# proper airflow in a drying cabinet?



## brent (Nov 3, 2006)

Hi all,
I got materials today to build my own drying/storage cabinet for screens. I plan on installing a regular window unit fan in the side, with a upside down chimney to allow air to come in without light hopefully, and a filter on the bottom so that no dust or dirt is introduced. I decided to use the window unit instead of a bathroom ventilation fan like I originally planned because it's adjustable and it'd save me money since I already have it. I am wondering tho, how much airflow is too much when trying to dry screens? I'd like for them to dry very quickly, but I don't want too much airflow if it'll hinder them somehow. I plan to build some baffling inside the cabinet so that the airflow is not directly upon the screens if there is an issue of too much airflow.
Thanks in advance for any advice on airflow amounts!


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## Fluid (Jun 20, 2005)

> I plan to build some baffling inside the cabinet so that the airflow is not directly upon the screens if there is an issue of too much airflow.


 You should be ok. Main thing is to keep the light out and try to keep the air temp consistent. without drastic changes in temp or humidity


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## brent (Nov 3, 2006)

Fluid said:


> You should be ok. Main thing is to keep the light out and try to keep the air temp consistent. without drastic changes in temp or humidity


Thanks, Fluid. You're full of knowledge. 
If there's no real concern with too much airflow, then I'm going to use a fancier window unit I have that has two fans, both of which can either blow in or out, and each has variable speed settings. Would having one blowing in on the high setting and one out on the high setting do better for drying screens than having them both blowing into the cabinet?
And the unit will be in my basement, where changes in temperature and humidity are very slow indeed.


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## Screenanator (Feb 14, 2007)

Humidity is the most important in drying screens..my cabinet has no circulation fan...i used a de-humidifier and it dries the screens in half the time or quicker than our air circulating cabinet. 30 screens yield about 2 gallons of water....i was amazed how damp of an envrioment the screes live in.


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## brent (Nov 3, 2006)

Screenanator said:


> Humidity is the most important in drying screens..my cabinet has no circulation fan...i used a de-humidifier and it dries the screens in half the time or quicker than our air circulating cabinet. 30 screens yield about 2 gallons of water....i was amazed how damp of an envrioment the screes live in.


Interesting idea, I'll give it some consideration, perhaps in addition or to replace the fan... Could you tell me more about the de-humidifier that you use? How quickly does your system dry a screen? Would placing a small dehumidifier in the cabinet work well? I could fit a very small one in there well and I won't be drying more than a few screens at a time, so a small reservoir wouldn't be a concern....


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## Screenanator (Feb 14, 2007)

the reason I went with a de-humidifier is because the fans were stirring up junk in the cabinet..Plus a screen printing legend Bill Hood came to my shop and told me to do it...LOL...we can cure 30 screens in 4 to 6 hours.There is alot of water in Emulsion..something like 80%??? So the faster you can get the water out....the faster it will dry.I also try to keep the temp right around 76-80 degree using a small thermo controled heater...DONT get it too high...dry...dont BAKE!


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## Screenanator (Feb 14, 2007)

I picked the De-humidifier up at a medical supply store...135.00...but it has a 3 gallon bucket.I've seen small ones at Wal Mart for 40.00....


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## brent (Nov 3, 2006)

Thanks for the info, Ronnie. I'm looking at small ones online. I plan on building my cabinet monday and i'll sell how quickly screens dry with just the fan. If it's not quick enough for me, I'll get a small dehumidifier that I can just set in there. If I decide to get one I'll just do my research (IE google) and find a small one with a compressor. I'd need one that is pretty small but can remove as much moisture as quickly as possible...


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## Screenanator (Feb 14, 2007)

Thanks...We have become the masters of been there done that...LOL...just hope to help small printers gain the upper hand....


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## Bill Hood (Apr 11, 2007)

Ronnie, thanks for the compliment even though it was followed by a Lot of Laughter! Hope all is going well for you out in sunny California. I am glad to hear that you are happy with your cabinet with the dehumidifier. I am always amazed at how many people don't get it that you don't 'dry' the screen as much as you 'remove' the water. Once people think about the process, they begin to understand much more.


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## snarley (Feb 9, 2007)

Hi Brent,

Here is a method I use to speed the drying of screens. As soon as I finish coating the screen I use a hair dryer to set the emulsion. Keep it about 4 to 6 inches from the screen moving back and forth so you cover the entire screen. Repeat on the other side. Do not point the drier at one spot for a long period as you can melt the screen. 

