12 ballroll mill

8/2/2019 12 Ballroll Mill

http://slidepdf.com/reader/full/12-ballroll-mill 1/62

ANALSYSIS OF BALL ROLL MILL USING FEM

ABSTRACT: The raw mill separator unit is an integral partof modern cement manufacturing industries.The unitconsists of main and auxiliary fan assemblies along with

many other accessories. The purpose of the raw millseparator is to create suction pressure and provide themeans to separate the fine cement particles from coarsecement particles.The fine particles are collected separatelywhile the coarse particles are again sent back to crushingunits and the cycle goes on.The cement comprises of twomain erodent in form of alumina and silica which causeswear loss of fan blade in raw mill seperator unit. Since this

wear loss is non uniform in nature, it causes thedevelopment of eccentricity in the rotating fan assembliesof seperator. This rotating un balance causes the wholestructure to vibrate. The foundation and other installedunits this raw mill seperator unit get thus vibrating.

Therefore it becomes important to analyze the vibrationcharacteristics of seperator unit for different cases of

unbalance and to find out suitable means to minimize thevibration. In this report, the computer aided solid modelgeneration of the seperator fan assemblieshas been donebased on the drawings. The modal analysis of the fanassembly attached with housing and supporting frame hasbeen done using finite element analysis software. To seethe effect of unbalance on supporting structure onesimplified approach has been used and vibration response

for unbalanced rotation has been analyzed. The root causeof unbalance in seperator fan assembly is non uniformwear loss of fan blade material. To contral this erosivewear loss from fan blade, one experiment has beenperformed to compare the wear loss from mild steelsubstrate plate coated with suitable hard material. Good

1



wear resistance result has been found for coated materialwhich can be used for fan blade to control the quick wearloss.

Chapter: 1 Introduction _______________________________________________________

This chapter deals with the basic things about the current work. It gives the need of recognition for

problem formulation. Literature survey and other essential technical aspects about the report

outline are the key parts of this chapter.

1.1 Motivation

Getting the exposure of practical problems and technological solutions has always been the

motive of any project work. Solving the industrial problem is an advantage as it gives an

opportunity to work on real life system. The present work is an attempt to analyze the effect

of unbalance in the rotating parts of raw mill air separator unit which is a part of cement

manufacturing industries. The present work is based on the actual data provided by the plant.

Vibration problem occur where there are rotating or moving parts in machinery. Apart from

machinery itself, the surrounding structure also faces the vibration hazard because of this vibrating

2



machinery. The effect of vibration is excessive stresses, undesirable noises, looseness of parts, and

partial or complete failure of parts. The study of vibration is concerned with the oscillatory motion

of bodies and the forces associated with them. All bodies possessing mass and elasticity are

capable of vibration. Thus most engineering machines and structures experience vibration to some

degree, and their design generally requires consideration of their oscillatory behaviour.

The work is backed by the literature survey for solid particle erosive wear and rotor

dynamic analysis. The mathematics for rotational unbalance, modal analysis, and finite element

analysis has also been incorporated for sake of completeness of the report. The conclusion and

future scope of work describes the utility of current work with recommendations and further scope

for enhancement of the work.

1.2 Raw Mill Air Separator Unit:

The raw mill separator unit is an integral part of cement manufacturing industries. Separator is

used in cement plant to remove fine grains of cement from coarse grains. It is based on

centrifugal force action. Fig 1.1 gives insight to the basic cement manufacturing steps and the role

of air separator unit.

3



Fig 1.1: The basic components of the cement manufacturing process

It is the last stage i.e. cement mill where the air separator is used. The basic components of the

cement mill can be shown in fig 1.2:

Fig 1.2: Cement Mill

In fig 1.2 the flow chart of the cement mill is shown. It consists of three main units. The separator

unit is the last one which is run by fans. The coarse grains from the separator unit are collected

4



separately and sent back to the drying section along with new feed material. This new feed material

is the clinker and the mixture is grinded in the grinding section by ball mills. The input to the air

separator unit is from the grinding section. Fig 1.3 gives more insight to the separator unit:

In general the raw mill air separator unit is a huge unit in the cement industry and

comprises of as many as of 20 parts, the main parts being main and auxiliary fan assemblies.

Fig 1.3: Separator unit outline

1.3 Erosive Wear

Wear may be defined as damage to a solid surface caused by the removal or displacement of

material by the mechanical action of a contacting solid, liquid, or gas. It may cause significant

surface damage and the damage is usually thought of as gradual deterioration. While the

terminology of wear is unresolved, the following categories are commonly used.

5



• Adhesive wear

• Abrasive wear

• Erosive wear

• Fatigue wear

• Corrosive wear

Mechanisms of Wear

Particle contamination can damage systems by causing a variety of types of wear. The primary

types of wear are shown in the table 1.1 below, along with the most common cause for that type of

wear. Each of these wear mechanisms result in the generation of particulate contamination capable

of causing further component damage.

Table 1.1 Wear Summary

Type Primary Cause

Abrasive Wear Particles between adjacent moving surfaces

Erosive Wear Particles and high fluid velocity

Adhesive Wear Surface to surface contact (loss of oil film)

Fatigue Wear Particle damaged surfaces subjected to repeated stress

Corrosive Wear Water or chemical

Erosive wear is caused by particles that impinge on a component surface or edge and remove

material from that surface due to momentum effects. This type of wear is especially noticed in

components with high velocity flows. Particles repeatedly striking the surface may also cause6



denting and eventual fatigue of the surface. Adhesive wear has been commonly identified by the

terms galling, or seizing. Abrasive wear, or abrasion, is caused by the displacement of material

from a solid surface due to hard particles or protuberances sliding along the surface. Erosion, or

erosive wear, is the loss of material from a solid surface due to relative motion in contact with a

fluid that contains solid particles. More than one mechanism can be responsible for the wear

observed on a particular part.

1.4 Problem Definition

The raw mill separator is a unit which is used in cement industries. The unit consists of main fan

assembly and auxiliary fan assembly on a rotating shaft. The fan assemblies consists blades

mounted on the central hub which is fixed with shaft. This unit is used to separate fine cement

particles from coarse cement particles. The discrimination of these particle sizes is controlled by

the suction pressure created by the fan rotation and the centrifugal force applied on the cement

particles when they enter rotor blade areas. The cement carries alumina and silica as ingredients in

their raw material configuration. This act as erodent for the blade materials. The high speed impact

of this erodent on the fan blade material causes the wear of blade profile. The random nature of

impact of this erodent on the rotating blades causes non uniform material loss from blades. This

leads to the shifting of centre of mass of the rotating assembly from the centre of shaft. As the shaft

and fan assemblies are rotating, this centre of mass shifting causes the development of eccentricity

in rotating structure which cause the rotating unbalance in the system. The air separator unit is

severely affected by this rotating unbalance as it cause the whole structure to vibrate which in turn

creates problems to other installed units besides and loosening of fixings and low cycle fatigue.

Thus it becomes important from safe operating point of view to analyze the vibration behaviour of

air separator unit.

