Issue link: https://www.e-digitaleditions.com/i/1252179
June 2020 / 23 Jet mills can mill materials to single-digit micron particle sizes in a single pass, increasing yield and operational ef ciencies, as shown in the graphs in Figure 1. Figure 1a. shows ball-milled material's PSD, while 1b. shows a jet-milled material. In this microniza- tion method, the mill injects high-velocity, compressed air into a chamber where a rate-controlled feeder adds the starting raw materials. As the particles enter the airstream, they accelerate and collide with each other and the milling chamber's walls at high velocities. Particle size reduction occurs through a combination of impact and attrition. Impacts arise from the collisions between the rapidly moving particles and between the particles and the wall of the milling chamber. Attrition occurs at particle surfaces as particles move rapidly against each other, resulting in shear force that can break up the particles. In addition to creating ne particles with a narrow PSD, jet mills have other qualitative advantages over ball and mechanical mills. A jet mill cools the tempera- ture of the air leaving the jets to about -200°F due to the Joule-Thomson effect, and the product leaves the mill no warmer than the air used for the grinding. The heat generated by the friction from particle-to-particle and particle-to-wall collisions is offset by the cooling effect of the expanding air. This allows for dry milling of a wider range of materials, especially more delicate, heat-sensitive materials. A jet mill allows the pharmaceutical manufacturer to grind a friable or crystalline material to an average particle size of 1 to 10 microns and to classify it in a very narrow particle size range at the same time. The mill has no moving parts to wear out or generate heat and no screens to plug or be punctured. Jet mills also develop no attritional heat because of the cooling effect of the jets. FIGURE 1 Particle size distribution of ball-milled and jet-milled material 1.000 10.00 100.0 Diameter (m) 1.000 10.00 Diameter (m) a. b. P031984-016-210 Spunbond polyester pleated bags with Ultra-Web ® fine fiber technology provide significantly longer filter life, energy savings due to lower pressure drop, reduced maintenance downtime and lower emissions. P031984-016-210 Spunbond polyester pleated bags with Ultra-Web ® fine fiber technology provide significantly longer filter life, energy savings due to lower pressure drop, reduced maintenance downtime and lower emissions. © 2020 Donaldson Company, Inc. Donaldson.com 800.365.1331 This filter is just one of over 100,000 replacement filters and parts Donaldson has in-stock and ready to ship today. Not tomorrow. Today. Find this filter and thousands more at shop.donaldson.com