The pouring urethane sidewall thread

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gozaimaas
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The pouring urethane sidewall thread

Post by gozaimaas » Sun Mar 10, 2013 8:44 pm

I thought I would start this thread so that info on pouring urethane sidewalls can all be found in one place. If you pour your sidewalls please post up.

Ill start.
I used smooth-on product smooth-cast 305. It works very well and machines up easily. It is also quite hard and impact resistant. It cures in a bright white which is nice too.
I have put around 40 days on one of my boards and have had no issues at all. I even forgot to put vds rubber on that board and have experienced no delamination at all.

My biggest issue was bubbles forming as it cured so I built a pressure chamber and put the cores in that while they cure, this has solved the bubble problem.

Data sheet
http://www.smooth-on.com/tb/files/Smoot ... ___310.pdf
Last edited by gozaimaas on Sun Mar 10, 2013 9:30 pm, edited 1 time in total.

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falls
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Post by falls » Sun Mar 10, 2013 8:50 pm

any surface preparation on the 305 prior to layup (sand/flame?)
i have mine sitting around waiting for time to experiment. 40 days seems like good enough feedback to try it in some skis.
Don't wait up, I'm off to kill Summer....

gozaimaas
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Post by gozaimaas » Sun Mar 10, 2013 9:01 pm

Some pics of my efforts.

Image

You can see some of the bubbles in this pic
Image

Image

The pressure box
Image

The first one I did at atmospheric pressure
Image

Image
Last edited by gozaimaas on Sun Mar 10, 2013 9:21 pm, edited 1 time in total.

gozaimaas
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Post by gozaimaas » Sun Mar 10, 2013 9:07 pm

falls wrote:any surface preparation on the 305 prior to layup (sand/flame?)
i have mine sitting around waiting for time to experiment. 40 days seems like good enough feedback to try it in some skis.
mine is just finished with a belt sander. There is definately no need to flame it, like I said I even forgot the vds rubber on the board I put 40 days on.

Upper Left Coast
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Post by Upper Left Coast » Mon Mar 11, 2013 12:37 am

Lesson learned: Don't try tinting poly with acrylic paint, stick to pigments suited for the purpose. "only a couple drops" is enough to turn your polyurethane into spray foam. oops.

Richuk
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Post by Richuk » Mon Mar 11, 2013 3:38 am

Two or three colours part mixed and poured to give marbling. The board looks sweat man!

Splitboarder
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Post by Splitboarder » Mon Mar 11, 2013 8:05 am

Hey gozaimaas. Can you tell me more about your pressure chamber? I've tried putting the smoothcast in a vacuum chamber before pouring and passing a flame over it while it cures. I still can't get rid of all the bubbles. What sort of pressures are you using? Are you running into time constaints pressurizing it in time before is cures? Thanks.

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chrismp
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Post by chrismp » Mon Mar 11, 2013 9:36 am

I've been using Adiprene LF950A with Ethacure 300 with very good results. Only downer is that it has an amber tint to it so it's not the best resin to use for bright colors. I use a diy vacuum chamber to degas the resin. It's an old pressure cooking pot with a thick acrylic plate as a lid. We routed a channel into the acrylic plate and filled it with sanitary silicone as a sealant. Add a vacuum port and you're there.

It would be great if you could tell us more about your pressure chamber and maybe post a few pics! :D

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MontuckyMadman
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Post by MontuckyMadman » Mon Mar 11, 2013 6:49 pm

Im thinkin the 70 shore d material is the ticket. In my tests the adeprine was softer than uhmw and deformed easier than uhmw., but bonded easier but was a pita to machine.
The elongation at break of the smooth on material is half the uhmw but it might not matterthe tensile strength is there and bonding would be better i bet. The bubbles are a problem however.
sammer wrote: I'm still a tang on top guy.

gozaimaas
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Post by gozaimaas » Mon Mar 11, 2013 6:55 pm

Ok, with the smooth-on product I find the bubbles dont form until right at the end as the heat increases, just before it hardens so trying to degas etc simply wont work.
I read on the smooth-on site that if you experience bubbles simply put it in a pressure chamber at 60psi. Easy for some, not so easy for what I was doing but I decided to give it a go as I really like pouring urethane for sidewalls. I think its the ultimate way of doing the job.
So I built that box from 17mm plywood and 30mmx50mm pine sides so I had some meat to screw into. I glued it all up with construction glue, put in a heap of big screws and let the glue cure. I also made an end plug that screws in with a silicone seal.
When I pumped it up one of the pine sides split along the grain at about 15 psi making a sound like a gunshot. I then put threaded rod and nuts all the way around and it held up fine but leaks a fair bit from the end cap. With the compressor running flat out it maintains 30psi in the chamber and the results are excellent compared to atmo but there are still some bubbles.
I didnt have time to correct the issue as I was flying out to japan in like 5 days and had 4 more boards to build so I did the rest at 30psi with not perfect but very acceptable results.
I am now going to fabricate a steel sleeve that will glue into the end and have some threads tapped into it so I can use a steel end plate with silicone oring to achieve a 100% seal on the end and hopefully achieve the 60psi smooth-on recommends.

I have no trouble getting it in the chamber and up to pressure before it starts to kick. I pull after about 30 mins from mixing.

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falls
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Post by falls » Tue Mar 12, 2013 2:12 am

For skis if you had a wide enough diameter fire hose you could seal one end and slide the core with poured polyurethane in. If you could then quickly seal the other end and have it in a narrow space in your press when you inflated the hose it would get to 60psi but the hose would stay flat enough so the core would still just sit on the bottom of the hose.
(Or even put a steel rectangular thick walled section in a piece of hose and slide the core inside it then seal the end and inflate?)
Don't wait up, I'm off to kill Summer....

gozaimaas
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Post by gozaimaas » Tue Mar 12, 2013 2:50 am

Interesting concept but from my experience you would end up with liquid urethane everywhere. If you tilt it even the slightest amount it pours out real fast.

gozaimaas
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Post by gozaimaas » Tue Mar 12, 2013 2:53 am

You could easily make a pressure chamber for a single ski core from some steel rectangle tube

Skierguy
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Post by Skierguy » Fri Mar 15, 2013 3:27 pm

How about using either an 8" or 10" dia. PVC pipe for a single ski's pressure chamber? It should give you enough more than enough space to make a small shelf within the pipe to place the core level. An 8” pipe should give you at least 7 ½” of usable width and a 10” pipe 9 ½” (Assuming 1 ½” tall working space)
One side with a glued cap and the other a threaded cap you should be able to slide the core in and thread the cap onto the pipe with plenty of time to pump the chamber up to pressure. Assuming you used schedule 40 pipe, it has a max pressure of 160 psi (water).
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Richuk
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Post by Richuk » Fri Mar 15, 2013 4:30 pm

Would it be possible to sandwich a piece of plastic (none stick) between two cores. Place the stack in the press, pressurise and pump the urethane in under pressure?

The urethane would be in a pressurised pot, open the tap and the fluid runs in. The pressured bead would flow around a circuit. The compromise would be a 2mm section - a dividing wall, so that the bead of urethane flowed from point A to point B, passes through the plastic into the top layer (second core) and exit via the bleeder hole. Both cores would have this 2mm compromise.

Thinking there would need to be a thin none stick film - polyprop, silicon paper etc, between the core and the plastic or hardboard or whatever. When it come out of the press, peel back the film

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