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TURK
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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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Hanaldo
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I'm sure the EC staff will be along soon to give you a better answer, but in the meantime my first thought is that the XenCast PX30 is of course a polyurethane casting resin, not a silicone. Meaning that it doesn't have the self-releasing properties of silicone, and you will need to apply release agents both to your plugs/mould boxes, as well as to the finished XenCast moulds themselves before you pour the epoxy resin. That might not be a big deal to you, but I thought I would point it out. Personally I would recommend still sticking to a silicone, but perhaps try a different one. Silicones can definitely take a bit of getting used to if you normally work with resins, their much higher viscosity certainly makes them a bit more difficult! However it is also certainly possible to get excellent results using silicone, and you will have a self-releasing mould with absolutely zero shrink. I'm not familiar with OOMOO 30, but I would suggest trying something with a longer pot-life so that you have a good amount of time to mix it gently and can pour it properly in a relaxed manner without having to panic and resort to trowelling it into the mould. Silicone normally has the unique benefit of being as thick as honey but actually flowing like water, so provided you get it into the mould inside it's pot-life then it should flow extremely well and not have any voids. If you do go for another silicone, just be careful if it is an addition cure silicone! The presence of styrene from the pattern coat on your plugs may prevent the surface of the silicone from curing. A condensation cure silicone is likely to not have this problem, or Easy Composites may have a more suitable product.
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TURK
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Group: Forum Members
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Many thanks for your response Hanaldo, and your recommendations, all of which make good sense. I did ask Warren to have a look at this post, but the lack of an answer would suggest that maybe he doesn't know. I've seen many videos on youtube on how to use OOMOO 30 silicon rubber ( which is partly the reason why I bought it in the first place ), I have come to the conclusion that my Gallon unit was 'faulty' some how ! As you say, silicon is supposed to flow like honey, mine however didn't ......... it was more like trying to mix thick tar, to the point of struggling to insert the mixing stick into it ! OOMOO 30 has a pot life of 30 minutes, so I had ample time to mix it thoroughly ( about 10 minutes, until all the streaks had gone ) and breaking two quite substantial mixing sticks in the process, but when it came to the pour, as you're supposed to pour in a 'high pour' fashion, I had to virtually turn my mixing bucket upside down. I didn't get a nice steady stream of the mixed silicon, more like big dollops of 'lava' falling into my mould ! and no self levelling at all ........ this is where I had to trowel it around the top of my mould. There had to be something wrong. Having said that, I did have it in stock for about 10 months ! .......... stored unopened in a room heated at about 20°C Would you say that that is part of the reason ? maybe it had gone off somehow, if that's the correct term. I know nothing about the presence of styrene in the pattern coat primer, so thanks for the tip on that, indeed my plugs are finished with Pattern-Coat Primer. I don't know whether I should try another batch of OOMOO 30 and use it right away, or try EC' silicon ........ As I noticed they have 'CS2' that is a condensation cure silicon. I just need something that I can mix and pour effectively. I may get in touch with 'Smooth-On', the supplier of the product and see what they say. So, many thanks for your help mate.  TURK
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TURK
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Group: Forum Members
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Visits: 662
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Hi all, This is all getting very confusing now, to the point of being frustrating .......... I've been looking at an alternative for the 'Smooth-On OOMOO 30' silicone rubber that I had a bad experience with. I'm pretty sure I've found an alternative, EC's 'CS25 Condensation Cure Silicone Rubber'. Reading the DataSheet shows it would probably suite my needs, but it shows that the viscosity is between 20,000 and 26,000 Cps. 'OOMOO 30' was rated at 4250 Cps ( like Maple Syrup basically ) ......... mine was more like trying to mix and pour tooth paste ! I've been searching around on the internet for a comparison, just trying to imagine what it would be like to pour it ........... unfortunately when you search for those terms, 20,000 Cps, the results compares it to 'Silicone Rubber' !  ya, I know ! So, any ideas guys ? I am really stumped here .......... all I want to do is to pour some silicon rubber in a mould  TURK
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Hanaldo
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Tough one to answer really. It does sound like there's something up with the OOMOO 30 you have, but it's so hard to say. It's not unusual for the stuff to be so thick and hard to mix that you snap mixing sticks, that happens. But it should flow like water, albeit slowly; so it should self-level superbly and it should pour in a thin stream very easily. My honest answer would probably be to give the EC stuff a go because at the very least you will have the technical support to help should it not go as planned. The CS2 shouldn't have any compatibility issues, condensation cure is much much more forgiving in that regard than addition cure silicones. Im not overly familiar with vacuum forming, but from my very basic understanding I would say that there's no reason to use addition cure over condensation cure unless you need to get a lot of parts out of the moulds.
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TURK
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Group: Forum Members
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Visits: 662
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Thanks for your continued support Hanaldo, very much appreciated. I know this forum is oriented toward carbon fibre, laminating, resins and vacuum bagging, so some of my questions may seem of little or of no relevance to what is usually discussed here. But the mould creation and preparation is still the same, once I have my moulds complete the procedure is different, agreed .......... but the vacuum forming stage using sheet plastics is only slightly different, whereas you guys would 'form' your final parts using fibre glass or carbon fibre. The 'CS2' product I've been asking about has actually been superseded by 'CS25', a new formula I believe. I will be placing an order for it, after all, it is definitely worth a try, it's so much more cost effective creating flexible moulds than 'OOMOO 30' .......... that mauve 'blob' you see in the images above cost me €196.00 ! from the first instant that I removed the lid from the silicon and began to pre-mix the contents, I knew there was something up .......
