Technical Developments in Induction Sealing
Whilst there have been marginal improvements in the induction power supplies and induction sealing head designs making machinery more compact and generally more reliable, in reality induction sealing has changed very little over the past 10 years. The main technical development in this area however has been the introduction of systems to allow induction heating to be used as a replacement for conduction heating in direct foil sealing applications.
Capless Induction Sealing
Traditionally the choice between induction and conduction as the means of providing a heat-sealed foil membrane to a container was determined by whether the foil was to be provided in the cap (induction) or applied directly to the container before or without capping (conduction). As end-users started to look for increased reliability & up-time, improved sealing performance, higher efficiency and greater operator safety, the question was asked, why can’t we use induction heating instead of conduction heating for applications where the foil is not provided as part of the cap?
Initially, the size & weight of the induction power supply and induction coil prevented easy integration into the appropriate kind of machinery whilst the switching speeds required by this type of system did not lend themselves to induction equipment which is designed to be operated in a steady state. In addition, there were questions over how a thin foil membrane is to be delivered to and located on the container and how the required sealing pressure is to be applied where a threaded cap is not used as the transfer and contact medium.
Capless induction sealing systems essentially fall into two main categories depending upon how the foil is delivered. Some machinery works with a pre-cut foil whilst others cut and apply the foil as one process. Which system is most suitable will depend upon the product design, filling, capping and process requirements and the way in which the machinery will integrate into the rest of the line. Advice should ideally be sought from an equipment supplier who can provide either solution since they can provide the benefits of an impartial opinion.
Directly applied flat membrane with lift&peel feature for easy removal – cut and sealed in one stroke operation
Pre-cut and formed skirted closure, induction sealed after locating on container[/wpcol_1half_end]Pre-cut foils can be either: formed into a foil cap by means of a capping press; partially cut from the web or supplied in disc form (however here handling is more complicated). Pre-cut systems are usually those where conduction heating is used as the default position, the foil is located on the container and the hot metal head is pressed down to bond it onto the container. It is however relatively straightforward to replace the conduction system with induction equipment where the foil is pressed onto the container by the ambient temperature induction head then the coil is energised and the foil heated to seal it to the container. Provided the correct induction equipment is specified, significant modification to existing equipment is not usually required in order to use induction systems within this kind of machinery.
Induction sealing heads fitted onto rotary turret for high speed operation within mono-bloc filler/capper. Induction system as direct replacement for conduction equipment.
Where foil is to be die-cut and applied in one stroke, it is possible to use a tool which will punch the foil, hold it in place using a vacuum whilst transporting it directly down onto the container where the required sealing pressure and induction energy are applied in order to form the seal. This kind of system has a number of advantages, seal location is extremely accurate (results of +/-25 micron have been achieved), it allows for thin foils to be used with minimal waste and since the entire sealing process (pressure, heat & time) is controlled by the machine, a consistent sealing result is delivered on each cycle. Again, these systems can be provided in stand-alone machine format or as component parts for installation in OEM filling & assembly equipment. A wide range of foil sizes and shapes can be sealed and the required output speed can be met by using the number of heads needed to achieve the desired production rate.