Heating a pressure tank?

[Knightjar]

Living in England, the weather isn't always great and I occasionally have problems with small resin parts not completely curing due to not generating enough exothermic heat in my rather cold workshop. When this happens, I generally heat the mold at a low temperature in the oven. This doesn't work very well with pressurised castings as I first have to take them out of the pressure tank. I can also solve the problem by heating the workshop like a sauna, but this tends to dry out all my paints and make it uncomfortable to work, so I avoid it.

So, I've been thinking of heating my pressure tank. I guess it needs to be heated from the outside as I won't be able to run cables into it. I considered the circular heating elements used in fan ovens, but ideally I want to come up with something that won't burst into flames and burn the workshop down. I thought of maybe using a couple of sealed ambient room heaters under the tank and wrapping the whole lot in insulating foam. This would be safe, but I'm not sure it would generate enough heat. I'm also wondering if the solution might be to use inductance to heat the metal of the tank itself, but this too is potentially risky, as well as complicated.

Has anybody attempted anything like this? Any suggestions? Maybe I'm missing something obvious. Any ideas welcome!

 

[IEDBOUNTYHUNTER]

Living in England, the weather isn't always great and I occasionally have problems with small resin parts not completely curing due to not generating enough exothermic heat in my rather cold workshop. When this happens, I generally heat the mold at a low temperature in the oven. This doesn't work very well with pressurised castings as I first have to take them out of the pressure tank. I can also solve the problem by heating the workshop like a sauna, but this tends to dry out all my paints and make it uncomfortable to work, so I avoid it.

So, I've been thinking of heating my pressure tank. I guess it needs to be heated from the outside as I won't be able to run cables into it. I considered the circular heating elements used in fan ovens, but ideally I want to come up with something that won't burst into flames and burn the workshop down. I thought of maybe using a couple of sealed ambient room heaters under the tank and wrapping the whole lot in insulating foam. This would be safe, but I'm not sure it would generate enough heat. I'm also wondering if the solution might be to use inductance to heat the metal of the tank itself, but this too is potentially risky, as well as complicated.

Has anybody attempted anything like this? Any suggestions? Maybe I'm missing something obvious. Any ideas welcome!

thats basically what we did, i would have to look to see if i still have the pics, but we used a heating coil, and wrapped the tank with insulation. it worked great. ill see if i can find those pictures, but the idea is sound, it does work.

Al

 

[Knightjar]

Ah, good to know it's not a crazy idea! Can you tell me what sort of heating coil you used? Were you able to regulate the temperature?

 

[Great_Bizarro]

Stateside we have electrical heat tape that you nail to the eves of your roof to melt the ice so it slides off the roof. You might try something similar and wrap the tank with it then insulation.

 

[Rebelscum]

I heat silicone molds in the oven all the time and put them in the pressure tank, both before and after they are poured with no problem.

They don't cool down very fast so you have quite a bit of time to put them together and put it in the tank before you lose any heat that matters, if that's why you don't want to take the mold out of the tank for heating.

Unless I'm missing something I know I'd never swap the oven heating process for attempting to heat the entire tank up very much.

 

[tango'd fett]

What about an underfloor heating kit , it comes as a roll of wire that you lay under tiles or concrete, this could be wrapped around the tank and you usually get a thermostat to control the temperature. Sure that would be safe and it just plugs into a socket or you could wire it into a switch

 

[exoray]

I use regular muscle pain heating pads for your back that you can find at just about any store for about $20, and an ACE bandage (if it doesn't include a strap already) to hold it around the tank...

If you have a big tank get an electric blanket...

http://www.walmart.com/search/searc...query=heating+pad&Find.x=0&Find.y=0&Find=Find

One thing to note you don't need to wrap the whole tank, even setting the tank on one of these pads will transmit a good amount of heat into the tank...

I also have several 'pig blankets' left over from my exotic animal selling days, that I set my molds on in cooler weather, they make for a nice heated table top... They are basically solid fiberglass heating pads that you use in barns on the floor to keep baby livestock warm... A little costly but they last forever and will actually pump out a good amount of heat, put your molds on the pad and place a plywood box or foam ice chest over them (even a cardboard box) and you have a nice little oven...

These also work well for post curing hot boxes...

 

[Knightjar]

Wow, some really interesting solutions, thank you! I hadn't come across mention of heating tanks before, so it's good to find that I'm not the only one who's had to tackle the problem.

@Rebelscum, The reason I would prefer to avoid removing the mold from the tank to heat it after casting is that as soon as the pressure is removed, any bubbles in the silicone will pop back up, affecting the surface of the piece, which is exactly the area that needs heat treating to cure. Pre-heating the mold is a very interesting idea.

 

[Rebelscum]

Wow, some really interesting solutions, thank you! I hadn't come across mention of heating tanks before, so it's good to find that I'm not the only one who's had to tackle the problem.

@Rebelscum, The reason I would prefer to avoid removing the mold from the tank to heat it after casting is that as soon as the pressure is removed, any bubbles in the silicone will pop back up, affecting the surface of the piece, which is exactly the area that needs heat treating to cure. Pre-heating the mold is a very interesting idea.

Here's what I know and use, stright from Smooth-on for casting urethane plastic.

Always post cure the silicone mold in the oven. Generally 4 hours.

Then, preheat the mold prior to the casting. Depending on the size of the mold, I use between 1 and 4 hours to preheat.

Then, put the halves together, pour, insert in the pot, and pressure away.

This works because the exothermic reaction starts in the thickest part of the mold and radiates outward during cure, as it does this it loses heat. By applying heat from the outside as well, you ensure there will still be enough heat there when you need it for the full cure. For urethane, since the mold rubber needs to be 160+/- degrees farenheit, I think it will take quite a bit of heat applied to the tank to get there if doing the tank itself. I do mine at 175 since my oven's minimum temp is 175.

I apologize if you know this already... It sounds like you have a mold that wasn't degassed? A degassed silicone mold shouldn't have bubbles and pressuring your cast should only be making any bubbles in your cast smaller. IE, degass the mold material to remove air, pressure the poured cast to make bubbles, if any, in your cast material insignificant.

 

[Knightjar]

It sounds like you have a mold that wasn't degassed? A degassed silicone mold shouldn't have bubbles and pressuring your cast should only be making any bubbles in your cast smaller. IE, degass the mold material to remove air, pressure the poured cast to make bubbles, if any, in your cast material insignificant.

No, I don't have a degasser. Instead, I cure my silicone molds under pressure, which has pretty much the same effect on the silicone as on resin - ie any bubbles are compressed. However, using the mold without pressure can result in the bubbles reappearing, albeit on a reduced scale.