Service life and reliability of railway wheel pairs operation are largely dependent on quality of their components, one of which is the railway axle. Therefore, during manufacture of railway axles it is required to conduct products regular non-destructive testing at all stages of their manufacture for in-time detection of unacceptable defects. More frequently an ultrasonic testing method is used for railway axles flaw detection with the scanning of testing zone provided by the NDT inspector and operator by means of manual device, which has a number of disadvantages, including:
- law testing productivity;
- operator influence on testing results (human factor);
- possibility of results distortion during the testing protocol preparation.
In addition, manually tested railway axles cannot be shipped to the European market, as according to Regulatory Documentations require obligatory automated ultrasonic testing with a formation of a protocol for each axle independently from operator.
In this connection JSC S. S. Monyatovskiy Lugtsentrokuz set a task to JSC UkrSRINDT to design a domestic Automated System for railway axles testing which are manufactured in accordance with the Domestic and International Standards (DSTU 31334, EN13261, M101, BN 918275, ISO 5948 and etc.).
JSC S. S. Monyatovskiy Lugtsentrokuz laded down requirements to the designed testing System:
- the System should provide ultrasonic testing of forged railway axles in immersion mode and correspond to testing rates (echo pulse technique for the presence of internal defects, mirror through transmission method for the axle metal structure testing) according to RD 32.144-2000, ISO 5948 , EN 13261, М101, DSTU 31334 and BN 918275;
- the System should provide testing of semi-finished axles with a roughness surface of Ra25 µm and according to this reliably detect defects that correspond the flat bottom hole with the diameter more than 3 mm (according to RD32.144-2000 and ISO 5948).
To solve the stated tasks JSC S. S. Monyatovskiy Lugtsentrokuz represented to JSC UkrSRINDT fragments of railway axles (with a length of 250 mm and diameter of 200 mm) with a surface roughness of Ra 25 µm to determine the possibility of immersion ultrasonic testing of objects with the specified surface roughness.
During testing works were carried out on selection of immersion PEPs frequency, selected an optimal immersion delay, designed a scanning device structure with the possibility to adjust a PEP`s solid angle to provide testing standards ensuring the flat bottom hole detection with the diameter of 2mm at a depth of 195 mm.
Fig. 1. The System of automated ultrasonic testing of axles SAUT «Uniscan – Luch OS – 4».
Results of experimental work on immersion testing of semi-finished axles, ensuring Domestic and International testing standards and engineering study provided the basis for the designed system of automated testing of railway axles SAUT «Uniscan – Luch OS – 4» (hereinafter is referred as System) (Fig. 1). This System consists of immersion tank, clamp spindles, scanning device with a linear drive and of a hardware and computing complex on the basis of industrial computer (Fig. 2).
Fig. 2. The Structural scheme of the System major units.
During carrying out the testing the railway axle is completely doused into the immersion liquid. The axle loading and uploading is carried out from the testing position by means of a crane with grips (Fig. 3). The process of carrying out the testing is fully automated and maximally simplified.
Fig.3. Loading of the tested axle to the testing position
Testing is carried out during the axle rotary movement at centers and linear movement of scanning devices along the axle. Herewith, the System independently carries out all required mechanical operations for the axle positioning into working position.
Due to the immersion technique and usage of immersion gate the high reception stability and radiation of ultrasonic vibrations are provided due to the acoustic coupling stability between the probe and the product radial surface. Filling and drain of immersion liquid is carried out by means of pneumatic valves. The System SAUT «Uniscan – Luch OS – 4» provides the possibility of liquid circulation inside the System with the possibility of liquid drain into reserve tanks or connection to the enterprise central water system.
Railway axle scanning is carried out using the carrier linear movement device consisting of 2 scanners. Each scanner includes four ultrasonic probes.
Nominal frequencies of ultrasonic vibrations of special-purpose probes are 2,5 and 5 MHz. The first scanner carries out testing of the axle left part (from the end surface to the middle position) and the second scanner – from the right part (from the axle middle position to its right end surface).
Data acquisition via all channels is carried out using two OKO-20 flaw detectors. Testing zones are attached to each probe during the setting. Loading of testing zones for a given longitudinal linear coordinate is carried out automatically during the scanning process.
