Rolling your own Fibreglass Mortars

[nick2354]

It is hard to find Mortars in Australia without buying from overseas at expensive shipping prices.

 

I want to make my own Mortars using Fibreglass. I know nothing about this and haven't found any information on this either, so please any help is much appreciated.

 

My plan so far is:

buy some rolls of this:

 

http://cgi.ebay.com.au/Fibreglass-Tape-100...p3286.m20.l1116

 

Buy some Epoxy Resin (I dont know which one yet)

 

Then the rest I have no clue about.

 

Does anyone know what process I need to roll a Mortar tube with it? I have tried looking but haven't found any information.

[Swede]

Interesting challenge. Most fiberglass is laid with polyester resin, the sort of stuff you can find at auto body stores, big box hardware, and marine stores. But epoxy would work fine and probably produce a stronger tube. The trick is in the moulding, and creating an accurate bore. Also, getting it layered thickly enough so that it has real strength. I'll ask my friend, who is an expert in composites.

 

If I were to guess, one way to do it would be to find a very thin cardboard tube of the correct diameter, and simply build up layers over that. If coated with release agent, you might be able to pull it out, leaving the composite tube behind. Failing that, just use it. The cardboard would eventually wear away, leaving you with a composite shell. Graphite cloth and epoxy is another option.

 

The "shrapnel" issue may be a problem. HDPE tubes are used because they fail in a benign fashion, whereas something like PVC shatters and sends chunks flying. The failure mode of a composite tube, if I were to guess, would fall somewhere in between HDPE and PVC or metal. I'm pretty certain fiberglass tubes are sold and see use in pyro, so I can't think of any reason it would not work, or would be unsafe.

[Arthur]

There is no reason why you should not do DIY fibreglass tubes. Look round the boat industry for the glass matt and the (usually) polyester resin, and you will need hardener/catalyst too.

 

This may be a good use for PVC in pyro mortars! Make a PVC former of the correct outside diameter then lay up the GRP round it. Keep it spinning slowly so that it sets evenly, then use an airline to blow pressure air up the core and blow the GRP tube off.

 

Keep looking for real mortars! When you find them you will wonder why you put the effert and mess into making some. Stout card tubes are used also. 10 - 20 mm wall.

 

I like GRP because you have an integral base plug.

 

HDPE water main pipe can be very usefull but hard to plug well. But a 6metre length is almost free here (well cheap anyway) so fitting the plugs is a viable project.

 

Get some practice before you make real mortars, GRP is messy and you need a former for each mortar you intend to make in a session, then when they harden you pull the product off the former (or blow it off with compressed air)

Edited March 7, 2009 by Arthur

[tentacles]

I don't see why you couldn't roll your own, but if you've ever worked with fiberglass before you'll know it's an incredibly messy, stinky proposition, with a SHORT working time. If you can manage to get more than 30 minutes pot life out of enough resin to do say a 4" gun, I'd assume you were working outside in freezing temperatures!

 

Fiberglass is messy. I know, I said that twice now. It gets on everything. It sticks like you wouldn't believe. It stinks - and I'm someone who doesn't mind solvent smells. Oh, and it's nearly impossible to lay flat if you're pasting it in by hand. Did I mention it's sticky? Think of it like corn syrup, except it can get hot and it's stickier and smells like an open pan of warm lacquer thinner. What you really need is a mandrel you can slowly spin, stick the fiberglass on and give it tension to wrap it tightly - oh and you need to apply the resin as well. Once it's wrapped, then you'll need to squeegee the resin in to make sure the fabric is well soaked. You can also use a paint and stick, shell pasting type of method, but like I said, ultimate sticky mess. That sets rock hard. It can't be stressed enough just how huge the mess can be.

 

I'd think you'd be better off finding an HDPE pipe extruder and asking them what they've got. Usually they won't have our sort of pipe in stock but make it fairly regularly (once or twice a year maybe) and can add your stick or two to the run for a nominal charge. Of course, that means waiting, which isn't terribly exciting.

Edited March 7, 2009 by tentacles

[FREAKYDUTCHMEN]

Good idea, many many mortar tubes are made of fiberglas, they are cheap, lightweight and very strong.

