Well several problems there: 1. LEDs will not do well in a 375F bake. Absolute Max temp for the junction of the new power emitters, running or not, is something like the 300F range. The case will probably be damaged before that too. 2. LEDs need to dissipate heat. Yes even the common 5mm T1-3/4. In fact those LEDs have the WORST trouble with heat. They rely on the leads and board traces to dissipate what heat they make. They don't make as much heat but their ability to dissipiate is really poor. In an encapsulated board it's basically a thermal coffin because it's cut off the lead/board dissipation. There are lots of tricks to any type of casting. Like I say, talk to Smooth-On. Yes some mold materials can contain chemicals which inhibit or poison the reaction. Tin cure silicones condense out an alcohol that inhibits polyurethane casting but you can bake it in an oven at like 250C for a few hours and it evaporates out and won't trouble you. But that's urethane. Ask Smooth-on about polyesters. Looks like the acrylic guys are making acrylic with the resin, then melting it the autoclave? Yeah I don't think you're gonna do that. What you'd do is get the acrylic casting resin, mix it in a cup, vacuum it out, pour it slowly and carefully to avoid adding bubbles, then if you REALLY want to get a good result put it in a pressure vessel, maybe a paint pot or a pressure cooker, and hook it up to your air tank. But this is potentially dangerous, if you exceed the pressure the container can handle you can have a significant explosion. Danny ---- Alden Hart wrote: > Start from the beginning. I've done a number of castings embedding > circuit boards with LEDs in clear polyester resin such as: > > http://www.tapplastics.com/shop/product.php?pid=75& > > The results have been satisfactory, but not of the crystal clear quality > of the "tombstones" produced by the deal lucite companies. Some castings > I made over 2 years ago are still slightly tacky on the surface. I need > a way to (1) get the air bubbles out, and (2) get a complete cure so the > surface doesn't pit over time. I had read somewhere that using silicone > molds for this type of resin can cause surface curing problems - so > maybe this is part of what I've experienced. > > When I talked to the deal lucite manufacturers they claim they use a > process that uses 6 atmospheres and 375 degrees in the autoclave. The > video looks to be accurate, but doesn't provide those details: > > http://www.youtube.com/watch?v=AWxu5KlvnM8 > > When I approached the companies about embedding live circuits they all > said their process would kill the circuit. So now I'm looking for a way > to do this myself with the something approaching the quality of the deal > lucites. > > Alden > > > dannym@austin.rr.com wrote: > > Best to start at the beginning- exactly what do you want to do? > > > > 375F is absurd for any casting process I'm familiar with. Injection molding of liquified thermoplastic, maybe, I dunno I never did injection molding. Reaction molding of 2-part stuff needs to be kept cool as stated before. If it's too cold, like below 70F, it'll take forever to cure. It generates its own heat and if it gets too hot then it can bubble as bits of it decompose or even burn. At very least there can be stresses created by the work expanding unevenly as it cures. > > > > Large pieces are indeed tricky. Hey look here's a guy casting a tree root inside 14,000 lbs of clear casting resin. I have no idea why, frankly. I'm not gonna drive to see it or anything. > > http://www.smooth-on.com/gallery.php?galleryid=309&cPath=1156 > > > > Smooth-on once featured a project where a guy cast thousands of pounds of clear resin into an empty cube. Thing went on display at one of the outdoor squares in Paris or London or someplace that do the big art displays. Again, no idea why. It's just a big chunk of plastic. > > > > Danny > > > > ---- Alden Hart wrote: > > > >> Thanks. This is helpful. I want to keep the electronics alive within the > >> resin. I know if can be done because this is standard practice for LED > >> manufacture after all, what is a 5mm LED but a die, some aluminum and an > >> acrylic encapsulation?. I did a bunch of live embedments a few years ago > >> - the encapsulated electronics are still working fine the but the units > >> never cured and some are still tacky (water-clear urethane in a silicon > >> mold - perhaps not the best combination). > >> > >> It's the deal toy guys that gave me the 375 degree number - I agree - > >> seems excessive. > >> > >> Alden > >> > >> > >> Jinx wrote: > >> > >>>>> I'm looking for a way to cure water-clear casting resins at low > >>>>> temperatures. The typical process (if you talk to the "deal toy" guys) > >>>>> is 6 atmospheres of pressure in an oven, with about 2 hours of 375 > >>>>> degrees (F) along with some gentle ramp up / down time. They seem > >>>>> to de-gas using pressure, not vacuum. Supposedly some dental molding > >>>>> processes use a UV process instead of heat. I'm trying to come up with > >>>>> a process that I can do myself that will not require excessive equipment > >>>>> or hazard > >>>>> > >>>>> > >>> 375 seems way excessive to me. I've done a lot of clear casting with polyester > >>> and often heat is the one thing you need to avoid, but that depends greatly on > >>> the volume and contents. Room temperature, 20C, is mostly adequate > >>> > >>> A couple of examples > >>> > >>> http://home.clear.net.nz/pages/joecolquitt/coaster.jpg > >>> > >>> http://home.clear.net.nz/pages/joecolquitt/pyrites.jpg > >>> > >>> The coaster is 97 x 8mm, which is a lot of surface area to lose heat from. > >>> If this was a plain chunk of resin I'd just put it in the warm box - about > >>> 40C - and let it do its thing. But the IC insert has a higher coefficient of > >>> expansion than the resin and there's a danger of silvering. This is when the > >>> object heats and expands during the curing phase and then contracts away > >>> from the resin when it cools, leaving a void. To avoid a void and unwanted > >>> bubbles, pre-coat the object and insert it after that coat gels. This is the > >>> best method with something like a bug or IC a thermionic valve which has > >>> a lot of fiddly bits that can trap bubbles. The other problem with once-live > >>> material is that any moisture left inside can evaporate and cloud the resin > >>> > >>> The pyrites example is 50mm high and is a reasonably bulky casting. Once > >>> again, excess heating should be avoided. For the insert reason above and > >>> also because if the block of resin overheats it can pull itself apart. The centre > >>> can get very hot, depending on catalyst level, whilst the outside is cooling > >>> > >>> A large pour with too much catalyst can catch fire, I've seen it happen. It's > >>> possible, but tricky, to do a large encapsulation in stages. They tend to be > >>> cooled rather than heated > >>> > >>> > >>> > >> -- > >> http://www.piclist.com PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> > > > > > > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist