The 12th International Conference of the Slovenian Society for Non-Destructive Testing »Application of Contemporary Non-Destructive Testing in Engineering« September 4-6, 2013, Portorož,

POSSIBILITIES OF AUTOMATIC INSPECTION ON MOUNTED WHEEL SETS WITH HOLLOW AXLE ON SLOVENE RAILWAYS

Viktor Jemec1, Janez Gorše2, Janez Grum3

1High school Domžale, Cesta talcev 12, 1230 Domžale, SI, [email protected] 2Slovenian Railway , Zaloška 217, 1000 Ljubljana, SI 3Faculty of mechanical engineering Ljubljana, Aškerčeva 6, 1000 Ljubljana, SI

ABSTRACT

Electro-motor passenger trains of Italian firm Fiat with mark ICS 310 and of German firm Siemens with mark 312 drive on . All these vehicles have hollow axles. Refractions of axle often occurred round the year 1980, therefore suitable employment of quality control on Slovene railways was necessary based on. Calculations of ultrasonic ways of signals of hollow axles for special examinations with at home made probe. Special ultrasonic probes were made to examine mentioned motor trains. Automatic inspection of wheels is still in initial phase of development. Detection of transversal and longitudinal failures and possibility of evaluation of signals will be presented in this contribution.

Keywords: Non Destructive Testing (NDT), hollow railway axles and shafts, wheel sets, failure, crack, refraction, testing with ultrasonic method

1. Introduction

The railway traffic concerns both transport of passengers and transport of dangerous materials that is why an increased safety and reliability of operation of all railway vehic1es is demanded. That is why technical systems maintenance protocols are necessary as they prescribe appropriate NDT methods and testing procedures, which meet the demanded traffic safety and order. The traction vehic1es are also equipped with appropriate safety devices, which exc1ude subjective mistakes of the operators during the operation, so as to prevent catastrophic failure of the parts or systems. Safe operation of locomotives and motor trains can be assured by detecting defects in the vital elements of locomotives, wagons and carriages, and with regular checking of rails. NDT methods which have to be both fast enough for testing and sufficiently reliable and cheap are often applied to detection of defects. Control of the characteristic parts is executed precisely according to the prescribed internal standards and regulations, which, beside the regular, also prescribe extraordinary tests after collisions, derailments or grazing of rail way vehic1es [1]. We tested the reliability of the subsystems and determined the critical parts, which need to be periodically checked so as to ensure the prescribed safety. Wheel-set axles are among the most loaded parts of railway vehicles and their defects or cracks in them lead to substantial material loss as well as endanger the lives of passengers and railway workers. That is why internal

153 standards were elaborated, which prescribe obligatory ultrasonic checks of wheel-set axles. They were later supplemented with additional descriptions and instruction s [2, 3].

2. A testing of hollow shafts and of axle with special ultrasonic probe for search of cracks from inside Wheel sets of high-speed trains feature hollow axles which have to be inspected periodically by ultrasound to detect potential defects and cracks at an early stage. The axles are tested from the bore hole for internal defects and cracks in the outer surface. Areas of interest are especially the axle journal, the dust guard seat, the wheel seat, the brake disc seat and all transitions of diameter. Hollow railway axels have a hole the entire length of the axis, most commonly the diameter of 60 or 90 mm. It does not, however, weaken the durability of the axel. Hollow axles are becoming more and more popular, being used in a lot of new equipment. The hole allows for ultrasonic examinations without taking apart the entire set. Tests on the hollow axel are performed on the entire volume of the material, placing the head into this hole. Because this is a place not easily accessible it is necessary to perform studies specifically designed for this system.

3. Modeling of surface crack

The fatigue behavior of surface flaws in round bars has been examined by several authors [4, 5] ，6,and 7, 8a] few. studi es h Cracks considered by many researchers are semi-elliptical and the center of the ellipse is placed on the surface of the cylinder. The hollow axle with a circumferential semi-elliptical surface crack, the center of which is lying on the outer surface of the cross-section, is shown in Fig.3a. The geometry of such a crack can be described by two dimensionless parameters, a/b and a/t, the so called aspect ratio and relative depth of the crack, respectively. Bending load is applied to a hollow axle in the vertical plane while the train running and the load aspect is downwards always. Suppose that θ is the angle between the axes through the crack center and the symmetry axes of bending moment M during rotating. The decomposition of the M in the two components Mx (θ=0°) and My (θ=90°) is shown in Fig. 3b [9, 10]. Stress intensity factors (SIF) calculation for circumferential external surface semi-ellipse crack in hollow axles subjected to rotary bending loads using a 3D finite element model.

