Fiberglassing big tubes?

Hi guys,

Getting ready to build a 12 inch diameter tube 4 feet long, with a 3/8ths wall. Eventually it will be a bow thruster, but I have to finish designing the gear box first.

My trial run with a piece of PVC was less than successful, so I'm in need of ideas as to how to build the form. (Tried using polyester, this afternoon I'm going to go grab some epoxy and try again out of hopes of less shrinkage!)

Ideally it'd just slide off the pipe, but I get the feeling the mandrel will some help before that happens!

Would you guys lay up the whole thickness with it on the form, or do just enough to support the shape and then slide it off? If I end up with polyester it'll all have to be done at once.

Thanks guys!

Zach

 

I was trying something similar but smaller. A stern tube. 1.5" OD over a pvc pipe. The idea was to infuse it with resin and hang it from the ceiling to keep it strait. Well it didn't work. Not enough surface area to compress the layup. Anyhow, I oiled the pvc tube and wrapped it with 2 layer of polyethelene film (visqueen) then started with 1 layer of basalt fiber tube and 5 layers of 18 oz biaxial fabric rolled on in one piece and another layer of basalt fiber tube. I was guestimating 1/4" thickness after infusion. Never made it that far though, the tubular shape is a b*tch to get a leak proof bag. I think I dickered with it for 3 hours before giving up. I'm really starting to think that these things (tubes) are better being spiral wound.

There's a guide on the sollercomposites dot com web site on making shafts using a shrink wrap type of arrangement. It might provide some ideas.

http://www.solarcomposites.com/composites/carbon fiber sleeves.html

Also the bateau dot com tutorial on making a carbon fiber spar

http://boatbuildercentral.com/howto/cf_spar.php

Good luck with your project.

 

plyla, on pvc pipe with poly resin you gotta wax & shoot multiple coats of pva to get reliable release, split molding at about 1/8" thick with diamond saw to ease peel off & replace pvc pipe with ply or chipboard circles but made of 2 semicircles probably about 5 sets should do then laminate the rest of your thickness, there is no need to do the whole poly laminate at once, you can do just one 1 oz layer a day if you really want to(but it would take a while). All the best from Jeff

 

I have made carbon masts over a steel mandrel, using fishing line as a release: Wind the fishing line tightly around the tube, then smear plasticine over it. Create your tube, then after cure, hook the tube behind a door post, and pull out the pvc tube. (might use some force, we sometimes used the car to pull the mandrel...)

Appying heat when curing helps the later release: PVC expands quite an amount when heated. Once cooled down, the PVC tube is smaller than your epoxy tube.

 

What failed? Couldn't you get the PVC pipe out afterwards, or was there another problem?

If the problem was nothing more than getting the PVC pipe out, you might try wrapping it with several layers of something thin and slippery first, before you start your layup. If the problem is that the pipe deformed while you were laminating, you might try pouring concrete into it first so it won't deform.

There is nothing wrong with using polyester and doing a hand layup all at once or one layer at a time, provided you use resin that has no wax added (use laminating resin not finishing resin).

 

knotty is right,,but for a FAST easy way,,buy the glass in 12" wide strips,,then wrap it around ya "prepared" pipe, like a candy cane kinda deal,,and keep going from end to end till you get the desired thickness,,i've never seen it done till i see them do it down here with oil pipe.

 

Use a cardboard sonotube to get the 12" diameter? Cheap enough.
Also, have you thought of glassing over pvc? It would be pretty strong and not too expensive.

Alan

 

Thanks guys.

Knotty: I really would like to try that infusion rig, real big attraction to not having to wet out a circle that keeps dripping on your shoes!

Jeff: Thanks for the idea, I looked into splitting the pipe but its got enough internal pressure that it snaps shut. Haven't cut the fiberglass long ways yet, as I don't really have a saw that'd cut it straight, unless I want it bisected on a bandsaw!

Herman: Monofillament! Great idea, I'll give it a try. Did you use as heavy a test as you could get, or did light weight stuff not stretch/break before letting go of the mold?

Ken: The first try with wax on PVC required a form the same size as the ID, and a vice set to the OD of the tube. Had to hammer on it to break it loose, and cracked the end that rest on the vice. I could make it longer and cut it short, but i really don't like destruction when making something new!


