How to make fibre glass tube

An idea came to me this afternoon as a woman threw away the inside card board roll of a some cling film. It was about 6 feet by 3 inches tube .. Others were talking of sacraficial mandrels and it occured to me that this cardboard could be soaked in water and then blasted out with a pressure wash.

 

As long as the tube is straight or only slightly curved, heat shrink tubing can be used for compression of the layup. Heat shrinkable plastic is also available as a continuous strip which can be spiral wrapped around the layup, including any curve, then shrunk to provide compression. I know with certainty that this technique works because at least 2 different commercial manufacturers are using this exact technique to make composite tubes.

Jimbo

 

Frosty, the main problem with a laminate wrapped mandrel, is the laminate sticks. Even if the mandrel is wrapped with a release agent or plastic, etc., it still sticks, maybe not so well, but well enough over a huge amount of surface area, that just over coming a 1 pound shear strength attachment is equal to imposable.

The solution is a mandrel wrapped with a multiple layered release system (as I mentioned previously). One layer can stick to the laminate all it wants, as the cured tube is removed, sliding over the inner most layer, which typically is also stuck to the mandrel. If you want to get really clever, you can make a set of release sleeve sections, much like what I've described and pull them out of the tube as you wrestle the tube off the mandrel.

What air does, if forced in with a chuck, is drive the release film (plastic sheeting) up and off the mandrel and down and off the laminate. This creates a cushion of air for the tube to slide on as you're pulling it off.

Lastly I've used heat shrink tubing and wrapping in layups. It works and makes for a clean, smooth surface when done as well. If spiral wrapped, you'll have some spiral seams, but these are easy to knock off.

 

How I have done many times is to:
Coat mould/tube in release agent (I use wax followed by PVA)
Once dry, wrap one layer of glass (440 to 800db) around mould
Once green, slice down length of tube with sharp utility knife and break/release slightly
THEN, continue with remainder of glassing.

Roger Simpson, an Australian Multihull designer, suggested for rudder tubes, doing multiple coats of epoxy thickened with graphite powder first, then 1 layer of glass.
When green, follow steps above, end result is a rudder tube with graphite bearing.

 

Is the mandrel then left in place to support further build up of the shaft once the initial surface tension has been relieved? You did say release slightly, so question answered, the mandrel is left in place.

 

No idea if this will work but drapery stores sell plastic sleeving to put over wood closet rails; it pretty's them up and allows the clothes hangers to slide easier. It is not a closed tube, just overlaps itself along its length, so it may need a strip of adhesive tape over the exposed edge. Being PVC I doubt resin would stick to it, and once the glass tube was formed it should be easy to remove by twisting it. Worth a try I'd say.

For larger tubes I would be inclined to make a thin walled wood tube from the lightest wood I can find, wrap the glass around it and just leave the wood in place. But I cheat at cards too . . .

 

Try this as described by Jim Marske in his book marskeaircraft.com/workshops

You lay up over a PVC pipe with outside diameter that is close to the inside diameter of the pipe to be fabricated. The PVC pipe can be supported by placing a steel pipe inside to keep things straight and eliminate sag.

The plastic pipe is waxed and 45 deg bias cloth layed up. The cloth wrinkles are worked out with a gloved hand from center out. The 45 bias acting as a Chinese finger trap tightening the cloth.

To seperate the tube the inside of the pipe is heated alternately at both ends with an air gun before it has fully cured thus expanding the pipe. Hold for 15 minutes then allow to cool. The PVC pipe shrinks away from the composite tube facilitating removal.


Dino

 

Something I will be doing soon is to make some f/g epoxy tubes (80D x 400L x 5mm thk.) to be glassed into hulls for aluminium cross spars to sleeve into.

The method is to have a turning mandrel, to buy a cheep wood lathe (eBay) adjust the gearing to slow the rotation speed right down. Set the PVC or aluminium tube mandrel up with 'turned up' wood ends into the tube slightly at incline so as to wedge into the mandrel.

Using methods from above to wrap plastic got from HWH/Bunnings (thinking membrane plastic or those 'warning tape-off area' rolls of plastic tape) and wrapped or wound spiral up the tube and taped down ends, should allow the tape to unwind when mandrel dropped or finished tube counter spun and dropped.

