Saturday, December 13, 2008

Wakebridge 9th December (3)

Thermit Welding is based on a chemical reaction between powdered iron oxide and aluminium. When heated the aluminium grabs the oxygen to form aluminium oxide and molten iron at about 3,000 degrees. This post shows the preparation and the next will show the exciting bit when the weld takes place.
1. The rails are laid out on the concrete base and then lifted onto temporary wooden blocks. The rail ends are cleaned by heating them.

2. The rails are very carefully positioned with the height being adjusted by metal wedges and lateral movement by an iron bar.
3. The final position is checked very carefully with a straight edge and then addional wedges similar to tent pegs are driven into the wood blocks to hold the position.
4. A mould for the molten metal is then constucted from a kit of parts. In the picture the left side is in place and the right side is lying on the gound.
5. Any gaps in the mould are filled with white sand and the mould is clamped together. In the picture the mould is complete and ready for the crucible.

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