Rotor Specifications?
01-16-2002, 01:49 PM
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Rotor Specifications?
What's up everyone, My problem is that my rotors have warped 3 times in 25,500 in my CL-S and the dealer have re-surface the rotors three times... I was wondering if anyone has the factory specs on the rotors... If they're out of specs, then Acura will be hearing it from me and my attorney!!! I appreciate all the feed back... Or if anyone has Acura's 800 # thanks
Has this happen to anyone... Steering vibration while braking from speeds btw 75- and up?
Has this happen to anyone... Steering vibration while braking from speeds btw 75- and up?
01-16-2002, 02:34 PM
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Do a search on brakes. You should have at least had your pads replaced by now. I would think after the second time milling the rooters they would have replaced them also. YMMV
01-16-2002, 02:47 PM
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I just took mine in for the second time. They told me they would change them out this time, however after looking at the paper work i noticed they had not changed them at all. They do have a service Bulletin for this. 
01-16-2002, 11:27 PM
#5
Suzuka Master
You might want to find some info on breaking in the pads properly. It sounds like a bunch of BS, but depending on the pad, it can really help...
got to go...
got to go...
01-17-2002, 01:26 AM
#6
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bdavid13 - Yep, I get the vibration when I hit the brake at highway speeds...around 60 and up it starts to vibrate pretty bad. I went to the dealer and got it resurfaced, but they said I didn't need to change the pads. I think I'll just buy some aftermarket pads.
01-17-2002, 07:12 AM
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I had this problem on my 2000TL, long before the service bulletin (I'm a rather high mileage driver, so I get to have the fun of finding all of the design flaws before they become TSB's!)
What I've seen from Acura, the spec on the rotors dictates that they be flat, +/- 3.0 inches:-) Once they mill them often enough to wear a hole in them, they'll replace.
Seriously, I found that they will NOT replace them if you don't ask. By ask, I actually mean demand. I had to place a call to Acura's national service center. I'm not sure what the number is anymore, but the dealer will generally refer to the zone service manager if you demand something they don't want to do (like new rotors), and that person will make the call. I went over the zone managers head, and got attention VERY fast.
Realize this - rotors warp for 2 main reasons - lug nuts too tight, and an inability to disipate heat. If you over torque the lug nuts, well, tough cookies. However, this is not the problem with Acura rotors - they are too thin for the weight of the car, and can therefore not deal with all of the heat. The distance between the outer surface, where the brake pads contact the rotor, and the inner slot, where a good deal of cooling occurs, is simply too great for our style of driving. The temperature gradient, which is the difference in temperature between metal on the outer surface and the inner slot surfce, is so large that the outer surface expands at a greater rate than the inner surface. Instant warp (and for an even greater effect, through some cold water on those hot rotor surfaces!!).
The point of that long-winded explination is that each time the rotors are milled, they get a little thinner. I leave it to you to connct the dots :-)
BTW, any time you replace the rotors, it is good practice (some may say not required, but I and others disagree) to replace the pads. I went through 2 sets of rotors on my TL, and the third time they finally listened and replaced the pads. No more problems after that.
Good luck!
Jason
What I've seen from Acura, the spec on the rotors dictates that they be flat, +/- 3.0 inches:-) Once they mill them often enough to wear a hole in them, they'll replace.
Seriously, I found that they will NOT replace them if you don't ask. By ask, I actually mean demand. I had to place a call to Acura's national service center. I'm not sure what the number is anymore, but the dealer will generally refer to the zone service manager if you demand something they don't want to do (like new rotors), and that person will make the call. I went over the zone managers head, and got attention VERY fast.
Realize this - rotors warp for 2 main reasons - lug nuts too tight, and an inability to disipate heat. If you over torque the lug nuts, well, tough cookies. However, this is not the problem with Acura rotors - they are too thin for the weight of the car, and can therefore not deal with all of the heat. The distance between the outer surface, where the brake pads contact the rotor, and the inner slot, where a good deal of cooling occurs, is simply too great for our style of driving. The temperature gradient, which is the difference in temperature between metal on the outer surface and the inner slot surfce, is so large that the outer surface expands at a greater rate than the inner surface. Instant warp (and for an even greater effect, through some cold water on those hot rotor surfaces!!).
The point of that long-winded explination is that each time the rotors are milled, they get a little thinner. I leave it to you to connct the dots :-)
BTW, any time you replace the rotors, it is good practice (some may say not required, but I and others disagree) to replace the pads. I went through 2 sets of rotors on my TL, and the third time they finally listened and replaced the pads. No more problems after that.
Good luck!
