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Author: Subject: Why are pencil sharpners magnesium?
cnidocyte
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[*] posted on 20-2-2011 at 07:45


What pencil sharpeners are made of magnesium and what percentage of magnesium is in them?
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[*] posted on 20-2-2011 at 08:54


KUM pencil sharpeners, I think it's almost 100% magnesium
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plante1999
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[*] posted on 20-2-2011 at 09:01


STAEDTLER sharpener also is Mg at 95% (arround).
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[*] posted on 27-2-2011 at 14:52


Did anyone answer the question yet?

I think: magnesium prevents the corrosion of the iron blade in the sharpener. Magnesium doesn't form a good oxide layer as aluminium does. The metal (magnesium) will have a direct contact with the iron blade - so electrons can easily flow (from or to?) the magnesium. The oxide layer of an aluminium sharpener might act like an isolator and prevent this flow of electrons (maybe!!!). Magnesium is less noble than iron. The magnesium works like a sacrificial anode. Instead of corroding iron the magnesium will corrode (very slowly). Without iron corrosion the blade will stay sharp! I've got such a 10 year old magnesium sharpener and used it many many times - it still is super sharp.

I don't exactly know - but this would be the only explanation of this magnesium "wastage" to me.

look here at "test 4" and "experiment 5":
http://translate.google.de/translate?hl=de&sl=de&tl=...

[Edited on 27-2-2011 by Pok]
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[*] posted on 28-2-2011 at 08:58
few old hard drives


good work POK

in my dumpster diving days i ran across quite a few old hard drives probably from main frames... upon taking them apart they had large MG labeled plates inside.....

got about a dozen or so of them---




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[*] posted on 28-2-2011 at 09:08


Yes, good post, Pok. Although I had been following this thread it was not until your post that I realized that it was not the blade but the base that was Mg. So it is a sacrificial anode for the iron blade. Now the use of Mg makes sense.

I looked for Staedtler or KUM sharpeners in my local office supply place but they did not have those brands.




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[*] posted on 5-3-2011 at 15:05


Quote: Originally posted by peach  
When everything of a similar nature is aluminium?


you cant make a pencil sharpener from aluminum because pencils use graphite, and graphite causes aluminum corrosion.
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[*] posted on 5-3-2011 at 15:13
more Mg in the house


I think it will be for cost reasons and ease of working it as it's cheap enough rather than weight saving as a sharpener isn't that much. I have a few of the Mg types around but never realised that is what they were made of or that graphite corroded aluminium. Still steel wouldn't be hard to cast and cheaper probably and not exactly heavy in your pocket.

I notice a lot of pedal bike parts are made from Mg due to lightweight but they tend to be a ripoff considering it is cheap and easy to work. Unsure on figures or if it's true but hear it isn't as strong as 6061 and 7005 alu alloys that most MTB parts are made from. 6061 is tougher and good tubing etc and 7005 harder so good for chainrings as well as tubing but for a fair few other parts it is good choice due to weight/strength ratio.

Main body of my front forks (bottom half of Rockshox Toras) are magnesium I think. Things like Mg pedals, brake calipers and so on are popular too although I use alu ones myself.

[Edited on 5-3-2011 by K10]

[Edited on 5-3-2011 by K10]
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[*] posted on 5-3-2011 at 23:34


Quote: Originally posted by ElectroWin  
Quote: Originally posted by peach  
When everything of a similar nature is aluminium?


you cant make a pencil sharpener from aluminum because pencils use graphite, and graphite causes aluminum corrosion.



You are actually wrong. MOST of the sharpeners are made of Al, and only a few fancy ones are made of Mg.

I don't see why on Earth graphite would corrode Al either. Graphite is really an inert thing.
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[*] posted on 1-10-2012 at 04:49


Quote: Originally posted by a_bab  

I don't see why on Earth graphite would corrode Al either. Graphite is really an inert thing.


don't believe me, try this experiment. take any aluminum part, like a sliding door, and try lubricating with graphite. it will seize up.
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[*] posted on 2-10-2012 at 03:59


They use Magnesium because they use the powder sintering process in manufacture

[Edited on 2-10-2012 by wallschem]
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[*] posted on 2-10-2012 at 06:31


I don't know if anyone here has tried to tap a screw thread into aluminium, if you have you'll agree with me that Al binds to the tap even with lubricant leaving you with an undesirable result, and the same with using fine threaded screws in an Al part, slightly overtighten and the thread strips.

This is why Mg is used, it's toughness allows for the use of fine threaded screws and hence the need for a fine threaded screw to secure the blade to a pencil sharpener.

Incidentally, any light metal part you come across that has fine threaded screw holes in it will most likely be or have Mg in it, that or Ti.




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[*] posted on 4-10-2012 at 15:13


Quote: Originally posted by froot  
This is why Mg is used, it's toughness allows for the use of fine threaded screws and hence the need for a fine threaded screw to secure the blade to a pencil sharpener.


I had a solder gun and the screws and the thing was aluminum. The screw broke after a couple of uses. Al is too soft. Idiot manufacturer!
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[*] posted on 7-10-2012 at 07:34


Quote: Originally posted by plante1999  
STAEDTLER sharpener also is Mg at 95% (arround).


I always wondered if Staedtler pencil sharpener turnings would be of sufficient purity for Grignard reactions.




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