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Layers in broken metal

 
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20035
Location: Richland, Washington State, USA

PostPosted: Wed Oct 09, 2019 10:22 pm    Post subject: Layers in broken metal Reply with quote

Let's start with the closeup stereo. This is about 1.5 mm high. I was impressed with the amount of layering visible in this piece of metal that I would have expected to be pretty homogeneous.



The story here is that today I was called to another house to fix a piece of equipment that was mostly not working but could be made to work sometimes if the power plug was held "just so".

It turned out that the wall socket needed replacing, but more importantly, so did the power plug. Replaced both, problem fixed, great.

However, the power plug problem was odd enough to attract my attention, because one of its prongs was quite loose in the plug. So I sliced apart the plug to see what had gone wrong.

Here's what I found: that prong had been bent far enough and/or enough times that it had simply snapped.



Here's the broken end of the prong, in its entirety. The stereo pair is the area outlined.



Again, I was surprised by the extent of visible layering in this piece of metal. Naively I would have expected it to be a lot more homogeneous. The cord and plug assembly superficially appeared to be high quality, but it seems that "under the covers", not so much.

I hope you find this as interesting as I did.

--Rik
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BugEZ



Joined: 26 Mar 2011
Posts: 782
Location: Loves Park Illinois

PostPosted: Thu Oct 10, 2019 3:54 am    Post subject: Reply with quote

How cords are assembled.

https://m.youtube.com/watch?v=UbDmZ5OljJI

Some discussion on the metals used in connectors here. Probably a copper-zinc alloy.

https://www.waytekwire.com/datasheet/How-Connectors-Get-Manufactured.pdf

Regarding the layering you mentioned, that would come from the rolling process used to form the strip stock. The v shaped bands I think I see are due to the squishing taking place between the rollers.

In the third photo, I suspect the crack initiated on the left and propagated to the right. Was the plug cycled up and down in the receptical? Vibration?

Nice photos!

Keith
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20035
Location: Richland, Washington State, USA

PostPosted: Thu Oct 10, 2019 9:34 am    Post subject: Reply with quote

Thanks for the links to documentation!

BugEZ wrote:
In the third photo, I suspect the crack initiated on the left and propagated to the right. Was the plug cycled up and down in the receptical? Vibration?

The wall outlet was severely worn and the plug's prong was bent outward, across the flat, as if someone had attempted to "adjust" it to make it fit tighter in the worn socket. The plug was for a piece of powered furniture, essentially fixed equipment with a long cord that doesn't seem subject to vibration or up/down cycling.. It's always possible somebody bumped the plug sideways. I really don't know the history, since in a prior life the equipment was a rental unit with probably a long line of users. This is one of the rare things I've gotten to fix without the background of having broken it myself!

I agree about the origin of the layering. I was just surprised to see that it was so obvious, complete with lumpy inclusions. Now I'm tempted to sacrifice a couple of prongs from replacement plugs, just to see what they look like when broken.

--Rik
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