Does a rotationally molded case need salt spray?

Answer: Only with metal parts. Hinges and keepers call for 48 hours neutral salt spray at grade 9, or rust water runs down the wall in six months.

How do I sample a small order?

Answer: Inspect everything below fifty pieces. Such a small sample carries little weight, and full inspection is faster than arguing.

Are eight thickness readings enough?

Answer: For routine acceptance. The eight points sit where walls run thin; if the first case fails, double them.

What does Delta E 2 look like?

Answer: Under standard light the eye barely separates the two. Above 2, cases from one lot show light and dark patches.

Where can a concession lot be used?

Answer: Only where there is no sealing or stacking duty, and the concession is marked on the shipping papers. A rotationally molded case accepted by concession never goes on a sealed order.

Rotationally Molded Case Acceptance Standards: Items and Limits

Quick answer: Acceptance for a rotationally molded case runs in three layers: zero acceptance for critical defects, AQL 1.0 for major ones, 2.5 for minor ones. Every item needs a limit that fits in a record, or inspection becomes a matter of feel.

Grading defects before listing items
Sampling and what counts as a lot
Limits for size and weight
Limits for appearance and colour
Re-verification and disposition
FAQ

1. Grading defects before listing items

The first decision is the defect grade, not the checklist. The same scratch is minor on a stacking face and major on the lid sealing face, where it lets a rotationally molded case leak. Grade by consequence: weakened protection is critical, affected assembly or service life is major, appearance alone is minor. Mix them and bad lots ship while good cases get picked over.

Grade	Typical items	Judgment	Disposition
Critical	through cracks, broken gasket groove	veto	reject the lot
Major	lid flatness, wall below minimum, colour shift	AQL sampling	reject or sort
Minor	flow lines, light scratches off the seal	concession	rework or accept

2. Sampling and what counts as a lot

Define the lot first: one mould, one material batch, one colour, one shift. An order of five hundred rotationally molded cases at level II gives a sample of fifty, which two inspectors clear in an hour.

Publish acceptance numbers so nobody asks permission: critical 0 and 1, major 1 and 2, minor 3 and 4. Below fifty pieces inspect everything; above three thousand two hundred the sample steps up.

Lot size	Sample	Critical Ac Re	Major Ac Re	Minor Ac Re
up to 50	all	0 / 1	0 / 1	1 / 2
51 to 500	50	0 / 1	1 / 2	3 / 4
501 to 3200	80	0 / 1	2 / 3	5 / 6

3. Limits for size and weight

Name the points and instruments, or the limits on a rotationally molded case mean nothing. Outer length, width and height take plus or minus 3 mm, the cavity plus or minus 2 mm, and the diagonals must sit within 4 mm of each other. The diagonal exposes mould distortion: a case can be right in length and width and still stack crooked.

Weight is indirect evidence of wall: plus or minus 5 percent of nominal, since the light pieces are usually the thin ones. Thickness is read at eight points, four base corners, base centre, lid centre and both side walls, the smallest above 85 percent of nominal.

4. Limits for appearance and colour

Appearance on a rotationally molded case is judged by face. Sealing face, stacking face and handle root take no scratches, sink marks or flash; other faces allow flow lines to 0.3 mm. Flash gets waved through, yet it holds a gap open under the gasket.

Colour is measured, not eyeballed: Delta E 2 within a lot and 3 between lots, sampled on a flat panel away from ribs. Metal parts add 48 hours of neutral salt spray at grade 9 or better.

Item	Method	Limit	Record
Outer size	tape, three readings	plus or minus 3 mm	value per case
Diagonals	tape, crossed	4 mm maximum	stop the line
Weight	scale	plus or minus 5 percent	value per case
Wall	caliper, eight points	85 percent of nominal	ten cases per lot
Colour	spectrophotometer	Delta E 2 within lot	three cases per lot

5. Re-verification and disposition

Re-verify on triggers, not the calendar: a new mould, material batch, supplier or structural change restarts the full set. Drop at 1.2 m on a corner, then check the gasket groove; hold 55 °C for four hours and confirm lid flatness moves under 1.2 mm.

A rejected rotationally molded case gets a red tag and its own stack. A concession states its scope and never goes on a sealed order; rework covers trimming, part replacement and re-marking only. Keep three cases per lot for twelve months, records for twenty-four.

Conclusion

Acceptance of a rotationally molded case rests on three layers: defect grades fix the consequence, sampling fixes the risk, limits fix the action. Write all three and nobody works by feel. If no one can say whether an out-of-limit reading is critical or minor, the standard is unfinished and no rotationally molded case should ship against it.

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.