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Engineering Materials

Aluminum Composite to Lower Weight in Brake Rotor

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RICKZ28
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Re: Heat Vs. Stoppability
RICKZ28   2/16/2012 5:39:12 PM
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Formula 1 racecar brake discs are made from carbon fiber composite.  I heard that the coefficient of friction increases as the F1 brake discs heat up, the opposite of cast iron brake discs.

http://www.formula1.com/inside_f1/understanding_the_sport/5284.html



William K.
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Aluminum composite for lighter brakes
William K.   2/16/2012 5:10:58 PM
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I have never had a rotor fail in an automotive disk brake system, but I have had many failures of the caliper mechanism over the years. The reason has been that Chrysler has consistently chosen designs for the caliper assembly that rust and stop sliding where they should. The results have been either brakes that drag and overheat, or brakes that only brake on one side of the disk, resulting in a buildup of an iron oxide material on the inoperative side, which has a much lower friction level, but is far more abrasive to the pads. This failure mode does destry the rotor, but not through any design error in the rotor or material.

The aluminum composite may be a very great improvement, but it would be very handy to find out about it's corrosion resistance to the southeastern Michigans salt brine roadways. If it can stand up to that test, where can we buy these rotors?

kleetus
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Silver
Re: Yet another strategy for weight reduction
kleetus   2/16/2012 5:00:05 PM
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@Dave Palmer: Lol... okay, maybe I'm dating myself with a cavalier, but your cobalt would be the same premise. A lower cost vehicle with a significant repair bill for normally wearable items.

Now having the price come down over time I can certainly believe, just look at cmputers, but there are a number of other items, like 'lubed for life' suspension components and u-joints that never lived up to the name, and were just as expensive if not more based on their novel idea that they are 'better'.

Time will tell.

John
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Gold
Heat Vs. Stoppability
John   2/16/2012 3:30:43 PM
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Is there any word on the stopping power Vs. heat buildup on these rotors?  I recently went from ceramic pads to metallic pads with new rotors all the way around.  There was nothing wrong with my old pads except for stress cracks from the heating and cooling cycle. 

Dave Palmer
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Platinum
Re: Yet another strategy for weight reduction
Dave Palmer   2/16/2012 1:15:54 PM
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@kleetus: I agree with you about cost -- at least for the time being.  When I worked on aluminum MMC brakes, it was for military applications, where cost vs. weight considerations are very different than in the civilian market.  But a lot of work is being done to find cost-effective ways of producing these materials.

By the way, there is no such thing as a 5-year-old Chevy Cavalier, since 2005 was the last model year for Cavalier.  My Chevy Cobalt -- the model which replaced Cavalier -- is more than five years old.

Dave Palmer
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Platinum
Re: Metal matrix composites
Dave Palmer   2/16/2012 12:28:36 PM
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@JimT: According to the brochure on REL's website, the material can only be machined using diamond tooling.

Heat from braking will cause organic brake pads to off-gas.  The idea of a dimpled brake rotor is that the dimples provide space for the gases to expand into, supposedly minimizing brake fade.  This is the same idea behind cross-drilled brake rotors.  The supposed advantage of dimpled rotors over cross-drilled rotors is that a dimple doesn't reduce the cross-sectional area as much as a drilled hole, so the rotor is less likely to crack. (I say "supposedly" for both of these things because I have heard people dispute both of these claims, and I haven't seen any objective data one way or the other).

It's possible to make MMCs using powder processes, but they are more commonly cast (or, sometimes, cast into billets and then extruded).  One way to cast MMCs is by stir casting, in which the reinforcement is stirred into the molten aluminum.  Another way is by squeeze casting molten aluminum into a fiber pre-form.  Based on the brochure, it looks like this is what REL is doing.

kleetus
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Silver
Re: Yet another strategy for weight reduction
kleetus   2/16/2012 11:35:24 AM
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I can't wait to see a $500 brake rotor for a $10,000 car. Materials will be 10% of the vehicles value. Can you picture this repair on a 5 year old chevy cavalier or equvalent vehicle? lol, I can't...

There comes a point where practicality and reality need to mix. Cna this be done, sure, but when I can go out and purchase an $80 brake rotor for a 1 ton truck, and instal it myself, I shudder to think what this new material would cost.

Remember when plastic bumpers were supposed to make cars cheaper? yeah... now it costs over $1k to get the stupid thing repainted when some jerk dings you up in a parking lot, where the metal one didn't show the mark in the first place.

 

Neat idea, but until it's economically feasible, it's a waste of time... much like EV's without gov't subsidation (which still comes from our pocket).

Dave Palmer
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Platinum
Re: Michigan Winter
Dave Palmer   2/16/2012 11:08:33 AM
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@wb8nbs: The gunmetal gray color of friction ring in the rotor in the picture makes me think that it is probably hardcoat anodized, so it is not just bare aluminum.  All other things being equal, I'd expect anodized aluminum to hold up a lot better than bare cast iron.  In fact, I'd even expect bare aluminum to hold up better than bare cast iron.

On the other hand, connecting an aluminum brake rotor to a steel wheel hub could be a recipe for galvanic corrosion of the aluminum.  Galvanic corrosion between steel hubs and aluminum wheels is also a common problem.  In either case, a thick coat of antiseize between the two parts might help to prevent corrosion by galvanically isolating the parts from one another.

VadimR
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Gold
Brake Rotors
VadimR   2/16/2012 10:59:20 AM
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This sounds good, but break systems in general need to be redesigned.  The current problem with breaks is that the break pads are essentially in contact with the disk at all times.  All the cars and motorcycles I've had, the rotor is never free to spin by hand without hearing the pads rubbing against the disk.  I understand that it gives quicker response to stop the closer the pads are, but imagine how much mpg and rotor/pad life is robbed by the current design.  Imagine riding your bicycle with the break pads rubbing all the time.  When we have so much horsepower available, we tend to ignore the obvious little inefficiencies.
From what I've read, I like what Tesla did with their brakes...zero binding when not breaking!

vandamme
User Rank
Silver
Re: Michigan Winter
vandamme   2/16/2012 10:16:51 AM
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Wonder how cast iron holds up to salt?

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