Figure 1: Geometry and loading parameters of the surface crack on hollow axles

Within year 1980/81 first refractions on shafts of diesel shunting of series 732 started to appear. Ultrasonic device [11, 12] for examination of shaft through bore was made. We were renting out ultrasound under corner to 45 ° with ultrasonic head. All surfaces on shaft was gradually checked with ultrasonic probe in direction x-axle and with rotation for 360° [13] including surface of crossings next to diameters of shaft, which is seen on figure 4.

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Figure 2: Ultrasonic testing principle of hollow axles or shafts Beginnings of cracks were appearing at crossings. Procedure was systematic and very efficient.

Figure 3: Ultrasonic probe for an examination of hollow shaft of series 732 Something years back electro-motor set of Siemens group of modular trains Desiro (marked SŽ 312) appeared on Slovenian railways. These motor functions have right such hollow shaft. Mr. Mitja Šipek made similarly ultrasonic device like at series 732 [14], only with other diameter. We avoid possible refractions of shaft like this, if we are carrying out protective examinations regularly 6 months with accurate observation of interior of shaft. Basic goal of task is to initiate extremely more reliable and useful manner checks of undercarriages of railway driven with NDT procedures without dismantlement of mechanical assemblies because of protective examinations. Procedure is ensuring shorter time of retention of locomotives and remaining vehicles within workroom. We concentrated on most vital part of vehicles - these are shafts and axles, that they must be faultless for safety of traffic.

4. Standard steels for axles

As mentioned before, European standards refer mainly to two steel grades: EA1N and EA4T. The first one is a normalized carbon steel for general purpose and the second one is quenched and tempered low alloyed steel for higher performances. Fatigue characteristics of these steel grades are included as reference into the norms for axles designing, while all the other minimum requirements for axles manufactured with these steels are mentioned in the product requirements standards EN13260 and EN13261. To have an overview of these steels, all their main characteristics are illustrated in the following tables 1 and 2 as mentioned into the standards. The ETR 480 is a tilting Electric Multiple Unit built by FIAT Ferroviaria (now Alstom Ferroviaria) since 1993, it is also known as Pendolino. It was developed from the first new-generation Pendolino, the ETR 460. The main difference between ETR 460, ETR 470 and ETR 480 is that the 460 run only on 3 kV DC, the 470 on both 3 kV DC and 15 kV AC, and the 480 on both 3 kV DC and 25 kV 50 Hz AC [15]. ETR 500 (Elettro Treno Rapido 500) is a family of Italian high-speed trains [16].

Table 1: Chemical composition for both kinds of steels Steel /elemen C Si Mn Pa S Cr Cu Mo Ni V EA1N 0,40 0,50 1,20 0,020 0,020 0,30 0,30 0,08 0,30 0,06 EA4T 0,22 0,15 0,50 0,90 0,15 0,29 0,40 0,80 0,020 0,015 1,20 0,30 0,30 0,30 0,06

155 Table 2: Mechanical characteristics for both kinds of steels

Regarding fatigue characteristics of the materials, European standards require all manufacturers to verify materials performances, in order to have a correctly dimensioned axle. According to the norms, it is necessary to estimate the fatigue limits to verify both the material and the product, in order to predict the behavior of the axle under in - service stresses. The fatigue limits determined with reduced test pieces are used to verify that the notch effect of the material used for the fabrication of the axle is in accordance with the security coefficient "S", defined in design standards EN 13103 and EN 13 104.

5. High strength alloyed steels

Advantages and comparison experience suggests that an important axle weight reduction (about 20%) is possible only having small diameters on all the axle zones: the bore on the axle can increase this reduction further, but it is not sufficient alone. To do this, higher allowable fatigue limits should be available to the designer for the verification of stresses on the axles and these can be obtained only with high performance steel grades. The steel grade object of this study is the high strength alloy steel 30NiCrMoV12 by Lucchini Sidermeccanica, widely used in Italy and Europe especially on high speed train wheel sets applications [17, 18]. The main characteristic of this steel is high fatigue strength together with notch sensitivity value similar to standard steel grades. This allows the designers to take fully advantage during the developing of the products and to reduce strongly the weight of wheel sets. As a consequence, reduction of vibrations of all un-sprung components, lower wear of wheel and rail, also under severe load conditions, and better dynamic behavior due to reduced inertia moment can be achieved. In the following tables 3 and 4, chemical composition and main mechanical characteristics of 30NiCrMoV12 steel are shown.

