What, in cardboard, dulls knives?

L

Lavan

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Nov 8, 2000
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Is there a material that exceeds the hardness of steel in cardboard? In fact, I will ask exactly WHAT it is that could dull steel as knives go dull no matter WHAT they are used to cut?

I'm not clear on dulling. I...think....diamond cuts forever on anything and is only subject to gradual chipping away.

Anyone explain dulling?

:confused:
 
clay.

clay and other dirt/minerals are used both in the matrix of and on the finish coat of cardboard products.
 
Actually it is the dense paper all by itself. Paper, for some reason which I DON'T KNOW is hell on fine edges (I suspect it is the abrasive nature of the random wood pulp particles). This was well known in the 1800's and earlier where some slipjoints of the era included an ivory "blade" just to open up letters so the primary steel blade would not be dulled by use on paper.

Just remember that a substance doesn't have to be harder than the steel to cause dulling. Your razor blade is clearly ALOT duller after a week of shaving and your facial hair certainly isn't harder than steel!
 
DaveH has it right, at least as far as paper is concerned. If you view most paper through an electron microscope the clay particles look like huge rocks in the matrix of paper fibers. Photocopy paper is an excellent example.
Phil
 
While the edge of a knife is hard it isn't actually very strong. If you take a very thin bladed knife and chop it into a hard knot you can easily take a huge piece out of the blade or make a massive dent. Even though the strength of the steel is high, the functional strength of it when the cross section is really low isn't.

Take a full HSS hacksaw blade for example at 65 HRC. You can easily grab that in your hands and band it, even though your hands are much softer than the steel, because it is only 1/16" thick, and once you flesh compresses a little, it is much stronger than steel of that thickness, plus you are loading them different.

It is the same thing with edges on a differnet scale, edges will blunt by rolling and denting a lot which is why hardness is so critical, they will also blunt by direct abrasive wear on some materials, or simply corrode, or actually crack from direct impacts or fatigue.

Phil Wilson had an excellent article on what causes blunting in general and how different knives need different steels to have good edge retention because how a knife blunts is different depending on what it is cutting and the enviroment.

-Cliff
 
I forgot about....CLAY... Yep, that'd do it.

Also whiskers.

And also hydrocutting of steel. Probly cud dull a knife by swishing it in water for long enough.
 
I have one knife that will eat yards and yards of cardboard, and not show much wear. The M2 that Benchmade uses on a few models of their knives will outlast most of my other knives by at least a factor of 3. It has a much higher Rc value than most steels are hardened to, so that is a factor. It WILL dull, though. It just takes a bit longer. I also find that the Black Teflon coating they use lets the blade slip through much more easily, and not bind like some knives.

Sorry if this is a bit off topic. Just thought I'd share.

Daniel
 
I believe it's something physically similar to subrin. Hardens plant cells, particularly in trees....turns parts of the tree into hard dead tubes, really. Of course, too small for us to see with our eyes.
 
Clay is part of the mix when you create paper. A common type is kaolin, same as used to make china. White writing paper has more clay than brown craft so all paper will dull knife edges if you cut enough. There are other silicates that occur naturally in plant fibers. Even whittling wood will eventually dull a knife.

The apex of a knife edge is capable of folding over or buckling. This is a function where pushing on the end of a thin object causes it to bend sideways at the apex or bow sideways behind the edge. Once it starts to bend it is even less able to stand up to the forces against the edge. This is related to a phenomenon called collumn buckling. Long thin structures don't support the forces that you would expect given their cross-section and compressive strength. That's because they bow out or tip over where they bend sideways. In an edge this can happen to small spots that encounter hard spots in the material. When the hard spots aren't uniformly distributed they can apply sideways forces that the edge is even less able to withstand.
 
When I did the cardboard cutting for the post comparing the edge holding of H1 to VG10, I was surprised at how quickly the knives lost their ability to shave. I was also surprised at how long they continued to cut after they had lost their shaving sharpness.



- Frank
 
frank k said:
I was also surprised at how long they continued to cut after they had lost their shaving sharpness.
Click to expand...

Blunting is highly nonliner, it is basically an exponential decay, very fast at first but rapidly declines. For example do a hundrend cuts on a abrasive material and the sharpness can be 10% of optimal, do three hundred cuts and it can be reduced just barely more to 8%. The change in the last 200 cuts was only 1/50 of the change in the first 100.

-Cliff
 
The bottom line is that using any blade will dull it. If I recall correctly even ceramic kitchen blades eventually dull, and I doubt that there is too much silica in the zuchinni
 
I think artfully martial is right about this, I don't remember much from my botany class but we learned about the minerals that build up in plants on a micro-level, can't remember what they're called but they form little deposits within the plant cells. Since cardboard is made out of wood fiber I suspect some of these mineral deposits get processed whole and remain in the cardboard. Cheese also seems to dull knife edges quickly, and I believe it's for the same reason, micro-size mineral deposits in the food.

Lagarto
 
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