Induction sealing
After the cap or closure is applied, the container passes under an induction coil, which emits an oscillating electromagnetic field.
As the container passes under the induction coil (sealing head), the conductive aluminum foil liner begins to heat as a result of the eddy currents being induced.
Seals applied by heat induction to plastic containers appear to offer a higher degree of tamper-resistance than those that depend on an adhesive to create the bond..."Some shipping companies require liquid chemical products to be sealed prior to shipping to prevent hazardous chemicals from spilling on other shipments.
Food companies that use induction seals do not want the liner residue as it could potentially interfere with the product itself upon dispensing.
In some applications, induction sealing can be considered to contribute towards sustainability goals by allowing lower bottle weights as the pack relies on the presence of an induction foil seal for its security, rather than a mechanically strong bottle neck and closure.
[5] Some manufacturers have produced devices which can monitor the magnetic field strength present at the induction head (either directly or indirectly via such mechanisms as pick up coils), dynamically predicting the heating effect in the foil.
Such devices provide quantifiable data post-weld in a production environment where uniformity – particularly in parameters such as foil peel-off strength, is important.
High speed power analysis techniques (voltage and current measurement in near real time) can be used to intercept power delivery from mains to generator or generator to head in order to calculate energy delivered to the foil and the statistical profile of that process.
Many other derivative parameters may be calculated for each weld, yielding confidence in a production environment that is notably more difficult to achieve in conduction transfer systems, where analysis, if present is generally post-weld as relatively large thermal mass of heating and conduction elements combined impair rapid temperature change.
Inductive heating with quantitative feedback such as that provided by power analysis techniques further allows for the possibility of dynamic adjustments in energy delivery profile to the target.
With an induction sealer, the contact face can be of a compressible material, ensuring a perfect bond each time.
