Most common simple correlation (with distinct errors possible) is the
inverse correlation between wear rate (many different kinds of wear
rates.... so beware...) and hardness (most of the differences between
the many measures of hardness don't seem to be of first order importance).
If you blindly follow the hardness vs wear correlation, you will often
be right, but occasionally quite wrong.
In short, there is more to wear (whatever that is) than hardness.
Experience still is valuable. So is being able to understand complex
phenomena exist, no matter how easy it is to pretend they are simple,
This is out of Sandy Stewart's work
Tool Wear Mechanisms
Woodworking tool wear has four major components; abrasion, adhesion,
diffusion and fatigue. These interact but some are more important
than others depending on the material being cut.
Typically tool wear is though to be all abrasion or mostly abrasion.
This is especially true in materials such as medium Density Fiberboard
(MDF) which contain adhesives and silica. ?Rubbing', ?plowing' and
?cutting of the blade' are the most common types of abrasion.
Adhesion is the formation of ?welds' between the tool and the
workpiece. This is considered more common in metal working but can be
very significant in man made materials with binders.
Cobalt leaching is also called diffusion and is caused by the
transference of atoms from the cobalt binder to new compounds formed
with the wood acids and similar. Obviously as the binder fails the
carbide grains fall out.
Fatigue is the east appreciated of the failure mechanisms but carbide
tips can fatigue just as metal fatigues.
Agreed to all that. I have some material on this from a lecture course on
tribology I give (well, gave, actually, since our academic committtee
decided that having a course on nanotechnology was more important...) that
might be useful....
Hardness exists as a material property, relative to other materials.
Generally speaking it is a bulk effect.
Wear only exists when there is contact between two materials. Generally
speaking it is a surface effect.
To illustrate, a machine tool is harder than the material it cuts. However
despite this it wears.
Wear is related to the _relative_ hardness of two materials, all "other
things" being equal. Then the harder material will wear less than the
softer. Those "other things" include: presence of lubrication, surface
roughness, Young's modulus, brittleness of material, loads experienced
(changing or otherwise), structure of the materials under consideration,
electrical properties like magnetism, chemical properties like mutual
corrosion or reactivity, the environment, and the presence of Yuri Geller.
Av> Dear All,