Post by thread:[OT] Bell Jar

Lemme tell you EXACTLY what to do. Go down to Hobby Lobby and they've got these clear hard plastic containers with a hinged, rubber gasketed lid. The hinge is made of bent chromed wire and forms a wire bail latch (snaps down, like a lager bottle). They're fairly thick and I believe acrylic. Drill a hole in the bottom of the container. Get a big rubber stopper- bigger than the hole, it's not going to stick in there like a stopper- drill a hole all the way through that, jam a barbed hose coupler in the rubber, and connect your hose to it. Remove the wire latch/hinge and discard. Set the lid on the table with its gasket. Put your target item on it. Set the container over it as a "bell jar", it's upside down so the hole in the bottom of the container is at the top. Put the rubber stopper with the vac hose sticking out of it over the hole and it will seal itself tight. In fact you don't want the stopper to be permanently attached to the jar or you'll need to find some other way to break the vac to open it because that lid ain't separating from the container. This way, you just grab that rubber and peel it sideways to pull it off. I vacuum urethanes, silicones, etc that I'm making like this to de-gas them. You really need a clear chamber for that because if you pull vac too fast they expand wildly and overflow a container even 5x bigger than the resin in it. Just what are you trying to do, anyways? Danny Rich wrote: > Thank you for the reply, Marcel. I need a glass or steel bell Jar with a > vacuum pump But your approach is certainly creative. > > {Original Message removed}

Fantastic advice. Answers a question I've had for a long time. Have you done any casting resin curing this way? 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. Any thoughts are appreciated. Alden Danny Miller wrote: {Quote hidden}> Lemme tell you EXACTLY what to do. > > Go down to Hobby Lobby and they've got these clear hard plastic > containers with a hinged, rubber gasketed lid. The hinge is made of > bent chromed wire and forms a wire bail latch (snaps down, like a lager > bottle). They're fairly thick and I believe acrylic. > > Drill a hole in the bottom of the container. Get a big rubber stopper- > bigger than the hole, it's not going to stick in there like a stopper- > drill a hole all the way through that, jam a barbed hose coupler in the > rubber, and connect your hose to it. Remove the wire latch/hinge and > discard. > > Set the lid on the table with its gasket. Put your target item on it. > Set the container over it as a "bell jar", it's upside down so the hole > in the bottom of the container is at the top. Put the rubber stopper > with the vac hose sticking out of it over the hole and it will seal > itself tight. In fact you don't want the stopper to be permanently > attached to the jar or you'll need to find some other way to break the > vac to open it because that lid ain't separating from the container. > This way, you just grab that rubber and peel it sideways to pull it off. > > I vacuum urethanes, silicones, etc that I'm making like this to de-gas > them. You really need a clear chamber for that because if you pull vac > too fast they expand wildly and overflow a container even 5x bigger than > the resin in it. > > Just what are you trying to do, anyways? > > Danny > > Rich wrote: > >> Thank you for the reply, Marcel. I need a glass or steel bell Jar with a >> vacuum pump But your approach is certainly creative. >> >> {Original Message removed}

