Induction Sealing

Understanding Induction Liners and Induction Sealing Machines

When properly applied, induction lined caps provide a hermetic, leak-proof, air tight and tamper evident seal. The FDA states that induction lined caps are one of the most effective methods for tamper evidence. Using an induction sealing system is ideal for extending product shelf life and preserving freshness.

How Induction Sealing Works

The typical induction liner has a multilaminate construction. It consists of a layer of pulpboard, a layer of wax, a layer of aluminum foil, and a layer of polymer.

An induction sealing system features two standard components: the power supply and a sealing head. The sealing head consists of a coiled conductor covered by plastic housing. When the power supply energizes the inductive coil, it produces an electromagnetic current, called an eddy current. The eddy current is dispersed into the aluminum foil layer, resulting in a resistance-type heating effect. The heated foil melts the wax layer, which is absorbed into the pulpboard, releasing the foil from the pulpboard. The polymer coating then melts, hermetically sealing the foil to the lip of the container.

Choosing the right sealing head option is dependent on the size of your cap and the speed at which the production line will operate. The two most common designs are flat sealing heads and tunnel heads.

Flat Induction Sealing Heads

Flat sealing heads widely disperse the electromagnetic field from above and are recommended for larger sized caps.
  • Advantages:

  • Accommodates various cap sizes without exchanging sealing head.
  • Disadvantages:

  • The less concentrated field can cause an inconsistent seal if a container is not correctly centered.

Tunnel Induction Sealing Heads

Tunnel sealing heads provide concentrated electromagnetic fields from above and the sides of the cap.
  • Advantages:

  • Uniformity in the current application which can provide a more consistent seal.
  • The deeper field allows for sealing thicker caps or with recessed liners.
  • Disadvantages:

  • Cannot accommodate a broad range of neck finishes.

Tips for Using an Induction Sealing System

The induction lined caps must be applied with proper torque. Correct torque ensures that the foil liner is in direct contact with the lip of the container. SKS has a helpful torque guide available.
  • The induction sealer power settings and the amount of sealing time are programmed. Too little heat: results in a weak seal, while too much heat: can cause burned or deformed liners.
  • There is space between the caps and the sealing head. The standard distance is 1/8 inch.
  • Ensure that the containers have been properly centered under the sealing head, so the liners will bond evenly to the lip of the containers.
  • Watch a video on using an induction sealing system.

Choosing the Right Container and Cap

Induction liners can work with HDPE, LDPE, PS, PET and PVC plastic jars and bottles, as well as glass containers. Plastic containers with plastic caps create the easiest and most consistent seal. It is possible to induction seal glass containers with plastic caps, but some of the containers may need to be treated in order to achieve a proper seal.

Frequently Asked Questions

  • What if a few containers within a production run haven't sealed?
    The first thing to review is the cap and container that did not seal. If the majority of the containers have a good seal, the settings on the machine and the machine itself are most likely in correct working order.

    Here are a few things to check:
    • Is the cap correctly screwed onto the container?
    • Is the liner in contact with the lip of the container?
    • Is the lip of the container warped?
  • How do I choose between high and low frequencies?
    Frequency is an important factor in the melting process of the wax layer. Some factors of the correct frequency are the size of caps, the type of production run and size of the machine.
  • How do I decide on my conveyor speed (Feet Per Minute FPM)?
    For a quick calculation use: Containers Per Minute (CPM) / # Containers Per Foot (CPF). For example, if you can fit 5 containers within a foot on your conveyor and your CPM is 100, your speed should be 20 FPM.
  • What are the advantages of induction liners over pressure sensitive liners?
    While purchasing an induction sealing system may increase your production cost at first, using an induction lined cap will reduce waste and increase sustainability over time, and can comply with packaging regulations more easily.

Enercon Induction Sealers

SKS will work with Enercon to locate the best induction sealing system for your needs. We have many options available now!

Enercon, one of the leaders in induction sealing systems and services, has developed and customized more cap sealing solutions than anyone in the industry. After purchasing an induction sealing system, you'll have access to full technical support and manuals.

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