Responses Thermoforming over Duraflex

Responses Thermoforming over Duraflex

Cheryl Lewis

4/29/2010

Hello All,

 

Thanks to everyone who responded - Once again this forum has answered my question quickly and with some tech tips thrown in! Thanks to Paul P. for continuing this important service.

 

I rec'd 18 responses. 11 suggested using a PVA bag - This was the technique I had been trying to remember as an alternative to the acetate. It didn't come to mind because I don't actually have PVA bags on hand. I have just opened an orthotic clinic and haven't had the need to order PVA bags - I guess I do now!

 

I am interested in the Hosmer product someone recommended - I like the paint-on idea but I am unsure of the toxicity. Treated nylons also are an option. Here is a list of most of the responses - I left out the use a PVA bag responses unless they had additional tech tips....


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We use a polyethylene dummie boot. It's cheap, fast, and the finished
product is very attractive.

 
 
Try a pva bag. Do not tie-off the proximal end. Cut it just over the trim lines and be sure to have a nylon under the bag to wick air. Making very slight pin holes in the bag make for extra vacuum ( mind you there will be tiny bumps in the latter pulled plastic). Tie off bag at toe out of trim lines. Sometimes the moisture in the bag can cause odd ripples only on the inside of pull, nothing major. To deter this as much as possible, i dry the bag out a little with a heat gun. Beware this will cause your bag to shrink...possibly into the trim lines. Good luck

 
 
Have you tried a treated nylon? The bulk nylons are sold treated and
untreated. We find the treated won't adhere to the AFO in the second pull.
 
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We remove the duraflex and place 1/8 aliplast over the mold before pulling the co-poly. That works well.
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I use puff dummies. You might try something different. I have had remarkable success with simple microcell puff inner boots. They are easy to make, soft, and hold up amazingly. I've never had to replace one. The kids grow out of them first. Call if questions.

 
Be sure to visit OandPtech.com for technical ?'s To answer your ?, have you tried a PVA bag? More details at OandPtech.com
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call hosmer. they have parting agent for plaster molds that my C-Fab is using very successfully.

 
 
We always pull a PVA bag over the SMO, and then vac over that. It's a pain
sometimes to pull the bag if you have a very large foot or very small one.
Just make sure you get all of the wrinkles out of the PVA bag, and be
careful not to tear it!!

did you try a wet then dryed PVA bag?
you can perforate for vac supply.
 

We have used a PVA bag similar to a prosthetic lamination as a
separator to keep the proflex from getting distorted from the heat of
the plastic. We also drop the temp slightly and use a bleeder valve to
decrease vac pressure slightly. The edges thin a little but it's better
than embedding the nylon into the proflex(or duraflex). We have also
tried the pelite dummy but it's never a complete match to the original
and difficult to finish out.
Good Luck
  When I use an inner PVA bag to laminate I always spray the inside with silicone to help ease positioning of the bag over the mold and this really helps.
 
      There are paint-on mold release waxes that can be applied to molding applications like you are attempting, however the solvents necessary to liquefy the wax are toluene and the like. If using acetone is an objectionable chemical to you, then the solvents in parting agent waxes would most likely be even more so.
 
     There is also a parting agent which is a spray-on or brush-on liquid PVA. It is usually a bright green color so that operator who applies to the mold it can visually determine how well the mold has been covered. The downside again is the solvents contained within the liquid PVA.
 
     One last thought. If you try the PVA bag technique there may be some bridging of the bag as you won't be able to place it under vacuum before the pull. I would suggest that once the PVA bag is supple and in position to facilitate your final pull of plastic immediately rather than letting the PVA bag dry and harden. This way the outer layer of hot plastic can easily draw the supple inner PVA bag into any nooks or crevices with little or no resistance or loss of contour. You should even be able to pull a treated nylon over your PVA bag to help facilitate wicking without fear of fabric weave imprint on your softer plastic.
 
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We use a pva bag it works great just pull it over the smo or inner boot put a nylon on and vacuum form i like to use air to cool where the edge is so it doesnt flow hope this helps
 

 


Cheryl Lewis BSc(HK), CO(c)

Certified Orthotist
519-436-9670 CK Ortho Inc

 
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