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Larry M
User Rank
Platinum
Re: Dissimilar Metals
Larry M   9/25/2013 11:49:56 AM
NO RATINGS
Exactly.  Billions and billions of these sockets have been sold and failure is very rare (and not very costly nor hazardous). In 40 years of home ownership I have had exactly two of these failures, in an outdoor fixture. I repaired one with a 2-56 machine screw, washer, and nut in place of the rivet and the other by compressing the rivet further with punch and hammer.

Jon Titus blogged the other day about a Woodford valve which failed due to bimetallic corrosion. I've had these on a house built in 1965 and they are still fine. I removed the knob recently to replace the faucet washer and the corrosion was insignificant. Bimetallic corrosion does exist but it is not as common as some would make it out to be.

Critic
User Rank
Platinum
Dissimilar Metals
Critic   9/25/2013 10:05:11 AM
Corrosion can result when metals that are far apart in the galvanic series are placed in contact with each other.  The amount of corrosion depends on the metals, the environment, and the relative areas of the metals. 

The more anodic metal (in this case, aluminum) is the one that corrodes, so it is desirable to make the area of the anodic metal larger that the area of the more cathodic metal (in this case, brass rivets).  This is done in the case of the lamp sockets. 

The bases of bulbs (lamps) are generally made of aluminum, so screwing an aluminum-based bulb into an aluminum socket doesn't cause a problem.  Screwing an aluminum-based bulb into a brass socket would cause the bulb base to corrode, and the bulb could get stuck in the socket.  The areas of the bulb base and socket are similar, so corrosion would be worse than it is in the case when the anode area is large compared to the cathodes (rivets).

When used in a controlled-humidity environment, such as someone's home, the aluminum sockets last for decades, and they have in my home.  Aluminum lamp sockets (with brass rivets) are not intended for use in damp or corrosive environments.  There are brass sockets (and other outdoor fixtures) available for outdoor use, and these are more expensive.  Some bases of bulbs intended for damp/corrosive environments are made of brass, not aluminum.  It would not be a good idea to screw one of these bulbs into an aluminum socket, because it could ruin the socket fast in a damp environment.

You get what you pay for.  The aluminum sockets were not necessarily poorly designed; they were designed to a consumer price target:  cheap!  If you want sockets, fixtures, and bulbs that will better tolerate damp/corrosive environments, you can get them, but expect to pay more.  Most people don't need to pay the extra money.

Zippy
User Rank
Platinum
Re: Is it OR isn't it?????
Zippy   9/25/2013 9:58:28 AM
NO RATINGS
Drive for lower-cost products + lack of customer awareness of hazard = inevitable

gusr19
User Rank
Iron
The UK is different !
gusr19   9/25/2013 9:56:39 AM
NO RATINGS
It is noted in the article that Europe uses bayonet sockets, but that was predominantly a UK case.  In my experience on the European mainland most lamps were Edison screw based, like the USA.  I have come across UK style bayonet based lamps on the mainland (France) a long time ago in locations where their use was a theft deterrent !

The UK may not experience the corrosion effects, but it suffers from broken "ears" on the bayonet sockets instead and bulbs that are stuck because of the pressure of the spring loaded baynet connections making large depressions in the soft solder areas that make up the contacts ... Which is often the cause fo the broken ears :-(

A quick check shows that the mainland now has bayonet or pin (GU24/MR16 etc.)  sockets on modern (halogen) lamp fixtures, but obviously the Edison screw type are still dominant !  All because of green regulations.




California has banned the Edison screw base from new fixtures to prevent people from using old style incandescent bulbs, so the GU24 pin connection type is the main one on sale there.  Maybe that will eventually take over in the rest of the USA ? CFLs with that base are available outside California even in some DIY stores here in Illinois, and of course on-line.

Nothing is perfect :-(

 

OLD_CURMUDGEON
User Rank
Platinum
Is it OR isn't it?????
OLD_CURMUDGEON   9/25/2013 9:38:04 AM
NO RATINGS
I'd be willing to bet that IF you went to an antique store, or to a Salvation Army depot, or some similar outlet which has old lamps for sale, and you inspected a typical screw bulb socket, you'd find that the outer shell was actually made from brass also, but was dull nickel plated for its anti-galling & corroding qualities.... just a hunch......

It's hard to fathom that major electrical device manufacturers, LEVITON, PASS & SEYMOUR, HUBBELL, BRYANT,.... the list is endless..... don't have qualified metallurgists on staff that would understand this physical phenomenon!  And, it's just as hard to fathom that the UL & CSA folks, responsible for approving these devices, haven't voiced their objections to such construction!  Or, that the Insurance companies haven't raised concerns over this situation......  How many homes have to burn down BEFORE action is taken?

I can't believe this was done solely as a cost-saving effort, although we've all seen a lot of pathetic examples in this MADE by MONKEES blog where that seemed to be THE sole reason!

JimT@Future-Product-Innovations
User Rank
Blogger
umm, disappointingly, ”YES”.
JimT@Future-Product-Innovations   9/24/2013 11:26:30 PM
NO RATINGS
I just bought two very cheap ($12/ea) desk lamps for my workbench from Wal-Mart, and both have aluminum sockets, with aluminum contact, and brass rivets.

Taking a quick check at galvanic corrosion of Aluminum on Brass vs. Copper, I see that Brass and Copper have identical potentials on aluminum, so it appears that the answer to your query is ,,,, umm, disappointingly, "YES".

Ann R. Thryft
User Rank
Blogger
Ocean air and metals don't mix
Ann R. Thryft   9/24/2013 11:30:45 AM
NO RATINGS
While I can't offer an explanation for why so many US sockets use the copper-aluminum combination, this reminds me of when I lived about a mile away from the ocean and had many problems with the metals in my apartment. That included the need to upgrade the socket on my favorite reading lamp.

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