Brake rotor material?

[Chad Summey]

I bought a old FSAE car last year and after redoing several thing got it running this past weekend. My question is it has aluminum brake rotors. How bad is this? I weld and machine for a living and know that aluminum clogs up grinding wheels and they will stop working as good unless you use some kind of cutting oil or coolant. If the rotors are OK do I need to use some special pads? It is only going to be an autocross car and may be some hillclimbs latter on.thanks Chad

[Mazur]

That is very strange. I would swap them out for steel. Cast iron if it's within your budget.

[Chad Summey]

I can make them at work no problem. What grade of cast should I use? nodular? And since I am redoing them would you make them two piece or just keep them one. They are flat with no kind of top hat or anything and fixed not floating. Thanks Chad

[thewoundedsoldier]

How interesting! Do the brakes work well? Have you put them through a good workout, getting them to temp and seeing how they handle abuse?

I'm on the SJSU Hybrid team and we decided early on to go with an aluminum rotor in the rear, and I am back and forth all the time on whether we should try it for the front or not. Wilwood makes the pad compound that lives peacefully with an aluminum rotor.

I've found it very hard so far to find examples of aluminum rotors being used--what actually turned me on to the idea was the sprotor concept.

Are the rotors on your car anodized?

[Chad Summey]

I just drove the car for the first time last weekend. I wasn't real impressed with the brakes but it was 35 degrees and I didn't drive it long. I hope to drive it some more this weekend it is going to be in the 50's. My calipers are wilwood and I my have those pads I don't know. I need to put fresh pad on before the season starts so I may buy a set just to try. I don't think they are anodized. If they are it was silver in color but to me they look bare. Chad

[Chad Summey]

What compound was that pad? Thanks Chad

[Ben K]

I would be concerned with the heat transfer properties more than anything. For instance, in alot of FSAE hub assemblies, without proper heat isolation, those aluminum rotors would transfer their heat straight to the bearings. Not so good.

Not to mention that their melting temp of aluminum is quite a bit lower.

Weren't old Russian vehicles built with Aluminum rotors....?

Ben

[MegaDeath]

1018 steel is cheap and works well as rotor material. You could probably get away with keeping them one piece if you're only planning on autoXing and hillclimbing. I don't think the brakes will get hot enough that you will have any problems with them expanding.

[thewoundedsoldier]

It's their "Q" compound. They only make it for certain calipers, so we are peeling them from the pad base, machining them to shape, then bonding them to PS1 pad bases.

Would you be able to send me some pics of the setup? I would really appreciate it.

[Demon Of Speed]

I am guessing no one in this thread is a metallurgist.

If you think that using steel is a better idea for such a low mass vehicle than a proper aluminium rotor then you are wrong.

Please do yourself a favor and know what you are talking about before you post.

As to the original question, make sure the rotors are hard anodized, and the anodizing has not worn off. I know Wilwood purple pads are specially designed for Al rotors, and I am sure you can find aluminium pads in other brands.

[exFSAE]

Aluminum rotors are certainly feasible with the right pads... but if you're just dicking around with the car, 1018 rotors are nice from a maintenance standpoint. One set will last a long time without having to worry about it.

With respect to metalworking, there are wheels of a special material that let you lightly "grind" on aluminum with no issue and no material loading on the wheel. They are not stone. Great for deburring.

[Demon Of Speed]

Originally posted by exFSAE:
Aluminum rotors are certainly feasible with the right pads... but if you're just dicking around with the car, 1018 rotors are nice from a maintenance standpoint. One set will last a long time without having to worry about it.

With respect to metalworking, there are wheels of a special material that let you lightly "grind" on aluminum with no issue and no material loading on the wheel. They are not stone. Great for deburring.

Yup, they defiantly do make special abrasives for aluminium.

I know proper Al rotors will last 20+ hours of hard use without a problem. That should be good enough for at least 2 years.

[Ben K]

Originally posted by Demon Of Speed:
I am guessing no one in this thread is a metallurgist.

If you think that using steel is a better idea for such a low mass vehicle than a proper aluminium rotor then you are wrong.

Please do yourself a favor and know what you are talking about before you post.

As to the original question, make sure the rotors are hard anodized, and the anodizing has not worn off. I know Wilwood purple pads are specially designed for Al rotors, and I am sure you can find aluminium pads in other brands.

Now I don't disagree that you COULD use aluminum as a rotor. But there are more negatives to positives here. Thermal expansion, transfer, as well as warping are all much larger issues in an aluminum rotor. With proper considerations, they MIGHT work, but for a starting team I certainly wouldn't consider it.

Ben

[thewoundedsoldier]

Who said anything about a 'starting team'? This appears to be a guy who purchased an old car and is wondering about its upkeep.

And it might be unfair to suggest that thermal expansion, transfer, and warping are the most important issues in rotor material design. How about coefficient of friction? How about young's modulus? Weight/strength ratio? Ductility? IMO all of those properties point towards a well-designed aluminum rotor.

