Wow this is a very good reply from George. Someone that has actually used that resin and has experienced the ins and outs of the different types. I am impressed and that should answer all of the OP questions. Good job.
The one point that scares me just a tad is the 80 lbs of air pressure. That is quite high and would not recommend this is if using pots such as those from Harbor Freight or whatever they call them over there. Make sure the pot is a good quality. If using those foam molds they may not withstand that kind of pressure either. One other thing when heat is applied to a pressure tank it can raise the pressure inside. With resins I believe you do not need such high pressure with any of them but I do not know that resin. This is just a side thought on a very well presented answer to the OP by George.
Thank you John,
I can elaborate a bit on your concerns and in a way your observations are important and relevant as we sometimes forget that not everybody has the same knowledge and experiences, therefore, I'm glad you brought those issues up so that I can discuss them a little further.
Yes, not all pressure pots are rated to 80PSI on even higher, most of the more economical pots are rated from 40 to 60PSI so that is important to note so that you are not using any higher pressures than what is "safe" for that particular pot. This brings 2 issues and those are what type castings are you considering to do and what type of pot you require. What I mean is, if you are only going to cast acrylic blanks, any 40 PSI pressure is more than sufficient but, if you intend to cast woods with lots of holes, crevasses, cracks, or something like Banksia pods and many other types of seeds/pods/materials you do require sufficient pressure to ensure the resin is forced into all those small crevasses, you then need as much pressure as possible the more the better so 80PSI is not excessive if you make sure your post is rated to those pressures, manufacturers give you the "recommended" max pressure but they have at least a 20% of safety margin to what those pots can withstand, mine are rated to 100PSI and I often use those pressures but I try not to mention that too often so that less inform folks do not attempt is based on the fact that I do it, that is not what I would expect but we all make mistakes, right...?
I have to stress the fact that you need to know the max rated pressure of your pot and as I said, purchased the right type of pot for the type of casting you intend to do. It is also a fact that is not the first time a pressure pot blows, mainly its lid, there have been close calls to injury so playing it "safe" is a good idea.
I never used foam molds so I can't tell you how they would perform in 80 or more PSI pressures, most folks make their molds out of the white kitchen board material which has a technical name I don't remember, that is mainly what I use, some plastic takeaway containers do also well.
Now, heat and pressure pots...! firstly I should make clear that putting a small fan forced heater a couple of feet from the pot(s) in those ice cold days/nights (below 10C) is the only way to get the resin to reach sufficient curing temperature inside the pot for an overnight up to 24 hours pot time. The temperature that these small fan forced heaters produce is not as high as some people may think, I can put my hand on the pot surface where the heater is blowing air/heat to and I can keep my hand in there without burning, remember that 2 feet distance on these small heaters the temperatures are reduced to half of the heater capacity to the surface is pointed at but at least the other half of the pot is exposed to those cold temperatures so the extra pressure the heat creates inside of the pressure pot is no more than 5PSI.
The question can be asked, what is the temperature inside the pot when the resin reaches its max exothermic temp or when the resin turns from liquid to a solid...? Well, I just looked everywhere for the pics I took from a test I made to obtain that exact information, I know that I have shown it in here but was mixed with some other thread either mine or someone else's, I can't find it nor the pics I took of that experiment but someone here may have a better memory and remember where that info is and confirm what I remember and that is, the max temperature reached inside the pot during the resin setting/hardening was about 60°C, the pot surface was about the same, the temps dropped quite quickly after that with the pot outside surface reaching the ambient temp fairly fast. An identical result was obtained when the heater was on in low weather temps, the exothermic reaction did happen when the air inside the pot reached the 60°C, the pot outer pot surfaces exposed to the heater showed about 65°C for a short period of time reducing fairly fast to 60C and then reducing about 10C's for the next 2 hours from where it kept the average heat exposed pot surface to about 35°C for the rest of the time the heater was on, when the pot was opened the blanks were solid and set, ready for work (demold, slice, sand, etc...!).
With all this said, REMEMBER that I didn't mention the surface temperature of the resin when reaches its mac exothermic temps, I could give you some numbers but I prefer to tell you, don't even think in touching it, it burns as bad as the burns from hot-glue guns, how do I know...? have a guess...!
I hope this gives you and others a bit more light on the issue...!
Cheers
George
