Can knife case standards be met by in-house inspection alone?

Answer: No. The factory measures a drawing, the site measures a working unit. Re-test 3 units for drop and immersion on arrival.

Why is the pressure hold limit 0.02 bar?

Answer: It matches the leak rate of a 6 litre cavity over 90 seconds. Tighter fails on gasket permeation, looser passes pinholes.

We sampled 32 and found 4 defectives. Can the lot ship?

Answer: No. Four is past the acceptance number. One defective would allow a second sample of 32.

Should the drop test use an empty case or ballast?

Answer: Ballast, at 1.1 times loaded weight. An empty drop only shows whether the shell cracks.

Who owns a field failure on a conceded batch?

Answer: Traceability decides. The note records defect and discount, and later claims on that defect are shared.

In-house pass, site reject: knife case standards in 4 checks

Quick answer: A knife case measured to a drawing in the factory and measured in service on site will not agree unless four checks are written down: dimensions, sealing, drop and stack, and disposition. Done properly, acceptance costs under 12 yuan per unit and returns stay below 1%.

The three document layers behind knife case standards
Appearance and dimensions a caliper can reproduce
Sealing: pressure hold and immersion
Drop and stack: reproducing them on site
Disposition: rework, concession, rejection
FAQ

1. The three document layers behind knife case standards

Acceptance arguments usually come down to three papers: a contract that says "to standard", a supplier inspection report, and a returns note. All three are genuine; none describes the same unit.

Knife case standards rest on three layers. The drawing carries cavity tolerance and minimum wall. The test method states hold pressure, drop height and stack tiers. The sampling plan states lot size and acceptance number, and that third layer is normally missing — under 500 units, sample 32 and accept on 3; above 500, sample 50 and accept on 5. Without it, each side reaches a different verdict on the same pallet.

2. Appearance and dimensions a caliper can reproduce

Colour shift and sink marks carry no units, so they only invite argument. Fold appearance into three measurable items: lid flatness read with a straight edge and feeler at 0.4 mm, seam width taken at four points with 0.3 mm allowed variation, and wall section.

Knife Case: low three-quarter view from the right front, plain black lid, handle recess curving into the side, grey base corner, two latches

Check	Instrument	Limit	Action if exceeded
Lid flatness	Straight edge, feeler	0.4 mm or less	Reject lot
Seam variation	Feeler gauge	0.3 mm at four points	Adjust tool
Wall section	Ultrasonic gauge	2.8 mm minimum	Scrap unit
Internal length	Caliper	350 mm plus or minus 1.0	Rework liner
Latch retention	Pull gauge	150 N minimum	Change latch

Knife case instruments belong in the same document. The same seam read with a 0.02 mm caliper and with a steel rule differs by 0.3 mm, which is the full width of the limit band. Name the instrument, or two parties each measure once and each feel right.

3. Sealing: pressure hold and immersion

There are two routes and the choice follows duty: units that circulate in storage get a pressure hold, units that travel get immersion. Running both doubles the cost.

Plug the vent before a pressure hold; a case that cannot be plugged goes to immersion. Charge the cavity to 0.3 bar, hold 90 seconds, pass at a drop of no more than 0.02 bar. That pressure sits inside the gasket's working range: higher takes a set, lower misses pinholes. Immersion sinks the knife case 200 mm for 30 minutes, then it is dried and opened; any water inside fails it.

A knife case trial in Sanya ran 48 samples through both routes. Of the 45 that held pressure, 3 took water in immersion, all traced to the latch axle bore: air creeps through that open bore slowly, water follows the axle fast.

4. Drop and stack: reproducing them on site

Drop tests go wrong more often than anything else. Push a case off a 1.0 m bench and it lands differently every time, so verdicts differ too. Do six faces over three rounds, one face per round, onto concrete, with ballast at 1.1 times loaded weight.

Knife Case: lying at an angle on a bluish white surface, dark seam between lid and base, one latch along the base edge

Test	Site condition	Criterion	Record
Free drop	1.0 m, six faces, three rounds	No crack, no latch release	Photo per round
Stack	5 tiers, 48 hours, 35℃	Deflection 1.2 mm or less	Four corner heights
Salt fog	72 hours neutral	No red rust at hinge	Cross-cut rating
Thermal	-25℃ to 65℃, 6 cycles	Seam change 0.3 mm or less	Re-measure each cycle
Hinge life	8,000 cycles	Play 0.5 mm or less	Log every 2,000

Stacking gets skipped because it occupies floor space. Five tiers for 48 hours at 35℃, with a lid sagging past 1.2 mm, fails; that figure comes from three months of warehouse creep. Measure the rig from the lowest point of the case, since reading to the bench adds 10 mm.

5. Disposition: rework, concession, rejection

A failed verdict is only the start; disposition decides the cost. Defects in a knife case fall into three classes, each with its own signatory.

Defect class	Disposition	Signatory	Follow-up
Dimension out of tolerance	Rework or repair	Quality manager	Re-inspect lot
Cosmetic defect	Concession	Buyer and user	3% price cut
Seal failure	Rejection	User	Supplier pays freight

Knife case rework runs about 12 yuan per unit; a rejection costs 60 yuan or more in freight and credit. Concessions need a trail too: the batch is packed separately and tagged red with the defect and discount written on it, because an untagged concession is forgotten in three months and the same units come back.

Conclusion

Between a factory pass and a usable unit sit four reproducible checks: dimensions that can be measured, a seal that can be tested, a drop that can be repeated, a disposition that can be signed. Write them into the knife case standards and nobody argues from feel. Once a criterion reproduces, a return becomes a record.

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.