Main Characteristics of Superabrasive Materials
Grinding tools, made of super-abrasive (super-hard) materials like CBN (cubic boron nitride) and diamond, find a wide application in different fields of industry.
Diamond is the hardest natural material known with the highest abrasive capability in comparison with all other used abrasive material. CBN (cubic boron nitride) is synthetic super- hard material with diamond-type crystal lattice; it is inferior by hardness to diamond only, but it has higher heat resistance.
Characteristics of Abrasive Materials
Diamond has low thermal resistance (~ 650 °C) and high reactivity with ferrum. These restrictions do not allow effective application of diamond wheels for grinding of steel, the base element of which is ferrum.
Diamond wheels are used for grinding and sharpening of carbide cutting-tools mainly. One more application area is grinding of different carbide parts: punches, dies, moulds, forming rolls, draw plates. Diamond wheels provide good productivity and perfect quality in grinding of ceramic parts, hard and fragile magnetic materials, cast iron; processing of abrasive tools.
The relatively new application area of diamond wheels is grinding of PCBN and PCD cutting.
Diamond wheels are used in grinding and cutting of quartz and optical glass, precious, semiprecious and synthetic stones, graphite-based materials.
CBN superior hardness (that is 3...4 times higher than the hardness of traditional abrasives) is an important advantage in grinding that allows to decrease grains wear significantly and to keep grains cutting ability for a long time.
High heat resistance is another advantage of CBN: noticeable oxidation of CBN grain surface takes place at temperature 1100...1200 °C. In the process of grinding such temperatures are very short term (contact time between a grain and ground surface is about 10"4... 10"6 sec), and appear in hard grinding conditions only. Obviously, CBN grains have good resistance to thermal loads.
One more important advantage of CBN - high chemical inertness. CBN does not react with acids and alkalis, it remains inert to all the chemical elements of steels and alloys. Especially, this concerns ferrum, which is the basic element of all steels. CBN is absolutely nonreactive with ferrum, whereas diamond is highly reactive with ferrum that leads to intensive wear of diamond wheels in grinding of steels.
The summary of the main advantages of CBN material :
- CBN grains stay sharp for a long time providing good cutting ability and long wheel life;
- CBN has good resistance to thermal loads that makes it possible to intensify grinding conditions;
- CBN allows grinding of complex alloyed steels and alloys without adhesive and diffusive wear of CBN grains.
- CBN tools are widely used by automotive industry, bearing industry, machine-tool industry, aircraft industry; in manufacturing of cutters, punches, moulds and measuring tools.