Jason
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01-17-2002, 02:03 PM
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wow, thanks for the quick response... though I spoke with lemon law attorney here in Ca.. and he said next time that I feel the vibration don't take it to acura but to call him.... granting this will be the 4th time I've had to take my car for the same problem and have not fixed it... I'm thinking of filing for lemon law.. Do you guys think I have a good case....And also, I'm thinking of getting my rotors check for spec... I wouldn't think the dealership would resurface them out of spec.. If they do.... i guess I can sue them for Liability..... I neep some opinions... thanks
01-17-2002, 06:36 PM
#9
Suzuka Master
Originally posted by jdl75
I had this problem on my 2000TL, long before the service bulletin (I'm a rather high mileage driver, so I get to have the fun of finding all of the design flaws before they become TSB's!)
What I've seen from Acura, the spec on the rotors dictates that they be flat, +/- 3.0 inches:-) Once they mill them often enough to wear a hole in them, they'll replace.
Seriously, I found that they will NOT replace them if you don't ask. By ask, I actually mean demand. I had to place a call to Acura's national service center. I'm not sure what the number is anymore, but the dealer will generally refer to the zone service manager if you demand something they don't want to do (like new rotors), and that person will make the call. I went over the zone managers head, and got attention VERY fast.
Realize this - rotors warp for 2 main reasons - lug nuts too tight, and an inability to disipate heat. If you over torque the lug nuts, well, tough cookies. However, this is not the problem with Acura rotors - they are too thin for the weight of the car, and can therefore not deal with all of the heat. The distance between the outer surface, where the brake pads contact the rotor, and the inner slot, where a good deal of cooling occurs, is simply too great for our style of driving. The temperature gradient, which is the difference in temperature between metal on the outer surface and the inner slot surfce, is so large that the outer surface expands at a greater rate than the inner surface. Instant warp (and for an even greater effect, through some cold water on those hot rotor surfaces!!).
The point of that long-winded explination is that each time the rotors are milled, they get a little thinner. I leave it to you to connct the dots :-)
BTW, any time you replace the rotors, it is good practice (some may say not required, but I and others disagree) to replace the pads. I went through 2 sets of rotors on my TL, and the third time they finally listened and replaced the pads. No more problems after that.
Good luck!
Jason
I had this problem on my 2000TL, long before the service bulletin (I'm a rather high mileage driver, so I get to have the fun of finding all of the design flaws before they become TSB's!)
What I've seen from Acura, the spec on the rotors dictates that they be flat, +/- 3.0 inches:-) Once they mill them often enough to wear a hole in them, they'll replace.
Seriously, I found that they will NOT replace them if you don't ask. By ask, I actually mean demand. I had to place a call to Acura's national service center. I'm not sure what the number is anymore, but the dealer will generally refer to the zone service manager if you demand something they don't want to do (like new rotors), and that person will make the call. I went over the zone managers head, and got attention VERY fast.
Realize this - rotors warp for 2 main reasons - lug nuts too tight, and an inability to disipate heat. If you over torque the lug nuts, well, tough cookies. However, this is not the problem with Acura rotors - they are too thin for the weight of the car, and can therefore not deal with all of the heat. The distance between the outer surface, where the brake pads contact the rotor, and the inner slot, where a good deal of cooling occurs, is simply too great for our style of driving. The temperature gradient, which is the difference in temperature between metal on the outer surface and the inner slot surfce, is so large that the outer surface expands at a greater rate than the inner surface. Instant warp (and for an even greater effect, through some cold water on those hot rotor surfaces!!).
The point of that long-winded explination is that each time the rotors are milled, they get a little thinner. I leave it to you to connct the dots :-)
BTW, any time you replace the rotors, it is good practice (some may say not required, but I and others disagree) to replace the pads. I went through 2 sets of rotors on my TL, and the third time they finally listened and replaced the pads. No more problems after that.
Good luck!
Jason
There is something else to consider -- if the pads don't absorb that heat away from the rotors (due to outgassing), it doesn't help to replace the rotors. If the "new" pads need to be broken in and aren't, the out-gassing can cause the very same problem -- warping.
The downside of the thicker rotor is that it takes longer to cool down vs. a thin one (all things being equal). So, for a single stop, the thicker rotor has more thermal mass to soak up the heat. However, it also retains heat better and makes multiple stops a problem.
Finally, I've had rotors from the same car company work fine, and then get another batch that would warp, then get a run of good rotors (with no warping) and so on...
Draw your own conclusions...
01-19-2002, 01:37 PM
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Originally posted by EricL
There is something else to consider -- if the pads don't absorb that heat away from the rotors (due to outgassing), it doesn't help to replace the rotors. If the "new" pads need to be broken in and aren't, the out-gassing can cause the very same problem -- warping.