7



The current work content of the dissertation report is solving the problem associate with

raw mill separator fan assemblies. The problem formulation is based on the reports, about the

excessive vibration caused by separator fan assemblies. According to the reports, the separator fan

assemblies are suffering through fan blade material loss due to erosive wear. The dynamic

balancing is temporarily used by them as a remedial action.

But that did not help to run the separator unit longer and frequently needed to repair the eroded fan

blades. This phenomenon of the wear loss of fan blade material can be explained in terms of the

erosive particles available in cement powder. The raw material is the source of abrasives. One

typical clinker analysis shows that it contains 21.5% SiO2 (silica) and 5.2% Al2O3 (alumina) by

weight. These two constituents are the major abrasive/erodent particles present in the cement

powder which when impinges on the fan blade at high speed cause the wear of the blade material.

This wear loss is non uniform in nature because of the varying erodent sizes, varying speed and

angle of impingement of the erodent particles. This non uniform material loss results into non-

uniform mass distribution of the fan blade around the main shaft.

Thus eccentricity is produced in the fan assemblies. This eccentricity is the source of vibration as

when fan rotates, this eccentricity causes the rotating unbalance in the system. It is thus required to

analyze this unbalance and vibration behaviour of the separator unit. As the modal analysis is first

step towards any harmonic or rotating unbalance analysis, same has been done effectively in this

report. The work is followed by one sample unbalance analysis and erosive wear experiments for

controlling erosive wear material loss. The non uniform wear loss is not easy to model exactly, but

from the data of the wear prone blade areas, the effect of the material loss in a definite pattern has

been created and its effect on vibration has been analyzed. This thesis work comprises the full

computer aided solid model generation of the air separator unit fan assemblies from the actual

8



detail drawing obtained, and its finite element analysis for vibration analysis. The system modal

analysis has been done first as it the most important step from vibration analysis point of view. The

system is rotating machinery hence the rotational mode shapes are very much important as they

cause low cycle fatigue.

Since the work does not include the redesigning of the system, the stress analysis is not done. Also

modeling of the system has been done from inertia point of view. The model generation of the

complete fan assembly has been done in Pro/ENGINNER software. The finite element analysis is

used to do the modal analysis and harmonic analysis, for which ANSYS software has been use. To

make the proper balance of result accuracy and computational cost (in terms of computational

resources and computational time), the system response for various cases of unbalance has been

abstracted by modeling the real three dimensional system into equivalent one dimensional system,

keeping the system characteristics in full account. As the vibration cannot be completely

eliminated, rather minimized, the long term solution of controlling vibration has been discussed.

The one is to design he tuned liquid mass dampers as they are mostly used to control vibration in

tall buildings and structures. The solution has also been looked from the root cause of vibration

generation, i.e. the material loss from wear.

Broadly, the thesis work can be categorized as:

1. Solid model generation of fan assemblies

2. Modal and harmonic analysis for vibration analysis

3. Wear test performance for coated materials

9



Chapter2. Literature Survey

_______________________________________________________________

Though it is not possible to contain the huge work carried out by past researchers in this little

article, still this literature survey covers the recent and important work carried out which is relevant

to the current work. The whole survey is classified in two classes. The first part addresses the work

related to modeling and finite element analysis issues of rotating structures while second part

emphasis the work regarding wear resistance materials.

2.1 Modeling and Vibration Analysis of Rotating Machinery

Though the literature on the finite element modeling and simulation of rotating structures are vast,

there is very little literature available on raw mill air separator unit as such. As it is a real life

industrial system, its modelling and analysis is purely confined to the design segment. Though for

current study there is no direct input from past literature still few work of past researchers has been

taken as help. The fact lies in the use of the fundamentals developed by researchers and their

addresses towards modeling and analysis issues. Following pages summarizes that work for sake

of completeness of the work of this report.

C.-W. LEE and Y.-G. JEI [4] have worked on modal analysis of continuous rotor bearing system.

They included the effects of rotary inertia and gyroscopic moment both to their model study. They

obtained whirl speeds and mode shapes, backward and forward, of a rotating shaft as spin speed

and boundary conditions vary, and the unbalance responses are calculated by using modal analysis.

H. Irretier [5] has worked on the experimental modal analysis of time-invariant rotating systems.

10



Basically, there exist two different types of rotating structures which, under certain assumptions,

are governed by equations of motion with time-invariant system matrices. The related models are

denoted as rotor dynamic models and structure dynamic models. The rotor dynamic model is based

on the assumption that one or more rigid disks (in a generalized sense e.g. also propellers, blade

stages, etc.) are mounted rigidly or elastically on an elastic shaft which is supported in elastic

bearings. In general, the equations of motion of these models are formulated in a stationary (non-

rotating) reference system where if both the mass distribution of the disks as well as the bending

stiffness of the shaft are isotropic. The structure dynamic model is used for rotating elastic

structures as disks, blades, bladed disks, etc., which are fixed rigidly or elastically on a rigid shaft

in rigid bearings. The equations of motion are generally formulated in a rotating reference system.

I. Bucher and D. J. Ewins [6] have extensively worked on the effect of spinning velocity on the

natural frequencies of the rotating systems. Though the natural frequencies of the systems are

assumed to be constant and system characteristics, they have shown in their work that due to

gyroscopic effect, the system natural frequency changes with change in rotational speed. They

have developed the model of rotating structures and solved them using the finite element analysis

method. Following figure helps in visualizing this phenomenon:

Fig 2.1:

11



Fig 2.1: Variation of structure’s dynamics with rotation speed. (a) The variation of natural

frequencies with speed of rotation for a typical rotating structure. (b) The variation of FRF with

frequency and speed of rotation (shown at two distinct speeds of rotation Tan et al. have done a

beautiful work in helping to visualize the mode shapes and vibration behaviour of rotating

structures . They have provided the design of an innovative laboratory based system to assist the

learner. Apart from development of mathematical models for modal analysis they have provided

many examples solved by the use of analysis software ANSYS. One of their important results

which are very relevant to current work is that adding masses onto the floors of the structure

lowers the natural frequencies for both the 1DOF and 3DOF models.

A practical relevance of the experimental rig is that the one can relate these tests to real-life

structures and by altering the mass; the structure’s natural frequencies can be altered to avoid

catastrophic failures. Apart from many work on symmetric rotors, J. S. Rao and R. Sreenivas [8]

have tried to investigate the dynamics of asymmetric rotors using the solid model and finite

element analysis. The uses of computational facilities in form of modeling, analysis software and

computing resources have been emphasized to solve the non-traditional rotor dynamic problems.

They emphasize on the fact of increased demand of CPU, RAM and Hard discs if the model

becomes complex. Yoo et al [9] . have addressed one major issue in their work regarding the

selection of reference frame. Since selection of reference frame is very important from

convergence point of view in modal and harmonic analysis, it is important to choose the correct

frame of reference. For simple structures, single reference frame usually provides well converged

and accurate results for equilibrium and modal analyses. However, for structures having more

general configurations such as multi beam structures, use of a single reference frame often results

12



in slow convergence and even erroneous analysis results. They worked on use of modelling

method employing multiple reference frames for dynamic equilibrium and modal analyses of

rotating structures .The proposed method was validated by the numerical work carried by them.

