EDGE STABILITY IN BUTCHER’S AND KITCHEN KNIVES

[Jan]

Great post  Jan and put very succinctly. Makes perfect and very logical sense to us. Your use of the term "crinkle" was, as our good friend Rupert would say, "spot on".

EOU, your positive feedback pleases me.
The verb originates from Old English crincan or Dutch krinkelen.

Jan

[Jan]

Mr. Mark, your interest pleases me!

The graph you are mentioning was copied from the famous book by prof. Verhoeven and so I hope it is a representative example of the correlation between UTS and Rockwell hardness.

I cannot tell you exactly why prof. Foell considers "yield strength" to be just another term for hardness. May be the reason is the absence of good definition what hardness is from the first physical principles. Hardness is defined by an indentation procedure only. This is in contrast with clear physical definitions of strength or toughness as example.

The original contribution of prof. Foell you can find here: https://www.tf.uni-kiel.de/matwis/amat/iss/kap_3/backbone/r3_1_4.html#Ultimate%20tensile%20strength

Jan

[KnifeGrinders]

Mr. Mark, your interest pleases me!

The graph you are mentioning was copied from the famous book by prof. Verhoeven and so I hope it is a representative example of the correlation between UTS and Rockwell hardness.

I cannot tell you exactly why prof. Foell considers "yield strength" to be just another term for hardness. May be the reason is the absence of good definition what hardness is from the first physical principles. Hardness is defined by an indentation procedure only. This is in contrast with clear physical definitions of strength or toughness as example.

The original contribution of prof. Foell you can find here: https://www.tf.uni-kiel.de/matwis/amat/iss/kap_3/backbone/r3_1_4.html#Ultimate%20tensile%20strength

Jan

Prof. Foell may have drawn his oversimplified catchy "What is commonly known as 'hardness' is nothing more than the yield stress, just measured in different units."  from the same Verhoeven's plot.
The almost linear correlation in that plot looks suspicious to us who've been following Jan's study on non-linearity of the HRC scale.
Verhoeven comments in his work that "The correlation becomes less reliable at HRC values above 55." (page 41) - in other words that plot is for soft and medium steels, not used in knives.
Again, the outcome depends on the way the steel is Q & T -ed - for low-alloy steels you may get a springy or stiff piece.

Hardness test indirectly tells of the strength, but hardness and strength are not the same properties of the steel, though relation between these two is closer than that of each of them with toughness. Approximation is too far to say "just measured in different units"

In view of all that, moreover impatiently we wait for Mike's experiments on the extent of edge rolling by steel hardness.

[Jan]

One or two numbers are surely not sufficient to fully characterise steel properties. Much more info can be gained from the stress-strain curve.
   

Jan

[Mike Brubacher]

Got a question for you KG if you don't mind. Have the meat processing guys in your corner of the world ever tried using ceramic knives? We've tested a few here and they are not very sharp out of the package (350-400) but they can be made sharper. I'm pretty sure that a ceramic edge isn't going to roll though. We'll test that theory to make sure it holds.  I suspect that this resistance to rolling is the primary basis for their reputation in holding an edge considerably longer than steel. I'm aware of the downside of ceramic edges (chipping) and blades (breaking) but has their use ever been considered seriously in the meat processing industry to your knowledge?

[KnifeGrinders]

Got a question for you KG if you don't mind. Have the meat processing guys in your corner of the world ever tried using ceramic knives? We've tested a few here and they are not very sharp out of the package (350-400) but they can be made sharper. I'm pretty sure that a ceramic edge isn't going to roll though. We'll test that theory to make sure it holds.  I suspect that this resistance to rolling is the primary basis for their reputation in holding an edge considerably longer than steel. I'm aware of the downside of ceramic edges (chipping) and blades (breaking) but has their use ever been considered seriously in the meat processing industry to your knowledge?

You know Mike, your ability to think out of square is quite disturbing.
On a serious note, I know for sure that no meat plant in the whole Australia has ever tried them.
They won't even think of ceramic because the volume sharpening equipment they have is not able to sharpen them... unless they outsource sharpening to us.
The factory edge on the cheaper ceramic knives I've sharpened was 775 BESS. On CBN and paper wheels with diamonds I quickly sharpened them to 55-115 BESS.

Please do SET-test them, and I will also test the 2 knives I have at hand.
Provided the testing is all good, I will do my best to convince the COO to try at least one ceramic knife at their meat plant for a day by one operator.
Using ceramic knives in boning rooms is a crazy idea - crazy enough to give it a consideration.
If the ceramic knife lasts through the whole work day in the boning room, cost-wise they may be times more effective.

[Mark Reich]

It is very interesting to know you can sharpen ceramic knives, Mr. KG.

Have you ever tried sharpening a sintered ceramic blade?

What angle do you use for ceramics?

[KnifeGrinders]

It is very interesting to know you can sharpen ceramic knives, Mr. KG.

Have you ever tried sharpening a sintered ceramic blade?

What angle do you use for ceramics?

Aren't they all sintered? 
15 dps, 30 included - but this was before SET, yet to see what min angle they tolerate.

[Mike Brubacher]

Thanks for the input KG. Yes, there is little doubt, if you put my brain in a duck he'd fly sideways. We sharpened our ceramic blade with the rotary sharpener we were developing and a 30 micron SC disc. We have had a fair amount of experience using SC to grind 45° bevels on ceramic optical ferrules. The ferrules were zirconia and have no idea what the knife was. We took it from 350 to 300 in pretty short order and quit at that point having proven what we wanted to prove... ceramic knives can be sharpened. I suspect that ceramic knife manufacturers produce these edges at the sharpness level they are for a reason. The thinner the edge, the more susceptible to chipping they become.

Now there's another sideways thought of mine. Chipping. From an aesthetic standpoint, not good. From a practical standpoint, what's the big deal? The Exchange recently featured several pages on a new product that was designed to put chips (or dents at least) in a steel knife edge under the premise that it made the knife cut better. Whether chips/dents make edges cut better or not, it would seem that the affected area of the cutting edge would be a very small percentage of the total in typical cases.

Seems to me KG that if you could put your commercial customer's knife at 200-250 and it just stayed there for a week without maintenance intervals (edge straightening) that it might be a good thing. Might not as well, but knowing you, you'll figure out if it is or isn't in fairly short order.

I'm assuming that there was no burr to be removed after sharpening. Am I assuming correctly? Wonder if there is any problem putting "tooth" in a ceramic edge. 250 with tooth is a lethal weapon in my estimation.

[KnifeGrinders]

...
Seems to me KG that if you could put your commercial customer's knife at 200-250 and it just stayed there for a week without maintenance intervals (edge straightening) that it might be a good thing. Might not as well, but knowing you, you'll figure out if it is or isn't in fairly short order.

I'm assuming that there was no burr to be removed after sharpening. Am I assuming correctly? Wonder if there is any problem putting "tooth" in a ceramic edge. 250 with tooth is a lethal weapon in my estimation.

... and having a commercial meat knife under 200 BESS for the 10-hour shift would free the whole industry of repetitive strain injuries (just letting my ducks fly sideways for 1 sec   )

Yes, with ceramic knives you omit deburring and can go from a CBN/diamond wheel straight to meat cutting; but for better edge keenness still benefits from some honing.

... 250 with tooth is a lethal weapon in my estimation.

Yes it is, below is a photo of a ceramic saw-edge off #1000 grit CBN


And a good news, I've arranged for the first trial of a ceramic knife in boning on the coming Monday - by a local veteran butcher on beef carcasses; if he OKs I will talk to the meat plant.