OPTIMIZATION OF MILLING PARAMETERS OF PLANETARY …...HOD of Automobile Engineering, Godavari Institute of Engineering & Technology (A), Rajahmundry, India Lingaraju Dumpala Assistant

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 11, November 2018, pp. 1579–1589, Article ID: IJMET_09_11_163

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=11

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

OPTIMIZATION OF MILLING PARAMETERS OF PLANETARY BALL

MILL FOR SYNTHESIZING NANO PARTICLES

Subrahmanyam Vasamsetti

Research Scholar, Jawaharlal Nehru Technological University Kakinada and

HOD of Automobile Engineering, Godavari Institute of Engineering & Technology (A),

Rajahmundry, India

Lingaraju Dumpala

Assistant Professor, Department of Mechanical Engineering,

Jawaharlal Nehru Technological University Kakinada, India

V.V. Subbarao

Professor, Department of Mechanical Engineering, Jawaharlal Nehru Technological University

Kakinada, India

ABSTRACT

In this paper an effort is made to find optimum parameters for synthesizing

nanopowders with ball milling. Vertical planetary mill with tungsten carbide (WC)

grinding jar and WC balls were selected for performing milling operation. Rice husk ash

(RHA) prepared in the laboratory by using muffle furnace was taken for milling. Very

important grinding parameters such as milling speed, time of milling and ball to powder

ratio were selected as factors and in each three levels were taken to design the

experimentation. Different mill speeds 250, 375 and 500 rpms as three grinding speeds,

10, 20 and 30 hours as milling time and 5:1, 10:1 and 15:1 grinding balls to powder

rations were chosen as factors of milling. Design of experimentation is done on Taguchi

L9 orthogonal array. The nine results were taken as responses and analyzed using

Taguchi technique and found a predicted value and verified by doing confirmation test

and found close result. The results shown that both increase in milling speed and the time

of milling decreased particle size of the material considerably, but the weight ratio of

grinding ball to powder had shown effect up to10:1 and not shown much effect after that.

Analysis Of Variance (ANOVA) shown error with in allowable limits and proved that the

results were satisfactory.

Keywords: Planetary ball milling, Mechanical attrition, Synthesis of Nano powders, Optimization of Milling parameters, Taguchi, ANOVA.

Cite this Article: Subrahmanyam Vasamsetti Lingaraju Dumpala and V.V. Subbarao,

Optimization of Milling Parameters of Planetary Ball Mill for Synthesizing Nano Particles,

International Journal of Mechanical Engineering and Technology, 9(11), 2018, pp. 1579–

1589.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=11

Subrahmanyam Vasamsetti Lingaraju Dumpala and V.V. Subbarao


1. INTRODUCTION

Metal Matrix Composites are widely using in various industries such as Automobile,

Aeronautics, Aerospace etc. The percentage of material utilization in Automobiles, Aeroplanes

and rockets are increasing day-by-day. If the reinforcing elements are in nano size the composites

are called as nanocomposites. Nanomaterials are the future materials [1-6]. Nano materials deal

with the study of properties of much smaller size elements with any one of the dimensions less

than 100 nanometer, their manufacturing, testing, performance and applications at appropriate

areas. Reducing the solid particles less than 100 nanometer size is called Attrition. There are

mainly two approaches of nanomaterial synthesis. 1. Bottom up approach and 2. Top down

approach. As the name indicates in bottom up approach the material is brought down to basic

units (atomic level) and then allowed to combine to nanoscale stable structures called

nanostructures. The techniques such as hydrothermal synthesis, solvothermal method, Chemical

vapor deposition (CVD), thermal decomposition and pulsed laser ablation are the widely

followed bottom up techniques. Though these fabrication methods are quicker, these are much

expensive and needs huge amount of heat. In top down approach initially larger structures are

reduced to nanostructures by mechanical means. Ball milling, etching through mask, X-ray

lithographic cutting, electron beam cutting, photo ion beam cutting and by the application of

severe plastic deformation are the widely used methods in top down approach. These methods

are cheaper than bottom up methods. Though these methods are comparatively slow, widely used

for commercial and research purpose.

Out of all the above methods, ball milling is the widely used nanomaterial synthesis method

due to its simplicity and applicability to wide range of materials preparation [7-15]. Using ball

milling, metallic and ceramic nanostructures are fabricated by mechanical attrition. In this

method kinetic energy from grinding balls is used to reduce the material size. Several types of

ball mills are available in the market. The machines may be attrition mills, vibration mills, pin

mills, vertical axis mills, horizontal mills or rolling mills. In attrition mills the bowl is kept

stationary and the material with grinding balls is rotated with impeller [16-18].

The ball mills can be classified into two categories according to the axis of rotation of the

bowl. 1. Vertical axis and 2. Horizontal axis.

Figure 1 Direction of rotations of drums in (a) Vertical and (b) Horizontal axis ball mills

In Vertical axis ball mill, the drum with material to be ground and grinding balls rotates about

its own axis and revolves about disc or table’s vertical axis, where as in case of horizontal axis

ball mill, the drum rotates about horizontal axis as shown in fig. 1.

