Brake temps

[TyphoonFiST]

So I guess....someone tell me why Porsche utilizes this in their 12-24 hr race cars and has seen rotors last the entire length of the race with pitting to change them out due to fatigue. So.....we all know who Porsche is and their capabilities in racing I'd say that Cryogenically freezing rotors can benefit a car if DONE RIGHT.

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[jeffreylyon]

So I guess....someone tell me why Porsche utilizes this in their 12-24 hr race cars and has seen rotors last the entire length of the race with pitting to change them out due to fatigue. So.....we all know who Porsche is and their capabilities in racing I'd say that Cryogenically freezing rotors can benefit a car if DONE RIGHT.

You answered your own question: they don't want to have to change rotors. Cryo rotors may be harder but have no more or less heat rejection. https://en.wikipedia.org/wiki/Cryogenic_hardening

I wonder if harder rotors wouldn't reduce pad bite, especially at non-endurance racing temperatures. That would probably reduce temps. but at the cost of reduced braking performance.

 

[maestromaestro]

Again - if anything, it will make the material of rotors (and, I'd imagine that the rotors for the Enduro race on the P-cars are not what Ford puts on the FiSTs) harder. Nothing to do with the heat. So, treating pads and other bits is just like putting nitrogen in your tires. Doesn't do anything.

 

[TyphoonFiST]

Again - if anything, it will make the material of rotors (and, I'd imagine that the rotors for the Enduro race on the P-cars are not what Ford puts on the FiSTs) harder. Nothing to do with the heat. So, treating pads and other bits is just like putting nitrogen in your tires. Doesn't do anything.

Where are your facts? Data? Personal Exp. Of with and without? I beg to differ.....that they are like nitrogen in your tires.

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[TyphoonFiST]

This doesn't make the metal harder....just more durable over the long haul and become more wear resistant so therefore it's not NITROGEN IN TIRES snake oil.

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[jeffreylyon]

This doesn't make the metal harder....just more durable over the long haul and become more wear resistant so therefore it's not NITROGEN IN TIRES snake oil.

Er..., that's a direct effect of "harder."

 

[maestromaestro]

Where are your facts? Data? Personal Exp. Of with and without? I beg to differ.....that they are like nitrogen in your tires.

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Well, I have degrees in materials science/metallurgy. So, there's that. Know a few things about the TTT diagrams, what with the austenite to martensite transformation.

 

[maestromaestro]

This doesn't make the metal harder....just more durable over the long haul and become more wear resistant so therefore it's not NITROGEN IN TIRES snake oil.

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Actually, that's the whole idea behind "cryogenic treatment", which is sometimes also called "cryogenic hardening". So - yeah, it does.

 

[TyphoonFiST]

Then you should know that it changes the crystalline structure to be more even. Can you make Gold since you have a degree in metallurgy? If so I'm in line for the first batch!

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[maestromaestro]

Typical "cryogenic treatment" does not lead to recrystallization. For that, you will need to first heat the material to high (enough) temperature, and these are treated from the room temp. So, no change in the grain size. Secondly, as I noted, this is targeting the retained gamma phase-iron to martensite transformation; to have any retained austenite, you first have to have it - and that is dependent on the material's chemical composition. If carbon content is sufficiently high - over 0.3% (and, given that most rotors are made from cast iron, with the carbon content over 2%)- then, you will have some RA, and as its Mf (martensite finish temperature) is below room temp, cooling it will have an effect of the austenite-martensite transformation (i.e., carrying it to completion), and thus will increase material's hardness (this comes with potential dimensional stability challenges).

This is what will produce greater resistance to abrasion. So - to repeat myself: harder rotors have nothing to do with heat transfer. I hope that this helps.

 

[jeffreylyon]

Typical "cryogenic treatment" does not lead to recrystallization. For that, you will need to first heat the material to high (enough) temperature, and these are treated from the room temp. So, no change in the grain size. Secondly, as I noted, this is targeting the retained gamma phase-iron to martensite transformation; to have any retained austenite, you first have to have it - and that is dependent on the material's chemical composition. If carbon content is sufficiently high - over 0.3% (and, given that most rotors are made from cast iron, with the carbon content over 2%)- then, you will have some RA, and as its Mf (martensite finish temperature) is below room temp, cooling it will have an effect of the austenite-martensite transformation (i.e., carrying it to completion), and thus will increase material's hardness (this comes with potential dimensional stability challenges).

This is what will produce greater resistance to abrasion. So - to repeat myself: harder rotors have nothing to do with heat transfer. I hope that this helps.

Thank you for that explanation. Is it possible that the increased resistance to abrasion may result in less coefficient of friction with the pads and, thus, less braking force?

Cue GIF....

 

[maestromaestro]

Thank you for that explanation. Is it possible that the increased resistance to abrasion may result in less coefficient of friction with the pads and, thus, less braking force?

Cue GIF....

I have a colleague whom I may ask about that. I suppose there is a possibility that hardfaced surfaces could lead to a decrease in friction, but I am sure that it is not a straightforward thing. Carbon ceramic rotors are quite hard and they last (ostensibly) for the life of the car - and they had better be, as they run $10K and higher - but they are considered to be superior, braking wise. I would think that roughness of the mating surfaces has an effect, as is the temperature (also, potential gas evolution and such). We don't seem to have an automotive engineer in our midst on this forum - and we could use a couple, one for suspension and one for braking.

EDIT: so, in the Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 212, No. 1111 (May 22, 1952), pp. 452-458 (8 pages), experimental work seems to indicate that there is indeed an inverse linear relationship between the friction coefficient (mu) and the surface hardness or yield strength. It is not dramatic, but seems that it is there.

But, in yet another article, in the journal Wear, Volume 118, Issue 1, 15 July 1987, Pages 113-125, another conclusion is reached that "there was no correlation with hardness increase when sliding against" tool steel.

....

 

[maestromaestro]

Then you should know that it changes the crystalline structure to be more even. Can you make Gold since you have a degree in metallurgy? If so I'm in line for the first batch!

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Why, yes of course - you can transmutate bismuth into gold (that is, achieve chrysopoeia), for instance. Instead of the philosopher's stone you'd need a particle accelerator. Quite expensive, tho.