How long does case refurbishment take?

Answer: 40 minutes for all three paths, with 11 minutes of drying and 12 of painting, so the case returns the same day. A seal alone takes 12 minutes, a latch pair 8.

Does a refurbished case still hold IP67?

Answer: Yes, if the sealing face is flat. A 0.3 kPa hold for 60 s must decay 0.05 kPa or less; more means the gasket is not seating or the faces have shifted.

How close is the repainted finish to the original?

Answer: Within ΔE 2 the eye cannot separate them, ΔE 3 reads one shade off. Adhesion is accepted at 4B; lower means the promoter was missed.

Why does the cost land at 35%?

Answer: 96 CNY of material plus 30 CNY of labour is 126 CNY, 35% of the 360 CNY replacement. Below 20 L, labour dominates and the figure reaches 40%.

How do I decide between refurbishment and replacement?

Answer: Measure crack length, diagonal spread and mould depth. Pass all three and refurbish; fail any one and replace. In between, use the 21-month line.

Case Refurbishment Options

Quick answer: Case refurbishment runs 40 minutes and 126 CNY, about 35% of a new case, and buys 24 months: two coats at 60 μm, a 45 CNY seal, 18 CNY latches.

Three Paths: Paint, Seal and Latch
Two Coats at 60 μm: Which Shells Are Worth Painting
A 45 CNY Seal and an 18 CNY Latch: How Costs Stack
The 35% Line: When Refurbishment Pays
Cracked, Warped or Mouldy: Replace Instead
FAQ

1. Three Paths: Paint, Seal and Latch

A 40 L black hard case costs 360 CNY new. Three years on, the lid is chalky, the gasket flat, one latch pin gone. A full pass of case refurbishment takes 40 minutes and 126 CNY.

The three paths are a sequence, not a menu: shell load capacity, sealing face, then colour and hardware. Once the shell fails, the rest is wasted money.

The 40 minutes are uneven: inspection and trial close 6, stripping the seal and latches 6, cleaning and drying 11, two paint coats 12, refitting 5.

Step	Time	What matters
Inspect and trial close	6 min	Crack length, diagonal spread, wall thickness
Strip seal and latches	6 min	Keep the old seal as a reference sample
Clean and dry	11 min	Surface moisture must reach zero
Two paint coats	12 min	30 μm per coat, 20 min flash-off
Refit hardware	5 min	Seal first, latches second
Total	40 min	Same-day turnaround

Those 11 drying minutes are the ones people cut: trapped moisture blows pinholes under the film and both coats are scrap.

Keep the old seal as a gauge: 1.5 mm under a new one and the gasket has to go.

2. Two Coats at 60 μm: Which Shells Are Worth Painting

60 μm is the total dry film: 30 μm per pass, 20 minutes flash-off between them. Below 50 μm the moulded texture shows through; above 80 μm paint pools in latch seats and the lid stops closing.

Only one surface deserves paint: colour faded while the polymer has not chalked. Drag a fingernail across the lid. If the scratch shows the same colour underneath, the damage is cosmetic and a 240-grit key will take a coat.

Case refurbishment at the paint bench: a black case open on grey, dark lid foam, channels holding silver shafts, two draw latches and one handle

If the scratch shows white powder and the surface crumbles under a thumb, UV has broken the chain. Paint lifts in sheets within 3 months, and the case belongs in replacement. A tape test settles it in seconds.

Polypropylene sits near 31 mN/m of surface energy, so an adhesion promoter is not optional. Skip it and cross-hatch testing lands at 1B, flaking under a fingernail. The acceptance line is 4B, no more than 5% of grid area lifted.

Colour is judged by ΔE. Painted lid beside the original body under D65, ΔE ≤2 is invisible, ΔE 3 reads one shade lighter. Tint a batch in one mix: two mixes drift past ΔE 2.5 and buyers call it two colours.

