The Basics of Induction Sealing

Induction Sealing, otherwise known as cap sealing, is a non contact method of hermetically sealing a highly technical engineered laminated structure to the top of plastic and glass containers. The sealing process takes place after the container has been filled and capped. The key to a perfect induction seal are three controllable variables - pressure, heat, and time.


The design of the neck and threads of the container must be matched to the closure so that the closure will give even pressure to the land area and the skirt of the closure will not bottom out on the shoulder of the container. This is known as the ‘H’ dimension of the container and closure. If the land area of the container has any defects, such as high spots (at seams) or possible low areas (saddle), you will have uneven pressure.


The distance of the induction sealing head to the foil in the liner is very important. A 3mm or 1/8" gap between the induction foil and the coil is recommended. It is also important that the induction sealing unit and conveyor are level, as is having the right profile of the induction coil for the job, ie a flat or tunnel coil. There are various induction coil sizes and styles to accommodate various package designs and sizes.


Time is needed when the closure is passing under the induction coil. This is called the dwell time. The induction seal liner needs sufficient time under the coil to be heated to the correct temperature for the sealing surface to melt and bond to the land area of the container. Time is needed after sealing to allow cool down, during which, the container must not be bumped, banged, roughly handled, or opened.

PHT™ Manual

This informative manual provides closure manufactures and CPG's with the latest leading facts on induction sealing. It discusses types and uses of induction seals, how to correctly set an operating window, and troubleshooting examples to eliminate weak or scorched seals. Find guidance for matching the closure to the container’s neck profile for even pressure, and design recommendations for liner geometry. Learn the do’s and dont’s of setting up an induction line.