I don't take anything at face value - I look things up.
However, I am not a metallurgist, so I first admit I didn't know if a rotor "can" or "cannot" truly warp (as in potato chip) at street speeds - so I looked up a few things about the temperature needed to cause true warpage of a cast-iron rotor...
Raybestos says: "Brake rotors do not warp from heat..."
This says: "Rotors are cast in extreme heat ?X three to five times greater than the most aggressive braking situation. Physically ??warping?? a rotor would require a similar application of extreme heat, which is impossible."
This says: "...the temperature required to make metal that resilient soft enough to simply bend would be tremendous."
This says that there are adverse effects starting at 1200dF: "When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness."
This says: "in more than 40 years of professional racing, including the Shelby/Ford GT 40s ?V one of the most intense brake development program in history - I have never seen a warped brake disc."
These say the myth of warped rotors started in the 1970's:
This non-scientific thread, which we can quickly assume isn't scientific so let's just take it as a reasonable point of view only, says that the surface may get to 600dF but the rest of the rotor is at a lower temperature than the surface.
I know you guys hate me for "book knowledge", but the answer on temperature seems pretty clear so I will argue no further unless actual references are supplied, as I already know tons of people *think* rotors warp, but it seems that anyone who has actually measured it, apparently thinks not (where true warpage would be easy to measure if you have the equipment to measure head warp).
Different equipment required. Just a dialindicatoraznd stand, and a micrometer.
Check for run-out on outer face then confirm no difference in thickness. If the runout is not linear and there is no thickness variation, it is warped.
The "cementite" formation is a lot more common than warpage
Warpage is less common on vented rotors than on solid rotors.
You don't need to take my word for it. There have been scientific studies done - independent of the "marketing departments" of the brake comnpanies that confirm dimensional instability (aka warpage) of grey iron rotors is a "significant cause" of brake judder.
Read the study - and then decide who's right and who's wrong here - -
- -
From
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Where you can see allthe diagrams and charts etc related to the tests
Journal of Materials Engineering and Performance
April 2013, Volume 22, Issue 4, pp 1129?1135| Cite as
The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks
Thermal distortion of gray iron brake disks due to residual stress and its effect on brake vibrations were studied. The residual stress of heat- and non-heat-treated gray iron disks was measured using neutron scattering. Dynamometer tests were performed to measure the friction force oscillation caused by the disk runout during brake applications. High-temperature tensile tests were carried out to find out possible plastic deformation due to residual stress during brake applications. The results showed that the average residual stress of the heat-treated disk (47.6 MPa) was lower than that of the non-heat-treated disk (99.6 MPa). Dynamometer tests at high temperatures (up to 600 °C) indicated that the residual stress pronounced the runout: the increase in disk runout after the tests for the non-heat-treated sample was more than twice that for the heat-treated sample. This difference correlated well with the neutron scattering results and the dimensional changes after a separate vacuum heat treatment. The high-temperature tensile tests showed severe reductions in yield strength at 600 °C, suggesting that disks produced with no stress relaxation could be deformed during severe braking.
Gray iron has been used to produce brake disks (or drums) since the early stages of vehicle development. This is because gray iron has good material properties for brake disks, such as high thermal conductivity, good machinability, wear resistance, good castability, excellent damping capacity, and low cost (Ref 1, 2). On the other hand, it also has several undesirable properties for brake disks, such as relatively high specific gravity, dimensional instability at high temperatures due to residual stress, and inherent casting defects. While other materials such as aluminum-based metal matrix composites and ceramic-based carbon fiber composites have been developed as alternatives for brake disks, most vehicles still rely on the tribological properties of gray iron for brake disks, and much effort has been devoted to improving the shortcomings of gray iron disks, such as their excessive wear and corrosion, which are known to be root causes of brake judder (Ref 3-5).
