Talk Composites - The Forum for Advanced Composites

Making a silicone bladder

http://www.talkcomposites.com/Topic39753.aspx

By chriscnf - 1/10/2021 4:56:25 AM

Hi guys I've decided that I need to move from Qualatex balloons to a silicone bladder.
I've got Smooth On rebound coming just because there isn't much available in NZ at the moment.
Its a three part mold and I've built fiber glass shells to go in the mold parts to correctly size the bladder.

I will mess around with some trials but I'm was a little bit confused about the right time to do second coats and joins last time I did this.
I was using dragon skin then and it seemed to go from runny to tack free without a good tack period to second coats and a complex join.

One thing I did learn last time is that acetic cure tube silicone sticks like s*** to a blanket with smooth on silicone for fixing seam flaws.
The idea is to make a thin patch with the smooth on silicone and then glue it on with the cheap tube silicone.

Any pointers would be massively appreciated...Chris
By Hanaldo - 1/31/2021 4:39:46 AM

 
chriscnf - 1/31/2021 2:57:26 AM
 
Hanaldo - 1/30/2021 9:55:41 PM
And you're not bleeding out too much resin without a perforated film between the peel ply and the breather? 

Good question that...I'm pretty new at this so I appreciate you asking it. This is a complex three part closed mold and I let the resin get almost tacky before putting it together which helps with trimming and extensive seams. And I don't use a lot of pressure, just closing down the seam and compressing the fiber a bit.
The appearance is very good so I hope I'm not removing to much resin. 

If it looks good then you're fine, the surface finish will suffer before anything else does. You may in fact still be quite resin rich, hard to say. If you wanted to know, you could weigh your carbon before starting, then weigh the finished piece afterwards and subtract the weight of the carbon. That would tell you how much resin is left in the piece and you could calculate your fibre:resin fraction.

 
chriscnf - 1/31/2021 3:47:21 AM

Just out of curiosity, how many cycles do you expect from your bladders?

Depends on a lot of things, complexity of the part, how difficult it is to release the bladder after, etc. With epoxy, typically only 15-20 pulls before the silicone starts to break down.