The1Much: I like the idea, but as far as strength goes I can't see a biax with fibers running on 45's being any stronger than one wrapped like a candy cane doing the same thing. Not really even sure what stresses are on a bow thruster tube and how to best align the fabric... but I've never heard of a failure on one. Overkill!

Alan: Sonotube is one I've pondered, but I like the perfectly smooth inside wall the PVC gives. I'll track some down for giggles and grins. Does it spiral apart when done from the inside? I know they use it to form concrete on the inside, so I'm wondering if it uncoils both ways.

Update: Finished wetting out a 6 inch tube, as the piece of 10 inch I found had ripples and was not the same shape throughout... Put about double the wax on it from last time.

Who do you guys use for supplies? I'm in North Carolina and will need a lot of this stuff by the middle of the week.

Any polyesters that shrink less? Vinylester any better as far as shrink goes?

I'm wetting out with a paddle spreader, and for flat surfaces it does fine... but this curved stuff it sucks! What would you guys be using? I've got way to many drips on the floor, and little air pockets (left my roller down at the boat, so I'll need to order a few of those too!)

Thanks for your help guys!

Zach

 

I made pipe for many years, what you use as a mold (mandrel) isn't important, PVC, metal, Sono tube, fiberglass tube, they all work about the same. The way you get around the shrink locking it in place, is to use corrugated card board and wrap it around the mold, this will allow for the shrink by being crushed. You can wrap cardboard around it until you get to the size you want if needed. We then wrapped mylar over the cardboard, you can use wax paper, polyethylene sheeting, tape, or whatever you might have, but no mold release is needed with these. While the mold rotates, wrap mat, then roving to whatever thickness you need, start at an angle and butt the material to the edge of the previous wrap. For a small pipe like that, 6" wide glass would work. You may not be able to rotate your mold, but you still should be able to wrap it.

With PVC, you can cut the pipe lengthwise before glassing, then force it open slightly with a couple of wooden disc's or something, We used treaded rod so it could expanded and contracted repeatedly. Just use tape over the expansion cut.

 

Does it spiral apart when done from the inside? I know they use it to form concrete on the inside, so I'm wondering if it uncoils both ways.

Inside or out, and if smoothness is important, cover the sonotube with something. Like a few wraps of shrink-wrap plastic.

 

You can also get a sono tube out by soaking it in water, it will sort fall apart after a short time. Or you can pre cut it like PVC.

 

My experience is that vinyl ester has less shrink than polyester, but I filled my vinyl ester with microspheres and just a bit of cabosil. To keep it from dripping so much, try brushing your resin onto the mold, laying the dry glass, rolling the glass into the resin, and just slapping some resin onto the dry spots with a 4" chip brush.

I'd go with Ondarvr's suggestion to split the PVC, keep it the correct shape with discs or threaded rod, and then pop them out when it's time to demold. Excellent suggestion, as was the idea of using corrugated cardboard to take the crushing from resin shrink.

 

overkill?,,,i was just saying that wraping that way is faster then curling a piece of glass around it,,and it helps keep it shape better then folding,,,,thats all,,,doesnt have to be any thicker or heavier then doing it the way ya are hehe

 

Plyla, if you wanna cut f/glass tubes a 4 1/2" or 5" diamond wheel available at hardware for cutting ceramic tiles set in a small grinder is all you need plus eye/ear/lung/skin protection, you can mark a strait line on your tube using a length of angle iron along it. Regards from Jeff.

 

The1much, I see what you mean! After wetting out this 6 inch pipe, I can't see handling a four foot width of cloth (or afford the price of the real wide stuff!)

Thanks for your tips Ondarvr, I'll do some expirimenting! I really love the expanding form, so the PVC is reuseable. 12 inch diameter is expensive to just throw away. I'll give cardboard a try over the top on the next one. Any tricks to get it to lay down smooth to the surface? I tried bending a piece of a box around the pipe but it creased pretty badly. Thanks!

Tinhorn, thanks for your experiences with vinylester vs polyester. I think I'm going to just use polyester (US Composites 404 tooling resin) and a gelcoat additive with the lesser cost.

Waikikin, great tip. I'll grab a diamond wheel and do some playing around. Seems like it would be a great replacement for a sawzall doing large repairs if it'll plunge cut!