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Mechanical joining, soldering and fasteners · Lesson 4 of 4

Mechanical joining, soldering and fasteners: defects, verification and case study

What unfilled laps, ridged beads, green stains, rusting rivet stems, loose rivets, buckling and cracks tell you, how to inspect a joint, and a stainless seam case study.

You will be able to: Diagnose a soldered or riveted joint defect from its symptom, name the published cause and corrective options, inspect a joint against a checklist, and document the evidence for review.

10 min · 11 slides · 7 questions

All lessons in this module
Slide 1 of 11

Read the defect

Each soldering symptom points to a cause the sources name:

  • Solder on top, lap not filled: iron too small or cold, faces untinned, or gap too wide
  • Ridged, lumpy bead: pasty solder, or the iron moving too fast
  • Solder will not take: oil or oxide left on, sandpaper resin, or heavy oxide that flux cannot lift
Correct and incorrect soldered and riveted jointsFour pairs, correct on the left and incorrect on the right. Solder: solder fills the whole lap, against a bead on the edge with the lap left empty. Grip: a rivet with a 0.063 to 0.125 in grip clamps a 0.064 in stack, against a 0.126 to 0.187 in grip rivet whose set body forms below the sheet and leaves it loose. Copper seam: a copper-alloy rivet, against a rivet with a steel stem that rusts. Aluminum sheet: an aluminum fastener, against a galvanized screw that rusts.CorrectIncorrectSolder through the whole lapStack 2 x 0.032 in = 0.064 inRivets in a copper seamFastener in aluminum sheetCORRECTINCORRECTCORRECTINCORRECTCORRECTINCORRECTCORRECTINCORRECTlap emptygrip 0.063-0.125 ingrip 0.126-0.187 inloosecopper-alloy rivetsteel stem rustsaluminum fastenergalvanized: rusts

Four pairs. Solder filling the whole lap, against a bead on the edge with the lap empty. A 0.063 to 0.125 in grip rivet clamping a 0.064 in stack, against a 0.126 to 0.187 in grip rivet left loose. A copper-alloy rivet in copper, against a steel stem that rusts. An aluminum fastener in aluminum sheet, against a galvanized screw that rusts.

Grips are POP manufacturer listings (AD42ABS, AD43BS). Copper rivets: Agans and CDA. Fasteners in aluminum: MCA. Schematic, gaps drawn large.

Sources

Videos for this lesson

What this video shows: CDA, narrated by Larry Peters, shows stitch types such as the butterfly stitch, and how to stitch and inspect a joint.

Video: How-To: Vertical Soldering, Lap Seam (Part 2, Stitching and Inspection) by Copper Development Association, on YouTube. Chosen from the video's published description.

What this video shows: From a tool supplier: a Sheet Metal Workers Local 19 mechanic stitches, or bridges, a box gutter seam, turning the iron down and laying a second bead.

Video: Soldering a Box Gutter - Stitching by John Stortz & Son Inc, on YouTube. Chosen from the video's published description.

Glossary

Cross-section sample
A cut through a trial seam that shows whether solder sweated through every layer.
Green discoloration
Staining beside a seam from active flux left on after soldering.
Small anode, large cathode
A small part of a less noble metal on a large noble sheet, which corrodes fast; MCA calls it undesirable.