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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 02-14-07, 06:43 PM   #1
Nims
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(Mis)information on Chrome plating

I've seen more than a few posts lately regarding the environmental impacts on chrome plating, so I thought I'd make a quick post to encourage discussion on the topic.

Tiny background: I'm an engineer (fluid control systems/structural/plastics) and our lil firm is attempting to make enviro friendly changes wherever we can in our design. I ended up doing a few hours of research on chrome plating and that is where the following info came from.

The short story for those that don't want to read is this. "Chrome Plating" generally refers to a process more accurately known as hexavalent chrome plating. A process that is very bad for everyone. It is very unhealthy for workers, and the chemicals involved end up being disposed of (often improperly), etc. etc. No one questions that it is a bad process. In fact, many changes are currently taking place that will effectively ban the current chroming process.

The good news! is that a process referred to as trivalent chrome plating does exist, and is becoming more cost effective as time goes on. As of now, it is effectively the same as hexavalent chrome plating in terms of surface finish, quality, hardness, surface friction, durability, plating tolerance, etc. etc. Really the only prohibitive aspect right now is that shops are required to make changes to their setup in order to plate in this way, so many outfits are resisting the change.

More and more shops are making this switch though, and not too far in the future (I hope), trivalent chrome will be the only chrome!

That said, don't be inherently afraid of new chrome plating, just do some research and find a shop that offers trivalent plating. Some shops are even finding cost savings for various reasons going to this process.

I suppose that wasn't a short answer, but I just felt like a nerdy post. If anyone is interested, here are a few of the basic info websites I found. I have papers and other boring crap, but I doubt anyone wants that.


http://www.metalfinishing.com/editor...7_Bjerklie.htm

http://es.epa.gov/techinfo/facts/ca-htm/htmfact9.html

/nerd
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Old 02-14-07, 06:44 PM   #2
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Thanks for the info Nims. your avatar made me lol BTW.
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Old 02-14-07, 06:56 PM   #3
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What's the difference between the molecular structures of hexavalent chromium and trivalent chromium (other than the number of bonds, I get that much) that leads to hexavalent chromium releasing harmful chemicals? Is it something left over after the chroming process that's not left over with trivalent chromium?

Also, more LOLz for B.I.L.F. I like Natalie Dee and Toothpaste for Dinner a lot.
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Old 02-15-07, 10:56 AM   #4
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Quote:
Originally Posted by veggiemafia
What's the difference between the molecular structures of hexavalent chromium and trivalent chromium (other than the number of bonds, I get that much) that leads to hexavalent chromium releasing harmful chemicals? Is it something left over after the chroming process that's not left over with trivalent chromium?
Information on potential hazards of hexavalent chromium
(Cr+6):
Many chromium compounds with a valence of 6 are
called chromates, dichromates, or chromic acid;
most have a yellow color, and all are toxic
[343,751]. Hexavalent chromium compounds tend to
be oxidizers and are associated with cancer risk
and kidney damage [751].
Hexavalent chromium is more toxic than the +3 form
because its oxidizing potential is high
[24,751,929] and it easily penetrates biological
membranes [24]. Chromium +6 is unstable [24] and
can be reduced to chromium +3 by many oxidizing
agents [751]. Metallic and acidic +6 chromates and
dichromates tend to be strong oxidizing agents

[751]. Strong oxidizing agents can cause damage to
DNA and many other tissue structures
.
Certain hexavalent chromium (Cr+6) compounds when
administered via inhalation at high doses have the
potential to induce lung tumors in humans and
experimental animals
[929]. However, at low levels
of exposure hexavalent chromium ions are reduced in
human bodily fluids such as gastric juice,
epithelial lining fluid of the respiratory tract,
blood, and other fluids, before the 6+ ions can
interact with DNA, unless the dose is sufficient to
overwhelm the body's reduction capacity [929].

Source
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