Wet out of cloth is done from a container made to hold a couple of rubber rollers to run the wetted out f/g tape through (much like a couple of disposable paint rollers?) to squeegee excess resin out, working up the tube then back down as the mandrel turns in the lathe. Could be automated with a spiral cogged geared set-up.

Wrap up with peel ply then wrap up in spiral plastic again, tape off, let gel then put into home made oven (mdf boxed up with insulation batting sandwiched and fan heater. let cool and then drop the mandrel to unwind release tape and release tube.

Hope it works, as a carbon tube spar company in Sydney quoted $300 p/lm to do this in f/g or c/f pretty much the same cost!

p.s. this system of turning mandrel reminds me of the big A1 plan printers and how they have paper rolls on tubes with end plugs for different size paper rolls.

 

Infused carbon tubes

So, we think we're getting close to perfecting an infused carbon tubing process. Here's an example of 3 1/2" tube we made. Its 45/45 UNi 45/45 sandwich.

Have a look.


Once we get this down, we'll see about doing different lengths, shapes and fabric loadings.

-jim lee

 

Thats really nice !!

 

I am pretty sure Im going to have to do something on these lines . I priced up a 6 meter length of 304 stainless at 2800 baht (thats 30 to the dollar)

A local gate maker wanted 7000 baht to make two 3 meter lengths with a 90 degree welded on the end and a meter on that,-- a L shape.

The 90 degree elbows are only 2 dollars--in 2 inch.

 

Back when this thread was hot I ran a thermal test on tubes, all close to 3/4"diameter. I was going to post it but did not because nothing was surprising. I warmed PVC , aluminum (.058" wall), aluminum rod stock, steel tubing, and HDPE rod stock. The measurement was the difference between 70 degrees F and 170 degrees F. With 100 degrees F difference I got almost no change in dimension from the metals (maybe .0005" from aluminum). Plastic was good for 2 to 4/1000 of an inch. Solid stock had less change than tubing/pipe. My conclusion was that the introduction of heat can certainlly be a help with plastic mandrels.

 

Thats good information . Using heat is a good idea and now makes this thread hot again.

I am nearly at the point to start to make some, I only need 8 meters but running through the whole process in my head I am stuck at how to keep a 4 meter PVC pipe mandrel straight as it hardens. All I can come up with is a line of house bricks leveled up on the drive way.

How did you anticipate putting heat into the mandrel --a hair dryer ?

Oh Oh I just though of maybe 4 of 5 gallon cans with the lip being less damaging to the hardening resin.

 

Some thoughts:

PVC pipe is prbably the best of the plastic pipes for long unsupported lengths.
Schedule 80 PVC pipe would be a lot stiffer than schedule 40
8 m sounds kinda long, if supported only at the ends sag would depend on the diameter
Your first post said 2/3" (as in 0.667") I assme you meant 2 to 3", maybe more for a 8 m mast
Try a shorter length first to estimate sag; mid-span sag is proportional to L^4
You could fill it with water to increase the weight and sag for a more sensitive measurment
If you extend the length of pipe and weight the ends it will reduce mid-span sag
Ensure you can extract the mandrel with a shorter practice length!
This link has a table of recommended support spacing for pipes of various sizes when they are full of water http://www.engineeringtoolbox.com/support-spacing-pvc-pipings-d_783.html

Theoretically pressurizing the pipe should stiffen it: allowable pressure depends on schedule and diameter but it is good to at least 125 psi, provided the end caps are rated to the same. It is safest to fill the pipe with water first before pressure testing it any higher.

 

I need 8 meters in 2x 4 meter lengths for transportation. I need the finished product to have 2 x 90 degree bends which I intend to use PVC water pipe bends inserted internally to give me room to glass over then and leave them in there.

I am un shure how to do the lay up,--ie shall I just cut a 4 meter length and wrap the pipe dry possible hold in place with elastic bands and then wet out , or --cut strips of matt to say 4 inch and wrap spirally around then wet out --Or wet out either way and wrap wet.


Ive a feeling im going to end up with a soggy mess either way