In particular, brake judder has been an important issue in vehicle comfort in recent years, and various methodologies for reducing this low-frequency vibration have been used (Ref 6-8). It is known that disk warping or uneven disk thicknesses induce pulsation during brake applications. While it is known that the system robustness is important for reducing the amplification of the vibration, the major source of brake-induced vibrations is the fluctuation of the friction torque produced at the sliding interface as a result of the dimensional variation of the disk. When the disk temperature is increased by friction heat during braking, the heat often causes dimensional instability of the disk, permanently modifying the runout or disk thickness variation (DTV) of a disk and producing brake judder. In particular, the residual stress, which is developed in a cast as a result of different local cooling rates, is known to be one of the important factors for reducing a disk?s propensity for juddering, and stress relief by heat treatment is known to be an effective method for ensuring the dimensional stability of a disk at high temperatures.
Residual stress can be measured using several methods, including x-ray scattering, hole drilling, indentation, and neutron scattering (Ref
9-11). The x-ray and neutron scattering methods are nondestructive, while the hole-drilling and indentation methods are semi-destructive. The measuring depth of an x-ray is very small (~5 µm), and this method is only applicable to crystalline materials (Ref 9). The hole-drilling method measures the strain around the hole during drilling, and the indentation method is similar to a hardness measurement (Ref 9). However, the hole-drilling and indentation methods do not allow precise measurement of the residual stress in gray iron. This is because the microstructure of gray iron is a mixture of graphite flakes in a pearlitic steel matrix, and the multiphase nature of gray iron often produces large amounts of scattering in the data (Ref 1,
2). On the other hand, the neutron scattering method measures the residual stress of the ferritic phase in the gray iron along three principal directions to a depth of 10 mm with good repeatability.
The residual stress of brake disks was investigated by Ripley and Kirstein (Ref 12). They measured the residual strain using the neutron scattering method and showed that the relaxation of the residual stress in the disk could lead to disk distortion. Although the residual stress induces elastic deformation at room temperature, the tensile strength and hardness of gray iron decrease abruptly above 450 °C, so that the maximum value of the residual stress can reach the yield stress of the gray iron at high temperatures (Ref 13, 14), causing plastic deformation and permanent warping of the disk. In order to remove the residual stress of the brake disks, therefore, heat treatment to release the residual stress can be performed at high temperatures.
In this study, the residual stress was measured using a neutron scattering technique (Ref 9, 15, 16), and its correlation with the judder propensity was investigated by examining the effect of heat treatment on the microstructure of the gray iron and on the residual stress. Heat treatment was carried out in a vacuum to investigate the distortion produced by the relaxation of residual stress at high temperatures. While the disk warping during heat treatment was measured using a static DTV measurement unit, the dimensional change of the brake disks during braking was monitored using a dynamic DTV measurement unit.
Experimental Procedures
In order to investigate the dimensional change (or runout) of brake disks due to the release of residual stress, three different experiments were carried out. First, the residual strain of as-cast gray iron disks was measured using a neutron scattering method. Second, the change in runout was measured after vacuum heat treatment at 580 °C. Finally, brake dynamometer tests were carried out to simulate the release of residual stress due to the large friction heat produced during severe braking. By comparing the three different test results, the effects of the residual stress on the changes in runout, DTV, and judder propensity were examined. Detailed experimental procedures are described in the following sections.
Gray Iron Disks
Commercial gray cast iron disks for a passenger car were used in this study. The carbon equivalent of the gray iron was 4.03, and the detailed composition is given in Table 1. The width of the rubbing surface of each disk was 57 mm. Each disk had 50 straight vanes, and the disks were 302 mm in diameter and 28 mm in thickness. The vane size was 19 mm (W) × 10 mm (H). An undercut was produced on the disk surface near the hat portion to prevent possible corning. Two different types of disks were prepared: heat-treated (Disk H) and as-cast (Disk NH) disks. To relax the residual stress, heat treatment was carried out by heating the disks at 580 °C for 5 h, furnace cooling them from 580 to 300 °C at a rate of 40 °C/h, and air cooling them from 300 °C to ambient temperature. The heat treatment schedule is shown in Fig. 1. In order to reduce the effect of machining on the residual stress, the heat treatment was carried out on the as-cast disks before a final machining process.
