulum on the weakest corner, with no through crack and no latch release. The corner is the load entrance of a Stackable Container: the weight above, the forklift nudge and the first contact of a drop all arrive there.

Low temperature brittleness is judged at -40 °C for four hours with a Charpy impact of at least 8 kJ/m². A lot above 20% regrind typically loses 30% of its cold impact value.

4. Sampling Plans and Pass or Fail Rules

Sampling follows general inspection level II: AQL 0 for critical, 1.0 for major, 2.5 for minor defects. A lot of 501 to 1200 pieces draws 80 samples.

Lot size	Sample	Major Ac
151 to 280	32	1
281 to 500	50	1
501 to 1200	80	2
1201 to 3200	125	3

Defect classes belong in the contract. A through crack, a failed latch or a stack collapse is critical; a short lip, a minus wall or a missing mark is major. A rejected lot gets one re-inspection on a doubled sample; tested samples never return.

5. Marking and Traceability at Dispatch

A mark has to bring one Stackable Container back within three years: material code, mould number, year and month, rated load in kilograms.

Mark	Form	Used for
Material code	Moulded	Regrind level, cold performance
Mould number	Moulded	Machine, shot count, process record
Year and month	Moulded	Recall scope
Rated load	Moulded, in kg	Stack height on site
Lot number	Laser	Test report, retained samples

Durability is checked by 50 isopropanol rubs. Three records must agree: samples held 24 months, process parameters archived by shot, regrind above 20% flagged.

Conclusion

Acceptance of a Stackable Container is not about a longer list but about clauses that hold: eight test items, two sampling levels, three records, each with a gauge, a limit and a record. Separate full inspection from sampling, write defect classes into the contract, mould the mark into the wall, and acceptance becomes evidence rather than opinion, which is what a Stackable Container standard is for.

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.