Some comments on Boker ceramic blades

[Cliff Stamp]

Sometime ago I was given a couple of ceramic blades made by Boker that needed considerable work. Both had large chips, up to 1 mm deep, and about 3-4 mm long. One also had a a few mm snapped off of the tip. They were quite mauled. I discussed the usage with the owner who basically commented that they had not been used carefully but the described use would not have done much except severely blunt a solid steel blade.

I have sharpened ceramics before with DMT's hones but this time did some experimenting to see what if anything happens whith softer abrasives. Interesting enough you can work these with cheap (3 for $5) AO belts. Now the work is slow, and I mean slow, but it can be done. What I would have stripped off in one pass with even a very wear resistance steel took many passes with the ceramic blades.

Leaving the power equipment alone I took the other blade and repaired it with an x-coarse 8" DMT hone. I was doing sets of 50 strokes per side on the hone. This would take a major chip out of a good steel blade, but did little to the ceramic. Many cycles were needed before I could see progress. Anyway after I had all the chips out I did some sharpening at various grits and compared the cutting abilities. It revealed something quite unexpected.

I first did some push cutting with the x-coarse DMT finish. As expected it performed really poorly. However I figured I had a great slicer - wrong, and I mean really wrong. I checked it under magnification and it looked like the blade was breaking apart rather than being smoothly cut. This means that the "micro serrations" that you get with a steel blade just don't happen. Instead you get large jagged spikes with very blunt regions in between them, bigger than the spikes.

As I increased the finish of the hones the blades started to both push cut and slice very well. I finished off with CrO 0.5 micron (9000 grit paper). When I checked under magnification the edges still needed work but since I had put in about 10x the polishing work that I would have for a steel blade I stopped for the day.

At this point it will slice paper nicely and cut 1/4" poly rope in once pass under moderate force (these are small blades). This is a rather low standard for a steel blade. When I get a few hours free time I will see if I can improve on the polish further. However you really need power equipment to work with these on a regular basis.

-Cliff

 

[S Dunbar]

Interesting results, meets my expectations and its nice to see it confirmed. I've been doing some research into ceramic blades recently and have discovered the following pertinent facts.
Ceramic blades such as Kyocera's are manufactured from Ytrium stabilised Zirconia in 3Molar ratio(5% by weight)and are referred to as 3Y TZP(tetragonal Zirconium polycrystal). The ceramic is typycally first formed in a press from the raw oxides and is then sintered in an electric furnace at ~1500C. The crystal structure of the resultant ceramic is around 0.5 micron, which explains the edge results you observed. The hardness of the ceramic is ~95 Rockwell. Since the blade is sintered, the cutting edge requires maximum support and the 0.5u structure purportedly results in a micro-micro serrated edge when honed as fine as possible. This lends itself to forming a good cutting edge at a larger angle than can be obtained with steel with resultant increased support of the edge particles. (unfortunately I have not yet discovered what is optimal). So try polishing that final edge at a large angle for optimal results.

Happy sharpening, Stuart Dunbar


[This message has been edited by S Dunbar (edited 04-05-2001).]

 

[A. G. Russell]

Originally posted by S Dunbar:
Interesting results, meets my expectations and its nice to see it confirmed. I've been doing some research into ceramic blades recently and have discovered the following pertinent facts.
what is optimal). So try polishing that final edge at a large angle for optimal results.

Happy sharpening, Stuart Dunbar

Great information, has anyone tried talking to a friend who is a lapaderist (?), one who cuts and polishes stones. I would think that using a diamond belt with a coolent would be the best way to put a polished edge on ceramic. I wonder if the ceramic blades offer a concoidal fracture like glass or flint? That may be the chipping you see when you try to sharpen with medium that is not as hard as the blade. A. G.