The yield strength at elevated temperatures was measured using a tensile testing machine (Instron 5881) according to an ASTM standard procedure (AFS-ASTM E21). The specimens were wire cut from the rubbing surface at the outer radius of Disk NH. The diameter of the specimens was 6.25 mm, and the gage length was 32 mm. A schematic of the specimen is shown in Fig. 2. The tensile tests were carried out at 25,
100, 200, 300, 400, 500, and 600 °C at a crosshead speed of 0.001 mm/s.
The microstructure of the gray iron was examined using an optical microscope (Leica DM1-LM). The graphite lengths of the disk were measured at outer, middle, and inner positions on the disk according to AFS-ASTM A247. The Brinell hardness test was carried out using a 10 mm diameter steel ball at a load of 3,000 kg.
Residual Stress Measurement Using Neutron Scattering
The residual stress was measured from the diffraction peaks in the three principal orientations (i.e., radial direction [RD], hoop direction [HD], and normal direction [ND]) from a 2 mm (W) × 5 mm (L) × 2 mm (D) gage volume of gray iron. The measurement was carried out using a beam of neutrons from a bent perfect crystal (BPC) Si (220) monochromator with a wavelength of 1.50-1.80 Å. The beam was scattered in the sample, and the scattered neutrons were collected in a position-sensitive device (PSD). A schematic of the neutron scattering experiment is shown in Fig. 3.
The location in the disk of the specimen analyzed by neutron scattering is shown in Fig. 4. The figure also includes a cross section of the disk with the exact locations to be analyzed and the three principal orientations with respect to the specimen geometry. The reference specimen was also cut from the same location on the disk and heat treated to achieve a stress-free state. The heat treatment for the reference specimen was carried out by heating the specimen at
580 °C for 10 h, after which it was slowly cooled in the furnace to ambient temperature.
Locations (A-D) used to measure residual stresses in the gray iron disk, along with the three principal orientations (normal, hoop, and radial)
The interplanar spacing of the (211) plane in ferrite was measured to compare the residual stress in the disks (Ref 12). The residual strain of the disk was calculated from the difference between the interplanar spacing of the target disks and that of a reference specimen using Eq
1 (Ref 9)
e=(d-d 0 )/d 0 , e=(d-d0)/d0,
(1) where d is the interplanar spacing obtained from the target disk and d
0 is the interplanar spacing of the reference specimen. The residual strain was converted into residual stress using Eq 2 (Ref 12)
s i =E1+? [e ii +?1-2? (e xx +e yy +e zz )], si=E1+?[eii+?1-2?(exx+eyy+ezz)],
(2) where E is Young?s modulus (135.65 GPa) and v is Poisson?s ratio for gray iron (=0.249). The elastic modulus and Poisson?s ratio were measured using a resonance method according to an ASTM standard (AFS-ASTM standard E1876-07) (Ref 12, 17).
Vacuum Heat Treatment
The vacuum heat treatment was carried out to simulate the release of residual stress via disk distortion. The heat treatment schedule consisted of furnace heating up to 580 °C followed by air cooling. The disks were hung on a steel rod to prevent dimensional changes caused by their own weight. Before and after the vacuum heat treatment, the runout and DTV were measured using a static DTV measurement unit (Describer-S?).
Dynamometer Tests
Dynamometer tests were carried out to simulate a hot judder mode using a single-ended brake dynamometer (Link Engineering Model 3000). The brake assembly used in this study comprised a commercial caliper with a single piston and was developed for a midsize passenger car. The test consisted of a preburnish, a 1st effectiveness check, a burnish, a 2nd effectiveness check, and juddering. The purpose of this test mode was to heat the disk above 580 °C and measure the changes in runout, friction coefficient, and disk temperature. The detailed dynamometer test procedure is listed in Table 2. The runout was measured by a static DTV measurement apparatus (Describer-S?) before and after the dynamometer tests. During the dynamometer tests, the runout was recorded by a dynamic DTV measurement unit (Describer-D?).
