Mad Rocketeer
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I've got a question about epoxy amendments. First some background, then the question. Please correct any misconceptions in the background stuff as well.
Background:
When glassing tubes (or Kevlar or carbon), the proper technique is to get the fiber and the tube wet with the epoxy then squeegee (or vacuum) out all the rest that one can. Then, lightweight epoxy-compatible fillers can be rubbed into the weave and over the top, to be sanded smooth. The idea is that more epoxy than this doesn't contribute to the strength, but only to weight. Sanding into the fiber matrix weakens the structure.
Adding milled fiber (tiny fiberglass filaments) to epoxy adds strength and hardness but also weight. Milled fiber can be added up to about 1:1 with the resin (not including the hardener). Adding Kevlar pulp to epoxy adds strength and impact resistance. Adding chopped carbon fibers to epoxy adds strength and stiffness. Chopped carbon fibers and Kevlar pulp are added at about 1:16 fiber to resin. Carbon will be lighter than the epoxy, and Kevlar may be too. Adding microballoons to epoxy reduces density and therefore the weight of the mix. Microballoons weaken the mix though, since they are hollow and largely air. Microballoons can be added up to about 3:1 balloons to resin.
Question:
What happens if one adds both reinforcing amendments (such as milled fiber, Kevlar pulp, or chopped carbon fiber) and microballoons, mixing the reinforcement in thoroughly first, then the microballoons? Will it end up strong and light, like a properly glassed tube (see above), or will the microballoons interfere with the proper matrix of fiber and resin?
Would it be better to go with layers like this (using fillets as an example)?
[Each new layer is added when the previous one is ready to handle but not fully cured.]
1.) Paint the tube and fin root area with a thin layer of straight epoxy for better penetration.
2.) Mix epoxy and reinforcement, and make a thin strong fillet.
3.) Mix epoxy and microballoons (or use some other prepared light epoxy-compatible filler) to finish the basic shape and size of the fillet. Smooth it.
4.) Paint over the filler with a thin layer of finishing epoxy, spray on a little 91% rubbing alcohol, and create the final glassy smooth surface.
Can steps (3.) and (4.) be combined?
Anything I'm missing?
Of course, I'd use gloves for all epoxy work and take precautions against inhaling fibers or microballoons.
Thanks.
Background:
When glassing tubes (or Kevlar or carbon), the proper technique is to get the fiber and the tube wet with the epoxy then squeegee (or vacuum) out all the rest that one can. Then, lightweight epoxy-compatible fillers can be rubbed into the weave and over the top, to be sanded smooth. The idea is that more epoxy than this doesn't contribute to the strength, but only to weight. Sanding into the fiber matrix weakens the structure.
Adding milled fiber (tiny fiberglass filaments) to epoxy adds strength and hardness but also weight. Milled fiber can be added up to about 1:1 with the resin (not including the hardener). Adding Kevlar pulp to epoxy adds strength and impact resistance. Adding chopped carbon fibers to epoxy adds strength and stiffness. Chopped carbon fibers and Kevlar pulp are added at about 1:16 fiber to resin. Carbon will be lighter than the epoxy, and Kevlar may be too. Adding microballoons to epoxy reduces density and therefore the weight of the mix. Microballoons weaken the mix though, since they are hollow and largely air. Microballoons can be added up to about 3:1 balloons to resin.
Question:
What happens if one adds both reinforcing amendments (such as milled fiber, Kevlar pulp, or chopped carbon fiber) and microballoons, mixing the reinforcement in thoroughly first, then the microballoons? Will it end up strong and light, like a properly glassed tube (see above), or will the microballoons interfere with the proper matrix of fiber and resin?
Would it be better to go with layers like this (using fillets as an example)?
[Each new layer is added when the previous one is ready to handle but not fully cured.]
1.) Paint the tube and fin root area with a thin layer of straight epoxy for better penetration.
2.) Mix epoxy and reinforcement, and make a thin strong fillet.
3.) Mix epoxy and microballoons (or use some other prepared light epoxy-compatible filler) to finish the basic shape and size of the fillet. Smooth it.
4.) Paint over the filler with a thin layer of finishing epoxy, spray on a little 91% rubbing alcohol, and create the final glassy smooth surface.
Can steps (3.) and (4.) be combined?
Anything I'm missing?
Of course, I'd use gloves for all epoxy work and take precautions against inhaling fibers or microballoons.
Thanks.