Ducting for recirc fan

[REAPER969X]

Ironing out some details on my oven build, and looking for ideas on fan ducting. Would it be better to duct it inside the oven or out? I'm thinkin there is a potential to blow some of the powder off. Anyone had experience with this?
Thanx
Matt

[ed_denu]

I ran my duct thru the walls.

As for blowing the powder off I personally don't think that would be a problem. But, I just installed a switch on the fan and only turn it on after the powder has flowed.

[johnsjj2]

Im using 2x3 gutter down pipes for duct work. It fits, easy to cut, and damn cheap. I also bought some 4" round pipe insulation in the even I run this duct work along the outside of the wall.

Josh

[JTW37]

Yeah, you got to have a bunch of air flowing to know the powder off. I have my fan on top and draw from the top inside and push it back in through the wall to a shut that I ran down toward the floor.

Check this out. It's a drawing of the way mine is setup, just to give some food for thought.

http://forum.caswellplating.com/atta...3&d=1201786420

[johnsjj2]

What kind of fan are you using in that picture? I planned on running the ducting from the fan in the upper rear of the oven to the lower front. I just need to figure out the fan I need to use.

Josh

[ed_denu]

Today I manually control the fan with a switch and usually only turn it on once the powder has flowed. I was looking at the pid manual and I'm thinking you could automate this setup using the alarm contacts. I think you could set the alarm parameters such that the fan would kick on when the temperature reached a specified level, say 200 degrees.

I might look at trying this with my oven and post the results.

[ed_denu]

The test worked as I hoped. If anyone wants to turn on their recirculating fan at a given temperature(like after the powder flows out) you can do this via the alarm contacts on most pids. With my pid(TC-408) I set AH1 to 200 degrees and AL1 to 195 degrees. I ran a hot feed to contact #4 and a feed from contact #5 to the + side of the fan motor(4 & 5 are the alarm J1 contacts). When the oven hit 200 the fan came on. My pid has a 3amp limit to its switching capacity, but that's plenty for the fan.