Outgassing? Could you explain that physical phenomina? I'm not familiar with that term.
Pads need to seat on the calliper, but there is such a large heat sink behind the pad that once the pad seats properly, the pad is able to pull what little heat it can with out much problem
The downside of the thicker rotor is that it takes longer to cool down vs. a thin one (all things being equal). So, for a single stop, the thicker rotor has more thermal mass to soak up the heat. However, it also retains heat better and makes multiple stops a problem.
I'm not quite sure what we're holding equal - if the thickness of the rotors changes, but all other ratios stay the same, or all other dimensions stay the same? If all other dimensions stay the same, yes, you will have an excess of heat build up, and the small gain in surface area around the edge of the rotor will not be enough to dissipate the stored heat. However, you must remember that braking generates a specific amount of energy, mostly in the form of heat, and that heat energy is dispersed over the mass of the rotors (and to a much lesser extent the callipers/pads).
If the ratios stay the same, then you will have an increase in surface area to go along with the increase in rotor mass. This is the ideal situation, and will help you avoid warped rotors. The more rotor mass you have, the larger the area available to spread the heat energy generated from a stop. If you have proportionally larger surface areas, the cooling will occur faster (that's why air cooled engines have fins on the exterior surfaces - more surface area).
Remember - the important point here is to devide the fixed amount of heat generated from a stop over the largest mass possible (single stop) - this will keep the overall temperature of the rotor down lower than a less massive rotor. For multiple stop considerations, it is important to increase the surface area (and therefore the cooling) capacity of the rotor.
Finally, I've had rotors from the same car company work fine, and then get another batch that would warp, then get a run of good rotors (with no warping) and so on...
Draw your own conclusions...
There is something else to consider -- if the pads don't absorb that heat away from the rotors (due to outgassing), it doesn't help to replace the rotors. If the "new" pads need to be broken in and aren't, the out-gassing can cause the very same problem -- warping.
Outgassing? Could you explain that physical phenomina? I'm not familiar with that term.
Pads need to seat on the calliper, but there is such a large heat sink behind the pad that once the pad seats properly, the pad is able to pull what little heat it can with out much problem
The downside of the thicker rotor is that it takes longer to cool down vs. a thin one (all things being equal). So, for a single stop, the thicker rotor has more thermal mass to soak up the heat. However, it also retains heat better and makes multiple stops a problem.
I'm not quite sure what we're holding equal - if the thickness of the rotors changes, but all other ratios stay the same, or all other dimensions stay the same? If all other dimensions stay the same, yes, you will have an excess of heat build up, and the small gain in surface area around the edge of the rotor will not be enough to dissipate the stored heat. However, you must remember that braking generates a specific amount of energy, mostly in the form of heat, and that heat energy is dispersed over the mass of the rotors (and to a much lesser extent the callipers/pads).
If the ratios stay the same, then you will have an increase in surface area to go along with the increase in rotor mass. This is the ideal situation, and will help you avoid warped rotors. The more rotor mass you have, the larger the area available to spread the heat energy generated from a stop. If you have proportionally larger surface areas, the cooling will occur faster (that's why air cooled engines have fins on the exterior surfaces - more surface area).
Remember - the important point here is to devide the fixed amount of heat generated from a stop over the largest mass possible (single stop) - this will keep the overall temperature of the rotor down lower than a less massive rotor. For multiple stop considerations, it is important to increase the surface area (and therefore the cooling) capacity of the rotor.
Finally, I've had rotors from the same car company work fine, and then get another batch that would warp, then get a run of good rotors (with no warping) and so on...
Draw your own conclusions...
01-19-2002, 01:43 PM
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Additionally, the higher the specific heat of the material, the better off you are (read: ceramics). The specific heat is the amount of heat energy that a material must absorb to raise its temperture. Ceramics have a very high specific heat - they don't heat up very well. However, they also have a very poor thermal conductivity - great for insullating, bad for transferring heat out of the material once it gets hot. Metal is just the opposite - it takes comparively less heat to heat the metal, but it cools quickly as well. A properly deisgned and proportioned metal rotor shuold do just fine for even the most aggressive open road drivers.
01-19-2002, 01:59 PM
#13
There is a specific service bulletin regarding this specific problem,ask your dealer to apply it your vehicle.I have done this specific bulletin on many cars and have had no problems with these cars since.The bulletin is recent so you may have had your car worked on prior to it being issued.Rotors are generally resurfaced unless they have warpage beyond what is allowed or they are too thin to permit resurfacing.Jens
01-19-2002, 05:50 PM
#14
Suzuka Master
Originally posted by jdl75
[B]
Outgassing? Could you explain that physical phenomina? I'm not familiar with that term.
