Composites Central

Go Back   Composites Central > General Composites Discussions > Composites Talk

Reply
Old 02-26-2015, 08:11 AM   #1
pontiackid73

Member
 
Join Date: Feb 2015
Location: IL
Posts: 13
Thanks: 0
Thanked 0 Times in 0 Posts



Default slightly better then newbie looking for component and layup advice

Hello everyone,

I am new to this forum but will be on here quite often as I am doing a lot of experimenting and part production in the near future. A quick background on my Composites experience is I Did a fair bit of both carbon fiber and glass layups while I was on my college's Formula SAE team. I made seats, intake manifolds, bodywork, other support structures ect. All that I know was self taught through books and trial and error while i was in school. Now I'm out and working as an engineer at a mechanical contracting company in the Chicago IL, USA area but Composites is a passionate hobby of mine more specifically geared towards race cars which is my other passion.

Now that all that is out of the way I have plenty of questions and am looking for help. While I was laying up parts for the FSAE team we had minimal tools so all the components were either wet lay up or wet layup then vacuum bagged. Honestly none of the parts I have made never really gave a satisfactory surface finish and I would like to improve upon that.

I did a few basic wet layup vacuum bag pieces in my garage on a sheet of plate glass over the last few days and they have all ended up with that surface porosity on the glass side where you get tiny pinholes where the strands cross each other.
My materials are:
2x2 twill 5.7oz carbon fiber
standard peel ply mesh
2 layers of breather cloth
standard vac bag film
U.S. Composites Epoxy Resin with medium hardener
surface prepped with 2 coats paste wax buffed on and off by hand

Something I should mention that i noticed about the actual bag material is it is very stiff as in there is little stretch to it. The last bag system I used had plenty of stretch and would conform to just about any shape. Not sure if that effects anything.I went with a resin rich mix the first time and the breather was fully wetted out when under vac, the second run was about a 55:45 ratio by weight of carbon to epoxy. Both netted the same pinhole surface finish. It is my understanding from reading some of these posts that that is simply just what happens with a wet layup vacuum system and i will have to clear the parts and do a significant amount of polishing to get the surface finish right. I have also tried laying thick coat of resin on the glass first then laying the first layer of carbon down, and i tried the opposite of laying the carbon down first the applying resin. All cases end up with the same ugly surface. In the past I have tried degassing the resin and still the result was the same.

I am not sure if It is the resin or technique that I am using that is wrong but I would like to rectify it. I also plan to experiment with infusion in the near future. I am not opposed to buying and trying different things, I know that starting up and getting a process down costs money and time. If you can recommend other epoxy systems or good sites that offer infusion systems/ materials It would be appreciated. Preferred that they are in the USA. I have only used US composites as they were a sponsor of our FSAE team in the past and that all that I really know of at the moment.

My ultimate goal is to make structural composite components for drag racing applications but that is a long way away. I want to get the simple things down first like making a trunk lid or door consistently well with a good process. I have a long way to go but i figured all the expertise here could help show me how uninformed I actually am haha. Thanks for all the replies in advance.
pontiackid73 is offline   Reply With Quote
Old 02-27-2015, 05:12 AM   #2
fossconcepts

Member
 
Join Date: Aug 2013
Location: Idaho, USA
Posts: 33
Thanks: 1
Thanked 2 Times in 2 Posts



Default

I use US composites resin and find it to work nicely for what I do. I mostly do infusion, but I occasionally do wet layup and then vacuum bag. I used to have the exact same problem. And I fought it for quite awhile. What is likely happening is that your vacuum is pulling all of the resin from the surface. I bet your parts are very strong and light. To get a nice finish, what I have found to work is pull full vacuum at the start, and then lower the vacuum at the end. I don't have a gauge, so I don't know the exact pressure I reduce to, but I definitely reduce the pressure significantly. With some testing you can get a nice surface finish without adding too much resin to the parts.

I also got started with composites in college in FSAE. Great to see others on here!
__________________
http://fossconcepts.com/
fossconcepts is offline   Reply With Quote
Old 02-27-2015, 10:46 AM   #3
pontiackid73

Member
 
Join Date: Feb 2015
Location: IL
Posts: 13
Thanks: 0
Thanked 0 Times in 0 Posts



Default

When you say you reduce the vacuum at the end what sort of timing are you talking about? The end being the relation to the gel time of the resin?

Also how large of a part have you done with infusion using that resin? Im looking to do an entire car hood which is like 4'x4'. Did you have to heat up the resin to change the viscosity?

The material sheet says its 600cps viscosity, Isnt that a little thick for infusions?

Last edited by pontiackid73; 02-27-2015 at 10:59 AM.
pontiackid73 is offline   Reply With Quote
Old 02-28-2015, 04:46 AM   #4
fossconcepts

Member
 
Join Date: Aug 2013
Location: Idaho, USA
Posts: 33
Thanks: 1
Thanked 2 Times in 2 Posts



Default

I reduce vacuum before gel state right after the part is fully infused. I do a lot of small stuff, the largest panel I do is 12" x18". The resin definitely is on the high end of viscosity for infusion. I just make sure to warm it up and make sure the surroundings are warm.

I really should test out other epoxy systems. I infused polyester once and it was a bit thinner and infused nicely, but I hated the smell of it. There are a lot of options for epoxy resins I just haven't explored too many more options.
__________________
http://fossconcepts.com/
fossconcepts is offline   Reply With Quote
The Following User Says Thank You to fossconcepts For This Useful Post:
tonhol (02-28-2015)
Reply

Bookmarks

Tags
advice, component, layup, newbie, slightly

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -8. The time now is 01:36 PM.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

Inactive Reminders By Icora Web Design