What metals do i need to know about

[gadfly56]

Cadmium coatings?

Where? Cadmium is a toxic metal. With the exception of specialty platings for use in the aircraft industry, cadmium plating has been replaced with zinc dichromate or nickel.

What many assume is cadmium plating on bus bars is likely nickel or tin.

What, you never cut a piece of Unistrut? It isn't offered anymore, but I have a PDF copy of the 2009 price book which lists cadmium plated as an option for Unistrut. IIRC, if you didn't specify, this was the default you'd get. It had a gold color to it, which is still availble with their phosphate-based coatings.

 

[K8MHZ]

What, you never cut a piece of Unistrut? It isn't offered anymore, but I have a PDF copy of the 2009 price book which lists cadmium plated as an option for Unistrut. IIRC, if you didn't specify, this was the default you'd get. It had a gold color to it, which is still availble with their phosphate-based coatings.

Why sure I have but probably thought I was cutting zinc and all the while shortening the trip to my eventual demise.



Something else had to be in the cadmium to make it gold colored as it looks like tin, zinc or nickel in it's elemental state. It's the phosphate in zinc phosphate that makes the color gold and shiny. Maybe that was also the case for cadmium plated strut.

 

[Besoeker]

I appreciated it!

And maybe Eddy was edified...

 

[hurk27]

Just sitting here and wondering how thermo-expansion didn't get mentioned? probably one of the most important effects of two dissimilar metal problem you can come across, and is one of the main reasons for conductor termination failures, while most dissimilar metal contact can be remedied by just sealing out oxygen with a sealing compound design to inhibit the galvanic action, in some cases dissimilar metal contact is intended to produce a voltage (voltaic pile) or to provide a very accurate varying resistance linear to the changing temperature in electronic thermostats or gages.

As for thermo-expansion goes if you use one type of metal to secure another type you will have an expansion rate difference which can result in conductors loosing up or getting so tight that the expanding conductor does what is called cold flow out from under the retention screw, this is where proper design of a terminal is most important that it allows this expansion and contraction without damaging the conductor, this was one of the main causes of aluminum connection failures and brought on the fear of using aluminum for current carrying conductors, even buss bars can have this problem when steel bolts or screws are used to connect busses together, which is fine to do if you also use something that can contract and expand with the connection without damaging the buss one such device is called a bevel washer, or a spring plate but bot use the same idea, if tightened down properly the will keep a connection tight as the metal expands and contracts like the springs on you car keep your wheels on the road even while you hit bumps, the idea is to provide a way for the expansion without trying to restrict it that keeps constant pressure on the connection, a fixed point connection that is of a metal with a slower expansion rate then the conductor is a problem such as a steel or brass set screw type connection that has no spring to allow a conductor to have a faster rate of expansion such as aluminum, this result in the before mention cold flow that when the conductor cools winds up being loose and starts heating so it starts the cycle over and over till the connection fails.

 

[cadpoint]

Did I miss someone else ask it? Is it the order of the conductivity that you need to know?

 

[kwired]

The purpose is to reduce eddy currents.

The OP does not want to hear about his demise:lol:

 

[Besoeker]

The OP does not want to hear about his demise:lol:

So we won't circulate it........

 

[Besoeker]

Did I miss someone else ask it? Is it the order of the conductivity that you need to know?

I don't think the OP made clear what he/she wanted to know about the properties of the metals. Just what metals he needed to know about.

 

[kwired]

I don't think the OP made clear what he/she wanted to know about the properties of the metals. Just what metals he needed to know about.

That is the way I see it also. Leaves the possible responses very wide open. Even though this is an electrical forum it does not necessarily limit the topic that much. We still have to deal with the physical, mechanical, electrical characteristics of metals in many ways in general in the electrical trade. IMO OP needs to be more specific as to what exactly it is he is wanting to know about, otherwise pick up general physics and chemistry books and start reading.

 

[Besoeker]

As for thermo-expansion goes if you use one type of metal to secure another type you will have an expansion rate difference which can result in conductors loosing up or getting so tight that the expanding conductor does what is called cold flow out from under the retention screw, this is where proper design of a terminal is most important that it allows this expansion and contraction without damaging the conductor, this was one of the main causes of aluminum connection failures and brought on the fear of using aluminum for current carrying conductors, even buss bars can have this problem when steel bolts or screws are used to connect busses together, which is fine to do if you also use something that can contract and expand with the connection without damaging the buss one such device is called a bevel washer, or a spring plate but bot use the same idea, if tightened down properly the will keep a connection tight as the metal expands.

I think your bevel washer might be a Belleville washer.

http://en.wikipedia.org/wiki/Belleville_washer

We use them stacked back to back* in the clamps for disk type SCRs. The idea is the same. It maintains clamping pressure.

*The larger diameters of adjacent washers facing each other and similarly with the smaller diameters.

 

[Electric-Light]

When you attach a more reactive metal (electropositive) than the structure, you form a shorted-battery and the more reactive metal becomes the anode.

Magnesium is more reactive than steel. So, when attached to steel and submerged or buried it erodes away while saving the steel.

This is called "sacrificial anode".... On the other hand... if it's an aluminum part that you're trying to protect and its in contact with a steel component... it's gonna erode away.

 

[PetrosA]

Probably rare to find nowadays, but they used to install silver plated copper in knob and tube systems. Worth knowing about, since the scrap is worth more than plain copper...

