Hi,
I’m interested in some DIY bladders if possible. prepreg 275 F cure. Aluminum molds. Love to be able to get a reasonable psi. (75-100)
What would be the pro’s and con’s for latex vs silicone?
Would silicone inhibit any secondary bonds with the finished parts? I was looking at some silicone over at smooth on.
I’ve looked at Piercan usa for the latex.
Any tips to making them yourself would be appreciated.
Thanks
How about some DIY bladder made from stretchable vacuum bag? For instance Stretchlon HT350, 700 or 800.
You can heat weld the Stretchlon films. The downside is that some resins will stick to them.
See this video for the heat welding technique and bladder usage. You can also see the demolding video which shows the bladder removal.
This is an older heat welding technique that has some other info on welding. I prefer sealing/welding over the roofing membrane (showed in first video) rather than the Mylar showed in this video.
I’ve found that making silicone and latex bladders take more effort and they don’t last all that long before failing. They can also be difficult to remove from hollow parts. Damaging them upon removal is common.
Thanks wyowindworks. I’ve looked at your threads at the rc group. Nice products.
A big question I have is how do you lay up the carbon on the bladder? I know you do yours different, but I planned to lay my fabric over the bladder then insert it into the mold. Therefore I need some type of bladder that is firm and aproximates the shape of the part I want to laminate.
Something similar to my product would be a bike fork. I can’t imagine they lay 5 or 6 or 7 layers in each side of the mold and then let a flap hold the two sides together. Maybe they do, but I imagined the carbon wrapping around the part as well as running lengthwise.
Here is how I do that:
Make sure that the bladder ports/connections are large enough to allow the sand to pass through. The downside to this technique is that it 1) it requires an additional tool, and 2) the parts have pinholes all over the exterior surface (better with UD materials). When the layup is positioned into the tool air gets trapped between the layup and mold surface. Most of this air doesn’t get pushed from the mold. That is why I prefer to the do the layup in the mold so no air is between the layup and mold surface. I have successfully done a layup consisting of 9 layers of 5.7 ounce carbon with this technique. This part was about 2" in diameter. The layers were staggered in the mold and the seaming flap ended up being 3/4" tall. Fortunately, I was able to insert the bladder after mold closer so I wasn’t in the way during mold closing.
With bladder molding you want to be very thoughtful about designing the bladder ports in the mold. Incorrectly designed bladder molds can be very frustrating.
To reduce pinholes try running bleeder and perf as the first layers on the inflated bladder. You’ll need to account for the additional thickness in your bladder mold. And of course you’ll need to be able to fish the bleeder out afterwards. You can run looped strings around the bleeder for this purpose.
Have you tried this?
I’ve tried it on thinner laminates and it made the problem worse.
For the air to be removed, from a closed system like bladder molding, the air must be pushed out of the mold cavity. Any air trapped in the bleeder prior to inflation must stay in the bleeder or get pushed out somewhere…which means it often get pushed through the laminate on it’s way out of the mold cavity between the mold halves. I suppose it’s possible to port the evacuation in a different manner and create a seal between the mold halves. The way the evacuation would be from the outsde-in rather than inside-out.
Thanks. That is a good idea (the sand). So it means two tools. I’ve seen talk of some people using small foam balls (like the kind from styrofoam maybe 1/8" balls).
The shop that I have visited laid a cosmetic 2x2 layer directly on the surface of the mold. That was cut flush with the top of the mold. The inside had the layup over the bladder inserted behind/inside the cosmetic layer.
What would an example of a pass through cansiter be?
My reason for doing this is to speed things up and get a better outer finish…I wonder if it is better than my current method which requires sanding of the outside surface. I’m using aquapour, laying up on that and then sanding the surface.
I have zero personal experience doing bladders. (trying to learn though).
It’s essentially a double bagging technique. Besides pulling air through the bleeder, the exterior (negative) bag helps to hold the tool together so that less clamping pressure is needed.
But to be fair, I haven’t used this yet but plan to based on reading I’ve done of the process.
Adam, why don’t you try it out first for me 
I don’t know what your would really call this thing. 
It’s essentially an air-tight canister that contains the correct volume of sand to fill the bladder. You can pressurize the bladder through this canister. While the bladder is pressurized through the canister you can tip it over and dump the sand into the bladder. My canister has a filter on one end so the sand can go back up the air feed line that goes to the compressor. It’s nice to also be able to apply vacuum through the canister. Once the bladder is full you can gently apply vacuum so the bladder stays the right shape. If you apply vacuum to quickly it will suck the sand back into the canister.
Sand works much better than foam balls and even copper BB’s. The sand flows into the bladder much better and locks together so the shape doesn’t change. The downside is that large bladders can get very heavy.
I was thinking about this while working this afternoon. The bleeder could work but would have be vented to the outside and a seal would need to be used between the mold halves. This way the migration pattern would be towards the bleeder and out. My technique uses the space between the mold flanges as the migration path. In this scenario, in a bleeder was used, the air in the bleeder would get pushed through this gap and very little resin would migrate into the bleeder.
Either way, the air that gets trapped between the layup and mold surface has to either migrate to the mold flange and out…or through the layup and into the bleeder. I don’t think that either technique will eliminate all the air. Air only moves if the resin moves. The key is have no air in there to begin with. I typically use twice the amount of resin than what is left remaining in the part. I want insure that the laminate is as air free as possible. The excess resin migrates out of the mold as the laminate is compacted to a thinner state.
Adam
Sounds like what you’re doing by using excess resin is a poor man’s RTM.
I’m hoping the double bagging will work with prepregged material so there’s no need for resin migration… we’ll see if it goes like the books say it should
Whens the last time you saw a hollow structure make with RTM?
I’m hoping the double bagging will work with prepregged material so there’s no need for resin migration… we’ll see if it goes like the books say it should
What book? Are you talking about double bagging in the traditional vacuum sense?
Last time I saw a hollow RTM product was when Alan Harper showed me… Indeed fill a bag with sand or fillite, RTM the part, then let the sand out.