Author Topic: Hard to machine CI  (Read 760 times)

Offline John Rudd

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Hard to machine CI
« on: February 28, 2022, 06:45:26 PM »
I just received a replacement casting for a steam engine I’m building….
Trouble is the casting is so hard to machine it beggars belief even with carbide inserts..

Can I heat treat it to make it softer ( anneal? ) or bin it and get another ( more £££££’s)

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Offline vtsteam

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Re: Hard to machine CI
« Reply #1 on: February 28, 2022, 10:11:25 PM »
John You can try heat treating it. I was successful with a hard cast water pipe cap that I wanted to use as a cylinder base in the pipe and nail engine ModUp several years ago. ( https://www.madmodder.net/index.php/topic,10261.msg117030.html#msg117030 )

Bring it to a dark cherry heat, and hold there for say an hour. Then bury it in wood ashes, which will insulate it and allow it to cool over 24 hours. The slow cooling is the trick that prevents the hardness from reappearing

My casting was small so I accomplished all of the above by putting it in the glowing embers of my wood stove.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline John Rudd

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Re: Hard to machine CI
« Reply #2 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…..🤣 👨‍🚒👨‍🚒
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Online awemawson

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Re: Hard to machine CI
« Reply #3 on: March 01, 2022, 07:54:48 AM »
Needs to cool slowly hence Steve's suggestion of leaving to cool in wood ash. Even better - leave it in the log burner overnight and rescue in the morning when you rake out.
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Hard to machine CI
« Reply #4 on: March 01, 2022, 08:56:40 AM »
Yup, it's the slow cooling that's important. Wood ashes are very insulative (I use a bucket full of them) and can take high temperatures (red hot), unlike most other insulation. In a wood stove you can sometimes find glowing embers buried in wood ash two days after a fire is out. Be sure not to disturb your casting as it cools for a day.

Hardening: heat to cherry red and cool rapidl (plunge)
Softening/anealing: heat to cherry red and cool very slowly
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Hard to machine CI
« Reply #5 on: March 01, 2022, 09:10:10 AM »
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.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Hard to machine CI
« Reply #6 on: March 01, 2022, 09:38:12 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…..🤣 👨‍🚒👨‍🚒

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.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Online awemawson

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Re: Hard to machine CI
« Reply #7 on: March 01, 2022, 09:41:47 AM »
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.
Andrew Mawson
East Sussex

Offline John Rudd

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Re: Hard to machine CI
« Reply #8 on: March 01, 2022, 09:42:59 AM »
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….🤞
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline John Rudd

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Re: Hard to machine CI
« Reply #9 on: March 02, 2022, 10:07:51 AM »
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….🤣🤣)
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline vtsteam

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Re: Hard to machine CI
« Reply #10 on: March 02, 2022, 11:00:09 AM »
That's great John!!!  :clap:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg