The lower density of XPS allows for a thicker core for the same weight. The fiberglass laminate on the surface provides the rigidity needed to protect the foam from permanent compressive deformation caused by sharp impacts. T his means that the laminate needs to be thicker in impact areas, which means more weight, negating some or all of the advantage in these areas.... decks and such. These areas normally would have a thicker laminate anyway for this reason, or an overlay of something like strips of teak, or ersatz teak, etc, so it's probably a non-issue.
I've had fantasies about laminating two foams together to make a progressive core also. The optimal load bearing sandwich would be sort of like the optimal beam structure, which would progress from a very high strength outer (fiberglass) that actually carries the tension and compression loads, to lighter and lighter structure as one approaches the neutral axis, then progressively stronger as one approaches the opposite surface. Charts of beam loading look like an hourglass. Obviously this is not practical in the real world. In a sandwich structure we have a load applied that is carried over a wide area. In extreme situations, such as testing to failure, the failure mode should be the glass shearing away from the foam, not failure of the glue line, but of the foam itself, and the two surfaces moving in opposite directions (relatively). In real world use, we simply are not going to see this, short of a catastrophic incident such as hitting a reef at speed, or a collision between two boats, etc. In that case any structure is likely to fail, and repairability becomes the issue, after the ability to make it into port intact.
In the minimal experimenting I have so far done with XPS, I've found that a "flash pass" with a sand blaster using fine media will open the surface layer of bubbles, much like proper hot wiring does, and is a matter of literally seconds of exposure. This should address any issues of peel strength. Any more than a quick "flash pass" will distort the surface. I don't own a shop sand blaster or glass bead cabinet, and have been playing with an ordinary undercoating gun. The only media I have at home is extremely course. The reflective beads used on highway centerlines..... I've got a 3 pound coffee can full of it from painting the sides of my flatbed trailer. They are very effective, but do not cut like regular media, but I want to do a try with a real sand blasting media. I know where I can grab some. The undercoating gun is a very cheap item, readily available anywhere. Mine was purchased for doing bed liner, which incidentally I suspect would probably make an excellent, rugged, grippy overlay for decks. I wasn't using it on a deck, but the stuff I used was extremely impressive. It was an epoxy / urethane hybrid by a company in Texas, called Rattleguard. No longer in business. Incredibly tenacious and rugged. I have two small pieces of XPS foam with epoxy / glass on them I laid up this morning. I'm not sure the weight of the woven fabric.... 7 oz? One was flashed with media first, the other not. The epoxy was the only epoxy I have in any quantity, a very high quality structural adhesive by System Three normally used for wood aircraft and boat building, T88. Not a laminating resin, but I see no reason not to use it for this. I have about half a gallon of it on hand.
Stay tuned for results........ I'll probably let it sit for a day or two before testing peel strength, etc.
H.W.
On 05/15/2018 05:03 AM, '.' eruttan@yahoo.com [harryproa] wrote:
>>Like are 3" H80 even cheaper per inch? Or is there a sweet spot? Probably better to ask Rob for the pricing situation. Rob, how does this work?
>As far as I know, D/cell is saw cut as the fumes are toxic. It is made in large blocks, which the manufacturer cuts into sheets.
But what about the pricing? Are thicker inches cheaper?
>> So this should be able to make thinner H80 sheets. Assuming you are gonna be scoring/routering and holing both sides of the sheets for infusion anyway, I cant see hot wireing bothering the surface to much. But I have no idea. Anyone got an idea?
>>
>>So if you could cut your own then you would save money. Less the wastage from the cutting.
>>
>> The hot wiring should not lose much material?
>Very little, but the surface will probably be sealed, so it would be like epoxy onto a pvc bottle. No good. The foam works because of the huge surface area from the broken bubbles. The scoring and perforations are too few/small to make much difference.
I don't know if you saw the link to the aviation foam, but it had the blue foam one uses for the Rutan and derivatives. It is a large cell XPS foam, and is hotwired into shape. You can see the open cells after hot wiring, if you did it right. It is not flat and smooth like a cast plastic after hotwiring. Also, it is epoxied to all the time with no treatment after, unless you had a hiccup, in which you sand the bump, or fill the groove. But you do learn how to do it. You have to get the hotwire the right tension and heat and move at the right speed. Not hard, but one learns skill.
I cannot say how pvc will behave, but I assume that with time and skill one would still have open bubbles. But i am often wrong.
>Do not put the fan behind you, it will form an eddy and suck the gas towards you. Better still, figure out if your life is worth the cost saving from cutting your own foam.
Well done. The fan in line with the hotwire and blowing along it is a much better system. And a jar of open ammonia positioned strategically would add even more protection.
I am not advocating such a thing. Just thinking on how one might do it safely.
It should be noted these toxins degrade quite quickly when exposed to moisture, apparently. So it should be ok to blow into nature
But if one can get 12mm sheets for 80+usd, and cut 3 (because some loss) 3mm sheets, for me, that cuts the price to 1/8th. So its worth thinking about. I cannot say if its worth doing.
>My local foam supplier uses an abrasive string for accurate cuts, I weill show him the vid.
Abrasive string is inexpensive. And perhaps a similar table could be made for an abrasive string machine? Perhaps oscillating? Or winding in a loop?
>> Does that mean the whole premise of a thicker foam core makes the infusion harder generally?
>>
>No, unless it has to bend which doesn't happen with Intelligent Infusion.
Do you mean no bending post mold, post infusion? Or no bending foam when laying out the mold for infusion?
>> I see some vendors are making multi density foam cores, where the outer layers have more compressive strength, and the fill a center core with a lighter core. Which is neat, cause its the same engineering math all over again for the light core supporting the heavier core. Seems we could diy that. Thin sliced H80 over whatever grade XPS is appropriate.
>>But is this practical in an intelligent infusion layup?
>>
>Not really as the resin needs to travel between the foams to glue them together, requiring a medium for the resin to travel along, so the weight gain may not be there. You could preglue the foams, and it would be worth experimenting, but I suspect it would be more trouble than it was worth.
>Make sure there is no squeeze out or lumps of cured glue on the edges of the foam.
I meant pregluing and scoring and holing the foam as a unit.
So many experiments, so little time.
Maker Spaces are a thing, and they often have a 4'x8' cnc router available, like a shop bot.
So one could cnc score and hole a surface with such a thing. Does that seem reasonable?
Posted by: StoneTool <owly@ttc-cmc.net>
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a new topic | • | Messages in this topic (62) |