Pulsed Magnetization for Ferromagnetic Eddy Current Testing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing non-destructive testing methods for ferromagnetic materials face challenges in accurately determining hardness and detecting surface effects like mill scale and 'hard spots' on rolled steel sheets, especially in mobile and inline testing scenarios, due to high energy consumption and interference from inhomogeneous mill scale.
Innovation Solution
A method using a periodic sequence of recurring bipolar, rectangular pulses for electromagnet excitation with a short pulse duration and low duty cycle, combined with an FET full-bridge circuit, allows for low-energy pulse magnetization, enabling effective detection of hardness and surface effects while masking mill scale interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional continuous excitation signals are used for electromagnet, then sufficient magnetization is achieved, but energy consumption is excessive for mobile testing
Solution Approach 1:
The patent applies periodic pulsed excitation signals instead of continuous signals. The electromagnet is excited with rectangular pulses having a duty cycle of less than 0.2 (preferably 0.05 to 0.1), creating periodic magnetization cycles that achieve sufficient magnetic field strength while allowing rest periods that dramatically reduce energy consumption for mobile testing applications.
2Measurement precision
If continuous magnetization is applied, then hard spots are detected, but mill scale interference prevents accurate hardness determination
Solution Approach 1:
The periodic pulsed magnetization creates time-varying magnetic fields that penetrate through the mill scale more effectively. The pulsed nature with duty cycle < 0.2 allows the magnetic field to penetrate the interfering mill scale layer and reach the underlying metal, enabling accurate detection of hard spots while the mill scale interference is temporarily overcome during the pulse duration.
Solution Approach 2:
The patent changes the excitation parameters by using bipolar rectangular pulses with specific duty cycles rather than continuous signals. This parameter change allows the magnetic field to achieve sufficient penetration depth through the mill scale during the brief pulse duration, while the low duty cycle reduces overall energy input that would otherwise be absorbed by the mill scale.
3Measurement precision
If high energy is supplied for magnetization, then testing accuracy is improved, but mobile and inline testing becomes impractical
Solution Approach 1:
By using periodic pulsed excitation with duty cycle < 0.2, the system achieves effective magnetization during the pulse duration while consuming minimal energy during the rest periods. This makes the testing device practical for mobile and inline applications where power supply is limited, while maintaining sufficient testing accuracy through the concentrated energy delivery during each pulse.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces energy consumption, enhances testing accuracy by masking mill scale interference, and allows for reliable detection of 'hard spots' in rolled steel sheets, particularly suitable for mobile and inline testing in rolling mills.
Implementation Method 1
an electromagnet (10; 10') having a U-shaped or V-shaped magnet yoke (10) with yoke legs (12; 12') pointing towards the test object (16) and with at least one field winding (14), wherein an excitation signal is fed to the field winding (14) in order to periodically remagnetize the test object (16), passing through its hysteresis curve
Implementation Method 2
passing through its hysteresis curve
Implementation Method 3
an eddy current test probe (20), which is arranged between the yoke legs (12; 12') and which is suitable for generating an alternating magnetic field and for detecting electromagnetic properties of the test object (16)
Implementation Method 4
the excitation signal of the electromagnet consists of a periodic sequence of recurring bipolar, rectangular pulses whose pulse duration (ti) is small compared to the period (tr) of the pulse sequence, so that the duty cycle ti/tr is less than 0.2
Data Source
Figure 1
Figure 2
AI summary
For the non-destructive electromagnetic testing of a test specimen (16) made of ferromagnetic material, an electromagnet having a U-shaped or V-shaped yoke (10) with yoke arms (12) pointing towards the test specimen (16) is supplied with a periodic bipolar electrical excitation signal. An eddy current test probe (20) is arranged between the yoke arms (12). The excitation signal of the electromagnet is pulsed, such that it consists of a periodic sequence of recurring bipolar pulses whose pulse duration (ti) is small compared to the period (tr) of the pulse sequence, so that the duty cycle ti / tr is less than 0.2, preferably less than 0.05, and more preferably 0.02 ± 0.005.