TL;DR: The highest-risk failure modes in metal tin and aluminium case production are not structural — they’re process-driven, and most can be scored and controlled before a single unit ships.
TL;DR: In our FMEA framework, a lacquer adhesion failure on a food-contact tin scores an RPN of 192, which automatically triggers a production hold and root-cause review before any batch release.
Hazard Identification Across the Metal Tin and Aluminium Case Production Chain #
Metal packaging carries a category of risk that paper-based packaging simply doesn’t: the combination of sharp edges, pressurised forming operations, chemical coating systems, and direct food or cosmetic contact creates a multi-layer hazard profile that needs to be assessed at every production stage, not just at final QC.
We map hazards using a four-zone framework we call our MH-04 Production Risk Register, which covers raw material receipt, forming and stamping, surface coating and curing, and outbound assembly. Each zone gets a hazard class (mechanical, chemical, thermal, or microbiological), a likelihood score from 1 to 5, and a severity score from 1 to 5. Anything scoring above 15 combined goes to immediate engineering review.
The table below shows representative risk entries from our MH-04 register across the main production zones:
| Production Zone | Hazard Type | Likelihood (1–5) | Severity (1–5) | Control Measure |
|---|---|---|---|---|
| Tinplate / Aluminium slitting | Mechanical — edge laceration | 4 | 4 | Cut-resistant gloves EN 388 Level D; automated slit-edge deburring |
| Draw-and-iron forming press | Mechanical — pinch/crush | 3 | 5 | Two-hand safety interlock; 300mm minimum exclusion zone |
| Solvent-based lacquer application | Chemical — VOC inhalation | 3 | 4 | LEV extraction maintaining <50 ppm benzene-equivalent; ATEX-compliant zone |
| UV/thermal curing oven | Thermal — burn / IR exposure | 2 | 4 | Interlock-triggered oven door; surface temp alarm at 180°C |
| Food-contact tin final inspection | Microbiological — contamination | 2 | 5 | ISO 22000-aligned hygiene zone; glove-and-sleeve protocol |
A likelihood score of 3–4 on slitting operations is realistic — tinplate slitting is a high-frequency task, and even with guarding in place, human interaction with the slit-edge during jam clearance is the scenario that causes most hand injuries in our experience across this category. The severity rating of 5 for forming press pinch points reflects OSHA 29 CFR 1910.217 requirement thresholds: any press operation above 10 tonnes of forming force is treated as potentially fatal, not merely injurious.
Where this table matters for brand partners: if your tin specification calls for a deep-draw lid with a recessed panel (common in premium tea tins and collector editions), the forming depth directly affects press tonnage and therefore elevates the crush-hazard score. We factor that into our pre-production risk sign-off.
What Goes Wrong, and the Mechanism Behind Each Failure #
Lacquer delamination at the seam weld zone. During resistance seam welding of tinplate side walls, the welding current generates localised temperatures between 600–900°C at the weld point. If the base lacquer coat has not been stripped back adequately within the 2–3mm weld margin, residual lacquer carbonises, creating a brittle interfacial layer. Over time — accelerated by fill product acidity or humidity cycling — that layer delaminates. The result is exposed bare tinplate inside the tin, which in a food application triggers an immediate non-conformance under FDA 21 CFR 177.1520 (polymer coatings in food contact). In our process, we specify a minimum 3mm lacquer exclusion zone at the weld margin and verify it by cross-section metallographic inspection on the first 10 units of each new tin construction. Missing this step is the single fastest path to a food-safety rejection on a production batch.
Aluminium anodising bath temperature drift causing surface hardness variation. Anodising is a time-temperature-concentration process. Our standard Type II anodising spec runs the sulphuric acid bath at 18–22°C for a target oxide layer of 8–12 microns. When bath temperature drifts above 25°C (common in summer without active chiller control), the oxide layer becomes softer and more porous. Hardness tested per ISO 2360 eddy-current measurement drops from a target 250–300 HV to below 180 HV. At that hardness, cosmetic scratching under normal transit conditions becomes visible, and more critically, the corrosion resistance of the case drops measurably. We log bath temperature every 30 minutes during anodising runs — our internal threshold for a process hold is any reading above 24°C for more than 15 consecutive minutes.
Sharp-edge burr formation on punched aluminium lids causing end-user laceration risk. Punching operations on aluminium sheet generate a burr on the die-exit face, typically 0.03–0.08mm height on well-maintained tooling. When punch-die clearance opens up beyond 8–10% of material thickness (which happens gradually as tooling wears), burr height can reach 0.15–0.20mm — enough to cut skin during normal lid removal. This isn’t detectable by visual inspection at normal viewing distance. Our QC-07 material risk procedure mandates burr-height gauge measurement on every 50th punched lid during a production run, with a hold limit at 0.12mm. The tooling replacement decision is triggered at that point, not after a consumer complaint.