Pads need to seat on the calliper, but there is such a large heat sink behind the pad that once the pad seats properly, the pad is able to pull what little heat it can with out much problem
[B]
Outgassing? Could you explain that physical phenomina? I'm not familiar with that term.
Pads need to seat on the calliper, but there is such a large heat sink behind the pad that once the pad seats properly, the pad is able to pull what little heat it can with out much problem
Do a look up for green fade on google...
There is a reason they put slots in some rotors. The brakes pads (when they are not properly broken in) will outgas -- volatiles in the brake pad create a "gas layer" that prevents the brake pad from conducting away heat (as well as it could). (Even properly broken in brake pads will release some amount of “gas”.)
I'm not quite sure what we're holding equal - if the thickness of the rotors changes, but all other ratios stay the same, or all other dimensions stay the same? If all other dimensions stay the same, yes, you will have an excess of heat build up, and the small gain in surface area around the edge of the rotor will not be enough to dissipate the stored heat. However, you must remember that braking generates a specific amount of energy, mostly in the form of heat, and that heat energy is dispersed over the mass of the rotors (and to a much lesser extent the callipers/pads).
If the ratios stay the same, then you will have an increase in surface area to go along with the increase in rotor mass. This is the ideal situation, and will help you avoid warped rotors. The more rotor mass you have, the larger the area available to spread the heat energy generated from a stop. If you have proportionally larger surface areas, the cooling will occur faster (that's why air cooled engines have fins on the exterior surfaces - more surface area).
If the ratios stay the same, then you will have an increase in surface area to go along with the increase in rotor mass. This is the ideal situation, and will help you avoid warped rotors. The more rotor mass you have, the larger the area available to spread the heat energy generated from a stop. If you have proportionally larger surface areas, the cooling will occur faster (that's why air cooled engines have fins on the exterior surfaces - more surface area).
Heat up a chunk of metal -- the bigger it is, the longer it takes to heat up AND cool down (all things being equal).
Analogy -- take a hollow metal brick, and heat it up. Let say it reaches 200-degrees C after 20 minutes; it will take a certain amount of time to cool back down (let's say 10 minutes). Now replace the hollow metal brick with one with that is solid (not hollow); if it now takes 30 minutes to reach 200-degrees C; it will also take a longer amount of time to cool back down. (The outside of the brick has the same dimensions and is exposed to the same temperature differentials (for heating and for cooling -- OK)
Remember - the important point here is to devide the fixed amount of heat generated from a stop over the largest mass possible (single stop) - this will keep the overall temperature of the rotor down lower than a less massive rotor. For multiple stop considerations, it is important to increase the surface area (and therefore the cooling) capacity of the rotor.
Multiple stop -- IT is much more important to supply cooling ducts and internal venting that allows as much cooling air as possible to remove the heat from the system. A complete cooling model would take hours to diagram and present here with all of the various thermal barriers, thermal resistance junctions, thermal mass properties, etc. Now add in the conduction, convection, and radiative heat transfer properties and your talking even more data. I will take a smaller rotor with good internal metal-to-air(carbon-to-air) heat exchange properties with forced air-cooling any day over a rotor size increase. Check out the carbon rotors on a modern F1 car -- they have a very low thermal mass, small diameter, with a very specially designed air plenum to direct air to the caliper and inner vents of the disk.
Finally, just to be clear – if the pads suck, change them out. I have noticed people who still had warping problems happen AFTER they got the new “magic” pads. As I mentioned, I would get batches of good rotors (would never warp through their service life) and others that would warp so bad, that they needed to be tossed (and I never could find a pattern).
01-19-2002, 06:08 PM
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Re: Rotor Specifications?
Originally posted by bdavid13
What's up everyone, My problem is that my rotors have warped 3 times in 25,500 in my CL-S and the dealer have re-surface the rotors three times... I was wondering if anyone has the factory specs on the rotors... If they're out of specs, then Acura will be hearing it from me and my attorney!!! I appreciate all the feed back... Or if anyone has Acura's 800 # thanks
Has this happen to anyone... Steering vibration while braking from speeds btw 75- and up?
What's up everyone, My problem is that my rotors have warped 3 times in 25,500 in my CL-S and the dealer have re-surface the rotors three times... I was wondering if anyone has the factory specs on the rotors... If they're out of specs, then Acura will be hearing it from me and my attorney!!! I appreciate all the feed back... Or if anyone has Acura's 800 # thanks
Has this happen to anyone... Steering vibration while braking from speeds btw 75- and up?
