Potential Methods for Limiting the Consumption of Machine Components Exposed to Abrasive Wear

Abstract

The analysis of the behavior in exploitation of the extraction, transportation and utilization of hard rock type mineral substances proved that one of the most extended and aggressive forms of wear is abrasive wear. The effects of abrasive wear on the machine components and their economic implications are significant, especially due to the operational pauses coming up in the technological flows that serve specific activities. This study presents two ways of limiting the consumption of tamping tools for the railway machines that are submitted to abrasive wear, namely, by reconditioning with the help of electrodes for overlaying welding with alloys of preestablished characteristics; by executing cast cleats from composite material in which metal carbides were infiltrated by diffusion. The great number of cast cleats tested in exploitation allowed a reliability and maintainability analysis to be made using the Weibull++ program, including the determination of the necessary number of cleats for 5000 h of functioning. The results of the experiments performed to this end demonstrated that both the reconditioning and execution of spare parts, with the help of reusable materials, could be solutions for sustainability in several economic fields, especially in those where the production costs are high.

1. Introduction

Technological flows include equipment necessary for performing activities in various fields being monitored from several points of view and with several aims, including meeting economic efficiency, since they change alongside with their physical and moral wear.

The solutions adopted for limiting the effects of physical wear on various components of machines and technological machinery depend on their manner and conditions of operation.

Such examples are found in the case of rock drilling, displacement or cutting tools, such as: a drill bit (Figure 1), excavator teeth (Figure 2) and a shearer pick (Figure 3), which, due to the manner of operation and strain, are submitted to intense abrasive wear, such that the costs of these spare parts represent sometimes 14% of the production costs.

The correct choice and rational use of technological equipment coming into contact with various types of rocks [1,2], which are discontinuous, nonhomogeneous and anisotropic bodies, depend on a series of factors, among which are the physical–mechanical characteristics of the latter (such as hardness and abrasiveness), and more so, that rocks are found to have various properties, even for the same sample.

In turn, the rock characteristics should be considered a function of the way in which they are submitted to various actions, such as impact, compression, cutting [1] or drilling.

Rock hardness and abrasiveness determine their capacity to wear down the machine and tool components. The Mohs hardness scale, developed by the German geologist Friederich Mohs, allows rock hardness assessment based on their capacity to scratch other materials; according to Mohs’s rating [2,3], 1 and 2 hardness rocks are considered “soft” and the “hard” ones’ hardness is over 7 and has high wear capacity.

The abrasiveness characteristic influences wear undergone by a part in the process of friction with rocks and is measured in milligrams, representing the weight loss of the part. Generally, to assess the rock behavior in the extraction, load and transportation process of useful mineral substances, wear resistance by friction is used (

Table 1. Physical–mechanical characteristics of basalt.

No	Characteristics
1	Compression resistance	147 (N/mm2)
2	Wear resistance by friction (for 440 rpm) in dry state	0.07 (g/cm2)
3	Density	2.94 (g/cm3)
4	Compactness	93.5 (%)
5	Water absorption	1.08 (%)
6	Total porosity	6.5 (%)

), alongside with other characteristics.

The properties mentioned in Table 1 were determined in the laboratory of rock mechanics of the University of Petrosani, in accordance with the standards, mentioning that wear resistance by friction was determined according STAS 6200/9-19921 (Romania).

Manufacturing and reconditioning [4,5,6] methods of the parts that come into contact with the rocks depend on the physical–mechanical properties of the rocks. Before choosing the adequate materials, as well as one manufacturing procedure or another, and for reconditioning especially, it is necessary to establish beforehand the rock properties with which they come into contact.

The reconditioning of tools working in contact with the rocks is usually performed by overlaying welding and, occasionally, by replacing the reinforcement of the cutting edge (in the case of mining machines) with new wear plates of tungsten and cobalt alloys.

In this context, we can exemplify spare parts such as the teeth of the front loaders, which are made of a carbon steel support or low alloy and a layer of material of high wear resistance (Figure 4).

In parts not lined with hard-wear material, reconditioning is required after approximately 700 h of operation (Figure 5).

