urethane / composite SIP question

[AndyL]

G'day all,

Quick question... maybe someone here can point me in the right direction...

Playing around with a SIPS design for a project, but having some issues with the urethane foam, when I calculate it out based on expansion ratio and volume, I can't seem to get it right - either I get voids, bulging, or both... I've tried injecting into assembled structure (sealed and with holes to allow air to escape), as well as open pan then laminating the 'top' after expansion but before the urethane looses its tack.... the later however doesn't work, seem to loose a lot of its strength by being assembled during cure - and isn't workable for the actual project...

I've tried a few different urethane products now - and having consistently inconsistent results...

Is there a trick to this? Am I needing compensate for temperature?

 

[Voi]

I have always heard of SIPS being made with a pre-existing panel of extruded polystyrene and then laminating OSB onto both sides with adhesive and a press or vacuum bag system.

Is there a reason why you're not doing that? Is it cheaper to essentially make your own polyurethane panels vs. buying a pre-extruded polystyrene panel? Or is it because you don't need adhesive and a press or vacuum system?

The idea of being able to cast a SIP either offsite or in place does sound intriguing but those expanding polyurethane foams seem to be pretty inconsistent. I have no suggestions on how to better predict expansion rates.

I have read some posts on other sites about DIY SIPS but don't remember where they were. I think most of the people posting were more in the grass roots research stage than there were people who had actually done it.

Sorry I couldn't be of more help. I'm intrigued to hear more about your project and experiences.

 

[AndyL]

Insulation value + strength, the main reason I'm going urethane... I did try polystyrene first, but as expected - the urethane was significantly stronger, and allowed for a thinner profile to accomplish the same task...

Main reason for the method - is compound curves... I'm not so much doing a SIP - as using the general SIP construction in the creation of a monocoque structure...

 

[Torque1st]

Without the proper equipment and knowledge urethane foam really isn't a DIY structural material. Do you have dry nitrogen? Do you have a vacuum degassing and mixing chamber? Do you know how to decant the mixed material? Do you have ovens for warming your material, drying the mold, and curing the completed structure? Are your molds sufficiently robust to withstand the expansion forces? If you have a specific project in mind you may need to seek out a company that is experienced with urethane foam structures.

 

[AndyL]

Yup, don't have most of that other than a vacuum chamber and strong enough mold - but roll forming machines don't have that either...and they seem to roll out SIPs by the truckload...