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#1
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----- Original Message -----
From: "Sal M. Onella" Newsgroups: rec.radio.amateur.antenna Sent: Friday, November 07, 2008 11:20 PM Subject: Aluminum to Copper interface "Cecil Moore" wrote in message ... I'm no metallurgist so forgive my ignorance. Most of us have had the problem of interfacing copper to aluminum. Is there some sort of alloy terminal block that will accomplish that feat? Seems simple enough to create an alloy that gradually transitions from copper to aluminum but what do I know? 1. I encountered dissimilar metal parts which had been joined by what was termed "explosive welding" and/or "explosive bonding" both of which terms show up nicely in Google. In my case, the parts were cylindrical sleeves, the top of each being stainless steel and the bottom being aluminum. I only saw one (out of thousands) with the bond fractured and I don't know what hit it to break it. They seem quite strong. Perhaps a vendor of such products has something you can use. 2. I see a lot of brass and darn little corrosion. Would a transition piece of brass be acceptable? "Sal" Red, yellow, and naval brass as well as aluminum bronze alloys are marginally anodic with respect to copper so these alloys would provide minimal corrosion protection. I know it might not be obvious, but steel would make a better intermediate metal. This will make sense if the actual voltages are included in the galvanic series. These voltages are in sea water and with respect to a standard calomel electrode. Zinc -0.98 to -1.03 volts Aluminum -0.70 to -0.90 " Cast Iron -0.60 to -0.72 " Steel -0.60 to -0.70 " Red Brass, Yellow Brass, Naval Bross, Aluminum Bronze -0.30 to -0.40 " Copper -0.28 to -0.36 " 73, Barry WA4VZQ |
#2
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![]() Red, yellow, and naval brass as well as aluminum bronze alloys are marginally anodic with respect to copper so these alloys would provide minimal corrosion protection. I know it might not be obvious, but steel would make a better intermediate metal. This will make sense if the actual voltages are included in the galvanic series. These voltages are in sea water and with respect to a standard calomel electrode. Zinc -0.98 to -1.03 volts Aluminum -0.70 to -0.90 " Cast Iron -0.60 to -0.72 " Steel -0.60 to -0.70 " Red Brass, Yellow Brass, Naval Bross, Aluminum Bronze -0.30 to -0.40 " Copper -0.28 to -0.36 " 73, Barry WA4VZQ Always use Antenna Grease or equivalent on Aluminum contact points to keep the oxidation and moisture out. Steel is subject to rusting, so Stainless Steel or Galvanized Steel is best for antenna hardware to clamp to the Aluminum, and use tinned Brass or Copper loop-eye terminals soldered to the Copper wire and bolted with Stainless Steel or Galvanized hardware. Stainless should have a little Petroleum Jelly, NoAlox or Antenna Grease to keep threads from seizing. I have used Stainless Steel hose clamps and they work fine for quite a while. Aluminum house wiring has been banned a lot of places and is a bad idea all around. The problem is that the Aluminum is weaker. As it is flexed and heated at the connections, it will migrate out and the connection will get loose and you will have a cascade of oxidation and increased resistance. The recommended answer for that failure (If your house didn't burn) was to use a copper wire pigtail out to a wire-nut connection to the existing Aluminum wire with no-alox in the mix. Obviously, there is a loss of integrity and "how to jam the wire nuts into the box" issues. If you have Aluminum house wiring, you should keep an eye on line drops all through the house and run new wiring for any big draw appliance addition. |
#3
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![]() "NoSPAM" wrote in message ... ----- Original Message ----- From: "Sal M. Onella" Newsgroups: rec.radio.amateur.antenna Sent: Friday, November 07, 2008 11:20 PM Subject: Aluminum to Copper interface snip 2. I see a lot of brass and darn little corrosion. Would a transition piece of brass be acceptable? "Sal" Red, yellow, and naval brass as well as aluminum bronze alloys are marginally anodic with respect to copper so these alloys would provide minimal corrosion protection. I know it might not be obvious, but steel would make a better intermediate metal. This will make sense if the actual voltages are included in the galvanic series. These voltages are in sea water and with respect to a standard calomel electrode. Zinc -0.98 to -1.03 volts Aluminum -0.70 to -0.90 " Cast Iron -0.60 to -0.72 " Steel -0.60 to -0.70 " Red Brass, Yellow Brass, Naval Bross, Aluminum Bronze -0.30 to -0.40 " Copper -0.28 to -0.36 " I saw those numbers decades ago -- in chem class, I guess. I cited brass only because it seems to resist corrosion well, not because I actually know what I'm talking about. g 73, "Sal" (actually KD6VKW) |
#4
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![]() "Sal M. Onella" wrote in message ... I saw those numbers decades ago -- in chem class, I guess. I cited brass only because it seems to resist corrosion well, not because I actually know what I'm talking about. g Hi Sal, As an instrumentation designer who worked mainly in the chemical industry, corrosion abatement and material selection were daily facts of life. On more than one occasion, the company metallurgists saved my rear end. For example, stainless steel can be both cathodic and anodic with respect to itself. While most folks consider stainless a panacea for corrosion problems, it is not. In fact stainless alloys have little resistance to salt water. There are many poor owners of stainless auto exhaust systems that learn this the hard way when streets are salted in the winter to melt ice. Copper, brass, and bronze alloys are used in marine environments because of their anti-biofouling properties (barnacles, coral, mussels, etc.). I try to make my posts educational when I can. Thanks for telling me that you had seen these numbers before. I hope they made a little sense this time. I think if we all were back in school, we might pay more attention this time. I know I would! 73, Barry WA4VZQ |
#5
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![]() "NoSPAM" wrote in message ... snip I think if we all were back in school, we might pay more attention this time. I know I would! Yup. A smarter man than I said, "We'll only need about five percent of what we learned in college; too bad nobody knows which five precent." |
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