Steel Revolution

3. The Siemens - Martin Process

There isn't much more I can say about the Siemens brothers, the Martins, or the Siemens-Martin regenerative open hearth furnace on top of what you find in the links.
The "details" and how it developed easily fill a book. So I just show some pictures instead.
Here is a nice schematic drawing that shows the operation quite clearly (if very simplified):
Siemens-Martin furnace operating
Siemens-Martin process
Source: Internet
Here is the real thing
Charging a Siemens-Martin furnace
Charging a Siemens-Martin furnace
Source: Internet at large; origin of picture unclear.

Tapping of a Siemens-Martin furnace
Tapping a Siemens-Martin furnace
Source: Internet
It is clear that for tapping you needed an opening that could be opened and closed from the outside - with liquid iron in the inside. Not an easy thing to construct and I don't know how it was done.
Below is picture of an actual hearth from the Clydebridge steel works in England, now a kind of museum. Unfortunately, the tapping mechanism is not shown.
Siemens-Martin open hearth
The hearth of a (big) Siemens-Martin furnace
Source: Clydebridge Iron Works Museum site
Finally , a modern Siemens-Martin furnace - actually the last of its kind. It's shown in the Industry Museum in Brandenburg an der Havel, Germany. When it closed down in 1993, the era of the Siemens-Martin furnace was finally over.
Siemens-Martin furnace modern
The very last Siemens-Martin furnace
Large size
Source: From the Internet pages of " Peter-Berlin" Berlin, Deutschland. Thanks, Peter!
Are there any problems with the Siemens-Martin process? You bet. It is too slow. Good old Bessemer / Thomas could transform 5 tons of pig iron to steel in 30 minutes! Siemens-Martin, with all its advantages couldn't beat that. Making 300 ton or so at one go is nice - but it takes time and is not very flexible. So find a way to keep the advantages of the Siemens-Martin process but with the speed of the old Bessemer / Thomas process.
That is what oxygen blasting or the electric arc furnace processes do (up to a point). A kind of renewed Bessemer - type of processing, just with oxygen instead of air and all the modern real-time analytics implemented, simply is cheaper per ton of steel produced.

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