Curing chamber....so to speak

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junosdad

junosdad

Member
Joined
Aug 8, 2008
Messages
71
Location
La Conner, WA
Greetings all from NW Washington.

I think I may have struck upon an idea that solves several issues, but wanted to run it past all you guys with way more experience than me.

Here are my (casting :biggrin:) issues:
* unheated shop [really a portion of an attached garage]
* weather here won't be consistently into the 70s until next July

Here are my concerns:
* fumes, especially considering the recent threads
* getting PR to set up

Here's my proposed solution:
Construct a plywood box, probably somewhere in the neighborhood of +/- 2 sq. feet. Affix some sort of insulation on the inside (not the raw pink fluffy stuff, but something with a liner). Add a vent on one end. Add a fan (am thinking somewhere on the order of a 4-inch computer fan @ 100 sq.feet/min give or take) connected to some 4 inch tubing on the other end of the box.

The theory being that I could place the curing PR in the box, which would also contain a small heater with thermostat set in the mid 70s. The heater and insulation would provide/maintain the proper atmosphere for the PR to set. The fan would suck air in through the vent on one side, and push it out the tubing on the other side, which would vent to the outdoors. Thus, I would only be heating a small box, instead of the entire garage, and I'd be able to enjoy the added benefit of reducing the fumes inside my workspace. I figure, this would allow me to cast year-round and could all be accomplished for less than $100.

Known possible issues that I didn't take into account : thermal gradient issues, and the issues surrounding keeping the air that's moving through warm....although perhaps less fan would be sufficient.

Anybody ever done anything similar?
Thoughts? Feelings? Questions? Comments?

Any input welcome, and thanks in advance,
Sam
 
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When i first started casting, i didnt have a toaster oven. I built basicly what you are talking about... All but the ventilation. I used a really big light as my heat source. To keep the heat source seperated from the blanks and fumes, I used clear plexiglass and mounted the light to the top with an insulator over it. The box was made from 1/2" corrugated fiberglass sheeting with a REALLY REALLY high insulation value. The inside of the box would only reach about 85 degrees. It took a really long time for the blanks to cure inside the box. It just didn't get hot enough. Now i have a toaster oven dedicated to post cure.

I think one of the biggest issues with the fumes is when you open the pressure pot and release all the gas that has been building in the pot. The post cure seems mild compared.

If you aren't using a pot, then the curing box fumes would be an issue. The thought of freshly curing PR near a heat source is a bit frightening. I know some guys have pretty much given up on the pressure pot, but i like to use it because it gives the blanks a chance to gas out quite a bit before they go in the oven.


I think the ULTIMATE resolution would be a pouring booth. Similar to a painting cabinet or what have you.. Something you could keep the pot and oven inside, as well as your colors and PR stock, with built in ventilation so the fumes go straight outside. BUT, I do know that you can get in trouble with the EPA for venting certain fumes outside without first filtering them.

OR.. You could adjust the heat with your MEKP. I like 4 drops per ounce, but when i first started, I used ten drops per. When i would pull the blanks out of the pressure pot they would already be hard, and HOT to the touch with no outside heat source. Hope all that helps... I am no pro by any means, and the above statements are just my experience so far. I am sure the master casters will be along soon to line us both out!! :)
 
What about recycleling the air?keep pumping the same air back through. 4 inch flex line should do the trick' Add a 1/2 inch pvc coupling and tubing to vent it outside. Get an in /outside thremometer so you can watch the temp. Just my thoughts
 
Back when I was making fiberglass laminated bows I made a "cooking chamber" out of insulating material. It was 2 ft sq and 8 feet long. I could get well over 160 degrees using three 300 watt bulbs. I had a thermostat that would turn off the light bulbs when the inside temp would reach 130. You can get a surprising amount of heat from just a single incandescent light bulb.
 
I have been thinking about the same issue. I had been putting the casts on top of my shop radiator to cure in the winter months. It can get up too 180 degrees and works great. However I have to leave the shop because of the curing fumes. I have been thinking about constructing a casting/curing booth. I think I would only need positive air pressure in the booth to vent it outside. I don't want to vent the heat so I don't want much air pressure, or pressure difference between shop and booth. I am thinking about using a computer fan to pressurize the booth/box and trying to control air flow by chocking the vent. This would require a very tight gasket/seal on the booth/box. In Michigan I sure don't want to blow too much shop heat outside. It can get plenty cold up here.
 
Exactly where I was coming from

That's exactly where I was coming from. For the next six months, the average temp in my daylight basement garage/shop will be +/- 40 degrees and at times, significantly lower.

Although, if I'm getting the intended message from above, adding more MEKP into the mix sounds as though it will get the PR to set up even at low ambient temp....especially if then cured in an el cheapo toaster oven. Alternatively, warmed (ultrasonic cleaner anyone?)prior to adding the MEKP, it should retain enough heat to keep things working until it sets up enough to go into the toaster oven.

So, my take at this point, is that ambient temp isn't so much a factor and the better reason to go about this project would be to reduce the fumes in my shop. If that's the case, then one would only need create a smallish pressurized container/box. Or, theoretically, only an airtight container that could be pressurized to vent to the outdoors. (I guess this is where somebody is going to suggest just opening the container outside, huh?)

I'll end with a total newb quesion....How long does this stuff off-gas for? Big ballpark numbers are wonderful.

Thanks for helping me work through this guys,
Sam
 
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I am working on a fume box myself. I am using a computer fan also but setting it up as a positive presure with the fam in the front blowing in and placing a small heater in front of the fan.. Venting it outside thru a dryer vent. this will keep it warm enough and also keep the heat source away from the fumes to avoid a spark ingnition causing a fire. My though only.
 
Geez, do you people sleep? j/k Have you considered using Alumilite? No fumes to worry about and cures much less finicky than PR. Just a thought. Also, have you conisdered an Ultrasonic cleaner? It would eliminate the pot and it has a heater built in so it would heat the PR to speed up the curing. You'd still want a box of soem kind to vent the fumes, but it could be a good alternative to the pot: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95563
I just bought one this weekend for 25% off ($60), could've used a 20% coupon too but I couldn't find one in time. They're out there every so often though.
 
Under the floor heater like radient heat? I would also look at heat tape for pipes Lowes has this with thermostats. May want a better tstat to keep temps up though.
 
The fumes issue will be solved simply by creating a neg air pressure situation. Basically this mean that the air pressure in the chamber is lower than the pressure outside the chamber. you fan idea will do that and you only need a vent to carry what air it moves out of the shop. if you make the chamber as air tight as possible you are not moving as much air. this actually makes the work on the fan less and the amount of air that needs to be heated less as well. as long as the pressure in the chamber is lower than the rest of the shop, any leaks in the chamber will have air flowing in. This idea comes from Asbestos removal and containment procedures. in that case the air being removed from the room must be filtered. So basically make a box with a fan that is removing the air and then keep that box as air tight as possible so there is as little air exchange as possible (you do want some but more of a draft than a wind tunnel).
If you get a the air flow rate low enough a light bulb will supply the heat.
 
For heat sources google germination mat. These are heated mats in different sizes and you can get thermostats with them. You could size your box to fit a mat or just lay the mat on a table. The heating elements are inside the mat so there wouldn't be a fire problem.

We use them at my office to raise mosquito larvae in pans of water and spills are no problem.

Jeff
 
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