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Reflow Oven Exhaust Temperature

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Reflow Oven Exhaust Temperature | 20 June, 2020

Hi all.

We recently expanded our assembly space and moved our Heller 1500 oven to a new spot. In the old arrangement, we used a Purex filtration unit, keeping the hot air in our space. Recirculating the fumes caused a massive headache in cooling the facility in the hot Florida sun! This time, we have an 8in flex duct going to an 8in rigid, with two 800CFM exhaust fans in series going out the back wall. In our old location, there was a large mini-split AC unit that blew directly on the top of the oven and ductwork. The current location does not have that.

The issue is, no matter what airflow rate we have tried, the duct is incredibly hot. We are talking upwards of 70c when on a lead-free profile, and 60c when using leaded. Our fans are only rated to 60c max, so this is, of course, a big issue. Also, the oven gets warm to the touch - maybe like 30-35c. Not sure if any of this is normal since again, our old space had an AC directly over it.

The heater outputs stay at around 10% - 30% tops. On the low end, we are at ~200CFM on the hot end exhaust, and 1XX CFM on the front exhaust. Full speed adds another 150CFM to each. We can't lower the speed without actually baffling the intake to the oven. We have a baffle installed, just not sure if that's the right approach.

Ideally, I would like to use some heavy insulation wrap on the entire ductwork, to reduce the amount of heat that goes to our space from the ductwork. But, of course, with the fan rating issue, this isn't an option, as it would worsen the temperature.

Any advice or suggestions? Or is this common? The options that I see are:

1) Add a few holes in the exhaust near the oven, allowing the intake of cold air to mix with the hot air inside.

2) Try lowering the CFM of the exhaust, reducing the oven output.

3) Using some fans to cool the ductwork. I hate this approach since it just moves to heat back to our space.

4) Use a high-temperature fan, and just ignore any of the temperature issues. If this is the case, please recommend a fan - I have searched everywhere for one, they all seem to be rated at 60c-70c.

Thanks! Kyle


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Reflow Oven Exhaust Temperature | 22 June, 2020

Using steel/aluminum duct work causes a radiator effect.

Our Heller's have flexible rubber tubing coming off both ends that feed into a T above them.

Just measured them at 57C on PbFree Profiles

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Reflow Oven Exhaust Temperature | 22 June, 2020

What I have seen used are belt driven roof mounted exhausts. There would be a drum fan that is driven by belt and motor. That way the fumes never go over the motor or the belt. We would have to replace the belt every couple of years or so but then it was in Toronto so there would be days where it would go below freezing. You have an inline blower. I don't think that is a good idea for the reason you have discovered. I did a quick search for what I was talking about but could not find one and forget the model.

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Reflow Oven Exhaust Temperature | 22 June, 2020

There are many things that can cause this and several solutions. Suggest having Heller Service Tech come in put some thermocouples at various points and determine the best course of action. If in-person visits are not possible at this time, we can walk you through the instrumentation and data gathering and work with you on corrective action. Please call us at 1-800-394-OVEN or email and we will be happy to assist.

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Reflow Oven Exhaust Temperature | 23 June, 2020

Thanks for your thoughts. So it seems then that the temperatures that we're seeing aren't unusual, and just need to sort out the fan issue...

@Sr. Tech: Yeah, totally understand the radiator effect. Once the fan issue is sorted, we plan on insulating the ductwork to keep the heat from getting to our workspace.

@Stephen: Duh... I don't know why I never realized that the belt-driven exhausts avoid the heat issue by just moving the motor out of the heat. That makes a ton of sense, thanks! They make inline versions that I found, but nothing under 12" round, unfortunately.

@Bilal: Thanks, I will give them a call.

So I found a company "Aero-Flo" that makes an all-metal inline fan rated to 130c. I contacted them, and they discontinued that line but had a few left. I ordered them - will report back how they work! They said they are rated for 100% duty cycle at 130c too, so there's plenty of headroom for us.

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