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In modern industrial manufacturing, eddy current testing technology has become an important tool for ensuring the surface quality of forged steel rolls. Eddy current roll surface detection is based on...
Defect detection on metal surfaces is crucial in the industrial field, and eddy test, as an advanced non-destructive testing technique, is widely used for quality control of various metal materials. This article will explore the commonly used methods of eddy testing in detecting defects on metal surfaces, along with the characteristics and application scenarios of these methods.
Eddy testing methods using low-frequency primarily rely on low-frequency alternating current to generate eddy currents. Traditional ultrasonic testing (UT) and radiographic testing (RT) methods have certain limitations in detecting internal defects. However, eddy testing leverages the skin effect, enabling effective detection of surface defects at lower frequencies. Low-frequency signals are typically controlled below 1kHz, or even a few Hz, which helps enhance the penetration depth of the eddy currents. This method, however, is mainly suitable for detecting millimeter to micrometer level defects and has limited capability for detecting very small defects.
Compared to low-frequency eddy testing methods, high-frequency eddy testing methods usually adopt frequencies above 1MHz. This method uses high-frequency signals to generate eddy currents that are mainly concentrated on the metal surface, suitable for detecting minor deformations and defects on the metal surface. Eddy testing with high-frequency methods can quickly and accurately perform detection, ideal for high-precision applications. For instance, in the flatness detection of niobium plates, high-frequency eddy current technology can provide color imaging detection results and achieve clear resolution of micron-level surface variations. The advantage of this method lies in its ability to quickly obtain accurate detection results, enhancing detection efficiency in industrial production.
To improve detection efficiency and accuracy, the field of eddy testing has also introduced multi-frequency eddy testing methods. This approach uses multiple frequencies simultaneously for detection, capable of handling complex detection requirements. When inspecting objects with complex structures, multi-frequency eddy testing methods help suppress interference factors and improve detection accuracy. This method can process multiple specific frequency excitation signals and achieve simultaneous extraction of various signals, which plays an important role in enhancing the efficiency and accuracy of eddy testing.
Eddy testing using the frequency-sweeping method employs cyclic excitation, causing the signal of the object under test to have only one frequency at a time. Sweeping frequency technology can cover a wide bandwidth from tens of Hz to tens of MHz, suitable for inspecting devices with complex structures. Through continuous frequency scanning, the frequency-sweeping eddy testing method can more easily detect impedance changes caused by surface quality discontinuities. This method is particularly well-suited for complex structural inspection needs, providing high sensitivity and accuracy in detection.
As an emerging eddy testing technology, array eddy testing methods use sensors with multiple excitation-detection coil combinations for inspection. These sensors operate independently, enabling multi-directional inspection of the object. Compared to traditional eddy current probes, array eddy current probes are more sensitive to the direction of defects, providing clearer imaging results. The flexible design of this method allows it to adapt to various test objects, significantly improving the effectiveness and efficiency of defect detection.