Overlaying welding depositions, rich in chromium carbide (in low manganese alloy steel matrixes) provided approximately 1000 h of operation for the bucket teeth.

The operation time for certain spare parts, loaders or crushers (

Table 2. Alloying elements for spare parts.

Part	Chemical Composition (%)
	C	Si	Mn	P	S	Cr	Ni	Mo
Excavator tooth Liebherr	0.44	0.253	0.80	0.008	0.05	1.00	0.169	0.207
Crusher jaw Sandvik	0.22	0.32	0.85	0.0025	0.0025	24.3	0.12	0.1
Sandvik crusher jaw Sandvik	0.8	0.35	12	0.0025	0.0025	0.3	1	-
Sandvik crusher spare part Sandvik	0.8	0.35	12	0.0025	0.0025	0.3	2–2.5	-
Bucket tooth for frontal loader Volvo	0.35	0.35	0.7	0.0025	0.0025	2	0.3	0.5

) can be increased by an additional alloying method or casting phase.

Alloying with manganese, but especially chromium, which easily forms carbides, increases the resistance to wear and corrosion, but it also has a disadvantage, namely, it negatively influences the welding behavior of the alloyed steels.

Table 2 shows the components of certain machinery in the existing machinery parks of Romanian quarries. The chemical compositions, given in Table 2, for these components were spectrally determined for these components.

As with the mentioned parts, the tamping tools (Figure 6) of the combined railway machines [7], which compact the gravel under the sleepers, are subjected to wear, particularly abrasive wear, both on the active surface (Figure 7) (cleat) and on the rest of the body.

In railway infrastructure, it is necessary to intensify the mechanization of the maintenance activities to achieve increased economic efficiency and support the performance of train traffic, with a direct effect on productivity increase.

The mechanized tamping operation is carried out with combined railway machines and consists of simultaneous vibration and compression of gravel under the lower sole of the sleeper. The machines’ tamping tools compact the gravel in a compact form under the sleepers so that the supports created under them would be as homogeneous, compact and permeable as possible, fixing the framework made up of rails and sleepers as well as possible, ensuring, in the meantime, the amortization of shocks and vibrations generated by the railway vehicles.

Vibrations associated with the friction between the tamping tools and the gravel influence the duration of the cleats, which have the highest values of defect occurrence frequencies, 60.51%, and of fixing times, 72.38%, compared to the other components, as can be seen in Figure 8.

The wear of the tamping tools’ cleats shows in the form of micro-fissures, pinches, as well as geometry modifications (by plastic deformation), specific to abrasive wear, both on its active surface (Figure 7) and on the rest of the body, where scratches occur caused by the microprocesses that take place during the operation, due to the movement and compaction of rocks.

The main producers in the field adopted the technological solution in their forging; the material used by Plasser and Theurer (Austria) for forged tamping tools is alloyed steel 36CrNiMo4V, according to DIN 17,200, with the following chemical composition: C = 0.33%, Si = 0.40%, Mn = 0.40 − 0.70%, Cr = 1.4 − 1.7%, Mo = 0.15 − 0.30%, Ni = 1.40 − 1.70%, V = 0.10% (HB = 248 hardness is for raw material).

In Romania, tamping tools are forged from various standardized steels, namely: alloyed steel 42MoCr11 (42CrMo4-DIN 17,200-69), with the following chemical composition: C = 0.38%, Si = 0.40%, Mn = 0.90%, Cr = 1.20%, Mo = 0.20% and 241 HB hardness; quality carbon steel for improvement with chemical composition: C = 0.45%, Si = 0.50%, Mn = 0.50% and 290 HB hardness.

The main shortcoming of the solutions with conventional steels used for tamping tools is the relatively low hardness (250–300 HB), which leads to rapid and uneven wear on the active edge, the frequent replacement of the tools and, consequently, additional interruption times for the combined railway machines.

Wear and renewal of equipment and subassemblies, and also of spare parts, generate costs, which should be managed in an optimal way, whereupon establishing ways of reducing expenses should be envisaged. For this purpose, the modeling of the appearance of defects over time is used, as well as the statistical estimation of reliability parameters, starting from the results of various trial types regarding the adoption of defect distribution laws.

