Quick answer: A folding case earns its place only when empty volume is the constraint — its 1:4 collapse ratio can turn four return trucks into one, but the 25 kg dynamic load and five-high stacking ceiling keep rigid cases in every heavy or high-bay slot.
Table of contents
- Count the return volume first
- Dynamic load: 25 kg against 50 kg
- Stacking and racking: five against eight
- Cleaning time and the 75 yuan price
- FAQ
1. Count the return volume first
Everything a folding case does well happens while it is empty. Fold the walls of a 600 × 400 × 320 mm unit and its height drops to 80 mm, taking 0.077 m³ down to 0.019 m³ — exactly 1:4. On a 1200 × 1000 mm pallet the open box stacks 24 units at 1920 mm; folded, 100 units at 2000 mm. A 9.6 m truck of 12 pallets returns 288 empty rigid cases or 1,200 folding ones — at 3,200 yuan a truck, that gap outgrows the box price.
| Item | Folding | Rigid |
|---|---|---|
| Empty volume per unit | 0.019 m³ | 0.077 m³ |
| Units per pallet, empty | 100 | 24 |
| Units per truck, empty | 1,200 | 288 |
| Return freight per unit | 2.7 yuan | 11.1 yuan |
| Unit weight | 2.4 kg | 3.0 kg |
On the return leg a rigid case has no answer.
That ratio is bought with wall thickness: 2.6 mm walls, a 3.2 mm base channel and a 2.0 mm hinge web on four pins, against a uniform 3.0 mm with no seam to thin. At a 60 mm folded height the pin drops to 4 mm, bore ovality passes 0.3 mm after 20,000 cycles and the walls rock.
2. Dynamic load: 25 kg against 50 kg
Dynamic load is the first rating a folding case gives up: 25 kg against 50 kg. The gap is load path, not wall thickness. A rigid moulding carries force from the base through a closed cavity into the feet; a folding body pushes four walls into the base channel, locks them with corner catches, and loads eight teeth at 3.1 kg each.
Hinge life is judged at 20,000 cycles — two seconds a fold, 12 a minute, 28 hours continuous. Tooth clearance may grow from 0.6 mm to 1.5 mm and no further, and wall-to-channel insertion stays above 8 mm; past 1.5 mm the walls rock and one trip leaves a stack 20 mm out of line.
| Metric | Folding | Rigid |
|---|---|---|
| Dynamic load | 25 kg | 50 kg |
| Base load, four high | 75 kg | 150 kg |
| Hinge or catch life | 20,000 cycles | no moving parts |
| Catches released, 0.8 m corner drop | 0 | 0 |
The 25 kg figure is no lazy margin. Stack five loaded units on one and the bottom teeth see about 1.9 kN of shear; a PA66 root with 30% glass fibre creeps near 2.1 kN, leaving a 0.4 mm dent after 72 hours. A rigid cavity spreads the same load around the perimeter, so its limit never sits on eight small teeth.
3. Stacking and racking: five against eight
Stack height is the number most often over-read on a datasheet. Five high for the folding unit, eight for the rigid one, and both assume 23 °C, even loading and 24 hours of rest, while the warehouse delivers a 38 °C top rack.
Measure residual deflection instead. Load four full tiers, 100 kg total, hold the case at 38 °C for 72 hours, then read the mid-wall: the pass line is 2 mm. A rigid case takes 175 kg over seven tiers and must stay under 1.5 mm. Pull three units; if two pass and one misses, the line is not five-high.
Racking adds a second gate. Footprint tolerance is ±2 mm and AGV fork entry sits at 120 mm; after a fold-and-reopen cycle the feet can sit 1.5 mm out, and pick failures climb from 0.5% to 3%. Five levels plus beams need 2.4 m of clear height.
4. Cleaning time and the 75 yuan price
Cleaning and unit price pull opposite ways on a folding body. A 0.8 mm seam runs between wall and base channel, with a 12 mm pocket at each corner catch, and rinse water stays in both until it is blown out. Across 0.5 m² of internal surface a wash and dry takes 30 seconds on the folding unit and 8 seconds on the rigid one, whose closed cavity has R3 corners. At 45 yuan a labour hour that is 0.375 yuan against 0.1 yuan; 300 washes a year is 82 yuan apart. Price runs 75 yuan against 58 yuan. Over four years the folding case amortises at 18.75 yuan a year, the rigid one at 9.7 yuan over six, and the 8.4 yuan saved per unit per return clears the 17 yuan gap in year one — if the truck count falls.
| Empty units per return | Returns monthly | Choice | Reason |
|---|---|---|---|
| Under 288 | any | Rigid | one truck already covers it |
| 288 to 1,200 | up to 2 | Mixed fleet | folding on light lanes |
| Above 1,200 | 3 or more | Folding | four trucks become one |
The middle row is what most warehouses run: under 20 kg in a folding case, above 40 kg in a rigid one, feet held to ±2 mm. If the return truck count does not move, a folding case just costs 17 yuan more.
Conclusion
Treat a folding case as a universal replacement and projects stumble in month three: a line designed around 25 kg drifts to 30 kg, clearance runs from 0.6 mm past 1.5 mm, and the stack loses alignment. Three conditions decide it — 25 kg or less per unit, five tiers or fewer, and at least three return trips a month carrying over 1,000 empty units. Meet all three and it is cheaper; miss one and the fleet should be mixed, heavy high-bay loads on rigid bodies, light short-haul returns on folding ones.
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.
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- Stackable case dimensions and tier conventions
- How to specify a stackable plastic box
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