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Polyurethane Rails attempt - SUCCESS!

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Polyurethane Rails attempt - SUCCESS!

downunder
This post was updated on .
Two days ago I've used the PU resin for my rails for the first time ($80/kg!).

Disaster.

The Polyurethane I've got from a marine shop is a way to soft. It's got a way to much air bubbles in it even after "resting" (de gassing) the resin in a full vacuum for a few minutes.

Flaming was not going well - it actually caught fire! The core is ok tho.

The green and orange color is dull.

In overall, I've made two cores with it and will try to pull the ba$tard out of the rails this arvo...

Adding some photos soon.

P.S.

Forgotten to say, this PU is also shrinking I would say. None of this is found on the Tech details.  

P.S.S.

I've made some calls now and in Australia for a 450 grams PU shore 94 is like $105!!! Sick. Will use epoxy.
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
The verdict (I'm still thinking what and how to use the PU):

"From one of the world authorities on the topic.

Moisture. 0.2% moisture content in the materials will cause the polyurethane to foam. By foam I mean like house insulation foam. It takes a great deal of care and heat to drive the moisture from the materials. In the case of the wood core, it is next to impossible to do;"

Ha.
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

mattma
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Wow. So its part of PU properties that it foams. I have used PU glue to glue the planks in the core together and it foams up but I thought that was some additive but seems like its not. Thanks for let us know.

The shore 94 you mentioned, I'm guessing that is A and not D hardness scale ?

Matt
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
Shore 94A, tough and expensive stuff. This one I've got is like 10 and
thinking to make a heat blanket of the rest of it.

Do you think this soft PU would work for a heat blanket up to 80C?

Are they any fumes going off on a silicone or PU blanket?
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
This post was updated on .
There we go, the PU & bubbles on the right and epoxy on the left.

I did vacuum it and flame it. No luck.




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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
Arrived today!

The PMC-790 is the real stuff. It's industrial. It's proven with the ski/snowboarding industry. And expensive.
Hopefully it will work for me.

The Mold Max 40A is for my heat blanket. I'm waiting for some nichrome wire from Germany. And PID.

But let's make some PU rails first! Can't wait.

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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

mattma
Administrator
Tell us about the PMC-790. What is it? Where have you seen it used? How much?
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
Hey Matt,

this guys are using it with the bamboo cores:






They say no air bubbles. My idea is to make a premade rails, maybe using some perspex with a channel and than placing it in a pressure chamber (which will need to build 

But seeing this photos I might try first on a my bamboo and see how it goes. It's shore 90A, about $60.

PMC-790 might be hard to sand or machine, will see. Tear strength  300pli, elongation at break 550%.

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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
In reply to this post by downunder
Guys,

I am very surprised with this PU.

No air bubbles at all after de-gassing and it will work with flaming too

The rails #6 and #7 done!


So here it is. De-gassing chamber


 
I just love this colors! You can see the core #5 behind (epoxy rails).

Some paper is for leveling. The rails looks quite curved but they are not.





The next stage is a top layer. Still thinking about it and how to do it this time.
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
Hm,

hoping that I've put enough hardener since 5 days after is still not rock solid.

They say it is stiff and with little flexibility. Well, not yet. Will see...
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
I'll bite the bullet and continue working on the rails.

When comparing epoxy rails and PU the PU has some more air bubbles on the surface. Here end there in the rails as well. But I'm happy with the result.

Trimming the PU excess first with an ultra sharp Japanese knife and than with a sander (bubbles visible):



See the bubbles here:



Sanded all 3 cores and ready for the next stage:





I do not know if using a PU is worth of effort at this stage. Yes, it is not so brittle as epoxy, but it is a lot of work and bonding with FG is still unknown (reports says ok). Might run some tests to confirm.

Hm. Maybe would be better if I did this before using PU on my cores. Duno. Time will tell.
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the precious advice coming from the kiteforum.com:

- to eliminate the air bubbles in the PU rails, seal the rails first with epoxy (sealer?). Keeps the wood moisture out of PU.
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

mattma
Hi Downunder,

what would you say is the benefit of PU over epoxy for rails?

Matt
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

downunder
Duno Matt.