01-19-2002, 06:10 PM
#16
Suzuka Master
Originally posted by jdl75
Additionally, the higher the specific heat of the material, the better off you are (read: ceramics). The specific heat is the amount of heat energy that a material must absorb to raise its temperture. Ceramics have a very high specific heat - they don't heat up very well. However, they also have a very poor thermal conductivity - great for insullating, bad for transferring heat out of the material once it gets hot. Metal is just the opposite - it takes comparively less heat to heat the metal, but it cools quickly as well. A properly deisgned and proportioned metal rotor shuold do just fine for even the most aggressive open road drivers.
Additionally, the higher the specific heat of the material, the better off you are (read: ceramics). The specific heat is the amount of heat energy that a material must absorb to raise its temperture. Ceramics have a very high specific heat - they don't heat up very well. However, they also have a very poor thermal conductivity - great for insullating, bad for transferring heat out of the material once it gets hot. Metal is just the opposite - it takes comparively less heat to heat the metal, but it cools quickly as well. A properly deisgned and proportioned metal rotor shuold do just fine for even the most aggressive open road drivers.
I don't think so....
Aluminum has a very high specific heat (heat capacity), but it also conducts heat well.
You can't judge or build a thermal energy conversion system based only on specific heat characteristics. There a issues that relate to the materials ability to withstand the clamping force of the pads, friction coefficients, and other material properties that swamp out the heat capacity issues.
If one were to choose a material with a great specific heat, why not just choose Aluminum (it also has very high thermal conductivity)? (I don't think you will find many brake applications (as the clamped material) and has the highest specific heat of any of the metals. Its heat capacity is about twice that of iron...
You need to sink the heat and to get rid of it *or* get rid of it at them same time heat is going into it...
Interesting that radiative heat transfer is governed by 4th power relationships to heat differentials...
01-19-2002, 06:16 PM
#17
Suzuka Master
Re: Re: Rotor Specifications?
Originally posted by acura_service
jesus, sue sue sue, thats all anyone wants anymore - if they are within thickness spects, they cut them, if they are going to go under based on the out of round amount vs thickness they get replaced, or if they are under min thickness after refinishing they get replaced - have your dealer look at them again, i don't know your driving habits, but if you drive in hilly terrain, you might want to downshift to minimize rotor warpage
jesus, sue sue sue, thats all anyone wants anymore - if they are within thickness spects, they cut them, if they are going to go under based on the out of round amount vs thickness they get replaced, or if they are under min thickness after refinishing they get replaced - have your dealer look at them again, i don't know your driving habits, but if you drive in hilly terrain, you might want to downshift to minimize rotor warpage
Thanks -- You realize the insanity of all of this...
There have been a few occasions where the very act of warping a rotor will "temper it" and it will not warp again (there are exceptions). I hope people realize that just putting on a different set of disks (just 'cause the current ones warped) is like a crap shoot -- you could just end up getting disks that aren't as good as the "cut" (current) ones...
01-19-2002, 07:37 PM
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Originally posted by EricL
Do a look up for green fade on google...
Heat up a chunk of metal -- the bigger it is, the longer it takes to heat up AND cool down (all things being equal).
Single stop mass -- point is correct (more thermal mass and capacity is better).
Multiple stop -- IT is much more important to supply cooling ducts and internal venting ...check out the carbon rotors on a modern F1 car -- they have a very low thermal mass, small diameter, with a very specially designed air plenum to direct air to the caliper and inner vents of the disk.
Finally, just to be clear – if the pads suck, change them out. I have noticed people who still had warping problems happen AFTER they got the new “magic” pads. As I mentioned, I would get batches of good rotors (would never warp through their service life) and others that would warp so bad, that they needed to be tossed (and I never could find a pattern).
Do a look up for green fade on google...
Heat up a chunk of metal -- the bigger it is, the longer it takes to heat up AND cool down (all things being equal).
Single stop mass -- point is correct (more thermal mass and capacity is better).
Multiple stop -- IT is much more important to supply cooling ducts and internal venting ...check out the carbon rotors on a modern F1 car -- they have a very low thermal mass, small diameter, with a very specially designed air plenum to direct air to the caliper and inner vents of the disk.
Finally, just to be clear – if the pads suck, change them out. I have noticed people who still had warping problems happen AFTER they got the new “magic” pads. As I mentioned, I would get batches of good rotors (would never warp through their service life) and others that would warp so bad, that they needed to be tossed (and I never could find a pattern).
A thermal model is not necessary - for this purpose it is pretty basic. The outgassing you speak of is also know as sublimation (a solid turning to gas w/o passing through the liquid phase) - more often seen in water, rarely seen in metal under normal circumstances, but I won't say it can't happen - the rotor-pad interface can achieve very high temperatures and pressures, and this would be required for sublimation of the brake pads.
