How do I get the cavity of a Plastic Box from its footprint?

Answer: Deduct two wall sections and 0.8 mm of draft per side, turning 600 mm into 592 mm. Take 8 mm of lip off the height and keep 5 mm clearance.

What load should a five-high stack carry?

Answer: Five tiers at 18 kg load the base with 72 kg. Rate 1.5 times for creep at 40 C, or 108 kg.

Is a thicker wall always stronger?

Answer: No. A 2.4 mm wall on a 90 mm rib pitch beats a plain 3.0 mm wall in a cold drop, and extra thickness alone adds sink and weight.

What latch force passes inspection?

Answer: 150 to 180 N holding and 25 to 40 N to open. Below 120 N the wall bulge releases it; above 200 N a gloved hand cannot.

Can a small order change colour without a new tool?

Answer: Yes. From 500 units, recolour an existing tool in 40 minutes of purging, holding 1.5 ΔE and regrind under 20 percent.

Plastic Box Selection: Five Criteria You Can Measure

Quick answer: Judge a Plastic Box by five measurable criteria rather than the catalogue footprint: internal cavity, base stack load, wall against rib pitch, latch holding force with its sealing grade, and a material window matched to batch size.

Five Criteria for Plastic Box Selection
Cavity Size and Stack Load Arithmetic
Reading Wall Thickness and Rib Pitch
Latch Holding Force and Sealing Grade
Material Temperature Window and Batch Size
FAQ

1. Five Criteria for Plastic Box Selection

The usual mistake is ordering a Plastic Box on outside dimensions and reading a static load figure as a stack rating. Four criteria settle on one sample with calipers, a pull gauge and an oven.

Order matters: cavity decides fit, stacking decides base ribs, wall and rib pitch decide drop behaviour, latch and seal decide the closing face, and batch decides cost last.

Criterion	Measure	Usual mistake	Line to hold
Internal cavity	Clear length, width, depth	Outside size used	5 mm clearance
Base load	Uniform load on the floor	Static read as stack load	1.5 times the tiers
Wall and ribs	Side and base thickness	Thickest point only	2.2 to 2.6 mm
Latch and seal	Holding force, IP grade	Judging by feel	Above 120 N
Material and batch	Temperature range, cavities	Pricing first	No fracture at minus 20 C

2. Cavity Size and Stack Load Arithmetic

On a 600 x 400 x 280 mm Plastic Box with a 2.4 mm wall, deduct two wall sections and 0.8 mm of draft per side: 592 mm remains. The lid lip takes 8 mm more, leaving 262 mm of usable depth.

Plastic Box: a single off-white hard box closed on a grey backdrop, two black latches on the front and a folded handle

Five tiers at 18 kg put 72 kg on the base. At 40 C for 48 hours the wall creeps 40 percent faster, so rate 1.5 times, or 108 kg, with two ribs 6 mm high. A 10 mm lid spigot engaging 6 mm keeps the column square.

3. Reading Wall Thickness and Rib Pitch

A load-bearing Plastic Box runs 2.4 mm sides, 3.0 mm base and 2.2 mm lid. Read 30 mm below the rim and 30 mm above the base, then judge the lower.

Rib pitch matters more than height: 90 mm with 6 mm ribs and a 1.4 mm root suits that wall; 60 mm sinks the outer face into shadows. Drop the loaded box from 1.2 m at minus 20 C on six faces, three edges and one corner; square rib roots crack, and an R2 fillet recovers them.

4. Latch Holding Force and Sealing Grade

An over-centre latch on a Plastic Box should hold at 150 to 180 N and open at 25 to 40 N. Under 120 N, an 18 kg load bulges the wall and the latch walks itself open.

Plastic Box: blue body under a white lid, two white over-centre latches at the front, vertical side ribs and corner feet

IP54 covers indoor dust and splash. Open-yard rain needs a 3 mm gasket compressed near 30 percent, since over-compression hardens the rubber in cold and leaks worse. Metal parts take 48 hours of salt spray, and red rust rejects the batch.

5. Material Temperature Window and Batch Size

At minus 20 C, demand a 6 J drop with no radial whitening behind the strike. A week in a 60 C trailer must not soften the walls, so keep 15 C of margin under the heat deflection temperature.

Small runs recolour an existing tool with 40 minutes of purging. Above 3,000 units a new Plastic Box tool runs on a 780 tonne press at a 62 second cycle and 300,000 shots, holding colour to 1.5 ΔE with regrind capped at 20 percent.

Batch	Tooling route	Amortised	First delivery
500 to 1,000	Recolour existing	0.8 CNY	12 days
1,000 to 3,000	Add cavities	2.4 CNY	18 days
Above 3,000	New single cavity	6.5 CNY	25 days
Above 10,000	New two cavities	4.2 CNY	30 days

Conclusion

Five numbers settle the decision: cavity from the footprint, a base rated at 1.5 times the load above, wall read with rib pitch, a latch holding 120 N at least, and material matched to temperature. Choosing a Plastic Box is arithmetic done before the order.

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.