Gas welding and tunnelling shield: what they have in common

1. Step 1. Gas welding — is used in — Welding. Gas welding.
2. Step 2. Welding — uses — Tungsten. TIG welding uses a tungsten electrode.
3. Step 3. Tungsten — is material for — Cemented carbide. Tungsten carbide.
4. Step 4. Cemented carbide — is material for — Tunnel boring machine. The cutters are cemented carbide.
5. Step 5. Tunnel boring machine — evolved from — Tunnelling shield. A development of the tunnelling shield.

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