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Billet InspectIR™
Modern Technology for high-speed surface inspection of cast & rolled billets, bars and tubes
© C
opyr
ight
H.R
ohlo
ff (
Pty)
Ltd
.Al
l rig
hts
rese
rved
. -1
-11
/05/
2007
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INTRODUCTIONIn today’s industrialised world the current demand for steel, particularly from the automotive industry, has become overwhelming. Although none of us can question the effectiveness of older NDT test methods for billets, it was essential that a modern, more efficient & faster method be developed for the in-line inspection of steel billets and tubes to comply with today’s demands and high safety- and quality standards.
The new system had to comply with, i.a. the following criteria: -
• Inspection has to be fast and safe.
• Inspection has to be sensitive and reliable and preferably contact-less.
• The ability to quickly categorize defects according to orientation, length and depth.
• To minimize the risk of human error, it was also necessary that the system isable to perform automatic evaluation and detailed traceable reporting.
Through modern infrared technology we have proven that all this is possible and that thermography as a NDT principle clearly has it’s applications in today’s manufacturing processes.
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Working Principle
When the surface of a steel billet is heated using a high frequency induction process, the edges of surface breaking defects are excited and display an increase in temperature compared to the surrounding areas.Only the surface area of the billet directly underneath the coil is heated and then only for a short time duration (micro seconds), depending on the speed of the billet through the coil.Temperatures on the billet’s heated surfaces are low and the billet cools down to ambient in seconds.
HF Coil
Excited surface area
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Working PrincipleFour special real time FPA (Focal Plane Array) infrared cameras are used to simultaneously capture data of individual billet sides at speeds in excess of 1m/s.A sophisticated signal processing system analyzes the captured data using proprietary algorithms to identify, quantify and display defects.
IR Camera Operator19”
Automated analysis
HF Coil
Direction of movement
Excited surface area
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Defect Categorization
Analysis of the data is two-fold and bi-directionalDetection, identification and positioning (Detection Algorithms)Temperature measurement
Defect temperature rise is related to defect depth (∆T)Our Billet InspectIR™ software performs defect categorization definable by operator, batch, steel grade, customer requirements etc.
PixelsTe
mpe
ratu
re
∆T2
∆T1D1 D2
Analysis direction X
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Defect LocationPositioning, Length & Depth
Duration of signal is proportional to defect length, billet speed & no. of pixelsMeasure the time from signal breaking through threshold until dropping below threshold againRelated to the measured speed of billet calibrated to pixel length
Maximum ∆T will give max. defect depthDetection generates a full set of defect position co-ordinates
Pixels
Tem
pera
ture
L2L1
∆T2∆T1
L1L2
Analysis direction Y
X2
X1Y2Y1
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Billet InspectIR™
Major Components include: -Camera Enclosure, Signal Processing System, Operator Control Cabinet, Induction Heater, Induction Coils, Water Cooling System, Conveyor, Defect Marking System
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Billet InspectIR™ – Camera Enclosure
Side view of camera enclosure
Front view of camera enclosure
Billet moves through enclosure on V-shaped rollersEnclosure moves in- & out-of-line for serviceCenter of enclosure adjusts for billet sizeDifferent induction coils fitted - billet size rangeHouses four special infrared camerasCameras’ MFD changes to billet size automaticallyPLC controllable
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Operator Control StationOptional SCADA & UT stations
LCD touch screen interface
Sophisticated control desk
Operator interface screen
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Induction heater
High frequency induction machine
Water cooled bus section & coils
Remote control utilizing SCADA
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Signal Processing System
Four PC-based signal processors
One PC-based Operator Interface
High-powered UPS
SCADA control
LAN switch
LCD touch screen
Utilities
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Marking Station
Four air knives remove excess moisture
Four defect marking guns
One reject marking gun
Servo-motor for automatic alignment
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Wetting Station
Wetting of round and square materialServo-motor for automatic alignment
Complete control of particle size
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Billet InspectIR™
Results, Investigation and Findings
22.5°C
33.1°C
24
26
28
30
32
LI01 LI03
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INVESTIGATION REPORT
REASON FOR INVESTIGATION:-
Defects were detected during surface inspection of hot-rolled square bars. The bars were rejected according to the acceptance/rejection criteria programmed into the Billet InspectIR™. The ∆T’s measured on the bars were between 12°-26°C and subsequently the Infrared inspection system rejected the bars.
