By Hockmeyer Equipment Corporation
Barry has been named on multiple patents for the Immersion Mill, NexGen™ Mill, NexGen™ RotorStator, Porous metal, and polymer screens for nano milling, and he also developed the HPAS 2000 particle analysis system.
We have developed a new type of rotor-stator that works virtually the same way the NexGen Mill works using vacuum. With the NexGen rotor-stator (HNGRS) (patent pending), a few changes have made a big difference in particle size reduction. These include vacuum, cavitation, tight tolerances between the rotor and stator, vacuum chamber recirculation, dual pumping rotor, rapid supply tank recirculation, high open area stator for high throughput, inline pigment feed, and air removal from feedstock during batch processing. Vacuum: The HNGRS uses vacuum the same way the NexGen mill does. The rotor and stator are enclosed in a small vacuum chamber. The feedstock is pulled from the supply tank under vacuum and enters through the top of the rotor-stator and is pulled down onto the top of the rotor. The rotor spinning at high tip speeds accelerates the feedstock into the upper part of the stator and through the stator into the vacuum tank. The feedstock is then pulled onto the bottom of the rotor and pushed into the stator and through the stator back into the vacuum tank. Once the vacuum tank is full, the feedstock is pulled out of the vacuum tank and passes through the diaphragm pump back to the feedstock supply tank for rapid recirculation back into the rotor-stator. Vacuum on the HNGRS is different than vacuum on most rotor stators. As previously mentioned, almost all rotor stators use vacuum to pull the product from the feedstock tank into the rotor-stator. As soon as the feedstock hits the rotor, it goes from vacuum to pressure for the return trip back to the feedstock tank. With the HNGRS, vacuum pulls the feedstock from the supply tank. Once the feedstock hits the rotor, there is a drastic increase in velocity of the liquid, but it is still under vacuum because the entire rotor and stator are enclosed in a vacuum chamber slightly larger than the rotor-stator itself. The feedstock remains under vacuum as it passes through the stator and slams directly into the inside wall of the vacuum chamber. The feedstock never changes from vacuum to pressure until it passes through the diaphragm pump for the return trip to the supply tank. Air is removed from the feedstock and agglomerates are more easily broken down and wetted out because of the voids created when the air is removed. Cavitation: Cavitation is generated inside the vacuum chamber during dispersion. The rotor and stator are enclosed in a vacuum chamber. As the feedstock enters the top of the rotor, cavitation develops on the rotor. Cavitation can be controlled by the amount of vacuum pulled on the system, using a valve on the feedstock supply tank. Cavitation is a phenomenon where rapid pressure change creates voids in the liquid where pressure is very low. These voids are short-lived, and when they collapse, they generate a shock wave through the liquid that also helps in particle reduction, much like a sonication disperser. Tight Tolerances: Tight tolerances between the rotor and stator create the perfect environment for particle reduction. There are many different types of shear going on inside the HNGRS: impact, rolling shear, cutting shear, and internal shear from air expanding inside the agglomerates as a result of the vacuum. Tight tolerances between the rotor and stator increase the rolling shear, impact shear, and cutting shear. Dual Pumping Rotor: The HNGRS is designed with a dual pumping rotor that has veins on both the top side and the bottom side separated by a center plate so that the top veins pump out of the top side of the stator and the bottom veins pump out of the bottom side. This dual-sided rotor provides multiple feedstock passes through the rotor and stator before it leaves the vacuum chamber. Rapid Vacuum Chamber Recirculation: The rotor on the HNGRS is built to pump from both the top and the bottom. The feedstock is pumped into the rotor-stator from the top. As the vacuum chamber fills up, the bottom side of the rotor starts to pump. The feedstock recirculates through the vacuum chamber and in and out of the bottom side of the rotor many times before it is pulled – still under vacuum – through the outlet and to the pressure side of the pump and back to the supply tank. Rapid Feedstock Supply Tank Recirculation: The HNGRS is a very rapid recirculation inline rotor-stator. An eight-inch rotor can pump upwards of 300 gallons per minute in water with low vacuum. Recirculation speeds and vacuum work hand-in-hand. Higher vacuum generates lower throughput, and lower vacuum generates higher throughput. The throughput rate is controlled by the supply tank valve and the diaphragm pump rate. High Throughput Stator: The stator on the rotor-stator is much like the screens on a media mill. For a media mill screen, you want as much open screen surface area as you can get for faster product recirculation. This is also true for the stator on the HNGRS. The H stator design uses interlocking “H” shaped slots for maximum stator open area. The interlocking H slot design gives the stator both vertical and horizontal cutting edges and also plenty of closed surface area for particle collisions when they are coming off the rotor at very high velocity. The clearance between the rotor and stator are very tight, creating very high shear rates for particle reduction. Vacuum Pigment Feed: Vacuum pigment feed is an option with the HNGRS inline system. The pigment will enter the liquid stream ahead of the rotor-stator, mix with the liquids, and then hit the rotor and stator for particle reduction. Pigment feed rates depend on pigment type and feed characteristics of the dry powder. Air Removal from the Feedstock: The HNGRS works under vacuum as air accumulates in the upper part of the vacuum chamber until it comes in contact with the outlet. At this point, the air travels back to the feedstock supply tank in large bubbles and floats rapidly to the top of the supply tank and pops. It is normal to see batches shrink in size during the pre-dispersion process because of air removal.
