The greatest dream of all production and R&D staff at companies using grinding and dispersion processes is to have a reference book listing the correct parameters and values for every paint, ink and coating production run — in other words, a constitution of grinding and dispersion. As we will explain in detail with all the reasons at the end of this article, unfortunately no such book has ever existed, will ever exist, or could ever exist. This is because chemistry is unique in each case: from the raw materials used to ambient conditions, from machine types to operating mechanisms, everyone has their own specific circumstances. So what should we do to make our current production processes more efficient? How should we interpret the messages our machines give us, and what actions should we take to make them more efficient? The main subject of our article, to be published in two parts in this issue of Boyatürk magazine and the next, is to show you, the users of grinding processes, ways to work at a fundamental level, and to indicate, even if only at a basic level, where the solution to each problem should be sought. Of course, for further assistance, you can get help around the clock from Bühler's specialized process and engineering teams, and organize test procedures and field studies together.
The ultimate dream of all companies using grinding and dispersion processes is to have a comprehensive handbook—a constitution of grinding and dispersion—documenting the correct parameters and values for all paint, ink and coating production.
Regrettably, as we will substantiate throughout this article, no such handbook has ever existed, will exist, or indeed can exist. This stems from chemistry's uniqueness: every operation has its own special conditions, from the raw materials used to ambient conditions, machine types, and working mechanisms.
So what should we do to make our current production more efficient? How should we interpret the signals our machine sends us, and which actions should we take to enhance its efficiency?
The fundamental subject of this two-part article, appearing in this issue and the next issue of Boyatürk magazine, is to show grinding process users the methods with which they can work at a fundamental level, and to explain—at least at a basic level—where solutions to particular problems should be sought.
Of course, for more extensive support, you can access round-the-clock assistance from
Bühler's specialized process and engineering teams, and together you can organize test processes and field work.
Quality Characteristics of Wet Grinding Systems
To improve our production process, it is appropriate to first define what "improvement" means—more precisely, to define the target quality characteristics. These are listed below in general terms:
1. Solid particle distribution in the dispersion: Particle size distribution in terms of position and shape, and values derived from particle size distribution.
→ d100 µm max. diameter…
→ d90 µm 90% of Qx is smaller…
→ d50 µm 50% of Qx is smaller…
2. Color characteristics
Related to particle size distribution. Color intensity resulting from light absorption, gloss resulting from light reflection, and transparency resulting from light transmission are fundamental characteristics sought in products regarding color properties.
3. Rheological properties
These include shear rate (particularly for sub-micron grinding), temperature, and degree of thixotropy.
4. Stability-related properties
These include resistance of solid particles to settling, redispersibility, stability against reagglomeration, and product shelf life.
5. Application-related properties
These include reactivity, conductivity, and insulating properties.
Now let us examine what needs to be done at the machine level to achieve these appropriate quality values, particularly particle size distribution. The process steps of wet grinding systems and pre-dispersion.
The entire operational flow of paint, coating, ink and similar production encompasses a process that largely begins with raw material stock and ends with packaging.
The heart of this flow is undoubtedly the grinding process. Although grinding stands out as the quality-determining step, there is another step of equal importance that directly affects this quality and grinding efficiency: the Pre-mixing and Pre-dispersion step.
Every pre-mixing operation conducted without proper pre-dispersion—more specifically, using the wrong dispersion machine, feeding powder at incorrect intervals causing agglomeration, employing incorrect mixing duration, or finishing without proper wetting—will return to you as inefficiency in the grinding stage.
For a product containing very large and irregular particles and poorly wetted pigments, it will not be possible to use small beads in the wet grinding mill and separation filters suited to these small beads.
Thus, achieving the desired particle size distribution and precise particle size distribution will either be impossible or will require very long periods.
After emphasizing this important point, we can examine the subject from the perspective of wet grinding mills.