Reliability determines maintenance [8,9,10,11,12,13,14,15,16,17], equipment life span, as well as their acceptable safety level.

The success of a reliability and maintainability study largely depends on the correctness of the data resulted from the follow up of an equipment and its components in exploitation.

Analyzing the known results regarding the wear of the mining tools coming into contact with the rocks [4], we have performed manufacturing and reconditioning experiments for manufacturing and reconditioning methods regarding tamping tools; to this end, initially, the material of the tool was selected and the treatments applied to the original parts. Conditions and operation requirements, size of the wear and limit performances can be obtained after manufacturing and reconditioning, respectively.

In the present paper, the results were obtained following the trials for creating manufacturing and reconditioning technology for the tamping tool cleats of the BNRI-85 type railway combined machines.

2. Materials and Methods

The problem of increasing the life of railway machine tamping tools required creating electrodes to overlay welding with alloys of preestablished properties, for the tool cleats, as well as the technology to cast them by using steel waste. Reliability and maintainability analyses were made for the cast and experimented cleats in view of establishing future research lines as well.

2.1. Reconditioning Procedures Used for Tamping Tools

The activity of reconditioning tamping tools, as part of the tamping machine maintenance, should be carried out with materials and technologies that would ensure hardness, elasticity module and thermal transfer of heat adequate for the functioning regime of the entire piece of technological equipment, simultaneously with the possibility of cleat replacement and reuse of the body itself (port-cleat) of the tool. At the same time, efficiency increase and tamping operation quality are in view, decreasing the number of interruptions required to replace the defected tools.

The analysis of the abrasive wear evolution for the tamping tool cleats showed the increase in the dependence on the friction distance and the friction time in contact with the rock but also on the tamping force applied and the working intensity; at the same time, the material hardness and the geometry of the tamping tool influence its life span.

There are countries, including Romania, where various techniques were used for the reconditioning of the worn cleats by:

• welding a coating on the worn edge, this procedure being used the most frequently;
• brazing of hard tungsten carbide plates (in the case of the original ones, which had reinforced edges) on the active edges of the worn cleats; the trials were carried out with the help of an induction heating installation (Figure 9), with medium frequency currents. The Romanian made installation is made up of: converter, transformer, water cooling installation, control and monitoring apparatus, including condensers to compensate for the power factor. The results were discouraging since the welding materials and technologies did not allow basic metal-brazing alloy–hard plate pairs to be obtained, as required in a high working stress environment.
• thermal spray deposition, an operation that can be repeated several times when the edge of the cleat is worn. To this end, a high-speed propane (or propylene) flame installation HVOF was used [18] for thermal spray deposition with tungsten and cobalt carbide alloy.

For the melting and spraying of tungsten carbide powder on the surface of the cleat, a Complete 2700DJH hand-held hybrid DJ Gun was used, supplied by Sulzer Metco (Figure 10). The tool can also be used to pre-heat the parts.

The disadvantage of this solution is that the spray-coated cleats are wear resistant only for rocks of low hardness.

Considering the parameters of the functioning regime, the stress and the way in which the tamping tool cleats are worn, the experiments that were performed in view of finding and adapting reconditioning materials and original technological manufacturing are presented.

2.2. Screening Testing for the Selection of Cleat Reconditioning Materials

In the maintenance process for parts with intensively stressed surfaces in operation, the realization through welding of wear protection layers [19,20,21,22] is a process of general utility by which the active areas have undergone changes from shape and size.

Technical and technological characteristics of the layers that constitute “intelligent” protection systems against wear are influenced by the welding technology, by the type and nature of the addition materials and by their compatibility with the basic material.

