Electromagnetic Testing Chapter 3- Electromagnetic Testing

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The Rollscan unit can automatically test parts with a cycle time of 5 to 60 seconds per part. The cycle time depends on test part size and the design of the material scanning system. Surface testing speeds of up to 3 ft/s can be used. Red LEDs provide quick visual indications of grinding burns. An oscilloscope and 0 to 2 V analog recorder output are also provided. The unit provides a rapid nondestructive alternative to chemical etching for the testing of grinding burns on camshafts, crankshafts, bearing races, drill bits, tool steel parts, rollers, piston pins, gears, and other items. Its response time is 30 ms at 0.02mm depth, which is standard for the unit. Charlie Chong/ Fion Zhang
3.17.5 Calibration and <strong>Testing</strong> Barkhausen noise measuring instruments are calibrated in terms of stress, N/mm2 or ksi. Comparisons of stress levels in materials also can be made in relative MP units. Uniform samples, typically 0.5 in. wide x 4 in. long x 0.25 in. thick, can be used to obtain more accurate calibration curves. Sample preparation consists of stress relieving the samples at 650°C and allowing them to slowly cool to room temperature. Then the samples are strained in tension and compression within their elastic limits using a tensile tester, while simultaneously monitoring the strain with strain gauges and a BN measuring instrument. Using this procedure, approximately 12 measurements were made with the samples in tension, and an additional 6 measurements were obtained with the samples in compression, to obtain the calibration curve shown in Figure 3.41. The three steels used to obtain this calibration curve had yield strengths ranging from 248 to 710N/mm2. As shown, the magnetic parameter is very sensitive to changes in internal stress. Magnetization settings are front panel settings. Charlie Chong/ Fion Zhang
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Electromagnetic Testing Chapter 3-
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Submarine Applications Charlie Chon
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Fion Zhang at Shanghai 6th April 20
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IVONA TTS Capable. Charlie Chong/ F
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Chapter 3. ELECTROMAGNETIC TESTING
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Barkhausen effect The Barkhausen ef
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Barkhausen Noise Charlie Chong/ Fio
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Figure 3.1 Eddy current principle.
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Figure 3.2 Schematic diagram of bas
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Figure 3.3 The effect of conductivi
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Figure 3.3 The effect of conductivi
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Another important influence on coil
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If the conductivity of the material
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Figure 3.5 The effect of a crack on
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FIGURE 8-49 Conductivity curve: (a)
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So far, we have described how eddy
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Figure 3.6 The effects of (a) condu
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3.1.2 Limiting Frequency f g of Enc
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Figure 3.7 The effect of degree of
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Charlie Chong/ Fion Zhang
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Eddy Current Heating Charlie Chong/
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Eddy Current Heating Charlie Chong/
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Eddy currents weaken the original m
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3.2 MAGNETIC FLUX LEAKAGE THEORY Wh
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3D Magnetic Field Charlie Chong/ Fi
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3D Magnetic Field Fig.1 THE PRINCIP
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Based on what we have learned about
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Charlie Chong/ Fion Zhang Figure 3.
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Magnetic Field - Simple Semi Ellipt
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Flux leakage sensors have small dia
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The frequency of the alternating fi
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Figure 3.14 Rotating magnet arrange
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3.3 EDDY CURRENT SENSING PROBES For
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As the probe moves over the defect,
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Figure 3.17 Differential surface co
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Figure 3.19 shows an encircling coi
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The application of eddy current sen
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Baffles and tube sheets. Charlie Ch
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Another important consideration for
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3.4.1 Induction Coils For an induct
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If the diameter of a surface coil i
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3.4.2 Hall Effect Sensors Hall effe
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Figure 3.21 illustrates the Hall ef
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Hall voltage Charlie Chong/ Fion Zh
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Since a 1 gauss (G) field produces
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Figure 3.22 Effect of magnetic fiel
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3.5 FACTORS AFFECTING FLUX LEAKAGE
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Defect & Flux Distribution Charlie
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The distance between adjacent defec
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3.6 SIGNAL-TO-NOISE RATIO The signa
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With flux leakage testing, signal-t
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As shown in Eq. (3.6), test frequen
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The characteristic frequency for a
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Charlie Chong/ Fion Zhang
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Figure 3.23 Magnetization or magnet
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By taking the product of B and H fo
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The rate of change of the opposing
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Figure 3.25 Encircling coils establ
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Figure 3.27 DC-MFL sensor illustrat
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Fill factors apply only to encircli
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For best results with encircling co
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3.11 INSTRUMENT DESIGN CONSIDERATIO
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Charlie Chong/ Fion Zhang Figure 3.
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TABLE 3.2. Comparison of Instrument
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Page 157 and 158: Figure 3.33 ET testing of hot coppe
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Page 161 and 162: 3.14 MAGNETIC FLUX LEAKAGE TESTING
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Page 179 and 180: 3.17.1 Introduction In 1911, Dr. He
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Page 187 and 188: Figure 3.38 A comparison of Barkhau
Page 189 and 190: Figure 3.39 Three-channel Rollscan
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Page 195 and 196: Comparative studies by Kirsti Titto
Page 197 and 198: 3.17.6 Current Applications Barkhau
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Page 217 and 218: 3.19.3 Butterfly Plot To aid interp
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Page 221 and 222: Figure 3.48 Flowchart selection of
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Page 225 and 226: Other applications include: • Ins
Page 227 and 228: Eddy Current Testing at High Temper
Page 229 and 230: Good Luck Charlie Chong/ Fion Zhang
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Electromagnetic Testing Chapter 3- Electromagnetic Testing

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