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The Immersion Mill MicroMill was designed to run small batches in the one-liter to one-gallon range, and we estimated that the flow rate through the Immersion mill would be in the one-liter-per-minute vicinity. Because of the mill design, we were not able to get an exact number on the mill discharge, as some of the product went through the side screen and some went through the bottom screen. A one-liter batch of water in the Immersion Mill was estimated to turn over once a minute, which is very fast for a media mill. The Immersion mill was one of the first basket-type media mills on the market. It did not need pumps and hoses; it produced its own vacuum using a propeller in the lower draft-tube to pull the feedstock through the media field.
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which uses a center-mounted low-speed Helical or Anchor Sweep blade that sweeps the mixing vessel wall, and two additional high-speed shafts. When using this disperser for your industrial milling project, a Rotor Stator can also be used as the third shaft to provide mechanical and high hydraulic shear which will be useful in the disintegration of solids into liquids or emulsification.
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This innovative RotorStator design produces an airless ultra-fine dispersion using an aggressive multi-prong approach to particle size reduction. Bridging the gap between milling and dispersion, the NEXGEN™ Vacuum Rotor Stator was designed for maximum dispersion. This innovative design with integrated vacuum delivers fast & pure dispersion — NO AIR, NO FOAM... 100% PRODUCT. DISPERSION TECHNOLOGY. FAST. PATENTED The process takes place in a temperature-controlled environment to preserve formulae characteristics and function. A thorough cooling system covering the chamber and return lines quickly mitigates the heat generated by the aggressive shear forces. The result is a deaerated dispersion, a narrow particle size distribution band, volumetric accuracy, and an optimal dispersion pre-mix for milling into the nanoparticle size range. It easily hooks up to your existing process tanks. Flexible, portable design. Easy cleanup and changeovers. Vacuum The air inside the agglomerates expands and forces the particles apart, exposing maximum particle surface area. Liquid and resin encapsulate each particle for fast and thorough wetting. Controlled Cavitation The rapid pressure change inside the vacuum chamber creates micro vapor cavities in the liquid. When these short-lived vapor cavities (bubbles) collapse, they generate a shockwave through the feedstock that further aids in particle size reduction. Extreme Shear Zone The Interlocking ‘H’ Stator Design creates a unique shear pattern of vertical and horizontal slots for ultra-dynamic impact while offering maximum open area for the greatest flow. The tight tolerances between the rotor and the stator create a short distance between particle acceleration and point of contact for the greatest shattering effect on agglomerates. Dual Pumping Rotor Design The NEXGEN™ Vacuum Rotor Stator is pulled from both the rotor’s top and bottom, doubling the number of collisions per particle. High-speed Recirculation ~300 gpm. The feedstock is recirculated through the shear zone at high velocity to maximize the number of passes for every drop. Powder Incorporation Direct powder incorporation into the liquid stream using an eductor that controls the flow and creates a venturi effect. This generates suction at the bottom of the funnel pulling powders into the flow. The high-speed jet coming out of the eductor mixes the powder and liquid before it reaches the rotor-stator. 2021 Patented design
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