Anyone done any vaccum bagging of fibreglass ? If so how much oomph do
I need? Are we talking Aquavac type sucking or an actual vaccum pump?
I want to make some protective shell covers for the induction furnace
cable cannectors to keep fingers off and they will end up quite three
All you are doing is consolidating the layup, won't stippling with a
brush and use of a metal washer roller suffice? You will of course
end up with a layup heavier than it could be and of less strength but
does it really matter?
When professionally producing items using prepreg (essentially pre
catalysed resin soaked fibre in "dry" form) it's normal to aim for a
minimum of 29" of mercury, or 30mb absolute, but unless you are aiming
for an ultra thin low resin fraction layup and curing in an autoclave
then much less will be ok.
You do realise that vacuum bagging will require a release layer/peel
ply, bleeder cloth and the vacuum bag ? None come particularly
cheaply, minimum orders for these could easily be approaching the
price of a reasonable (aircon service) vacuum pump.
Another approach is commonly used in wood veneering that uses an old
fridge compresssor producing around half an atmosphere of "suck" with
an air bleed to avoid stall,
Forgot to mention, another problem with the vacuum cleaner approach is
the motor usually relies on airflow for cooling.
Depends - if you are trying to get excess resin out through a peel layer
into an absorbing layer then you don't need or want a very high vacuum,
about 8 psi is okay - if you are trying to get air out of and consolidate
prepreg then a high vacuum is needed.
Its the shape - imagine an open box 13.5" x 8" x 2" with 4 half rounds
of 1.5" diameter sticking out of the long side, there is a flange
round the edge so two of these can clamp together round four cables.
I'll try it just laying it up, and get more exotic if I cannot get the
glassfibre to stay in the odd shape.
You could try making a positive mould out of building insulation (blue
foam), complete with all the lumps and bumps you need. then layup over
it, and once cured 'melt' the foam out using thinners. Its quite a
quick technique for awkward shapes, and it doesnt sound like you need
'showroom' finish on the gel coat side. One thing to watch is iirc
polyester resin attacks the foam (not certian about that but pretty
sure), Ive only use the technique with West system epoxy.
For very small parts ive used a pressure cooker and 'roasting bags',
just squeeze out as much air as you can, seal the bag and cook for a
Success - I made a positive mould from plywood and polyfilla, a bit of
surreptitious 'fast drying' in the oven at 50 deg C, a couple of coats
of aerosol paint and a good waxing with a beeswax furniture polish,
and I've been able to pull two shell moulds off today that are fit for
purpose (if not entrants to the beauty competition). They fit together
nicely and even (phew!) match the spacing of the cable connectors that
I'm covering up. A quick run at 75 deg C in the oven has nicely cured
them, but I did have to confess to the wife about the Resin sisters
(Polly and Ester) being in the house today as she could smell their
The shells were green / floppy in about an hour and able to come off
the mould and be trimmed to size. I then left them for an hour and
then cooked them in the oven for perhaps 15 mins and allowed them to
cool on a flat surface. Then drilled them for the retaining bolts and
fixed them in place, so any further warpage would be resisted.
I used materials from Bondaglass-Voss as they are in easy driving
distance and I was in a hurry, but had I had time to wait for a
delivery I would have gone to CFS (
) who are
much cheaper. I bought much more than I needed for this job as it's
handy stuff to have on the shelf, so my Bondaglass price was £70. I
did a comparison from CFS and it would have come to £49