Table 2 Dynamometer test sequence used in this study to simulate severe braking conditions
Test sequence
No. of Stop
Stop condition
Pre burnish
10 From 80 ? 2 kph, 0.3 G and 100 °C (IBT)
Effectiveness check
5 From 160 ? 80 kph, 0.4 G and 100 °C (IBT)
Burnish
200 From 80 ? 2 kph at 0.3 G and 100 °C (IBT)
Effectiveness check
5 From 160 ? 80 kph, 0.4 G and 100 °C (IBT)
Judder
15 From 160 ? 50 kph at 100/200/300/400/500 °C (IBT) and at 0.2/0.35/0.5G
IBT, initial brake temperature; G, deceleration; kph, kilometers per hour
Results and Discussion
Mechanical Properties of the Cast Iron
It is known that the mechanical properties of gray iron are strongly affected by the lengths of the graphite flakes, which are in turn determined by the composition and cooling rate during casting (Ref 1). This is because the flaky graphite in the pearlitic matrix allows stress to be concentrated at the flake tips, so that it plays a crucial role in determining the tensile strength. The thermal conductivity of gray iron is also determined by the size and the distribution of the graphite flakes. This is an important property for brake disks, as the thermal diffusivity of the disk is critical for avoiding brake fade (loss of friction force at high temperatures) (Ref
18). The microstructure of the disk showed typical A-type graphite flakes (AFS-ASTM A247 designation) embedded in a pearlite matrix (Fig.
5). The maximum graphite lengths of the disk were measured at outer, middle, and inner positions on the disk according to AFS-ASTM A247. They were 180.5, 200.8, and 243.7 µm, respectively. There were slightly longer flakes in the inner section of the disk because of the difference in the cooling speed during casting. The pearlite microstructure of the disk, however, showed little difference among the different locations in the disk. The morphology and distribution of the graphite flakes and the pearlite microstructure also did not change after heat treatments. The microstructure and hardness (HB) of Disks NH and H did not change after heat treatment. The Brinell hardness values of Disks NH and H were 210 and 205, respectively.
The tensile strength of the gray iron was measured as a function of temperature. Figure 6 shows a drastic decrease of the yield strength above 600 °C: the yield strength at room temperature is 257.9 MPa, and it decreases to 66.7 MPa at 600 °C. Particularly noteworthy is the finding that the residual stress in the cast can plastically deform the disk during braking at elevated temperatures, leading to permanent distortion of the disk.
Residual Stress in the Brake Disks
The residual stress in a cast is known to be affected not only by locally different cooling speeds during casting but also by the final machining processes. This is because while the residual stress present in the cast is generated by the temperature gradient in the cast, it can be released by removing the constraint imposed by the surface when a portion of the surface is removed by machining. In order to study the effect of heat treatment on thermal distortion of a gray iron disk, the residual strain of the disk before and after the heat treatment was measured after final machining.
From the residual strain measured using a neutron scattering method for four different locations (Fig. 4) in the disk, residual stresses were calculated along the three principal orientations (Fig. 7). The figure shows the residual stresses for tension (positive) and compression (negative), and no correlation was found between the location in the disk, the principal orientation, and the heat treatment with respect to the nature of the stress. On the other hand, the amount of stress was relatively small at location A, presumably due to the undercut (rain groove) near the hat section of the disk produced by machining. While the residual stresses were obtained from a single location in the disk and do not represent the stress distribution of the whole disk, they provide information about the relative amount of stress present in the disks with and without heat treatment.
Residual stresses measured for the four different locations (A-D) illustrated in Fig. 5 along the three different principal orientations
To analyze the effect of residual stress on the disk distortion, the residual stresses in the normal orientation were compared first, as the deformation is easier along the normal orientation as it is least constrained compared to the other two directions. Figure 7 shows that the residual stresses along the normal orientation were reduced after heat treatment. The maximum residual stress before heat treatment was found at location C and was 123.5 MPa. This was reduced to 57.5 MPa after stress relief heat treatment, indicating possible permanent deformation along the normal orientation when Disk NH is exposed to heat during braking. This is because the residual stress at point C of Disk NH is greater than the yield strength of gray iron at 600 °C. On the other hand, the plastic deformation of the disk is not likely to occur in Disk H, as the remaining residual stress after the heat treatment is smaller than the yield strength at high temperatures. Figure 7 also shows an inconsistent change of the stress state for both Disks NH and H in the radial and hoop directions, which is attributed to the vanes in the middle of the disks.
