Hi all,




My name is Craig and live in Cambridgeshire, Been looking at this forum a few weeks now and seems like a great place to learn as im a newbie to composites.

Really enjoying looking at what everyones doing.

Im trying to build a pair of wheel spats which id eventually like to do in carbon. So far ive made a plug out of mdf and foam and taken a 2 piece mould from it which im quite pleased with except I now wish id made the flanges larger. 

Over the easter break ive had my 1st attempt at doing a vacumm bag layup. my layup consisted of 4 layers of 200g woven glass cloth, pelply then breather cloth then bag. For a 1st go im quite pleased as the part came out of the mould easily but to my un trained eye, it looks like my parts are starved of resin. Also the bag connector has left an imprint in the surface.

Time for the questions,

Am I pulling too much vacumm?, is my bag connector in the wrong place or is this also due to too much vacumm?. From what ive read I guess I might need to invest in a regulator?. I left my pump running over night which I was a little dubious about, is this correct?.

Am I right in thinking that it if try using infusion instead then the pump is turned off after infusion is complete.

Im sorry for all the questions on my first post!!.

Any help and advice is greatly appreciated.

Cheers

Craig    

It's difficult to pull too much vacuum. Ideally, you want to place the connector off the part, every time the connector has been on the part, it prints through

Thanks for your reply ajb100, Little confused about vacumm pressures, I was under the impression it was possible to bleed too much resin out of the stack ??. Assuming I manage a perfectly seal bag, how do I judge when to turn off the vac pump? On my first couple of trys ive left the pump on overnight and ended up with resin in my catch pot. I know its difficult to judge from my poor photos but does my laminate look dry to you?

Again Thank you for your help.




Craig

When I vac bag I tend to work the resin in really well and get as many bubbles out as possible on the first couple of layers and make it really resin rich then just normal resin quantity for most of the others, then an almost dry layer as the final one, then peel ply, bread wrap then breather that way when the vacuum pulls it doesn't starve the mould surface layer. You're not going to pull huge amounts of resin out of the stack so don't worry about that too much (unless you work on 40% fibre 60% resin or higher and the carbon is swimming!!)

What you have to think about when vac bagging is if you have a perfectly sealed bag then you should use the pump to bleed out the resin then once you are happy with that (but remember a bit will still bleed out into the breather fabric), clamp the pipe then you will get the compression from the vacuum from the air pressure on the bag. keep the bag sealed until the resin has cured

Welcome along!  Nice spats, what are they from?

WRT your mouldings, they dont look too bad at all, you should be pleased.  A nice coat of paint and the mark from the vac fitting will dissapear.  As said above you can avoid this by having the vac fitting off the moulding.  I use a breach unit in mine for easy connection.  When I wetlay I layup and (as suggested) work the first layers in with resin pretty well.  The perf release film will let some resin through into the breather.  If you're worried about too much resin you can use multiple layers of breather fabric to absorb it.  It certainly shouldn't be reaching your vac line.

One trick I use with moulds with small flanges is to use an envelope bag.  If you do this you can run a strip of breather from the mould into an open area of bag and have the vac fitting there.  No risk of imprint and there should be no resin anywhere near the vac line at all.  If you dont get a perfect seal and you end up running the pump overnight you can get pin holes in the surface.  It doesn't mean the laminate is too dry, you just have to deal with the surface finish.  If you're painting then its no trouble at all.  If you want that nice carbon weave pattern it can be a bit awkward but its not too bad to deal with.

Thanks for your help ChrisR and FLD its much appreciated, its all a bit of a steep learning curve for me but im enjoying it!!. The spat plug was just a home made foam and glass cloth finished in 2k. My long term project is building a little single seat plane called a corby starlet, mostly built of spruce but I want to do these wheel spats cowl etc in carbon as every gram of weight saved helps.

pretty sure the vac bag was leaking on the first attempt's, last night I played around just trying to get good vacuum round the mould with no layup inside it. After a fair while hunting for leaks I found the bag had been perforated from a tiny spike of glass on the rear face of the mould.




After looking again at my trial parts, it looks like the first layer of cloth has ended up in contact  with the mould with no resin underneath. Will this always case if I vac bag without first applying a gel coat. These parts will end up being sprayed so finish out of mould isn't top of list, more best achievable strength/weight.     

What bagging material are you using? this "glass shard", is that a shard of cured resin/glass, broken glass, or just a fibre from CSM or alike?

I used to have problems with getting a good seal but now when it comes to bagging up I brush down, hoover then use a rubber mat (garage flooring tiles, you know the ones you can get from halfords or Aldi) then unwrap the vac bag material and go from there. cleanliness is key to a successful vac bag. I also keep my bagging mateial wrapped up in 2 layers of bubble wrap and a sheet of thick plastic (builders DPM)

If you are envelope bagging you need to make sure the back of the mould is smooth and free from sharp edges etc. I go over the back of the mould with the orbital sander to remove any "spikes". Also make sure the edges of the flange are rounded off, I put gaffer tape over the edge to soften it a bit. The smallest sharp edge can puncture the bag when you pull vac. You can also cover the back of the mould with breather cloth, although this can soak up resin and be a pain to remove. If you put some PVA on the back of the mould this will make it easier to knock of any resin that has tracked onto the back of the mould, these lines of resin can puncture the bag when you come to use the mould again.

Warren

Carbon Copies Ltd

[quote]ChrisR (23/04/2014)

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What bagging material are you using? this "glass shard", is that a shard of cured resin/glass, broken glass, or just a fibre from CSM or alike?





the bagging film is from EC, the 'glass shard' was just a tiny piece of cured resin/glass on the back of the mould. Ill do as you guys suggest and give the back of the mould a good rub down to make it smooth and round of the flanges/cover with tape.

Cleanliness of my work shop wasn't really given a thought, Ill have to have a good 'stop it and tidy up'

Ill report back after I've had another go.

 cheers

craig

Hi all,

Just pulled my first attempt with carbon out of mould, well chuffed. Lay up consisted of 1 layer of 201g , one of 375g and then another 200g piece in centre to spread loads of mounting point. weighs 156g as is. Seems stronger than needs to be so might play around with lay ups to try and get weight down further.

This time I used bread wrap as suggested and made it much easier to remove breather cloth, still need to practice getting a fully sealed vac bag!!.