drying oven question

[ch0ban]

i have to solve a drying problem in an enamelling facility... attached is the picture that describes the type of the products that are dipped into an enamel slip (60% powder, 40% water), which needs to be 100% dryed before it is fired in the enamelling furnace. My problem:
everything has to be 100% dry
150-170 degrees celsius for 10 minutes
all the steam has to be put out of the chamber and fast, because if it condenses in any way or stays around the enamelled products, it removes some powder paint or coating from the product, making it useless
i have to design and make the drying oven in a matter of days
how would you install the heaters and what sort? infrared? where? on all the walls AND the door AND the bottom of the drying oven?
Air intake and out? Install a chimney of some sort? I have seen that people talk about some sort of "vent condensers", but my problem is that not a single drop of the condens from the steam coming out of the products can fall onto the product
would you suggest an aditional 50 centimeters or so to be "empty" at the top of the chamber where the steam would go, not to be arround the products?

if you have any other questions regarding the subject, please ask... I have no skills on the given subject and am begging for your help

 

[ch0ban]

the picture is attached

http://img291.imageshack.us/my.php?image=susilica.jpg

 

[vpl]

Ch0ban

Is this the same problem that you were discussing in thread378-238685? That's where I see the mention of vent condensers.

I'm not an expert on enamelling, but it sounds like you need someplace for the water in your enamelling dip to go when you bake the enamelled object -- that's the source of the steam. From your earlier post, it also sounds like this is partially a production problem when you put "dozens" of enamelled objects in your self-designed oven; perhaps as compared to only putting a few objects in at a time.

Getting rid of the steam requires a vent (i.e., an opening in your oven) so the steam has someplace to go rather than hanging around your product. The vent should be on the top of the oven as steam likes to rise. Instead of just having an opening, adding piping and a vent condenser (basically a small heat exchanger) allows the steam to condense back to water away from the oven -- a cost saving as you can then reuse the water.

If that's too expensive, you might want to look into something called a "fume hood" to keep any other gases released from the enamelling solution from collecting around where you breathe or around your product. This might be required by OSHA, if you're located in the US (or by similar agencies in other countries.) It is basically a pipe with fan and a filter attached to a larger collector hood.

If you don't allow some sort of vent in your oven, there is no place for the water molecules to go except back on your product.

Go take a look at your kitchen oven or even a microwave. They've got vents, and may give you an idea of where to locate the vents for your drying oven and the size you need.

You might also want to visit a home hardware store, if there is one by you. There will probably be someone there who can show you relatively inexpensive vent condensers or fume hood arrangements. If you're not near a hardware store, then google will bring up thousands of hits which basically describe what they are such that you could probably build your own.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[Compositepro]

By far the quickest, cheapest, and easiest way to make a drying oven with no condensation problem is to make insulated box using polyisocyanurate insulation board from the hardware store (it can take that temperature) and hair dryers from Walmart ($15). Hair dryers have an output temperature of about 200F so they will not burn skin and hair. The hairdryers stay outside the box and blow hot, dry air in near the bottom and warm humid air can be vented near the top of the box. This is once through airflow, which will not be the most energy efficient, but it will be very cheap and effective with no condensation. Clothes dryers work in a similar way. If you are really, really cheap a cardboard box will work.

 

[IRstuff]

Sounds like your problem is a bit more complicated by the high air flow required to purge the steam. This implies that you need to heat the air stream itself. Otherwise, you could see a situation where the heaters are heating up the parts, but the cold air coming in is cooling them back down on the surface.

Note also that your drying time is so short that there is only a 67% volume exchange during that time.

If there's a problem with steam, then you probably need a much higher exchange rate than the 4V/hr specified in your OP. You'd need at least a couple of exchanges during the actual drying time, which means that your air will need to be preheated so that it does affect the enamel drying. Also, it may mean that your air flow needs to be strictly designed and constrained to not recirculate within the volume, i.e., air flow in one direction across the work pieces and then exiting.

Your linear air flow is only about 1.3 mm/s, which is quite slow. Something more like 50 mm/s, and the air should be preheated to avoid cooling the parts.

TTFN

FAQ731-376