Subject: Re: [harryproa] Re: extruded polystyrene core questions
From: "Rob Denney harryproa@gmail.com [harryproa]" <harryproa@yahoogroups.com.au>
Date: 5/11/2018, 6:20 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Great thread.  Thanks to all the contributors.  Plenty to think about.

As far as I am aware, there is less range in the extruded polystyrene available in Aus.  I am looking into this, and will do some tests when i get everything else finished.  I have also been trying to get some PET foam for months, but Airex are hopeless and afaik, there are no other local suppliers.  I may end up getting both from the US.  The blown polystyrene available here is not vacuum proof.

We have come up with a 'new, improved' rudder system which I am building a test version to try on Elementarry before including it in the plans.  To make the build easy, I infused a carbon spar 25mm/1" square and glued it into a piece of Bucket Lists chopped up hull (15mm/0.6" H80 with 400/12 oz double bias each side).  To do this, I had to cut out a trench with a cicular saw.  Did some tests while I was at it.  A 25mm wide strip of double bias peeled off the foam, taking a layer and some chunks of the foam with it.  Once the strips got down below 12mm wide, the top layer of the double bias separated before the foam.  Chiselling the couple of mm of foam off the other face was hard work.  I am happy with both the core and the bond.  

Please be nice to each other.   If you want some argy bargy, visit Sailing Anarchy and mention that you think harryproas are a good idea.  

rob 

On Fri, May 11, 2018 at 6:16 PM, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
 

I compared mainly the density, since it seems to be fairly proportional to strength (compressive, tensile, shear). The cheap xps seems to be about 25-30 g/cm3. And the strongest xps I've found had 45g/cm3. The other foams where 80-100g/cm3. So 1/4 was from 25/100, and 1/2 from 45/80.

With what do you agree?

What's the spec of the xps used in aircraft construction?

On Fri, May 11, 2018, 05:20 '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
 



On May 9, 2018 3:54:58 PM UTC, "Björn bjornmail@gmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
>So 1 sqm 80g/cm3 is ~36 AUD or ~20 GBP for 12mm, while 1 sqm 100g/cm3 Armacell PET is ~11 GBP for the same thickness. To be compared with 1-2 GBP for XPS in standard density (~1/4 of the strength).

 I'm not sure here, but i have no idea what grade you are getting of XPS.... And if you are paying 1-2 GBP, there is no way it is 1/4 the strength on H80. Do you mean 1/4 the strength of the PET?

And which grade of PET? Because they have some comparable to H80

And, I know we are kinda being informal, but by strength, you mean compressive strength, right?

I am using compressive strength, for the same reasons groper did in that boatdesign.net thread.

Now I am not sure that's right. But given all those disclosures...

Yes, Björn, i agree completely.


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Posted by: Rob Denney <harryproa@gmail.com>
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