- Practice · 6 marks
Temporary and permanent joints; soldering, brazing, welding
Short answer
Temporary joints (bolts, screws, keys) can be dismantled; permanent joints (rivets, welds, brazes) cannot. Soldering uses filler below 450 °C without melting the base metal; brazing uses filler above 450 °C, base metal unmelted; welding melts the base metal. Solder gives low strength, brazing medium, welding highest.
Classify joints as temporary and permanent with examples. Differentiate between soldering, brazing and welding.
Types of joints
- Temporary joints can be taken apart without damaging the parts: bolts and nuts, screws, studs, keys, cotters, pins, couplings.
- Permanent joints cannot be separated without damage: riveting, welding, brazing, soldering, adhesive bonding.
Soldering, brazing and welding
| Point | Soldering | Brazing | Welding |
|---|---|---|---|
| Filler melts at | Below 450 °C | Above 450 °C but below the melting point of the base metal | The base metal itself melts and fuses (filler, if used, is of similar composition) |
| Filler | Tin-lead solder | Brass (Cu-Zn) or silver alloys | Same as or similar to the parent metal |
| Heat source | Soldering iron, torch | Torch, furnace | Gas flame, electric arc, resistance |
| Joint strength | Low | Medium to high | Highest, close to the parent metal |
| Parent metal | Not melted | Not melted | Melted |
| Flux | Rosin, zinc chloride | Borax | Not always; flux coating or shielding gas |
| Use | Electronics, tin cans, plumbing | Tool tips, bicycle frames, pipes | Structures, vessels, pipes, machinery |
Brazing works by capillary action, like soldering, with a gap of 0.05 to 0.25 mm. It can join different metals (steel to cast iron or copper) and uses less heat, so it causes less distortion than welding.
✓ Answer checked by Claude Opus 5.5 (high effort)
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