Homemade Atmosphere Chamber (Glove Box)

Looks like you've got it. I'd go with reusable desiccant packs that can be dried out.

Here's a site that includes drying capacities, and reasonable prices. I haven't bought from them.

http://www.desiccantsonline.com/index.php?_a=viewCat&catId=25

Do you want to increase, or decrease them?

What specific type of foam and catalyst are you using.

Open mold or closed?

My experience is mostly with toluene diisocyanate cured foams and we usually threw them into a 150F oven, after mixing at room temperature and 50% RH.

Don't recall any problems foaming at room temperature though, and never even considered barometric pressure.

As always, the manufacturer of the foam is always the best source for technical help.

Its a Visco-elastic (memory type) PU foam from these guys:

http://www.sunmatecushions.com/dsi/Products/FoamInPlaceSeatingFIPS.aspx

I've gotten good results with the material this past winter - cooler and lower humidity - but recently I cant get the characteristics I want.

The manufacturer just uses it for custom wheelchair seats - and they said that they aren't picky enough to worry too much about temp and humidity, but lower humidity and temps 60-70F are preferred.

So I figured if I could lower both the temp and humidity, I might get closer to what I want.

Thanks, you guys are quick :)

"... you guys are quick" Yeah...

But it is usually the girls who feel the need to point that out to me.

^{Naughty step, here I come!}

To control humidity in a box very similar to yours, we used a small air pump (you possibly could even use an aquarium pump), a dessicant column, and a humidity sensor with a simple controller.

The column should be 2-3" in diameter and about 12 - 18" long. Gravel-sized dessicant can be used, but a perforated plate should be placed in the bottom of the column before filling. Orientation should be vertical, pumping air from the column down into the top of the box.

While the sensor detects the RH (relative humidity) in the chamber, the pump is pumping air out of the chamber, through the column, and back into the chamber.

If the actual RH is above the setpoint (SP), the controller turns the pump on. Once it reaches the SP, the pump is turned off.

Pretty easy to set up.

Some links:

http://www.omega.com/Temperature/pdf/RHCN-1_RHCN-2.pdf

http://www.sag-automation.com/PDF/Rotronic/Data%20Sheets/SF65.pdf

Probably a good thing would be a dual controller (both temp and RH) use a heat source (not sure what you could use here) and a thermocouple along with the above and get control of both.

If you want to simply have constant temp., e.g. room temperature, keep the box in an air-conditioned room.

As previously mentioned, barometric pressure will probably have negligible effect.

Purge your box with an inert gas like argon.

Would a small portable air conditioner work? It takes moisture out of the air and a thermostat controls the temperature.

Thanks for all the suggestions, Still not certain how I am going to set it up, but I'll definitely be using silica desiccant for the RH control. I'll post some pics of what I end up doing once I finish it.

Any off-the-wall or unexpected suggestions are still more than welcome :) Those seem to me to often be the most beneficial and educational in my opinion

As you know RH is directly linked to both H2O vapor and ambient air temp, that is why they call it Relative Humidity. Would it simplify your exercise by mainly focusing on the temperature of the box? As the temp goes up the RH goes down and vice versa. So just adding an incandescent lamp inside the box set to a rheostat would give you the ability, at low cost, to adjust temp up. You could still add silica to the mix for extra drying.

Not sure how much the increase in pressure, due to increase in heat, will effect the box. Maybe you could put a simple hand operated relief valve on the top or bottom of box (depending upon whether you wanted to let the hotter or cooler air out - probably not much temp delta)

If you need to keep temp constant while adjusting humidity then the earlier suggestions of desiccants and dehumidifier are your best bets.

Good luck

I am actually looking to lower the temp as well as the humidity. Pressure is another variable I was planning on controlling, even though some people don't think it will effect the results much. A simple hand pump/vacuum should be sufficient to tweak the pressure a small amount. Thanks

We use many glove boxes for our welding. The most common method for using desiccants is in a drying column. This has distinct advantages over desiccant packs or loose desiccant. The real question is how dry you need to maintain the box interior. Your urethane material is water vapor permeable, so you might never be able to achieve minimum internal water concentration.

You might try a product called molecular sieves. It is a powder material, you would want a pore size of 3 or 4 angstroms. I have actually used it mixed directly into the urethane to absorb water from the system (a contaminate of the hydrogen donor side). It is also available in hard bead forms from some suppliers. You could scatter it around your glove box. In my experience it is more effective than silica gel or calcium sulfate driers.

Also, as suggested already you might try a dry nitrogen purge if you can get absolutely dry nitrogen. You do not need to purchase an entire tank, it can be obtained in small cans. I have often used it to blanket cans of the diisocyanate.

It all depends on how dry you want to maintain the interior of the box. The common methods for drying an atmosphere interior include, refrigeration gas driers, purging with dry gas, desiccant dryers, and dry gas generators. The best method will depend on your dew point requirements, how much dry gas you need, and how often you need it. Loose desiccant is not a good idea because the desiccant will slowly become saturated and your dew point will increase as it does. Desiccant stacks are used because the stack output remains fully dry until the top of the stack becomes saturated.

Thanks, that makes sense. As far a how dry it needs to be, I'm not certain yet. I don't imagine it'll need to be less than 20% or so, as I was getting good results this past winter in my basement without modifying the standard indoor air characteristics. All I know is that the current spring weather and 50-80% humidity isn't working well for it.

As for a column of desiccant, if I put a fan at the bottom of a column of pebble sized silica with mesh on the bottom, will either of these setups work? or does it need to be an air pump and something more sophisticated?

thanks again for all the suggestions

You have the right idea. A fan will work if it can generate enough static pressure to obtain a reasonable gas flow through the column. I'd be tempted to use a blower or something that will deliver higher pressure. Many industrial stack driers use 2 stacks and valves to switch from one to the other. The stacks have built in heaters so one can be valved off and regenerated while the other is in service.

Thanks again for all the suggestions - I ended up using the compressor out of a small refrigerator for cooling, and a silica desiccant column to help dry the air. Its nothing too fancy, but it worked for what I needed.

Thanks for letting us know what worked. I wish more people had the decency to do the same.