Prepreg

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Egil
Posts: 5
Joined: Wed Nov 20, 2013 11:45 am
Location: Sweden Åre

Prepreg

Post by Egil »

My thoughts on prepreg in short.. ( I got a question in a other tread but felt it was better to start a new.)

I don't think prepregs are any good for DIY the main reasons are:

1. The prepregs I've used Needs a temp of 120deg C for 30min and needs to be kept below 123C as that's when the base melts.. To regulate that with a electrical heating blanket will be tough. The press I've used are water heated so the hole ski will hold the same temp as there are quite high flow of that water and massive amount of power, the heater is 40kW for the single stage press and 120kW for the double.

2. Depending on prepreg, but the ones used before needed ca 16bar pressure so you need a BIG press. the beams in the Langzauner are ca 50cm high and made out of 10-100mm thick plate. the newer prepregs have less flow and less glue in them so they need less pressure like 3-6bar but they need a more uniform pressure so you don't press out all glue and create dry spots.

3. they dry out if kept in room temp for a few days to weeks depending on type so you need a big freezer to stor it in.

4. Frozen materials creates condensation and if that water gets in to the pressing cycle you will delaminate your skis at first turn.
Monoskis rule!
Richuk
Posts: 1146
Joined: Sun Jan 31, 2010 9:53 am
Location: The Duchy of Grand Fenwick

Post by Richuk »

Thanks Egil - welcome to the forum!

You've made some interesting points, not sure I agree with the conclusion. A sympathetic composite supplier will send you a sample if you can make your case - a 120oC cure isn't required, we have more time on our hands. If the pre-preg does require a higher temp i.e. 100oC, then:

INSULATING THE HOSE WOULD BE A KEY ISSUE TO RESOLVE.

Uniform pressure will depend on press design, mold and cassette materials - some upgrading may be required. A solid press, tempered hardboard faced mdf mold, 3mm cassette, a four linear activators and cat-track stablisers should resolve most issues. The forum will generate a ski shaped freezer made from random stuff, if needed.

Pre pregs, or a good equivalent, can be made as required using a resin impregnator. It won't get down to 20% - nor should you try, but you will explore the technical rational e.g. optimal resin ratio, reduce waste and decrease your direct exposure to epoxy. Small scale resin impregnators aren't difficult to make, the only thing you really need to perfect is the accuracy of the final set of rollers.
Damon
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Joined: Thu Oct 09, 2008 9:14 pm
Location: Tacoma, WA
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Post by Damon »

I agree prepreg is inappropriate for skibuilding, but for only one reason: it's cost prohibitive.

There are prepreg epoxy systems designed to cure at low temperatures, and with minimal (e.g. atmospheric) pressures. Prepreg is superior to wet-layup in just about every aspect, except cost. You're also not going to find a direct replacement to 19/22oz triax. Finding a 19oz biax might be tough too. 9oz PW is most likely.

Damon
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richie
Posts: 184
Joined: Wed Jun 23, 2010 7:25 pm
Location: New Zealand
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pre-preg resin

Post by richie »

I have decided my next batch of resin I will use a pre-preg resin , but still do a wet layup with it. This resin will cure fine at my usual 60 deg cel temp and to all intents is close to identical to what I am using right now, its just extremely slow to cure at ambient temps. So the idea here is that I will have more time in my splitboard layup which is painfully complex for me and I run too close to resin gell'ing , had a few close calls. My suppliers are expert as they are the "chemists" that make this resin to their own spec's, so they can advise me precisely which is reassuring. I will let you guys know how this goes for me.

One of the surprises is that this resin is half the price of what I use currently!!!!!! STOKED.

cheers, Rich

http://adhesivetechnologies.co.nz/adrseries.html
ADR 240 Series Pre-preg Epoxy Resin:
ADR 240 is a unique system used in the manufacture of prepreg for current "state of the art" high performance composite construction. The main hardener, ADH341, offers pot-lives up to 24 hours, working times of up to 72 hours and requires curing temperatures in excess of 50º C under vacuum.
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Richard Harcourt | www.splitn2.com | Christchurch New Zealand
rich@splitn2.com | www.facebook.com/splitn2
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