A Braai with a Difference or Case Hardening 101

[Tom Macrery]

You learn something every day. While I had heard of ‘case hardening’, I never had the pleasure to attend the braai. Robert made new pins for the motion of the 24; the old ones had warn and were too loose. This is the sequence of events, which can be followed in the photos below:

1 – Robert started with a mild steel bar, turned it down on a metal lathe to the correct diameters, cut the pieces to the required length, and then cut the necessary groves.
2 – The next step is to light the braai (Now I wonder where we got the coal?) and stoke it to high temperatures with compressed air.
3 – Now heat each pin directly in the coals until they are glowing red.
4 – Immediately place the pin in case hardening compound, which is a coarse powder-like substance consisting of carbon and probably other trace elements.
5 – The red-hot pin will melt the compound, cause some of it to adhere, and then absorb the carbon into its surface, probably only to a depth of microns.
6 – The pin is then placed back into the fire, again until glowing, which will continue the absorption of the compound.
7 – Then immediately into cold water, the quenching.
8 – When cool enough to handle, clean the pin of any excess carbon.
9 – The pin has now been case hardened and is tough enough to last under the punishing rotary motion of a steam locomotive.

Surely some of you will know much more about this, either metallurgically, or from a steam-fitter’s point of view. Please share your knowledge.

[Steve Appleton]

What an interesting account, Tom. Told with humour too! Thank you for this - I learnt something new!

[Steve Appleton]

I read from Wikipedia that a traditional way of case hardening includes urine! I am glad that method was not used here or, if it was, that you chose not to picture the supplying of the urine!

The traditional method of applying the carbon to the surface of the iron involved packing the iron in a mixture of ground bone and charcoal, or a combination of leather, hooves, salt and urine, all inside a well-sealed box. This carburizing package is then heated to a high temperature, but still under the melting point of the iron, and left at that temperature for a length of time. The longer the package is held at the high temperature, the deeper the carbon will diffuse into the surface.

Wikipedia http://en.wikipedia.org/wiki/Case_hardening

[ch.janssen-schmidt]

Interesting!

Regards,
Charles