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Thanks to all who responded to my request for information regarding my
question to PVA over (rigid) Foam:
Hi List Server Members
I wondering if any of you have experience in doing lamination over
foam. The main problem is the PVA bags keep on ripping whenever I try
to place them over the Foam. This is due I think to the fine specks of
foam on the carved model and the fact that the PVA back keeps on
sticking to the foam. (yes I use plenty of talcum powder) The only way
that I have had any success is by placing a couple of stocking over
the model before placing the PVA Bag. Can anyone offer any advice.
Thank you to all those who replied. It seem that the most common method
used to overcome this problem is by applying a some sieglhartz over the
rigid foam and then lightly smoothing it and placing a thin nylon sock
over it. I have tried this and it works. However I will in due time try
applying some of the other methods mentioned below.
I assume you are using rigid foam. I have always sealed the foam with
sieglhartz or any acrylic resin and smooth; fabricate a non-copressible
end
cap over the distal ankle area to prevent the bag from getting snagged.
I
imagine you are using the PVA bag over the foam to release the outer
lamination from the foam, to hollow out the leg for lightness, or
whatever.
Otto Bock has a great system for this procedure, and you should contact
their
technical department. Good luck! RLFCPO
Hi John,
We use a sheer nylon.
John Hattingh
John
Seal the foam by painting it with Siegelhartz- Otto Bock Sealing
lacquer.
The foam also releases gas for a period of time (24 hours or so) in its
curing process which may get air in your lamination layers. By sealing
the
foam and then after it has set (only takes about 10-15 minutes if you
use
a lot of promoter) lightly sand the surface with some sandpaper in order
to
get neater adherence to you lamination. That should solve your problem.
Good luck
No problem. I don’t use any PVA bags directly on my foam. After shell is
ready for lamination, mix needed amount of sealing resin (siegelhartz)
with a few drops of acetone (this will thin the sealing resin enough to
not allow tear drops forming). Paint over foam form, after drying, sand
lightly with water paper (without the water). If you don’t intend
removing the foam, laminate directly on the foam. If you do intend
removing the foam, place PVA bag on now and continue as usual.
Clive
CPO (SA)
One more thought:
Are you soaking the PVA bags in water? I am not sure what the
vendor/manufacturer (we get ours from USMC and find them to be the best
we’ve
seen) recommends as I’ve been thought only by watching techs with far
more
experience. We usually wrap the pva bag in a wet towel for 10 minutes.
This
makes it flexible enough to go over most shapes. I was also taught that
you
may simply (while holding both ends shut to make sure no water runs in)
flash
the pva bag under a faucet and hang to drip-dry. It has been some time
since
the tech that used that method did that or worked with us, but it seems
he
would hang it until dry to touch or about 5-10 minutes. This you would
have
to play with, but the towel method I am sure of as I use it myself.
Good Luck
If you are using a rigid foam , try sealing it with a resin hot mix and
the
lightly sand it smooth. Laminate over a nylon will help slide you PVA
bag
on.
Good luck
Steve
DEAR JOHN,
HAVE YOU TRIED PVC INSTEAD OF PVA BY USING ACETONE AS
A THINNER?
YOU COULD ALSO TRY LATEX RUBBER SLEEVE.
HOPE THAT GIVES YOU BETTER RESULTS!
VIKRAM CHOUDHARY.
BPO,
MUMBAI
John,
Try applying a thin layer of automotive body filler, or lightweight
polyester (Otto Bock)
putty over the urethane foam prior to your lamination procedure. I use
the edge of a strip
of 1 mm polyethylene sheet material to smooth the body filler over the
foam before it sets
up.
A light sanding of the body filler just after it cures, while it is
still warm, creates a
smooth finish. This should help to prevent perforation of the PVA bag,
and doesn’t add much
weight to the finished product.
Geoffrey Hall, C.P.
Victoria, B.C.