Pintelon etal [10] have worked on Operational modal analysis (OMA) which allows identifying

the modal parameters from the measured response to unknown random perturbations of a

mechanical structure in operation .Though his work is mostly related to the experimental things, it

gives methods for suppressing the influence of harmonic disturbances with unknown varying

frequencies in operational modal analysis. Y.S Chen et al [11] have worked extensively on the

issues related with the effect of unbalance on rotating structures. Though their main work is related

to induction motor system, it makes the knowledge of rotor dynamics updated. They have

developed solution module to find vibration amplitude as resulted from the bearing wear, damping

effects, mass unbalance, and the passing of system resonance critical speeds. For the analysis of

vibration suppression with different eccentricities of the unbalanced masses, they noticed that the

adding of balance masses will normally suppress the vibration amplitude effectively until the point

where an optimum amount that causes the minimum balanced vibration amplitudes is observed.

Their work helps in modeling the continuous system into simple models.

2.2 Solid particle erosive wear of coated metals

The literature for the raw mill separator unit as such is not available because it is a part of cement

industry. Also, erosive wear characteristics of coated materials have been analyzed in past for

13



different type of base metals and different coating materials. Here, little important work relevant to

the present work has been presented. Besides plain WC–Co and WC–Ni coatings, several

chromium-alloyed compositions are commercially available. However, the influence of the type of

binder metal and the role of chromium additions on phase composition and coating properties on

erosion and sliding wear resistance is only poorly understood. This is due to several difficulties;

one of them being the lack of availability of commercial powders with systematically varied

compositions. L.-M. Berger etal.[12] studied the influence of the type of binder metal (nickel or

cobalt) and chromium as an additional alloying element on the microstructure, mechanical

properties and wear resistance of high velocity oxy-fuel (HVOF)-sprayed WC-based hard metal

coatings. Wear plain WC–Co and WC–Ni as well as five chromium-alloyed compositions were

sprayed with a liquid-fueled HVOF-spray process from commercial and experimental

agglomerated and sintered feedstock powders. The coating characterization included optical

microscopy and SEM of metallographically prepared cross-sections, hardness measurements,

determination of the Young's modulus and phase composition by X-ray diffraction. Erosion and

dry oscillating sliding wear were studied. The resistance to erosive wear was found to be improved

when cobalt was used as binder metal.

14



Fig 2.2: Dependence of the erosive wear of the coatings on the impact angle. Annealed low carbon

steel is given for comparison.

Overlay coatings are mostly used to change an existing wear situation from a destructive to a

permissible type. Correct selection of wear resistant materials can cut downtime and considerably

reduce maintenance costs. Wear should be regarded as a system property as its intensity depends

on environmental conditions, applied materials and operating conditions. Numerous industrial

components are subject to erosive or abrasive wear. The examples are the blades and casings of

fans transporting gases containing solid particles. These fans are used, for instance, to provide gas

flow in a rotary kiln used for cement production. Tadeusz Hejwowski [13] studied in detail about

erosive and abrasive wear resistance of overlay coatings. The erosion and abrasion resistance of

PTA, TIG and flame deposited coatings was investigated by him. He found that hardness of

coatings has almost no effect on erosion resistance and incubation period.

But the microstructure of coatings has significant effect on erosive wear of coatings. In his study

he found no significant correlation between results of abrasive and erosive tests The aim of his

work was to determine erosive and abrasive wear resistance of coatings deposited by means of

15



different methods, to find the effect of some test variables on wear resistance of materials and,

finally, to explore the effect of microstructure and chemistry of overlay coatings on their

behaviour. According his study it is evident that microstructure of coatings has significant effect

on erosive wear of coatings. Statistically significant correlation was found between erosive wear

intensities determined in tests carried out at similar angles. The total content of boron and carbon

correlates with mass loss in abrasion test and erosive wear intensity at normal incidence. Also, the

hardness of coatings does not correlate with erosive wear resistance.

2.3 Contribution to the Thesis

Though in literature, people have analyzed different rotating systems of different dimensions and

shapes. The current work is all about analyzing one unique model of raw mill separator fan

assemblies. The main contribution to the thesis can be summarized in following points:

a) Modeling: The computer aided solid model has been generated with the help of

Pro/ENGINEER modeling software. The model dimension is fully based on the detail drawings

provided by the plant.

b) Analysis: In analysis part, the modal analysis has been performed of the fan assemblies, using

ANSYS software. This gives the natural frequencies of the system. The boundary condition has

been modeled to resemble much closer to the real system environments. The full model is then

converted into one simple one dimensional model keeping the characteristics of the system same.

Then the response of the rotating unbalance has been analyzed for one sample cases of unbalance

using mathematical approach.

16



c): Experiments: To control the wear loss of fan blades, experiments are performed. This

experiment compares the erosive wear loss of the uncoated mild steel plate and coated mild steel

plate coated with chromium boride.

2.4 Organization of Thesis

Apart from abstract and introduction, there are total 5 chapters in the thesis. The first chapter gives

the insight to the introductory part of the thesis. The air separator unit has been described through

the outline of the unit figure. The cause of the unbalance is the rotating fan assembly i.e the erosive

wear loss has been discussed. So the same has been discussed with reference to the few selected

papers. The third chapter takes through mathematical aspects of the related articles. The fourth

chapter is the main work content. It includes the descriptions of computer aided solid model

generation. Then it goes through the modal analysis to find out the system natural frequencies. It

includes the simulation result of the modeled unbalance in the rotating fan assembly. The fifth

chapter provides the coated with chromium boride. The comparative results have been discussed

for wear loss of uncoated and coated samples. The sixth chapter is conclusion and future scope of

work. In this chapter simulation result of unbalance and wear experiments have been reproduced

with discussion of their physical significance. The future scope of work proposes further work

strategies which can be performed to improve the scope of work. Finally it is accompanied by the

references.

17



Chapter: 3 Mathematical Back ground

_______________________________________________________________

It is essential to revise the basic mathematics and theory used behind the modal analysis and rotor

unbalance analysis for the sake of completeness of the report work. Since the modal analysis has

been performed using the finite element analysis method, hence the theoretical coverage of finite

element methods are also done in this chapter.

3.1 Finite element method

The finite element method is a numerical method like finite difference method but is more general

and powerful in its application to real-world problems that involve complicated physics, geometry

and/or boundary conditions. Finite element analysis is a way to simulate loading conditions on a

design and determine the design’s response to those conditions. The design is modeled using

discrete building blocks called elements. Each element has exact equations that describe how it

responds to a certain load. The sum of the response of all elements in the model gives the total

response of the design.

In the finite element method, a given domain is viewed as a collection of sub domains, and over

each sub domain the governing equation is approximated by any of the traditional variational

methods. The main reason behind seeking approximate solution on a collection of sample

polynomials. Of course, each individual segment of the solution should fit with its neighbours in

the sense that the function and possibly derivatives up to chosen order are continuous at the

connecting points.