Simulation of Thermal Distortion by Heat Treatment Using a Vacuum Furnace
The dimensional change (warping) of the disk was monitored after the heat treatment in the furnace. This simulation was designed to evaluate the possibility of adopting a prescreening process for disk selection at an initial stage of brake system development by simulating the temperature under a severe braking condition. The distortions of Disks NH and H after the vacuum heat treatment are shown in Fig. 8. Among the dimensional changes, the maximum difference was about 8 µm in Disk NH at an angular position of 150°, while
Aged castings, in general, tend to be more stable than "green " castings as the stressed tend to reduce over time.
I have had rotors thet were "warped" right out of the box. Confirmed by accurate measurement. Machine THAT rotor true, and it will NOT warp in use.
The stresses came out of the casting after it was machined at the factory.
In years past,castings were allowed to "age" or "rest" for a significant period of time before final machining - and a lot of high quality equipment was rough machined from an aged casting, then allowed to age some more before the final precision machining was done. The rough machining allowed the surface stresses to relieve so the casting was fully relaxed and stable before final machining. Themal "normalizing" can also be used - it speeds up the process. So does "vibratory stress relief"
My initial take? a. The journal sounds decent: Journal of Materials Engineering and Performance b. The date sounds decent: April 2013, Volume 22, Issue 4, pp 1129?V1135 c. The topic? I'm not sure it's related yet: The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks
Gray Iron? "pig or cast iron containing much graphitic carbon which causes its fracture to be dark gray"
Residual Stress?
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"Residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed."
Abstract: Thermal distortion of gray iron brake disks due to residual stress and its effect on brake vibrations were studied.
Heat-treated discs did better than non-heat-treated discs (on residual stress created runout).
They tested up to 600dC (1112dF) where "residual stress" made runout worse,
That's it for the abstract. I'm not sure this paper has anything to do with warp though (as in potato chip).
I'll read the rest, but the abstract talks about "runout" which is a completely different thing than warp (yes, I know that if a disc is warped, it will also have runout - but they're still completely different things because a disc can easily have runout without being warped - as in potato chip).
You should be warned that I'm intelligent so I can *read* a peer-reviewed scientific paper, unlike, it seems, most people, who can't comprehend what a paper says. I've read a billion of them, so, bear in mind that I can understand what the authors are trying to say, even as they use words differently than we do.
Reading onward, I think the authors make a critical mistake in not defining their terms, particularly when they use the word "warp" in this sentence, which is the first time it appears in the paper... "It is known that disk warping or uneven disk thicknesses induce pulsation during brake applications."
Clearly it is well known that "warp" (as in potato) and "uneven thickness" are two completely different things - which means that this particular set of Asian authors (M. W. ShinG. H. JangJ. K. KimH. Y. KimHo Jang) are likely ignorant of what "warp" means - or - they simply assume that it means something that it doesn't mean (i.e., warp and thickness variation are completely different things - they just are).
They then compound their errors in a sentence not far from that last horrid sentence, saying "When the disk temperature is increased by friction heat during braking, the heat often causes dimensional instability of the disk, permanently modifying the runout or disk thickness variation (DTV) of a disk and producing brake judder."
WTF?
These Asian guys don't seem to comprehend the English language. It's well known that DTV and runout are two completely different things. They just are. Everyone knows that (except them).
I think the reason they didn't care to use correct words is that they didn't really care about any of those things - what they cared about, it seems, was the effect of heat treating on residual stress which resulted in a less pronounced runout measurement.
The end of the introduction concludes with the idiotically worded sentence: "While the disk warping during heat treatment was measured using a static DTV measurement unit..." Which clearly shows they're using the word "warp" differently than we are (simply because it's a fact that warp and DTV are two different things).
It appears that Ripley and Kirstein (Ref 12) paper might be more appropriate since they showed that the relaxation of the residual stress in the disk could lead to disk distortion. (We have to look at that paper to find out how they defined "disk distortion" though.)
