mg grinding day at p&g 2010pdf

Milling WorkshopP&G Technical Centre

Longbenton24th February 2010

Mojtaba Ghadiri

Iain Crosley

John Sherwood

Introduction

Industrial Relevance & Key issues

• Selection of appropriate mills is conducted by trial and error – particularly true for organic solids for which our fundamental understanding is limited.

• Costly and time consuming

Milling Issues

Process Engineering:• Scaling of power consumption, energy utilisation and capacity• Milling aids• Method of application of stresses, i.e. point loading,

distributed loading or loading accompanied by frictional traction, etc.

Material-Related Issues:• Feed and product characteristics

• Smallest possible particle size which could be comminuted.• Size distribution of comminuted materials for feed materials larger

than this limit.• Level of stresses required for comminution to a certain size

range.• Mechanical activation and mechanochemical processing

Energy Laws

Walker et al. (1937):

Rittinger (1867): n = 2

Kick (1885): n = 1

Bond (1952): n = 1.5

nx

dxkdE −=

Bond

Rittinger

Kick

Energy utilization: AESΔ

EA

Coupled Effects of Process Engineering – Product Characteristics

Polymorphic form- Phase change - Product size range

Product Quality- Amorphous content and stability -

Methods of Stressing Particles

1. Impact

2. Compression

3. Shear

4. Attrition

Milling is an art at present. The science of size reduction is at its infancy and cannot yet satisfy the demands of industry. As a simple example, we cannot even predict the size distribution of a given material impacting on a single rigid target! Empiricism is still the order of the day.

Scope of Lectures

• Equipment: Iain Crosley

• Product characteristics affected by the process and feed: John Sherwood

• Fundamentals: Mojtaba Ghadiri

School of somethingFACULTY OF OTHER

Putting Science into the Art of Milling

Procter & Gamble Grinding Day24th February 2010

Mojtaba Ghadiri

Objectives & Methodology

To establish a functional relationship amongst evolved product characteristics, feed material properties and mill dynamics for milling of organic materials

Characterise single particle breakage

under high strain rate at ambient conditions

Analysis of milling based on dynamics and

single particle properties

Indirect measurement of mechanical properties under chosen conditions

10

�

�(a)

�

�(c)

�

�(b)

�

�(d)

(a) rigid-perfectly plastic,

(b) elastic-perfectly plastic,

(c) rigid-plastic with work-hardening, and

(d) elastic-plastic with work-hardening.

Deformation Modes

Breakage Modes

Brittle Failure Mode

• Pre-existing internal and surface flaws affect the strength.

• High compliance: surface flaws

• Low compliance: internal flaws

• Stress field is independent of strain rate.

• Predictive analysis is difficult.

• Statistical analysis, e.g. Weibull distribution is used to describe the data.

Semi-Brittle Failure Mode

• Cracks are initiated by plastic flow.

• Indentation fracture analysis can be used to describe the breakage.

• Lateral cracks are responsible for chipping and wear.

• Radial and median cracks are responsible for fragmentation.

• Predictive models are available.

Resistance against elastic deformation

- Young’s modulus, E

Resistance against plastic deformation

- Yield stress and hardness, Y & H

Resistance against crack propagation

- Fracture toughness, Kc

Material Properties Accountingfor Breakage

Temperature and strain rate affect these parameters

Characterisation of Breakage and the Effect of Mechanical Properties

The volume of chips is estimated based on the propagation of lateral cracks. The calculation of the ratio of volume of chips to the volume of original particle gives rise to a dimensionless group which describes the breakage propensity for this mode (Ghadiri and Zhang, 2002).

2c

2

KH l v ρ

ααηξ ==

Analysis of Breakage for Semi-BrittleFailure Mode: CHIPPING

Various Materials

α-Lactose H= 640MPa

Kc=0.16MPa.m0.5

SucroseH=645MPa

Kc=0.08MPa.m0.5

Aspirin H=140MPa+

Kc=0.16MPa.m0.5

MCC H=168MPa

Kc=0.76MPa.m0.5

Starch H= 78MPa

Kc not yet available

SorbitolH=645MPa+

Kc=0.08MPa.m0.5

Material H/Kc2 Tm, oC Tc,

oC

Sucrose 100781 186 60-75α-LM 23795 201 118Aspirin 3570 139 -30MCC 293 265 160Starch (☼) 250 170*

H – Hardness; Kc – Fracture toughness☼ Not yet available* Decrease with increasing moisture content+ Measured using nano-indentation on single crystals

X-ExtMailInfo: <[email protected]> bdc-notes003.na.pg.com [155.125.116.11]Subject: Squeeze Mechnical propertiesTo: Mojtaba Ghadiri <[email protected]>Cc: [email protected], [email protected]: [email protected]: Thu, 15 Mar 2001 13:41:37 +0000X-MIMETrack: Serialize by Router on BDC-NOTES003.NA.PG.COM/PGI(Release 5.0.3 (Intl)|21 March 2000) at 03/15/2001 08:43:21 AM

Dear Mojtaba,

Attached is a write-up of the mechanical properties of Squeeze that we feel is

the reasons behind the particle low propensity for fracture under plant

conditions of compressive, shear & impact conditions. I thought there may be

time for you reveiw before meeting tomorrowing morning.