18



3.1.1 Variational Methods

Variational methods provide a background for the development of finite element models. The

equation is put into an equivalent weighted integral form and then the approximate solution over

the domain is assumed be a linear combination of approximately chosen functions φ j and

undermined coefficient c j. We seek approximate solution in the form of ∑ c j φ j. Undetermined Coefficient c j

is then determined to satisfy the given equation. Rayleigh-Ritz, Galerkin, Least square methods

differs from each other in the choice of the integral form, weight functions and/or approximation

functions. The main limitation of classical variational methods that prevents them from being

competitive with traditional finite difference method is the difficulty encountered in constructing

approximate functions. Since the quality of the approximation is directly affected by the choice of

the approximation function. The construction process becomes more difficult when the domain is

geometrically complex. Finite element method over comes this disadvantage by providing a

systematic procedure for the derivation of approximation functions over sub region of the domain.

It is element wise application of Rayleigh-Ritz or weighted –residue method which is variational

method.

3.1.2 Need of Weighted-Integral Statement

In almost all approximate methods used to determine the solution of differential and/or integral

equation, we seek a solution in the form

n

u ( x ) = U n ( x ) = ∑c jφ j ( x)

j =1

Where u represents the solution of a particular differential equation and associated boundary

conditions, and Un is its approximation that is represented as a linear combination of unknown

19



parameter C j and known function φ j of position x in the domain Ω on which problem is posed. The

approximate solution U n is completely known only when C J are known. Thus it is desirable to find

a mean to determine C J such that U n satisfies the equation governing u. When the exact solution

cannot determine, the alternative is to find a solution U n that satisfying governing equation

approximately. Approximate solution does not produce sufficient number of equations to obtain

the value of undetermined coefficient c j. Hence weighted-integral statements are required in order

to generate the necessary and sufficient algebraic equations to solve for the parameter c j in the

approximate solution.

3.1.3 Rayleigh Ritz Method

In the Rayleigh-Ritz method, the coefficient C j of the approximation are determined using the

weak form of the problem, and hence, the choice of weight functions is restricted to the

approximation function w =ϕ j (w = u). Hence it places weaker continuity requirement on the

approximate solution that the original differential equation or its weighted- integral form. In

Rayleigh Ritz method we have following relation.

Weight function = Approximation function.

3.1.4 Sources of Error in a Finite Element Solution

In the finite element analysis, choice of the element type, number of elements and the density of

elements depends on the geometry of domain, problem to be analyzed and degree of accuracy

desired. No specific formula exits to get this information. Analysts are mostly guided by their

technical background, insight to the physics of the problem and their experience in finite element

20



modeling. There are three sources of error in the finite element solution, which are as follows:

(a) Those due to the approximation of the domain.

(b) Those due to the approximation of the solution.

(c) Those due to numerical computation (e.g., numerical integration and round off errors in a

computer).

The estimation of these errors, in general, is not a simple matter. However, under certain

conditions, they can be estimated for a given element and problem. The accuracy and

convergence of the finite element solution depends on the differential equation, its integral form,

and the number of element used. "Accuracy" refers to the difference between the exact solution

and the finite element solution, while “convergence” refers to the accuracy as the number of

elements in the mesh is increased

3.1.5 Steps in the Finite Element Solution of a Problem

a): Discretization of Domain: This is the first step in which the given domain is discretized into a

collection of pre selected finite elements. Steps in discretization are:

1. Construct the finite element mesh of pre selected element.

2. Number the nodes and elements.

3. Generate the geometric properties (e.g. co-ordinates) for the nodes of the problem.

b): Derivation of Element Equations: It involves the following steps:

1. Construct the weighted-residual or weak form of the differential equation.

2. Assume the form of the approximate solution over a typical finite element.

21



3. Derive the finite element equations by substituting the approximate solution into the

weighted residual or weak form.

c): Finite Element Model: The model can be developed for an arbitrary degree of interpolation.

Following Rayleigh-Ritz procedure and substitution of approximation function into the weak form

the required algebraic equations are obtained.

[k e ]U e = F e +Qe

The matrix k e is called as the coefficient matrix or stiffness matrix in the structural mechanics

application, which is symmetric. The column vector F e is the source vector or force vector in

structural mechanics problem. The column vectors U

e

and Fe called primary and secondary

element nodal degree of freedom.

d): Assembling: To obtain the finite element equation of the total problem, it is desirable to put

the elements back into their original positions. Connectivity of elements is the identification of

inter element continuity condition among the primary variables by relating element nodes to global

nodes i.e. last nodal value of the element is the same as the first nodal value of the adjacent

element second. Balancing of the secondary variable at the connecting nodes are done.

e): Imposition of boundary condition: After the assembly of different elements, the boundary

conditions imposed in the global matrix formed. This is done by identifying the specified global

primary degree of freedom and identifying the specified global secondary degree of freedom.

f): Solution: After imposing the boundary condition the global matrix is solved to get the value of

primary variable at different nodes.

g): Post processing of the Results: the solution of finite element gives the nodal values of the

22



primary unknown (e.g. displacement, velocity).Post processing of the results includes one or more

of the following.

1. Computation of an secondary variables e.g., the gradient, stress, heat transfer.

2. Interpretation of the results to check whether the solution makes sense (an understanding of the

physical process and experience are the guides when other solutions are not available for

comparison)

3. Tabular or graphical representation of results.

3.2 Modal Analysis Definition

When external forces act on a multi degree of freedom system, the system undergoes forced

vibration. For a system with n coupled ordinary differential equations of second order. The

solution of these equations become more complex when degree of freedom n is very largeor

when the forcing functions are no periodic. In such cases it is more convenient to use modal

analysis. Expansion theorem is used in the modal analysis and displacements of the masses are

expressed as linear combination of normal modes of the system. This linear transformation

uncouples the equations of motion so that we obtain a set of n uncoupled differential equations of

second order. The solution of these equations is equivalent to the solution of the equations of n

single degree of freedom systems, which can be readily obtained. The goal of modal analysis in

structural mechanics is to determine the natural mode shapes and frequencies of an object or

structure during free vibration. It is common to use the finite element method (FEM) to perform

this analysis because, like other calculations using the FEM, the object being analyzed can have

arbitrary shape and the results of the calculations are acceptable. The physical interpretation of the

eigenvalues and eigenvectors which come from solving the system are that they represent the

frequencies and corresponding mode shapes. Sometimes, the only desired modes are the lowest

23



frequencies because they can be the most prominent modes at which the object will vibrate,

dominating all the higher frequency modes.

