Carbon fiber 2 stages rocket build.

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Zertyme

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Again, writing this while waiting for the prepreg to get to room temp...
After sanding down the tube a little bit I realized that some of the ridges were too high: to remove them I would have to sand down through too much fiber.
The third time the charm I suppose.

What I'm planning to change:
  • Turn the first layer around to maybe get more resin on the ID.
  • a layer of vacuum bagging film before the shrink tape to try and reduce the ridges.
  • tape dam on both edges of the layup to prevent the resin from escaping there (probably tacky tape)
  • Perhaps reduce the step over even more? But that would increase the pressure applied by the shrink tape.
IMG_20201231_102242.jpg


I forgot to mention that the Chemlease 2693w did a perfect release after the second use.
 

Zertyme

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IMG_20201231_142701.jpg

Tacky tape as dam

IMG_20201231_144122.jpg

Release-coated vacuum bagging film instead of mylar (I don't have any on hand)


IMG_20201231_155127.jpg

Shrink tape wrapped around.

1609462224524.png

Cooling down. I did notice a some resin bleed on the edges. But it's much better than last time.

1609462537404.png

The ridges are still... present. At this point, I think I need to change to another shrink tape (currently using Dunstone 220R).

1609463354333.png

After """"a bit"""" of sanding. Looks good to me.

1609463432176.png
 

Zertyme

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IMG_20210101_163629.jpg

The third time the charm, maybe.
I also want to try thermo shrinkable peel ply (Diatex 1500) + modifying my lathe for shrink tape winding.

I won't be working with composite for quite some time now as I won't have access to my garage : /
So fincan aside for a while.

Next up: Pro98 6gxl custom closure, interstage coupler.
 

Zertyme

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The nosecone mold...
There are a few things I need to keep in mind while choosing the type of mold I'll be making.

-High temperature capable (100degC for an extended period of time)
-Dimensionally stable and accurate
-Capable of bladder molding and/or vacuum bagging

Options I've/I'm considering:

Machined out of a solid chunk of aluminum:
It would be the best option in terms of stiffness and probably accuracy. with such a mold, the bladder could be inflated to +100psi
Issues: Aluminium CTE mismatch, Price, seems kind of a waste tbh...


Machined out high-temperature epoxy tooling board:
Maybe cheaper than aluminum
Issues: also CTE, stiffness would be lower than aluminum thus I will only be able to use the bladder at lower pressure or vacuum bagging.

Composite molds:
High-temperature mold resin, followed by glass or carbon and backed with laminating/casting ceramic.
This is probably the cheapest option.
Issue: different shrinkage between the "epoxy part of the mold" and the plaster: can lead to wrinkles...

High-temperature mold resin, followed by glass or carbon, and backed with Poraver.
Issue: I'm unsure about how poraver+epoxy deals with high temperatures for an extended period of time.

High-temperature mold resin, followed by glass or carbon backed with high-temperature molding paste and G10 Ribs
This is the solution I'm leaning toward for a few reasons. First of all the plug and parting board won't be affected by thermal expansion as an initial high-temperature cure is not necessary. Second, the high-temperature molding paste should help with the temperature distribution (Aluminium filled). And lastly, the G10 ribbing should provide additional support and stiffness.



These are some of the options I've come up with... They all have their advantages and drawbacks, I'm opened to any ideas and feedbacks.
To be continued...
 

watheyak

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Which resin are you planning to use for the part?

The reason I ask is because there are some great high temp resins that are room temp initial cure, with a great elevated temp post-cure. In which case you wouldn't need to worry about the mold withstanding high temperature.

That's how I got around it, anyway.
 

Zertyme

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Which resin are you planning to use for the part?

The reason I ask is because there are some great high temp resins that are room temp initial cure, with a great elevated temp post-cure. In which case you wouldn't need to worry about the mold withstanding high temperature.

That's how I got around it, anyway.

I haven't decided on the exact resin I'll use yet. One of the high temp resin I have requires a 100degC initial cure and has a final Tg of 238degC after post cure. I also want to be able to use prepreg...
 

AeroAggie

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Unless you have a good digital controller that can follow a temperature ramp rate and dwell time, I don't think a high temp cure is worth the extra effort. You won't know what kind of laminate quality you will have if your cure doesn't match the spec. As Scott said, there are some great resins that cure at room temp with a free standing post-cure that are much easier to get right, and more likely for you to be successful with.
 

Zertyme

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Unless you have a good digital controller that can follow a temperature ramp rate and dwell time, I don't think a high temp cure is worth the extra effort. You won't know what kind of laminate quality you will have if your cure doesn't match the spec.
I know that having precise temperature control is very important to get to the specified mechanical and thermal properties of the resin.
I don't see the hot initial cure as much of a problem as the same thing can be said with post-cure cycles for any resin.
Overall, yeah, it's "trickier" to get right, but it's something I want to experiment with.

Also, making a wet layup is my last resort, the main goal is to use prepreg in combination with the silicone bladder.
Thank you for your input.
 

AeroAggie

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I don't see the hot initial cure as much of a problem as the same thing can be said with post-cure cycles for any resin.
That's not true at all. Nailing the ramp rate, temps, and dwell time on a high temp cure is far more critical. Get it wrong and it doesn't cure at all, or you get a partial cure.

By definition, a post cure on a room temp resin is just improving the properties of a fully cured matrix. It's so easy. Cure above 72F. Post cure a little warmer to improve Tg. Done.

If you have the equipment, by all means go for it. I'm just advising you that it's more complicated than you may think, and you could end up with worse properties than with an easier method. Please do let us know how it turns out.
 

hobie1dog

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Some people have all the knowledge and skill. Thanks for all the pictures. Launch should be EPIC :bravo:
 

Zertyme

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Decided to take a go at vacuum bagging airframes, after 3 attempts and slight tweaking, here's the result I was looking for.



 

OG1959

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Just scanned over this thread. Nice work with the composites! I have some experience with carbon fiber building RC gliders. Your work is top notch!
 
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