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What is in brake rotors?

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airmodel:
I had four samples from different brake rotors analysed five years ago to see what is in them. Cast iron 1 starts on the lefthand side of the page and cast iron 3 is on the righthand side of the page. Most elements were trace amounts. What interests me the most is how much Cr, S, C, is in them and would explain why they are stronger than normal cast iron. If you are going to make ductile iron the S level should be low as possible like in sample "C". Have a look at the methods used to analyse the samples, it gets a bit technical.

CI:
I am not that up on my element chart, so I had to verify a few things.

Fe=Iron
C=Carbon
Mn=Manganese
Si=Silicon
S=Sulphur
P=Phosphorus
Ni=Nickle
Cr=Chromium
Mo=Molybdenum
Cu=Copper
V=Vandium
Nb=Niobium
Ti=Titanium
Al=Aluminum
Mg=Magnesium

I have long been aware of how strong chrome-moly (metal with Cr and Mo) steel is, especially when used in automobile frames.
I am also aware that the sulphur content in iron must be low (not sure what the definition of "low" is) in order to make dutile iron.
The sulphur content can be lowered by adding calcium carbide.

I would use standard gray iron scrap, which for me is electric motor end bells.
It breaks consistently with a sledge hammer, with no visible white spots in the break; has significant strength; and does not appreciably bend before it cracks (high compressive strength, low tensile strength).

I have not used scrap brake rotors, but given the significant forces acting on them, it seems obvious that they are very strong and semi-ductile.
I have seen some folks break rotors with a hydraulic shear, and while rotors will break, they don't break easily, and they can fly out of the shear at potentially lethal velocities, which to me indicates there is a significant amount of spring inherent in them.

I think VT mentioned that brake rotors could be cast as a material that approximates ductile iron, but that hypothesis would have to be tested.

I know crankshafts must be cast from ductile iron, or forged/cast from steel.
The Speedy Twin steam engine was offered with a stock cast iron crankshaft, and for a significant amount of additional money, an optional cast steel cranckshaft could be purchased.

Given that most hobby casting folks will not have access to lab testing for metal composition, it would seem to make sense to start with a known and consistent gray iron scrap, and go from there to attempt to make ductile iron.
I have heard that sometimes or perhaps often, spectral analysis of metals may give incorrect results.
If making ductile iron using standard gray iron scrap is successful, then the castings obtained could be compared with similar or the same castings made with untreated (no additives) rotor iron.
I don't have any rotors, but I think I could obtain some of those.

The daytime temperatures here are beginning to receed a bit, so hopefully I can try casting some things.
The good part about living in the south is that if your oven or stove happen to break, you can always cook on the dash of your car.

.

Vixen:

--- Quote from: CI on August 12, 2025, 11:20:02 AM ---
The good part about living in the south is that if your oven or stove happen to break, you can always cook on the dash of your car.


--- End quote ---

If the dash of your car is not hot enough, you can always use the armor plate of your tank (photos, Libyan Desert WW2) Best if you like gritty eggs with touch of oil/diesel garnish.





Sorry to go of topic with this post

Cheers

Mike

CI:
Baked cookies is best on the dash, but a bit of diesel would give them an edge.

.

Michael S.:
At a recent meeting of people from the historic combustion engine scene, a report was made about making piston rings for pistons from brake discs. This suggests that the alloy could be used for this purpose!?

Michael

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