After drying about 3 or 4 minutes per side, place it in a horizontal position in your light proof cabinet and it should be ready, normally in about 30 to 60 min. We have been using this method for several years at our Regional Occupational Program for screen printing.

Bill M


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## Solmu (Aug 15, 2005)

snarley said:


> Here is a method I use to speed the drying of screens. As soon as I finish coating the screen I use a hair dryer to set the emulsion.


Funny you should mention that...


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## Bill Hood (Apr 11, 2007)

I had posted this earlier in another thread, but thought it needed to posted here as well...

The use of a hair dryer to hasten the removal of moisture is certainly not a good idea for several reasons.

1. It is not heat that 'dries' the screen, but the 'removal' of the moisture by evaporation.

2. A dehumidifier is the best tool for removing the moisture from the screen.

3. Heated air holds more moisture than cold air - envision a sauna.

4. Any heat above 100 degrees will cause the mesh to relax and thus the mesh openings will become smaller. When the mesh cools the mesh openings will not return to their larger size.

5. The smaller holes will hamper the transfer of ink and thus the screenprinter will need to make two or more passes of the squeegee to transfer a sufficient amount of ink. There is no need to make more than one pass at any time, ever!

6. The use of 'uncontrolled' heat will cause the mesh to relax in a haphazard manner and wreak havoc in the future printing of halftones or other patterns.

7. Emulsion is as susceptible to heat as it is to ultraviolet energy. Any heat above 100 degrees will start the polymerization (hardening) of the emulsion and cause the exposure time to be lengthened to get a proper exposure. If the emulsion is allowed to get too hot it will actually become so hardened that it can no longer be exposed.

Why is it that screenprinters are always trying to find the cheapest or fastest way to accomplish a task, with no regard as to the real cost or repercussions? That is a rhetorical question as I understand the answer surely must be that no thought went into creating a comprehensive solution for bringing control to the screenprinting process. Still, it is a strange phenomenon.


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## kid.twist (Jan 7, 2010)

I know this is old, and is but one point among many, but - 


> 3. Heated air holds more moisture than cold air - envision a sauna.


No. This is simply not true. Air in any given place is as wet (humid) as it is. Adding heat does not increase the amount of moisture. To create a wet heat in a sauna you pour water over coals.


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## RichardGreaves (Nov 7, 2006)

*Relative humidity*



kid.twist said:


> I know this is old, and is but one point among many, but -
> 
> No. This is simply not true. Air in any given place is as wet (humid) as it is. Adding heat does not increase the amount of moisture. To create a wet heat in a sauna you pour water over coals.


Bill didn't write that "_adding heat increased the amount of moisture_".

"Heated air holds more moisture than cold air" is a common scientific principle. When you heat air, *it expands,* and it *can* hold more moisture. That is why we measure *relative humidity*. Humidity that is relative to the temperature variables. This is also why moisture is squeezed out of air when it is chilled - because there's too much for the air to hold. Condensation.

There is more actual water vapor in 85°F air at 50 Rh%, than 65°F air at 50 Rh%. This is why screens dry faster at 85°F than 50°F. This is why you have to keep drinking water in the desert because the dry air sucks all the water from your body in an attempt to reach equilibrium. 

Dry warm air will suck the moisture from the stencil because Mother Nature likes equilibrium.


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## Bill Hood (Apr 11, 2007)

Thanks, Richard for that very enlightening post. I could not have said it so eloquently. I could have said it, but again not anywhere near as well. Thanks!


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## chuckh (Mar 22, 2008)

We used to do the fan, then the fan and a dehumidifier, and now we use just a small space heater. I do keep the dehumidifier as it drains outside of the drying cabinet only because my screen prep, which is in the cellar, becomes very humid in the summer since we have a high water table. Otherwise, I crank up the heater and I'm ready to expose in 15 minutes. We use primarily capillary film. Reclaim, apply the film, expose in 15 minutes. Can't beat it.


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## gjbh18 (Mar 5, 2010)

I'm all for the dehumidifier route, but it is out of budget for me at the moment to buy an anywhere decent one.

I wonder what peoples thoughts are on using a tubular heater (to warm the air and allow it to hold more moisture), coupled with a fan blowing air in at the bottom of the cabinet and a fan blowing air out at the top on the other side of the cabinet - thus creating a draft through the space.

My thoughts are that this will remove the moist air - as a dehumidifier would - and the heater will speed up the removal of water due as the air will want to suck it out of the screens as it expands.

