Fiberglassing over plastic nose cone

[ghostfather]

I want to fiberglass over a 3" PML phenolic tube and PML plastic nose cone to make them one piece, glueing the nose cone into the airframe. I'm concerned about the epoxy adhesion to the plastic nose cone.

Likewise, I use a rattle can plastic primer made for automotive bumpers before painting plastic nose cones, and it works pretty well. Is this good enough for epoxy adhesion? Or are there other techniques?

 

[bjphoenix]

Sand the outside surfaces with very coarse sandpaper and see if that improves the adhesion. If you have any way to do it I would recommend doing some tests on scrap material.

 

[SolarYellow]

Might read up on using the Bulldog adhesion promoter that you can buy at O'Reilly Auto Parts.

 

[ghostfather]

I'm aiming for a combination of physical adhesion (sanding) and chemical adhesion (Bulldog or other plastic primers). I prefer chemical adhesion to the polypropylene. Presently, I've had good results using Motip plastic primer in a spray can, at least for painting. It seems to have the same kind of nasty chemicals (tuolene, styrene, ethelbenzene, etc) as the Bulldog primer.

Thanks for the feedback

 

[dhbarr]

You could get a bit of woven tubing from e.g. Soller Composites and finger trap it as well, particularly if you're already going to glass or carbon the tube.

 

[ghostfather]

You could get a bit of woven tubing from e.g. Soller Composites and finger trap it as well, particularly if you're already going to glass or carbon the tube.

That's a great idea, I've got some of that tubular stuff in a drawer somewhere. It doesn't address the adhesion question, but a great tip nonetheless. Thanks

 

[jimzcatz]

Don't even try it, use a glass nosecone.

 

[ghostfather]

Don't even try it, use a glass nosecone.

Sorry, not very helpful

 

[Steve Shannon]

I want to fiberglass over a 3" PML phenolic tube and PML plastic nose cone to make them one piece, glueing the nose cone into the airframe. I'm concerned about the epoxy adhesion to the plastic nose cone.

Likewise, I use a rattle can plastic primer made for automotive bumpers before painting plastic nose cones, and it works pretty well. Is this good enough for epoxy adhesion? Or are there other techniques?

The plastics used in blow-molded nosecones really are very difficult to get epoxy to stick. The adhesion promoters may help. Darrel Mobley used to swear that he could promote adhesion by flame treating the plastic.
In my opinion, the fiberglass epoxy matrix will probably delaminate from the plastic on the first hard landing, and I suspect that’s why Jim discouraged it.
But, if you put enough layers of glass fabric on the nosecone who cares if it delaminates.

At 3” you would be better off trying to find a balsa nosecone and laminate it in place. It will not easily delaminate.

 

[ghostfather]

The plastics used in blow-molded nosecones really are very difficult to get epoxy to stick. The adhesion promoters may help. Darrel Mobley used to swear that he could promote adhesion by flame treating the plastic.
In my opinion, the fiberglass epoxy matrix will probably delaminate from the plastic on the first hard landing, and I suspect that’s why Jim discouraged it.
But, if you put enough layers of glass fabric on the nosecone who cares if it delaminates.

At 3” you would be better off trying to find a balsa nosecone and laminate it in place. It will not easily delaminate.

Steve, thanks, I know it is difficult to epoxy to a plastic nose cone, but I've seen it done, at least on a rocket I inherited from an experienced rocketeer that has passed away. That was a 4" PML Phenolic and PML plastic nose cone. It was pretty bullet-proof, but it seemed to have had several layers of fiberglass. Maybe that's the trick.

I've heard about Darrel's flame treatment, and I understand that it could add a bit of oxygen to the surface of the polyolefins (as well as burning away any traces of mold release), which would help adhesion. I've also heard of it used by body shops on plastic bumpers.

Anyway, I have the plastic nose cone, and I have the phenolic airframe. Sure, I could do it all in fiberglass (or with balsa), but I have these materials already.

 

[cls]

put me in the "don't bother" camp. best you can do is really clean the plastic nose cone over and over with somethnig like orange cleaner to get the PVA mold release off it, rough it up with like 80 grit sandpaper, and laminate a few times.

good luck cutting the gores in the glass fabric to lay down over the cone. that's a math problem, but solvable; holding the glass together through wetup and layout s another. I never tried vacuum bagging but I thng it might be helpful there.

