The case costs 540 RMB, so why 1,100 RMB over four years?

Answer: Inserts and spares. Two remakes add 300 RMB, a latch and gasket kit 180 RMB, desiccant 60 RMB. One leak pushes the total near 5,300 RMB.

Rotomoulding costs 320 RMB more, so when does it break even?

Answer: At 1.8 RMB saved per trip, 178 trips recover the gap, four and a half years at 40 a year. Below 100 trips the premium is unearned.

Aluminium is lightest, so why does daily handling cost more?

Answer: Weight only affects freight. A dent breaks the seal and reshaping starts at 320 RMB; two years of repairs passes the price gap.

For air-freighted equipment, which structure fits?

Answer: Thin-wall injection or sheet metal under 5 kg tare. At 22 RMB per kilogram, 3.8 kg less than rotomoulding saves 83.6 RMB a trip.

A dozen units moving twice a year — is a case worth owning?

Answer: No at that frequency. Renting costs 200 to 300 RMB a trip, far below 540 RMB plus storage and inspection.

Four-Year Ledger: When an Electronic Equipment Case Costs Most

Quick answer: Add insert rework, one repair after a leak and scrap value to the price, and an Electronic Equipment Case often costs twice its label over four years. On one-way deliveries, low rotations, light short hauls and air freight, cheaper alternatives win per trip.

Four Costs That Only Add Up Over Four Years
Where Injection Moulding Wins: A 52-Second Cycle
Rotomoulding Trades 3.8 kg for 200 More Trips
An Aluminium Dent Never Springs Back
Corrugated and Foam Work Exactly Once
Four Duties to Skip the Case Entirely
FAQ

1. Four Costs That Only Add Up Over Four Years

A 600 x 460 x 260 mm case with a 520 x 380 x 210 mm interior puts one cost on the tag. Insert rework, a repair after water ingress, and scrap value stay outside it.

Cost line	Amount	When it lands	On the tag
Body and insert	460 + 80 RMB	First build	Yes
Insert rework	80 to 220 RMB	Every equipment revision	No
Repair after failure	From 4,200 RMB	Leak or cracked corner	No
Residual value	0 to 15 per cent	Disposal	No

The repair line needs unpacking. A control board runs 1,800 RMB, two technicians spend six hours each, three lost hours bill at 400 RMB, and seals plus desiccant pass 4,000 RMB. It lands once, on the case that failed, which is why planners delete it, yet it sets cost per trip: 120 rotations cost 4.5 RMB each clean, 39.5 RMB after one leak. That is nine times, not a percentage.

2. Where Injection Moulding Wins: A 52-Second Cycle

Polypropylene is cheap because it is fast: two cavities, a 52-second cycle, under 20 RMB of machine time per piece, a 3.8 mm wall and a 4.6 kg empty case.

The cost hides in geometry. A 1.5 degree draft forces a straight seal groove held by compression alone, and the latch keepers and hinge bosses, formed in the same shot, thin out first when the outer dimensions are squeezed.

Electronic Equipment Case: dark grey case open on a white bench, foam-lined lid, base cut for a module, coiled cable and small board

Failure keeps a fixed order. The 5 mm nylon hinge pin shears at the third 1.2 m six-face drop; the keeper, 2.6 mm at its root, whitens and lets go when the lid corner lands. Neither repair is dear; failing under power is.

In the ledger this build sits at 4.5 RMB a trip, and one leak moves it to 39.5 RMB, returning 119 trips of saving in one invoice. Injection moulding is a bet that nothing goes wrong.

3. Rotomoulding Trades 3.8 kg for 200 More Trips

A rotomoulded HDPE case runs 6.5 mm and weighs 8.4 kg, 3.8 kg above the injection part. The mould is a welded aluminium shell, so a cavity change moves a weld bead, thickness follows the corners, and no weld line remains.

The asset is trip count: 40 rotations a year over eight years gives 320 trips, carrying an 860 RMB build at 2.7 RMB each, six tenths of the injection figure.

Air freight reverses it. The extra 3.8 kg bills at 22 RMB per kilogram, 83.6 RMB a trip, or 3,344 RMB a year against a 320 RMB price gap. On that route tare weight is the fare.

Short rule: heavy road rotation favours rotomoulding, air freight eats the advantage.

4. An Aluminium Dent Never Springs Back

The magnesium-aluminium case weighs 3.9 kg, 1.5 mm sheet on a riveted frame, the lightest of the four, and its dimensions barely move between -30 °C and 70 °C.

Electronic Equipment Case: navy case open on a stainless bench, six flat modules set in dark foam, workshop brick wall behind

Past yield, aluminium dents and stays dented, where polyethylene springs back. A dent across the seal groove breaks the seal at once, and rivet holes concentrate stress, so hammering the panel back only ovalises the holes.

Repairs start at 320 RMB for drilling, beating and re-riveting, close to the price of an injection moulded case. After 96 hours of salt spray, corrosion begins at the rivets, white first, then along the seam.

Light weight saves freight, not repairs. In a fleet that loads daily, two years of repairs buys another case.

5. Corrugated and Foam Work Exactly Once

A corrugated carton with foam costs 38 RMB, carries 4.5 kN, stacks five high empty, and lands near 1 RMB a trip, the cheapest of the four.

Its limit is count:

One blade through the board while unpacking ends it.
Thirty minutes of rain halves edge crush strength.
No latches, no relief valve, no replaceable gasket.
The return leg carries nothing, and a replacement carton plus packing costs 60 RMB.

One-way logistics is its only ground: unpacked on site and discarded, no return, no warehouse stay, where 38 RMB against 540 RMB is a factor of fourteen. Add a return leg and two round trips in replacement packaging pass 120 RMB.

6. Four Duties to Skip the Case Entirely

Some duties make the case the priciest option.

Duty	Better fit	Why
One-way delivery, discarded on site	Corrugated plus foam	38 RMB against 540, no return leg
Under five rotations a year, original packaging kept	Rental flight case	Paid per use, no storage
Under 3 kg, short city moves	Hard-shell trolley case	Under 200 RMB, one hand
Air freight billed by weight	Thin-wall injection or sheet metal	Every extra kg adds 800 RMB a year

Two conditions together make price irrelevant: over 20 rotations a year, and a single failure above 3,000 RMB. When both hold, the body falls below a tenth of the four-year total. Settle those numbers before arguing resin or wall thickness.

Conclusion

Spread over four lines, an Electronic Equipment Case costs about twice its tag: injection wins on cycle time, rotomoulding on trip count, aluminium on tare weight, corrugated on one-way work. Which is cheaper comes down to annual rotations and the cost of one failure. Get those right and the case appears where it belongs, not on every project by default.

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.