Table 3: Chemical composition (maximum percentage contents)

Steel /element C Si Mn Pa S Cr Cu Mo Ni V 30NiCrMoV12 0,26 0,40 0,60 0,40 2,70 0,08 0,32 0,40 0,70 0,020 0,015 1,00 0,20 0,60 3,30 0,13

Table 4: Mechanical characteristics

6. Realization of a test

We are carrying out tests on driving and free axles and shafts of series 312 round internal instruction [19]. Material of specimen: EA4T round railway standard UIC 811.1. Object of testing is axle by wheels and bearings.

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Figure 4: Free axle

Figure 5: Driving axle

On figure 7 and 8 are showed free and driving axle to electric series 312. Axles are hollow, which is making testing possible for us with specially ultrasonic probe. On Slovene railways (SŽ) is organized suitable job for maintenance, traction and technically wagon activity. It is unique, because services for reliable and safe operation of the railway vehicles offer it all on one address. Job is carrying out complete solutions for partners on all locations round Slovenia. Maintenance job is ensuring quality and reliable services on three key fields: diagnostics, repairs and maintenance of the railway vehicles. Job is arranging entire maintenance of car pool of Slovene railways, professional personnel for needs are ensuring a haulage contractor in passenger and freight traffic and it worries so above technical condition and equipped of the railway vehicles. Services of maintenance of all kinds of the railway vehicles are known and appreciated also outside of frontiers. Quality maintenance demands specific knowledge’s and competences, so they are braced for every new challenge at owners of vehicles on wider European market. Numerous partnerships are created with state railways and some largest private owners wider round Europe both in Slovenia. They were finished careful tests on full and hollow axles and shafts in laboratory for NDT at Slovene railways. Positions of special ultrasonic probes are determined in hollow axle, that they would check foreseen critical position surely, above all in places from change of diameters of axle. On figure 9 and 10 are showed both kinds of axle. Beside plan of scanning within interior of axle with corner probe also expected repulsions are showed without failures at axle or shaft.

157 Reference Depth of Path of number probe ultrasonic within wave axle (mm) (mm) 1. 349 121 2. 867 122 3. 1879 121 4. 1974 91,9 5. 2180 70,7

Figure 6: Plan of scanning with corner probe and table of repulsions of driving axle-gearbox side

On base of movement of special probe made still calculations of sound ways from probe to fringes on hollow axle that an operator knows, where ultrasonic repulsions are appearing on which distance on screen.

Reference Depth of Path of number probe ultrasonic within axle wave (mm) (mm) 1. 349 121 2. 1536 122 3. 1879 121 4. 1974 91,9 5. 2180 70,7

Figure 7: Plan of scanning with corner probe and table of repulsions of driving axle- opposite side of gearbox

Next probes were chosen for plan of scanning: -normal straightens probe of 2 MHz B2S or 4MHz B4S for test from the front of full axle or shafts, -special corner probes 2 MHz WB45 for scanning hollow axles or shafts. We chose calibration range: -for normal probe and position of scanning of full shaft from front is Sj = 2500 mm, -for specially corner probe and position of scanning in hollow shaft is Sj = 250 mm.

Calibration samples of axle are being used for calibration and determining of sensitivity with artificially created referential search lights and natural failure are being used for calibration of sensitivity.

a b Figure 8: Echogram checks full shafts from a front (a) and checks of hollow shaft with corner probe without mistake (b)

In accordance with regulations on maintenance of the railway vehicles the performer of the NDT testing of wheel sets records in technical documentation realization of maintenance intervention

158 on an individual vehicle. The expert in workroom must to lead special records on investigation with access of the report for inspectors [20].

Records must contain next data: -reference number, checks date, number of axle, year of making of axle, -kind of the NDT testing, -drove number with built-in wheel sets, -result of the test with signature must an authorized specialist. A report can be issued per special demand of a client.

Figure 9: Ultrasonic probe for Fiat Figure 10: Ultrasonic probe for Siemens Pendolino hollow axle or shaft Desiere hollow axle or shaft

Automated realization of testing of wheel sets is planned with a particularly feed device, that will be programmatically watery and therefore quicker and more reliable for detection of internal inclusions. Large industrial systems demand a bursting an extremely quicker testing just represents extremely shorter time of loss of a vehicle from operation.

