posted
Has anyone tried using HDU with the two part expanding foams? I had an idea and I was just wondering about the compatability as far as expansion and adhesion. If the expanding foam had larger air pockets would it expand at a different rate. If so do the different weights of HDU expand at different rates or are they compatable? For example would it work to use two 1" faces of HDU with a six inch layer of expandable foam between and what would work to finish the edges.
-------------------- “Did you ever stop to think, and forget to start again?” -Winnie the Pooh & A.A. Milne
Kelly Thorson Kel-T-Grafix 801 Main St. Holdfast, SK S0G 2H0 ktg@sasktel.net Posts: 5496 | From: Penzance, Saskatchewan | Registered: May 2002
| IP: Logged |
posted
NOT a very good idea! 1. 2 part foam is highly toxic (icocyates). 2. you need something strong to contain it (will break a container reinforced with 2x4s.
Companies that make the molded foam shaped items use steel presses to hold the molds together during the process.
-------------------- Si Allen #562 La Mirada, CA. USA
(714) 521-4810
si.allen on Skype
siallen@dslextreme.com
"SignPainters do It with Longer Strokes!"
Never mess with your profile while in a drunken stupor!!!
Brushasaurus on Chat Posts: 8831 | From: La Mirada, CA, USA | Registered: Nov 1998
| IP: Logged |
posted
I use expanding foam quite often and this is what I can tell you:
1. Depending which weight of expanding foam you use, adhesion could be a problem. 2lb foam is a lot of air and because of that the cell walls are very thin, which means they don't offer much shear strength. The cell walls will break easily which negates the bond with other materials. The foam won't delaminate from the other material, it will physically break apart from itself! You can use a higher density expanding foam, up to 15lb and 18lb and even higher are available, which will reduce the above problem but then you're adding a ton of weight, which is what I suspect you're trying to get away from.
2. You're going to have a lot of finish work.. you'll have to fill the edges of the foam to make it smooth, sand it, prime it, paint it, etc etc.. but first you'll need to trim the surface/edges to make it flat, which will make a HUGE mess... it's worse than cutting/carving/sanding HDU.
You'd be better off building a box frame to use as a backer for the HDU.. less mess and hassle!
-------------------- "If I share all my wisdom I won't have any left for myself."
Mike Pipes stickerpimp.com Lake Havasu, AZ mike@stickerpimp.com Posts: 8746 | From: Lake Havasu, AZ USA | Registered: Jun 2000
| IP: Logged |
posted
Kelly, The 2 will bind together fine as it is the same material(Polyurethane) but as Si & Mike pointed out the expansion is a Biggy. I usally machine Aluminum Mold boxes to to compress the foam to around a 15 to 20# density and will still get a little deformaty...(its not cost effective for short runs so I usally just use Reisn with fillers and get around a 80# foam if you can call it that) You see the way they make HDU. They Have huge stainless Forms and pour the liquid in and then put this lid on and it expands to the proper density.. Quite a science..
Si, Just for reference HDU has Isocyanates in it also. But Im fairly sure its Inert after it cures. (Least I sure hope so) Not that it would matter as I have 2 55 gallon Drums of liquid sitting here anyway.
posted
OK, guess that puts that idea down. I had a local industry that uses alot of the foam that said they would be willing to try this for me, but we really hadn't discussed the how tos and logistics of it. I didn't realize that there was so much force created by the expansion.
-------------------- “Did you ever stop to think, and forget to start again?” -Winnie the Pooh & A.A. Milne
Kelly Thorson Kel-T-Grafix 801 Main St. Holdfast, SK S0G 2H0 ktg@sasktel.net Posts: 5496 | From: Penzance, Saskatchewan | Registered: May 2002
| IP: Logged |
![[Eek!]](eek.gif)
and I was just wondering about the compatability as far as expansion and adhesion. If the expanding foam had larger air pockets would it expand at a different rate. If so do the different weights of HDU expand at different rates or are they compatable?
Printer-friendly view of this topic