Should a portable plastic case be injection or blow moulded?

Answer: Injection above 500 pieces a year, blow moulding near 200 for rounded shapes, rotomoulding under 50.

Is a 2.5 mm wall too thin?

Answer: It depends on ribs; at 30 mm height and 90 mm spacing a 2.5 mm shell matches a 4 mm wall at 30 percent less weight.

PP or ABS for the shell?

Answer: PP copolymer for cold and chemicals; ABS for gloss, at 15 percent more weight and a higher price.

Can a broken living hinge be repaired?

Answer: No, only the lid can be replaced; once the fold whitens, move the model to a steel pin.

How much regrind is acceptable?

Answer: Above 20 percent impact falls a fifth and colour drifts, so visible parts stay at 10 percent.

Portable plastic case: five criteria for buyers

Quick answer: Most of the price gap between two portable plastic case quotes comes from the moulding route and the resin, not the look. Pick injection, blow or rotomoulding from annual volume, choose the grade from service temperature, fix rib and draft details, then agree latch design and incoming tolerances.

Portable plastic case moulding sets wall and batch
Resin grade decides heat resistance and impact
Ribs radii and draft angles carry durability
Latches and hinges moulded in or metal
Tolerances and batch consistency on arrival
FAQ

1. Portable plastic case moulding sets wall and batch

Injected, a portable plastic case with a 440×320×160 mm cavity runs a 2.5 mm wall on a 48-second cycle, tool from 80,000 CNY. Blow moulding gives 4 mm for 30,000 CNY but keeps corners rounded; rotomoulding reaches 6.5 mm at the lowest tool cost and holds the machine 20 minutes.

An injection tool built for 300,000 shots spreads its cost at 500 pieces; blow moulding starts at 200, rotomoulding at 50.

Route	Wall	Tool	Minimum	Cycle
Injection	2.5 mm	80,000 CNY	500	48 s
Blow	4.0 mm	30,000 CNY	200	90 s
Rotomould	6.5 mm	18,000 CNY	50	20 min

2. Resin grade decides heat resistance and impact

PP copolymer is the default for a portable plastic case: 0.91 density, 100 °C deflection, 6 kJ/m² impact holding at -20 °C. Homopolymer PP is 15 percent stiffer but keeps a third of that impact in cold.

Portable plastic case in dark grey, five blue latches and a blue handle, foam holding a keypad panel and a coiled cable

HDPE wins on chemical resistance and cracks under load; ABS gives gloss at 15 percent more weight; PC reaches 60 kJ/m² at three times the PP price.

Grade	Density	Deflection	Impact	Trade-off
PP homopolymer	0.91	105 °C	2 kJ/m²	stiff, brittle cold
PP copolymer	0.91	100 °C	6 kJ/m²	best balance
HDPE	0.95	85 °C	5 kJ/m²	chemicals, cracks
ABS	1.05	95 °C	12 kJ/m²	looks, weight, price

Regrind hides in cheap quotes: at 20 percent impact falls a fifth and colour greys, so visible parts stay at 10 percent.

3. Ribs radii and draft angles carry durability

Ribs are structural: on a portable plastic case the rib runs 0.6 times the wall, past 0.8 the outer face sinks into a read-through. Height stays under 12 times the wall; a 1.5 mm root radius cuts stress concentration about 40 percent.

Draft decides whether the tool survives: walls at 1.5 degrees, cavities at 1 degree, plus 1 degree per 0.025 mm of texture. Too little drags the wall white. Cooling takes 18 seconds at 2.5 mm, 26 at 3.5 mm, at 45 °C.

4. Latches and hinges moulded in or metal

A moulded PP living hinge folds 100,000 times at no cost while the lid stays under 1.2 kg. Heavier lids need a steel pin and eight rivets, face flat to 0.3 mm.

Portable plastic case corner in blue, black over-moulded guard covering the lid seam, fine pebble texture and rounded edges

Latch pull force near 80 N is the useful band: under 60 N the lid pops open on rough ground, over 120 N a gloved hand fails. Past 500 mm, two latches hold the middle.

5. Tolerances and batch consistency on arrival

Warp comes first: corner height across the base of a portable plastic case stays within 0.8 mm over 300 mm, or it rocks on a bench.

Colour is held at ΔE 1.5 across three samples. Moisture above 0.05 percent leaves silver streaks, and drop testing runs at 1.2 m and -10 °C.

Check	Method	Pass line	Failure
Warp	plate and gauge	0.8 mm per 300 mm	rocking base
Gap	feeler gauge	under 0.5 mm	light leak
Colour	spectrophotometer	ΔE 1.5	grey batch
Moisture	analyser	0.05%	silver streaks
Drop	1.2 m at -10 °C	no through-crack	chipped corner

Warp and colour drift most by the second shipment as tools wear and lots move; comparing each lot to the first-article report beats sorting parts.

Conclusion

Choosing a portable plastic case is subtraction: no injection tool for a small batch, no saving on copolymer where cold is real, no living hinge under a heavy lid. Run the five criteria and every line on the quote has a reason. The right portable plastic case is the one whose route, grade and tolerances fit the job.

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.