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Engineering Materials
Aluminum Composite to Lower Weight in Brake Rotor
2/15/2012

An aluminum composite brake rotor that weighs 60 percent less than cast iron and lasts three times as long is expected to cut about 30 pounds from midsize sedans. 
(Source: NYU-Poly)
An aluminum composite brake rotor that weighs 60 percent less than cast iron and lasts three times as long is expected to cut about 30 pounds from midsize sedans.
(Source: NYU-Poly)

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Dave Palmer
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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.

kleetus
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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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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.

Dave Palmer
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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.

John
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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. 

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.

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?

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



Charles Murray
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Blogger
Re: Heat Vs. Stoppability
Charles Murray   2/16/2012 8:38:22 PM
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If the automakers aren't taking a hard look at this, I'd be shocked. Cutting 30 lbs from the weight of a mid-size sedan is a gigantic change. Engineers typically fight to cut a pound or two from their vehicles. If they can cut 10 lbs, they're heroic. Thirty is off the scales.

Jerry dycus
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Gold
Re: UNSPRUNG Weight Reduction!
Jerry dycus   2/16/2012 9:12:09 PM
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                  Does anyone know why Carbon brakes are not getting cheaper?  After all carbon isn't that expensive a feedstock.  How are they made?

                 They would be much lighter than even this advance with the lower weight advantages in handling and mileage.

                Some brakes come with retracting clip springs that pull the pads off the rotor.  In every EV I do I always check the brakes and many other drags like diff fluids, new low rolling resitance tires, aero mods, etc which can literally increase range 10-50%!!   Or cut the battery pack/cost/weight as much for the same range.

               Of course the best brake is one that doesn't have to stop all that excess weight most cars have by designing in lightness, KIS.

 

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