Several researchers employed ball milling successfully for synthesizing nanostructures of

different materials or to study the structural changes in the materials during ball milling [19-28].

Wen-Tien et al developed mesoporosity in eggshell and characterized by milling with planetary

ball mill [29]. Hui Li et al studied characteristics of fly ash on ball milling [30]. Hiroshi Mio et

Optimization of Milling Parameters of Planetary Ball Mill for Synthesizing Nano Particles


al simulated balls specific impact energy with Discrete Element Method (DEM) and also

simulated ball mill computationally using scale-up method [31, 32]. Jin-Hua Dong et al studied

dynamic simulation of small planetary ball mill using virtual prototype technology ADAMS

(Automatic Dynamic Analysis of Mechanical System) [33]. Lu Sheng-Yong et al simulated ball

motion and also estimated conditions for standard operation to get better energy transfer [34]. L.

Guzman et al applied PFC a 3D software tool for simulating planetary ball mill [35]. F.J. Gotor

et al found various parameters influencing milling with planetary mill [36]. M. Broseghini et al

simulated the jar shape effect on efficiency of planetary ball mill [37, 387]. P.P. Chattopadhyay

et al mathematically analyzed mechanics of planetary ball milling [39, 40]. Y.T. Feng et al

simulated the dynamics of planetary ball milling using DEM [41]. A. Yazdani et al estimated

temperature, energy and particle size in planetary ball mill [42]. M. Abdellaoui et al modeled

planetary ball mill kinematically and studied mechanical alloying in planetary ball mill [43].

2. EXPERIMENTAL PROCEDURE

2.1. Methodology

Vertical axis ball mill is also called as planetary ball mill which is widely used in laboratories. A

generalized planetary ball mill which is used in laboratories is as shown in fig. 2.

Figure 2 a. Planetary ball mill, b. Bowl charged with material and grinding balls and c. Bowl locked in

position

The ball mill consists of a bowl or also called grinding jar, made with hard material such as

stainless steel or tungsten carbide (WC). The bowl consists of a cap with same material that can

be firmly locked in position by locking mechanism. Hard metal grinding balls similar to jar

material i.e. stainless steel or WC are kept in bowl with the material to be ground. The bowl is

mounted at the end of a rotating disc or also called table, and is allowed to revolve with the disc

and also rotates about its own axis but in opposite direction as shown in fig. 3. That is if the disc

rotates in clock wise direction, then the bowl rotates in anti-clock wise direction. Due to two

different motions the vertical milling machine is also called as planetary ball mill. There may be

more than one bowl for increasing output.



Figure 3 Directions of rotation of bowl and disc

The principle involved in ball milling is that the material which is taken in bowl is subjected

to high energy collisions. So these ball mills are called High Energy Mills (HEM). During ball

milling the material is subjected to severe plastic deformation, fracture and cold welding. The

particle deformation causes change in particle size and fracture breaks particle into smaller size.

Cold welding causes rejoining of particles and increase in size. Due to two opposite directions of

motions of disc and bowl, like and unlike centrifugal forces act on the grinding balls alternatively.

The grinding balls roll over the wall due to like centrifugal forces. The grinding balls impact

among themselves and also against the bowl wall due to unlike centrifugal forces. The material

is subjected to plastic deformation and fractures due to crushing between the grinding balls and

also between the grinding balls and walls of the bowl as shown in fig. 4.

Figure 4 Crushing of material between grinding balls and wall of bowl and also between the grinding

balls

A large number of process variables affect the performance of ball milling such as milling

time, powder to ball weight ratio, speed of milling, eccentricity of the bowl on the disc, volume

of the material to be grounded, medium, type of mill, jar dimensions, milling temperature, milling

environment etc [44].

2.2. Materials

Rice husk is an industrial waste which is the outer cover of the rice. Since oxidation of rice husk

is exothermic in nature, a huge amount of heat is liberated while burning. So rice husk can be

used as fuel in mini power plants and small scale to medium scale industries such as rice mills,

sugar industries, edible oil industries etc. Rice Husk Ash (RHA) is formed after combustion of

rice husk. RHA is an industrial waste and is used for preparation of bricks for civil constructions.

Balls

Crushing material



In this experimentation RHA is selected for finding the optimum parameters for ball mill

process. The RHA obtained from industries is black in colour which has carbon content and is

not thermally stable. For the experimental work RHA is prepared in the laboratory.

Subrahmanyam et al [5, 6] explained preparation of RHA in the laboratory using muffle furnace.

Masoud Salavati-Niasari et al synthesized Silica nanoparticles by ball milling RHA for the

application of drug delivery [45]. Ramadhansyah P.J. et al analyzed thermal behavior and

pozzolanic index of RHA at different milling times [46].