Look forward to seeing you tomorrow,

(See attached file: Squeeze Mechanical Property Definitions.doc)

Kind Regards sam

Squeeze Mechanical Property Definitions.doc

Project Sqeeze used this approach

Project Sqeeze used this approach

1. A water-soluble and/or a water-dispersible particle having a mean particle diameter of less than 20mm, preferably less than 2mm, and having a Hardness (H) of 500 MPa or less, when measured at a temperature of 20oC, a relative humidity of 20%; and a Fracture Toughness (Kc) of 0.04 MPa.m1/2 or greater, when measured at a temperature of 20oC, a relative humidity of 20% and a strain rate of 30 s-1; said particle comprises an active ingredient, said particle is obtained by a non-freeze dry process.

2. A particle according to any preceding claim, wherein said particle has a Fracture toughness of 2 MPa.m1/2 or greater and/or a Hardness of 200 MPa or less, when measured at a temperature of 20oC and a relative humidity of 20%.

3. A particle according to any preceding claim, wherein said particle has a ratio of H/Kc2 of 312500 Pa-1.m-1/4 or less, preferably from 50 Pa-1.m-1/4 or less.

Extension of radial and median cracks causes fragmentation. Based on crack extension proposed by Ghadiri and Zhang (2002), the fragmentation force is given by:

313434cfr HlKF ∝

2 3 4 5 6

Analysis of Breakage for Semi-Brittle Failure Mode: FRAGMENTATION

Plastic Deformation-Chipping Transition

Critical load for lateral fracture (Marshall et al., 1982):

For velocity:

22121

4c

ch l ρ HE

] HK

[ V --∝

Transition Velocities

4c

cl ]HK

[ E F ∝


Chipping – Fragmentation Transition

Hutchings (1992) specified a critical load for fragmentation based on the indentation fracture model of Hagan (1981):

For velocity:3

4c

cf HK

F ∝

221-214

cfr l ρ H ]

HK

[ V -∝


Particle Shear & Impact Prototype Design

RotameterOrifice

Cabinet Seal

Porous ring (1mm thickness)

Roller abrasion

Etching Bracket

www.leeds.ac.uk/ipse www.lipse.org+44 (0)113 343 2404

[email protected]

Feeding funnel

Glass tube

Photodiodes

Collection chamber

Target

Filter

Vacuum line connection

Vacuum line

Manual feeding

PI Collection chamber

PhotodiodesGlass tube

Target

Filter

Single Particle Impact Testing

Single Particle impact testing

Experimental procedure

• 2 g of sample used in each test for statistical reliability• Product sieved using 2 sieves below original• Extent of breakage

on the assumption that handling losses are due to a combination of losses from mother, debris and feed particles• Extent of breakage R* related to where

%100MM

MR

dem

de* ×+

=

21

* v cR =

2C

1 Kl H ρ α

c =

Single Particle impact tests - Results

Size range μm C1 C1/l R2

425 - 500 0.0483 104.4 0.996

355 - 425 0.0415 106.4 0.981

300 - 355 0.0319 97.4 0.989

250 - 300 0.0231 84.0 0.988

• Breakage propensity increases with particle size and impact velocity

• C1/l remains relatively constant with particle size

• Well described by Ghadiri & Zhang model (2002)

Aspirin - ambient temperature and humidity


Material C1 Error C1/density R2

Aspirin 0.0129 ± 6.3 E-04 9.21 E-06 0.96

Sucrose 0.00113 ± 8.0 E-05 0.71 E-06 0.94

Results of single particle impact Tests

Material (C1/ρ d)aveAspirin 0.0700

Sucrose 0.0244Sorbitol 0.0356α-LM 0.0058MCC 0.0028

Starch 0.0018

=

=

21

21 ,cc K

H

d

C

K

HdC α

ρρα

-0.04

0

0.04

0.08

0.12

0.16

0 200 400 600 800

Particle size, micron

C1/

( ρd

)

Aspirin Sucrose Sorbitol

MCC Starch Lactose

Mechanical properties from impact test (ambient temperature)


Effect of temperature on breakage of Aspirin

Temperature C1 R2

(-) 20 °C 0.0281 0.986

25 °C 0.0410 0.994

70 °C 0.0561 0.989

• Breakage propensity increases with temperature

• Value of C1 increases with temperature

• Ratio of H/Kc2 increases with temperature

• Similar results obtained from two separate studies

21

* vcR = 2C

1 Kl H ρ α

c =


Effect of temperature on breakage of Aspirin

• Effect of temperature fits well to Arrhenius plot

• Activation energy – May be described as the energy required to move dislocations and initiate fracture