Development of the electrode system for welding depositions with alloys of preestablished properties for the cleats of the tamping tools, and the procedure to obtain them as well, should provide, in the end, resistance to abrasive wear on the deposited layers by correlating the technical and technological possibilities. This aim can be reached by:

• high efficiency electrodes, which can deposit by welding hard structural globular constituents over the surfaces of the parts subject to abrasion, as well as fatigue stress and mechanical shocks;
• an alloying system that would include some of the necessary layer elements [23,24,25,26], which would provide protection against oxidation, Cr, W, V and Ti; at the same time, the germination and precipitation of complex carbides of high hardness and tenacity are observed;
• easy welding by developing and carrying out endothermic, high basicity coating containing, in concrete working conditions (for example in quarries), gas and slag generating substances of preestablished viscousness;
• limiting the content of diffusible hydrogen in deposits by using mineral substances with a minimum content of water of crystallization in the coating;
• good electrical conductivity and low surface tension of the elements of the coating composition, in the liquid phase, in order to make rows of welds with a thickness/width ratio of approximately 1/4;
• oxidation protection of the alloying elements, when the drops pass through the electric arc, with sacrificial elements, located on the oxygen affinity scale, in front of those to be protected.

Considering the losses by burning of the alloying elements through the electric arc, as well as the safety buffer for diluting with the basic material, the required chemical composition was established for the material layered on the cleat, which might ensure a higher hardness for the shell.

Alloying was chosen to be from wire and layer.

Metallographic structure of the layering was designed with the help of Schaeffler diagram, and was carried out by alloying and microalloying so that the weld layered metal would show a structure rich in complex carbides of Cr, W and Ti, of fine granulation and approximately 55HRC hardness.

In the planning of the alloying system, we had in view the chemical composition of the S12MoCr170 STAS 1126 (SR EN 12072:2001) rod, and the required components for the electrodes layers were established by trials.

The basic components of the electrode layers are: those with a slagging role (marble, fluorine, rutile); those with the alloying and deoxidation roles (metal tungsten, ferrosilicon, ferrochrome, graphite); those with a plasticization role (talc); those with a binder role (Natrium and Kalium silicate).

The chemical composition of the deposited metal was determined, on samples (Figure 11) by the spectral method (Figure 12).

Finalization and verification of the new alloy behavior was performed on a test stand (Figure 13) intended for this end by determining the abrasion resistance of samples obtained by welding layers of material with the help of experimental electrodes; in parallel, a sample of the same size was tested, taken from the support material of the deposit.

The stand used allows an F pressing force to be applied on the sample on the rubber drum surface in the presence of 0.4 mm basaltic sand; the force value can be changed to up to 100 N by means of a spring. The n revolution of a rubber drum (200 mm diameter), identical to the one of the driving motors, was set to 3000 rpm, and the sand flow was adjusted by the installation diaphragm.

Trials on the stand provided only the assessment of the alloy behavior in testing by welding, and the test time was limited.

It was considered that wear resistance can be considered relevant after the practical trials of the reconditioned cleats with the proposed alloys.

Behavior assessment on loading productivity was performed by the use of prototype electrodes with the above-mentioned content, and the welding of the test samples was carried out at 140 ± 5 A direct current; the determined welding efficiency (ratio of deposited mass carried out with one electrode and the mass of the nude welding rod) was 118%.

2.3. Research on Manufacturing Cast Cleats of a Composite Material

Worn cleats are distinct elements of tamping tools; therefore, they can be replaced by welding new ones to the body of the tool itself.

In view of casting cleats on sand forms, numerous trials and experiments were made in order to determine their optimum composition using steel waste, such as scraps from the casting process, deoxidating and alloying materials, namely, ferromanganese, ferro silicomanganese, ferrochrome, as well as tungsten carbide waste.

The forms were made of quartz sand with granulometry corresponding to good permeability and refractoriness (reinforced with carbon dioxide) and an inorganic binder for the foundry, hydrolyzed sodium silicate, in a liquid state.

The basic material of the cleat was, thus, a composite (made by casting) having Fe-C-Mn-Cr type metal matrix, in which metal carbide waste infiltrated by diffusion, reinforcing its active area.

The tungsten carbide granular material (Figure 14) in the range of 2 and 0.85 mm had the chemical composition and physical–mechanical characteristics shown in

Table 3. Chemical composition of the granular material for matrix reinforcement (%).

Material	WC
W	95–96
C	3.8–4
Fe	<0.5
Cr	<0.2
V	<0.2
Ti	<0.1
Mo + Co + Ni	<0.3

and

Table 4. Physical–mechanical properties of the granular material for matrix reinforcement.

