OT: RoHS was: SBC6120 (a build-it-yourself PDP-8 clone) Last Buy and End of Life

Chuck Guzis cclist at sydex.com
Sun Jun 4 12:47:46 CDT 2006


I've never fully understood the logic behind removing lead from tin-lead
solders in the name of "hazardous substances".  It seems to me that in its
metallic state, lead is pretty benign.  I recall that the city used it for
water pipe when I was a boy--the feed to the water meter was a lead pipe
swaged inside a brass fitting.  Connections to cast-iron sewer pipe was
usually made by first stuffing a filler gasket of oakum in to the joint,
then pouring insold molten lead as a sealer.  Stained-glass windows are
full of the stuff and my brass instruments are put together with tin-lead
solder.  Roof flashing used to be made of sheet lead and it'd last a few
hundred years.

Certainly the problem must lie in disposal of old electronics and other
things using tin-lead solder.  Yet it would seem one of the easiest
substances to reclaim.  Why ban it then?

Most of the major European musical instrument manufacturers have moved to
lead-free solders.  One of the aspects of tin-lead solder that's heavily
exploited in manufacturing a brass instrument is the fairly wide liquidus
range.  Essentially, joints are fluxed, then heated with a torch, then
solder is applied, which is promptly drawn by capillary action into the
joint, resulting in a strong airtight seal.

Lead-free (and I've tried a bunch of them) solders just don't have the nice
flow characteristics of the leaded varieties.

When bending brass tubing, a filler material is used to keep the tube from
collapsing.  Traditionally, this material has been lead, which is
wonderfully ductile and forgiving.  However, I've moved to a low-melting
point (153 F) alloy, Wood's metal, which, while it doesn't contain lead,
does contain cadmium, which to my mind is worse than lead in terms of
toxicity.  Most of the big commercial manufacturers now use either the
low-temp alloys, a frozen slurry of water and soap, or pitch, none of which
is quite as satisfactory as lead.

Free-machining alloys, including some brasses, are made with a bit of lead
in the mix and the result is something that's a joy to work with on the
lathe.

If disposal of lead-bearing products is the real problem, why not tackle
that issue instead of banning them altogether?  What's next?  Are we now
going to dig all of the lead ores out of the earth, package them up and
shoot them into space?

Forgive the Sunday rant.

Cheers,
Chuck





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