ZIMSEC O Level · Metal Technology and Design · Form 2, Form 3, Form 4
Temporary and permanent joints
- Temporary: nuts and bolts, screws, machine screws – can be taken apart.
- Permanent: rivets, soldering, brazing, welding, adhesives.
Riveting
Rivet heads: snap (round), countersunk, flat and pop rivets (used where only one side can be reached). A rivet set and snap shape the head.
Soft soldering
Uses solder with a flux (to clean the joint and stop oxidation) and a soldering iron; used for electrical work and tinplate. Low strength.
Brazing (hard soldering)
Uses brass spelter and borax flux at a higher temperature (gas torch); stronger than soft soldering.
Welding
Melts the parent metals together, usually with a filler rod.
- Arc welding: an electric arc between an electrode and the work; used for steel fabrication (gates, frames).
- Gas (oxy-acetylene) welding: a hot flame; can also cut steel.
Safety: helmet with filter lens, gloves, ventilation, keep flammables away.
Adhesives
Epoxy resin joins metals to themselves or other materials.
Exam tip: Compare joining methods by strength, temperature needed and whether the joint is permanent.
Check yourself
- Give one use of pop rivets.
- State the purpose of flux in soldering.
- Which joining method is commonly used to make steel gates?
Show answers
- Joining where only one side of the work can be reached (e.g. sheet metal boxes, gutters).
- To clean the joint, prevent oxidation and help the solder flow.
- Arc welding.
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