Possibilities of Automatic Inspection on Mounted Wheel Sets with Hollow Axle on Slovene Railways
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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, Slovenia 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 Ljubljana, Zaloška 217, 1000 Ljubljana, SI 3Faculty of mechanical engineering Ljubljana, Aškerčeva 6, 1000 Ljubljana, SI ABSTRACT Electro-motor passenger trains of Italian firm Fiat Pendolino with mark ICS 310 and of German firm Siemens with mark 312 drive on Slovenian railways. 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. 154 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].