Why Cubic Boron Nitride Is Better Than Diamond for Grinding
Diamond grinding tools have always been an industrial mainstay but Cubic Boron Nitride (CBN) may be a better solution in many applications. CBN grinding wheels provide the same benefits as diamond tools and even perform better in some applications.
The desirable characteristics of any abrasive include:
- Abrasion resistance
- Thermal and chemical resistance
- Ability to maintain sharp cutting edges during use
Hardness is perhaps the most critical property of every abrasive. Abrasives tend to lose hardness during application as a response to very high temperatures. One of the greatest advantages to using CBN is that it maintains its hardness at room temperature and over a wide variety of temperature ranges.
CBN is the second hardest material after synthetic diamond. The process of making CBN abrasive is similar to that of synthetic diamonds: scientists treat hexagonal boron nitride at high temperature and pressure to create cubic boron nitride and treat graphite in the same way to create diamond.
Machinists make CBN grinding wheels by electroplating CBN particles on steel, using electroplated nickel to hold grit in place. A single layer of CBN grit applied to the surface of a metal disc can grind even the hardest surfaces and last for years.
CBN has several attractive characteristics that make it superior to diamond:
- Withstands heat, especially during high-speed applications
- Does not cause grit that can dull bits
- Stays sharp and cool because it does not react with steel
Diamonds can also react with transition metals, limiting their usefulness for grinding certain materials. Cubic boron nitride is stable and does not tend to react unfavorably with standard transition metals.
But What About Diamonds?
Diamond super-abrasive grinding wheels do have their advantages in some applications, especially in grinding abrasive or hard materials such as aluminum oxide, ferrites, ceramics, tungsten carbide, gray and ductile iron, and carbon. These grinding wheels also have the ability to cut freely with a cool cutting action, which is handy in applications where coolants could damage materials. Diamonds will likely remain a popular choice in many grinding applications in the future but nanotechnology may propel CBN into the top position.
Nanotechnology and CBN
In January 2013 issue of Nature, a scientist from University of Chicago’s Center for Advanced Radiation Sources and his colleagues reported they had been able to make ultrahard CBN by drastically shrinking grain size. The researchers were also able to rearrange the crystals into a zigzag formation of boron and nitrogen rather than in conventional flat layers to give it super resilience.
“Now, we can make this material as hard as single crystal diamond,” says the lead scientist, Yanbin Wang. “In some ways, it’s a better tool than diamonds, especially given its high fracture toughness.”