Arrhenius relationship

TR

EAk a 1

lnln

−+=

Temperature C1 R2

(-) 20 °C 0.0281 0.986

25 °C 0.0410 0.994

70 °C 0.0561 0.989

Agglomerate Breakage

Agglomerate Breakage

Breakage energy is related linearly to the incident energy (Moreno, 2003):

23

3

4

2

1VRN ANC πρ∝Γ

The damage ratio is given by:

A

VR

N

NC

Γ∝

23ρ

35

23235

/

//C VED

N

N

Γ∝ ρ

32 /2C EDDV

N

N

Γ×

Γ∝ ρ

Now from LEFM: Γ= EKc2

This gives the damage ratio as:

32

2

/

c

2C ED

H

E

K

HDV

N

N

Γ×

×∝ ρ

Analysis of Breakage for Brittle Mode

Weibull Analysis (1951): Probability of fracture, S, when a brittle material is subjected to stress:

−−=

m

s

zexpSσσ

1

Vogel and Peukert (2002):

( )[ ]min,kkmat WW x fexpS −−−= 1

where fmat is a material parameter, x is particle size, Wk is kinetic energy and Wk,min is the minimum kinetic energy which causes breakage.

Impact Breakage in Brittle Mode

Methods:

• Compression

• Shear

• Fluid bed

• Ball mill

• Tumbler

• Vibration

Features:

• Reflect particle interactions

• Close to industrial case

• Difficult to interpret

• Only useful for relative comparison

• Hydrodynamic interactions depend on scale

• Misleading

Bulk Tests

Analysis of Bulk Milling

Can common conceptual models be analysed with recourse to single particle breakage characteristics?

First Order Rate Process:

Population Balance model:

iii M K-

t dM d

=

i

n

1jiii,jjj

j M S B M S- t d

M d∑

+=

+=


[email protected]

Dt = d50 of the mill sample at time t Dl = d50 of the sample at milling limit

D0 = d50 of the feed material, d50 = median of the sample

First Order Milling Rate

( )tKexpDDDD

pl0

lt --

-=

Detachable cooling jacket

Stainless steel milling jar

Counter weight

Detachable jar holder

50 mm (11 ml)

x

z

Jar movement

12 mmy

Example: Analysis of Single Ball Milling

Develop a predictive model for milling

?


Determine the material properties

Analyse the mill performance

3D-DEM Simulation

Single Ball Milling

Approach

• MCC is widely used as excipient or inert in the pharmaceuticals industry.

Microcrystalline Cellulose (MCC) <250 mm (BS410 Sieve)

100 µm Ranges selected for testing:• 212 – 250 mm• 180 – 212 mm• 150 – 180 mm• 90 – 106 mm• 63 – 75 mm

Samples


[email protected]

0 1000 2000 3000 4000 5000 6000

0.0

0.2

0.4

0.6

0.8

1.0

Kp = 0.0016, R2 = 0.9946

Kp = 0.0024, R2 = 0.9978

Kp = 0.0041, R2 = 0.9947

Kp = 0.0047, R2 = 0.9943

Kp = 0.0057, R2 = 0.9965

Kp = 0.0038, R2 = 0.9864

(Dt-D

l)/(D

0-Dl)

Time, t (s)

Original MCC 212-250 µm 180-212 µm 150-180 µm 90-106 µm 63-75 µm

Milling of MCC at 18 Hz


[email protected]

0 1000 2000 3000 4000 5000 6000

0.0

0.2

0.4

0.6

0.8

1.0

Kp = 0.0045, R2 = 0.9735

Kp = 0.0108, R2 = 0.9823

Kp = 0.0129, R2 = 0.9793

Kp = 0.0144, R2 = 0.9689

Kp = 0.0073, R2 = 0.8837

(Dt -

Dl)

/ (D

0- D

l)

Time, t (s)

Original MCC 212-250 µm 180-212 µm 150-180 µm 90-106 µm

Milling of MCC at 25 Hz


[email protected]

K p = 6.262E-05 d

R 2 = 0.9410

K p = 2.463E-05 d

R 2 = 0.99820

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

50 100 150 200 250 300

Mean Sieved Feed Size, d (µm)

Kp

(s-1

)

18 Hz

25 Hz

Milling Rate Constant at 18 & 25 Hz

dem

de

MMM

R+

=*

Mde = mass of debrisMm = mass of mother particles

The extent of breakage (R*) is determined by gravimetric analysis.


