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Trapped Air !!
2

Trapped Air !!

Trapped Air !!

(OP)
Folks,
I am working on a project to produce a prosthetic product for trans-tibial amputees (below knee)

The product is tapered in the length direction and closed at the smaller end. It is circular in cross-section and thin-walled (5mm). It is approx 500mm in length and the larger outer diameter is 150mm (approx). A cross section has a 'U' shape.
  
A fabric is placed over the core of the mould and a soft elastomeric material is injected in through the bottom. For this stage there is no air evident in the product. The product is then removed from the mould and ‘ turned inside out’. It is put back on the core, the mould is closed and the product is re-formed with the fabric on the outside of the product. This is achieved by heating and then cooling the core.
 Everything works fine, except for a small amount of air, which is trapped between the core and the product as it is turned. This manifests itself as a few air bubbles on the inner surface of the product. I have produced a number of products and all have this air bubble, regardless of how much I message the product and try to work the air out. I have even tried putting a small flexible pipe between the core and the product and drawing a vacuum but to no avail.

Any suggestions greatly appreciated!!

Speedy

RE: Trapped Air !!

I worked on a  product where all the materials (resin and cloth) had to be vacc'ed before and during the moulding process. In the case of the resins we also zapped them with ultrasonics to speed the de-gassing process. I only saw the proto version of this close up, in production all the resins were handled in pressure tanks.

Oh, it might be moisture , not air - make sure everything is hot and dry as well as free of air.



Cheers

Greg Locock

RE: Trapped Air !!

This is a left field response but is there a chemical additive that can scavenge the air when heat is applied?

RE: Trapped Air !!

(OP)
Guys,

Thanks for your help. We managed to solve it. The fabric was locking in one direction which created folds in the gel when it was turned. It was within these folds that the air was trapped. We changed the fabric and EUREKA.

Speedy.

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