Pear-shaped steel vessel and programmable logic controller: what they have in common

1. Step 1. Pear-shaped steel vessel — is part of — Bessemer converter. A steel vessel with a refractory lining.
2. Step 2. Bessemer converter — evolved into — Open-hearth furnace. A more controllable process.
3. Step 3. Open-hearth furnace — is made of — Brick. An open-hearth furnace is built of firebrick.
4. Step 4. Brick — is material for — Chemical plant. The furnaces and towers are brick.
5. Step 5. Chemical plant — has part — Programmable logic controller. Process control automation.

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