Your statement about the mass differences in correct, but you ignored my point of increasing the surface area - a disk that is larger / thicker will by design have a larger surface area to promote increased cooling. Also, we are working with available passive cooling (same principle that explains why air cooled motors have fins). Any basic heat transfer text will cover this under convection.
As for F1, well, I would love to have forced cooling on my cars brakes! But forced cooling changes everything, and would require a much more indepth, detailed discussion (and it would involve the need for partial differential equations, so I don't wan't to go there! This is fun, not work!!)
01-19-2002, 07:58 PM
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I don't think so....
Aluminum has a very high specific heat (heat capacity), but it also conducts heat well....If one were to choose a material with a great specific heat, why not just choose Aluminum (it also has very high thermal conductivity)? (I don't think you will find many brake applications (as the clamped material) and has the highest specific heat of any of the metals. Its heat capacity is about twice that of iron...
You are begining to bore me. Yes, Aluminum has a high specific heat (900 J/kg-K), compared to iron (448 J/kg-K) or 316 stainless (504 J/kg-K). But compared to many ceramics that have Cp values in the thousands, aluminum sucks. Besides, aluminum gets brittle after it is heated to an extreme. The rotors wouldn't warp, they would break!
You can't judge or build a thermal energy conversion system based only on specific heat characteristics. There a issues that relate to the materials ability to withstand the clamping force of the pads, friction coefficients, and other material properties that swamp out the heat capacity issues.
Well, we can certainly change the scope of the discussion - friction coefficients are an important consideration - no friction, no stop! If it crushes, no stop! If it melts, no stop!
However, if you want to discuss the material and design properties that affect warping, you must look at the thermal characteristics and stability of the material.
Interesting that radiative heat transfer is governed by 4th power relationships to heat differentials...
Uhh, yeah, so? You mean q(ij)=A(i)F(ij)*omega(T(i)^4-T(j)^4) ? Who cares? Your T values are so small that radiation transfer of energy is going to hardly get noticed!
01-19-2002, 08:42 PM
#20
Suzuka Master
Originally posted by jdl75
I think we are talking about more or less the same thing.
A thermal model is not necessary - for this purpose it is pretty basic. The outgassing you speak of is also know as sublimation (a solid turning to gas w/o passing through the liquid phase) - more often seen in water, rarely seen in metal under normal circumstances, but I won't say it can't happen - the rotor-pad interface can achieve very high temperatures and pressures, and this would be required for sublimation of the brake pads.
Your statement about the mass differences in correct, but you ignored my point of increasing the surface area - a disk that is larger / thicker will by design have a larger surface area to promote increased cooling. Also, we are working with available passive cooling (same principle that explains why air cooled motors have fins). Any basic heat transfer text will cover this under convection.
As for F1, well, I would love to have forced cooling on my cars brakes! But forced cooling changes everything, and would require a much more indepth, detailed discussion (and it would involve the need for partial differential equations, so I don't wan't to go there! This is fun, not work!!)
I think we are talking about more or less the same thing.
A thermal model is not necessary - for this purpose it is pretty basic. The outgassing you speak of is also know as sublimation (a solid turning to gas w/o passing through the liquid phase) - more often seen in water, rarely seen in metal under normal circumstances, but I won't say it can't happen - the rotor-pad interface can achieve very high temperatures and pressures, and this would be required for sublimation of the brake pads.
Your statement about the mass differences in correct, but you ignored my point of increasing the surface area - a disk that is larger / thicker will by design have a larger surface area to promote increased cooling. Also, we are working with available passive cooling (same principle that explains why air cooled motors have fins). Any basic heat transfer text will cover this under convection.
As for F1, well, I would love to have forced cooling on my cars brakes! But forced cooling changes everything, and would require a much more indepth, detailed discussion (and it would involve the need for partial differential equations, so I don't wan't to go there! This is fun, not work!!)
You are assuming that the volailes are sublimating -- they may or may not be. In any event the material is creating a gas layer that impedes heat transfer. If a pad is not broken in properly, it just has more of a problem with this issue. (The sublimation is an assumption...)
1. You think that the increased cooling is via the surface area -- of what the outside of the disks. It is the internal venting that is impacts the cooling (to a large extent). Remember, vented brakes. Certainly you would agree, that there is more surface area in the metal-to-air area inside the disk than outside. The outside would have a more uniform plate-to-air temp differential (in most cases), but the internal vents would expose much more area from the metal-to-air (just like a nice heat sink). The current F1 cars get forced air from the front and feed it into the center of the disks. Why fight centrifugal force?