Does Metal Packaging Require a Separate Chemical Safety Assessment from the Fill Product? #
Yes, and the fill product chemistry drives the assessment entirely, not the packaging form.
A decorative tin with no interior lacquer coating is unsuitable for acidic products (pH below 4.5), high-salt formulations, or water-activity above 0.85 — all of which accelerate electrochemical corrosion of exposed tinplate at a rate that produces detectable tin ion migration within 6–12 months of fill. For products in those categories, a two-coat epoxy-phenolic interior system tested to ASTM B117 salt spray for a minimum 500 hours is the baseline we specify. For cannabis, pharmaceutical, or nutraceutical fills, the assessment extends to EU Regulation 10/2011 migration limits, even for tin packaging, because some cured lacquer monomers are listed substances under Annex I.
This holds for standard aluminium cosmetic cases as well. For fragrance or essential oil fills, the solvent compatibility of the anodised or lacquered interior must be tested against the specific carrier chemistry, not assumed safe.
Specification Notes for Brand Partners #
When you brief us on a metal tin or aluminium case project that involves food, cosmetic, pharmaceutical, or chemical fill products, we need your fill product specification before we can finalise the interior coating system. Specifically: pH range, water activity or moisture content, salt or acid concentration if applicable, and any regulated active ingredients.
The most common brief gap we see is brands specifying the tin exterior aesthetic in full detail — pantone colours, emboss depth, finish type — while leaving the interior coating as “standard.” There is no universal standard that covers all fill types. Selecting the wrong interior lacquer for a high-acidity fill product can result in a failed EU 10/2011 migration test, which means the production batch cannot be placed on the EU market. That failure typically surfaces at the compliance testing stage, 8–12 weeks into a project, and forces a full production re-run.
Provide the fill chemistry data at brief stage and we can specify the correct coating system from the start. Our typical sampling timeline for a new tin construction with a specified interior coating is 20–25 working days from approved specification sheet. Complex drawn-and-ironed constructions or multi-part aluminium cases with hinge mechanisms add 5–7 working days to that window.
Frequently Asked Questions #
What PPE is required when handling metal tins and aluminium cases during production?
Cut-resistant gloves rated to EN 388 Level D are mandatory during slitting and stamping operations. For lacquer application zones, nitrile chemical-resistant gloves and half-face respirators with organic vapour cartridges are required where LEV extraction maintains solvent concentrations below 50 ppm. Eye protection is mandatory across all forming and punching stations.
How is FMEA scoring used in your production process for this category?
We score each failure mode on Occurrence (1–10), Severity (1–10), and Detection (1–10), giving a Risk Priority Number up to 1,000. Our production hold threshold for this category is RPN ≥ 160. A lacquer adhesion failure on a food-contact tin scores Occurrence 4, Severity 8, Detection 6 — RPN 192 — which sits above threshold and requires documented root-cause correction before batch release. For non-food decorative tins, the same failure mode scores lower on severity, dropping the RPN to around 120, which triggers a corrective action record but not a hold.
Can a standard decorative tin be used for food contact without additional testing?
It depends on the fill product and the interior coating specification. An uncoated or single-coat tinplate tin is not suitable for acidic, high-salt, or high-moisture fills without a validated interior lacquer system. The relevant compliance framework for EU market entry is EU Regulation 10/2011 for plastic components and, where applicable, national guidelines under Council of Europe Resolution AP(2004)5 for metallic packaging. A tin that passes decoration QC may still fail food-contact migration testing if the coating system was not selected for the specific fill chemistry.
What is the typical burr height tolerance on punched aluminium lids, and why does it matter for safety?
Our acceptable limit is 0.12mm maximum burr height, measured per our QC-07 procedure on every 50th punched unit. Above that threshold, end-user laceration risk increases to a level we consider unacceptable for consumer-facing packaging. Tooling wear is the primary driver — punch-die clearance beyond 8–10% of material thickness reliably produces burrs above 0.15mm. Replacement is triggered at the 0.12mm gauge reading, before the limit is exceeded in production.
How do you handle emergency response if a lacquer VOC incident occurs on the production floor?
Our ATEX-compliant lacquer application zone has automatic solvent vapour detectors set to alarm at 25% of the LEL (lower explosive limit). On alarm, the line halts, LEV extraction shifts to emergency high-flow mode, and personnel evacuate the zone per our emergency response procedure ER-03. If concentration reaches 50% LEL, the building section isolates automatically. First aid response for solvent inhalation exposure follows the SDS protocol for the specific lacquer system in use, with the nearest hospital briefed on our chemical inventory as part of our annual site emergency drill.
Planning a packaging project? Contact our team to request a complimentary specification review and sample quote.