Material	WC
Hardness (HV 50)	>2000
Density (g/cm3)	16.5
Melting point (°C)	2525
Particle size (mm)	2–0.85

.

Due to the high casting temperatures of steel, its low fluidity and solidification conditions, manufacturing cleats that were cast from the previously listed elements required a design for the casting form in such a way as to obtain the contraction, solidification and quick filling with hot metal of the casting form; the procedure applied was static (gravitational) with 1625 °C casting temperature.

The heat treatment for uniformization of the structure of the cast parts was performed in a flame furnace with a mobile horizontal hearth and discontinuous operation. The main parameters of the treatment regime (Figure 15) were: heating to 880–900 °C temperature, maintaining this temperature for 15–20 min, followed by accelerated cooling of the parts in air.

406 prototype cast cleats were followed up during use (Figure 16) for 18 months, directly on the tamping machine, until various forms of major wear were noticed, and they were replaced.

The results obtained by the experiments made with cast cleats contributed to a reliability and maintainability study using distribution laws, estimation methods of the parameters of this distribution, using Weibull++ program.

Repartition (distribution) laws express the dependence between the values of the investigated characteristics and the related probability, so that coming from mathematical statistics, they are adopted when they involve a reliability function in an adequate form that would be compatible with a certain physical interpretation.

The advantage of the Weibull++ application [27] lies in the fact that a classification of the acceptance for distribution law (

Table 5. Classification of the distribution law acceptance.

Current Results Matrix Matrix Order Distribution	Ranking	LKV	BIC	AIC
2P−Weibull	1	−2249.2	4510.5	4502.5
3P−Weibull	2	−2251.2	4520.3	4508.3
Logistic	3	−2260.5	4533.1	4525
Normal	4	−2268.5	4548.9	4540.9
Gamma	5	−2270.7	4553.5	4545.5
G−Gamma	6	−2271.3	4560.6	4548.6
Loglogistic	7	−2285.2	4582.5	4574.5
Lognormal	8	−2312.4	4636.8	4628.8
2P−Exponential	9	−2330.4	4672.9	4664.8
1P−Exponential	10	−2353.9	4713.8	4709.8
Gumbel	11	−2771.8	5555.7	5547.7

) suitable for the defect in question was obtained without the need to study each repartition law individually.

For the function of the practical experience of the user, the first or one of the first laws of this classification can be used. In the present case, we chose the first law, the normalized bi-parametric Weibull distribution (

Table 6. Adopted normalized bi-parametric Weibull repartition law parameters.

Results Report
Report Type	Weibull++ Results
User Info
Name	Vlad Alexandru Florea
Company	University of Petroșani
Date	8 April 2022
Parameters
Distribution	Weibull 2P
Analysis	RRX
CB Method	FM
Ranking	MED
Beta	1.727884
Eta (h)	132.550909
LK Value	−2249.230137
Rho	0.973971
Fail\Susp	406\0
Local VAR/COV MATRIX
Var − Beta = 0.004633	CV Eta Beta = 0.059734
CV Eta Beta = 0.059734	Var − Beta = 16.297369

), a widely used distribution in reliability analyses.

The data obtained also allow the necessary spare parts to be established, namely, the cast cleats. When normalized bi-parametric Weibull distribution is applied, the value of the necessary number of spare parts N, which is cast cleats in this case, for T time, is determined by calculation (or tables regarding normal standard distribution tables are used) with the equation [28]:

$$\mathrm{N}={\left[\frac{\mathrm{d}·\mathrm{CV}}{2}+\sqrt{{\left(\frac{\mathrm{d}·\mathrm{CV}}{2}\right)}^2+\frac{\mathrm{T}}{\mathrm{MTBF}}}\right]}^2$$

(1)

where CV is the distribution variation coefficient, which is calculated with the equation [28]:

$$\mathrm{CV}=\frac{\sqrt{\mathrm{D}}}{\mathrm{MTBF}}=\frac{\mathsf{\sigma }}{\mathrm{MTBF}}$$

