case study regarding the chain excavator- i.popescu and co

8/6/2019 Case Study Regarding the Chain Excavator- I.popescu and Co.

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CASE STUDY REGARDING THE CHAINEXCAVATOR

Ionel Popescu1, Radu Mihai Negr iu2, Cr istinel Besleaga2, Sor in George

Badea2, Mihai Stef anescu2

1Industrial Biogas Solutions, Rokura Group, Bucharest, Romania

2Econet Prod Bucharest, Romania

1

[email protected];

2

[email protected];

2

cr [email protected]

Abstract: The chain excavator is the main technological part of a cleaning machine which is used for technological oper ation of maintenance of the r ailway. The

purposes of his su bassem bly are to excavate the crushed stone (ballast) from the

r ailway, under the sleeper and to tr ansport of this to the screen where will be

cleaned, sorted and reused. The chain excavator is loaded to bending, abr asive wear ,

shock , tension and another stresses. Due of these stresses, the chain excavator has

defects like fr actures, f atigue, wear and another. These defects can lead to a

dangerous malfunction, defects or immo bilizations of the cleaning machine with

dangers (r isks) for safety work and important loses of productivity and value. In this pa per we will establish and present the stress system, the wear zones and some

defects and fr actures of elements which compound the chain excavator. Another important novelty will be analyze with FEM using CAD some extreme cases by stresses and the compar ison the conclusions of this analyze with exper imental

conclusions in situ. Effects of some type of usual defects are analyzed.

Key words: chain excavator , cleaning r ailway machine, stresses, fr acture, f atigue, wear ,

FEM, CAD.

1. INTRODUCTION

The technical conditions for exploiting the r ailway in utmost safety and



comfort, require a certain constructive structure of pr ism from ballast (crushed stone), which must have elasticity and permeability qualities (Fig.1,

pos. 1, 2, 3). Also, the r ail- sleeper system must have certain geometry

(dimensions, sha pes, positions) not only in the tr ansversal section, but also in the longitudinal one.

Figure 1.Tr ansversal section of the r ailway: 1- soil; 2- under lairs of sand and

gr avel; 3- ballast (crushed stone); 4- sleeper; 5- r ail (the main wire); 6- protection

panel with multi ple roles ( phonic, safety); s- super elevation

The crushed stone starts to degr ade because of physical and natur al

phenomena, leading to the clogging and contamination of the crushed stone

pr ism. Some of these phenomena are: the fr iction between the surf ace and

the edges of the crushed stones, under the effects of loadings and

displacements, which leads to the a ppear ance of wear particles; the var iation

in temper ature between the natur al cycles of freezing and thawing, whichleads to the cr ack ing and break ing (shredding) of the stones; the depositing

of solid particles which are in suspension in the air or the leak ing of

mater ials from the wagons; the humidity and preci pitations under the form of

r ain and snow which lead to washing, displacement, depositing and

concentr ation of small and f ine particles in clogging phenomenon and s.a.

The contamination or clogging of the crushed stone pr ism over a certain

clogging degree (>30%) has unf avor able/unwanted effects over the r ailway

properties.

Through the mechanical oper ations of screening of the crushed stone and

the removal of waste from the crushed stone pr ism the elasticity and



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permeability qualities are reestablished, o btaining important technical and

economical advantages [1]. The technological oper ation by cleaning of the ballast¶ pr ism is made by

the ballast cleaning machine. The chain excavator takes the ballast bed

mater ial from the tr ack. In f igure 2 is presented a cleaning r ailway machine.

This type of the excavation chain uses f ive exchangeable scr a per f ingers.

The chain links are made of high-alloy steel (Fig. 3).

Figure 2.Ballast cleaning machine

Figure 3.Chain excavator

The high-alloy steel is made from 120Mn12 or TMn13. The main



char acter istics are: C= 1,25-1,40%; Mn= 12,5-14,5%; S= 0,50-1,10%; Cr =max.1%; Ni= max.0,50%; P= max.0,11%; S=max.0,05%; c = 250- 400

[N/mm2]; r = 800- 1000 [N/mm2]; A5 = 40- 55%; Z= 35- 40%; KCU 30/2=

20- 30; 180- 220 [HB].