... but all this begs the question: what is your goal of glassing the nose cone? is yur rocket going mach 4 for 2 minutes and you're worried about heat? I'd say screw it, a deformed melted nose cone is the badge of honor, and it's a consumable for the flight.

you mentioned glassing over the upper airframe section. is your goal to reduce the vortexes off the nose-airframe discontinuity? OK, that's a different question.

 

[Sterk03]

So stupid question coming up but working in the SBR Fusion with a 3D printed nose cone. So I’m to put a coat of thinned epoxy over it for strength but have not got far enough to see what I’m using or how I’m painting it so is this the same problem your discussing now or what paints qualify to paint over thinned epoxy coat?

Thanks

Sterk03

 

[ghostfather]

what is your goal of glassing the nose cone?

I want a section of the airframe attached smoothly with the nose cone, making the nose cone roughly twice as long, thus a smooth transition is what I'm after. I'll put a bulk plate and eye bolt further down by the coupler. It's just a long custom nose cone, I suppose.

The rocket's nothing extreme, flies on J-L 54mm motors to max 4000 m (12000 ft), max speed 1.3 Mach. Glassed phenolic can handle that easily enough, and a long glassed phenolic/plastic nose cone should have no troubles.

 

[tsmith1315]

I've seen it done, at least on a rocket I inherited from an experienced rocketeer that has passed away. That was a 4" PML Phenolic and PML plastic nose cone. It was pretty bullet-proof, but it seemed to have had several layers of fiberglass. Maybe that's the trick.

Agreed. I’ve used fiberglass over an Aerotech plastic nose cone. It was a heavy layer, probably 1/4” or more thickness, to reshape and enlarge the cone. Sanded only, no primer. A ½" dowel through the tip and plywood ring for a shoulder probably gave the epoxy a bit more to lock into than a simple wrap.

However, it survived a deep impact after a ballistic flight with no hint of separation and flew again with no repair.

 

[ghostfather]

So stupid question coming up but working in the SBR Fusion with a 3D printed nose cone. So I’m to put a coat of thinned epoxy over it for strength but have not got far enough to see what I’m using or how I’m painting it so is this the same problem your discussing now or what paints qualify to paint over thinned epoxy coat?

Thanks

Sterk03

My standard paint over any kind of epoxy is just automotive primer. After that, some acrylic automotive paint in your favorite color.
Paint sticks to epoxy fairly well, though you should sand it slightly to take off the waxy layer on cured epoxy. Works on fillets.

I've done some non-structural 3D printed transitions and tail cones using my favorite PET filament. Not much sticks to PET, though some polyurethane does work well bonding with the PET. I had some PU varnish left over from a wood floor, and it works well bonding to most plastics. It's not very strong structurally, not a good substitute for epoxy

 

[gldknght]

Having had a lot of negative experience trying to fiberglass various kinds of plastics, I tend to agree with the "don't try this" school of thought. It doesn't only require a hard knock to delaminate, but temperature changes cause flex in the plastic and can cause delamination. Also, fiberglass does not like to stretch around the compound curves on a nose cone, which further enhances the epoxy adhesion issues.

You would be better off using a good automotive glazing or spot putty that contains toluene to fill in and smooth out the gap between the nose and airframe. The toluene will allow a chemical bond with most kinds of plastic.

 

[Hobie1dog]

Don't even try it, use a glass nosecone.

I'm going to agree with Jim as you're going to have many hours of the remaining time of your life messing with this and, You could have very poor results. fiberglass is tough and smoother than a baby's behind.
When you are on your third application of Filler and trying to get that coarse fiberglass cloth smooth, remember this post.

 

[SolarYellow]

I want a section of the airframe attached smoothly with the nose cone, making the nose cone roughly twice as long, thus a smooth transition is what I'm after. I'll put a bulk plate and eye bolt further down by the coupler. It's just a long custom nose cone, I suppose.

I haven't been following this thread closely. With the OP's purpose, I'd do the following:

-wash the cone with warm water and Dawn to remove any mold release before doing anything else to it
-cut off the bottom of the shoulder
-sand the shoulder with 80-grit
-apply adhesion promoter to the shoulder
-epoxy the BT section to the shoulder using whatever glue is best. Might be PU. I have this on my bench, so I'd give it a try: https://www.jbweld.com/product/plastic-bonder-syringe It definitely has more solventing properties than typical epoxy and bites into the plastics I've used it with.
-apply adhesion promoter to the cone
-paint the assembly with primer
-use Bondo one-part or Evercoat 2-part filler on the seam
-sand/blend/primer-filler/etc.

Haven't tested it, but that's the approach I would take.