(2)

where D is dispersion and σ the standard average deviation of the random variable, or it is chosen from Tables [12,29], the function of β shape coefficient;

d is the parameter expressed with the help of the inverse Laplace function Ф⁻¹(γ) for various confidence levels γ [28]:

d = Ф⁻¹(γ);

(3)

Mean time between failures (MTBF) is the time average of good operation and is calculated with the equation [28]:

$$\mathrm{MTBF}=\frac{1}{\mathrm{n}}·{\sum }_{\mathrm{i}=1}^{\mathrm{n}}{\mathrm{t}}_{\mathrm{i}}$$

(4)

where n is the number of defects, and t_i is the operation time between two defects of the same type.

The problem in determining the N number of spare parts to be found as a backup has risen with a given probability, γ (confidence level) so that all the necessities could be covered for T time.

Table 7. Values of the parameter d for different confidence levels γ.

γ	0.99	0.95	0.90	0.75	0.50
d = Ф−1(γ)	2.33	1.64	1.28	0.67	0.00

shows the parameter values obtained with the help of the inverse Laplace function Ф⁻¹(γ) for common values of confidence level γ.

3. Results and Discussion

3.1. Results Attained with the Help of Prototype Electrodes

The practical confirmation of a formula to improve prototype electrodes was obtained by determining the composition and quality of the metal layer deposited by welding on the cleats.

Table 8. Chemical composition of metal layered with the help of prototype electrodes (%).

C	Mn	Si	Cr	W	Ti	V
1.86	1.3	0.7	24.3	4.8	0.99	0.6

gives the chemical composition of the weld-layered metal, spectrally determined, with the help of Fe and highly alloyed steel programs.

Prototype electrodes have the advantage that their layering efficiency is high and ensures a high resistance to deposit and tear with a low tendency for fragilization.

Testing in working conditions of a series of prototype electrodes (Figure 17) was carried out by deposition by welding 14 edges of the worn cleats (made of 42MoCr11 alloyed steel).

The deposited metal sample used to determine the chemical composition was processed in compliance with SR 5000-97 and STAS 5500-74 standards, in view of the metallographic analysis (Figure 18).

A fine martensitic structure can be seen in Figure 18, rich in complex carbides, evenly distributed, of spherical type. This is explained by the presence in the alloy of mechanically micro-alloyed substances. The presented structure is rich in complex Cr, W and Ti carbides of fine granulation, which ensure good wear resistance to abrasion.

Structural examinations were accompanied by hardness determinations (

Table 9. Deposited metal hardness values.

Hardness (HV10)
627	606	665

) on the deposited metal sample (Zwick 3212 hardness tester was used).

Layers made up of a Cr 24%-W 4%-Ti 0,8%-V 0,63 type are rich in complex carbides of high hardness (Table 9) and provide good resistance to abrasive wear. The cleats that have no wear protection layers have lower hardness (HB = 310).

Reconditioning of the tamping tool cleats with prototype electrodes was performed in a maintenance shop for technological equipment and allowed a 27 km compact railway to be covered without replacement, which means double the performance of the original tools.

In the practical trials carried out with reconditioned cleats, with the help of prototype electrodes, only the cleats with the adequate weld layer were used.

The results of the analyses regarding the behavior of the reconditioned cleats were encouraging, pointing out that it is necessary to optimize the reconditioning procedure in order to avoid the occurrence of fissures in the layer.

3.2. Results Attained with the Help of Cast Cleats

The large number of the results obtained regarding the practical use of the cast cleats allowed graphs to be developed on their reliability evolution in time (Figure 19 and Figure 20).

These representations show relatively low values for cleat reliability; therefore, the probability that the tool would not fail after 126 h of effective operation was only 40%. This shows that for a 40% confidence level (a 60% risk margin being very high), we should expect the necessity of replacing the part.

If an 80% reliability is imposed, which is a reasonable technical value, only 55.7 h of operation with no failure is to be expected, which means that after approximately 7 days of effective operation, the part would be replaced. The time considered, both for the reliability and maintainability analysis, does not include repositioning time. The calculation is made for an eight-hour shift per day.

