How thick should the insulation in a temperature-controlled case be?

Answer: 40 to 50 mm of polyurethane foam with a foil facing, about 13.6 W of loss at a 40 K split.

How is heater power sized?

Answer: Two to three times the coldest steady loss, so 13.6 W of loss takes a 36 W film.

Why does the interior overshoot after closing?

Answer: A lid probe drops 3 °C, control calls full power, and the case overshoots 2 °C.

What seal compression should the lid run at?

Answer: Thirty percent, so an 8 mm cord sits at 5.6 mm and 4.2 N/cm gives about 75 N.

How is a temperature-controlled case tested before shipping?

Answer: Warm-up, an 8-hour hold, door recovery, then one unit per batch.

Temperature-Controlled Case Structure: Five Key Points

Quick answer: Five items settle a temperature-controlled case: layer order in the wall, heater margin, probe placement, seal compression at the lid, and calibration before shipping. Skimp on any one and the internal curve drifts within four hours.

Five Layers in the Wall: Order and Thickness
Heating Power and Holdover Without Mains
Controllers and Sensors: Placement and Hysteresis
Seals and Lid Seam: Stopping Heat Leaks
Rotomoulding, Foaming and Factory Calibration
FAQ

1. Five Layers in the Wall: Order and Thickness

A temperature-controlled case wall is five layers: 3 mm HDPE skin, 0.2 mm hot-melt film, 45 mm polyurethane foam, 2.5 mm liner, 0.05 mm foil facing. About 51 mm in total, with foam carrying seventy percent of the resistance.

Density decides whether that resistance lasts: at 38 to 42 kg/m³ and 0.022 W/(m·K), loss stays under five percent for three years; below 32 kg/m³ resistance falls ten percent in a season.

Thicker is not better: 45 mm to 60 mm adds thirty percent resistance but takes a 40 L case from 6.8 kg to 8.4 kg.

Layer	Material	Thickness	Job
Skin	HDPE	3.0 mm	Impact, UV
Bond	Hot-melt film	0.2 mm	Adhesion
Foam	Polyurethane	45 mm	Thermal resistance
Liner	Modified PE	2.5 mm	Wipe-down surface
Facing	Aluminium foil	0.05 mm	Reflects radiant heat

2. Heating Power and Holdover Without Mains

Power in a temperature-controlled case follows the coldest duty. At 40 L, a 40 K split and 0.62 m², steady loss is 13.6 W; a 36 W film leaves a factor of 2.6 and lifts -20 °C to 20 °C in about 22 minutes.

Temperature-Controlled Case: lid seam close-up, two fine grooves along the rim, latch root and rounded corner at right, pebbled surface texture

Film on the liner responds fast but runs 6 °C above the mean, so the probe beside it reads high and control quits early; buried in foam it is four minutes slower and even. Film bonded to a 1.5 mm plate first holds face difference inside 2 °C.

Holdover is a phase-change pocket, not a bigger battery: 1.2 kg at a 20 °C switch point and 180 kJ/kg keeps the interior above 15 °C for about five hours.

3. Controllers and Sensors: Placement and Hysteresis

Accuracy comes from probe position, not the ±0.5 °C on the label. A probe inside the lid drops 3 °C on opening, the film hits full power, and the interior overshoots 2 °C.

Two probes, liner return side and usable volume centre, weighted 0.7 and 0.3, hold better. Hysteresis at 0.8 °C saves twenty percent against 0.3 °C and keeps swing inside ±1 °C.

Setting	Typical	Too tight	Too loose
Hysteresis	0.8 °C	Relay cycles 60 times an hour	Swing ±2.5 °C
Sample rate	5 s	Standby draw up 8%	20 s to react
Probes	2	Extra leak paths	Drift and overshoot

4. Seals and Lid Seam: Stopping Heat Leaks

A third of the heat entering a temperature-controlled case comes through the lid seam. A twin-lip gasket sets an outer lip against water and dust, an inner lip against air, with a 1.2 mm cavity closing to 0.35 mm. That rim is also a bridge into the lid.

Temperature-Controlled Case: white case open, white pouches in the liner pockets, a small dark-screen device in the centre, twin front latches

Compression runs at thirty percent: an 8 mm EPDM cord at 5.6 mm gives 4.2 N/cm, about 75 N around 1.8 m. Fifty percent will not close; fifteen percent hardens at -20 °C.

Group feedthroughs onto one 60 by 40 mm block, pot the bores, and fit a 0.02 MPa breather: a 40 K split otherwise pulls the lid in 0.6 mm.

5. Rotomoulding, Foaming and Factory Calibration

A temperature-controlled case body rotomoulds at 260 °C on an 18-minute cycle, thickness set by charge weight: 4.5 mm takes 12 kg. Liners form on a 650 t press, rest 24 hours after demould, then foam.

Foam closes in a 40 °C fixture and demoulds at 8 minutes: early and the wall drums, late and it tears the liner. Calibration waits 72 hours.

Three curves decide the label: warm-up inside 25 minutes, an 8-hour hold within ±1 °C, recovery within 12 minutes after a 60-second opening.

Step	Parameters	Acceptance
Rotomoulding	260 °C, 18 minutes	Wall 4.5 ± 0.3 mm
Foaming	40 °C, 8-minute demould	38 to 42 kg/m³
Calibration	72 hours after demould	Three curves pass

Conclusion

Five items decide a temperature-controlled case: layer order, heater margin, probe placement, seal compression and calibration. Cheapen any one and the curve drifts. Put the numbers on the drawing and the inspection card, and a temperature-controlled case becomes predictable.

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.