Pressure does not de-gas, what it does is force the bubbles into solution but AFAIK you still need to de-gas first or there will be too many bubbles, and too large. I'm sure it depends on what resin we're talking about. High viscosity resins are difficult to get bubbles out of. You need to vac in a different container typically. I tried to pour into a mold and vac and there were bubbles coming up that were clearly too many to have been from the already degassed urethane I just put in (pouring often traps small bubbles between the resin and mold and I wanted it out, plus I needed it to flow into an undercut which kept trapping air). The silicone mold itself had trapped air that was coming out apparently, and it seemed to have no end. Plus it'll loft up and overflow your mold. So you generally can't vac it after it's in the mold, but your previously degassed solution is no longer completely bubble-free after pouring. That's where the pressure casting comes in, pressure is not a problem for the mold. Do not use tin-cured silicone molds in a heated oven. It breaks down in a few cycles.. You need the more expensive platinum-cure. http://www.smooth-on.com/ are the guys to deal with. Lots of products, very knowledgeable, carry mfg specs, good prices. A lot of other suppliers buy their stuff or the same stuff from their mfg, relabel it, and don't know crap about it and have no specs. Danny Alden Hart wrote: {Quote hidden}> Fantastic advice. Answers a question I've had for a long time. Have you > done any casting resin curing this way? > > 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. > > Any thoughts are appreciated. > > Alden > > > Danny Miller wrote: > >> Lemme tell you EXACTLY what to do. >> >> Go down to Hobby Lobby and they've got these clear hard plastic >> containers with a hinged, rubber gasketed lid. The hinge is made of >> bent chromed wire and forms a wire bail latch (snaps down, like a lager >> bottle). They're fairly thick and I believe acrylic. >> >> Drill a hole in the bottom of the container. Get a big rubber stopper- >> bigger than the hole, it's not going to stick in there like a stopper- >> drill a hole all the way through that, jam a barbed hose coupler in the >> rubber, and connect your hose to it. Remove the wire latch/hinge and >> discard. >> >> Set the lid on the table with its gasket. Put your target item on it. >> Set the container over it as a "bell jar", it's upside down so the hole >> in the bottom of the container is at the top. Put the rubber stopper >> with the vac hose sticking out of it over the hole and it will seal >> itself tight. In fact you don't want the stopper to be permanently >> attached to the jar or you'll need to find some other way to break the >> vac to open it because that lid ain't separating from the container. >> This way, you just grab that rubber and peel it sideways to pull it off. >> >> I vacuum urethanes, silicones, etc that I'm making like this to de-gas >> them. You really need a clear chamber for that because if you pull vac >> too fast they expand wildly and overflow a container even 5x bigger than >> the resin in it. >> >> Just what are you trying to do, anyways? >> >> Danny >> >> Rich wrote: >> >> >>> Thank you for the reply, Marcel. I need a glass or steel bell Jar with a >>> vacuum pump But your approach is certainly creative. >>> >>> {Original Message removed}

Thanks a lot. Good info. Alden Danny Miller wrote: {Quote hidden}> Pressure does not de-gas, what it does is force the bubbles into > solution but AFAIK you still need to de-gas first or there will be too > many bubbles, and too large. I'm sure it depends on what resin we're > talking about. High viscosity resins are difficult to get bubbles out of. > > You need to vac in a different container typically. I tried to pour > into a mold and vac and there were bubbles coming up that were clearly > too many to have been from the already degassed urethane I just put in > (pouring often traps small bubbles between the resin and mold and I > wanted it out, plus I needed it to flow into an undercut which kept > trapping air). The silicone mold itself had trapped air that was coming > out apparently, and it seemed to have no end. Plus it'll loft up and > overflow your mold. > > So you generally can't vac it after it's in the mold, but your > previously degassed solution is no longer completely bubble-free after > pouring. That's where the pressure casting comes in, pressure is not a > problem for the mold. > > Do not use tin-cured silicone molds in a heated oven. It breaks down in > a few cycles.. You need the more expensive platinum-cure. > > http://www.smooth-on.com/ are the guys to deal with. Lots of products, > very knowledgeable, carry mfg specs, good prices. > > A lot of other suppliers buy their stuff or the same stuff from their > mfg, relabel it, and don't know crap about it and have no specs. > > Danny > > Alden Hart wrote: > >> Fantastic advice. Answers a question I've had for a long time. Have you >> done any casting resin curing this way? >> >> 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. >> >> Any thoughts are appreciated. >> >> Alden >> >> >> Danny Miller wrote: >> >> >>> Lemme tell you EXACTLY what to do. >>> >>> Go down to Hobby Lobby and they've got these clear hard plastic >>> containers with a hinged, rubber gasketed lid. The hinge is made of >>> bent chromed wire and forms a wire bail latch (snaps down, like a lager >>> bottle). They're fairly thick and I believe acrylic. >>> >>> Drill a hole in the bottom of the container. Get a big rubber stopper- >>> bigger than the hole, it's not going to stick in there like a stopper- >>> drill a hole all the way through that, jam a barbed hose coupler in the >>> rubber, and connect your hose to it. Remove the wire latch/hinge and >>> discard. >>> >>> Set the lid on the table with its gasket. Put your target item on it. >>> Set the container over it as a "bell jar", it's upside down so the hole >>> in the bottom of the container is at the top. Put the rubber stopper >>> with the vac hose sticking out of it over the hole and it will seal >>> itself tight. In fact you don't want the stopper to be permanently >>> attached to the jar or you'll need to find some other way to break the >>> vac to open it because that lid ain't separating from the container. >>> This way, you just grab that rubber and peel it sideways to pull it off. >>> >>> I vacuum urethanes, silicones, etc that I'm making like this to de-gas >>> them. You really need a clear chamber for that because if you pull vac >>> too fast they expand wildly and overflow a container even 5x bigger than >>> the resin in it. >>> >>> Just what are you trying to do, anyways? >>> >>> Danny >>> >>> Rich wrote: >>> >>> >>> >>>> Thank you for the reply, Marcel. I need a glass or steel bell Jar with a >>>> vacuum pump But your approach is certainly creative. >>>> >>>> {Original Message removed}

