tin & terne coated steel. resistance welding lesson objectives when you finish this lesson you...

Tin & Terne Coated Steel

Resistance Welding

Lesson ObjectivesWhen you finish this lesson you will understand:•

Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line workbook

Keywords

Tin Plating

• Hot Dipped• Electro-tin Plating

• Chromate• Painted

Post Plating Treatment

Tin Coated - 3% US Product is Hot Dipped

Making & Shaping of Steel, USS, 1964


Zeta Eta


FeSn2

Eta

FeSn zeta

Tin Coated - 97% is Electrolytic

Acid Process:

Alkaline Sodium-stannate Bath:

oSne2Sn

oSne4Sn


Coating Melted to give Bright Appearance

Alloying?Alloying?

Line speed = 2000 ft/min

Tin Coated


14 Million Tons of Electrolytic Tinplate per Year

Typical• Light Gage Strip 0.006-0.012 inch

• Thickness 6 to 30 .in

Chromate Passivation Film

Oil Application

Typical Applications of Tin Coated Steels

• Black Plate (no Tin)Temper Roll Start Material

• Tin CoatedOrnamental Uses

• Tin Coated & ChromateOil filter Heater componentsFood Storage Containers

• Tin Coated & Painted Gas Tanks

Resistance Seam Welding Most Common Process• 60 Hz AC Seam Weld• 400 Hz AC Seam Weld• DC Seam Weld• Soudronic Weld

SteelTin

Tin Oxide

Steel

Temper Roll Roughness/Oxide

Black Plate

Hot Dipped Tin

20 40 60 80

Electrode Force (kg-f)

10

100

1000

Resi

stan

ce (m

icro

-ohm

)

Static Dynamic

• BP higher Static R (cold worked)• HDT low R (annealed in HDT low R (annealed in HD), higher F causes HD), higher F causes reduction (break of oxide)reduction (break of oxide)• Dynamic BP reduced R (CW annealed), HDT increased R (Temp effect) Ichikawa, M, “The study of high-

speed seam welding of material for cans” Trans ISIJ, 1983

400 Hz Seam Weld Electrolytic Tin-Chromate Coated Steel(Effect of Coating Thickness)

SteelTin

Metallic ChromeChrome Oxide

Variations in Coating Thickness (listed on next slide)

Yoshida, M, et al “Effect of Tin Pre-treatment on Seam-weldability of Chromium Plated Steel Sheets”, Trans. Iron & Steel Inst. Of Japan, 1987

Sn [g/m2]

Cr [mg/m2]

R [m}

Available Current Range [kA] 3.5 4.0

0/0 71/66 26.3 zero 0/5.6 80/78 30.2 zero

1.0/1.0 6/6 0.11 {----} 1.1/1.1 89/90 0.11 {-} 1.7/1.7 78/84 0.08 {-----} 2.8/2.8 6/6 0.05 {---- --------} 2.8/2.8 83/80 0.05 {----}

400 Hz Seam Weld Tin Coated Steel• Available Current Range Extends as Tin Coating Weight Increases• Contact Resistance Decreases, Soft Sn allows Cr oxide to break• With only one side Sn the resistance is still too high



One Side Sn Coating

• Coating on only one side causes center of heat zone to depart from interface

Hansen, Constitution of Binary Alloys,McGraw-Hill 1958

Welding of Tinplate bySoudronic Welding of Cans

A = FeederB = Roll-FormerC = Can Body TransferD = Welding

AWS Welding Handbook

To Assure Consistent Weldability of Tinplate, You Must Specify:

• Base Metal Composition, thickness, temper, & surface finish• Coating Thickness & Reflow Process• Passivation Treatment• Oil Treatment

Welding Problems with Tin Plated Steels

A Level of 0.5% Tin in Weld Metal Can Cause Embrittlement

Kimchi, M, et al, “Weldability of Hot-Dipped Tin-Coated Steel Sheet”, Welding Journal, June 1995

Surface Cracking

• Sn Liquid Metal Embrittlement• Originating at Knurl Marks• Prevalent in AC & DC Seam Welds• Not Common in Soudronic Welds

Terne Coating

Clean Sheet

Palm Oil

Terne Metal80%Pb - 20%Sn (3-20%)620 - 680 F(Pb Insoluble in Fe, Sn helps wet)

