Visible defect size in ceramic

[geoffthehammer]

I'm not sure if this is the correct forum but none of the others seem to be right, so here goes:

We buy in a ceramic cutting blade. The inspection criterion for the edge that we have agreed with the manufacturer is that there should be no visible defects along the cutting edge when viewed at 15X magnification. OK, so this is somewhat subjective but it works satisfactorily and we have no complaints.

For entirely different reasons we would now like to quantify the size of any defects that are not visible at 15X magnification.

Question: What would be the largest defect (i.e. a notch)that could be present but remain invisible at 15X mag. Assuming 20/20 vision and a quality 15X microscope.
Grain size of the ceramic is 0.5 micron diameter.

 

[CoryPad]

The human eye has a resolution of approximately 0.2 mm to 0.5 mm. At a magnification M = 15, the resolvable object size would be 13 [µ]m to 33 [µ]m.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[tomwalz]

We use a similar system for tungsten carbide. What a person can “see” also depends on training. A person can “see” things that are too small to actually see by picking up on a discontinuity in light on an edge for example.

We typically use 30x as a standard and specify by three dimensions.

The simplest way is to insert a reference object in a digital photo or use a calibrated set up.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[tomwalz]

I posted a simple version of what we use.

http://cs4u.org/Basicsawtiporderingwithquality.pdf

In all honesty I have been in too many meetings where everyone had their own micrometer (or other instrument) and everyone was trying to figure out if the parts were in spec or not. I think that trying to go with a crack you can see could cause problems.

In addition I think the materials you are working with are most likely sintered and incidental edge roughness caused before sintering is entirely different than edge roughness cased after sintering.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[IRstuff]

Very impressive, Tom.

There is a minor typo in the 3rd item in the Chips and Cracks. External is misspelled as "extrenal."

TTFN

FAQ731-376