2. Forced cooling -- no need for partial differentials equations. Just grab the high-speed air coming the front of the car and pump in towards the center of the internal vents in the vented disks. A good vented rotor works as a natural air pump -- the air is driven from the inside of the disk to the outside; this presumes that there are open vents at the inside of the disks. When a car is moving, it is just like the fan on a heat sink (I'm sure you knew this)
3. Brakes are forced air-cooled devices -- they have air flowing past them and they heat is also transferred by conduction to the wheels by way of the hubs. (The car is moving when brakes are really needed)
I happen to enjoy working with differential and differencing equations. I'm not so sure that a partial differential solution would be needed for some rough iterative design issues.
It is not like there is some requirement to establish boundary values or equilibrium conditions in a "heated plate" problem. The notion of radiative heat transfer refers to the large dissipative energy that is possible via carbon brakes.
There are a number of sources of information on where brake technology is going...
01-19-2002, 09:11 PM
#21
Suzuka Master
Originally posted by jdl75
I don't think so....
Aluminum has a very high specific heat (heat capacity), but it also conducts heat well....If one were to choose a material with a great specific heat, why not just choose Aluminum (it also has very high thermal conductivity)? (I don't think you will find many brake applications (as the clamped material) and has the highest specific heat of any of the metals. Its heat capacity is about twice that of iron...
You are begining to bore me. Yes, Aluminum has a high specific heat (900 J/kg-K), compared to iron (448 J/kg-K) or 316 stainless (504 J/kg-K). But compared to many ceramics that have Cp values in the thousands, aluminum sucks. Besides, aluminum gets brittle after it is heated to an extreme. The rotors wouldn't warp, they would break!
You can't judge or build a thermal energy conversion system based only on specific heat characteristics. There a issues that relate to the materials ability to withstand the clamping force of the pads, friction coefficients, and other material properties that swamp out the heat capacity issues.
Well, we can certainly change the scope of the discussion - friction coefficients are an important consideration - no friction, no stop! If it crushes, no stop! If it melts, no stop!
However, if you want to discuss the material and design properties that affect warping, you must look at the thermal characteristics and stability of the material.
Interesting that radiative heat transfer is governed by 4th power relationships to heat differentials...
Uhh, yeah, so? You mean q(ij)=A(i)F(ij)*omega(T(i)^4-T(j)^4) ? Who cares? Your T values are so small that radiation transfer of energy is going to hardly get noticed!
I don't think so....
Aluminum has a very high specific heat (heat capacity), but it also conducts heat well....If one were to choose a material with a great specific heat, why not just choose Aluminum (it also has very high thermal conductivity)? (I don't think you will find many brake applications (as the clamped material) and has the highest specific heat of any of the metals. Its heat capacity is about twice that of iron...
You are begining to bore me. Yes, Aluminum has a high specific heat (900 J/kg-K), compared to iron (448 J/kg-K) or 316 stainless (504 J/kg-K). But compared to many ceramics that have Cp values in the thousands, aluminum sucks. Besides, aluminum gets brittle after it is heated to an extreme. The rotors wouldn't warp, they would break!
You can't judge or build a thermal energy conversion system based only on specific heat characteristics. There a issues that relate to the materials ability to withstand the clamping force of the pads, friction coefficients, and other material properties that swamp out the heat capacity issues.
Well, we can certainly change the scope of the discussion - friction coefficients are an important consideration - no friction, no stop! If it crushes, no stop! If it melts, no stop!
However, if you want to discuss the material and design properties that affect warping, you must look at the thermal characteristics and stability of the material.
Interesting that radiative heat transfer is governed by 4th power relationships to heat differentials...
Uhh, yeah, so? You mean q(ij)=A(i)F(ij)*omega(T(i)^4-T(j)^4) ? Who cares? Your T values are so small that radiation transfer of energy is going to hardly get noticed!
It would be nice if you read to the end of the reply. As you clearly see, I pointed out that there were many other properties that were important rather than heat capacity and heat transfer. Hence, the fact that Iron is used in lieu of Aluminum based on additional material properties. So you treat me like an idiot when I mention the Aluminum, but still insist on leaving in your insulting statement when I explain that without considering other material properties, bulk properties and conduction (and other issues) are moot..
You tend to pooh-pooh the radiative transfer of energy, yet it is rather important in carbon brakes -- the brakes are glowing red hot and it is important.
You might argue that glowing red brakes don't apply to "our" cars or non-F1 cars. I can tell you first hand that I've had brakes on a track glow bright red. Please don't tell me that radiative cooling is of no consequence. (Get in a home with a 160F attic temp with no radiative insulation barrier, then turn the inside thermostat down to 60 degrees and you tell me if you feel cool. If you ever have a chance to experience this, you will find the sensation of being heated while shivering rather interesting.)
