Coating higher speed

Other coatings, such as TiAlN (96), TiCN, Zr02, and ZrN (97), and CrN (98) were developed for special appHcations. The last was developed for higher speed machining of titanium alloys. Sometimes a coating is developed not for its wear-resistance but for its heat insulation. The case in point is alumina coating of cBN to reduce the heat conductivity at the surface so that the cBN performance can be enhanced (99). 

The dispersions used in this process are formulated in such a way that they wet the carrier sufficiently and tolerate higher shear at the wire-wound bars due to a relatively high coating belt speed. This is accomplished by a combination of nonionic surfactants (e.g., octyl phenoxy polyethoxy ethanol) and fluorosurfactants. This subject is discussed in detail in Reference 14. 

As with the electrostatic bells, the originally installed disks were rotated at 1800-3600 rpm. Because of the introduction of new types of coating materials, presently installed disks are rotated at higher speeds (20,000-30,000 rpm). They are also smaller in diameter. Such equipment can handle both high-solid and waterborne materials. 

The above steps show that rheologioal properties of a Uquid are complex. They must at least involve a higher viscosity at a low shear (lowers penetration) and a low viscosity at a high shear (reduces thickness of coating, allows for higher speed of withdrawal, and improves surface properties of coating). 

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