Re: Vacuum assisted casting

Re: Vacuum assisted casting

M. Britt Spears CPO

6/26/2004

Hello list,

I too have been reading the various posts about vacuum assisted casting. When I was at Northwestern last month, Mark Edwards-the instructor, was explaining a new technique that was being developed there utilizing sand under vacuum. It would be nice to get his input on the subject, explaining their respective reasoning and technique including the equipment and tools needed.

Thanks,
M. Britt Spears CPO

Carstens < <Email Address Redacted> > wrote:
Dear listmembers,

I have been reading the discussion about vacuum casting and I can't help and
express my opinion about it to the list. Please prove me wrong but in my way
of viewing vacuum assisted casting I come to the conclusion that it is only
beneficial if the liner over which the cast is applied is either
compressible or if it has flow-properties as e.g. the TEC liner has (under
pressure in one direction it will flow to the direction with lesser
pressure, i.e., it will elongate when compressed radially). If the cast is
made over a regular silicone liner, for instance, vacuum casting is not
doing anything at all but compressing the layers of plaster of Paris (or
other cast material) and the liner. Why do I think this is so? Well, what do
we do when we apply vacuum over a cast using a flexible sealing layer? We
draw air out of the space between said flexible sealing layer and the
residuum (liner). This happens evenly all around. What pressure do we have
to compress the residual limb (and this is what we hope to achieve, don't
we?)? The only pressure that does compress the residual limb is the
atmospheric pressure and that has been there anyway to start with before we
applied any suction action! We have not created any additional pressure on
the residual limb by merely sucking air out of a gap between layers
sandwiched on the limb.
The casting systems out there wich are inflated (like e.g. the ICECAST or
the like) work differently for they do create additional pressure on the
residuum while the cast sets. Thus, those inflatable systems really do
achieve the desired effect of compressing the limb evenly all around while
casting.

I felt it might be worthwhile to point out what I think is a widespread
misconception. In case there are arguments to prove me wrong, I am looking
forward to learning about them and I am open to discuss the issue in more
detail.
Please excuse my english, but it is not my mother tongue.

Felix Carstens
Dipl.-Ing., MSE, CPO (D)
CO-MET GmbH
Germany