Convection Oven Design Questions

[custsteel]

Hello all. I'm a structural engineer involved in the business of steel fabrication. My goal is to design/build an electric convection oven to cure powder-coated parts. I'm in the early stages of design and am attempting to determine some rough operating cost numbers. Here's the specs I have so far-

Interior dimensions of oven- 18'x7'x7'
Power Source- 200A @ 480V 3ph
Required Cure Cycle- 400degF for 30 minutes

I'm looking to cost/benefit the following things-
1. R value of walls/ceiling
2. Heating system/fans/ducting
3. Ability to reduce interior volume when appropriate
4. Supplementary gas/propane heat source
5. Supplementary solar heat source

I'm a little out of my element and could use a little guidance about what it might cost to build/operate a brute force electrical system to accomplish this. Then I can cost/benefit items 1 through 5. Thank you for your time.

-Stuart

 

[chicopee]

I hear that propane for the time being is the cheapest fuel.
Is this for batch curing or a continuous cycle curing process?
For oven design, about studying the more mundane type which is being sold to domestic households.
I do have specs on two large electric convection ovens that we bought from Pittfield GE over ten years ago but these are over large in sizes and we used them to speed curing time of diagphrams coated with an epoxy system. If you are interest let me know.

 

[custsteel]

Thanks chicopee. It's a batch oven. If your specs are in the same order of magnitude with what I'm doing they may prove useful.

 

[MintJulep]

There are a whole slew of UL and insurance regulations to deal with - especially if you introduce fire as a heat source.

If you think you are out of your element now...

There are plenty of companies that manufacture this sort of thing. Do yourself a favor and just go and buy one.

 

[custsteel]

I appreciate your opinion but I'm interested to learn more about the engineering concepts and use the resources I have. I am not interested to climb into bed with another monthly payment.

 

[MintJulep]

Well, none of it is particularly difficult. But there are many more things that you need to consider than you have listed so far.

In just a few minutes I came up with the following. It's far from complete.

Can you load parts at room temperature and bring things up to the cure temperature, or do you need to have the oven at temperature first?

If room temperature loading, how quickly do you need to bring the oven up to cure temperature? This will be what determines the heat source sizing.

How quickly do you need to cool it down after the 30 minute bake?

What are the ventilation requirements to address anything that might evolve during the cure?

How uniform does the interior temperature need to be?

How high can the air velocity be without causing problems with the finish?

If you are going to use gas or propane, can you use direct fire, or does it need to be indirect?

Does your insurer and local code require a FM or IRI compliant gas train?

Fire suppression? Safety interlocks?

 

[danw2]

for DIY, check out the comments here (be sure to scroll down for the meat)

http://www.finishing.com/336/29.shtml

 

[chicopee]

The ventilation cycle that I had done, was to set the make up air and exhaust ventilation at 10% of the LEL within the ovens. We also had to make sure that interlocks were provided to deenergyze the heating filaments in the event the air circulation system was not working otherwise the heating filaments would burn up.

 

[psafety]

NFPA 86 needs to be adhered.