Zinc
description
Transcript of Zinc
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Zinc
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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
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Zinc• Specific Gravity 7.14, slightly less than iron• Low melting temp 787F (419C)• Low boiling temp 1665F (907C) - Fuming, Vapor• Electrical Conductivity 25% of Copper (2 x steel)
Zinc Alloys• Two Alloy Types
• Cast Zinc• Rolled Zinc
• Zinc Alloys Brittle at RT, elevated temp mechanical working• Zinc Alloys have recrystallization temp at or below RT• Recrystallization reduces strength in rolled alloys• Use low heat input to reduce HAZ Softening (Resistance Weld)• Mechanical Clean & Abraded to clean surface
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Uses• Cast forms• Roofing• Chemical Processing Applications
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Resistance Welding of Rolled Alloys
Spot & Seam Welding• Equivalent or Slightly Lower Current than steel (lower resistance, lower melting temp)• Lower Force than steel (softer)• Low inertia head, more indentation needs faster follow-up• Disp Strengthened Electrodes, High alloying with copper• Mechanical clean surface• Internal defects or cavities common, low boiling point
•Forge force can help
Seam Welding• Increased roll speed requires increased current
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Cu Zn
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Rolled Alloy Spot & Seam
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Cast Alloy Spot & Seam Weld
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Electrode: class 2 with 3 in radius dome
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Electrode: class 2 with 15 degree bevel and face radius of 3 inches
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Resistance Welding of Cast Zinc Alloys
• Start with the same recommendation as Rolled Alloys• High Resistance Films (electro-deposited & others) Removed
The castings generally have extra coatings