Can a converted ammo box still be marked IP67?

Answer: Not by the converter. IP67 belongs to a complete box, and new gaskets or a sanded flange break that link. Re-test at 1 m for 30 min, or by 20 kPa decay.

Moulded or steel, which converts more easily?

Answer: Moulded, since 4 mm to 6 mm of wall leaves room. Steel keeps margin only in the seam, so it suits paint and lining work instead.

Do the stencils have to come off?

Answer: Ownership decides. Codes belong to whoever held the box, so the method is their call; the box-side rule is not to lose 10% of the wall doing it.

Can a vent be added later?

Answer: Yes, on the flat of the lid, 8 mm clear of the groove, matched to the vent thread, then re-tested at 20 kPa with decay under 1.0 kPa.

How high can it be stacked?

Answer: By bulge, not rated load. Two tiers at 22 kg are fine while the wall stays under 2 mm; past that it belongs in one tier.

Ammo Box to Civil Use: What Can Change

Quick answer: Ammo box civil use turns on three measurable lines: wall left after sanding, gasket compression, and stencil depth. Cross one and the box drops a class.

Three Lines That Decide the Conversion
Walls and Latches: Measure What Is Left
Gaskets, Vents and the Pressure Drop
Markings and Paint: Where to Stop Sanding
Inserts: From Steel Dividers to EVA
The Cost Sheet, and When to Buy New
FAQ

1. Three Lines That Decide the Conversion

Surplus stock comes in two builds. The steel pattern is 1.2 mm cold-rolled sheet with a lock-seamed edge and a flat sealing flange; the moulded one is 4 mm to 6 mm of polyethylene, with latch and hinge seats grown from the same wall. In both, the load path is fixed: handle, side walls, four bottom corners. A conversion can touch fittings, lining and paint. It cannot touch that path and still call itself the same box.

Item	As built	Limit	If crossed
Wall	1.2 mm steel, 4–6 mm PE	90% left after sanding	2 mm bulge when stacked two high
Latch rivets	6.0 mm holes	Growth ≤ 0.5 mm	1.5 kN falls to 1.3 kN per latch
Gasket	EPDM cord, 8 mm, 25–30%	Old glue ≤ 0.2 mm	IP67 drops to IP54
Vent	Cracks at 0.2 bar	Replace core and membrane	Pressure lifts the latches

Markings are a separate question from margin: who may use the box, not how much box is left. Settle that before anyone lifts a sander.

2. Walls and Latches: Measure What Is Left

Sanding is the first step taken and the easiest to overdo. Powder coating runs 60 μm to 90 μm, and two passes at 120 grit take off 0.05 mm. Removing a laser etch plus primer costs 0.15 mm to 0.2 mm. Moulded walls already carry ±0.6 mm, so a nominal 4.0 mm may measure 3.4 mm; another 0.2 mm puts it under the line.

Ammo box in white, lid open on a steel bench, grey foam and divider strips inside, two latches and a centre handle, shelving behind

Steel keeps its margin in the lock seam. Three layers overlap there, giving 3.6 mm of local thickness that the flange rests on. Grind it flat and two thirds of that stiffness goes; the lid then sits 1 mm proud at one corner and the seal is finished.

Latches are a rivet calculation. Four at 1.5 kN give 6 kN, against roughly 1.2 kN on the lid of a lower box in a two-high stack at 22 kg each. Open a 6.0 mm hole to 6.5 mm and bearing area drops 15%, taking each latch to 1.3 kN. Add 0.14 bar of internal pressure and most of the margin is gone.

3. Gaskets, Vents and the Pressure Drop

Pressure decay beats a water dunk on the floor. Charge to 20 kPa, hold 60 s, pass anything under 1.0 kPa, which matches IP67 at 1 m for 30 min. A stored box reads 0.4 kPa at 28% compression.

State	Compression	Decay in 60 s	Verdict
Original cord, untouched	28%	0.4 kPa	Pass
Relined, closed once	26%	0.6 kPa	Pass
Relined, 20 cycles	21%	1.4 kPa	Marginal
0.3 mm glue in groove	17%	2.2 kPa	Fail

Lining work is what disturbs it: 20 open-close cycles drop compression to 21% and decay to 1.4 kPa, and a 0.3 mm film of old adhesive pushes decay to 2.2 kPa because the new cord never seats.

The vent gets skipped because the box is not going to altitude. That forgets temperature. Seal at 30 °C, truck to -10 °C, and 40 K removes about 13.8 kPa by p·ΔT/T. On a 0.3 m² lid that is 4.1 kN, close to 70% of what four latches hold. The part costs 6 CNY.

4. Markings and Paint: Where to Stop Sanding

Stencils sit in one lid corner, 0.10 mm to 0.15 mm deep, read by the shadow in the recess. Three passes with 1500 grit take off 0.08 mm. The risk is going local: a 0.3 mm hollow at that corner means the gasket never reaches 25% and one corner decides the whole seal.

Ammo box in white, closed on a concrete floor, scuff marks on the lid corners, folding handle and a round vent knob, steel shelving behind

Paint is two coats: 40 μm epoxy primer, 40 μm polyurethane, 80 μm total, cross-hatch adhesion grade 1, and 96 h of neutral salt spray without red rust on steel. Polyethylene does not rust but does fade, so outdoor boxes need a hindered-amine grade and a colour difference inside ΔE 2.

5. Inserts: From Steel Dividers to EVA

Dividers are 1.0 mm steel on 42 mm centres, bracing the side walls as a side effect. Pull them for instruments and bulge under a two-high stack goes from 0.8 mm to 2.2 mm. The replacement is 30 kg/m³ EVA at 20 mm, routed to ±0.5 mm, a tenth of the weight but no brace at all, so a 5 mm PVC base plate sends stack load to the floor.

6. The Cost Sheet, and When to Buy New

Operation	Cost	Labour	Note
Strip and sand	35 CNY	0.8 h	Seam left alone
Powder coat	60 CNY	—	80 μm at 180 °C
EPDM cord, 8 mm	18 CNY	0.3 h	Groove cleaned
CNC EVA, 20 mm	120 CNY	0.5 h	Routed to drawing
Four rivets	12 CNY	0.2 h	Holes checked
Total	245 CNY	1.8 h	—

A new box lists at 320 CNY. Rebuilding saves 75 CNY, a fifth of the price, but leaves IP54 and two years against IP67 and five; per year it costs 40 CNY more. Three things must hold: 50 units or more, every reading above 90%, and a duty that never needs IP67.

Conclusion

The line for ammo box civil use is margin, not appearance. Keep 90% of the wall, 6.0 mm rivet holes and 25% compression, and the rebuild earns its 75 CNY; lose one and the repair bill lands inside two years.

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.