yup, i think thats gonna do it
if you wish to take the intensifiers out, you will have to make them out of silicone , i highly doubt they going to come out
look forward to the results !
Hopefully they will, by bagging them they should be able to be extracted after the bladder is removed. I do have some shore 70 urethane that I was going to attempt to make a bladder out of, this may be a good material to use, it seems to not stick to the epoxy, but silicone may be much better. After determining the solution, different materials can be used to find the best fit.
Here is a thought; if I used urethane or silicone to construct intensifiers, could they then be molded into the bladder to make a single unit? Basically thinner in the bladder area and thicker areas in the corners to concentrate force?
also be aware that silicone can expand significantly under heat and lead to even greater forces acting on the clamped mold.
your idea of thinner and thicker bladder areas sounds good imo.
Hi
For you shape it might be worth trying qualax balloons. They are used a lot in the Rc glider building.
Making and end cap for your mould so you can use 2 spaced apart slightly to fill the but area or maybe one will fill out enough.
Use a long hollow fiberglass rod for air and one tiny hold at the far end as you need the balloon to fill from far end back , this will enable it to hopefully fill into your tight corners ok. Also you need to make nice round end on the shaft ( drilled marble works well) so your balloon doesn’t pop from there.
They are very tough about $.50 each depending on what size you get. And will blow up to 1ft dia so conforming to your mould shouldn’t be a drama.
For you tube
You might have to make it out of brass or something that you can bend to conform to the shape of your mould and get ballon around corners. That if you can not see end of mould line of sight
Tim
Like this.
Check out this video on YouTube:
And and …
Ok, I have some updates after attempting layup using the intensifiers, the improvements are significant. I chose to use the existing SL 800 bladders to avoid changing too many variables, and not knowing which one made the improvements, here are the results.
First image is of the most agressive corner on the mold, new part using the intensifiers is on the right. You can see the first two parts (left and center) both consistently have the same issues in similar locations.
Again, new part on the right
The next improvement is the bladder, I am currently molding a “anatomically correct” bladder out of shore 60 urethane, which should apply a fair amount of pressure in these problem areas. Thanks for all the input so far, the results are great!
what a difference eh …
funny enough, im struggling with the same problem , but im getting inconsistent results even with an intensifier :S
That are just bridging problems. If you would lay the fibres more accurate you would not need an intensifier.
Nice to see this beginning to work out as I am kinda thinking I might attempt something a bit similar.
But a question to all - how do you actually go about making a DIY silicone, latex or PU bladder? Pour into the mold and slush around, then pour out and build up layer by layer? I know you could brush it onto the tool/plug, but if you wanted to reduce the buildup in size could you actually do it in the mold as per above?
You may think it has been covered a lot, and it kinda has, just not down to the detail of actually making one;-).
(Except one poster mentions he “rotomolded” by hand with silicone inside the mold.)
I have been working on making bladders with shore 60 urethane, which is fairly rigid yet flexible. The issue is when I try to brush it in and then close the mold, when dry it wants to fail on the parting line. I think the way to do it would be to apply a thinner material (liquid silicone, etc) and attempt a “roto mold” to evenly distribute the material. You can brush it in, but you would definitely want to apply more and close it to bridge the two sides while curing.
I am working through the process, so pictures and updates will follow.
I’ve had similar void issues in some of my bladder molded components and the cause was always bridging of the fibers.
I had one particular mold that always gave the same voids in the same areas so it was a good tool for me to evaluate why it happens and how to prevent it.
One would think that simply increasing the bladder pressure would result in better compaction in problem areas, but that wasn’t the case. The fibers are not elastic and depending on the type of reinforcement, the weave, fiber orientation and fiber length in the problem area - no amount of pressure can force them into some contours. Mine was even a fairly simple contour that I would never have suspected to cause such problems. The solution I found was to ensure that the reinforcements were as close to the shape of the mold cavity as possible. The idea is to compact the inner layers of reinforcement against the outer layer (which rests against the mold surface), not to try and expand the entire laminate stack to the shape of the mold.