> > 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

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: {Quote hidden}>>> 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 > >

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 <spam_OUTalden04TakeThisOuTharts.org> wrote: {Quote hidden}> 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 > > > > home.clear.net.nz/pages/joecolquitt/coaster.jpg > > > > 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 > > > > > > --

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 .....dannymKILLspam@spam@austin.rr.com wrote: {Quote hidden}> 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 <alden04KILLspamharts.org> 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 >>> >>> home.clear.net.nz/pages/joecolquitt/coaster.jpg >>> >>> 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 >>> >>> >>> >> --

Starting 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 below 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 - wrote: {Quote hidden}> 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 >>> >>> home.clear.net.nz/pages/joecolquitt/coaster.jpg >>> >>> 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 >>> >>> >>> >> --

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 <.....alden04KILLspam.....harts.org> wrote: {Quote hidden}> Start from the beginning. I've done a number of castings embedding > circuit boards with LEDs in clear polyester resin such as: > > 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 > > > EraseMEdannymspam_OUTTakeThisOuTaustin.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. > > 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 <alden04spam_OUTharts.org> 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 > >>> > >>> home.clear.net.nz/pages/joecolquitt/coaster.jpg > >>> > >>> 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 > >>> > >>> > >>> > >> --

> The results have been satisfactory, but not of the crystal clear quality > of the "tombstones" produced by the deal lucite companies "water clear" polyester generally has a blue tint. The resin itself may be water clear but the promoter is often a metal salt and they are coloured. The peroxide at some level reacts stoichiometrically with the promoter and effectively de-colourises it. You know from basic chemistry that metal salts of different valences have different colours. Similar thing. If you under-catalyse, the resin retains the blue tint. Over-catalyse and it may go a bit pink, depends on the reagents and how the promoter is eventually bonded into the chains > Some castings I made over 2 years ago are still slightly tacky on the surface The styrene linking in polyester can be easily upset by other materials. Surface oxygen and moisture are two. What I do with my castings is to cover the exposed surface with a piece of laminating plastic (as you'd find at a laminating shop). This excludes air and moisture and the surface cures hard. Just about nothing that cures hard sticks to laminating plastic I do use glass occassionally, but you have to have it scrupulously clean and give it a good polished coat of carnauba or mould-release wax or you'll end up with more pieces of glass than you started with > I had read somewhere that using silicone molds for this type of resin > can cause surface curing problems Can't say I've had that problem too badly. Silicone should cure inertly. It can be expensive for 'unimportant' jobs though. For re-useable moulds I have meltable (180C) rubber that I melt on the stove in a pot in a sand bath to buffer it from the element. Very handy for copying. I used it not so long ago to make a mould of parts on one side of a plaster-cased clock to repair chips on the other

