HF Welding
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Transcript of HF Welding
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Electric Resistance Welded Tubing(Low Frequency Resistance Welding)
High Frequency Induction Welding
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ERW & High Frequency Welding
Lesson ObjectivesWhen you finish this lesson you will understand:• The difference between low frequency Electric Resistance Welding and High Frequency Welding• Applications of each
Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line
workbook5. Do Homework
KeywordsElectric Resistance Welding, High Frequency Welding, Tube Welding, Proximity Conductor, Induction Coil, Induction Current, Impeder, Seam Annealing
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Resistance Tube Welding (ERW)
W. Stanley, Resistance WeldingMcGraw-Hill, 1950
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The Making Shaping & Treating of Steel,USS Corp, 1964
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The Making Shaping & Treating of Steel,USS Corp, 1964
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Current Flow in a conductor as a function of Frequency
DC 60 HZ AC KiloHertz ACHigh Frequency
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Appreciating Hig-Frequency WeldingWelding Journal, July 1996
High Frequency Induction Welding
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Metals Handbook, Vol 6ASM International, 1983
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Impeder Inside the Core Promotes Path ADC
Linnert, Welding MetallurgyAWS, 1994
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High Frequency Welding Applications
[Reference: Welding Handbook, Volume 2, p.653, AWS]
Tube Butt Seam Tube Butt Seam Tube Mash Seam
HF
HF
HFInduction Coil
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High Frequency Welding Applications (CONT.)
Strip Butt T-Joint
Spiral TubeSpiral Tube Fin
HFHF
HFHF
[Reference: Welding Handbook, Volume 2, p.653, AWS]
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High Frequency Welding Applications (CONT.)
Projection Seam
Pipe Butt Bar Butt
HF
HF
HF
InductionCoil
[Reference: Welding Handbook, Volume 2, p.653, AWS]
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AWS Welding Handbook
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Typical Tube Welding Conditions for Steels
30 m/min (100 ft/min)at:600 kW power for12 mm-wall (1/2 in);diameter of 200 - 1200 mm (8 - 48 in)
60 -240 m/min (200-800 ft/min)100-400kW power0.6 - 1.6 mm walls (0.025 - 0.065 in)diameter of 25 - 50 mm (1 - 2 in)
Note high speed
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Frequency KHz
Cur
rent
Pen
etra
tion
Dep
th, i
n
Met
er
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Metals Handbook, Vol 6ASM International, 1983
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Circuitry & Control
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Control Devices
Input Voltage Regulation• SCR’s control input voltage constant• Filters used on rectifier output to reduce ripple• Variations cause intermittent fusion “stitching”
Speed Control• Feedback Control on weld power as a function of mill speed• Reduces scrap on start and stop
Weld Temperature Control• Optical Pyrometer aimed at “v” adjusts weld power
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AWS Welding Handbook
460 V60 Hz
ReduceRipple
Solid State
50 - 65% Efficient
>80% Efficient
DC
Circuit Made of Three Components• Filter• Tube or SS HF Converter• Tank Circuit
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)onload(I)offload(I)onload(I
Effp
pp
Ip=Plate CurrentIg= Grid CurrentEp= Plate Voltage
If Efficiency is Below 55% Modifications are neededNominal Target =75%
Ishizaka, HF Resistance Seam Welding,The Fabricator, Nov 1993
GridFeedback
Circuit
Ep
Ip
AC/D
C Co
nver
ter
HF R
eson
ance
Circ
uit
Ig
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Efficiency Improvements Can Come From Two Sources
• The Power Circuit• The Workpiece Arrangement
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Ishizaka, HF Resistance Seam Welding,The Fabricator, Nov 1993
Proper Matching
Relationship between the plate voltage and plate current; and the relationship between plate voltage and grid current are nearly coincident with the rated impedance line.
GridFeedback
Circuit
Ep
Ip
AC/D
C Co
nver
ter
HF R
eson
ance
Circ
uit
Ig
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Ishizaka, HF Resistance Seam Welding,The Fabricator, Nov 1993
Overload Matching
Occurs when load impedance is too small in comparison with the rated impedance
GridFeedback
Circuit
Ep
Ip
AC/D
C Co
nver
ter
HF R
eson
ance
Circ
uit
Ig
• Increase the turns ratio of current transformer• Reduce tank capacitance
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Ishizaka, HF Resistance Seam Welding,The Fabricator, Nov 1993
Light Load Matching
GridFeedback
Circuit
Ep
Ip
AC/D
C Co
nver
ter
HF R
eson
ance
Circ
uit
Ig
• Reduce the turns ratio of current transformer• Increase tank capacitance
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Current flows more to edge when• Edges are closer• “v” length is shorter
Caution: Can get Premature Arcs
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• Insert Impeder• Impeder Mass Closer to Tube• Cool Impeder
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Effect of Weld Speed on Power and Performance
Power = E*IB = Fixed Power (losses etc)A*Sp = Weld Power
U=The relative power B:A
B has less of an effect at higher travel speeds
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AWS Welding Handbook
Induction Coils• Cu Tubing or Bar• Normally water cooled• Surround = efficiency• Mag. Strength reduces with distance = 1/8 - 1 inch between coil and work
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AWS Welding Handbook
Contacts• Cu or Hard Cermets• 0.25 - 1 in2
• 500 - 5000 Amps• Cooling required• 5 - 50 lbs force• Life = 1K - 300K feet
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Impeders(Current Flow Around inside Surface of Tubes can cause reduced efficiency. The impeder increases the inductive reactance around inside wall of tube.)• Ferritic Material• Cooled: keep below Curie Temp• Extend from “v” to 1 1/2 tube diameters upstream of “v”
Mandrels• Used to treat inside weld bead shape or scarfing• Nonmagnetic Material like Austenitic SS (Impeders also needed)
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Seam Annealing
Robotron Web Site
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Advantages of High-Frequency Welding
• Produce welds with very narrow heat-affected zones
• High welding speed and low-power consumption
• Able to weld very thin wall tubes
• Adaptable to many metals
• Minimize oxidation and discoloration as well as
distortion
• High efficiency
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Limitations of High-Frequency Welding
• Special care must be taken to avoid radiation interference in
the plant’s vicinity
• Uneconomical for products required in small quantities
• Need the proper fit-up
• Hazards of high-frequency current
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Some Products of High-Frequency Welding
[Reference: Welding Handbook, Volume 2, p.665, AWS]
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HF Welding