The hardest part is finding a mold I think.

You'll need one of these:

http://www.polymat.nl/assets/www.polymat.nl/store/Store/ontluchtingsroller.JPG

Its a tool to roll the airbumbs out.

 

Try to find a polyesterfactory, they sell the materials much cheaper. Repair sets are way too expencive.

[FrankRizzo]

The model rocketry guys have been doing this for years. Granted, the body tubes are usually only a few wraps, but scaling it up shouldn't be the end of the world. Google "Fiberglass body tube" or something like that, and you should find plenty of resources.

[Arthur]

Why not find a local GRP repairer and give them the specification and get the tubes by van a week later. They should have glass and resin at bulk prices and good skills with mould making.

 

DIY isn't always the only way, you don't keep a cow just to have milk in tea, shopping is simpler and safer.

[mike_au]

It is hard to find Mortars in Australia without buying from overseas at expensive shipping prices.

 

What state are you in?

 

Have you considered paper? I know they are generally considered to be less robust than fibreglass or hdpe, but properly treated I believe they can be fairly tough.

 

HDPE is apparently available over here in the west, so maybe you could ship some from here. Still expensive but better than international.

[Arthur]

Paper tubes of suitable size are highly regarded for mortars as their failure mode is lots of small pieces of well shredded paper. They are also easy to plug -simply pour some polyester resin in to about the same depth as the tube diameter. Just do NOT get the tubes wet they do not recover!

[swervedriver]

The fiberglass "tape" you mentioned is a good weight, but wrong size I think. 200g/square meter should be flexible enough to work easily. You would be much better off getting a width of cloth at least as tall as the mortar you are building instead of the short roll you listed above.

 

The trick to strong composites is the fiber being fully saturated with resin, then the compression of the resin and air back out from the voids in the fibers. A 1 to 1 ratio of fiber:resin by weight works well. In other words, compression via vacuum or external pressure to remove any trapped voids is ideal.

 

EPS, aka "styrofoam" can be shaped to a cylinder ID of your choice, or just use a paper tube and reinforce it with composite. Epoxy resin is more expensive, and likely doesn't have any added benefit over polyester resin for this application. (EDIT- other than possible pyro chemical detriments with polyester, in that case, I'd have no idea which resin is better. I do know that alcohol and nitromethane attack cured polyester, so solvents are different) Neither epoxy nor polyester resins will attack styrofoam, use gasoline or other resin-safe solvent to dissolve the EPS styrofoam mold or core after the resin is fully cured. Polyester cure time is controlled by the amount of hardener added, if you stay on the lighter side of hardener addition, you can work in thin layers for several hours time. "Pot life" of the resin in the mixing container is shorter of course due to heat buildup of the curing reaction. Heat speeds cure time, cold delays cure time, and can even stop the cure time.

 

That said, you could make the wall thick enough without using a vacuum table to work as a mortar, I'm certain. You'll need to use more resin and mat though. Lots of work, but certainly feasable. I would use plastic sheeting with a thin coat of mold release or wax to roll the wet tube up in under even pressure, then peel it off after it cures. "Peel-ply" works good for this.

 

Oh yeah- a roller like the one pictured above will certainly help, those are used more for flat surfaces, but better than nothing. Squeegies make the cloth slide around and also pull out resin creating air pockets without using a vacuum or compression, hence the roller. I would use a lightweight glass weave cloth in several layers, and just roll it up on a flat surface inside plastic sheeting as described above to help prevent air pockets and aid in compression.

 

Carbon fiber would be one badass lookin' mortar, albeit more expensive. Kevlar would be harder to work with due to its' stiffness.

Edited March 8, 2009 by swervedriver

[TheSidewinder]

I took Minwax Spar Varnish, thinned it 50% with isopropyl alcohol, then immersed the tubes in that for a few minutes.

 

Let hang to dry, and note that you should leave them for at least one week to fully dry. I hung them up for ten days and that was just about right for the atmospheric conditions at the time.

 

I made a 4-shot rack of 2-inchers that I donated to the WPAG. The mortars were still in great shape last time I checked, and that was when they were a couple years old.