Dear John,
After reading your post regarding PVA and foam, I would advise you to
ALWAYS use a barrier between the PVA and the foam. We tend to suggest a
lightweight sock or even a Ladies stocking. This doesn’t create much
additional space between the Laminations, and will most certainly
protect
the PVA from the foam.
Kindest Regards,
Alister.
Try sealing the foam portion of the model with a sealing resin and then
sanding it relatively smooth. No need for a mirror finish, merely seal
the cavities. Then pull a couple of layers of nylon stockinet (or
your proposed lay-up) over the sealed surface. Choose the appropriate
size PVA bag, moisten it well in a wet towel. Should go on without
tearing with some gentle coaxing.
Enjoy!
Richard
You can also try lacquer on the foam, then one layer of fine hose. that
will
not really distort your dimensions.
good luck,
Wade Bader
Hi John,
Sprinkle some baby powder, or the like, in the PVA bag before pulling it
over the model and your problem will be solved!
Terrance Bloom
You may want to try a few things, although we mostly still use plaster
moulds,
Stoner Silicone spray, and try that direct to foam, or over a single
nylon,
then spray with stoner, that usually works good for me, lets it slide
easy.
The bag shouldn’t move or anything once taped and vacuumed.
Also, what brand of PVA bags are you using? I had a problem for a
period of
about 3 months with USMC bags breaking, that was only a few months ago.
So i
don’t know if there was a quality problem with them, and that may cause
you
some problems if you are using that brand.
If you wouldn’t mind, let me know what what you try and if you have any
luck!
I have worked through my share of problems too!
Good Luck
Troy, Pros Tech
Dear John,
Likely your foam is not sanded smooth enough. You must use 180 grit or
steel wool to smooth foam model. If you do not want to sand smooth, you
may
first size the foam with some resin, then sand lightly. Depending on
the
application, you may also use Vaseline on the foam to minimize
friction. In
any case, the foam should look absolutely smooth and all the loose
particulate should be blown from the model. If you use Vaseline, you
need
only lubricate the problem areas like sharp edges or large circumference
radius of a bulbous TT or TF model. Let me know how you come out
Regards
John Spaeth
John: I always seal the foam with seigleharz – helps keep the air
problems down, as well as
providing a smoother surface. I have pulled a nylon over, once the foam
has been sealed, so
that the PVA bag slips over it easily. I have heard of someone using
vaseline for that
purpose, as well.
Good luck.
John T. Brinkmann, CPO
John,
What sort of foam are you using? We have had consistent success with
pelite
liners. Is this what you mean? If so, I can only see one major
difference
in our lay-ups. We use a moderate coating of silicone, sprayed directly
onto
the foam, or with a nylon stocking first. The silicone does not appear
to
have any effect on the PVA bags other than to lubricate it’s placement.
Good Luck
John,
The shear stockings is good or try a larger dry PVA bag-not wet or
moist.
regards
Les
Hi John,
I have done a few laminations over low density (Rough) cad foam and
while it is a bit tricky, I managed to get a pva bag directly over the
foam. Mind you, my shapes were fairly smooth and conical, and it was
easy to get the bag over. You might want to try the (Sheer) stocking, as
this will add little to the thickness/size of the shape. Another trick
is to place a open ended sheer stocking or stockinet over the cast,
then pull the pva bag over with the sheer stocking so that the stocking
and the bag move over the cast together. You might want to give me a
ring as I could probably explain this better over the ‘phone.
Stephen Hockey
Technical Officer
La Trobe University
National Centre for
Prosthetics and Orthotics
What you need to do is mix up some resin take a paint brush and brush
the
foam so it is sealed with a light coat. Once it’s dry take some very
fine
steel wool, rough it up a little bit then you are ready to laminate.
Bill Millar C.O./C.P
Millars Orthotic & Prosthetic Inc.