2. ANALYZE OF THE BEHAVIOR OF THEELEMENTS OF THE CHAIN

To perform this analysis we used data gathered from maintenance

activities for 5 years where were used 6 ballast cleaning machine and were reconditioned 1000 km of r ailway.

In gener al, in normal conditions, in the ballast there are no foreign

o bjects and waste deposits. In these conditions, the stress that is produced in

elements from the chain is not harmful to the chain integr ity. From the analysis of the way the deter ior ation of the chain¶s elements

occurred, resulted the following:

a. In the contact zone between the surf aces of the chain¶s elements with

the ballast pr ism, the stones forming the ³wall´ behind the chain excavator have a wear-like action on the metallic elements of the chain which is in

motion. If the contact between the metallic elements and the stone is made through a corner or a sharp edge, in f avor able stress conditions, a cutting type phenomenon occurs, that leads to the removal of a portion of the metal.

This removal of metallic mater ial will produce a scr atch, whose dimensions

will depend on sever al f actors (Fig. 4). The scr atch may act like a tension accumulator , with corresponding consequences on the maximum tension

state of the analyzed area, or it may contain a cr ack/micro cr ack. In the inter ior of the scr atch, it is possible that micro cr acks may exist which in f avor able conditions can evolve over time. The wear phenomenon has been

previously studied by the authors [2-5].

b. If the contact takes place on larger surf aces and is smaller in intensity then a normal wear phenomenon occurs (Fig.5), which reduces over time the dimensions of the metallic elements that form the chain (Fig.10).

c. Wear can also a ppear at the contact between the metallic elements that

form the chain. In this type of joint, the dust (dry or wet), in the beginning having the dimensions of a very small particle, enters in between the moving

elements (Fig.5, 6, 7). Dur ing the movement time, the wear phenomenon increases the space between moving elements so larger rock particle may enter. In this way, the wear phenomenon continues f aster and f aster.



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Figure 4.Wear of the elements of the chain by micro cutting

Figure 5. Normal wear of the elements of the chain, on the contact surf aces (sliding)



Figure 6.The chain excavator where there are deposits of particles that f avor wear

Figure 7.The chain excavator where there are deposits of particles that f avor wear

d. Wear at the corner of scr a pers. The scr a pers have a conic sha pe with acorner at the end. The contact between the scr a pers and the crushed stone

produces wear , which leads to the increasing of the corner¶s r adius (Fig.8).



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Figure 8.Wear of the scr a pers

e. Fr acture of the metallic elements of the chain. This phenomenon has

been o bser ved in the connecting chain links and scr a per shovels, also. (Fig. 9, 10).

Figure 9.Fr acture of elements of the chain (connecting chain links)



Figure 10.Fr acture of elements of the chain (scr a per shovel)

In gener al, the major ity of fr actures occur in the bolt assem bling area.

From analyzing the fr actures, we o bser ved:

- the fr actures occur in the case of a overloads determined by foreign

elements in the ballast or by stones from the ballast which are united (³glued

together´ or clogging) by dust mixed with water , oil and s.a.;

- the fr actures a ppeared only in areas of high wear in the presence of

concentr ators leading to the decreasing of dimensions in the assem bling bolt

areas (Fig.4, 5 and 10);

- when the fr acture didn¶t occur in an area with high wear , the structure of

the mater ial was analyzed and we noticed structure defects in the mater ial

(Fig. 9);

- the fr acture does not occur in normal functioning conditions;

- the wear is at an acceptable level in normal functioning conditions.



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3. THE ANALISES WITH FINITE ELEMENTS

Two situations where analyzed: the normal functioning situation

(cha p.3.1.); the overload situation, in the case where the overload acts in the

least f avor able position (cha p.3.2.).

The chain was modeled using the AutoDesk Inventor progr am. There where

modeled 2 connecting chain links, one scarper shovel, two bolts and f ive scr a pers. In the modeling, we neglected the constructive details and the

ser ies of design elements that did not contr ibute neither to the increase nor

the decrease of the equivalent tensions which do not influence the stress

state, these being considered to have only a technological role. We also

neglected the connecting r adius from the model [6, 7]. Because the

maximum equivalent tensions are not in these areas, this a pproximation does

not lead to errors in the simulation. The design was a pproached in this way

because any additional surf ace in the model leads to a bigger num ber of

f inite elements. A big num ber of f inite elements require an un justif ied

consumption of resources dur ing the simulation. The model used in the

simulation is descr ibed in Fig.11, 12.