3. A 45 CNY Seal and an 18 CNY Latch: How Costs Stack

The gasket is priced per run: a 40 L case carries about 1.6 m of seal channel at 45 CNY. Cut it 20 mm long and it buckles at the corners, never seats, and airtightness drops a grade.

Latches cost 18 CNY each and are replaced in pairs. Spring force differs by about 15% between old and new, so a mixed pair tilts the lid and compresses the gasket 30% on one edge against 22% on the other.

Labour converts at 45 CNY per hour, so separate visits cost more: three strip-downs add 5 minutes each and beat a single 40-minute pass.

Path	Material	Labour	Total	Share of 360 CNY
Paint only	15 CNY	9 CNY	24 CNY	6.7%
Seal only	45 CNY	9 CNY	54 CNY	15.0%
Latch pair only	36 CNY	6 CNY	42 CNY	11.7%
All three in one pass	96 CNY	30 CNY	126 CNY	35.0%

Material of 96 CNY plus 30 CNY of labour is 126 CNY, exactly 35% of the 360 CNY replacement. Smaller shells climb past 40%.

4. The 35% Line: When Refurbishment Pays

126 CNY over 24 months is 5.3 CNY per month. A new case at 360 CNY over 60 months is 6.0 CNY. Refurbishment wins by 0.7 CNY, which makes 35% a threshold, not a target.

The break-even sits on service life: 126 divided by 6.0 gives 21 months. Anything past 21 months beats replacement; a case that dies at 12 months costs 10.5 CNY a month and turns the job into a loss.

Case refurbishment samples on a wood-grain bench: large open black case, vials in foam cavities, a case with looms and tools, a small blue-insert case

A second pass needs its own arithmetic. Material stays at 96 CNY, but the shell is thinner and the inserts are worn, so labour rises to 50 minutes: 252 CNY over 48 months, still 5.3 CNY monthly.

A third pass rarely works: the sealing face holds a permanent groove, so the gasket touches on a line rather than a band.

Three measurements decide whether 24 months is realistic: remaining wall thickness (3.0 mm new, risky below 2.6 mm), hinge bore ovality (a φ8 mm plug rocking 0.3 mm is loose), and whether the foam has taken water.

5. Cracked, Warped or Mouldy: Replace Instead

A crack is the hardest veto. Longer than 20 mm, or within 30 mm of a hinge or latch seat, and load keeps running along it. Paint hides that crack for about 2 months.

Warp shows on the diagonal. More than 3 mm between lid and body misaligns the sealing face, and a new gasket cannot pull it back. Reassembled, the case fails a 0.3 kPa hold of 60 s with decay above 0.05 kPa.

Foam mould is judged by depth. Surface bloom can be re-covered; mould 10 mm deep, or foam that crumbles when pinched, means 80 CNY of insert on top of 96 CNY of material, past half the price of a new case.

One more case is unrelated to the shell: discontinued hardware, where a scrapped tool cannot be bought and a sound shell drops to storage duty.

The order is fixed: shell, sealing face, insert, hardware. Any veto ends the review, and judging before working is what keeps case refurbishment cheap.

Conclusion

Case refurbishment reduces to one subtraction. A new case at 360 CNY over 60 months costs 6.0 CNY monthly; a refurbished one at 126 CNY over 24 months costs 5.3. The 0.7 CNY gap means the job defers a 360 CNY purchase by two years rather than saving money.

What decides it is the 6-minute inspection: a crack past 20 mm, a diagonal spread past 3 mm, mould deeper than 10 mm, and the 35% is thrown away. A sound shell is the highest-return asset on site.

Judge, choose the path, pull parts against the material list, then finish all three in one strip-down. The table below copies into a maintenance log.

Path	Material	Labour	Total	Life added	Per month
Two coats at 60 μm	15 CNY	12 min	24 CNY	12 months	2.0 CNY
New gasket	45 CNY	12 min	54 CNY	12 months	4.5 CNY
Latch pair	36 CNY	8 min	42 CNY	18 months	2.3 CNY
All three combined	96 CNY	40 min	126 CNY	24 months	5.3 CNY

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.