3.3 Method of solution

The methodology presented here deals with the mathematical formulation of modal analysis

for forced vibration of undamped systems. The equation of motion of a multi degree of

freedom system with external excitation is given by:

(3.2.1)

Where F is the arbitrary external force vector. To solve the equation with the help of modal

analysis, it is necessary to first solve the eigenvalues problem.

i.e ω2[m]X=[k]X (3.2.2)

the above equation gives the natural frequencies ω1, ω2, ω3,....., ωn and the corresponding mode

shapes X1, X2, X3,........., Xn. According to the expansion theorem, the solution vector of

equation (3.2.2) can be expressed by a linear combination of the normal modes as:

x(t) = q1(t)X1 + q2(t)X2+ q3(t)X3+............+ qn(t)Xn (3.2.3)

Where q1(t), q2(t), q3(t) ....... qn(t) are the time dependent generalized coordinates or modal

participation coefficients. By defining a modal matrix,[X] in which the j th column is the vector

X j, i.e,

[X] = [[X] 1 [X] 2 [X] 3 ....... [X]n ] (3.2.4)

Equation (3.2.3) can be rewritten as:

x(t)=[X]q(t) (3.2.5)

24



Where,

q1 (t)

q2 (t)

q3 (t)

q (t) =

qn (t) (3.2.6)

Since [X] is not a function of time, from equation (3.2.5), we obtain

(t) = [X] (t)

Using equations (3.2.1) and (3.2.6) we can write equation as

[m][X] + [k] [X] q = F (3.2.7)

Per multiplying the complete equation by [X] T, we get

[X] T [m] [X] + [X] T [k] [X]q = [X] T F (3.2.8)

We know that the normal modes are normalized, i.e

[X] T [m] [X] = [ mr ] (3.2.9)

Where,

mr1 0 . . . 0

[ mr ] = 0 mr2 . . 0

. . 0

0 0 mrn (3.2.10)

And;

25



[X] T [m] [X] q = [ kr ] (3.2.11)

Where,

k r1 0 . . . 0

[ kr ] = 0 k r2 . . 0 (3.2.12)

. . 0

0 0 k rn

And

ωr =

(3.2.13)

by defining the vector of generalized force Q(t) associated with generalized coordinates q(t) we

have

Q (t) = [X] T F (t) (3.2.14)

Now the equation (3.3.8) can be expressed as:

(t) + [I] ω q (t) = Q (t) (3.2.15)

Where I is the unity matrix of order n x n and

=ω

(3.2.16)

Equation (3.2.15) denotes a set of n uncoupled differential equation of second order

26



r (t) + ωr qr (t) = Qr (t),

(3.2.17)

It can be seen that equation (3.2.17) has precisely the form for differential equation describing the

equation of motion for dumped single degree of freedom system. The solution can be expressed as:

(3.2.18)

r=1,2,3. . . . . n

The initial genralized displacements and the initial generalized velocities can be obtained from the

initial values of physical displacement and physical velocities as

(3.2.19)

Where;

(3.2.20)

(3.3.21)

(3.2.22)

Once the generalized displacements are found, using equation (3.2.18) and (3.2.19) the

physical displacements can be found with the help of equation (3.2.5)

3.3 Rotating Unbalance

27



In this article response of a damped system under rotating unbalance has been discussed with

suitable figure and mathematical equations. Unbalance in rotary machinery is one of the main

causes of vibration. Figure below shows a simplified model of such a machine. The total mass of

the machine is M, and there is one eccentric masses m in opposite directions with a constant

angular velocity ω. The centrifugal force due to this mass will cause excitation of the mass M. The

vertical components of excitation act along the vertical axis. If the angular position of the mass is

measured from a horizontal position, the total component of the excitation is always given by:

(3.3.1)

Fig 3.1: Rotating unbalance mass

The equation of motion can be derived by the usual procedure,

( (3.3.2)

This can be rearranged as:

(3.3.3)

28



The solution of this equation will be identical to the response of the damped system under

harmonic excitation. Solution can be expressed as:

(3.3.4)

And

φ = tan−1

cω

k −mω 2

(3.3.5)

Where X and Φ denotes the amplitude and phase angle of vibration.

By defining ωn = √(k/M), ξ = c/cc , cc = 2 Mωn and r=ω/ ωn, equation ( 3.3.4) and (3.3.5)

Can be rewritten in non dimensional form as:

(3.3.6)

And

φ = tan−

1 (2ξ r/ 1 −r 2) (3.3.7)

The variation of MX/me with r for different values of ξ is shown in Fig (3.2).

The following observations can be made from equation (3.3.6) and fig (3.2):

1. All the curves begin at zero amplitude. The amplitude near the resonance (ω = ω n) is markedly

affected by damping. Thus if the machine is to be run near resonance damping should be

introduced purposefully to avoid dangerous amplitudes.

29



Fig (3.2): variation of MX/me with r for different values of ξ

2. At very high speeds (ω large), MX/me is almost unity, and the effect of damping is

negligible.

3. For 0< < the maximum of MX /me occurs when,

(3.3.8)

The solution of above equation (3.3.8) gives

With the corresponding maximum value of given by:

Thus the peaks occur to the right of the resonance value of r = 1.

4. For , do not attain a maximum. Its value grows from 0 at r = 0 to 1 at r

Chapter: 4 Model Generation and Analysis

_______________________________________________________________

30



This chapter describes modeling and analysis of the air separator fan assemblies. The computer

aided solid model generation of the assembly has been done from the detail drawings available.

The modal analysis has been performed to find out the natural frequencies and mode shapes. The

chapter also includes one sample unbalance analysis based on mathematical assumptions.

4.1 Solid Model Generation

For modal analysis and unbalance analysis of the raw mill separator fan assembly, the computer

aided model has been generated. Pro/ENGINEER Wildfire 4 has been used as modeling software

which is developed by Parametric Technology Corporation. It is a powerful program used to create

complex design with a great precision. The design intent of any 3D model or an assembly is

defined by its specification and its use. It is a parametric feature based solid modeling tool and it

not only unites the 3D parametric feature with 2D tools but also addresses every design through

manufacturing process. The bidirectional associative nature of this software ensures that any

modification made in the model is automatically reflected in the drawing views and any

modification made in the dimensions in drawings views automatically updates the model.

The main parts of the raw mill separator unit can be grouped into following;

(a) Main fan assembly

(b) Auxiliary fan assembly

(c) Housing

(d) Supporting Frame

The solid model has been generated from the drawing available.

31



4.1.1 Main Fan Assembly

The Main fan assembly comprises of 14 components. The table 4.1 gives the path and its

quantities:

Table 4.1: Components in main fan assembly

Part No. Description No. of Components

1 Top Shroud 1

2 Bottom Shroud 1

3 Main Fan Hub 1

4 Fan Blade 8

5 Wear Plate 32

6 M18 Hex Nut 4567 M16 Spring Washer 464

8 M16×50LG CSK HD. Screw 104

9 M16×40LGCSK HD Screw 352

10 M20 spring Washer 80

11 M20×55LG HEX HD. screw 80

12 M16×50LG HEX HD Screw 8

13 M30×125LG CAP SCREW 12

14 M30 Spring Washer

Out of all these parts, only parts no. 1 to 5 is important from analysis point of view. Though it is

possible to model the assembly using all these components but the bulky number of the nuts and

bolts will simply increase the complexity of the model when it is used for the finite

element analysis. Figures 4.1-4.6 describes the component outlook and assembly.

32



Fig.4.1 Top shroud fig 4.2 Bottom shroud

Fig 4.3 Fan Blade fig 4.4 Wear Plate

Fig 4.5 Hub

33



Fig 4.6: Main Fan Assembly View

4.1.2 Auxiliary Fan Assembly

Auxiliary fan assembly comprises of 9 components. The table 4.2 gives insight to their names, and

number of quantities:

Table 4.2 Components in auxiliary fan assembly

Part No. Description No. of Components

1 PL.6.THK 2

2 RIB PL. 12 THK 4

3 RIB PL. 12 THK 2

4 PL.6.THK 48

5 PIPE 48.6 O/D 24

6 PIPE 42O/D 4

7 HEX HD Bolt M20×90LG 4

8 HEX Nut M20 4

9 Washer A21 28

34



In auxiliary fan assembly, the nuts, bolts, and the pipes are not modeled as they will increase the

as they will increase the number of contacts and the complexity of the system substantially.