I just posted a query to alt.usage.english as to why these particular Asian authors can't seem to comprehend the difference between "warp" and "runout" and "dtv", all of which they clearly equate in their paper - where all of them are different things. Why can't people figure out warp versus runout versus disc thickness variation
Unfortunately, since the Asian authors don't even comprehend what "warp" actually means, that paper is useless for our purposes, IMHO, simply because they never once measured warpage. Not once.
I completely understand how they *used* the term "warp"; but it's not the same thing that I'm talking about.
What they measured was DTV and runout, and what they were caring about was how heat treating affected those due to the interaction of residual stress after subsequent heating.
This article, by apparently American authors, uses the terms the way I do:
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Stop the Warped Rotors Myth and Service Brakes the Right Way
They advise: "Starting today, remove ?warped rotor? from your vocabulary."
Where they discuss "lateral runout" and "disc thickness variation", which are NOT the same thing as warp (as in potato).
OK smartass - define warpage . Explain how lateral runout can happen without "warpage". What, other than "warpage" would happen due to the relaxation of captured stess in a casting due to application of heat????
What, other than "warpage" would cause lateral wunout in a rotor???????
That paper clearly and obviously measured two things: a. Lateral runout b. Disc thickness variation
Never once did that paper mention measurement of warp (as in potato chip).
I'm OK if people suggest a paper because I love to learn, but you have to assume I'm intelligent enough to know that just googling for the word warp connected with temperature doesn't mean the paper shows *anything* about warp happening with temperature.
Maybe most people here deal with people who can't comprehend what a paper says, but I can read almost any paper (I read Physics papers all the time) and if I want to, I can comprehend what they say.
That paper said absolutely nothing about warp (as in potato chip).
I'm not chastising you. I *appreciate* that you tried to show that the disc can get to a temperature that is hot enough to cause warp, as I had already provided multiple references which said that such temperatures are impossible in street use.
It's a valid question.
If someone can provide a paper that proves that such temperatures actually commonly happen, I'll *read* (and comprehend) that paper.
But don't throw a paper at me that says absolutely zero about warp. (Please assume I'm intelligent enough to read & comprehend the paper.)
:) I am NOT chastising you. I'm just telling the truth - which is that paper had nothing to do with warp even though the Korean authors used the word in the paper.
They were talking about: a. Lateral runout, and, b. Disc thickness variation (among other things, like heat treating effects.)
There are good reasons to give a f*ck, since, a) Clare suggested the paper, so I read it. b) Are you chastising me for reading Clare's reference? c) Or are you chastising me for *understanding* what it said?
Similarly, I don't know how many dollars are wasted every year on people
*thinking* their rotors warped, when they can't possibly warp (according to the references I provided) simply because the temperatures needed are impossible to attain for the entire rotor thickness.
Let's just assume that a billion dollars a year are *wasted* by morons who can't comprehend the difference between disc thickness variation, lateral runout, and true warp.
Worse - if I ever have a judder (and, at times, I do), then it matters a lot that I *know* that warp can't possibly occur - so I know that the long-term solution is not to buy "Tundra upgrades", which people spend hundreds of dollars on that common but worthless imaginary panacea all the freaking time!
This is a group that is supposed to *understand* that which we fix, right?
If this group is supposed to *understand* a problem well enough to fix it, then it matters that brake rotors just don't warp (they can't get hot enough, based on the references I already quoted).
If someone can show a reference that shows that brake rotos can get hot enough in street use to actually warp (as in potato chip), then I'll *read* that reference.
You guys love to hate me for having "book knowledge", but having book knowledge is better than having the wrong solution isn't it?
The reason it matters is that people implement the wrong solution because they can't comprehend that rotors can't get hot enough to warp in street use (according to multiple references - which hasn't been refuted by anyone here).
Note, that Korean reference that Clare provided may have been translated from Korean (we don't know yet), where this seems to be a portion of the funding (apparently):
1.Department of Materials Science and EngineeringKorea University Seoul Republic of Korea
2.R&D Division Hyundai Motor Company and Kia Motors Corporation Hwaseong-si Republic of Korea
Let's give up on this topic. The same thing that is happening now, happened before.
It happens every time we discuss this topic.
