Herman Hockmeyer, President of Hockmeyer Equipment08.30.23
Much has been said about the significance of Kilowatt Hour (KWH) measurements as applied to media milling technology. The thinking has been energy in equals results. This is a simplification of a more complex matrix and is dependent upon other variables such as raw material characteristics, media size and density, as well as the design and conditions under which the mill operates. The purpose of this paper is to “get into the weeds” about how relative measuring performance in KWHs can be.
To begin, one must ask if KWH consumption can be influenced by the efficiency of the device being used to perform the dispersion. What would affect performance to cause this? Enhancing the conditions in which the energy transfer is occurring is one example.
Using the identical media size, type and amount with identical KW input, the time to standard will diminish by anywhere from 20% to 80% providing allowance of another dimension of thought when formulating: looking at the ratio of surface area of the solids to the vehicle rather than just the weight or volume.
For example, we know that as we grind down an aggregate, the surface area of the now dispersed particles increases exponentially. It is not truly exponentially, due to the imperfection of leaving a remainder of something less than a D100 target. However, the closer to D100 target, the more perfect the uniformity at the target.
By using the ratio of surface area solids to vehicle as a measure, solutions to dispersion problems become more apparent. As the particles are brought to their true size or ground down beyond that size, additional vehicles must be added to compensate the demand of the additional surface area. If not, the viscosity will increase, flow through the mill will decrease and the dispersion will slow and eventually stop improving. It will likely become unstable if pushed beyond those boundaries, resulting in re-agglomeration of particles. Depending upon the desired characteristics of the finished dispersion, particle size will have a great influence as will any vehicles suspending and separating the particles.
Conventional dispersion is done under pressure in media mills, resulting in a decrease in efficiency in unnecessary KWH consumption. This is due to the back pressure and cushioning effect of the entrapped air within the premixed feedstock. Air entrapment is further exacerbated by pressuring the large air bubbles into smaller air bubbles creating a more uniform impurity in the dispersion. The entrapped microbubbles distort both the weight and volume of the finished product, leading to accuracy distortions during the filling process. The entrapped air will also affect the quality and durability of the finished product. This is particularly true of water-based dispersions.
Efficiency of the dispersion process can be substantially enhanced through willingness to embrace this different perspective. Change is challenging but it is the only way to progress into the future. Here are changes that will improve the process:
1) Premix should be dispersed under vacuum either with the appropriate vacuum rotor-stator or vacuum media mill. This depends upon the size and characteristic of the aggregate or agglomerate that will allow the device to accomplish its mission in the shortest time.
Both machines generate their own internal vacuum during the process, extracting air from the feedstock. This is paramount and without it, distortional time variations during the final milling process will occur.
2) Prior to fine milling, the appropriately sized filter must be used to extract any trash or aberrant particles from the initial dispersion. Otherwise these contaminants will continue to exist and distort the purity and uniformity of the fine dispersion to follow. The premix should be as close to a D100 target as possible.
Media size and type should be complementary to the particle size in the next step. Fine grinding should be done in a vacuum media mill, allowing for vehicle additions to satisfy the increasing surface area demand of the solids as their particles are continuously separated and exposed to the vehicle. Unless this is permitted, the proof of efficiency, quality and performance of the finished product cannot be reached.
3) Details such as media size, density, quality, peripheral speeds of the mill, throughput, etc. are factors that require knowledgeable judgment. Kilowatt hours compressing the air in the feedstock are wasted in a pressure mill. Localized grinding under pressure creates hot spots resulting in temperature zones and increased media and mill wear.
4) Vacuum milling amplifies throughput while simultaneously reducing KWHs, hot spots, media wear, mill wear and air. Temperature control is greater than that of pressure mills because the feedstock is drawn through a much larger screen by downstream suction.
Dwell time in a vacuum mill is a matter of a second while recirculation rate is thousands of gallons per hour. The resulting rapid reduction of oversized particles in the premix is consequential since they will be the “fly in the ointment” and cause costly, extended milling time in the fine grinding part of the process.
The takeaway from this discussion is that KWHs are a measure of energy over a period of time. How they are consumed is a measure of efficiency. Efficiency is a function of conditions and formulation. Performance is a function of perception confirmed by proof.
All aspects of proof of this improvement are available at the Hockmeyer testing laboratory with the guidance of our R&D group that developed the technology. Open minds
open doors.
