Gallery, Projects and General > How do I??

Hard to machine CI

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vtsteam:
More info about hard iron:

If iron cools rapidly in a mold after pouring, it gets "chilled" or hardened. This can happen more easily in smaller castings or thin sections of castings which cool more rapidly. The chilling actually produces carbide in the iron, which is why it is so difficult to machine.

The other cause for chilling is if the mold is broken open too soon for curiosity or cost reasons, the casting cools too rapidly and you get chill.

There are additives like ferrosilicon, which allow pouring thinner castings with less likelihood of chill, but they also weaken the metal, and are expensive. Ideally the foundry adjusts all parameters to produce good machining iron. Appropriate cooling time is a better way to get good metal than simply throwing additives at it.

vtsteam:

--- Quote from: John Rudd on March 01, 2022, 03:52:56 AM ---Steve,
I have a gas torch that I use for silversoldering, also some 12 fire bricks. I can put the casting in the fb and heat, then just let cool?

Or I can fire up the bbq…..🤣 👨‍🚒👨‍🚒

--- End quote ---

John you can use any method that gets the metal up to at least dark cherry red and can hold it there for awhile (depending on thickness -- if thin, it doesn't need long), and then get it into several inches of wood ashes for long cooling.

awemawson:
For parts that need a hard surface it was / possibly still is, the practice to incorporate a ‘chill ‘ in the molding sand with only a thin skim of facing sand over it so that face of the part was white iron.

John Rudd:
Ok,
I don’t have a wood fire, coal fire or any other kind….,

So, lacking in choice, I’ve warmed the casting in an ‘oven’ formed with my fire bricks . I heated the casting on the hard  areas until starting to turn orange. Meanwhile while it was warming up slowly(😂) I lit my bbq lighter…l this is a steel tube about 5-6” in dia and about 12” high….Once the coals were glowing I placede casting in amongst the coals and left it… it is currently sat in about 3” deep charcoal, “cooking slowly “

Hopefully this will do the trick….🤞

John Rudd:
Right, thought I’d give some feedback on this……

Firstly, the casing is the vertical engine standard from a Stuart 10V, so there isn’t a great mass of metal…ergo if the molds are broken open early, then yes they will cool down pretty rapidly due to the lack of hot material surrounding the casting.

So, with that in mind, I heated it with my medium size torch running propane an my makeshift oven.But, I concentrated the heat mainly on the areas that needed to be machine…
While it was heat soaking, I fired up the bbq starter, like I said above. Once that was well under way, I
It the casting in among the hot coals, topped off with more charcoal and left alone.
It soaked in heat for about 5 hours and gradually cooled over that time too…..
This afternoon, I machine the top flange ready for the cylinder…….What a difference….!!

So, thanks for all the advice guys, something else I’ve learned…( another use for the bbq….🤣🤣)

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