Material development and discs machined in one piece from carbon-carbon have resulted in lightweight brakes with consistent performance. The uprights, calipers, wheels, and tires stabilize at a temperature that is limited by the characteristics of individual components, and their ability to absorb energy at a rate greater is small. The disk and pads have a limited thermal inertia and rise in temperature quickly when the brakes are applied. Heat must be conducted away from the friction surfaces and transferred by forced convection into the airstream. Although the friction properties of carbon-carbon are maintained at high temperature, the wear rate rises sharply when the oxidation temperature of 650-700C (1200-1300F) is reached. Wheel uprights are designed to duct air from the brake cooling ducts on the inside of the wheels, through the vaned internal structure of the upright (cooling the wheel bearings in the process), and to pre-swirl the cooling air into the eye of the disk. Radial holes in the disk centrifuge the air though its core. Air is bled from the ducts to cool the pads and critical areas of the caliper. Ducting air directly onto the friction surface is not desirable because it increases the speed of the oxidation process and hence increased wear.
It is the very low-conduction and low-thermal bulk properties of carbon-carbon that make this material so appealing as it reduces the load on the surrounding parts that are subject to heat breakdown problems
So, know that you know this -- are you so sure that it is a great thing to have a non-matrix high thermal bulk capacity material for great stopping?
01-19-2002, 09:55 PM
#22
Racer
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You've gone far beyond the scope of this post, or our cars for that matter. Have fun, I've got other things to do.
By the way, you do need a PDE to solve non-SS heat transfer problems.
By the way, you do need a PDE to solve non-SS heat transfer problems.
01-19-2002, 10:55 PM
#23
Suzuka Master
NO PDE with 1D
Originally posted by jdl75
You've gone far beyond the scope of this post, or our cars for that matter. Have fun, I've got other things to do.
By the way, you do need a PDE to solve non-SS heat transfer problems.
You've gone far beyond the scope of this post, or our cars for that matter. Have fun, I've got other things to do.
By the way, you do need a PDE to solve non-SS heat transfer problems.
Yes, I have done them and even reduced them to difference equations (1D representations). Most simple semiconductor heat conduction issues (transient and steady-state) can be reduced to much simpler models and do quite nicely when determining 1) initial conditions 2) transient and 3) steady state conditions...(junction-to-case, case-to-heat sink, heat sink to air)
I have Macsyma and PDEase so I am familiar with the requirements. Hopefully, know one will be asking for a FEA time stepped representation of a full system with full color representation of the temps/gradients in each component.
01-21-2002, 12:52 PM
#24
Intermediate
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Wow, That was a great debate Eric L and jdl75, hey you guys are Gods of explanation, I really appreciate all the great comments and arguments regarding rotors... that was very enlightening. I was told by the dealer that I drive at high speeds.. Is 65-80mph considered high speeds..... I dunno, I think our cars have poorly made parts and Acura isn't doing anything about it. I 've talked to the Acura home office, you know that 800 # and have express my concerns about the vehicle and they said next time it happens, just to call them. As Far as Acura_ Service, I'm under the impression that you work for a dealer right? I think your comments regarding legal actions are bias. It's okay to express your feelings regarding the subject, but if you need a hug bro, I don't think you'll find it in this thread
Eric L and jdl75 thank you very much.
Eric L and jdl75 thank you very much.
01-21-2002, 02:37 PM
#25
Burning Brakes
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Originally posted by bdavid13
I dunno, I think our cars have poorly made parts and Acura isn't doing anything about it. I 've talked to the Acura home office, you know that 800 # and have express my concerns about the vehicle and they said next time it happens, just to call them. As Far as Acura_ Service, I'm under the impression that you work for a dealer right? I think your comments regarding legal actions are bias. It's okay to express your feelings regarding the subject, but if you need a hug bro, I don't think you'll find it in this thread Eric L and jdl75 thank you very much.
I dunno, I think our cars have poorly made parts and Acura isn't doing anything about it. I 've talked to the Acura home office, you know that 800 # and have express my concerns about the vehicle and they said next time it happens, just to call them. As Far as Acura_ Service, I'm under the impression that you work for a dealer right? I think your comments regarding legal actions are bias. It's okay to express your feelings regarding the subject, but if you need a hug bro, I don't think you'll find it in this thread
Eric L and jdl75 thank you very much.
Acura_Service is right. You can sue anyone in the U.S. over just about anything. It doesn't mean you'll win or that the case will even be bound over for a hearing. Other than the annoyance you've experienced, what are your damages? To the best of my knowledge, no CL or TL driver has been involved in an accident due to the brake issue. I'll be the first to agree that a $30K shouldn't "shake" when braking, but safety doesn't appear to have been compromised in any way by the problem. As long as Acura repairs the car and gives you a loaner, I don't think you really have a case. Good luck though if you do try to sue.
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