Responces to Poly Pro spreading- I forgot this one.
Gabriel Beversluis
Description
Collection
Title:
Responces to Poly Pro spreading- I forgot this one.
Creator:
Gabriel Beversluis
Date:
6/15/2005
Text:
I noticed on the list serv that you are having some spreading problems with polypropylene. I need to know a few things before I may find a solution to your problem.
I would assume that the orthoses that you are making are unlined. Most spreading problems appear on these types. Lined orthoses can cause a curling problem (the exact opposite of what you are experiencing). These problems are due to the fact that the interior surface and the exterior surface of the plastic are cooling at different rates.
In the case of lined orthoses, the liner acts as an insulator and keeps the inside surface of the plastic hotter while the outside surface cools down much faster. This causes the plastic to draw inward thus producing a curling effect. The way to minimize this is to not use compressed air to cool the exterior surface. This makes the cooling differential even greater and compounds the problem. One can also make a large cardboard box and slip it over the newly made orthoses and seal up the ends. This keeps the heat inside the box and equalizes the cooling effect. Make sure that the exterior surface has cooled sufficiently to prevent any scuff marks prior to placing the box over the orthosis.
In the case of spreading like you are experiencing, the inside of the plastic is cooling at a rate faster than the exterior. In this case, heating the positive model with a heat gun and using compressed air will lessen this phenomenon. I have known some facilities that would immerse the orthosis in water to cool it down. Again, this technique should only be done after the exterior has cooled slightly to prevent any water blisters from forming on the exterior surface.
I hope some of these tips will help. Unfortunately, the O&P industry's methods of vacuum forming thermoplastics are extremely crude compared to today's plastic industry standards.
There are many variables that can affect the outcome.
I would assume that the orthoses that you are making are unlined. Most spreading problems appear on these types. Lined orthoses can cause a curling problem (the exact opposite of what you are experiencing). These problems are due to the fact that the interior surface and the exterior surface of the plastic are cooling at different rates.
In the case of lined orthoses, the liner acts as an insulator and keeps the inside surface of the plastic hotter while the outside surface cools down much faster. This causes the plastic to draw inward thus producing a curling effect. The way to minimize this is to not use compressed air to cool the exterior surface. This makes the cooling differential even greater and compounds the problem. One can also make a large cardboard box and slip it over the newly made orthoses and seal up the ends. This keeps the heat inside the box and equalizes the cooling effect. Make sure that the exterior surface has cooled sufficiently to prevent any scuff marks prior to placing the box over the orthosis.
In the case of spreading like you are experiencing, the inside of the plastic is cooling at a rate faster than the exterior. In this case, heating the positive model with a heat gun and using compressed air will lessen this phenomenon. I have known some facilities that would immerse the orthosis in water to cool it down. Again, this technique should only be done after the exterior has cooled slightly to prevent any water blisters from forming on the exterior surface.
I hope some of these tips will help. Unfortunately, the O&P industry's methods of vacuum forming thermoplastics are extremely crude compared to today's plastic industry standards.
There are many variables that can affect the outcome.
Citation
Gabriel Beversluis, “Responces to Poly Pro spreading- I forgot this one.,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 5, 2024, https://library.drfop.org/items/show/225040.