AIM:-Determination of defect depth and profile classification of defect(s) detected by means of infrared inspection / testing technique.
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Procedure of Investigation
1. Visual examination: -The bars were scrutinized after being inspected by means of Infrared camera viewing and image processing. The defects were also visible to the naked eye and appeared as ‘long seam-type and scab/sliver type defects’. Three (3) sections approximately 300 mm long were marked and cut-out for further microscopic examination.
2. Microscopic examination: -
After careful consideration, sub-samples were marked out, cut and prepared for optical light microscopy using standard metallographic techniques. The defects were found to be scab/sliver type defects. The defect depths did vary slightly but in general the defect shape did not change significantly (see photo-micrographs on following slides).
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Microscopic…
Magnification 50x, Defect depth 0.19 mm
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Microscopic…
Magnification 50x, Defect depth 0.19 mm
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Microscopic…
Magnification 50x, Defect depth 0.40 mm
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Microscopic…
Magnification 50x, Defect depth 0.15 mm
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Natural defects found…
Small defect 0,2mm deep on the edge of the radius
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Corner defect
0,28mm deep defect on the radius
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Center defect
Center defect 0,17mm deep
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Center defect
Center defect 0,23mm deep, partially ground
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Pinholes…
Pinhole type defect 0,25mm deep
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Thermal Results
1121
3141
51
61
71
S1 S4 S7
S10 S13 S1
6S
19 S22 S25 S28 S31 S3
4
0
5
10
15
20
25
30
35
40
tance
Temperature
End Defect
35-4030-3525-3020-2515-2010-155-100-524.7°C
45.2°C
25
30
35
40
45LI01
Calibration Billet
°C
20
30
40
∆ T = 6°C
Leading Edge Defect 1
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Natural defects
Natural defect on leading edge in recessed area.Found joined sub-surface.
21.9°C
28.6°C
22
24
26
28
20
30
40
50∆ 6 - 26 °C
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Shot Blasted Billet – defects & slivers
17.3°C
27.7°C
18
20
22
24
26
LI01 LI02
15
20
25
30
35
17.3°C
27.7°C
18
20
22
24
26
LI01LI02
16
18
20
22
24
26
28
17.3°C
27.7°C
18
20
22
24
26
LI01 LI02 LI03
15
20
25
30
35
40
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Un-shot Blasted Billet – slivers
21.9°C
28.6°C
22
24
26
28
LI01LI02
15
20
25
30
35
40
Sliver identified and verified in top corner area
Note: transverse nature
Note: scale has lower temperature – below background temperature
12.4°C
40.2°C
15
20
25
30
35
40
LI01LI02
15
20
25
30
35
Same defect – after shot blasting
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Calibration Billet – artificial defects
Side 1 Bottom ∆ 6.4°C
22.5°C
33.1°C
24
26
28
30
32
LI01 LI03
15
20
25
30
35
Side 1 Center ∆ 7.2°C
22.5°C
33.1°C
24
26
28
30
32
LI01 LI03
15
20
25
30
35
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Shot Blasted Billet – defects & slivers
17.3°C
27.7°C
18
20
22
24
26
LI01 LI02
15
20
25
30
17.3°C
27.7°C
18
20
22
24
26
LI01 LI02 LI03
20
30
40
50
60
17.3°C
27.7°C
18
20
22
24
26
LI01 LI02 LI03
20
30
40
50
60
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Billet InspectIR™
Modern, High-Speed Billet Inspection
Head Office: -Technology House 188 Northlands Business Park29 Newmarket Street2194 North RidingSouth Africa
Postal Address: -H.Rohloff (Pty) LimitedP O Box 2652162 North RidingSouth Africawww.rohloff.co.za
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QUESTIONS ?
