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Inspired by Dr Kazuo Hishinuma's standard text, published by DesTech, Heat Sealing. Technology and Engineering for Packaging, Principles and Applications. For the Jaws Heat Seal app see HSC-J

© Copyright 2013 Abbott Apps
Induction Heat Seal Calculator

This is a brief summary of the app. For more details read the User's Manual.

Note: For complicated numerical reasons the app is relatively slow on something like an iPad. Choose short times and relatively low powers if you are working on a hand-held device

You have a Cap and a Container made of materials of your choice. In between you have an optional Wax layer, a layer of Aluminium and a Heat Seal layer which is also a material of your choice. For numerical reasons the thicknesses of these layers are set in steps of 4μm - if it allowed 2μm resolution calculation times increase by a factor of 4! You can choose the melting point of the wax.

You are heating the Aluminium via induction. This depends on the Power setting and also on the diameter of the Cap. If you double the Diameter you reduce the effective power by a factor of 4. The induction time is t-Heat and should initially be kept short till you have sorted out the other parameters. If you want to follow the cooling behaviour, set a cooling time t-Cool) of maybe 1sec to get an idea of what's involved and the time it takes for each calculation When you click the Calculate button (these thermal diffusion calculations take a little time so you can't get instant feedback by moving the sliders - and they are slower for Induction than for Jaws) you get a graph showing the temperature versus time at the point where the Heatseal layer meets the container, as well (above it) the temperature in the Al layer. Moving the mouse over the graph gives you a readout of time and temperature

As we are taught by Hishinuma, it is vital to know TSeal and TBad. These are shown on the graph. The temperature should rise to a little above TSeal in the timescale of your process window, but should not have a chance to rise to TBad if you extend your process time for some reason.

The diagram on the left shows the temperature distribution top to bottom from Cap to Container, with clear jumps at the boundaries between polymers (marked with horizontal dashed lines) because of their different thermal properties. The diagram is colour-coded through time - violet is short time and red is long time. Moving the mouse gives you distance and temperature and if the mouse is over a line it indicates the time as well. The maximum temperature of the graph is set by GMax.

The model has to calculate the heat dissipating to at least 500μm of Cap and Container. The graph shows only the nearest 12μm of each. The large heat loss into Cap and Container is a key aspect of induction heating. Some numerical tricks are used for the 500μm of Cap and Container gaining a lot of speed an losing only a little in precision.

The choice of polymers dictates their thermal conductivities, heat capacities, densities and MPts. Where a polymer is followed by, say :105 that means that the effective melt temperature is 105°C (221°F). The polymers are further distinguished with a designation of N for Narrow melting range and W for Wide melting range. Modern heatseal polymers tend to be a wide melting range which makes the set-up less critical.