Figure 11: Hollow shaft with measure (left) and photograph of entry of probe in hollow shaft (right)

7. Conclusions

Testing hollow axles or shafts with ultrasound method with special probe is very reliable. At series 732 felt so far learned and prematurely excluded from traffic regarding 20 axles or shafts still before the introduction of control with ultrasonic probe through hollow axle or shaft. At newer vehicles with use of special probe for the test of hollow axles and shaft wasn't to detect mistakes and the bursting in material and no cracks were found. In future Slovene railways plan automated special ultrasonic testing of wheel sets with different shaft bore diameters with longitudinal and transverse waves with the comprehensive analysis of signals and low space requirements on dismantled hollow axles or shafts. A device must be extremely smaller, it will be ensuring high adjustability and have high measurement accuracy with possibility of filing of data for further statistical treatment at investigation of different shapes of hollow axles at repeatable results, swiveling probe head construction, short testing time

159 and easy changing of probe heads. The device for investigation of hollow axles must be simple for installing of probe and she must ensure short times for investigation. With consideration of standard of DIN 27201-7 a good educated specialist restrained procedure of investigation on universal device. For automatic work will be ultrasonic device also to future ensured high quality of testing of hollow axles or shafts regardless of their form features and geometry.

8. References

[1] Internal Standard of JŽS V3.006, Zajednica JŽ, Službeni glasnik ZJŽ br. 9, Beograd 1971 [2] Official Communications of Slovenian Railway of Ljubljana, No.: 19, 1979. [3] GRUM, Janez, JEMEC, Viktor, BECI, Anton. Experimental system for ultrasonic testing of axle sets of diesel-engine trains. Insight (Northamp.), 2000, vol. 42, no. 12, pp. 782-788 [4] Carpinteri A. Shape change of surface cracks in round bars under cyclic axial loading, International Journal of Fatigue 1993;15:21–6. [5] Lin XB, Smith RA. Fatigue growth simulation for cracks in notched and unnotched round bars [J]. International Journal of Mechanical Science 1998;40:405–19. [6] Forman RG, Growth behavior of surface cracks in the circumferential plane of solid and hollow cylinders. Fracture mechanics: 17vol, ASTM STP 905. 19 86:59–74. [7] Andrea Carpinteri, at. Alter, Fatigue growth simulation of part-through flaws in thick- walled pipes under rotary bending[J]. International Journal of Fatigue 2000 (22): 1–9 [8] Gao H, Herrmann G. On estimates of stress intensity factors for cracked beams and pipes[J]. Engineering Fracture Mechanics 1992;41:695–706. [9] M. Madia, at alter, An investigation on the influence of rotary bending and press fitting on stress intensity factors and fatigue crack growth in railway axles. EFM 2008: 1906–1920 [10] Zhou Suxia, at alter, Simulation of SIF of Surface Crack on Railway Hollow Axles during a Cyclic Load, School of Mechanical-Electronic and Automobile Engineering, Beijing, China, 2012, International Conference on Mechanical Engineering, Vol.10, 79-83 [11] JEMEC Viktor, ŠIPEK Mitja, Ultrazvučno ispitivanje lokomotivskih osovina, IX. International Symposium of Non-Destructive control,Collection of papers-Pančevo, 1981 [12] SPEIER Peter: Traditional and new opportunities in the railway industry GE inspection technologies, Bon, 2004 [13] DIN 27201-7, State of railway vehicles - Basic principles and production technology - Part 7: Non-destructive test Deutsches Institut Fur Normung E.V. 2006 / 22 pages [14] ŠIPEK Mitja, Uporaba UZ za kontrolo osi hitrega vlaka, Prevalje, 2009 [15] http://en.wikipedia.org/wiki/FS_Class_ETR_480, (4. 3. 2013) [16] http://en.wikipedia.org/wiki/FS_Class_ETR_500, (4. 3. 2013) [17] UNI 6787 [18] MANCINI, at alter, Design of railway axle in compliance with the EN: high strengthalloyedsteelscomparedtostandardsteels,http://www.uic.org/cdrom/2006/wcrr2006 [19] Internal instruction: TN UZ, Testing axles EMV 312, SŽ, 2006 [20] Ur. l. RS, No. 53/2002,

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