> 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 Polyester is a completely different plastic to Lucite so getting it white water clear will be a problem. You'd have to do some experimenting with catalyst levels and try various brands. The company I worked for made a clear polyester that was better than our opposition up the road for example I've got encapsulations of electronic parts going back 30 years and they show no sign of corrosion. Of course there's no oxygen or moisture in the middle of the potting which helps. Sensitive parts can be pre-coated in epoxy to protect it from free styrene, but polyester crosslinking is very much impaired by improperly-cured epoxy so you have to watch that, especially if the object's epoxy coat doesn't have much of a polyester layer on it. You may find there's a soft patch I did have a look at PVA once, with a view to making big permanent bubbles. You dissolve the granules, make a bubble, and it 'sets' by evaporation. Worked OK but might be hit-and-miss for encapsulations. And PVA is quite soft, although it's water clear and you could put an epoxy coat on. With some expert spraying or dipping it could come out alright but you'll probably not get the finish of a good mould

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Sat, Nov 22, 2008 at 09:28:22PM -0500, Alden Hart wrote: {Quote hidden}> 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 below 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. I've also inquired about that kind of stuff with companies. Though, on the one hand some of their sales staff enthusiasticly told me about how they've put lots of watches through the process, when it came to actually trying to put an order through they'd refuse saying that the heat would kill the electronics, the batteries would explode, and/or chemically react (never mind they're hermetically sealed) and it'd ruin LCD screens. (that one is rather possible) At school we have acrylic casting equipment, and I have done some encapsulation of electronics, which has always worked just fine. The only thing I've seen happen is that the chemicals seem to react with the ink on the tandiran lithium primary batteries I uses and cause it to smudge in interesting ways. Thanks for the video BTW... The cardboard molds are a very good, and simple, idea. - -- http://petertodd.org 'peter'[:-1]@petertodd.org -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFJKZwI3bMhDbI9xWQRAunxAJ9Bh5UTZlIVNlQ2b9Hcjqkb7e4R/QCbB7nZ 7vuekrS+R/dZUAVE49/PQek= =EVLj -----END PGP SIGNATURE-----

Ive used Smoothon body double platinum cure silicone to make good copies of various fingers, and other general molding stuff. I even used it to cast a bit of 63/37 solder, didnt come out perfect but it didnt melt or make any bad smells. Air bubles in it like to stick at corners sometimes, I suspect using the proper mold release they suggest would fix that however. On 11/22/08, Danny Miller <@spam@dannymKILLspamaustin.rr.com> wrote: {Quote hidden}> Pressure does not de-gas, what it does is force the bubbles into > solution but AFAIK you still need to de-gas first or there will be too > many bubbles, and too large. I'm sure it depends on what resin we're > talking about. High viscosity resins are difficult to get bubbles out of. > > You need to vac in a different container typically. I tried to pour > into a mold and vac and there were bubbles coming up that were clearly > too many to have been from the already degassed urethane I just put in > (pouring often traps small bubbles between the resin and mold and I > wanted it out, plus I needed it to flow into an undercut which kept > trapping air). The silicone mold itself had trapped air that was coming > out apparently, and it seemed to have no end. Plus it'll loft up and > overflow your mold. > > So you generally can't vac it after it's in the mold, but your > previously degassed solution is no longer completely bubble-free after > pouring. That's where the pressure casting comes in, pressure is not a > problem for the mold. > > Do not use tin-cured silicone molds in a heated oven. It breaks down in > a few cycles.. You need the more expensive platinum-cure. > > http://www.smooth-on.com/ are the guys to deal with. Lots of products, > very knowledgeable, carry mfg specs, good prices. > > A lot of other suppliers buy their stuff or the same stuff from their > mfg, relabel it, and don't know crap about it and have no specs. > > Danny >