Four Different Tips on How to Improve Vacuum for Plastic Moulding

Tip 1. Adding orthotic nylon overtop the cast.

By adding an orthotic nylon overtop over the cast and continuing over the vacuum pipe, it creates a wick as well as prevents hot plastic choking off the airflow once the vacuum is turned on.

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Tip 2. Taking a hot piece of plastic scrap to seal a leak.

Sometimes a hole in the plastic can occur during thermoplastic mouldings. Often this happens when there is not a sufficient seal between the cast, and the vacuum pipe. A tip to fix this leak is to wrap a piece of excess hot plastic around the pipe.

Tip 3. Adding a wick on the front of the cast (e.g., AFO - where the strip is out of the trimlines).

Another trick to achieve vacuum is to place a wick that goes direct against the cast (outside of the trimlines), then placed into the vacuum pipe. This way air will be further drawn out from underneath the plastic.

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Tip 4. Perforating a cast during moulding setups.

By drilling holes diagonally in the cast, it ensures airflow reaches within trimlines when draping and therefore reduces risk of vacuum being cut off.

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Tech tips by Mihai Pacurar, 2013, Dominique Gauthier-Plante, 2015, and Tia McQuarrie, 2018.

Thanks to Sick Kids Hospital for this technique.