2.3. Design of Experimentation

The planetary ball mill under experimentation is utilizing Tungsten carbide (WC) jar of internal

diameter 79mm and depth 48 mm. It consists of number of equal sized WC grinding balls of

diameter 10mm and weight 7.7 gm. Different factors and levels of the experimentation are given

in the table 1. The number of grinding balls and RHA sample of quantity was taken into grinding

jar according to design of experiment, so as to maintain 5:1, 10:1 and 15:1 ball to powder ratio.

The speed of the machine can be adjusted using electric regulator such as 250 rpm, 475 rpm and

500 rpm.

Table 1 Different Factors and Levels chosen for the experimentation.

Factors

Levels

C1 C2 C3

Speed of Mill s in rpm Time of Milling in Hours Ball to Powder ratio

1 250 10 5:1

2 475 20 10:1

3 500 30 15:1

2.4. Structural Analysis using Dynamic Light Scattering

The size distribution of the milled samples in this present study was estimated with the help of

Particle size analyzer. After each milling operation the samples were collected and the average

particle size was tested using Dynamic Light Scattering (DLS) device. Figure 5 represents a

typical DLS histogram of a sample after completion of ball milling.

Figure 5 Histogram of particle distribution of an RHA sample showing nano size particles.

3. RESULTS

3.1. TAGUCHI METHOD

L9 design of experimentation was chosen to find optimum parameters for the preparation of

nanostructured materials using planetary ball mill. The design of experimentation is given in the

table 2. After completion of all the experiments the grain sizes were fed as responses into Taguchi

orthogonal array design of Minitab software.

The response cures with respect to the factors under consideration were presented in the fig.

6. From the graphs it was revealed that increase in both the milling speed and the time of milling



decreased particle size of the material considerably, but the weight ratio of grinding ball to

powder had shown effect up to10:1 and not shown much effect after that.

Table 2 L9 Taguchi orthogonal array design of Experimentation and response of grain size.

C1 C2 C3 C4

Ex. No. A B C Responses

(Grain size in nm)

1 1 1 1 237

2 1 2 2 207

3 1 3 3 178

4 2 1 2 192

5 2 2 3 118

6 2 3 1 92

7 3 1 3 124

8 3 2 1 101

9 3 3 2 57

Figure 6 a. Main effects plot for means and b. Main effects plot for SN Ratios

Taguchi Analysis: C4 versus A, B, C

Table 3 Response Table for Signal to Noise Ratios (Smaller is better)

From the table the optimum levels are L3, L3 and L1.

The Predicted value can be found using the formula given in the equation (1)

YP = YE + (YA-YE) + (YB-YE) + (YC-YE) (1)

Where, YP: Predicted Value,

YE: Experimental Value = Average of responses = 145.11

YA: Average responses of A at optimum level (L3) = 94



YB: Average responses of B at optimum level (L3) = 109

YC: Average responses of Cat optimum level (L1) = 140

Therefore the Predicted Value, YP = YA+YB+YC-2YE = 52.78 nm.

3.2 Confirmation Test:

A confirmation test was conducted to compare with the predicted value. The confirmation

test at levels 3 3 and 1 for A B and C factors respectively i.e. at 500 rpm milling speed, for 10

hours of milling time and with 15:1 ball to powder ration. A particle size of 56 nm is obtained at

these parameters and the result is found satisfactory.

A Scanning Electron Microscope (SEM) image of the confirmation test result is also taken

which shows the presence of nanoparticles which is shown in the fig. 7. The huge particles are

the aglomerated particles due to cold welding.

Figure 7 SEM image of the sample of confirmation test.

3.3. ANOVA RESULTS

Analysis of Variance (ANOVA) graphs presented in the fig. 8 which also reveals the same result

that the milling speed and the milling time are the primary factors of reduction of the particle size

and the ration of ball to powder has less effect and 10:1 is the better value. Hence, the results

were validated.



Figure 8 Graphs from ANOVA

Table 4 ANOVA table

Source DF Adj. SS Adj. MS F Value % Contribution

A 2 79.3900 39.6970 4.89 61.98

B 2 40.7900 20.4000 1.40 31.84

C 2 0.4060 0.2029 0.01 0.32

∑= 94.14%

From the ANOVA results given in the table 4 the Percentage error is calculate as 5.86, which

is less than 10 percent. So the error is within allowable limits and proved that the results were

satisfactory

4. CONCLUSIONS

With the results the following conclusions were made.

• Ball milling is the better way to produce nanostructured materials with ease.

• The Speed of milling and the Time of milling are the two predominant parameters

which influences the particle size of the synthesized material.

• The ratio of Ball size to the material to be ground has less effect on the particle size

of the powder synthesized.

• Ball to powder ratio of 10:1 is enough for getting better results.

• The synthesized particles were subjected to agglomeration while in nano size.

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OPTIMIZATION OF MILLING PARAMETERS OF PLANETARY …...HOD of Automobile Engineering, Godavari Institute of Engineering & Technology (A), Rajahmundry, India Lingaraju Dumpala Assistant

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