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Break through innovation on wire rope NDT inspection by using weak magnetism technology


 Weak Magnetic Inspection Technology Principle

About Weak Magnetic Inspection Technology
The founding principle of TCK•W® weak magnetism inspection technology is the “Spatial Magnetic Field Vector Resultants” theory. As an innovative and proven NDT technology, it adopts large air-space and non-contact weak magnetic testing devices(see Fig.1 and Fig.2),and is capable to detect quantitatively both internal and external flaws of the test wire rope by monitoring and extracting signals of magnetometive force changes of the test wire rope, which is preconditioned by TCK.W weak magnetic loader.
TCK•W® weak magnetism inspection instruments comply with international testing and evaluating standards (ISO 3154) for wire ropes. By testing magnetometive force changes of the counties cross sections of the test wire rope, which reflect the synthetical degeneration status of each cross section, it provides the needed scientific and technical reference for evaluating in-service wire rope’s residual bearing capacity, safety co-efficient and service life.
Note: Magnetometive force change is the distribution and variation of the magnetic field. A cross section element is the axial segmentation differential of the wire rope. The synthetical degeneration status of a cross section’s bearing capacity reflects both LMA (Loss of Metallic Area) and LF (Localized Flaws).

Magnetic Characteristics of Ferromagnetic Materials
According to quantum mechanics, “magnetic domains “exist among adjacent electrons of ferromagnetic medium, which are lined up in a certain shape because of the interactive and coupling effect of the electrons ‘spin magnetic moment. Inside each magnetic domain, the direction of spin magnetic moment is the same. (See Fig.3).
When the magnetic domains are distributed in disorder, the ferromagnetic medium is not magnetic. When the distribution of magnetic domains is dominant along one direction, the ferromagnetic medium is magnetic.
Under given condition, external magnetic field reaction will change the quantity of magnetic domains in a certain direction, meanwhile it will make the ferromagnetic materials to store or release certain magnetic energy. Furthermore, these changes will not be recovered by the withdrawal of the external magnetic field(i.e. Generating magnetic loading).The magnetic loading will form magnetometive force in certain symmetrical space, which will last for a long time in the ferromagnetic materials unless there is violent mechanical vibration, high-temperature change and etc.
Wire Rope under the Natural State
The distribution of the magnetometive force of the wire rope relies on the load-bearing ferromagnetic materials of the numerous cross-sectional elements, and its density is decided by magnetic loading. The magnetic loading of the wire rope resulted from such activities as manufacturing, storing, transporting, installing, and operating is unordered (see Fig.4),and cannot factually reflect the material characteristics of the cross-sectional elements or unable to distinguish between normal and abnormal conditions of the load-bearing metallic materials. Therefore, there is a need for a method to make the magnetic loading and the physical characteristics of the load-bearing metallic materials correlated.
Weak-Magnetic Programmed Method
Weak-magnetic programmed method, a method for weak-magnetic energy programming, is also called weak-magnetic loading method. By programming the wire rope with a given magnetic load (as illustrated by Figure5), all the load-bearing ferromagnetic materials of the rope will have the designed low level magnetic energy density. If the load-bearing ferromagnetic materials are distributed equally and continuously along the axial direction, the magnetic energy density of each cross-sectional elements of the wire rope should be continuous and distributed equally and the magnetic flux passing through each cross-sectional element should also be equal(as shown in Figure6).
Note: Magnetic energy density reflects the magnetic energy loading storage level per unit volume of the ferromagnetic materials, which is similar to the potential energy of a motion system in Physics.
Wire Rope Flaws and Magnetic Characteristics
A wire rope subjected to repetitive mechanical loading stresses such as pulling, bending, twisting, wearing and etc. will deteriorate through their entire service life. Deformation, degradation, abrasion and stress concentration will appear in some sections. This deterioration process will destroy the original continuity and uniformity of the load-bearing materials of the rope, resulting in variation of the magnetic energy density of cross-sectional elements, as shown by Fig. 8.
The deterioration modes of cross-sectional elements of the wire rope could be categorized as LMA flaws (elastic rope diameter shrinkage, abrasion and corrosion) and LF flaws (broken wires caused by fatigue, plastic wear, martensitic embrittlement or mechanical damage). When passing through these deteriorated cross-sectional elements of the wire rope, the magnetic lines of force will be distributed along those irregular paths with lower magnetic resistance. As a result, the magnetic flux density and the distribution of magnetic energy products change accordingly. Differences of magnetic energy potentials are thereby produced. Also, the more deteriorated the wire rope, the more different the magnetic energy potentials.
If a normal or standard cross-sectional element of the test wire rope could be chosen and its magnetic energy potential could be correctly defined, then a benchmark value is available for inspecting the wire rope. By comparing the extracted magnetic energy potential information of all tested cross-sectional elements with the benchmark value, the variation of magnetic energy potentials along the axial direction becomes clear. This variation of the magnetic field reflects the mechanical changes of the load-bearing ferromagnetic materials. With over 20 years R&D efforts, W® has discovered the correlation between these two variables, which enables the quantitative, qualitative and positioning detecting of all modes of deterioration of the in-service wire ropes.
Weak Magnetism Inspection Method
The working of TCK•W® weak magnetism inspection technology involves three magnetic fields: the known magnetic field of the Dou sensors, the unknown but programmed magnetic field of the test wire rope and the inductive magnetic field by and between the above two magnetic fields .Because of its low magnetic energy level, the TCK•W® tester comes with the following capabilities: background noise signals shielding, large air-gap signal extracting, high speed response, high sensitivity and precision.
After high-speed and continuous sampling from the test wire rope, the test data is analyzed by TCK expert mathematic module. The variation or differences of magnetic energy potentials of all the cross-sectional elements along the axial direction of the wire rope is to be analyzed and evaluated in graph, statistics and data tables. The end test report includes quantitative descriptions of all detected flaws that affect the mechanical bearing capability of the wire rope, which could be used as objective references for assessing the wire rope’s safety status.

