Scoring Foam Core For Infusion

[Herman]

Try to avoid saw-cut, it will cost a loy extra resin and a lot extra weight.

[spiritgide]

I got an impulse about two years ago to build a unique boat. I do proto construction for a living, so used to going outside the box. This was a compact or small-water bass-boat, with big-boat features. The idea was to use a foam core but with some kind of honeycomb effect.

I ran across a company that makes an iso foam compatible with marine resins and available in several densities. The company provides foam in plain, scored, perforated or v-notched form and many thicknesses. The perforated offered a way to create a honeycomb structure. I played with some samples and liked the result, so the boat was built with it. The hole pattern I chose was 1/8" diameter holes, 2" on center. That puts about 1150 holes in a 4x8 sheet of foam. The foam was 5/8 thick, resulting in just over a 1" final thickness on the sides- 1/4" outer skin, 3/16 inner skin, about 60/40.

When you install the foam over forms, the holes add flexibility. Not as much as you might get from scoring of course, but in my case enough to pull and hold all the curves into place using screws from the backside forming. When you glass the outside, you keep your initial resin coat light to seal over the holes without dripping through. Once that kicks, you can build it heavier, then continue to lay up the outside. However when you turn the hull over to do the inside, you use a flood coat and spreader to fill every hole fully with resin before you put the first glass down. This creates resin posts between the inner and outer layers. This ties the two sides mechanically to each other as well as to the foam. This stiffens the sandwich substantially and adds impact resistance. I was building with epoxy, thus even stronger. I suppose the proper term would be "posted foam-core" or something like that. The material was easy to work with, and compared to others, more economical.

Worked out very well; the hull is light and stronger than expected. The foam came from Elliot Company- http://www.elliotfoam.com

I know they make a variety of densities, and of course they get stiffer as they get heavier.

[Herman]

I am trying to contact someone who should know, and who is probably willing to share info.

On spiritguide: also check a product called "structiso". Same principle, but even glass reinforced.

[jiggerpro]

Hi Herman, please do so, our next year purchases of scored core: for the tooling and for the first parts, considering the price differences between scored and non scored almost surely will offset any money spent in some kind of scoring "invention".

My problem is mainly "moral" I can not accept the fact that just the scoring can cost more than the material itself ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡

As you know, we have a CNC router, so we planned on cutting and chamfering our own core kits which we will certainly do, but it would be a real sahme not to be able to score it as well and then complete the manufacturing of our core kits completely inhouse.

[Herman]

Hold on: scoring costs more than the material? What do you pay for scoring?

[KnottyBuoyz]

I saw a picture on the net somewhere, thought it was Steve Marshall, but not sure, but he rigged up a scoring machine with a shaft, some old circ saw blades and a half inch electric drill. Just fed the foam through the blades. Kind of like a bread slicer. If I can find the pic I'll post it again.

[Herman]

Sawing is relatively easy, as you get rid of the sawdust, and make a path for the saw to travel. However, as said, you do not want sawcut, for the huge resin uptake.

Try running 1 knife through Core-Cell, cut 20mm deep in 1 go. Multiply the force needed by 40, and then you can make double cut in 120cm width, 30mm block size.

[Sand crab]

This is on ebay. They have 1/2 and 5/8
http://www.ebay.com/itm/DIAB-DIVINYC...item2c5fc7deb5
BOB

[Herman]

Am I stupid, or is that Ebay auction utterly expensive?

I presume it is sold by the sheet, which is 0,99 m2 and costs 80 USD.

My regular price for Airex C70.55 material (direct replacement) is 30,38 euro (USD 49,52 including 19% tax), excluding any discount.

Besides that, the pictures show "double cut" and not scrimmed. Double cut actually is cheaper.

And as a side note: I would not use 60 kg/m3 in boat hulls.

The stock I advertise in my signature even has considerably lower prices.

[jiggerpro]

Hi Herman, the difference in prices I mentioned between scored and plain, was not from the same vendor, it is when you compare a composites vendor scored products with a construction/insulation vendor plain products that " the scam " shows up.

Apart from outrageous profits which IMHO are unmoral, I have technical reasons for wantin to do it inhouse, those are the fact that I could cut the contours and chamfer the edges much more easily with our CNC router if the material is plain ( unscored)
than if we try to do it with the material already scored because then is much less consistent because of it being formed by many small squares attached to a scrim ...

There has to be a way, in regards to your comments about running a knife thorough corecell 20 mm deep in one go, you should consider that there is no need to do it in one go, the CNC machine can do the cutting passes with any depth that you want so the cutting force does not need to be that much, for example passes can be easily programmed to be of for example 5 or 10 millimeters, and the blades ( carpet cutter blades ) could be angled in a fashion that does not crush the foam.

I "have" a supplier that could supply polyurethane sheets in any density and in any thickness whith a price around 5 euros/m2 ( for around 25 mm thickness) and this would be ideal for the rigidization of all our tools (moulds) if interested let me know ..

Maybe I have the scoring machine idea quite ready already and is time for some tests, I just do not want to take more time from our main goal which is advancing towards our boat launch day ... but this seems to be another neccessity ...

[Herman]

You are not seriously comparing polyurethane foam with PVC and SAN foam, are you?

The price for PU foam (35 kg/m3) is around 200 euro / m3, so that fits exactly into what you pay. But I would not reinforce my moulds with this material, but use balsa instead.

[jiggerpro]

Hi Herman, no I am not comparing those materials I know PU to be much inferior, I am talking about the reinforcment of our moulds not our boats, in our hull mould and to avoid it being too heavy we want to give it rigidity thorough the use of a sandwich and for this static purpose with no water around PU foam of enough density is more than capable to whithstand the loads. the price differences I have commented are both for the same material PU foam.

The boats themselves, will also have sandwhich but in this case we will use corecell exclusively since in the boats there will occur dynamic loads and the possibility of water permeation so the use of any SAN or PVC chemistry foam is needed in order to achieve a durable resilient laminate.

In regards to balsa yes of course is probably the best becuas ein the case of end grain it has the best compressive strenght but it also is quite expensive, and for sure it has some strenght to weight advantages against PU, but weight is not so important as to be worth the price increase (IMHO)

What we are looking for right know is not for the best boat foam, but are looking for the best price to quality ratio in a foam for the moulds whcih off course have different requirements than a boat due to different loads and different environment.

Having said that I will gladly accept any offer you might make me in regards to a good price to quality core for our moulds, we need 70 square meters for our hull mould only ( 50 m2 is the exact measure but we want to have some spare material )

You know my e-mail please let me know what you can offer, you could also include some 400 kg of mat and some 300 kg of some "mainly unidirectional" reinforcment fabric to be used in the outside of our mould to give it some more rigidity length wise which is the direction of the loadas when it will eventually be suspended in the turning mould system.