# Cast Iron Quality in my Foundry (From Brake Rotors)



## Xyius (Jan 19, 2017)

Hello everyone,

First time poster here.  This is a weird question, but I am really curious as to what is going on.  I hope this is the appropriate place to post.  I don't know who else to ask!

I have a home foundry, from which I do mostly iron castings (at least right now).  Recently I melted down some old brake rotors I had in the scrap bin.  I cut them up into pieces and just for fun, I wanted to measure the density of the rotors and compare them to my other scrap iron from which I had already melted down and formed into ingots.

The density of cast iron is about 0.28 lbs / in^3.  And this is what my iron ingot measured when I weighed it and measured the volume.  However the rotor piece only measured 0.24 lbs /in^3.  I checked a few times too!

When I melted them down, they seemed to have a LOT of slag.  So I figured they were just cheap rotors and were probably alloyed with something else for what ever reason.  But then I took an ingot that I made purely FROM the rotors and measured the density again and STILL got 0.24 lbs/in^3!  I thought for sure it would go to to 0.28 since I assumed all the impurities would come out as slag.

Does anyone know what is going on here? What the heck is in these rotors?


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## silence dogood (Jan 19, 2017)

Except for a high school class way back when, I know little about foundry  so I can't answer your question.  However,  what does the "^3" mean?


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## CluelessNewB (Jan 19, 2017)

silence dogood said:


> what does the "^3" mean



inch cubed or cubic inch


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## Ulma Doctor (Jan 19, 2017)

i'm wondering if there was some steel in the rotors


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## FOMOGO (Jan 19, 2017)

For the price they sell those Chinese rotors, I can't imagine it being anything to exotic. If you can imagine what ever the cheapest alternative is, that's probably it. Mike


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## Xyius (Jan 19, 2017)

Thanks for the replies.  Yes ^3 means raised to the third power, in other words, cubic inch.

I don't think it was steel, steels density is pretty much the same as iron and it is much harder to melt than iron.  I was reading today that the cheap rotors are made from the "bottom of the barrel" scrap iron, so you never know what is in it.  I guess I just wanted something along the lines of "oh! it is probably XYZ!" But I think this is as good as I am going to get.  Mystery scrap iron lol.


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## 4GSR (Jan 19, 2017)

I can't speak for brake rotors, but I have some general knowledge of cast iron and ingredients that goes into the mix to make cast iron.  When I was involved with real cast iron made at Alamo Iron Works in San Antonio, Texas back in the 1980's, we were told that heat consisted of pig iron and A-36 structural scrap.  Nothing else was added to the heat.  It was melted in a electric furnace.  It yielded a fine grade of Class 40 gray iron.  (To this day, I think the ground under the Alamo Stadium had a little to do with it too!)  Now, brake rotors, are basically cast iron but with things like silicon and maybe nitrogen added and I can't think of the other ingredients, to make it more of an nodular iron.  This makes it more heat resistance as well as wear resistance also.
I'll go find my iron casting handbook and review it a little and report back.  BTW- True ASTM A-48 Class 40 gray iron or even class 20 or 30 iron, there is no control on the chemistry.  So foundries will add such things as nickel, copper, and stuff like this to get the strength up there to meet tensile requirements.

EDIT.  My Iron Casting handbook says that brake rotors are made from "pearlitic" gray iron.  I remember that quite well from the cast iron we used to use.  Ken


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## RJSakowski (Jan 19, 2017)

The Engineering Toolbox gives a density range for cast iron from 6800 - 7800 kg/m3 which is .24 - .28 lb./in3


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## brino (Jan 19, 2017)

Xyius said:


> I have a home foundry, from which I do mostly iron castings (at least right now).



Hi Xyius,

Sorry I have no answer for you, just a couple questions. What's your heat source? Using propane and a homemade burner I can currently reach temperatures for aluminum. I have some plans for a waste oil burner that's supposed to reach cast-iron temps. Is yours home made or something purchased?

Thanks,
-brino


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## Xyius (Jan 19, 2017)

4gsr said:


> I can't speak for brake rotors, but I have some general knowledge of cast iron and ingredients that goes into the mix to make cast iron.  When I was involved with real cast iron made at Alamo Iron Works in San Antonio, Texas back in the 1980's, we were told that heat consisted of pig iron and A-36 structural scrap.  Nothing else was added to the heat.  It was melted in a electric furnace.  It yielded a fine grade of Class 40 gray iron.  (To this day, I think the ground under the Alamo Stadium had a little to do with it too!)  Now, brake rotors, are basically cast iron but with things like silicon and maybe nitrogen added and I can't think of the other ingredients, to make it more of an nodular iron.  This makes it more heat resistance as well as wear resistance also.
> I'll go find my iron casting handbook and review it a little and report back.  BTW- True ASTM A-48 Class 40 gray iron or even class 20 or 30 iron, there is no control on the chemistry.  So foundries will add such things as nickel, copper, and stuff like this to get the strength up there to meet tensile requirements.
> 
> EDIT.  My Iron Casting handbook says that brake rotors are made from "pearlitic" gray iron.  I remember that quite well from the cast iron we used to use.  Ken



Thanks so much! This is exactly what I was looking for!



RJSakowski said:


> The Engineering Toolbox gives a density range for cast iron from 6800 - 7800 kg/m3 which is .24 - .28 lb./in3



Oh really? Huh that makes me feel better then!



brino said:


> Hi Xyius,
> 
> Sorry I have no answer for you, just a couple questions. What's your heat source? Using propane and a homemade burner I can currently reach temperatures for aluminum. I have some plans for a waist oil burner that's supposed to reach cast-iron temps. Is yours home made or something purchased?



