A thought about fans...

[wetdream]

I see most of the circulation fans are taking air from the outside?? Wouldn't it be better if there was duct work at the top and bottom of the oven, put the fan in the middle so it recirculates the air sucking it from the top and returning it at the bottom?? I would think this would make the oven equal all the way around. I have been thinking of doing this with my oven. Small rectangle duct at the bottom left and top right. Put the fan in the middle outside the back of the oven and keep the air moving inside the oven...

What do you think??

[CarWiz]

I think you have a great idea! I also think you misinterpreted photos of other ovens. Most will use recirculating fans to do what you propose. They are simply mounted on the outside to remove the fan motor from the heat flow.

Venting fans are something different. These are used to cool the oven after a curing cycle. Care must be taken not to cool the PC too quickly though.

[ed_denu]

carwiz is correct in stating most fans are mounted on the outside to remove the fan motor from the oven temperatures. The Dayton fans like the one I use have an external cooling blade that helps cool the motor shaft. I'm not sure actual placement of the motor is important although moving it away for the inlet air source may slightly reduce motor temperatures.

Rather than placing the discharge in one of the lower corners, you might consider placing it in the bottom middle and using a diffuser to distribute the air.

[wetdream]

Does anyone know where you can get a fan like this? Something with an in and out.

[roadsterdude]

hello. hey i put the blower i got from grainger model #4mh34 on the center of the back wall , mounted the fan so the motor it is out side of the oven, made a header pipe and returning the hot air down both sides of the back wall of the oven using 2 1/2 in. exhaust pipe. the hot air blows directly pass my elements, should work, building oven door know. jack

[ed_denu]

I found my fan on ebay. Here is one site that sells Dayton hi-temp fans.

http://www.electricmotorwarehouse.com/dayton_blower.htm

[wetdream]

How many CFM did you guys buy?

[CarWiz]

Calculate the volume of your oven. Moving that volume once per minute is more than enough. Half that would be better. WxDxH/2= CFM for the fan. (or nearest rating.) If you go too high, it will also diminish the effectiveness of your heating coils and raise heat-up times. In this case, more is not better. Also, any dust in your oven will be spread over your parts during curing if the fan is blowing too high a volume.

[JTW37]

Originally Posted by CarWiz

Calculate the volume of your oven. Moving that volume once per minute is more than enough. Half that would be better. WxDxH/2= CFM for the fan. (or nearest rating.) If you go too high, it will also diminish the effectiveness of your heating coils and raise heat-up times. In this case, more is not better. Also, any dust in your oven will be spread over your parts during curing if the fan is blowing too high a volume.

On that statement, my figures out to be 27 CFM. So I should be using that or half of that. So if I had double of that CFM, I'm defeating the purpose of the whole heating thing, correct? So would you say 12 to 15 CFM is better then 27?

[ed_denu]

I think you're making this to complicated. Without some additional calculations, cfm is just a number. Actual air flow is affected by many things, duct size, dampeners, static pressure, etc. etc. A couple of other things to remember is that CFM is the AMOUNT of air coming through a duct. Velocity is the SPEED of air coming through a duct.

IMO most any cfm fan can be made to work, just add the ability to throttle the air flow by using a dampener or smaller duct and add a diffuser at the discharge point.