Controlling clay slips with a process vibrational viscometer

The apparent viscosity of concentrated clay dispersions is a key control parameter in the ceramic industry, particularly in the manufacture of sanitaryware. Slips, the final industrial dispersions, are complex in their rheological behavior, featuring non-Newtonian flow and thixotropy. In this work, a resonance vibrating-rod viscometer (VRV) was utilized to evaluate the viscosity evolution over time, showing advantages over a classical rotational viscometer. Notably, while both viscometers were sensitive to small quantities of a deflocculant, the VRV effectively described the typical increase in the viscosity of clay dispersions at rest (thixotropy), the experimental data being properly fitted by a phenomenological model. As a relevant technical aspect, the superior suitability of the VRV for in-line process control was highlighted in the continuous monitoring of stirred clay dispersions and slip casting in plaster moulds. Additionally, a fitting model was developed to elucidate viscosity evolution during the casting process. In summary, this study underscores the versatility of the VRV as a control instrument in the sanitaryware industry. • The vibrating-rod viscometer (VRV) monitors sanitaryware clay dispersions. • Thixotropy characterization differs from classical rotational viscometers. • It provides a rapid response in stirred suspensions and slip casting. • Phenomenological models are applied for understanding viscosity data. • The VRV can function as a process control device in the ceramic industry.