electric resistance welded tubing (low frequency resistance welding) high frequency induction...

Electric Resistance Welded Tubing(Low Frequency Resistance Welding)

High Frequency Induction Welding

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

Resistance Tube Welding (ERW)

W. Stanley, Resistance WeldingMcGraw-Hill, 1950

The Making Shaping & Treating of Steel,USS Corp, 1964

The Making Shaping & Treating of Steel,USS Corp, 1964

Current Flow in a conductor as a function of Frequency

DC 60 HZ ACKiloHertz AC

High Frequency

Appreciating Hig-Frequency WeldingWelding Journal, July 1996

High Frequency Induction Welding

Metals Handbook, Vol 6ASM International, 1983

Impeder Inside the Core Promotes Path ADC

Linnert, Welding MetallurgyAWS, 1994

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

High Frequency Welding Applications (CONT.)

Strip Butt T-Joint

Spiral Tube

Spiral Tube Fin

HFHF

HFHF

[Reference: Welding Handbook, Volume 2, p.653, AWS]

High Frequency Welding Applications (CONT.)

Projection Seam

Pipe Butt Bar Butt

HF

HF

HF

InductionCoil

[Reference: Welding Handbook, Volume 2, p.653, AWS]

AWS Welding Handbook

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

Frequency KHz

Cu

rren

t P

enet

rati

on D

epth

, in

Met

er

Metals Handbook, Vol 6ASM International, 1983

Circuitry & Control

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

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

)onload(I

)offload(I)onload(IEff

p

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

/DC

Con

vert

er

HF

Res

onan

ceC

ircui

t

Ig

Efficiency Improvements Can Come From Two Sources

• The Power Circuit• The Workpiece Arrangement

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

/DC

Con

vert

er

HF

Res

onan

ceC

ircui

t

Ig

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

/DC

Con

vert

er

HF

Res

onan

ceC

ircui

t

Ig

• Increase the turns ratio of current transformer• Reduce tank capacitance

Ishizaka, HF Resistance Seam Welding,The Fabricator, Nov 1993

Light Load Matching

GridFeedback

Circuit

Ep

Ip

AC

/DC

Con

vert

er

HF

Res

onan

ceC

ircui

t

Ig

• Reduce the turns ratio of current transformer• Increase tank capacitance

Current flows more to edge when• Edges are closer• “v” length is shorter

Caution: Can get Premature Arcs

• Insert Impeder• Impeder Mass Closer to Tube• Cool Impeder

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

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

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

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)

Seam Annealing

Robotron Web Site

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

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

Some Products of High-Frequency Welding

[Reference: Welding Handbook, Volume 2, p.665, AWS]

HF Welding