Software of the System of automated ultrasonic testing SAUT «Uniscan – Luch OS – 4» is oriented for the performance of three main testing steps: acceptance level of sensitivity, testing performance itself and review of testing results. Herewith the System interface is intuitive and maximally optimized for the user convenience.
Adjustment of acceptance level of sensitivity provides a set of testing zones for each probe of the scanning device and adjustment of acceptance level of sensitivity itself for each zone by artificial reflectors on enterprise calibration block. Set of testing zones is carried out by linear coordinates of the axle starting from the left end surface and sensitivity adjustment - by DAC curves (Fig.4). Also, there are three curve levels – search, testing and rejection. For each axle dimension type there is its own testing setting that is stored in the computer database. Loading of listed data is enough required for the axle testing.
Fig.4. Adjustment of testing zones and acceptance level of sensitivity.
Operation of the System SAUT «Uniscan – Luch OS – 4» is carried out by one operator who can perform testing of the loaded axle by pressing "START" button, after the System conducts all preliminary operations and launches the testing process.
During the data reading there is a visualization of a testing process on defectograms in a form of B-scans or peaks set (by the operator option) in real-time for each channel involved in testing (Fig. 5). If required an operator can set the main testing parameters: speed of the axle rotation, speed of the scanning device movement, frequency of probe pulse generator and etc.
Fig. 5. Representation of a testing process in a form of B-scan.
After ending the process the System outputs an acceptance report in a form of B-scan attached to the axle, summarized results and a conclusion SERVICABLE/ REJECTION (Fig. 6). Dropping the axle to the upload position is also carried out by pressing "UPLOAD" button.
Fig. 6. Representation of preliminary results after the ending of the scanning.
All testing results are stored on a hard drive of the industrial computer. If required the System can output testing protocols as for each separate axle and as in a form of statistic in relays reports what maximally simplifies the reporting procedure. Possibility to archive the data and its analysis on the other computer. Results are stored in a form of detailed information for each separate defect:
- equivalent area and defect diameter;
- defect special orientation;
- echo signal from the defect.
Fig.7. Review of testing results
At reviewing of testing results there is a possibility of B-scan scaling or of a mirror through transmission method curve for a more detailed analysis and review of each separate deviation from the norm (Fig. 7).
System SAUT «Uniscan – Luch OS – 4» allows to carry out testing of all dimension type axles and also various items of a complex cylindrical form (Fig.8). It is only enough to create a required setting and save it in the database. This incredibly improves the manufacturing effectiveness and reduces testing efforts.
Fig. 8. Testing performance of a semi-finished axle at JSC "S. S. Monyatovskiy Lugtsentrokuz".
TECHNICAL SPECIFICATIONS OF A SYSTEM SAUT UNISCAN- LUCH OS-4
- ………… a 100% ultrasonic testing of finished axles,
- ………… of axles after preprocessing (Ra 25)
- Frequency of immersion PEPs, MHz:
- for mirror through transmission method(testing of the axle internal structure)………………………2,5
- for flaw detection(presence of internal defects) ……………………………………………………..4-5
- Time of one axle testing(not including loading/ uploading) is not more than………………………….8 min
- Time of the System reconfiguration for different dimension types is not more than…………………15 min
Testing results output:
- ………………………………………in online mode
- ………………………………………statistics testing protocols
- ………………………………………protocols on one axle with representation of all parameters of detected defects
Saving of testing results:
- …………………………………… in a general database
- …………………………………… testing results archivation
- …………………………………… recording of information on the optical carrier
Implemented testing methods:
- For the presence of internal defects and metal structure - by longitudinal waves from the radial surface
- For the presence of internal defects in a fillet transition area - testing by transverse waves (using angle probes)
The System of automated ultrasonic testing of railway axles SAUT «Uniscan – Luch OS – 4» is integrated into the JSC S. S. Monyatovskiy Lugtsentrokuz production line in a section of preprocessing of railway axles where semi-finished axles are tend to be tested as of European type and of RU1III type. Testing of metal structure for the presence of internal defects is carried out in accordance with the Regulatory Documentations RD 32.144-2000, EN 13261.Implementation of such System allows detection of rejections from the norms even at preliminary manufacturing stages (testing of semi-finished axles) allowing to speed up the production process and provides serviceability and quality of shop operation on finishing processing of railway axles.