How to make fibre glass tube

I was thinking just roll some wetted fibre glass matting around a PVC pipe and leave the PVC pipe in rather than cut it out and re join the pipe!! or should I cut it out.

How would 'you' make some pipe approx 2/3 inches dia.

 

Frosty,

I made some carbon tubes for the hiking wings of my International Moth.

They are of larger diameter than your 2/3" (44 mm and 29 mm, both with 2 mm wall thickness), but I think the same principles could be used in your application also.

Mandrels were PVC pipes from the local DIY store (40 mm drain pipes and 25 mm electrical conduits). It's important to apply mould release wax thoroughly.

Layup was carbon unis in axial direction plus some fibres in +/-45° to prevent the whole thing from splitting under bending load and a final layer of 80 g/m² glass cloth to finish the tube later (something to sand into). I used to wet out the fibres on a workbench, lay the mandrel on top and reel it in to keep the fibres straight. Everything was compressed and consolidated with a really tight wrap of peel ply that also squeezed out excess resin.

Demoulding was easy: Since the mandrel was longer than the carbon tube, one could grab it at the carbon part and slam it down (axially) on the ground (concrete floor) to release the tube from the mandrel. As the PVC tubes are rather flexible the carbon tubes went off quite easily (compared to metal mandrels) but they may be too soft if your glass tubes have to be really straight. In that case you might be able to find some metal tubes or rods that fit inside the PVC tube to stiffen it while the resin cures.

Another technique I used successfully is to reel the mandrel with a layer of paper, wrap parcel tape (the brown stuff) around and apply release wax. By doing so you get a sleeve that doesn't stick to the mandrel at all and that can be pulled off with no effort. Thanks to the parcel tape and the wax you can then remove the paper sleeve from the finished carbon or glass tube (use a stick to peel it off everywhere).

 

There are some websites that talk about doing something similar for model aircraft, but add the idea of vacuum bagging to really consolidate the structure.

I have had success using non-stick oven paper for polyester and epoxy layup. It comes off very easily as long as you don't have any wrinkles. Unfortunately you don't get the best finish ever; but hey, inside the tube...

The other question is do the glass/carbon tubes available from the 'net meet your requirements? there are a few suppliers around.

Tim B.

 

Thanks very much guys I think the bit about putting some paper between the mould and the fibre woulf be a good diea , my mind is already racing with ideas of allumium foil.

Im goin to look today for some very thin wall PVC water pipe.

I assume furniture wax applied copiously would suffice,--its going to have to. Ive used furniture wax before but did not polish it ,I left it quite thick on the surface.

 

Wrap your mandrel with two separate layers of clear plastic sheeting. The 'glassed tube can be easy slid off, as the one layer of plastic sheeting scoots past the other, which will be very lightly stuck to the 'glass work. It may resist at first, which you should be accustomed to with trying to find a date, but a blast of air from an air chuck, between the two exposed layers at one end of the mandrel will usually free it up.

 

Seems easy enough then, I mean making the pipe not getting a date.

What if I wanted to make a rounded mould as I would with say a 3 inch plastic flexible pipe held in shape and glassed.

I guess I would need to split that and cut it out,---yes?

What about a PVC pipe split in half and the 2 halfs glassed inside the 2 halfs then joined and clamped. The thickness of the cut on the PVC pipe would be similar to the ammount of glass in the join????

 

what about infusing the layup, has anyone done this?

What im thinking is to wrap the layup dry around the PVCtube/mandrel held neatly in place with spray tack glue followed by the peel ply and use a resin transfer media over the top and seal the bag to the exposed ends of the PVC tube - not bag the whole thing so the tube itself isnt under vacuum and wont draw resin in the void. The resin feeder lines might be rings around the tube at 500-700mm intervals and infuse it from one end to the other.

I dont like the idea of trying to wrap wet glass around a tube - would be a messy affair and probably end up with lumps and balls of fibre everywhere... Infusing it would be neat, clean, and provide a high quality laminate with probably alot less work than trying to lay it up wet - and minimal fairing afterwards...

leaving the tube in or removing it - i dont see a problem with either - depends on how weight sensitive the part needs to be...

Id be inclined to use around 2/3-3/4 of the layup as uni directional and 1/3-1/4 double bias...

 

Biggest problem with making tube is getting off the mandral or mould it can be anything steel pipe plastic pipe steel shaft what ever depends on the dia you are wanting !, Petroleum jelly and a wrap or mylar ! Coat the mould with a nice coat of petrolium jelly and then a wrap of mylar and the jelly holds the mylar in place and allows it to slide off gently and the mylar will leave a beautiful smooth shiney surface inside
First layer use tissue glass, then csm 450 and then your woven any width and more csm then more woven and if the tube is able to turn slowly then you wrap the glass tight the resin bleeds all the way through and can finish off with peel ply . and no steel rolling is required
You can make nice looking tube using glass braid in the form of a sock any size any length in Glass , carbon , kevlar .

