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Hi all, I've got a few questions regarding the 'new' product 'XenCast Flexible Polyurethane Rubber' advertised on your website. Basically I'm making a couple of moulds with the intention of casting 'Vac-Cast Epoxy Resin' into them, what I need to end up with are two perfectly reproduced tooling plugs for vacuum forming my final parts into ABS plastic. The following image will hopefully explain in greater detail my procedure. I've recently used a product from 'Smooth-On' called 'OOMOO 30', but had a disastrous result. I must admit, as good as it seems to be I just hate working with it. Here's what my original mould box looks like with my plug secured in the base, I then poured the silicon rubber into the mould box ......... it was an awful lot of work, trying to mix what was a consistency of partly molten lava, and the impossibility of pouring made the job needlessly difficult, the result was a failed pour and a very badly formed mould ! >>  Pouring the mix in a thin stream in a low corner was just impossible, I almost had to resort to 'trowelling' it in ! >>  When I demoulded the following day, it wasn't too bad, but strictly speaking an appalling result. Not something I would want to cast resin into that's for sure ......... I put it down to a good learning experience >>  Because the silicon rubber wasn't 'fluid' enough, full coverage of my plug wasn't achieved, leaving large voids and air pockets >>  So basically, my question is, would that 'XenCast flexible Polyurethane rubber' be an alternative to OOMOO 30 ? I've been looking at the 'XenCast PX30', it seems to have the same characteristics as the OOMOO 30 ( both Shore A of 30 ), how will it react to Vac-Cast Epoxy Resin being poured into it ? |
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Hi guys, Thanks for those kind words guys ........ yeah, really happy with the way it turned out, resulting in two immaculate silicone moulds 
After only having one attempt at mixing and pouring RTV silicone prior to these ( the outdated OOMOO 30 fiasco ), preparing and mixing just over 4Kg of silicone can be a stressful experience for a novice such as myself. What calms the situation is the knowledge that the CS25 has a pot life of around 60 minutes, so there's no need to panic as you would probably would do with other silicones with shorter pot lifes. Things did almost go pear-shaped immediately though ....... the scales I bought from EC, really aren't up to the job I don't think. Not EC's fault as they didn't design them, who in his right mind would design a product like that, that are an 'Auto Shut-OFF' system !? I was midway through pouring the silicone into my weighing bucket when the scales turned themselves OFF ! then when I tried to re-weigh again, to the point where the scales shut down, I got different readings !  everytime I re-weighed, I got different weights !
I have bought myself some decent postal scales made by Steinberg accurate to 0.5 of a gram, but I won't be receiving them from Germany till the end of February ! and they're mains powered 
I happened to mention that ideally I would of liked a silicone with a higher Shore A rating, purely because of the situation that can be observed in the picture below. The cured silicone mould on the left was the one I had just completed ........ the completed silicone mould on the right however, is the one I had made the previous day. Already you can see that the mould' wall is moving away from the mould set up box under it's own weight. I think because the silicone is quite flexible, thus soft, it's 'falling' inward. A firmer silicone would undoubtedly be able to support itself. It's not a major disaster, and I think the only remedy would be to tape the side of the silicone to the mould set up box wall to give more support >>
Thanks Warren for the info ...... I've come to the conclusion that the gauge could be faulty also. I understood that by piercing the bung would in effect 'set' the gauge to the atmospheric pressure that I was working at ( on average 450m above sea level where I am ). But even after a couple of days it still hadn't set itself to zero, so then I removed the rubber bung for an entire day ........ nothing really happened so I replaced the bung. Now that I've used the system about a dozen times, it's still doing the same. After about 3 minutes of the vacuum degassing process, the needle goes way past the -30 Hg mark ! As for the air bubble in the gauge itself, it's the entire top third of the gauge ......... I'm by no means an expert with these things, but I suspect that' there's something wrong here 
As with anything in life, particularly work related, we all develop our own styles of doing things, I'm still felling my way around this business, learning the processes and the different materials. I don't leave things to chance I research everything ...... Am I dissatisfied with CS25 ? ...... no, not all, I'm very happy with it and believe I will continue using it on this project. I did look at the AS40 Addition Cure silicone originally, and will undoubtedly be trying it out in the future, as I now have the correct equipment. But for the time being I'm very happy using CS25 on my headlight project.
Next up ............ casting 'Vac-Cast Epoxy Resin' |