Tom Walz
12-19-2007, 1:25 PM
A couple miles of Western Red Cedar for something like a C-1 carbide. Longer for a C-4.
In a test at Forintek (Forest Industries Technology) at the University of British Columbia Kennametal’s K3030 carbide showed 25.4 microns of wear at about 5,000 lineal feet. Cermet showed the same wear at about 20,000 lineal feet.
How Carbide ‘Wears Out’
Typically people think that carbide is worn away. There are other considerations that are often much more important.
How long a material runs for you depends on what you are doing and what you mean by sharp.
Tungsten carbide is actually tungsten carbide grains cemented with a metal, usually cobalt.
A. You can have individual grains breaking or pulling out.
B. You can generate an electrical potential through rubbing that will accelerate this.
C. You can get a chemical leaching that will dissolve the binder and let the grains fall out.
D. As with any chemical reaction of this sort the acids create a salt that protects underlying binder until the salt is abraded away so grain size and binder chemistry are also important.
E. You can get welding between the carbide and the material being cut depending on the carbide grade and the material.
F. Heat from rubbing can affect carbide so a slicker grade can increase life.
G. You can get macro-fracturing (breaks large enough to see) and micro-fracturing. With some grades a good hit can start a fracture (fracture propagation) that will sometimes run and sometimes not (fracture propagation).
H. The binder is a metal so it can flex and fatigue.
I. If there is too much binder the part can deform.
Theoretical considerations
1. Macrofracture – big chunks break off or the whole part breaks
2. Microfracture – edge chipping
3. Crack Initiation – How hard it is to start a crack
4. Crack propagation =- how fast and how far the crack runs once started
5. Erosion – the binder leaches away and the carbide grains fall out
6. Electrochemical effect – erosion compounded by the differences in electrical resistivity between carbide and cobalt
7. Wear – the grains and the binder just plain wear down
8. Physical Adhesion – the grains get physically pulled out. Think of sharp edges of the grains getting pulled by wood fibers.
9. Chemical adhesion – think of the grains as getting glued to the material being cut such as MDF, fibreboard, etc.
10. Metal fatigue – The metal binder gets bent and fatigues like bending a piece of steel or other metal
11. Heat – adds to the whole thing especially as a saw goes in and out of a cut. The outside gets hotter faster than the inside. As the outside grows rapidly with the heat the inside doesn’t grow as fast and this creates stress that tends to cause flaking (spalling) on the outside.
12. Tribology – as the tip moves though the material it is an acid environment and the heat and friction of the cutting create a combination of forces.
Actual Practice
1. Straight wear – almost never found alone and typically not the most important reason.
2. Fracture of individual grains
3. Grains being torn out
4. An electrical effect through rubbing that will accelerating grain fall out.
5. Chemical leaching that will dissolve the binder and let the grains fall out.
6. Chemical leaching is affected by grain size
7. and binder chemistry
8. You can get welding between the carbide and the material being cut depending on the carbide grade and the material.
9. Heat from rubbing can affect carbide so a slicker grade can increase life.
10. You can get macro-fracturing (breaks large enough to see) and
11. micro-fracturing.
12. With some grades a good hit can start a fracture (fracture propagation) that will
13. sometimes run and
14. sometimes not (fracture propagation).
15. The binder is a metal so it can flex and
16. fatigue.
17. If there is too much binder the part can deform.
In a test at Forintek (Forest Industries Technology) at the University of British Columbia Kennametal’s K3030 carbide showed 25.4 microns of wear at about 5,000 lineal feet. Cermet showed the same wear at about 20,000 lineal feet.
How Carbide ‘Wears Out’
Typically people think that carbide is worn away. There are other considerations that are often much more important.
How long a material runs for you depends on what you are doing and what you mean by sharp.
Tungsten carbide is actually tungsten carbide grains cemented with a metal, usually cobalt.
A. You can have individual grains breaking or pulling out.
B. You can generate an electrical potential through rubbing that will accelerate this.
C. You can get a chemical leaching that will dissolve the binder and let the grains fall out.
D. As with any chemical reaction of this sort the acids create a salt that protects underlying binder until the salt is abraded away so grain size and binder chemistry are also important.
E. You can get welding between the carbide and the material being cut depending on the carbide grade and the material.
F. Heat from rubbing can affect carbide so a slicker grade can increase life.
G. You can get macro-fracturing (breaks large enough to see) and micro-fracturing. With some grades a good hit can start a fracture (fracture propagation) that will sometimes run and sometimes not (fracture propagation).
H. The binder is a metal so it can flex and fatigue.
I. If there is too much binder the part can deform.
Theoretical considerations
1. Macrofracture – big chunks break off or the whole part breaks
2. Microfracture – edge chipping
3. Crack Initiation – How hard it is to start a crack
4. Crack propagation =- how fast and how far the crack runs once started
5. Erosion – the binder leaches away and the carbide grains fall out
6. Electrochemical effect – erosion compounded by the differences in electrical resistivity between carbide and cobalt
7. Wear – the grains and the binder just plain wear down
8. Physical Adhesion – the grains get physically pulled out. Think of sharp edges of the grains getting pulled by wood fibers.
9. Chemical adhesion – think of the grains as getting glued to the material being cut such as MDF, fibreboard, etc.
10. Metal fatigue – The metal binder gets bent and fatigues like bending a piece of steel or other metal
11. Heat – adds to the whole thing especially as a saw goes in and out of a cut. The outside gets hotter faster than the inside. As the outside grows rapidly with the heat the inside doesn’t grow as fast and this creates stress that tends to cause flaking (spalling) on the outside.
12. Tribology – as the tip moves though the material it is an acid environment and the heat and friction of the cutting create a combination of forces.
Actual Practice
1. Straight wear – almost never found alone and typically not the most important reason.
2. Fracture of individual grains
3. Grains being torn out
4. An electrical effect through rubbing that will accelerating grain fall out.
5. Chemical leaching that will dissolve the binder and let the grains fall out.
6. Chemical leaching is affected by grain size
7. and binder chemistry
8. You can get welding between the carbide and the material being cut depending on the carbide grade and the material.
9. Heat from rubbing can affect carbide so a slicker grade can increase life.
10. You can get macro-fracturing (breaks large enough to see) and
11. micro-fracturing.
12. With some grades a good hit can start a fracture (fracture propagation) that will
13. sometimes run and
14. sometimes not (fracture propagation).
15. The binder is a metal so it can flex and
16. fatigue.
17. If there is too much binder the part can deform.