–Boundary_(ID_/9f4Q3R8fUE/yKnZRyhTrg)
Content-type: text/html; charset
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Content-transfer-encoding: 7BIT
Thanks to all who responded to my request for information regarding
my question to PVA over (rigid) Foam:
Hi List Server Members
I wondering if any of you have experience in doing lamination over
foam. The main problem is the PVA bags keep on ripping
whenever I try
to place them over the Foam. This is due I think to the fine
specks of
foam on the carved model and the fact that the PVA back keeps
on
sticking to the foam. (yes I use plenty of talcum powder)
The only way
that I have had any success is by placing a couple
of stocking over
the model before placing the PVA Bag. Can anyone offer
any advice.
Thank you to all those who replied. It seem that the most common
method used to overcome this problem is by applying a some sieglhartz over
the rigid foam and then lightly smoothing it and placing a thin nylon sock
over it. I have tried this and it works. However I will in due time try
applying some of the other methods mentioned below.
I assume you are using rigid foam. I have always sealed the foam
with
sieglhartz or any acrylic resin and smooth; fabricate a non-copressible
end
cap over the distal ankle area to prevent the bag from getting snagged.
I
imagine you are using the PVA bag over the foam to release the outer
lamination from the foam, to hollow out the leg for lightness, or whatever.
Otto Bock has a great system for this procedure, and you should contact
their
technical department. Good luck! RLFCPO
Hi John,
We use a sheer nylon.
John Hattingh
John
Seal the foam by painting it with Siegelhartz- Otto Bock Sealing lacquer.
The foam also releases gas for a period of time (24 hours or so) in
its
curing process which may get air in your lamination layers. By
sealing the
foam and then after it has set (only takes about 10-15 minutes if you
use
a lot of promoter) lightly sand the surface with some sandpaper in
order to
get neater adherence to you lamination. That should solve your
problem.
Good luck
No problem. I don’t use any PVA bags directly on my foam. After shell
is
ready for lamination, mix needed amount of sealing resin (siegelhartz)
with a few drops of acetone (this will thin the sealing resin enough
to
not allow tear drops forming). Paint over foam form, after drying,
sand
lightly with water paper (without the water). If you don’t intend
removing the foam, laminate directly on the foam. If you do intend
removing the foam, place PVA bag on now and continue as usual.
Clive
CPO (SA)
One more thought:
Are you soaking the PVA bags in water? I am
not sure what the
vendor/manufacturer (we get ours from USMC and find them to be the
best we’ve
seen) recommends as I’ve been thought only by watching techs with far
more
experience. We usually wrap the pva bag in a wet towel for 10
minutes. This
makes it flexible enough to go over most shapes. I was also taught
that you
may simply (while holding both ends shut to make sure no water runs
in) flash
the pva bag under a faucet and hang to drip-dry. It has been
some time since
the tech that used that method did that or worked with us, but it seems
he
would hang it until dry to touch or about 5-10 minutes. This
you would have
to play with, but the towel method I am sure of as I use it myself.
Good Luck
If you are using a rigid foam , try sealing it with a resin hot mix
and the
lightly sand it smooth. Laminate over a nylon will help slide
you PVA bag
on.
Good luck
Steve
DEAR JOHN,
HAVE YOU TRIED PVC INSTEAD OF PVA BY USING ACETONE AS
A THINNER?
YOU COULD ALSO TRY LATEX RUBBER SLEEVE.
HOPE THAT GIVES YOU BETTER RESULTS!
VIKRAM CHOUDHARY.
BPO,
MUMBAI
John,
Try applying a thin layer of automotive body filler, or lightweight
polyester (Otto Bock)
putty over the urethane foam prior to your lamination procedure.
I use the edge of a strip
of 1 mm polyethylene sheet material to smooth the body filler over
the foam before it sets
up.
A light sanding of the body filler just after it cures, while it is
still warm, creates a
smooth finish. This should help to prevent perforation of the
PVA bag, and doesn’t add much
weight to the finished product.
Geoffrey Hall, C.P.
Victoria, B.C.
