Vaccum Bagging

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
dimensional.
AWEM
Reply to
Andrew Mawson
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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.
Reply to
Mike
Hmmm. Sot vacuum cleaners may not be ideal for powering vacuum tables either.
Just goes to show that vacuum cleaners suck, I guess...
Regards, Tony
Reply to
Tony Jeffree
have got a new good quality vacuum pump if you need to borrow not being used brought as its going to be useful one day
Reply to
Andrew Bishop
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.
Reply to
Peter Fairbrother
message
oomph do
furnace
Thanks Andrew but I have one 'under the bench'
AWEM
Reply to
Andrew Mawson
oomph do
furnace
vacuum,
consolidate
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.
AWEM
Reply to
Andrew Mawson
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 bit...
Dave
Reply to
dave sanderson
vaccum
quite
cables.
Dave,
I've just laid up one on a positive mould - waiting to see how it comes out with fingers crossed.
AWEM
Reply to
Andrew Mawson
don't know about the process your using but when I did some hub centres for a car I had to leave for about 24hrs before removing from mould as they can go out of shape if there still green
Andrew
Reply to
Andrew Bishop
centres for
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 perfume
AWEM
Reply to
Andrew Mawson
That was fast, I assume you are using something like isopon resin, else Im well out of touch with green times.....
Dave
Reply to
dave sanderson
message
polish,
together
sisters
their
Dave,
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 (
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) 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
AWEM
Reply to
Andrew Mawson

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