Following figures 4.7 to 4.14 describes the component and assembly outlook:

Fig 4.7: part 1 Fig 4.8: part 2

Fig 4.9: part 3 Fig4.10: part 4

35



Fig 4.11: part 5 Fig 4.12: part 6

Fig 4.13: Auxiliary Fan Assembly View

Fig 4.14: Main and Auxiliary Fan Assemblies Mounted on Shaft

4.1.3 Housing and Supporting Frame

Housing for the raw mill air separator fan assemblies is a cylindrical casing which is fixed on the

supporting frame made of reinforced concrete. Basically the fan assembly lies on third floor of the

36



whole building. The supporting frame has been modeled as a frame having the same height and

intermediate trusses of rectangular cross sections. The cross section dimensions and the heights of

their location have been abstracted from the main drawing sheet of building. Main shaft carries the

main and auxiliary fan assemblies inside the housing. Here one view of the modeled housing

attached with the frame is shown in fig 4.15:

Fig 4.15: Housing with supporting Frame

The above figures 4.15 demonstrate the components of the fan assemblies and frame with housing.

It is difficult to show all the dimensions of the component on the above figures.

The original copy of the drawings has been provided by plant.

4.2 Modal Analysis

A modal analysis determines the vibration characteristics (natural frequencies and mode shapes)

of a structure or a machine component. It can also serve as a starting point for another, more

37



detailed, dynamic analysis, such as a transient dynamic analysis, a harmonic response analysis,

or a spectrum analysis. The natural frequencies and mode shapes are important parameters in the

design of a structure for dynamic loading conditions. The modal analysis of the current model

has been performed using ANSYS-11 workbench software. ANSYS is general purpose finite

element analysis (FEA) software and is widely used. The basis of FEA relies on the

decomposition of the domain into a finite number of sub domains (elements) for which the

systematic approximate solution is constructed by applying the variational or weighted residual

method. In effect, FEA reduces the problem to that of a finite number of unknowns by dividing

the domain into elements and by expressing the unknown field variable in terms of assumed

approximating functions within each element. These functions are defined in terms of the values

of the field variables at specific points, referred to as nodes. The finite element analysis method

requires the following major steps:

1. Discretization of the domain into a finite number of sub domains.

2. Selection of interpolation functions

3. Development of the element matrix for the sub domain

4. Assembly of the element matrices for each sub domain to obtain the global matrix for the

entire domain

5. Imposition of the boundary condition

38



6. Solution of the equations

7. Additional computations if required

In following pages, the modal analysis steps for the separator fan assemblies have been discussed

with figures, which are followed by results. The main contents of the modal analysis can be

summarized in following points:

4.2.1 Model

The solid model is first brought to the ANSYS working window. This is done by having an

interface between the modeling software Pro/ENGINEER and the analysis software ANSYS

workbench. The interface allows updating the model from CAD software working window in

continuation with ANSYS without changing the CAD model into IGES or other supporting files.

The working unit for the FEA has been kept consistent as:

Table 4.3: UnitsUnit System Metric (mm, kg, N, °C, s, mV, mA)

Angle Degrees

Rotational Velocity rad/s

39



Fig 4.16: Model View in ANSYS Window

Though the fan assemblies are not visible because of the housing over them, it can be seen from

different angle in figure 4.17.

Fig 4.17: View into Housing: Insight to Fan Assemblies

4.2.2 Material Properties

The material data has been provided to the software from user input. As the most of the

components are made of mild steel except the supporting frame, mild steel has been used s the

40



common material for the assembly. Though for the supporting frame, the equivalent properties of

the reinforced concrete has been used. Also, as the analysis does not include the stress analysis,

only the young’s modulus of elasticity, density and poison’s ratio are the sufficient material

properties for the analysis. Following table gives the data.

Table 4.4: Material Data

Mild Steel

Young's Modulus 2.1e+005 MPa

Poisson's Ratio 0.29

Density 7.8e-009 tonnes/mm³

Reinforced Concrete

Young's Modulus27560 MPa

Poisson's Ratio 0.20

Density 2.5e-009 tonnes/mm³

4.3.3: Contact definition

All the contact has been formulated as bonded except that of between main shaft that of between

41



main shaft and housing. Though in real system, the shaft is fitted into suitable bearings, here

bearing has not been modeled because of the lack of data. Instead, the contact between the shaft

and housing has been defined as frictionless. Since the tolerance is very low, it is assumed that

contact is sufficiently enough to cause the force transfer from shaft and fan assemblies to that of

housing and frame. At the same time it provides rotational degree of freedom to the shaft.

Following figures gives insight to the defined contacts.

4.3.4 Mesh

42



Meshing of the model is done using meshing software; hyper mesh gives the fine mesh and

meshing of compliticated shapes are done easily and it is a fast meshing tool.

4.3.5 Boundary Conditions

The boundary conditions application is the specification of the end conditions. The shaft is retaine

to move along its axis. It has already got rotational degree of freedom in contact definition. Since

the supporting frames are rigidly fixed to the ground floor foundations, they are modeled as fixed

in space. Thus the four bottom faces are fixed in space i.e they are provided with the zero degree of

freedom.

4.3.6 Analysis Setting

Analysis setting is the step where the things like number of mode shape and natural frequencies to

be abstracted, solver method and output control are decided. The mode shapes corresponding to

these natural frequencies have also been calculated. The software uses block Laconze solver tool to

converge the results. The mode shapes have been normalized with respect to the mass matrix by

the software.

4.3.7 Solution

The modal analysis has been performed for the model with above mentioned conditions. The

solution for the initial 20 fundamental frequencies is given in table 4.5. Few frequencies lie very

closer to each other whereas others are clearly distinct. It is evident from the results that the tall

structures and large machineries are of low natural frequencies.

4.3.8 Mode shapes

Corresponding to each natural frequency, there exits one unique mode shape. Mode shape is

defined as the mode of the system when each part of system vibrates with the same natural

frequencies. Consequently there are deformations of the system parts. Following table gives the

43



maximum and minimum deformation of the system model and their locations. Initial 6 mode

shapes have been shown in figure 4.24 to give the insight to the system response under free

vibration at corresponding natural frequencies. The red zone indicates the maximum deformation

while the blue is the minimum deformation zone.