I see a lot of stigma in formula student--some of it is for good reason and some of it makes me scratch my head.

[Mbirt]

I've seen a team get two competitions, two non-sanctioned competitions, an SCCA auto-x, and plenty of testing out of one set of 4 aluminum rotors. They use the aforementioned Wilwood pad. The rotors can and do last in an FSAE application.

[Ben K]

As I said, they might work. I haven't done the design work specifically for an aluminum rotor, so I stand corrected if someone has actually been able to pull them off for long term use.

[Demon Of Speed]

Originally posted by Ben Kolodner:
As I said, they might work. I haven't done the design work specifically for an aluminum rotor, so I stand corrected if someone has actually been able to pull them off for long term use.

Please see MBirt's response.

[Adambomb]

We used Al front rotors in '03. The car was 450 lbs, and as I recall the rotors were about 0.25" thick and 9" OD, built for Wilwood Dynalite calipers. Had cooling grooves, but the combination of low thermal mass and low high-temp hardness caused severe galling.

We used an Al rear "sprotor" from '04-'05. 0.25" thick, something like 12-13" diameter, designed for Wilwood Dynalite calipers. Both of those cars were also about 450 lbs. After something like 30 hrs of run time all of the sprotor teeth went from being radially oriented to something that resembled a circular saw blade with several missing teeth.

[chrisbowie]

1018 steel is an good option. It is generally available in round rod, square bar, and rectangle bar. It has a good combination of all of the typical traits of steel - strength, some ductility, and comparative ease of machining. Chemically, it is very similar to A36 Hot Rolled steel, but the cold rolling process creates a better surface finish and better properties.

[PatClarke]

I can't believe it!!!

A real live semi useful response from a spambot!!!

Pat

[AxelRipper]

You sure Pat? 1018 steel rotors?

[Adambomb]

Originally posted by AxelRipper:
You sure Pat? 1018 steel rotors?

Better than the Ti rotors our solar car team used a few years ago...

[Demon Of Speed]

Originally posted by Adambomb:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by AxelRipper:
You sure Pat? 1018 steel rotors?

Better than the Ti rotors our solar car team used a few years ago... </div></BLOCKQUOTE>

And still not nearly as good as iron (the material).

[Ben Coburn]

As a completely serious question:

Ignoring that aluminum is lower strength and loses strength more quickly as it heats up, I was under the impression that the thing that is fixed in a brake rotor is total heat capacity, not strength or weight. That is, an aluminum rotor should need to weigh as much or more than a steel or cast iron one for the same application.

Am I missing something obvious here? I guess maybe in practice for fsae cars an iron rotor that is actually at the limit heat capacity wise would need to be too small to actually work ?

[CB23]

Some years back - it is unclear how many - someone made an alloy of aluminum that they called "Aluminum Metal Matrix." And made brake rotors from it. It was wildly successful, had a brilliant reputation, and professional race teams quickly bought all that had been produced. This experiment was not repeated. A few years back another someone created another alloy, calling it the same thing, and made (is making?) brake rotors from it. I have heard nothing of the success.

My perspective is that the brake pad material is the real problem with such a solution. With steel or iron rotors you have a large number of brake pads that you can use, each with different properties. For example, to get proper balance with my brake system I use a different compound front and rear (and yes, I have also modified my calipers and master cylinders). With aluminum, or AMM, or titanium, you are very much more limited.

[Owen Thomas]

someone made an alloy of aluminum that they called "Aluminum Metal Matrix." And made brake rotors from it.
Metal Matrix Composite (or MMC) rotors were and are still around in the automotive industry, and yes, there have been aluminum based MMC's used for brake rotors. You can find more information about them on the googles.

In MMC brake rotors when aluminum is used (as far as I know) they often solve the issue of pad material by bonding a ceramic to the effective braking surface. I don't see any reason why it wouldn't also be possible to braze something like cast iron onto the surface either, but I'm not really certain of that. Since MMC's can be manufactured in intricate shapes like say, a honeycomb core rotor, the strength can be extremely high while allowing the bulk of the rotor to remain thin enough to bond a material with suitable braking qualities.

[Gruntguru]

Originally posted by Ben Coburn:
Ignoring that aluminum is lower strength and loses strength more quickly as it heats up, I was under the impression that the thing that is fixed in a brake rotor is total heat capacity, not strength or weight. That is, an aluminum rotor should need to weigh as much or more than a steel or cast iron one for the same application.

Am I missing something obvious here? I guess maybe in practice for fsae cars an iron rotor that is actually at the limit heat capacity wise would need to be too small to actually work ?
You have missed something obvious - the specific heat of the material. The specific heat of aluminium is double that of iron. So an aluminium rotor will absorb twice as much heat as an iron rotor of the same mass for the same temperature increase. That is good.

On the other hand high thermal conductivity is good and bad. The bad is that plain (not ventilated) rotors are cooled from the same surface as the heat is applied (the friction surface). During heavy braking, an iron rotor is much hotter on the surface than internally. This improves heat transfer from the rotor.