Induction Cap Sealing - The Principles  

1) The seals are commonly made of four parts, a pulpboard layer, a wax layer, the sealing foil and a layer of polymer which is compatible with the material from which the container is made. This seal is cut to size and placed inside the cap by the cap manufacturer.

2) After filling, the cap (with the seal liner inside), is applied as usual and then the container passes on the conveyor under the induction sealing head. The induction head emits an electromagnetic field through which the containers pass. This induces an electric current in the sealing foil causing very rapid heating. As the foil heats up, the polymer layer is melted onto the top surface of the container creating a hermetic seal, at the same time, the wax is melted and absorbed into the pulpboard layer, releasing the seal.

3) When the consumer opens the cap on the product, there is a perfect seal on the top of the container and the pulpboard remains in the cap as a liner.

The induction sealer itself comprises an induction generator, an induction coil and a cooling system.

The induction generator has to supply enough power to the coil to ensure a good seal, the power required is a factor of the size of the seal, the speed of the production line and the type of closure which is being used.

The induction coil can come in a variety of configurations, each suited to the size and kind of closure used. Unlike most other equipment, the majority of closure types and sizes can be sealed using the standard
Relco Induction Sealing Head unit thus eliminating the time and cost of change parts. Unusual closures
such as flip-top lids and sport caps require the use of a Relco tunnel coil where the induction field is generated from the side of the closure rather than the top.

Due to the power and high frequency of operation, Induction Sealers on continuous running lines require some form of cooling. This can either be done by blowing air at ambient temperature over the system or by the use of a heat exchanger which uses water to take the heat away from the system. Manual units are not
run continuously and heat is naturally dissipated. For continuous units, water cooled systems are more expensive but provide a much more efficient means of removing the excess heat and give much lower running temperatures. Operating at a lower temperature decreases component stress thereby improving
long term reliability, lowering operating costs and reducing the risk of unwanted down-time.

Why use induction cap sealing ?
The seal provides a good oxygen barrier, improving shelf life of products
It shows tamper evidence
Avoids spillage
 
What container materials can be sealed ?
Most container materials can be sealed, including
PVC
PE
PP
PET
Glass