Table 4.5 First 20 natural frequencies of fan assembly

ModeFrequencies,Hz

1 02 03 2.21E-044 2.85415 5.94196 6.00137 6.01998 6.029 7.2166

10 7.228911 7.258312 7.2971

13 7.386414 7.451915 7.484416 7.53417 7.981418 8.825719 10.12220 10.125

44



45



Fin 4.18 First Six modes of vibration of fan assembly

Chapter: 5 Erosive Wear Test

It has been discussed in the problem definition of chapter 1 that the root cause of the unbalance in

the rotating fan assemblies of air separator unit is the non uniform erosive wear loss of the fan

blade material. As the dynamic balancing of the separator fan assemblies have not helped to

control the vibration problem of separator unit building as suggested by plant, the root cause of

unbalance has been looked into in terms of non uniform wear loss of fan blade material. This non

uniformity lies in the fact that the erodent particles in the cement are of different particle size and

shape.

Their angle of impingement on the fan blade is also of varying nature. At the same time speed of

the impact of erodent particles are also varying because of their varying mass. Thus it is evident

that wear loss of fan blade material is non uniform in nature. The mathematical model for

prediction of wear loss for different set of erodent and base substrate has been developed over time

by researchers which take into account of many parameters like hardness of base substrate,

coefficient of restitution and energy exchanges between the erodent particle and base substrate.

Here, in present work, rather than modeling of wear loss of fan blade material, one experimental

work has been performed to show that there is a considerable improvement of wear resistance of

the base metal (mild steel) when it is coated with some hard material. The whole experiment can

be summarized in following steps:

(d) Material selection

(e) Development of coated surface

46



(f) Sample preparation

(g) Erosive wear test

(h) Erosive wear test results

5.1: Material Selection

Overlay coatings are mostly used to change an existing wear situation from a destructive to a

permissible type. Correct selection of wear resistant materials can cut downtime and

considerably reduce maintenance costs. In past, much work has been done on wear test of coated

surface. Earlier trials showed that heat treatment of blade steel has only marginal effect on

erosion resistance and that it is justifiable to use steels of higher hardness in a normalized

condition. Another potential method of increasing durability of components subject to this type

of wear is an application of hard facings to protect the surface. Researchers have tried different

materials and different coating methods to develop the coated surface. Based on the literature

available and the ease of use we have selected the Chromium Boride as coating material. It is

available in the market as the commercial name of Super fuse 123. It is a wear resistant paste

alloy based on ultra hard chromium boride crystals. It is the most abrasion/erosion resistance

material for anti wear applications. Due to high hardness and needle like microstructure, thin

overlay of super fuse 123 gives outstanding resistance to abrasion and fine particle erosion. The

base metal i.e. the substrate is of mild steel. To perform the solid particle erosive wear test,

Alumina has been selected as an erodent as it is the main erodent constituent of the cement

powder. Table 5.1 gives the complete list of materials used.

47



Table 5.1: List of Materials

Description Material Remark

Substrate ( Base Metal) Mild Steel Hardness: 10-15 HRC

Coating Material Chromium Boride (Super fuse 123) Hardness: 67-71 HRC

Erodent Alumina (Al2O3) Size: 50 Micron

5.2: Development of Coated Surface

The coated surface was developed according to the guidelines provided in the user specification.

The coating material was in paste form which was put on one long mild steel plate which is 5

mm thick. The thickness of the coating was kept 1 mm. The surface cleanness was kept in mind

to keep it dust or oil free which was achieved by polishing of the surface. After the paste was put

over the base plate, it was allowed to dry completely in air which took 1 hour. To fuse the coated

material into the base plate, thermal spray of carburizing flame (oxyacetylene process) was

applied over the coated surface. Movement of flame along was kept at a rate sufficient to keep

the sweating ahead of flame.

5.3: Sample Preparation

48



The wear test has been performed on erosive wear tester in laboratory, which can accommodate

one sample of size 25×25mm with 5mm thickness. So the samples of appropriate size were

prepared to carry out the experiment. The coated surface becomes very hard and is difficult to cut

by simple means. The Wire EDM method was used to cut the samples. The wire EDM setup is a

very high precision machine which cut the sample with good tolerance. After the samples were cut,

they were polished on the coated surface side to make the surface flat and smooth. Following

figures gives insight to the sample outlook.

Samples of size 25×25mm

Fig 5.1: Uncoated samples before wear test

Polished Coated Surface

49



Coating at Edges

Fig 5.2: Coated samples before wear test in polished condition

5.4: Erosive Wear Test

The test has been performed on Air Jet Erosion Tester- TR470. It is a setup which provides with

basic arrangement of sample holding in a chamber where the erodent particles are made to impact

at high speed at a particular angle. The tester has facility to change the discharge rate of erodent

and their speed of impingement over samples. The angle of impingement may also be changed.

The air jet pressure is maintained by a parallel compressor running beside the tester. The erodent is

feed through a separate chamber. The air jet and erodent are mixed in a nozzle shaped torch and

comes out through small orifice which is pointed over the sample. Following figure gives the

insight to the tester setup:

Erodent Supply

Control Part

Power Unit

Sample Holding Chamber

50



Fig 5.3: Air jet erosion tester setup

51



Wear Tester Air Jet and

Erodent Supply

Compressor

Sample Holder

Fig 5.4: Different Views of Air Jet Erosion Tester

Following steps were carried in performing the test.

1. The samples weight was taken on digital weighing machine (accurate up to 0.0001g).

2. The sample was held on holder and the chamber was locked.

3. Power was switched to on. Air jet pressure, erodent discharge rate and speed of

impingement were set. The time for wear was also set.

4. After the test again the weight of sample was taken to find out the wear loss.

Following parameters are relevant to the current test performed:



1. Jet Velocity: 20 m/sec

2. Air Jet Pressure: 2Kg/cm2

3. Angle of Impact: 30 degree

4. Number of Samples Tested: 8

5. Time Unit: Minute

6. Erodent Discharge Unit: gm/minute

5.5: Erosive wear test results

The test has been conducted using 8 samples. They are from two classes, one is from uncoated

samples and another one is from coated samples. The test is done for two time steps of 10

minutes and 15 minutes, at two discharge rate of erodent as 10 gm/minute and 20 gm/minute.

The anti wear resistance has been shown in terms of wear loss of material in gm. Following table

gives the complete detail about the input conditions and weight of samples before and after the

wear test:

Table 5.2: Uncoated sample tests data

S.N. Erodent Feed Time of Test Weight before Weight after Weight LossRate (minute) Test (gm) test (gm) (gm)

(gm/min)

1 10 10 24.805 24.713 0.092

2 10 15 24.699 24.580 0.119

3 20 10 24.432 24.302 0.130

4 20 15 24.728 24.572 0.156



Table 5.3: Coated sample tests data

S.N. Erodent Feed Rate Time of Test Weight before Weight after Weight Loss

(gm/min) (minute) Test (gm) test (gm) (gm)

1 10 10 20.490 20.463 0.027

2 10 15 22.166 22.120 0.046

3 20 10 19.187 19.140 0.047

4 20 15 22.071 22.005 0.066

From table results it is evident that for same input conditions, the wear loss of coated samples is

greatly reduced in comparison to that of uncoated surface. Though the real damaged surface can be

seen at microstructure level using electron scanning microscope (ESM Test), still it can be seen in

following figures that the surface damage after wear test is less for coated material than that of

uncoated material.



