Hi Phil
I think it would be better not to think of this as recycling, its not even
re-using.
All you are doing is returning to the solder pot material that you
accidentally just removed a moment ago. 
In other words to get the dross out you also tend to remove unoxidized
metal. So it's prudent to squeeze that out from the oxides, spent flux
residues etc that you don't want and return it to pot. This doesn't affect
the metallic composition in anyway.
Thereafter yes you are right, you need to run a continuing check programme
on the metallic impurities and main ingredient balance on the pot itself. 

Small aside.
Analysis of the squeezed out solder maybe very slightly different from the
pot, but in reality not much different from your analysis samples as these
also are usually just scooped out from the top of the pot. Sorry to be sound
slightly cynical here :), I'm trying to be a realist.
In truth the absolute amounts of impurity don't matter so much as long as
they are reasonably accurate and consistently taken/done. What you are
looking for is trends and results. You know what your soldering results are
and you can plot those against the numbers from your assays. These will
predict (after the first time or projected to an arbitrary amount) when you
next need to change the solder for impurities, or adjust alloy balance. They
are also your failsafe to highlight a sudden cause for concern.



Regards


Mike 
-
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]] 
Sent: Monday, September 17, 2012 2:56 PM
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] Recycled solder?

Mike,

In all my reading of notes here on Technet and in the trade mags and web
sites we are supposed to monitor our solder pots for levels of copper, gold
etc. that are "stripped off" the boards as they are soldered.  If we simply
squeeze out the "good" solder from the dross aren't we also getting the
higher levels of contaminants that would have been in the solder pots?  So,
do we really consider this recycled solder as pure as the new stuff that
comes from the likes of Metallic Resources, Kester, Alpha Metals, et al.?

Phil Nutting

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Friday, September 14, 2012 4:23 PM
To: [log in to unmask]
Subject: Re: [TN] Recycled solder?

Oh, I think it's stretching a bit to call it recycling, but it was nice of
them to tell you.
Most people over-skim their pots and "dross" usually contains a significant
amount of good metal. There are a number of mechanical devices which rely on
this and work by squeezing out the metal to get it back.
A little while back someone or other promoted a new chemical additive for
aiding this process. Bemusingly, at least for me, there was quite a lot fuss
about this as I remember, including on this forum. I think one supplier even
got an award for it. Actually none of this is new - just another example of
recycling. These products/techniques were common from the earliest days of
wave soldering.
Footnote.
Ironically, the money/credit they get for their dross will go down
dramatically, as it really will be dross. [Assuming their recycler/supplier
has been playing an honest game with them.]



Regards


Mike


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete
Sent: Friday, September 14, 2012 2:56 PM
To: [log in to unmask]
Subject: Re: [TN] Recycled solder?

My understanding is that they will do the recycling themselves, on site.
They said the recycling would be mechanical, not chemical, so maybe it is
just squeezing out the droww.  They also said it was an effort to be
environmentally conscious, but they are in China, so I'd think it's really
cost.

We are among their smaller customers, so I can't make a lot of demands.
They asked if we would accept boards made with recycled solder.  I suppose
the best I can do is reply with a list of concerns and ask for test results.

Thanks!

Pete



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