Travel Speed Controls Thickness

Typical Applications of Terne Coated Steels

• Long TerneGas tanksFuel linesBrake linesRadiator partsHeater partsAir cleaners

Seam Welding of Terne Coated Steel

Resistance Seam Welding - Most Common0.025-0.062 inch thick steel

0.16 to 0.42 oz/sq ftSteels thicker than 0.125 are difficult to weld

Typical Electrode Face = 0.20 to 0.31 in.Welding Speeds = 60-100 ipm

Precautions often Taken• Removal of Dirt and Oil Films Recommended• Oxide Build-up on Wheels often Continuously Removed

Electrode Wear

Electrode

KnurledDriveRoll

Greer H, Begeman M, “Resistance Seam Welding of Terne Plate” Welding Journal, June 1960

Electrode Deterioration

Centerline Crack

Pb Sn

Water SprayLess Cooling

More AlloyingIn Center

Only about ½ Electrode life compared to Galvanized


Pb Sn ZnBoiling Point C 1725 2270 906

(Zn Vaporizes Before Alloying)

Additional Cooling Water Improves Electrode Life

Initially Initially Arcing occursArcing occurs

Electrode StickingElectrode StickingShortlyShortly

Alloy LayerAlloy LayerKnurl ImpressionsKnurl Impressions

Molten TerneCoating Flows Out Heat Flows Heat Flows out with out with coatingcoating

Higher Electrode ForceRequired to get Coating Out

Electrode Force/Weld Current(Pulse 3 on - 2 off)

Resulting in Higher Weld Current Needed


(Pulse 3 on - 2 off)

Entrapped CoatingRemains as Inclusion Defect

60 ipm

100 ipm

Region of Optimum Weld

(Current, Force, Travel Speed, Pulse 3-2)


Travel Speed


Current Range as a

Function of Gage

Region of Optimum Weld

(And Defects)


Flashing, Surface ScaldingHigh Current, Low Force, Excessive Penetration, Surface Expulsion

Transverse CracksHigh Penetration, Hot Surface, Liquid Metal Embrittlement

Severe Surface IndentationHigh Force, Very high Current, High Penetration, Hot Deformation

PorosityHigh Current, High Force, Expulsion Pores

Inconsistent, Insufficient PenetrationLow Current, Low Force, Small nugget

PorosityLow Force, Low CurrentShrinkage Pores

Current Pulse Control

Variable Heat Time• Only slight effect on penetration• Increase heat time increased nugget length, improved overlap

Increased Cool Time• Sharply reduce the amount of current required to produce a given nugget penetration SEE NOTES



Welds made with 3 cycle cool time were about equal in quality to 2 cooling cycles except nugget overlap was lacking

A cool time of 2 cycles normally A cool time of 2 cycles normally produced good welds with less produced good welds with less porosity and shrinkage defects.porosity and shrinkage defects.

Reducing the cool to 1 cycle tended to overheat the weld area and cause porosity and shrinkage cracks in the nugget

Spot Welding of Terne Coated Steel

Resistance Spot Welded - AWS Reports Good Results Obtained With

Class II ElectrodesTruncated Cone with 0.25 Face Diameter

Current, Time, Force = 15-30% Greater Than Bare Steel

Some Comparisons Between Tin and Terne

Welding

Comparison Study – Seam Welding of HD Tin and Terne(Painted and Unpainted)


Weld Speed (ipm)

We

ld C

urr

en

t (k

A)

Expulsion orOverheatingor SurfaceErruptions

Non-ContinuousWeld

Paint orCoatingRemovalProblems

AC SeamWeldLobe Curve

Effect of Paint on Terne and Effect of Tin Coating Thickness (0.35 mils/side & 0.55 mills/side)

•Thick Sn = High R Low I• Paint = High R Low I

Increased CoatingThickness or Paint


Effect of Substrate Thickness on AC Seam Welding of Tin Coated

SubstrateThickness


Effect of Painting on AC Seam Welding of Tin Coated

Painted Terne

Painted Tin

Un-Painted Tin

Painting


Un-Painted TinAC Seam Weld

Un-Painted TinDC Seam Weld

Painted GalvannealPainted Galvanneal

Painted ZnNi

Effect of DC Seam Welding on Tin Coated Steel



DC @ 110 ipm(Max Speed w/o Defects) Soudronic

@ 320 ipm

Soudronic @ 400 ipm

Results of Soudronic Welding on Unpainted Hot Dipped Tin Coated Steel

tin & terne coated steel. resistance welding lesson objectives when you finish this lesson you...

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