Manual feeding

PI Collection chamber

PhotodiodesGlass tube

Target

Filter

0 20 40 60 80 1000

1

2

3

4

5

6

7

8Fitting Equation: R* = C v2

C = 0.0007

R2 = 0.9877C = 0.0008

R2 = 0.9924

C = 0.0009

R2 = 0.9915

C = 0.0003

R2 = 0.9671

R* (212-250 µm) R* (180-212 µm) R* (150-180 µm) R* (90-106 µm)

Ext

ent

of B

reak

age

(%)

Impact Velocity, v (m s-1)

22

* v

KdH

Rc

ρα=

Extent of Impact Breakage

K p = 16.237 C

R 2= 0.9965K p = 6.3714 C

R 2= 0.93570

0.0020.0040.0060.0080.01

0.0120.0140.016

0 0.0002 0.0004 0.0006 0.0008 0.001

C (s2 m-2)

Kp

(s-1

)

MCC-18 HzMCC-25 Hz

Dependence of Milling Rate on Particle Properties

x

zy

Spring

Compressive force

Knηn

wnDashpot

ws

Ks

ηs

Slider

Shear force

µf

φ

tw

wKF nnnnn ∆

∆+∆= η( )

( )t

rrw

rrwKF

ss

sss

∆∆+∆+∆+

∆+∆+∆=

2211

2211

φφη

φφ

DEM Simulationsto estimate input energy

DEM simulation at 25 Hz of milling frequency in the single ball mill

DEM Simulations

∑=

=n

jjn mvE

1

2

21

• Each simulation is run for up to 3 s of real time (t ) with a time step of 0.2 ms.

• Milling power (Pn ) is deduced from:

• Milling energy (En ) is deduced from the relative

velocity (v ) and reduced mass (m) of the two objects in contact by:

tE

P nn =

Milling Power

P n = 0.1954 d

R 2 = 0.9677

P n = 0.0853 d

R 2 = 0.95840

50

100

150

200

250

0 250 500 750 1000 1250 1500

Particle Size, d (µm)

Mill

ing

Pow

er, P

n (

J s-1

)

At 18HzAt 25Hz

Simulation Results of MCC

K p = 0.0003 E n

R 2 = 0.9713

00.0020.0040.0060.008

0.010.0120.0140.016

0 10 20 30 40 50

Power, P n (J s-1)

Kp

(s-1

)

MCC-18 Hz

MCC-25 Hz

Dependence of Milling Rateon Power

K p = 0.1386 P n α H / K c2

R 2 = 0.9902

00.0020.0040.0060.008

0.010.0120.0140.016

0 0.02 0.04 0.06 0.08 0.1 0.12

P nα H / K c2 (m2 s-1)

Kp

(s-1

)

MCC-25 Hz

MCC-18 Hz

Unification of Results


[email protected]

α-Lactose Monohydrate (αLM)

<710 µm

Semi-Brittle

Sucrose

<1000 µm

Brittle

Starch 1500

<300 µm

Ductile

Additional Samples

K p = 0.1218 P n α H / K c2

R 2 = 0.9826

00.010.020.030.040.050.060.070.080.09

0 0.1 0.2 0.3 0.4 0.5 0.6

P nα H / K c2 (m2 s-1)

Mill

ing

Rat

e C

onst

ant,

Kp

(s-1

)

MCC-18 HzMCC-25 HzαLM-25 HzStarch-25 HzSucrose-12 HzSucrose+Aerosil-25 Hz

Unification of Results

The results presented provide evidence that the milling behaviour of a material can be quantified from the knowledge of mechanical properties and the mill dynamics as follows:

Kp = milling rate constant Pn = milling energy

H = hardness Kc = fracture toughness

Conclusions

:c

np K

H PK ∝

What to do next?On Milling:•Short term: Consultancy•Medium term: Four months MSc projects•Long term: PhD, KTP and PDRA

On continuing training:•Powder Flow•Mixing and Segregation•Sizing, etc

Analysis of Segregation of MixturesVibrated heap experiment

High Speed Video at 1000 fps

Experimental Set-Up

Heaps of binary mixtures of glass beads

(b) CASE 2 (c) CASE 3 (a) CASE 1

Analysis of Segregation of MixturesVibrated heap experiment

•First test - CASE 1:• For case where both types of beads are free flowing, system segregates (a)•Second test – CASE 2:• Light fine beads cohesive to different levels, solid coarse beads free-flowing • At higher cohesion level light fine beads formed clusters that accumulated at the

bottom and the top of the heap (b)•Third test – CASE 3:• Solid coarse beads cohesive to different levels, light fine beads free-flowing • At an increased cohesion no segregation was observed (c)

(b) CASE 2Highly segregates

(c) CASE 3Does not segregate

(a) CASE 1Segregates

Analysis of Segregation of MixturesVibrated heap experiment: different size, density and cohesion

Thank you for your attention.

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