Any thoughts?


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## RichardGreaves (Nov 7, 2006)

When you heat air, *it expands,* and it *can* hold more moisture, but be careful, heated air over 104 degrees F will begin to do damage to the stencil. 

*IF* the hotter, relatively drier air is drier than the liquid emulsion, the moisture will move from the emulsion to the drier air until an equilibrium is reached.

The fans don't contribute much to the evaporation except to change the air in contact with the stencil. 

Fans _are_ an excellent way to blow dust around the room so it can settle and stick in the drying emulsion.

If you know a place where you can get a small piece of dry ice, gather your friends in the screen drying room. Turn off any fans and drop the dry ice in some hot water. Watch how quickly the fog gets to every corner of the room without any help from fans. Think of how you can smell perfume or a cigar scent without the help of a fan. Fans are over used.


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## gjbh18 (Mar 5, 2010)

Thanks for that Richard - as you say the air will hold more moisture until an equilibrium is reached and then accept no more, which is why I suggested the fans - these would push out the 'saturated' air and replace with fresh air that would then be warmed by the heater, so the process can start over.
To avoid the issue of dust I was thinking of placing a filter on both fans (I am planning on making a cabinet not a room, so dust on the floor etc should be minimal if not non-existant with regular cleaning).

(p.s. I totally get the logic with the dehumidifier, but am unable to spend the necessary bunce on a decent one with all the other expenses I have in setting up - I'm hoping this will be an acceptable compromise until cashflow allows me to get a dehumidifer)


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## wormil (Jan 7, 2008)

Moving air speeds evaporation. It works because the air next to the surface of the screen becomes saturated and it gradually absorbs less and less moisture. Basically the fan is exchanging moist air for drier air.

A dehumidifier does the opposite, it uses a fan to blow the moist air over a cold surface to condensate out the water.

Either way you're using a fan, it's just that a box fan is designed to move larger volumes of air for evaporative cooling.


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## RichardGreaves (Nov 7, 2006)

In extreme humidity (August in Florida), you can drive a car at 60mph with your arm out the window and it feels like a hair dryer. In the Bahamas when it's 90 degrees F and 85% relative humidity, a fan will help dry the surface of your stencil, bu not the inside.

In low humidity, air blowing makes your skin feel cooler as the dry air pulls moisture out of your skin. 

Like mixing sugar into iced tea, *stirring the air *will help change the air in contact with the stencil, but as the moisture moves from the stencil to the air - the air will equalize and balance - all by itself.

Fans are over rated. They do no harm, but my point is - don't be distracted and think the fan is doing the evaporating it's the dry air.


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## wormil (Jan 7, 2008)

_Edit_, nevermind. I found a diagram of how these are built. The drying rack is a closed system. I learned to print in a sign shop and many of our screens were gigantic so we had open drying racks.


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## eyekon1 (Nov 26, 2008)

this is kind of an odd question... but I run a humidifier in my drying cabinet. My humidifier sucks in the air and spits out hot air.

I'm wondering, should I be venting this hot air out of the cabinet?


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## Screenanator (Feb 14, 2007)

eyekon1 said:


> this is kind of an odd question... but I run a humidifier in my drying cabinet. My humidifier sucks in the air and spits out hot air.
> 
> I'm wondering, should I be venting this hot air out of the cabinet?


I hope you mean a dehumidifier......you want to take moisture out not add it in....


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## eyekon1 (Nov 26, 2008)

Screenanator said:


> I hope you mean a dehumidifier......you want to take moisture out not add it in....


yes, I meant to say dehumidifier.


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## Screenanator (Feb 14, 2007)

As long as the inside the cabinet temps dont reach 100 plus degrees you'll be fine....you dont want to cook the emulsion.


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## eyekon1 (Nov 26, 2008)

Screenanator said:


> As long as the inside the cabinet temps dont reach 100 plus degrees you'll be fine....you dont want to cook the emulsion.


if my dehumidifier collects the water...and the air blown out isnt vented... would it not just re-circulate that moisture? 

I guess I could just pipe out the water thru a hose out the cabinet.


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## Screenanator (Feb 14, 2007)

eyekon1 said:


> if my dehumidifier collects the water...and the air blown out isnt vented... would it not just re-circulate that moisture?
> 
> I guess I could just pipe out the water thru a hose out the cabinet.


your dehumidifier should have a catch bucket...the hot air is dry air....


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