Figure 11.Modeling of the elements of chain excavator



Figure 12.Meshing of the elements of chain excavator

The simulation of the stress states using the f inite element method was realized using the Ansys Work bench 12, Academic version. A f ine mesh

(Fig.12) was used with the ref ining of the areas of interest. Over 1000000

f inite elements where used.

3.1. THE NORMAL FUNCTIONING SITUATION

In the normal functioning situation the stress was considered a pulsating stress. In this simulation we determined the maximum equivalent tensions

and the estimated functioning life span, expressed in num ber of cycles. The

o btained results for the equivalent tensions are descr ibed in Fig.13 and 14. In Fig. 15 and 16, the life spans are descr ibed, expressed in num ber of cycles.



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Figure 13.The equivalent stress state (von Mises) in the elements of the chain

Figure 14.The equivalent stress state (von Mises) in connecting chain link



Figure 15.The life spans of the scr a per shovel

Figure 16.The life spans of the connecting chain link



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3.2. THE OVERLOAD FUNCTIONING SITUATION

The overloads are produced by foreign bodies which may be found in the ballast pr ism. In these simulations we determined the equivalent tensions. It

is considered in this situation that the movement of the scr a per shovel is

stopped. This constr ain was a pplied to the f arthest scr a per. In Fig. 17 and 18,

the maximum equivalent tensions are descr ibed not only in the entire chain but also in its components (scr a per shovels and connecting chain links).

Figure 17.The equivalent stress state (von Mises) in the elements of the chain

Figure 18.The equivalent stress state (von Mises) in connecting chain link



4. CONCLUSIONS

After analyzing the ways of deter ior ation and the simulations that have

been realized, it can be concluded:

The main deter ior ation is caused by wear. Dur ing normal functioning,

the tension state is not dangerous. It can become dangerous if the wear of the

bodies reaches a cr itical value and if mater ial (structure) defects are present in the cr itical area. The life span, expressed in num ber of cycles, is very big,

with the exception of a very small area from the assem bling zone between

connecting chain link and bolt. A relative small rounding of this area

removes the possibility of cr acks a ppear ing over time.

At overload, the tension state may become cr itical in the case of repeated

high stresses and the presence of wears and structure defects of the mater ial.

It must be mentioned that the maximum stresses can be repeated for different

values. More stresses repeated by smaller values that the maximum

overload, can lead to fr acture by accumulating of deter ior ations. The plating of the areas that are load to strong wear phenomena withmater ials that have a high resistance to wear can be a solution, especially for

the scr a per shovel.

REFERENCES

[1]. Helmut Misar , Cr iter ia for cost-effective ballast cleaning: machine

design consider ations, Rail Engineering International Edition, num ber 4, pp.

11-16, 2005;

[2]. Cr. Besleaga, Contr ibutions regar ding the increase of the lastingness

of tamping tools, doctor ate thesis, 625.144.5(043-2876) B-UP 1, Bucharest,

2006;

[3]. S. G. Badea, R easearch regar ding the compar ative study of the

lastingness of tamping tools, doctor ate thesis, Polytechnic University of

Bucharest, 2010;

[4]. C. Beleag, I.C. Popescu, R .M. Negr iu, S.G. Badea, Study case -

tamping tools with the reinforcement by tungsten car bide at the tine,

Tehnologia inovativa ± ÄConstrucia de maini´ Review, nr. 2-3 /2009, p.5-

10, ISSN 0573 ± 7419;

[5]. Cr istinel Besleaga, Radu Mihai Negr iu,Ionel Popescu, Sor in George

Badea, Case study regar ding the tamping tool type BNR I 85, New Trends in

Fatigue and Fracture Congress- NT2F10, 30/08 ± 01/09/2010, Metz ±

Fr ance;



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[6] I.C. Popescu, Introduction in computer aided analysis of the process

equi pments, Printech Publisher , ISBN 973- 652- 951- 7, Bucharest, 2004;

[7] I.C. Popescu, T. Pr isecaru, B. Finite elements Analysis of Pressure

Equi pment, Computer Aided Engineer ing Solutions for Design, Analysis and

Innovation, (ANSYS & FLUENT User Group Meeting), Sinaia, 26-27 A pr ilie

2007

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