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

JooJoo SeungSeung ChaeChae, , HyounHyoun--SooSoo Kim,Kim, Jin Rae Jin Rae ChoCho

A g e n c y f o r D e f e n s e A g e n c y f o r D e f e n s e D e v e l o p m e n t ( A D D )D e v e l o p m e n t ( A D D )

Y u s e u n gY u s e u n g

P . O . B o xP . O . B o x

3 53 5 -- 4 2 , 4 2 , D a e j e o nD a e j e o n , K o r e a, K o r e a

High Explosives Group, ADD

IntroductionIntroduction

Characteristics of HMX

�1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane

(Octogen), C4 H8 N8 O8

�High performance explosive�6 differential class�Dv = 9.1 km/s�Sensitive of Impact and Friction→Coated it with polymer binder and plasticizer

H2C N

N

H2C N

O2N

CH2

N NO2

CH2

NO2

NO2

High Explosives Group, ADDRef) ICT database & MIL-DTL-45444C

IntroductionIntroduction

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 5�in t he

process of HMX grinding

High Explosives Group, ADD

BackgroundBackgroundProcess 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

High Explosives Group, ADDRef) Y.Mori, G.Jim

b

o, J. C h e m . E n g . O f J a p a n , 22, 363 (1958)

BackgroundBackground

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

High Explosives Group, ADDRef) Y.Mori, G.Jim

b

o, J. C h e m . E n g . O f J a p a n , 22, 363 (1958)

Schematic diagram of Fluid Energy Mill (JSchematic diagram of Fluid Energy Mill (J--OO--M)M)

Com pressorC.A Dryer

Hum idityCheck

Surge Tank

C.A Heater

Ejector

Packed Scrubber W et Scrubber Bag Filter Cyclone

J-O-M

M anom eter

Feeder

High Explosives Group, ADD

Calibration curves of Volumetric feederCalibration curves of Volumetric feeder

RPM

0 200 400 600 800 1000

Feed

ing

rate

(g/m

in.)

0

200

400

600

800

1000

HMX class-AHMX class-CHMX class-F

High Explosives Group, ADD

The effect of the grinding materialThe effect of the grinding material’’s feed rates feed rate

Feed rate (g/min.)

Ave

rage

par

ticle

siz

e (m

m)

0

1

2

3

4

5

46 500 1055600

High Explosives Group, ADD

The effect of feed air pressureThe effect of feed air pressure

Feed air pressure (kPa)

400 500 600 700 800

Aver

age

parti

cle

size

(mm

)

0

1

2

3

4

5

feed rate = 500g/min., mill air pressure = 672.2 kPa

High Explosives Group, ADD

The effect of mill air pressure at constant feed rateThe effect of mill air pressure at constant feed rate

Mill air pressure (kPa)

0 200 400 600 800

Ave

rage

par

ticle

siz

e (m

m)

0

4

8

12

16

20

feed air pressure = 344.7 kPafeed air pressure = 482.6 kPafeed air pressure = 715.0 kPa

High Explosives Group, ADD

The grinding result according to variations in mill pressureThe grinding result according to variations in mill pressure

Volume equivalant diameter (μm)

0.1 1 10 100 1000 10000

Diff

eren

tial p

roba

bilit

y

0

2

4

6

8

10

Cum

mul

ativ

e pr

obab

ility

(%)

0

20

40

60

80

100

Volumetrice equvalent diamter (μm)

0.1 1 10 100 1000

Cum

ulat

ive

prob

abiti

ty (%

)

0

20

40

60

80

100

Diff

eren

tial p

roba

bilit

y

0

2

4

6

8

10

Volumetrice equvalent diamter (μm)

0.1 1 10 100 1000

Diff

eren

tial p

roba

bilit

y

0

2

4

6

8

10

Cum

ulat

ive

prob

abiti

ty (%

)

0

20

40

60

80

100

Before Grinding

Volumetrice equvalent diamter (μm)

0.1 1 10 100 1000D

iffer

entia

l pro

babi

lity

0

2

4

6

8

10

Cum

ulat

ive

prob

abiti

ty (%

)

0

20

40

60

80

100

Mill pressure : 70kPa

Mill pressure : 200kPaMill pressure : 340kPa

Type II

Type I

Type II

High Explosives Group, ADD

Volumetric equivalant diameter (μm)

0.1 1 10 100

Diff

eren

tial p

roba

bilit

y

0

2

4

6

8

10

Cum

ulat

ive

prob

abilit

y (%

)

0

20

40

60

80

100

Class-C : 2.91μmClass-F : 2.83μmClass-A : 2.89μm

High Explosives Group, ADD

The grinding results of The grinding results of HMXsHMXs with respect to with respect to average particle size variationaverage particle size variation

Pre & Post Grinding process SEM images of HMXPre & Post Grinding process SEM images of HMX

Before Grinding After Grinding

High Explosives Group, ADD

ConclusionsConclusions

- 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 340kPa, 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.

High Explosives Group, ADD

ConclusionsConclusions

- 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.

High Explosives Group, ADD