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VD-20NF Eddy Current Flaw Detector

The principle of operation of the VD-20NF eddy current flaw detector

The principle of operation of the VD-20NF flaw detector is based on the generation of eddy currents on the surface of the controlled part and subsequent analysis of the signal at the output of the converter, which correlates with the characteristics of the active secondary field.

The device consists of two main blocks: electronic one and electromechanical one, in which an eddy current converter of transformer type is installed. The controlled products (bearing rollers) enter through the input tray into the electromechanical unit of the flaw detector, where they move sequentially and fall under the pressure rollers of the overhead converter holder. The clamping mechanism is adjusted to each size of the rollers, so as to ensure tight contact with the curved surface and fix the tip of the transducer at the required distance from it.

The detection of defects occurs due to the imbalance of the converter when it is located above the surface of the controlled product, caused by the interaction of the primary electromagnetic field generated by the converter with the secondary electromagnetic field of eddy currents induced in the controlled product by the primary field. When cracks are detected, the electronic unit of the flaw detector gives sound and light warning signals, and also triggers the electromagnet of the sorter, which directs the controlled roller into the tray for defective products. In the absence of defects, the controlled roller is directed towards the output tray of the flaw detector.

Design features and advantages

The VD-20NF eddy current flaw detector is equipped with removable input and output trays, power-on switches and a drive for feeding controlled products to the converter, as well as handrails for convenient transportation of the unit.

The mechanisms of the electromechanical unit are protected by a frame made of steel plates. The electronic unit of the flaw detector is portable and can be installed both on the top panel of the electromechanical unit and on the surface of the desktop. Controls and indications of defect detection are located on the front panel of the electronic unit. The delivery package also includes a power adapter for the electronic unit and a tuning sample. The advantages of the VD-20NF flaw detector include:

high reliability (the service life of the flaw detector is more than 10 years);
it is easy to set up and operate;
it has several types of defect detection alarms;
the high probability of detecting defective products (at least 99.9%);
low number of false positives (less than 5%).

Scope of application

According to the current standards of safety and product quality control during repair work in locomotive depots and repair plants, bearing rollers that have passed visual inspection and are recognized as suitable for further operation according to the criteria of geometry and condition of the working surface are subject to mandatory additional control using eddy current flaw detection to detect fatigue cracks invisible during visual inspection on the rolling surface of the rollers. The VD-20NF eddy current flaw detector allows for quality control and automatic disassembly of bearing rollers of various shapes and sizes both in laboratory and factory conditions in full compliance with the requirements of the regulatory documents of Rosstandart and the methods of performing control measurements used in JSC "Russian Railways".