The second component that reduced bridging was to inflate the bladder slowly and incrementally over time, allowing things to move into position and expel air/excess resin slowly.
What you are describing with using intensifiers under your reinforcements isn’t really helping your issue by increasing pressure in certain areas as much as they are making your bladder more closely match the contour of your mold cavity so your preform doesn’t have to try and expand as much.
Having a bladder/mandrel/etc that closely matches the shape of your mold, altering your layup in areas where significant movement is required, and inflating your bladder slowly and methodically should help eliminate bridging problems.
I thought I would update the post in regards to the new bladder design. I chose Dragon Skin 20, which is a two part platinum based silicone for the molded bladder. The dragon skin 20 seemed to have the lowest mixed viscosity, as well as the highest resistance to tearing, and it gives plenty of cure time to be able to brush in the mold and swirl around before curing. The mold had previously been treated with Chemlease sealer and release agent, but I decided to apply a few layers of Partall PVA for a easy release. Application was performed by brushing a thick even coat on both sides of the mold, followed by a heavier coat on one side focusing on the parting line. The mold was then bolted closed and turned over every few minutes, again to ensure the parting line and both sides were mated with no voids. The end result was a fairly thin and very strong and flexible bladder, with amazing strength and elongation properties.
De-mold time was only 4 hours, next is to work out a air attachment for the rear of the bladder and attempt to lay up a part. A 1/2" air hole was molded into the rear of the bladder during layup. The hope is to remove the need for intensifiers since the bladder is a exact cast of the interior, and to be able to easily remove and reuse the bladder.
Here is a pic of what the first attempt yielded.
Looks great, but you forgot to allow for the thickness of the part, your bladder is too large… Put a layer of sheet wax on the mold surface that is a little thicker than the part you are making, then you are good to go…
I did consider that, and the first attempt may not work. The part is layed up in 4 layers of 6oz e glass, so it is fairly thin.
Any updates about this? I found this whole thread really fascinating and I’d like to know the outcome for future projects 
did the shaped bladder end up making a much better part? Was it too big?
UPDATE; I have attempted to layup two parts using the new bladder, with some positive results. First, it appears the need for intensifiers is no longer an issue. Second, due to the elasticity and tear strength of the silicone bladder, it is extremely easy to remove from the finished part, which was a big issue with previous bladder designs.
There are still some small voids and pinholes in the finished product, but I suspect that more care needs to be made during layup and even using a bubble roller to work the air out before the mold is closed. I will get some pics up shortly.
Are you debulking? Definitely try that. It’s more work but will help you remove your trapped air.
You should also look into smooth-on’s brush on vacuum bagging rubber. It has nearly the same characteristics as dragon skin 20, but with much higher service temp. The only way it performs worse is in elongation, but your bladder shouldn’t be stretching 400%.
I am doing something very similar with silicone bladders and I will be curious to see how many re-uses you get out of them. Also, are you hand turning the mold for 30 minutes while the silicone cures?
It would be fairly difficult to debulk. I am using a wet layup before the bladder is inserted. Using the original bladders (SL800) there was a substantial amount of material shift, which caused inconsistent bridging. Having a bladder that is properly shaped fixes that issue.
I think I have been relying too much on air being released by bagging the mold and pressure from the bladder, I have taken very little effort to ensure trapped air is removed during layup by using a bubble roller and corner roller.
I have laid up a few additional parts using a few new techniques. First, the silicone bladder does seem to solve a lot of past issues, the part no longer needs intensifiers, and bridging seems to be much better since the entire inner surface of the laminate has pressure. Second, previously I was not using a bubble roller durring layup, and I had been wetting the glass in the mold. The last attempts, carbon was wet out and rolled on a flat surface, placed in the mold, and bubble rolled into place. Next, the bladder was inserted, mold closed and vacuum bagged, and 20 psi applied to the bladder. More pressure would have been applied, but the bladder got pinched in the mold and was leaking slightly. Overall, very pleased with the progress, but there are still small voids, and the occasional larger air pockets.
