Steve,
With three machines all running on the same exhausting make sure that you
have an exhaust controller at the reflow to regulate your exhausting to
exactly 500cfm. Too much exhaust can pull the heat right out of your oven.
I think the moisture should be o.k. in the ducting. Airflow should carry the
moisture out and heat should evaporate. You should make sure you have a T
duct at the machines (assuming your ovens connect to the exhaust duct at the
back of the machine and not the top) with a 1 foot section below the
connection to the ovens and cleaner. This will allow the condensed water to
drip into a "drippan" rather than into the ovens.
Brian
>Hi there Stve I am an HVAC/Mechanical Engineer I will appreciate to help
>you if you will.
>Ruben E. Irizarry
>Mechanical Engineer
>
>
>
>
>[log in to unmask] on 05/12/98 11:37:54 PM
>
>Please respond to [log in to unmask]; Please respond to [log in to unmask]
>
>To: [log in to unmask]
>cc: (bcc: Ruben Irizarry)
>Subject: [TN] ASSY: Reflow, Wave, and Cleaner Exhaust Issues...(again!)
>
>
>
>
>Hi Folks!
>
> I hate to keep beating a dead horse so to speak, but I've still got a
>few issues with the exhaust system I'm trying to set-up in our start-up
>facility. I should say it's not me that has the issue, but others that seem
>a little hesitant with what I want to do.
>
> I did get some more quotes, and was able to cut that $11,000 one
>almost in half...the latest one was for $5,960, and the gentleman that came
>out and did the quote said that there shouldn't be any problems with the
>exhaust fan I have...
>
> BUT, I guess since this is one of the first times I've actually dealt
>with the "nuts and bolts" of this stuff, a few other people that don't know
>anymore than I do about these things, have gotten involved with this
>project...talk about too many cooks in the kitchen! SHEESH!
>
> If you remember, I have a Dayton 5,700 CFM 2-hp, belt-driven,
>centrifugal ventilator fan up on the roof (that's less than 2-years old)
>that was left by the previous tenants. They also left a large portion of
>the ducting inside the building as well. We're going to have 4 pieces of
>equipment to exhaust; a Heller reflow oven (500 cfm req.), a Soltec wave
>solder (700 cfm req.), a Trek Triton IV cleaner (1800 cfm req.), and a
>Roilguard water evaporator (has it's own blower @ 1600 cfm) coming off a
>ultrasonic stencil cleaner.
>
> The evaporator is going to have it's own duct to the roof because it
>has it's own blower. One of the "Guru's" here on the TechNet pointed out
>to me to exhaust the evaporator by itself as it would lower my main fan
>efficiency if I tried to plumb it in with the main duct, and that makes
>sense, so that's what I'm a doin'...
>
> But what seems to be not setting well with others, is that I want to
>use one fan to exhaust the other three machines. They seem to feel that
>because I'm going to plumb the cleaner into the same duct system that will
>be exhausting the reflow oven and wave, the moisture in the air that will
>be coming from the cleaner is going to somehow work it's way against the
>flow of air, backwards, and fill the reflow and wave ducts full of water.
>
> I know about the condensation that could occur, and how you need to
>orient and position the duct run to prevent a problem like that from
>occurring. That's exactly why I'm placing the cleaner right beneath the
>exhaust fan, so that the exhaust duct will be making a shot straight-up
>thru the roof (which is only about 12-feet).
>
> The exhaust fan has a rectangular plenum beneath it which is around
>2-ft X 2-ft X 4-ft. The cleaners exhaust duct will tap into the bottom of
>the plenum, and there will be one duct that will tap into the side of the
>plenum and run horizontally with a very slight downward angle towards the
>plenum to keep any water (if it should happen to condense in the duct) away
>from the ovens...I really don't think that'll happen though.
>
> This horizontal duct will run above the wave and reflow, and each
>machine will have one duct with a volume damper that will tap into that.
>
> Right now, I'm just trying to use my common sense with this project,
>and I've worked at companies before where we've had multiple machines
>(reflow and cleaners) sharing an exhaust system without any sort of
>problems. I will readily admit that I'm not a HVAC engineer, but I'm trying
>to learn fast though, I went and bought a book called; "Elements of
>Thermal/Fluid System Design" and been studying that for the past few days
>and have learned more about different fan types and figuring loss
>coefficients for duct elbows and such, than I ever thought I would need to
>know. But I guess I haven't come to the chapter yet that talks specifically
>about setting-up an exhaust system for a printed circuit manufacturing
>floor.
>
> Every book I've looked at talks mostly about air conditioning. I
>haven't been able to find a book that was recommended to me by a Technetter
>called; "Industrial Ventilation; A Manual of Recommended Practices" from
>the American Association of Industrial Hygenists...
>
> Oh, another curve was tossed at me today too. Someone had said that
>they had heard that is was very detrimental to mix the exhaust from a
>cleaner with exhaust from reflow or wave because the moisture in the
>cleaner exhaust would react with the vapors coming from reflow and wave and
>then make some sort of toxic substance...I know better than that, but
>trying to find something published that says "It's okay to exhaust a
>aqueous cleaner, reflow oven, and wave solder together in the same duct
>system." Is pretty tough if ya' know what I mean...
>
> I'm sorry I'm going on and on about this, but does it sound like I'm
>doing things logically? Or am I way off base? I've called Trek by the way,
>and sorry to say they've not been much help at all...
>
> I know that if it were a perfect world and we had a lot of money I
>would've said to pay the $11,000 and be done with it, but we're just
>starting out and you all know how that is.
>
> I would appreciate any feedback at all...and don't be shy, if I'm
>screwing up let me know please!
>
>Thanks in advance!!
>
>-Steve Gregory-
>
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