A Study on the Grinding Process of HMX using Fluid Energy Mill

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1 A Study on the Grinding Process of HMX using Fluid Energy Mill Joo Seung Chae, Hyoun-Soo Kim, Jin Rae Cho Agency for Defense Develop ment (ADD) Yuseung P.O.Box 35-2, Daejeon,, Korea

2 Introduction Characteristics of HMX 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (Octogen), C H 8 N 8 O 8 High performance explosive 6 differential class Dv = 9.1 km/s Sensitive of Impact and Friction Coated it with polymer binder and plasticizer H 2 C O 2 N N H 2 C NO 2 N N NO 2 CH 2 N NO 2 CH 2 Ref) ICT database & MIL-DTL-5C

3 Introduction Aim of this study Study on the grinding process of HMX using fluid energy mill Find the optimum operating parameters for the purpose of average particle sizes below 5in t he process of HMX grinding

4 Background Process of Grinding through jet Type I - relatively hard material (ex, Silica sand) - the mechanism of separation through attrition - the separation of particles occur primarily within the surface or in the edge - the characteristics of the particles are maintained throughout the process of separation - progressively as the quantitative amount of the larger particles diminish, there occurs a dramatic production of the smaller sized particles simultaneously - during the grinding process, the formation of particle distribution retains and maintains a similar format Ref) Y.Mori,G.Jimbo, J. Che m. Eng. Of Japan,22, 363 (1958)

5 Background Process of Grinding through jet Type II - relatively soft material (ex, Sulfur) - the mechanism of separation through fracture - when the particles are exposed to a greater amount of internal stress than it s capacity and are thus fractured and broken down into smaller particles subsequently - all particles become smaller compared to its original size and the status of particle distribution is also gravitated towards the smaller side Ref) Y.Mori,G.Jimbo, J. Che m. Eng. Of Japan,22, 363 (1958)

6 Schematic diagram of Fluid Energy Mill (J-O-M) Com pressor C.A Dryer Surge Tank C.A Heater Hum idity Check Ejector Feeder Manometer J-O -M Packed Scrubber W etscrubber Bag Filter C yclone

7 Calibration curves of Volumetric feeder 1 8 HMX class-a HMX class-c HMX class-f Feeding rate (g/min.) RPM

8 The effect of the grinding material s s feed rate 5 Average particle size (mm) Feed rate (g/min.)

9 The effect of feed air pressure 5 Average particle size (mm) Feed air pressure (kpa) feed rate = 5g/min., mill air pressure = kpa

10 The effect of mill air pressure at constant feed rate 2 16 feed air pressure = 3.7 kpa feed air pressure = 82.6 kpa feed air pressure = 715. kpa Average particle size (mm) Mill air pressure (kpa)

11 The grinding result according to variations in mill pressure Differential probability Cummulative probability (%) Type II Differential probability Cumulative probabitity (%) Volume equivalant diameter (μm) Before Grinding Type I Volumetrice equvalent diamter (μm) Type II Milpressure : 7kPa Differential probability Cumulative probabitity (%) Differential probability Cumulative probabitity (%) Volumetrice equvalent diamter (μm) Milpressure : 2kPa Volumetrice equvalent diamter (μm) Milpressure : 3kPa

12 The grinding results of HMXs with respect to average particle size variation 1 1 Differential probability Class-C : 2.91μm Class-F : 2.83μm Class-A : 2.89μm Cumulative probability (%) Volumetric equivalant diameter (μm)

13 Pre & Post Grinding process SEM images of HMX Before Grinding After Grinding

14 Conclusions - The particle size and distribution were greatly influenced by mill air-pressure, but feed air-pressure and feed rate had little effect. - When the air-pressure exceeds 3kPa, we can stably obtain an average fine-powder particle size below 3 regardless of feed rate. - Under the normal circumstances and conditions within the operation of the JOM, with increase in air pressure, we were able discern the co-existence of the 2 different types of grinding mechanisms.

15 Conclusions - Through the SEM image analysis, the fine-powder particles which underwent grinding were found to have a smooth surface and clean surface. - We judge this to contribute towards the added insensitivity of the plastic bonded explosive s characteristics.

For a given material, a required separation point may be duplicated repeatedly simply by setting the dial control at the same position.

For a given material, a required separation point may be duplicated repeatedly simply by setting the dial control at the same position. GENERAL The C-1 is designed to meet the increased technological and scientific requirements for constant optimum particle uniformity in the subsieve range. The C-1 is the first classifier that can produce