 

[Eddy Current]

So which is the most rust resistant aluminum?

 

[K8MHZ]

So which is the most rust resistant aluminum?

All non ferrous metals are rust resistant, since rust is iron oxide.

Aluminum will corrode into aluminum oxide.

Gold is the most corrosion resistant poly crystalline metal and only very strong acid mixes, like aqua regia will corrode, or etch it.

Maraging 314M single crystal stainless steel super alloy is the most corrosion resistant metal in existence. Nothing will corrode or etch it, even aqua regia and aqua regia super O, which will make most metals look like an alka seltzer in water. 314M single crystal is so resistant to corrosion that metallography and photomicroscopy cannot be done on it.

 

[kwired]

So which is the most rust resistant aluminum?

Are you asking which kind of metal is most corrosion resistant?

If so you have to keep in mind when selecting a metal to use the overall strength needed for the application as well as cost and you do need to consider what sources of corrosion will be likely. You may end up compromising to come up with your final selection.

Stainless steel is pretty good when talking corrosion resistance, is more expensive than mild steel, not sure how it compares strength wise for same sized object.

Now since this is an elecrical forum we could be talking about which conductors are best suitable for use as conductors.
Some of the best conductive elements are gold and silver, but are too expensive and the use of copper and aluminum becomes the better choice because of cost. Gold and silver are used in limited amounts in areas where they provide better performance for a particular application.

 

[K8MHZ]

Are you asking which kind of metal is most corrosion resistant?

If so you have to keep in mind when selecting a metal to use the overall strength needed for the application as well as cost and you do need to consider what sources of corrosion will be likely. You may end up compromising to come up with your final selection.

Stainless steel is pretty good when talking corrosion resistance, is more expensive than mild steel, not sure how it compares strength wise for same sized object.

Now since this is an elecrical forum we could be talking about which conductors are best suitable for use as conductors.
Some of the best conductive elements are gold and silver, but are too expensive and the use of copper and aluminum becomes the better choice because of cost. Gold and silver are used in limited amounts in areas where they provide better performance for a particular application.

In order of conductivity based upon area, the order of conductivity of elemental metals are silver, copper, gold then aluminum.

Aluminum is the most conductive of all elemental metals based upon weight only.

I have never seen gold or silver used as wire, just as a plating for wire. Same for terminals. Elemental gold and silver are not malleable or ductile enough to make electrical wiring from without some base or alloying.

 

[K8MHZ]

FWIW, I used to be a tech doing metallurgical research for this company:

http://www.alcoa.com/howmet/en/home.asp

 

[iceworm]

... Maraging 314M single crystal stainless steel super alloy is the most corrosion resistant metal in existence. Nothing will corrode or etch it, even aqua regia and aqua regia super O, which will make most metals look like an alka seltzer in water. ...

I have not heard of this. Most SS is only corrosion resistant if it is exposed to O2. For example, SS foundation bolts will corrode right at the concrete surface. SS marine fittings will corrode if they are in an area where the water does not circulate and becomes O2 depleted.

Q: Does this "Maraging 314M single crystal stainless steel super alloy" require exposure to O2 to maintain its corrosion resistance?

ice

 

[iceworm]

I buy a lot of Silicon Bronze bolts for making up bus work and cable connections

I'm not sure why that is any better than cad plated steel (at least I thought they were cad plated steel - kind of yellow colored and definitely steel)

ice

 

[K8MHZ]

I have not heard of this. Most SS is only corrosion resistant if it is exposed to O2. For example, SS foundation bolts will corrode right at the concrete surface. SS marine fittings will corrode if they are in an area where the water does not circulate and becomes O2 depleted.

Q: Does this "Maraging 314M single crystal stainless steel super alloy" require exposure to O2 to maintain its corrosion resistance?

ice

We were doing alloy research for single crystal applications. Most of our alloys were nickel based, but we did experiments on just about anything.

To do metallography, a test piece is mounted in a type of epoxy. The piece is then ground flat and polished to a near optically perfect surface. That meant no visible deformaties at 1000x. Mirror quality. Then, an etchant was applied and the microstructure of the crystal would become apparent. That sample was then put in a microscope with a camera on it. We would then take a picture and look at the dendrites and interdenritic areas.

One day I was given some 314M to make a crystal out of. I did and when I went to etch it, nothing would touch it. I had access to every chemical known to man and even hydroflouric acid charged with 30 percent hydrogen peroxide wouldn't touch it. I left it in over nite in aqua regia and supercharged aqua regia. Nothing. Now, etching a regular sample takes about 4 seconds once the right etchant discovered. You would just swab on the acid and just before it started to burn, you would rinse it off. This stuff was metal legends are made of. Other SS alloys could be etched, but never made it to production because the nickel based alloys were superior.

The sample is probably still in a locker somewhere. My boss had no interest in the crystal because he couldn't make jet engine parts out of it if it could not be etched as we needed to see the orientation in 3D of the crystal of each part we cast.

Another project that was cool was using titanium sponge to store hydrogen gas in. They filled a tank with sponge, pressurized it to about 1000 psi with hydrogen and then shot it with a 30-06. All that happened was the '06 punched a hole in the tank and a little tiny flame was burning at the hole. The sponge absorbed the hydrogen so once the pressure was removed the molecules intertwined and the hydrogen was released slowly. To compare, they also shot a tank with no titanium in it and it blew up like a bomb.

That's probably stashed somewhere at Howmet, too.