About Weak Magnetic Inspection Technology
TCK•W® Weak Magnetic Inspection Technology, based on “Spatial Magnetic Field Vector Resultants” theory, adopts a new type of electromagnetic-magneto electric effect sensors and achieves a non-destructive testing green technology for the ferromagnetic component.
TCK•W® high sensitivity sensors are composed of magnetism releasing device and magnetism evaluating device. The magnetism releasing device provides a given weak electromagnetic field Bx, which interacts with the weak. Magnetic field B of each cross section of the test wire rope. Together they generate the inductive magnetic field By, which the magnetism evaluating device converts the magnetometive force changes of By into electric signals accurately. Because of the structure particularity of steel cord conveyor belt,
TCK•W® Conveyor Belt Inspection System adopts horizontal + vertical response sensor arrays as the detection device: the horizontal sensors can induct the extent characteristics of metal distribution(the intrinsic component) sensitively, so that achieve the accuracy testing for breakage (including splice), fatigue, abrasion, and corrosion of steel cord through the amplitude output signals from horizontal sensors; while the vertical sensors will be more sensitive for the movement characteristics of metal distribution(the induced component) like splice, breakage…etc. open-ended signals. The combination of two kinds of sensors will fully guarantee the positioning and quantitative detection performance.
After sensor arrays pick up the electromagnetic signals of steel cord of conveyor belt, the signals will be converted into digital signals through technical shaping, filtering, and A/D conversion and then input to the 32-bit ARM processor; trechometer/ speed-measuring device outputs a pulse signal which will enter the 32-bit ARM system through tachometer circuit. Both of them take a synchronous spatial domain sampling, and upload the sampling data to the display terminal and large-capacity memory.
Display terminal and detection unit are communicated with each other by industrial Ethernet, compatible with cable or fiber-optic transmission. The Inter Process Communication is adopted unique software architecture and advanced programming techniques to achieve the real time transmission, processing, storage and display of testing data; synchronously support the functions like real time alarm, curve analysis, SMS, image reconstruction and test report print etc.
The diagram of Splice displacement and steel cords breakage in the same section of conveyor belt installed at main shaft of Zhulinshan Mining.
1)    Method for Measuring splice displacement value in splice area
When inspection software runs for the first time, it will collect all splice information of the conveyor belt (length, broken point position and etc.) and save it to sample database. After that the system enters real time inspection mode and compare the real time calculated splice length L’ to sample splice length L. Finally obtain the splice length displacement value. Formula is L=| L’-L|=L1+L2
2)    Method for Measuring flaw in non-splice area
When inspection software runs for the first time, it will collect all splice information of the conveyor belt (scope, position and etc.) and save it to sample database. The information will be regarded as known sample information of current status of conveyor belt. Then the system enters real time inspection mode. If the known flaws take changes or new broken rope, corrosion appear, the PC will figure out the change of known flaws and Quantitative and positioning information of new flaws.


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