> Date:    Sat, 14 Feb 1998 17:12:34 -0500
> From:    "J. Warhelere" <[log in to unmask]>
> Subject: Why DI?
>
> Technet,
>
> The recent discussion surrounding tap water versus DI for black
> oxide rinses begs the question
>
> Why use DI anywhere in the PCB shop?


{stuff omitted}


> In a past life a shop had a DI system that leached hydrochloric acid
> after regeneration and maybe still does (?).  That was something in
> its own to deal with.
>
> What does one do when the DI unit needs regenerated for water?  Shut
> down operations?
>
> The input of manufacturers and users is welcomed because the issue
> seems one of debate, and I'd like to hear some real facts. Please
> respond by actual experience as most manufactures recommend DI, but
> perhaps not all of us use DI continuously in all areas?
>
> Or better, yet, if there are alternative water improvement systems
> out there, what are they? Is there something more reliable and less
> cost intense?

I.  DI is always needed for bath makeup.  Unless you have unusually
pure water coming in at the tap, the ions in solution will change
the makeup of the bath in question and possibly change your process
parameters (others will probably reply in greater length and detail).

2. A single bank DI needs minimum storage of 1.5 x the regeneration
time.  You can also go to a two bank system where while one is on
line, the other is regenerating.

3.  Previous shop problem - Leaking HCl is due to insufficient
rinsing.  Was chloride ion coming out or just low pH?  Low pH is due
to dissolved CO2 and results from high carbonate and bicarbonate in
the incoming water.  A degassifier will reduce the CO2 and increase
the pH.  If you are going to run a DI, you need to understand the
chemistry (most don't).

4. The lowest cost and least labor intensive alternative for small
shops is Reverse Osmosis (RO) followed by throwaway mixed bed.   The
 RO takes out all but Sodium and chloride ions and at 500 ppm going
in, you're at 5ppm coming out.

If you need 18 meg water for makeup, mixed bed resin is about
$170.00/cu. ft.  At 12.7 kgr/cu. ft, crunching the numbers.....

<crunch>
<crunch>
<crunch>
<crunch> ...bing!

You will get 11,363 gallons per cu. ft. of resin.  How many baths can
you make up with over 11,000 gallons of water (about $.015/gal)?

If you use the RO water for rinsing and the mixed bed 15-18 meg
water for bath makeup, you will be cleaner than anyone recycling
water and cleaner than most with inhouse regenerating DI systems.

Bob Mesick
[log in to unmask]


Remco Engineering
Water and Wastewater Treatment Systems
http://www.remco.com
[log in to unmask]

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