Visual seal inspection, leak testing and checkweighing answer different questions

What does each check actually establish?

A transparent flange with trapped food may be easy to flag optically. The same contamination under opaque print may be invisible. Conversely, a seal can have a normal appearance but an inadequate bond. Define the defect, the condition of the pack and the required outcome before choosing equipment.

What do the cited test standards describe?

The public scope of ASTM F88/F88M describes measuring the strength of seals in flexible barrier materials by separating a test specimen containing the seal. The public scope of ASTM F2096 describes detecting gross leaks by internal pressurisation and observing bubbles. These examples illustrate different measured properties; they are not a recommendation that either method automatically applies to every tray, material or food product. Select the applicable method, version, preparation and acceptance limits with the packaging specialist.

Where should a camera sit?

Before sealing, a camera may see food or damage on an exposed tray flange. After sealing, it may see a displaced lid, a crease or an exposed seal region. Those views have different blind spots and may need separate tracking. A post-seal check cannot recover information hidden beneath opaque film. Test the actual pack decorations, flange geometry, condensation and product residue at the planned inspection point.

How should the combined process be validated?

Create a defect-to-method matrix. Assign an independent reference method to the characteristic being assessed and retain the sample identity. Validate camera false rejects and missed visible faults on the defined pack families, and validate the separate integrity or strength method within its own scope. A destructive sample test cannot be recorded as an individual test of every pack in the batch. Report the inspection coverage and sampling plan plainly.

What should happen when results disagree?

Treat disagreement as evidence to investigate rather than choosing whichever result allows release. A visually rejected pack may have harmless printing or condensation, or the leak test may not address the visible defect. A visually accepted pack that fails integrity testing shows that appearance alone was insufficient for that failure mode. Hold affected material under the quality procedure, identify the cause, and revise the control plan with documented validation. A checkweigher remains a separate mass control even when its reject shares a conveyor.

Tray seal-area inspection · Pouch and sachet checks

Appearance, strength and leakage answer different questions

A seal is both a physical bond and a barrier. An optical image records the visible surface under a chosen light and view. A strength test applies a mechanical load and records a response. A leak test looks for a pathway through which a medium can pass under specified conditions. These measurements can be related, but none is a universal substitute for the others. A visually smooth seal may contain a subtle channel; a strong section of seal may coexist with a leak elsewhere.

The public scope of ASTM F88/F88M-23 concerns seal strength in flexible barrier materials, and its significance section discusses process validation, capability and control. The public scope of ASTM F2096 concerns gross leaks by internal pressurisation. (ASTM F88/F88M-23: seal strength of flexible barrier materials) (ASTM F2096-11(2019): gross leaks by internal pressurisation (bubble test)) This article uses those published scopes to distinguish the methods. It does not reproduce the paid procedures or prescribe their test conditions for an unvalidated package.

For South African food premises, R638 provides the hygiene context for packaging operations. (South Africa: food premises and transport hygiene regulations R638, 2018) The product’s hazards, packaging design and approved quality programme determine which integrity evidence is needed. Installing a camera does not make the package compliant with every food-safety or transport requirement.

Choose evidence for each failure mechanism

Begin with the functional seal region. Decorative edges, tabs and areas outside the bond can contain wrinkles that do not affect the defined requirement. Conversely, a small particle crossing the functional band may matter more than a large cosmetic crease elsewhere. The packaging owner should mark the region and acceptable boundary samples before image tools are tuned.

Lighting should expose the selected feature. Reflection from a glossy laminate can hide contamination; a transmissive view may be useful only when the material and product allow it. HIKROBOT’s light-source glossary describes these geometry choices. (HIKROBOT Light Source Catalog, 2025 Q3, glossary) A learning-based detector does not remove the need for visibility or correct labels. If training data label every wrinkle as a leak, the model learns an unsupported relationship.

A hypothetical combined validation study

Hypothetical example: collect identified packs from the approved process, packs with visible seal-band contamination, packs with wrinkles outside the band and packs representing the integrity faults the packaging team needs to detect. Image each pack under the proposed station conditions, then apply the selected physical test where appropriate. Preserve identity between the image and the test result. This is a study design, not a claim that any particular defect size is detectable.

Review the disagreements explicitly. An optical reject with a satisfactory physical result may be a conservative visual rule, an irrelevant cosmetic feature or a physical test that does not address that particular defect. An optical pass with a failed physical result demonstrates a coverage gap; it cannot be corrected by declaring the camera’s image authoritative. Decide whether another view, another method or process control is needed.

Destructive tests alter the pack. Plan the sequence so the evidence relates to the original condition, and do not repeatedly test a modified specimen as though it were an independent new package. When samples are scarce, record that limitation rather than multiplying the apparent sample count by photographing the same specimen many times. Retain the packaging material and process conditions with the results.

Use the methods together during production

A practical control plan states which checks run on every package, which physical tests are sampled, how frequently challenge checks occur and what happens when any check fails. Those choices come from the validated process and risk assessment; there is no universal interval that this article can assign. A camera alarm should identify the visible reason so maintenance can distinguish dirty optics from changing seal appearance.

After film, foil, tray, adhesive or sealing-parameter changes, review whether the original validation still applies. The image can change because of colour and reflection even when the bonding process is unchanged, and the bond can change without an obvious visual difference. Treat optical configuration and physical integrity evidence as related but separately controlled records.

Evaluate classification using independent reference judgements and separate populations for good packs and each important fault class. NIST’s proportion guidance helps explain the uncertainty of finite trials. (NIST e-Handbook, 7.2.4.1 Confidence intervals for a proportion) For a trained vision model, keep the final evaluation set separate from training and threshold selection, following the general dataset-splitting principles described by Google. (Google Machine Learning Crash Course: dividing datasets)

The associated tray, pouch and yoghurt inspection solutions describe camera placement and station integration. This article helps a packaging engineer choose the evidence needed before using a visual result as a release input. It deliberately makes no claim that an appearance score is a leak rate or that a strength measurement alone proves whole-package integrity.