PVC Structure and Laminations

Just to test the idea of sticking epoxy to PVC I made up some samples. Several sections of 3/4" pipe were used all with WestSystem, 205 hardener and their fillers 403, 404 and 406. The pieces with unabated surfaces, thickened and unthickened attachment didn't survive the slightest of bending movement before delamination began. The abated surfaces held on a bit better, though I surmised the mechanical keying on the roughed up surfaces had as much to do with this as anything else. As I expected the colloidal silica thickened joints did the best whereas the unthickened joints the worst. I leveled the first few, flush with the tops of the pipes, but soon realized that I was tossing a bunch of filler and epoxy at this and the weight issue came to mind. This would be a very heavy laminate. The structure is 30% epoxy and reinforcement, when you make a cut through it with a chop saw. Not a good use of materials and in light of the costs of this structure limited to say the least.

You do save some money in the use of PVC, but it requires a bunch of epoxy and reinforcement, though fairing is reasonably easy with the pipe tops as a guide for the plastic applicators I used to fill the gaps.

I didn't try to fill the pipes as the structure has enough cross link built in using the pipes between sheaths. A better idea would be to chemically weld the pipes into position, strip plank style, fair then skin, but with polyvinyl or polyester. I'd think polyvinyl or polyester would have a much better chance of sucess then epoxy and would cost conciderably less.

 

If I recall well, an ISO-NPG polyester bonds to PVC.

Why fill the pipes with something? If you hit something, some pipes may fill with water. But as the pipes are hollow, they will also drain water easily. Besides that, a boat is a big hollow thing. dividing this in more smaller hollow things is nothing to fear. as long as there are still plenty of single skin boats around...

Nida-Core is a polyethylene cell structure, with polypropylene film thermally bonded to close the cells, and a polyester scrim melted in the pp for bonding purposes. (at least, the type suitable for composite construction is composed this way, there are plenty more types)

 

Had an idea for changing the shape of the PVC tube. By heating it and then rolling it thru some sort of die. Perhaps round corner square could be made. This might be easier to glue together with the increase of surface area in the joint.

Secondly, I was thinking the pipe could be woven together or lashed together with fibers. The fibers could be "set" with resin.

 

Hawdy...

Sorry it took so long to host this out...had to lecture a little to begin to get resorces ready for my design to enter home production. The wifey is of-course having a knip-fit...but tada.

What in Neptunes green sea have I stormed here. Too much information happening. Par... ahem, I ahh, you beat me to the first part of the test by 2 days and ahh, well you know...you may have been...ahem, maybe I wasn't totally, well, you were not so wrong. There I said it. The piece still looked like it had some development possibilities but I almost threw out a hip and had a hernia trying to move it. It was mad heavy! I'm trying to see how it would compare to a solid glass piece in weight, not thickness.

I see that this thread has evolved into some serious think tank with lots and lots of great unthought ideas. All worth exploring. Nero...no! Bad boy you trying to change the whole shape. The purpose is the strength inherent in the circle not the square and no no no. I will look into all of these and I guess that this is a good time to start an "experiment to do list" in case if I need to prioritize these different brainstorms or if they come in too fast.

Okay...keep them rolling in...

Fair winds,

Jay

 

Par...

Care to elaborate...

Jay

 

Care to share some more info?

Jay

 

Excellent!!!!! How far apart would the holes be and would we have to learn some kind of medical stitching process in order for this weaving to take place?
Would it be sewn together longitudinally two at a time or vertically all at once?

Jay

 

As we know PVC can be welded, both heat and chemically (the little cans of cleaner and goo on the shelf where we keep the plumbing stuff) This bond is the best and will provide a water tight connection between surfaces. I picture a strip plank affair over molds, one pipe welded to the other with some sort of temporary clamping used during the short cure time needed for the chemical weld to work. You'd then have a continuous structure of tubes, welded along the contact points (rather small area though) which could be filled. I'd use a two step filling operation, the first being one to fillet the pipes together using a structurally reinforced poly, then a second coat to fill and level the surface using a light weight filler set in poly, then the sheathing on each side.

The only reason I'd fill the pipes would be to insure no water weight gain in the event of a breach. A crack across several pipes could amount to a great deal of water weight entering the craft, possibly upsetting the balance enough to capsize a small boat. A light weight (low density) foam could be injected in each pipe rather easily during construction.

