Could someone explain how a bladder works? Do you expand it inside the two pice mold after inpregmating the composite with resin?
Precisely. The bladder, when inflated, pushes the laminate up against the mold surface to give you a uniform finish on the front side as well as the back side of the laminate.
Are the bladders custom made for the specific shape? Also where do you get these bladders?
I am a prosthetic tech and everything we do is off a positive mold. My plan for this particular project was to use a positive inner mold with the CF layed over the mold. Then place a 2 piece neagtive mold over the whole thing and use a combination of vacuum and pressure to inject the resin. Then break out the plaster like I would on a prosthesis. Sound like it could work??
There is no reason to be breaking out plaster when you are bladder molding. You would have what we call a female mold closed and bladder to push the carbon to the walls. see what i mean? no reason for the male mold.
Bladders are made from uncured silicon sheets. You cut them out to whatever size/shape you need and glue it all together with silicon adhesive. You’ll need to bake it afterward to cure it and voala, you got your silicon bag. Your ideas are sound, so you should be able to pull it off. If you need help obtaining the silicon materials, let me know and I can order them from my supplier. They also sell a paste where you can just brush it on to make your bladder instead of using sheets.
I am understanding the concept behind this but have a couple more questions.
Obviously the bladder is used instead of my plaster male mold. But how do I go about wetting out the carbon? I had planned to use a carbon sleeve for this since I have it at work. Unless I am missing something this seems really hard.
How do I vacuum infuse with a bladder? Everything I have done is layed up dry and the the resin is infused under vacuum. Also are there any websites that might show the process using a bladder?
Thanks
If you infuse, you don’t even need to use a silicon bladder. Layup dry as you would, close the two mold havles together and then make a tube out of another bag. Place this bag-tube inside along your tube and then place everything inside the big bag. Once you apply vacuum, the air is going to get drawn out of the mold and at the same time inflate the tubebag that you have placed inside. I learned this trick a while back and it seems to work wonder. Unfortunately I’m not doing anything that require this process now so I couldn’t illustrate it for you.
What kind of surface finish will this leave on the inside of the part? This particular project needs to have a even, smooth surface on the inside. Do I use some kind of breather ply?
I am assuming that the bag that goes on the inside of the mold must be totally sealed?
Last question is how do you reinforce the part at the parting line of the mold. Problem I see is it being very hard to get inside the mold once it closed up. I have big hands…LOL
This does sound like a less labor intensive way than I was thinking of with a positive and negative mold. Just need to figure out the little things and make it work.
Thanks for your help.
If you seal the inner bag, then just fill it a little bit of air. Loosely, not too much and not to little air. Or you can make the bag with a tube coming out of it. This tube will be stick through the outer bag as well. That way when vacuum is drawn, the inner bag will inflate and the tube will allow air to enter the inner bag.
The inside surface is going to be as smooth as you make the bag. Peel ply will help. You don’t have to reinforce the parting line afterward because you’re going to lay it up with some excess so that they’ll overlap when you close the two mold halves together.
Evan