In order to analyze the cleat maintainability (Figure 21 and Figure 22), running through the same stages as those presented above, a probability of 40% was obtained for the tamping tool cleat to be replaced in 104 min. When an 80% maintainability level was imposed, we should expect a longer time, that of 144 min, for the cleats to be replaced.

In order to improve the correction times, the implementation possibility of a maintenance system that would take into consideration the results obtained in this maintainability study is required.

Using Equation (1), we have obtained the necessary spare parts, which were cast cleats, for various confidence levels (

Table 10. Calculation of the necessary number of cast cleats, depending on various confidence levels.

Confidence Level γ	0.99	0.95	0.90	0.75	0.50
Necessary cleats (pc)	52	49	48	45	42

).

The necessary number of cast cleats, according to the proposed technology, is established for 5000 h of operation, T time.

The system availability is warranted when the necessary spare parts N, in this case cleat, are permanently in reach.

4. Conclusions

The abrasive use of sub-assemblies belonging to technological equipment, especially for mining and loading–transporting, require the development of advanced materials that would simultaneously present high values as a tenacity–hardness pair and more. In this context, it should be pointed out that resistance to abrasive wear for sub-assemblies and spare parts materials is adversely influenced, leading to high maintenance costs.

In view of increasing the functioning life span of the structures of technological equipment, especially of those that come into direct contact with hard rocks, trials were performed aiming at the development of advanced–intelligent technologies and materials, with characteristics adequate for the working conditions.

It should be emphasized that in order to accomplish the objective mentioned above, concrete working conditions for various technological pieces of equipment and some of their spare parts were followed up, particularly those with high specific consumption, tools that come into contact with hard rocks, such as the cleats of the combined railway machines.

In this context, a series of factors influencing the abrasive wear, which is tribomechanical properties of the materials of the parts, the parameters of their working regime and the rocks’ physical–mechanical properties, were considered.

The reconditioning solution for the tamping tools cleats with prototype electrodes of alloys of preestablished properties required new formulae to be developed, as well as their execution process. The results obtained by the experimentation on cleats with welding depositions made by prototype electrodes have proven to double the performances compared to those obtained with the original tools (Plasser), since 27 km of compact railway could be covered with no replacement.

The advantage of welding depositions with prototype electrodes is that it can be directly used in the maintenance and repair shop for railway equipment.

The technological variant proposed in order to obtain cast tamping tool cleats is based on reusable materials and allows the waste resulted from casting to be reentered in the economic circuit, as well as the milestones found by the end of their useful life.

The economic analysis of the costs of the cast cleat shows the suitability of the recovery and reuse in the economic circuit of the tamping tools with worn cleats, since approximately 26% cost reduction can be obtained by cleat replacement (200 Euro/pc., respectively 148 Euro/pc.).

Casting the tamping tools cleats by using steel waste, such as casting grids and feeders, deoxidizing and alloying materials, ferromanganese, ferro silicomanganese, ferrochrome, respectively, as well as tungsten carbide wastes, provide longer service life for these spare parts. The disadvantage is the necessity for adopting technological flows, including carrying out molds from the materials mentioned above.

The experiments for cleats reconditioning will be continued:

• to establish maximum limits of wear for cleats with no protection against abrasive wear, for which reconditioning by overlaying welding is recommended with prototype electrodes function of the physical–mechanical properties of the rocks in which they work;
• to establish economic efficiency for reconditioning by overlaying welding with prototype electrodes for cleats with no wear protection.

Immediate practical implications of the study refer to the correct choice of the tamping tool type by people in charge with railway machines maintenance and exploitation, namely:

• tamping tools consumption depends on the exact knowledge of the physical–mechanical properties of the rocks in work, especially abrasive wear resistance; cleats with no protection against wear (without tungsten carbide plates) cannot be used in hard rocks;
• tamping tools reconditioning by overlaying welding requires electrodes with preestablished properties depending on the physical–mechanical properties of the rocks at work.

The paper can be considered a methodology guide for approaching and solving the problem area of machine components that come into contact with various rock types. It is necessary to underline that before a way of approaching and solving is found, the physical–mechanical properties of rocks and the wear type determined by them should be known.