Based in Elizabeth City, NC, Hockmeyer Equipment Corp. has been a provider of wet grinding and dispersion process solutions for more than 80 years.
To begin, one must ask if KWH consumption can be influenced by the efficiency of the device being used to perform the dispersion. What would affect performance to cause this? Enhancing the conditions in which the energy transfer is occurring is one example.
Using the identical media size, type and amount with identical KW input, the time to standard will diminish by anywhere from 20% to 80% providing allowance of another dimension of thought when formulating: looking at the ratio of surface area of the solids to the vehicle rather than just the weight or volume.
For example, we know that as we grind down an aggregate, the surface area of the now dispersed particles increases exponentially. It is not truly exponentially, due to the imperfection of leaving a remainder of something less than a D100 target. However, the closer to D100 target, the more perfect the uniformity at the target.
By using the ratio of surface area solids to vehicle as a measure, solutions to dispersion problems become more apparent. As the particles are brought to their true size or ground down beyond that size, additional vehicles must be added to compensate the demand of the additional surface area. If not, the viscosity will increase, flow through the mill will decrease and the dispersion will slow and eventually stop improving. It will likely become unstable if pushed beyond those boundaries, resulting in re-agglomeration of particles. Depending upon the desired characteristics of the finished dispersion, particle size will have a great influence as will any vehicles suspending and separating the particles.
Conventional dispersion is done under pressure in media mills, resulting in a decrease in efficiency in unnecessary KWH consumption. This is due to the back pressure and cushioning effect of the entrapped air within the premixed feedstock. Air entrapment is further exacerbated by pressuring the large air bubbles into smaller air bubbles creating a more uniform impurity in the dispersion. The entrapped microbubbles distort both the weight and volume of the finished product, leading to accuracy distortions during the filling process. The entrapped air will also affect the quality and durability of the finished product. This is particularly true of water-based dispersions.
Efficiency of the dispersion process can be substantially enhanced through willingness to embrace this different perspective. Change is challenging but it is the only way to progress into the future. Here are changes that will improve the process:
1) Premix should be dispersed under vacuum either with the appropriate vacuum rotor-stator or vacuum media mill. This depends upon the size and characteristic of the aggregate or agglomerate that will allow the device to accomplish its mission in the shortest time.
Both machines generate their own internal vacuum during the process, extracting air from the feedstock. This is paramount and without it, distortional time variations during the final milling process will occur.
2) Prior to fine milling, the appropriately sized filter must be used to extract any trash or aberrant particles from the initial dispersion. Otherwise these contaminants will continue to exist and distort the purity and uniformity of the fine dispersion to follow. The premix should be as close to a D100 target as possible.
Media size and type should be complementary to the particle size in the next step. Fine grinding should be done in a vacuum media mill, allowing for vehicle additions to satisfy the increasing surface area demand of the solids as their particles are continuously separated and exposed to the vehicle. Unless this is permitted, the proof of efficiency, quality and performance of the finished product cannot be reached.
3) Details such as media size, density, quality, peripheral speeds of the mill, throughput, etc. are factors that require knowledgeable judgment. Kilowatt hours compressing the air in the feedstock are wasted in a pressure mill. Localized grinding under pressure creates hot spots resulting in temperature zones and increased media and mill wear.
4) Vacuum milling amplifies throughput while simultaneously reducing KWHs, hot spots, media wear, mill wear and air. Temperature control is greater than that of pressure mills because the feedstock is drawn through a much larger screen by downstream suction.
Dwell time in a vacuum mill is a matter of a second while recirculation rate is thousands of gallons per hour. The resulting rapid reduction of oversized particles in the premix is consequential since they will be the “fly in the ointment” and cause costly, extended milling time in the fine grinding part of the process.
The takeaway from this discussion is that KWHs are a measure of energy over a period of time. How they are consumed is a measure of efficiency. Efficiency is a function of conditions and formulation. Performance is a function of perception confirmed by proof.
All aspects of proof of this improvement are available at the Hockmeyer testing laboratory with the guidance of our R&D group that developed the technology. Open minds
open doors.
Based in Elizabeth City, NC, Hockmeyer Equipment Corp. has been a provider of wet grinding and dispersion process solutions for more than 80 years.