People invariably "google" for "warp" and without comprehending the reference, they throw whatever reference they find at me, as if I'm too stupid to comprehend what it actually says.
Then, when I prove what the reference says, they change their definition of "warp" because they feel that I chastised them and they don't like that.
So I'm sorry that the paper you provided doesn't say a single thing about rotor warp. I really am sorry. I wish it did. But it just doesn't.
That's a fact.
Let's give up on this topic if the only way we can have an adult discussion is that we have to use two different definitions of warp, where one definition means anything you want it to mean, and where the other definition is what all the references I quoted explain it to mean.
Here's just one quote from that last reference: "They?re not warped and they never were warped."
I won't respond further unless someone provides a reference that backs up their point of view, as I've already provided plenty of references from where I obtained my "book knowledge" that everyone seems to hate.
I don't mind a good healthy technical discussion, but I have no interest in redefining what "warp" means when it's already very well defined in technical terms.
If someone provides a paper that supports their viewpoint, I'll read it and comment upon it - but otherwise - we're just spinning our wheels if we have to change the definition of warp to prove that rotors do it in street use.
I apologize if I drop off (unless a reference is provided).
All you need toi do is get it warm enough to release the stresses that were not released from the casting before machining
What is "true warp" as opposed to "lateral runout" when it is induced by operational heating and coolong??? Semantics. That's all. and bullshit from an electrical engineer trying to understand the mechanics of materials.
You do NOT "KNOW" that the judder is not caused by thermally induced lateral runout (aka - WARPAGE) - you just CHOSE TO BELIEVE it is impossible.
Been doing the fixing and the investigating for 50 years.
Your references are BS.
What do you mean "potato chip"? WARPAGE can cause lateral runout - usually inconsistent lateral runout. - which is MY definition of WARPAGE
Not whenthe book knowlege is limited and does not agree with documented real life experience.
Better no "knowlege" tha a load of BS.
It has been refuted by me. Perhaps the cite was poorly weitten,and poorly understood by you - but thermally induced runout of grey iron roptors DOES happen - just as warpage of cyl heads (which. by the way, do not reach NEARLY the temperatures rotors reach under hard braking--
- - -
I think the engineering was a whole lot better than the translation -
- - - and they were correct about a lot of things - disregarding poor wording.
They missed the ONE thing that can cause lateral runout of a rotor - warpage due to poor manufacturing whick allows casting stresses to be released after machining - sometimes immediately, and sometimes after they have been heat cycled. No extreme heat required, and NOTHING a driver can do to prevent it. In the case of those that release the stress after heat cycling, nothing a tech can do about it either - other than machine it true -(once the stresses are ALL relieved, it will not warp any further) after the fact.
When the stress comes out "in the box" or "on the shelf" machining the rotor before installing has a 50/50 chance of solving the problem. The rotor MAY be stable, or it may release more stress when heat cycled.
We had many cases of both at Toyota in the early to mid 80's. It was a production problem which was eventually solved - and was only evident on replacement rotors.
I had the same problems with the "economy" rotors from UAP (now NAPA)
- and it was on integrated front rotors (cast with hub) which elimiunated ANY chance of it being an installation problem
I think 50 years experience actually diagnosing and repairing the problems - and troubleshooting the issue for Toyota Canada beats your "book learnin'" and cites from "automotive writers" - many of whom couldn't tropubleshoot their way out of a wet paper bag if it was open at both ends./
Now you are believing the "marketing BS" from the manufacturers/supplying who are saying the brake puilsation problems are NEVER their fault - blame it on the mechanic or the driver. Thought you didn't believe "marketing BS"
ANd I say, in many cases they are right - but saying there is no such thing as a warped rotor is total BS. And the guy writing this last article could just as well be you. He's no professional mechanic, and no materials engineer,
The references you have quoted are NOT scientific reviews - they have no more (and generally less) veracity than the cite I provided for you (which, by the way WAS - TOTALLY on topic.
Give me that definition. I've given you what I accept as the definition of warpage in this case - thermally induced lateral runout without thickness variation, caused by the release of cast-in stresses in the rotor.
You can forget about any more help from me. Bye Bye
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