Non-contact cap-liner sealing
Induction sealing uses an electromagnetic field to heat a compatible foil layer in a closure liner so it bonds to the prepared container sealing surface.
Sealing principle
An induction sealer passes a capped container beneath a sealing head that creates an electromagnetic field. A compatible foil layer in the closure liner heats and activates its sealing layer against the container neck. The cap applies the pressure needed to maintain contact while the seal forms and cools.
A machine cannot create a reliable seal from incompatible components. The container material and neck finish, foil construction, sealing polymer, closure design and cap application must be selected together. Neck damage, contamination, poor flatness or an incorrectly seated cap can prevent uniform contact.
The product also matters. Residue on the neck, foaming, hot-fill conditions or aggressive contents can affect the liner and bond. Trials should use filled production containers, final closures and the intended liner from the approved supply route.
Process window
Seal quality is created by the complete component and process window. Power and line speed are only useful when the cap, liner and neck remain in controlled contact.
| Variable | Why it matters | Check during trials |
|---|---|---|
| Cap application | Controls liner contact and pressure against the neck. | Cap seating, thread engagement and closure consistency before sealing. |
| Container neck | Provides the bonding surface. | Flatness, damage, flash, cleanliness and dimensional variation. |
| Liner construction | Must match the container material and required peel or retention behaviour. | Approved supplier specification and performance after cooling. |
| Head position and conveyor | Controls field exposure and repeatable passage beneath the sealing head. | Container height, spacing, stability and head clearance. |
| Product and temperature | Can affect contamination, pressure and material compatibility. | Filled packs under normal and difficult process conditions. |
Line control
Induction sealing normally follows cap application, so the line should detect gross cap absence or misplacement before the container reaches the sealing head. A no-foil or seal-presence system may be considered where the application requires it, but the inspection objective and response to uncertainty must be agreed rather than assumed.
The conveyor should maintain stable container position and spacing through the sealing field. Controls need a defined response to stopped conveyor movement, sealing-head faults and rejected packs. Heat generated in the liner can continue to develop briefly after exposure, so the agreed inspection point should reflect the component supplier’s sealing process.
Buyer questions
Containers can be induction sealed when the neck finish, container material, closure and foil liner are designed to create a compatible bond. The same liner does not suit every plastic or glass pack. Final components and filled product should be tested because neck condition, cap pressure and contamination affect the result.
Conventional cap-liner induction sealing normally requires the closure to hold the liner against the container neck during exposure and cooling. The cap, liner and neck therefore form part of the process. The closure should be applied consistently before sealing and checked for seating or absence.
An induction seal can fail because of incompatible liner or container materials, poor cap application, damaged or contaminated necks, incorrect head position, unstable conveyor speed, insufficient or excessive exposure, or component variation. Diagnosis should inspect the unsealed components and process condition before changing machine settings.
Induction-seal inspection may include checking liner presence, cap condition, external indicators and destructive or non-destructive seal tests agreed for the pack. No single sensor proves every aspect of seal integrity, so the inspection plan should define what is detected online and what is verified through quality sampling.
