Rheological Measurement
Calculation of how quickly mechanical energy is converted into heat within a fluid under deformation determines the stability of coating formulations. During the application of coatings, shear dissipation rate influences the temperature rise in high speed coating heads where paper or board is treated. If the rate is too high, the viscosity of the coating can change unexpectedly, leading to streaks or uneven coverage.
This property is a function of both the fluid properties and the geometry of the application system.
Thermal Impact
Excessive heat generation from high shear can cause the premature evaporation of water or the destabilization of synthetic binders. Shear dissipation rate must be managed to prevent the formation of aggregates that clog the filters or damage the surface of the moving web. In blade coating operations, the narrow gap between the blade and the substrate creates an environment of intense friction.
Engineers use the dissipation rate to design cooling systems or to select additives that lower the internal resistance of the liquid.
Coating Quality
Consistency in the application depends on a stable shear environment throughout the run. Monitoring the dissipation rate allows operators to adjust the speed of the line or the pressure of the blade to maintain a uniform film thickness.