The pipe will slide off the mandral with a little effort but do it at a early stage not days later or the resin will have shrunk and tightened up !!,a rope glassed to one end on the glass pipe and a rope on the other end of the mandral and use any method avalible to pull the two apart , a car on one end and a fence post or something solid and gently drive away . We used a crane in the factory and a chain dyna bolted to the floor , made 6 metre lengths one after the other all day long from 50mm dia to exhaust pipe 6inchs dia vinylester resin gel time 25 minutes cure 3 hours and off . Made any thickness for any situatuation !!

 

A tube can be made without having to split the mandrel or the tube in the process. Also wrapping 'glass around a mandrel is easy and not lumpy, unless you're fairly messy about your work habits. Bagging can improve the resin/'glass ratio, personally, I think infusion would be a waste of setup time and materials for such a small task, unless setup previously to infuse.

Simply put, the double plastic wrap trick works well for the spar tubes I've made. You can usually pull one layer of the plastic wrap out, between the mandrel and laminate, particularly if you've slit into a few inch wide strips. I've found the air chuck thing to be just the thing, it pops the light bond and even can scoot the tube off to a small degree.

 

I am still not getting it about the date, about getting stuck, and blowing to release things. You mean I need to blow my date, instead of vice-versa?

Anyhow, I also saw someone winding fish wire tightly around a mandrel, then applying thinned down plasticine over it, to get a good releasing mandrel. Lot of work, though, and a bit masochistic. I think the double-plastic one is most easy.

Another customer of mine makes masts by making a very thin glass laminate over a suitable mandrel, cutting it open, removing it, then beafing it up with more laminate.

 

I was thinking about trying that! Actually, two half molds. Wasn't thinking very hard about it, but its good to see the process works and I wan't crazy to consider it.

-jim lee

 

I have thought on this subject more than once. My plan was:

Start with thin wall PVC.

Do a spiral wrap of plastic sheeting strips with 50% lap to ensure release.

Build a cradle to set the whole thing in and keep is straight (two 2x4s screwed together to for a L section)

Cap one end of the pipe and insert an expansion plug with pressure tap in the other. Pressurize the PVC to 125# air pressure to expand it slightly.

Apply glass/carbon/epoxy to suit

Wrap exterior in a spiral wrap with plastic sheeting. If it is thicker than normal this can be applied with sufficient tension to compress the glass/carbon/epoxy quite a bit.

Place the assembly in the cradle to keep is straight while setting up.

Depressurizing the mandrel should make pulling it out a sure thing.

 

As I posted before I think If I do this I would do the thick wall pipe cut down its length and fibre glass the insides and slop it together with a couple of G cramps or wrap with tape with edges dripping out the sides.

This would with no doubt come apart and the process could be repeated very quickly.

No fairing required or very little once the sharp edges ground off. Taking into consideration fairing and labour, sand paper etc this method works in my head best.

 

I have used a mandrel with the double poly wrap with good results on very short pulls (1.125" mandrel in a split oar blade mold, a 6" pull). I would like to do long pulls (6' or more with a 1.125" or 1.5" mandrel). My project would also be fairly light (thin walled) so I am not sure the crane pull is an option and still have a tube in one piece. Paul MacReady used thinwall composite tubes in his Gossamer Condor (human powereded flight Kremer prize winner). They were willing to use a sacrificial mandrel of thin walled aluminum tubing in very long lengths, wrapped and cured with a very thin composite then soaked in a trough of acid to dissolve the aluminum. Clever solution for a tough problem with a lot of money and prestige on the line, but not the solution for most of us.

My first thought here is that temperature and coefficients of thermal expansion, CTE, could be an ally here. A plastic mandrel (PVC, polyethelene, etc.) still double wrapped in poly but cured with the composite sleeve at elevated temperature (limited of course by the plastic chosen) could after cure and return to ambient temperature or below give up the part more easily. I am thinking, of course a low shrink epoxy, and carbon or Kevlar sleave. One would have to support the part/mandrel in a horizontal oven with perhaps a well supported angle of steel or aluminum opening up "V".

This is an older thread, but any thoughts or experience with this would be of interest so please comment.

 

These are several options. If you want to do the heat trick, but want to keep things straight, choose aluminium. You can double-wrap it, release coat it with a high-slip release (semi perm, for instance Zyvax, one of their high slip versions) or apply self adhesive teflon film to the tube.
Then laminate your pipe, and install a heat gun which blows through the pipe, or toss the thing in an oven. You need 80C or more to have this work really well.

Another option for long, thin things is to wrap a tube with fish wire (laboursome, but doable). Then smear thinned plasticine all over it, to smooth it off. Laminate your pipe, then pull the mandrell out, which should be relatively easy. Then pull the fish wire out, and clean up.