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Compliance is a documentation trail, not a steel feature
FDA 21 CFR and EU 10/2011 do not specify steel grades. They specify that materials in contact with food must not transfer substances to the food at levels above specified migration limits. The steel grade is a tool — the compliance lives in the resin data sheet, the passivation record and the processing history.
That said, standard food-contact practice favours passivated austenitic and martensitic stainless steels. S136 and 2316 are the two most common grades for injection moulding food-contact tools. The mill certificate is required, and the passivation record is part of the compliance package.
FDA 21 CFR vs EU 10/2011 — what matters
FDA 21 CFR Part 177 covers plastics in contact with food; Part 178 covers indirect additives including metals. The key requirement for tool steel is that no substances migrate from the tool surface into the food-contact resin at levels above specified thresholds. EU 10/2011 is the corresponding EU regulation covering plastics in contact with foodstuffs, with a more structured migration-testing framework.
The practical implementation for tool steel: use a passivated stainless grade, document the passivation procedure, keep the mill certificate for the block, and test for migration from the tool surface into the resin at the worst-case processing temperature.
Choosing the grade
Use S136 when the food-contact part is a cosmetic or optical component — a transparent lid, a housing with a visible surface, or a part that needs a mirror polish. Use 2316 when the part is disposable, multi-cavity or internal, and corrosion resistance and polish are secondary to machining speed and cost.
Both grades have to be passivated, and the passivation has to be re-done after every welding or repair operation.
Passivation and surface control
Passivation removes free iron from the cavity surface, which prevents iron transfer to the food-contact resin and prevents corrosion during production and storage. The passivation procedure is a documented process using citric or nitric acid, verified with a free-iron indicator test, and re-done after every repair.
The cavity surface finish matters. A rough cavity holds resin residue that can become a microbial growth site during production. Ra 0.8 μm or better on all wetted surfaces is the normal starting point for food-contact tooling.
Common mistakes
- Assuming "stainless steel = compliant". The grade is necessary but not sufficient — traceability, passivation and migration testing are also required.
- Passivating then welding without re-passivating. The weld area is a migration risk.
- Using a tool-shop polish that leaves abrasive residues on the cavity surface without thorough cleaning.
Frequently asked questions
How do I know this category is the right starting point?
Start with the failure mode. If the resin is corrosive, go to the corrosion category before volume. If the resin is abrasive, go to the wear category before polish. If the cavity has to run above 150 °C, go to high-temperature before anything else. The category you land in decides the steel family, and the grade is then chosen within that family.
Can a tool span multiple categories?
Yes — a PEEK tool with a glass-filled resin runs both the high-temperature and abrasive categories at the same time. Where categories overlap, pick the more restrictive one first. A corrosive resin with abrasive filler starts with corrosion resistance; the wear requirement is then layered on top with inserts or coating.
Why not just pick the hardest grade in this category?
Hardness buys wear resistance and indentation. It does not buy toughness, hot strength or corrosion resistance, and it costs schedule and money. The categories deliberately trade one property for another — that trade is what each is designed around.
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