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Superabrasives materials are:
• CBN (Borazon®), cubic boron nitride
The assignment of “superabrasives” derives from the fact that their hardness is significantly higher than all other conventional abrasives, such as corundum, carbide silicon, etc. The Diamond has hardness 10 in the Mohs scale, the CBN is slightly lower.
In the scale of “Knoop hardness”, the Diamond has over 8500 Kg/mm2, the CBN more than 4500 Kg/mm2. There are different types of Diamond: when it’s naturally occurring, it’s called “natural Diamond”. Other different varieties are produced industrially, and called “synthetic Diamond”.The CBN does not exist in nature: it’s only produced industrially.
The production consist to apply very high pressures at high temperatures to pure carbon, which then turns into Diamond,or to nitrogen and Boro, which are transformed in cubic boronnitride. The different sintering conditions applied canproduce superabrasives with different characteristics about cutting and friability.
KNOOP HARDNESS TABLE
Electroplated tools (galvanic bond)
Electroplated tools consist in a single layer of superabrasives grains (Diamond or CBN) fixed on the blank by a nickel galvanic process. The thickness of the layer of nickel depending by the thickness of the grain so that it projects for about half its diameter.
The individual grains are firmly held, but partially exposed respect to the tool surface, so it’s very aggressive and has ample space for the discharge of the “chip”.
The profile of the electroplated tools is totally covered by a single layer of superabrasives grains.
For these is not possible to perform operations dressing and/or correction, but is possible create tools with complex profile.
The worn tools can be regenerated with a process that allows removal of superabrasives without alteration of the support steel.
This is especially convenient in the case of complex or big dimensions tools.
AVT brazed tools
In the AVT tools the single layer of superabrasives is fixed to the blank by a metal brazing, performed in conditions of low pressure. The result is that the grain is much more exposed than in the electroplated tools.
greater aggressiveness, especially with coarse grit sizes
greater duration (3 to 5 times than electroplated)
lower costs of maintenance (less fatigue during the process extended tool life and reduces the maintenance action)
allowed for use on granite of medium hardness