My furnace burns waste oil.  I actually have a YouTube channel where I am documenting building a steam engine from scratch.  Making the castings, machining them etc if you are interested.  One of my videos explains how my furnace works (although I HAVE made some upgrades to it since making that video, mostly in the burner assembly, the one in the video is a bit crude).  The channel can be reached here: (Sorry for the shameless plug, I just figured you might be interested)

https://www.youtube.com/channel/UCbpe1Qd_ZKzcViwfxzFgeiA

Thanks all for the replies!


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## gi_984 (Jan 20, 2017)

I have only cast aluminum and lead.  Hoping to do cast iron eventually.  I segregate my ingots based on what the source metal was.  I reserve the high quality stuff for the fine detail castings.  Old steam radiators are supposed to be very high quality cast iron.


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## rwm (Jan 20, 2017)

The guys I know who do iron try to steer away from brake rotors. They feel the alloy is inferior and inconsistent. Also if you intend to machine your castings you should add some ferrosilicon before pouring. That helps fluidity and to prevent areas of chill which cannot be machined (easily.)
Robert


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## Xyius (Jan 21, 2017)

rwm said:


> The guys I know who do iron try to steer away from brake rotors. They feel the alloy is inferior and inconsistent. Also if you intend to machine your castings you should add some ferrosilicon before pouring. That helps fluidity and to prevent areas of chill which cannot be machined (easily.)
> Robert



Thanks! My castings are definitely very difficult to machine.  I NEED to use carbine, especially for first machining the outer skin.  I will give ferrosilicon a try!


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## Bob Korves (Jan 21, 2017)

http://chestofbooks.com/home-improv...tion-V-Hardening-And-Softening-Cast-Iron.html


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## Xyius (Jan 21, 2017)

Bob Korves said:


> http://chestofbooks.com/home-improv...tion-V-Hardening-And-Softening-Cast-Iron.html


Thanks, I will read this through later tonight. 

One of the things I do to mitigate the casting being so hard is leave it in the mold for sometimes 24 hours, to cool VERY slowly.  It still ends up being harder than a coffin nail though.  But that is actually fine for what I want to use it for, namely, making an engine.  I would rather my parts be very hard and difficult to machine, but stand up to wear very well.  I have never broken an iron casting out of the mold immediately after solidifying, as I am sure that would lead to something WAAAY harder and more difficult to machine.


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## rwm (Jan 21, 2017)

You should joint Alloy Avenue if you are not a member. There are a few guys with good cast iron experience that would be happy to help. Just search the archive and there are plenty of "how to" iron threads.
Robert


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## 4GSR (Jan 21, 2017)

rwm said:


> The guys I know who do iron try to steer away from brake rotors. They feel the alloy is inferior and inconsistent. .........
> Robert



I tend to agree, but as I said above, class 20, 30, 40 gray iron, ASTM A-48 does not govern chemistry, which leaves a big hole to what can be added to the mix.  There's also a Automotive SAE specification J431 that covers things like brake rotors, engine blocks, heads and so on which is pretty much the same specification as A-48 but for Automotive use. (Bruce might be able to add to this)  In my opinion, the cast iron used to make these parts is to specification and should not be questioned.  Now with offshore manufacturing of brake rotors, yes I agree, the cheaper one's I would suspect are not made to specifications but I bet they melt just as good as any other iron out there.  There's an art to making iron castings and its not as easy as you would think.  Cut up and melt some brake rotors and see what you wind up with.  And chill rate is part of the process.  Also, the making of the sand mold, too.

One thing a person almost has to have in this business is a Stereomicroscope.  This allows you to look at the sample of iron microstructure and determine if it is correct or not.


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## 4GSR (Jan 21, 2017)

Another "iron" that melts good and makes a decent casting is G-2 Dura Bar. You almost don't have to add anything to the melt including Silicon, it has plenty.  I have plenty of it on hand if want a piece to play with.  Ken


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## Mister Ed (Jan 21, 2017)

Interesting videos. I have not done any foundry work in 40 years, and then only aluminum in HS. But since I restore old farm windmills, this definitely has my curiosity up.


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## Xyius (Jan 21, 2017)

Wow so many awesome replies.  You guys are great, my first post here as certainly been a positive experience.



rwm said:


> You should joint Alloy Avenue if you are not a member. There are a few guys with good cast iron experience that would be happy to help. Just search the archive and there are plenty of "how to" iron threads.
> Robert



I will do that!



4gsr said:


> One thing a person almost has to have in this business is a Stereomicroscope.  This allows you to look at the sample of iron microstructure and determine if it is correct or not.



I am *very *intrigued by this.  Where can I read up what to look for in the grain structure to determine if the iron is correct or not for casting?



4gsr said:


> Another "iron" that melts good and makes a decent casting is G-2 Dura Bar. You almost don't have to add anything to the melt including Silicon, it has plenty.  I have plenty of it on hand if want a piece to play with.  Ken



Wow that would be great! I will send you a PM of where to send it to, I can send you a payment through Paypal to pay for the shipping.  I need to make some small castings soon and it would be a very fun experiment to use *only *the Dura bar and see how differently they machine. Thanks!


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## Davd Flowers (Jan 24, 2017)

It could be that you are melting vented rotors and they had alot of oxides formed in the vents "rust".  But its more probable that the furnace environment is causing it "oxidizing".
  Its pretty common with the hobbyist iron caster, and can be very difficult to manage.  What type of furnace set up do you have and what is the fuel source?  How large of a melt are you performing?


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