To answer your question, JCFARER, the structure has plenty of cross sheath connection. Picture pipe set in a row, lots of circles, butting against eachother. Every inch there is a 1/4" wall where the two adjacent pieces are married with the weld and bridging the core width. With the added fillets, a strong, if heavy structure.

I would not puncture the pipes in order to secure for the weld or gluing process. First it would add a great deal of unneeded effort and it would also provide more ways to let water enter the core or worse, start a stress crack. Unless a sure fire adhesive could be found, welding is the only option I'd consider. Welding makes two pieces one, glue doesn't unless it can attack the surface chemically, which I suspect poly could do. In the end, I'll bet Red Western Cedar, Balsa or other core would make a lighter core, but maybe not as cheaply.

How about, very well sealed pipes, with a lighter then air gas injected (don't run into any pointy stuff) to help overcome the weight issue . . .

 

Excellent!

I will take some time to do some of this.

Jay

 

The weight of the structure would be to high. Have you calculated it?
The cost would also be too high. The amount of glass and resin to fill all the voids would be close to that of a solid laminate.
The cost of PVC compared to wood or foam is higher too; specially if you are planning on foam filling the pipes.
Any structure needs a cost/weight/durability/construction time study to compare it to others.

 

you should be preocopide about it ability to pass share tress. you can space the pipes in such a maner that the foam will pass all the stress. It is common pracrics in ferrocement construction.

 

Hawdy Gonzo...

Jay here. Perhaps you're right, maybe not. All that you said has merit but it is all relative. Heavy for a multi maybe, light for a mono maybe. Cost also is relative, for the working mass like us, cheap or free is right, for others, well the more they spend the better they feel. I'm not so sure the cost of the materials is lower than PVC...I have to check but I'm inclined to disagree. We do agree that it is almost like a solid laminate but that tells me that the construction time piece of the study is going to reflect that it will be easier, simpler and faster...therefore cost reduction on the hard costs, labor, etc. I am almost inclined to say that the skill level will probably be that "anyone will be able to do", unlike laminating a male or female form. Durability is without a doubt going to be high...will it be structurally durable is another subject which we are exploring here.

Thank's for the thoughts...have some more you care to share?

Jay

 

Hallo Amitik...

I think that I am super preoccupied with the shear loads and other structural concerns in order to make any sense of this idea. Have you read the thread...there were some good suggestions by Par, Nero and others...but I think that right now, spacing the pipes would change the whole idea which is the simplicity of having the pipes together and the inherent strength of the radius which may be reduced if they are not against each other.

A couple of the fellas came up with some great, great ideas on bonding the pipes and we're exploring it right now. I think were in agreement that there are drawbacks but there is definite possibility for developing different procedures and or materials to reach what designers call " a compromise".

Jay

 

Par...

Do you think that maybe we should leave the ahh, well you know, the explosive element stuff in its free state instead? Capturing and compressing sounds explosive. It's one thing to scramble out of the bunk wild eyed due to those things that go bump in the wee hours of the night...it's quite another to become a human projectile attempting to evade and egress due to those things that cause a kaboom and kapow. I mean you know, one explosion and the whole hull will desintegrate instead of just having a hole, know what I mean?

Jay

 

No hole drilling for passing fibers thru. Just use two tows at the same time. One comes across the pipe from one side and the other tow from the other side. Perhaps kelvelar tows (okay it is not cheap) would work the best. Or perhaps nylon strapping. Or maybe that cheap polyethelene rope from Wmart.

Going back to being a bad boy. I think squared pipes would give the following advantages.
1. Larger bonding surface for the pipe to pipe joint.

2. less bog and fairing putty. the flute area is transformed to the inside of the pipe.

3. larger flat surface to bond the skin to. Assuming someone finds something that will stick a fabric to the PVC.

On filling the pipe. This may be a challenge. I have tried to fill steel tubes with foam-in-a-can. It does not work! The foam will not cure or rise except at the ends. It seams this makes sense that the chemicals needing to leave can't.

Screaded white polystyrene foam with something might be a way. The pipes can be stood on end, the morter poured or funneled in, and then put on the form before the mortar sets. Will have to be carefull that the cement agent does not shrink when it cures. Also something that is not water based. Inside a plastic tube the stuff would never cure.