Before I plan on using a particular product I research everything ( as I'm doing here with the CS25 ), one of the videos I saw was this one. The interesting bit begins at 0:54 where he's already pre-mixed it and begins the pour >
So after seeing that I new that was the stuff for me, judging by the shape and size of my mould. The actual completed silicon mould will only be used to once, as it's for making permanent vacuum forming tooling plugs. I'll be using 'Vac-Cast Epoxy Resin' for that, as it's specially formulated for vacuum forming applications. Imagine having a bucket of tooth paste ....... now imagine trying to mix it with a wooden mixing stick ! ........... there's no way you can mix that, let alone pour it in a nice thin stream 
I've since then emailed the company who produce it, 'Smooth-On' ........ awaiting reply. Also I've emailed the company who sold it to me ...... waiting on reply.
As with any product like this, including resin, there is a shelf life. But one would assume that the shelf life ( if correctly stored, as mine was ) that the shelf life would be extended, like six months to a year. As opposed to a product that been opened, once the air gets in you have to use the remainder of the product as quick as possible. I've spent the entire weekend reading gibberish on every single website I could think of who may be using something like this. And then I found two guys who had the exact same problem as me ! ........ even if the product remains unopened, it goes off ! the longer you store it, the thicker it gets.It must be used right away ......... and the recommendation is when placing your order is ask for a new batch.
You live and learn  .......
I'll be placing my order for CS25 at some point today, I'll let you know how I get on if you're interested.
While I'm there ( @ EC ) I may as well order a degassing system from them ........ been chatting to Warren, apparently they've got a new system in  |
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Warren (Staff)
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Hi Turk, Must have missed this one.
Although PX30 could be used in this way, as already pointed out, the PU lacks the self releasing properties you ideally would want.
CS25 seems a better all round solution having both the self releasing properties and also a much lower viscosity than the oomoo product you mentioned above. The CS25 will pour into the mould boxes fairly easily and being lower viscosity should be easy to mix too. Like most silicones, if you are not degassing, we would recommend you stretch pour it to help remove any gas from mixing.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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TURK
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Group: Forum Members
Posts: 101,
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Hi Warren ....... No worries mate
I think I've just sent you an email ( EasyComposites - sales ) ......... With a barrage of questions, sorry about that. Looking at buying the Vacuum degassing system, so a few questions in that department, and a few questions about certain supplies that I couldn't find on the website, but are listed in your brochure.
I've been talking to the company who supplied me the 'OOMOO 30' silicone rubber, they have agreed that all is not well, and that it may be at fault ....... they're currently deciding whether they'll replace it FOC ! 
So, I'm kind of stuck between a rock and a hard place right now. I really wanted to order the CS25 at the same time as my degassing system, shipping costs to France can be quite expensive ! Can I at this point ask about this 'Howto' that one of your colleagues made. Very interesting stuff ! I know you've changed the vacuum pump from the one in the video as I've already asked that one, but what silicon did your colleague use ? > |
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Warren (Staff)
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Group: Administrators
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Hi Turk, If they replace it FOC then you might as well try it out. I'd push for a refund too for the hassle - you never know your luck! The silicone used in the video link is our Addition Cure Silicone Rubber which is a fair bit thicker than the CS25. It is also a bit harder and is translucent. The addition cure realistically needs degassing for best results (as seen in the video).
Warren PenalverEasy Composites / Carbon Mods - Technical Support Assistant
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TURK
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Group: Forum Members
Posts: 101,
Visits: 662
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Hi Warren, I'm pretty sure that they'll say what I already suspect ......... I've had that particular 'OOMOO 30' in stock for far too long ! over 6 months I think 
If I'd been made aware that this sort of product 'goes off' even though it's unopened, I wouldn't of pre-ordered it ....... I would of waited till the last minute to place the order for it. There's absolutely no information or disclaimer that the product must be used 'fresh' ! expensive way to find out ! but at least now I know ( and members on this forum ), so, guys ........ buy and use right away, and that goes for any silicone.
As I'm learning about these compounds and materials, this is beginning to make sense now actually. Particularly 'Condensation Cure' silicones, 'Condensation' being the operative word here. Even in it's container, where there is condensation present, the silicon will begin to harden !
While 'Smooth-On' are mulling and Rrrrr' ing over the replacement, I'm buying a Degassing system from yourselves anyway. If they choose not to replace it because of my stupidity, I'll be buying the CS25 from yourselves and trying that. And I'll also be in the position to degas it as well. Personally, I would really like to give that CS25 a trial run ......... it's half the price of the OOMOO 30.
As I have many moulds to make ( various prototypes ), it would indeed be a more cost effective way of producing vacuum forming moulds.
So, loads more to follow chaps.
And, thanks all  |
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