Can a cleanroom run on plastic boxes alone?

Answer: ISO 8 can, with surface resistance between 10⁶ Ω and 10⁹ Ω, corners at R3 and no 121 °C steam; ISO 5 cannot, since a molded Ra of 1.6 μm fails the wipe residue and abrasion counts.

Is a lower Ra always better on a stainless tool box?

Answer: 0.8 μm is the value point. Ra 0.4 μm costs 30% more and still takes three passes, while a Ra 0.2 μm mirror scratches visibly.

What fails first after 50 steam cycles?

Answer: The silicone gasket and the galvanized spring. Compression set reaches 22% and the spring rusts at cycle 30, while the body stays within 0.1%.

Does a stainless tool box need grounding?

Answer: Yes. A conductive body is not a grounded one, and insulating casters still let charge build. Fit an M5 stud with a 4 mm² braided strap and keep resistance under 10 Ω.

Stainless vs Plastic Tool Box in Cleanrooms

Quick answer: A cleanroom box is chosen on three tests at once, a surface that wipes clean, a body that sheds no particles and a structure that survives sterilization; a stainless tool box wins the first two, plastic keeps the weight and the price.

Three Hard Requirements for a Cleanroom
Surface Finish: Ra 0.8 μm Against a Molded Skin
Sterilization: Steam, VHP and Wiping
Particles and Ion Release
Weight, Handling and Static
Cost and a Mixed Layout
FAQ

1. Three Hard Requirements for a Cleanroom

Whether a stainless tool box belongs in a cleanroom has nothing to do with the label on the steel; three requirements must hold at once. Cleanability: every wiped surface must be reachable by the disinfectant, with no groove, rivet hole or rolled edge as a hiding place. Low shedding: the body releases no particles when moved, opened or knocked. Sterilization: repeated steam, vaporized hydrogen peroxide or chlorine leaves dimensions and appearance intact.

The room class sets how tight they are. Under ISO 14644-1, an ISO 5 area allows 3,520 particles per cubic metre at 0.5 μm and above, ISO 7 relaxes to 352,000 and ISO 8 to 3,520,000. A wipe is itself a dust event, so stricter classes put more weight on cleanability.

Plastic struggles on the first two: molded texture and parting lines hold residue, a crystalline PP skin sheds fines under rubbing, and static pulls particles onto the wall.

2. Surface Finish: Ra 0.8 μm Against a Molded Skin

Roughness turns requirement one into a number. A 316L sheet mechanically polished reaches Ra 0.4 μm, electropolishing delivers Ra 0.8 μm, and a mirror grade goes to Ra 0.2 μm, while a molded PP body stays between Ra 1.6 μm and Ra 3.2 μm even from an SPI A-2 tool.

Stainless tool box compared with plastic in a workshop, olive case open on a steel bench, black foam in the lid, empty racks behind

Over a 100 mm by 100 mm area, Ra 0.8 μm needs three wipe passes to reach every micro-valley, while Ra 3.2 μm needs five.

Welds are harder than parent metal: an intermittent weld leaves a 0.2 mm gap, wide enough for disinfectant and too narrow to wipe, so a settle plate above it grows colonies. The answer is a continuous weld, reinforcement ground under 0.3 mm, then electropolishing. Plastic corners come from geometry: an R2 molded radius, but rib roots and latch seats stay grooved unless the tool goes to R3 and adds 0.4 mm of wall.

Surface item	316L electropolished	316L mechanical	Molded PP
Roughness Ra	0.8 μm	0.4 μm	1.6–3.2 μm
Inner corner	Polished weld	Polished weld	R2 in tool
Wipe passes	3	3	5 or more
Residue risk	Weld, screw hole	Weld, scratch	Rib root, latch seat

3. Sterilization: Steam, VHP and Wiping

Sterilization is the harder divide. Saturated steam at 121 °C for 15 min, repeated 50 times, moves a 316L body under 0.1% and keeps hinge and latch clearance under 0.5 mm; a molded PP body warps around cycle 20, with the lid closing 1.2 mm out of line.

Vaporized hydrogen peroxide takes another route. At 400 ppm for 30 min it barely touches the passive film of 316L, while PP whitens and chalks by round 15. Chlorine is blunter: 200 wipes at 1000 ppm sodium hypochlorite leave 316L open to pitting, and PP loses over 15% of its gloss.

The weak point of a stainless tool box is the fittings, not the body. Silicone gaskets reach 22% compression set after 50 steam cycles and a galvanized spring rusts at cycle 30.

4. Particles and Ion Release

Shedding is hardest to self-check because nothing shows: in an ISO 5 area one 0.5 μm particle trips a live counter, and fines from opening and pushing land upstream of the airflow.

Stainless tool box corner detail, brushed steel latch on a grey body, rounded interior corner, translucent divider in its slot, fine matte texture

316L relies on its passive film. With 16% to 18% chromium and 2% to 3% molybdenum, the surface regrows a 2 to 3 nm oxide layer in air and wear is measured in nanometres; a particle counter 100 mm away for 1 min stays within 3 counts of background.

PP sheds two ways: abrasion grinds out 1 μm to 10 μm fines, and low-molecular additives migrate to the skin, where one alcohol wipe lifts them off.

Ion release is quieter: a passivated 316L body holds chloride release under 0.1 μg/cm², while PP carries no halogen itself but picks up additives from flame retardant and antistatic packages.

5. Weight, Handling and Static

At the same 60 L usable volume, a stainless tool box weighs 22 kg and a molded PP body 6.5 kg, a 15.5 kg gap. Cleanroom access adds gowning and air showers, so body weight decides whether one person carries it.

Load runs the other way: a 316L body in 1.2 mm sheet with two folded edges holds 120 kg static without distortion, while a PP body deflects 2 mm at the same load.

Static is where plastic hurts. Plain PP sits near 10¹⁴ Ω and holds a sheet of dust, so an electronics area needs a grade between 10⁶ Ω and 10⁹ Ω at 20% more cost; a stainless body only needs a ground strap under 10 Ω.

6. Cost and a Mixed Layout

At 60 L a stainless tool box runs 2200 CNY against 420 CNY for molded PP, a factor of 5.2; over 8 years against 3, the annual figure falls to 275 and 140 CNY.

Zone class	Main body	Liner	Reason
ISO 5	316L stainless tool box	Stainless trays	No shedding, sterilizable
ISO 7	316L or electropolished stainless	Modified PP trays	Cost and cleaning balanced
ISO 8	Modified PP body	None	Surface resistance is enough
Perimeter	Standard PP body	None	Never enters the core

A mixed layout often beats either choice. A stainless trolley stays at a fixed station, tools ride in PP trays that lift out as a unit and pass through the hatch after disinfection, so the steel rarely moves and the plastic covers transfers only.

Conclusion

The order in a cleanroom is zone class first, sterilization method second, weight and cost last. In ISO 5 a stainless tool box holds Ra 0.8 μm, continuous welds and a 316L passive film at once; in ISO 8 a modified PP body is cheaper as long as surface resistance lands between 10⁶ Ω and 10⁹ Ω. Neither 22 kg against 6.5 kg nor 2200 CNY against 420 CNY goes away, so most plants keep steel fixed and plastic on the transfer route.

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.