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Subject:
From:
Jim Gryga <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 13 May 1998 07:42:52 -0500
Content-Type:
text/plain
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text/plain (162 lines)
Steve,
I'd look at it this way.  If you exhaust three of the four machines through
the same blower, and the blower goes down for some reason, now you've
essentially shut down your plant.

Blowers are a whole lot cheaper than lost production time.

Jim Gryga





SteveZeva <[log in to unmask]> on 05/12/98 09:37:54 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to SteveZeva <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: James A Gryga/Mequon/RA/Rockwell)
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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