Coated samples

Worn out region

Uncoated samples

Fig 5.5: Surface damage view of coated and uncoated samples



Based on the data obtained from wear test of coated and uncoated samples, following plots are

made which indicates the behaviour of wear loss:

W e i g h t l o s s [ g ]

0.14

0.12

0.1

0.08

clad substrate

0.06

0.04

0.02

0

10 15Test duration [min]

Fig 5.6: wear loss as a function of test duration at a discharge rate of 10 gm/min

W e i g h t l o s s [ g ]

0.2

0.18

0.16

0.14

0.12

0.1

0.08 clad substrate0.06

0.04

0.02

0

10 15

Test duration [min]

Fig 5.7: test duration at a discharge rate of 20 gm/min



It is evident from plots that the wear loss for substrate is more than the clad i.e. coated

sample. Also the increased discharge rate causes more wear loss of material. The longer

testing time gives increased wear loss of material. In the figure 5.8, the combined behaviour

of the wear resistance in terms of amount of wear loss (gm) is described.

0.2

0.18

clad

substrate

0.1620gm/min

[ g ] 0.14

10 gm/min

0.12

l o s s

0.1

W e i g h t

0.08

0.06

0.04

0.02

010 15 10 15

Test duration [min]

Fig 5.8: Comparative wear behavior clad (coated) surface and substrate (uncoated)

Wear results are summarized as under:

1. The wear resistance of coated surface is greatly improved in comparison to

uncoated surface. It is due to the hardness of coated material.

2. The increased discharge rate increases the wear loss as more erodent particle hit the

target surface per unit time.

57



3. The wear loss from coated surface is reduced almost 3-4 folds compared to that of

uncoated surface.

Thus it is concluded that the super fuse 123 is a good anti wear coating material and can be

used for anti wear applications. Application of such coatings would reduce the wear rate from

surface blades of separator fan in cement plants where most wear is caused by alumina

present in cement (4-5%). Reduced wear rate would delay the imbalances of separator fan

assembly and related vibrations associated problems. More analysis of the surface damage

behaviour is to be done by ESM (Electron Scanning Microscope) testing.

58



Chapter 6 Conclusion and Future Scope of Work

____________________________________________________________

In this work attempt is made to model the air separator fan assemblies of raw mill air

separator unit used in cement plants. The computer aided solid model generation has been

done successfully based on the realistic data provided by plant in form of detail drawings and

other related parameters. The finite element analysis software has been used to do the modal

analysis of the separator unit. The initial 20 fundamental frequencies of the separator unit

have been found out. The attempt has been made to model the unbalance in the fan assembly

of separator unit and its effect has been analyzed successfully in terms of vibration response

of separator housing. The erosive wear test has been performed successfully to control the

wear loss of fan blade.

6.1: Conclusions

Following are the conclusions arrived at from the results obtained from the modal analysis,

rotating unbalance analysis and wear test experiments:

1. The root cause of the vibration of separator unit is the non uniform material loss from

fan blade due to erosive wear.

2. The separator unit’s initial fundamental frequencies are quite low. In mode shape

behavior it is observed that at low frequencies the top of the unit is more deformed.

3. Separator unit runs in the range of fundamental natural frequency which may cause

59



damage to the unit.

4. The effect of unbalance is severe for the housing and supporting frame of the unit.

5. The wear test over coated surface and uncoated surface reveals improved wear

characteristics of coated surface which may be attributed to the hardness of the coating

material.

6. In sample experiment on erosive wear test, it has been observed that the wear loss

from coated surface is reduced 3-4 times than that of uncoated surface. It may thus be

recommended to use the coated material for fan blade to control the erosive wear loss.

6.2 Future Scope

The wear loss in fan blade material of air separator unit is a continuous process which cannot

be eliminated completely because the source of the erodent particle is the raw material itself.

Though the use of coating materials will help in reducing the material loss which in turn will

lead to longer running time for fan assemblies, still there must be other provisions to reduce

the vibration of the separator housing and supporting frame. One such method may be the

design of tuned mass liquid dampers which will absorb the vibration. To design such dampers

it is essential to know the extreme case of vibration caused in separator unit because of

rotating unbalance. The following things are proposed for future scope of the work:

1. To analyze the system vibration response for extreme case of unbalance. This can be

done by considering more realistic data related to the separator unit and real environment

boundary conditions.

60



2. To design appropriate dampers to reduce the vibration of separator unit. One such damper

may be tuned mass liquid damper which is used to reduce the vibration of tall structures and

buildings.

References

1. Hakan Benzer, “Modeling and simulation of a fully air swept ball mill in a raw material

grinding circuit”, Powder Technology 150 (2005) pp.145– 154

2. Petr J.Blau, “Fifty years of research on wear of metals”, Tribology International, vol- 30,

no-5, pp 321-331(1997)

3. H G Midgley, “The composition of pleochroite in high alumina cement clinker”, Cement

and Concrete Research. Vol. 9, pp. 623-630, (1979).

4. C.-W. LEE AND Y.-G. JEI, “Modal analysis of continuous rotor-bearing systems”,

Journal of Sound and Vibration (1988) 126(2), 345-361

5. H. IRRETIER, “Mathematical foundations of experimental modal analysis in rotor

dynamics”, Mechanical Systems and Signal Processing (1999) 13(2), pp.183-191

6. I. Bucher and D. J. Ewins, “Modal analysis and testing of rotating structures”,

10.1098/rsta.2000.0714

7. Andy C.C. Tan, Gregory D. Paterson, Joseph Mathew & Matthew Dunbabin,

“Visualization of vibration mode shapes to assist students in the learning of mechanical

Vibrations”, World Transactions on Engineering and Technology Education, 2002 UICEE

Vol.1, No.1, 2002

8. J. S. Rao and R. Sreenivas, “Dynamics of Asymmetric Rotors using Solid Models”,

Proceedings of the International Gas Turbine Congress 2003 Tokyo,November 2-7, 2003

61



9. Hong Hee Yooa, Jung Min Kimb, Jintai Chungc, “Equilibrium and modal analyses of

rotating multi beam structures employing multiple reference frames”, Journal of Sound and

Vibration 302 (2007) pp.789–805

10. R. Pintelona, B. Peetersb, P. Guillaumec, “Continuous-time operational modal analysis in

the presence of harmonic disturbances”,Mechanical Systems and Signal Processing 22 (2008)

pp.1017–1035

11. Y.S. Chen, Y.D. Cheng, J.J. Liao, C.C. Chiou, “Development of a finite element solution

module for the analysis of the dynamic behavior and balancing effects of an induction motor

system”, Finite Elements in Analysis and Design 44 (2008) 483 – 492

12. L.-M. Berger, S. Saaro , T. Naumann , M. Wiener , V. Weihnacht , S. Thiele , J.

Suchánek “Microstructure and properties of HVOF-sprayed chromium alloyed WC–Co and

WC–Ni coatings”, Surface & Coatings Technology 202 (2008) pp. 4417–4421

13. Tadeusz Hejwowski, “Erosive and abrasive wear resistance of overlay coatings’, Vacuum

xxx (2008) 1–5

14. Sham Tickoo, “Pro/Engineer wildfire for engineers and designers, release 2”, Dreamtech

press, New Delhi, 2005

12 ballroll mill

Documents