Will report back after I build this boards. Bonding might be a huge issue here. I will use G-Flex epoxy just to wet the rails before a FG. There must be no delam issues or I'll dump the PU completely. But, now I'm off to short holidays...Ah, yeah, check my blog, a new baby just arrived into the building!
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Re: Shinai 131x41, bamboo, FG, carbon-kevlar

sijandy
you shouldn't have any bonding issues if you make sure and scratch up the surface well. I also have had bubble issues with the pu, will try the epoxy seal idea next time!
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So, who want's PU rails?

downunder
In reply to this post by downunder
This is my second attempt with different PU. Cost up to date around AU$140

Enjoy this video


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Re: So, who want's PU rails?

downunder
This post was updated on .
Learning from experience.

Whoever is using the above PU for snowboards and reporting good bonding with epoxy - WRONG.

It was a disaster even bigger than my first PU (manufactured in AU). This one was a second attempt, and how easy was to peel this off a bamboo core?

In overall I took the whole thing off in one quick move. With my hand. No - two fingers

I would suggest to stay clear from the PU rubber of ANY toughness, even 100A (similar to 60D) wont cut it!

So this time (3rd time  ) I am going with this:




This is PU liquid plastic. Pot life 20mins. Xtend-IT nitrogen gas to extend the shelf life of my PU resins.

Cost for both AU$60.

"The Smooth-Cast® 300 Series of liquid plastics are ultra-low viscosity casting resins that yield castings that are bright white and virtually bubble free. Vacuum degassing is not necessary. They offer the convenience of a 1A:1B by volume or 100A:90B by weight mix ratio. The differences between them are pot life and demold time."


This one is based on another snowboard maker who claims good bonding as well:

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Re: So, who want's PU rails?

downunder
I moved this posts into the separate thread under this forum....


Anyways, the bonding with 310 is not the issue. It bonded with bamboo hard, really hard. If you imagine a plastic hard - that is it.

The issue with Cast 310 is mixing with pigments. It doesn't reproduce colors well since it will cure in a pure white. Snow white. Which is nice I think since very visible on the water.

The other issue is air bubbles and foaming. I do not know why but it might be because I tried flaming it and it foamed.

Extreme foaming and extreme air bubbles on wood. EXTREME! Did I say EXTREME?

However, the leftovers in a mixing cups cured perfectly. No air bubbles or foaming at all. PERFECT RESULTS!
I even cut some in half's just to see if there are some air bubbles inside. None. Zero. Nada. Nula. Nistica...

Photos soon.
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Re: So, who want's PU rails?

Chris
Maybe it's reacting with the resin in the wood? Have you tried it on another type of wood to see if you get the same result?

Have you tried vibrating the mould once placed and still liquid to try to migrate any bubbles to the surface?

How hard is the stuff once cured? Could you cast lengths of the correct cross section then gently heat it to soften and bend into the rail shape required? Obvioulsy the problem with that solution is bonding to the core/laminate after placing so you would have to roughen the bonding face to give a mechanical key rather than some form of chemical bond
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Re: So, who want's PU rails?

downunder
Chris wrote
Maybe it's reacting with the resin in the wood? Have you tried it on another type of wood to see if you get the same result?
Maybe. I did not tried it yet and got only bamboo to work with.

Chris wrote
Have you tried vibrating the mould once placed and still liquid to try to migrate any bubbles to the surface?
Hm, this is interesting - no air bubbles after pouring in a first few mins. It's very liquid, much more than anything I've worked with. Crystal clear as well. No need for vacuum - no bubbles at all after mixing.

It foamed some time after pouring. Duno when. But ONLY on wood tho. As said, mixing pots are perfect.


Chris wrote
How hard is the stuff once cured? Could you cast lengths of the correct cross section then gently heat it to soften and bend into the rail shape required? Obvioulsy the problem with that solution is bonding to the core/laminate after placing so you would have to roughen the bonding face to give a mechanical key rather than some form of chemical bond
Really hard but a bit softer than epoxy. Can't imprint my finger nail into it - impossible.

You could cast it, as the name says - Cast 310

But do not know if can be soften and bend. A new experiment? Anyway, the idea is to make a precured rails.

If can't be done, than sealing rails really well before a PU might get very good results.
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