Had a go at vacuum bagging at the weekend. I've had all the equipment (off Easy Composites of course) for six months and made the mold 3 months ago and at last got round to it.
I'm making a carbon fibre bumper for a 1960's car (Hillman Imp), took a mold off a good steel one. Unfortunately the bumper actually wraps back on itself at the ends so it meant either a two or three piece mold. I went for a 3 piece so I could make quarter bumpers if i want. I added approx 30mm around the outside of the bumper .
 I used easy-lease release agent, six coats + 1 one hour before molding. GC50 epoxy compatible gel coat brushed in followed by 1 layer of carbon cloth, one layer of class cloth and then 1 layer of carbon. I added a strips of carbon tape in the area of the mounting bolts.
  The process went quite well, but I had a few problems when i came to release. One side came out well with a little bit gel coat stuck in the mold, the other side left most of the gelcoat attached to the mold. The bumper seemed quite dry with the layers delaminating as I removed it from the mold.

Reasons (i think) for the problems

1, - I had the thro-bag connector sitting on the perforated release layer on the part - bad move, it left marks in the carbon and sucked up resin, should i put it off the mold area ?
2 - I think I had miles to much vacuum, I read 20% vacuum, which I read as 20% off full vacuum for some stupid reason which meant I had the bag set 80% vacuum. The combination of this and mistake 1, meant that the pump was sucking up resin through the tube. This probably explains the dry result and the lack of adhesion to the gelcoat. (and a bunged up valve!!)
3. The resin (EL2) is approx 4 years old,left over from a previous job - could it have gone off?
4 The carbon cloth is some I was given 15 or so years ago, unknown thickness and origin, not sure if this matters?

Apart from this it went well :-)
For my next attempt, I will move the thro-bag connector to somewhere off the actual mold area, maybe add a ledge at the side for it.
Reduce the vacuum !!!!. Should I start at high vacuum  to initially bed everything down and the reduce it or just set the regulator to 20 % from the start ?
I think I will make it all from carbon to help with the delamination, or was that just because I sucked most of the resin out. 

Sorry for the ramble, but do people think  I have identified most of my problems and my next go might be better, or I'm talking rubbish (won't be the first time)
Cheers
Eric

You can put a pad of breather under the through bag connector to stop any print through.

Sounds like you definitely sucked out too much resin.  A dry laminate is more likely to delaminate than one properly wetted out one.

4 year old resin will be 3 years out of date so well past its best.  Assuming it cured fine, you have been quite lucky.  The hardeners tend to degrade by  slowing down.  This means you may have demoulded it slightly green which won't have helped with demoulding.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks Guys. I'll get some new resin and sort out an area for the breather and give it another go. I'm not beaten this easily.

I don't know, why Steve never had problems with dry areas, but the international consensus is, that you don't use full vacuum in a wet lay vacuum bagging process. This would degass your resin inside the fabric, where it is unlikely to escape. And there will be air in your resin, at least because you used a brush. And degassed air inside the resin is what is called "pulled to much resin out" or "dry fabric".

My question is: if you are able to achieve a good vacuum, why don't you infuse the part? Imho it is easier, in the end faster and will give a perfect finish. At least much more likely, than a wet layup would.

Hi Steve,

We haven't actually done a video on Vacuum Bagging assisted wet lay (as opposed to Resin Infusion or PrePreg) which is why you probably haven;t seen mention of it in a tutorial, however, in most circumstances we recommend a maximum vacuum level of 20-25% for this kind of process (hence why the VB Starter Kit is offered with a vacuum regulator); the theory being that with higher vacuum levels, resin is drawn away from the surface of the mould, through the perforated release film and into the breather/soaker. Different forms; laminate thicknesses, materials, etc. will require varying levels of vacuum pressure so there is no hard and fast rule.

A 2:1 fibre:resin ratio and perfect surface finish with wet-lay vac bagging? That would be 66% fibre and 33% resin. Given most OOA pre-pregs are around the 40% resin mark, as is resin infusion, I am somewhat dubious - however if that is the case, I think you have made a mistake by switching to pre-preg!