I am new to this forum so please excuse me if this is not in the correct place. I have done some searching on the forum for answers to my question but have not found much.
I am doing some home hobby work with composites and could use some help. I will be making a two piece female aluminum mold and I want to make a custom bladder.
My cure temp will be around 350F so I am looking at using silicone.
Can someone suggest a type/source of silicone that can be used as a bladder?
Thanks
I have been producing in-house silicone bladders for a bit for two part closed mold layup. I have had very good results with both brush in and dragonskin silicone from Smooth-On. The dragonskin is significantly thinner yet has a very high tear strength. I switched to the brush in and use the silicone thinner (10% max by volume), which aids in areas where you may need a little less viscosity. Actually both products work very well together and I will often ise dragonskin for the initial layup of the bladder followed by the thicker brush in for internal intensifiers or for bridging the two halves together.
You will need to de-gas after mixing, so keep that in mind. I usually lay up the two mold halves in 2-4 layers with about an hour in between, followed by a bridging bead applied to the ridges of both sides and then clamp the mold together. The highest temps I use for curing is 275, but the bladders don’t have any issues at those temps, it is rated to 450 f.
Let me know if you have any specific questions about the process.
Composite man, what material are your molds made of? Are there any design guidelines for the mold that will work better for bladder method. Do you undersized the bladder to offset for material thickness, like laying vinyl wrap material in the mold.
I was going to ask the same. I looked up the dragon skin. There are multiple options to choose from. If we could get an example of which type was used it would help me understand the process better.
I work as a machinist at an aerospace company so I have a general idea of how composit layup works. We don’t do bladders so all I know is what I have read. I didn’t even think about bonding the two halves together. It is something that a will try for sure. For some reason I thought you could make the bag using an undersized male plaster mold.
I chose the Dragonskin shore30, which seems to have the highest tear resistance and the cure time is not too fast or too slow, it gives you plenty of work time. For the thickness offset, use Freeman sheet wax with the adhesive backing, it can be ordered in various thicknesses to closely match your part.
The original molds were fiberglass with polyester resin and tooling gel coat, new molds are high temp epoxy with DT-082 high density filler.