lay flat tubing for bladder molding

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#1

I would like to know where I can purchase lay flat tubing used in bladder molding. Curing carbon fiber prepreg at 250F.
What is the typical mil thickness of the tube? Can I use the polyethylene lay flat tubes thats readily available at places like ULINE or mcmaster?

#2

Lookup lay flat discharge hose for lower pressures and fire hose for high pressures. If I understand your intentions correctly (inflating the lay flat tube to compress your layup), I can’t imagine PE sleeving from Uline is rated for any kind of pressure. McMaster certainly sells discharge hose though…

#3

My application is similar to how carbon composite bike frames are made. They thread a plastic lay flat sleeve through the interior of the laminate that’s sitting in the clam shell mold. One end of the plastic sleeve(tube) is sealed off while the other end is connected to an air source. Mold is closed and heated. Bladder expands and compacts the laminate against the walls of the mold.

#4

Ah! Sorry, I was picturing a compression molding setup. With the closed mold, the burst pressure isn’t the same concern. I have only used silicone mandrels in bladder applications, though I am sure other people on here have other experience. Good luck!

#5

I’ve made silicone bladders for my parts but run into two problems.

  1. I can’t find a material to fill the bladder with so that it remains firm when I place the carbon on the bladder. I’ve tried sand, glass beads but bladder remains floppy. I’ve poured hot wax into the bladder and let it sit till it solidify’s. Problem with wax is that it causes a leak in the bladder when I’m curing the part at 250F.
  2. Nothing sticks to silicone. My prepreg won’t stick to the silicone so it’s not possible to get a compacted laminate.

Any tips on how to resolve the above dilema?

I’ve made a mandrel and dipped it in latex to make a bladder. Built up a thickness of about 1.75mm. At about 225F the latex bursts (@35psi). The latex I have is typically used for mask making etc. I’ve post cured the latex at 120F for 8 hours to build up strength. It helps a lot but still cannot withstand the heat. Do you know of a source that sells high temp. liquid latex for bladder molding applications?

#6

I can’t offer any insight into latex bladders (never tried it, but the process sounds interesting). For silicone bladders retaining their shape three things come to mind:

  1. I have done some simple shapes with a core in the bladder (like a slightly undersized dowel sitting inside)
  2. Other times the laminate is layed into the female mold halves and the flash is later trimmed.
  3. Finally, sometimes heat is used to expand a solid mandrel instead of compressed air. Silicones like TC-5045 have a very high thermal expansion - pairs nicely with prepregs.

For the sticking to silicone problem, I am assuming you mean just gripping well enough to build up the prepreg…the compaction should come from the expanding bladder. Have you tried spraying a wax release on the silicone to create a waxy surface?

#7

In addition to Mattman’s ideas above.
You can use nylon vac bagging film for a start and you can look up customised vac bagging shapes if your part is really complex and don’t want to seam them yourself. Lay flat tubing does work but is limited in shape.
Not overly familiar with the US market but I understand Transition Composites and Piercan USA can do proper latex bladders.

#8

Thank you guys for your input! You’ve given me some more ideas to try.

#9

May be use EPS foam as a mandrel, dip the the foam core in latex, lay up your part on top, put it in the clamshell mold.

Airtech sells a specific liquid silicone for bladders.

The EPS shrinks at higher temperatures.
I remember some cycle manufacturer used it.

#10

Thanks for your input. I am doing exactly as you stated. XPS mandrel machined, repeatedly dipped in latex, layed up and placed in mold. The latex I have ruptures at 200F, @35 psi. The latex can’t handle the high temp. I would like to buy latex that is suitable to high temperature bladder molding but can’t seem to find any! Do you know of a source?

#11

There is a nylon lay flat tube bag film available. I have received a sample of some that was 3" wide when flat.

#12

Where did you get your samples?

I tried contacting Airtech but no response. They have a release film called Dahlar that come as a lay flat tube.

I found some autoclavable sterilization sleeves in various diameters that are made from nylon as well. They’re used in the dental and tattoo businesses. I ordered some to see how they handle pressure and temperature. They’re 2 mil thick. Haven’t tried it yet but assume that there is no release coating on it.

#13

I got mine from Lavender Composites in Australia but I believe it is a Cytec product, red film available in lay flat tubes, 60mm, 75mm,150mm,180mm,200mm,250mm and 400mm.

http://www.e-aircraftsupply.com/MSDS/14390cytec%20Vacfilm300R%20TDS.pdf

#14

Thanks for the information.