Dear John,
After reading your post regarding PVA and foam, I would advise you
to
ALWAYS use a barrier between the PVA and the foam. We tend to
suggest a
lightweight sock or even a Ladies stocking. This doesn’t create
much
additional space between the Laminations, and will most certainly protect
the PVA from the foam.
Kindest Regards,
Alister.
Try sealing the foam portion of the model with a sealing resin and then
sanding it relatively smooth. No need for a mirror finish, merely
seal
the cavities. Then pull a couple of layers of nylon stockinet
(or
your proposed lay-up) over the sealed surface. Choose the appropriate
size PVA bag, moisten it well in a wet towel. Should go on without
tearing with some gentle coaxing.
Enjoy!
Richard
You can also try lacquer on the foam, then one layer of fine hose. that
will
not really distort your dimensions.
good luck,
Wade Bader
Hi John,
Sprinkle some baby powder, or the like, in the PVA bag before pulling
it
over the model and your problem will be solved!
Terrance Bloom
You may want to try a few things, although we mostly still use plaster
moulds,
Stoner Silicone spray, and try that direct to foam, or over a single
nylon,
then spray with stoner, that usually works good for me, lets it slide
easy.
The bag shouldn’t move or anything once taped and vacuumed.
Also, what brand of PVA bags are you using? I had a problem for
a period of
about 3 months with USMC bags breaking, that was only a few months
ago. So i
don’t know if there was a quality problem with them, and that may cause
you
some problems if you are using that brand.
If you wouldn’t mind, let me know what what you try and if you have
any luck!
I have worked through my share of problems too!
Good Luck
Troy, Pros Tech
Dear John,
Likely your foam is not sanded smooth enough. You must use 180
grit or
steel wool to smooth foam model. If you do not want to sand smooth,
you may
first size the foam with some resin, then sand lightly. Depending
on the
application, you may also use Vaseline on the foam to minimize friction.
In
any case, the foam should look absolutely smooth and all the loose
particulate should be blown from the model. If you use Vaseline,
you need
only lubricate the problem areas like sharp edges or large circumference
radius of a bulbous TT or TF model. Let me know how you come
out
Regards
John Spaeth
John: I always seal the foam with seigleharz – helps keep the
air problems down, as well as
providing a smoother surface. I have pulled a nylon over, once
the foam has been sealed, so
that the PVA bag slips over it easily. I have heard of someone
using vaseline for that
purpose, as well.
Good luck.
John T. Brinkmann, CPO
John,
What sort of foam are you using? We have had consistent success
with pelite
liners. Is this what you mean? If so, I can only see one
major difference
in our lay-ups. We use a moderate coating of silicone, sprayed
directly onto
the foam, or with a nylon stocking first. The silicone does not
appear to
have any effect on the PVA bags other than to lubricate it’s placement.
Good Luck
John,
The shear stockings is good or try a larger dry PVA bag-not wet or
moist.
regards
Les
Hi John,
I have done a few laminations over low density (Rough) cad foam and
while it is a bit tricky, I managed to get a pva bag directly over
the
foam. Mind you, my shapes were fairly smooth and conical, and it was
easy to get the bag over. You might want to try the (Sheer) stocking,
as
this will add little to the thickness/size of the shape. Another trick
is to place a open ended sheer stocking or stockinet over the cast,
then pull the pva bag over with the sheer stocking so that the stocking
and the bag move over the cast together. You might want to give me
a
ring as I could probably explain this better over the ‘phone.
Stephen Hockey
Technical Officer
La Trobe University
National Centre for
Prosthetics and Orthotics
What you need to do is mix up some resin take a paint brush and brush
the
foam so it is sealed with a light coat. Once it’s dry take some
very fine
steel wool, rough it up a little bit then you are ready to laminate.
Bill Millar C.O./C.P
Millars Orthotic & Prosthetic Inc.
–Boundary_(ID_/9f4Q3R8fUE/yKnZRyhTrg)–
