CBN grinding fluid
Water soluble grinding fluid for CBN (Cubic boron nitride)
|SHC-POE base oils||9.2||CBN grinding wheels with vitrified bonds (VIT-CBN)|
It is known that the G ratio of CBN grinding is lower when water based coolants are applied, leading to higher tool costs. The chemical decomposition of CBN is frequently associated with its interaction with high temperature steam in grinding. This interaction can be similar to the phenomena described in where CBN grains can be destroyed in the wheel firing process where several constituents of the bond are chemically reactive with the grains. These oxidation reactions result in the formation of Boron oxide (B2O3) on the surface of CBN grains, a protective layer that prevents further oxidation.
A water based grinding fluid would not be successful in cases where the described reactions are relevant to the process performance. So, the study of these phenomena should be the first step before trying to develop a water based fluid for grinding.
The resulting CBN grains from the chemical reactor test were evaluated qualitatively using X-Ray diffraction spectroscopy and the water samples from grinding tests were analyzed quantitatively by Inductively Coupled Plasma-Optical Emission Spectroscopy. While the objective of the first test was to verify the existence of the described reactions, in the second test the concentration of Boron in water was determined. CBN is chemically very inert but it can be hydrolyzed by steam resulting in B2O3 and NH3. However the temperature for this reaction is not well known. Since grinding temperatures can reach 600°C in normal conditions the test was performed using 600°C as maximum value.
The chemical reactions between CBN grains and water are not a significant factor in the wheel wear mechanism in the tested conditions.
- The proposed vegetable oil based soluble grinding fluid provided good results in the grinding tests similar to the ones obtained with the neat oil. Wheel wear, grinding forces and surface roughness were reduced when the new cutting fluid diluted at 45% was used.
- The fluid proposed in this work has fulfilled all environmental requirements and provided a good grinding performance. This opens new perspectives for the development of fluids for CBN grinding.