[OT] car brakes

Ben C wrote:
On 2008-05-05, wrote:
[...]
I find the defense of the gas theory, that arose from auto mechanics,
a form of religious faith. "I read it in Road & Track". As I
explained, in auto repair the cause of drum brake lockup was not
recognized as the same effect that caused total brake fade. That disk
brakes decouple application force and brake force, being at right
angles to one another, seems to elude many folks. When I worked in
brake development in F1 design in Europe, we were aware of myth and
lore that surrounded brakes.

Since you worked in brake development, do you know what causes pads to
glaze and what are the best solutions to the problem?

Slotted disks scrape the glaze off and perhaps also create channels for
fumes and powder (or something-- whatever it is it smells bad) to depart
via thus preventing it from vitrifying.

Cross-drilling seems to be done for similar reasons-- to let material of
some kind escape (although the cheese-grater effect seems to be an
unwanted side-effect).

so when is one of the knuckle-draggers going to mention the effect of
water on braking surfaces??? wet brakes can be spectacular for almost
total ineffectiveness. drilled/slotted brakes otoh are much more
effective in this situation.

wrote:
Kerry Montgomery wrote:

[...]

I find the defense of the gas theory, that arose from auto
mechanics, a form of religious faith. "I read it in Road &
Track". As I explained, in auto repair the cause of drum brake
lockup was not recognized as the same effect that caused total
brake fade. That disk brakes decouple application force and
brake force, being at right angles to one another, seems to elude
many folks. When I worked in brake development in F1 design in
Europe, we were aware of myth and lore that surrounded brakes.

Since you worked in brake development, do you know what causes
pads to glaze and what are the best solutions to the problem?

The occurrences I witnessed came from using drum brake friction
material hardly modified for disk use. The problem was that higher
temperatures developed with the pressure needed to make pads with
smaller area than drum shoes caused molten material to agglomerate
on the surface.

There is a basic rule in friction that when two materials slide
over one another, one or both must melt locally at asperity
contacts in the absence of a lubricant. Therefore, surface
morphology will change if the material is not suited for the
operating temperature at the interface, rather than the bulk
temperature. As I mentioned previously, brake friction material is
an insulator, making its surface extremely hot while the bulk
remain far below that. Matthauser didn't know that and put useless
cooling fins on the back of his brake pads.

Today's racing F1 brakes use carbon disks and pads whose wear
debris is CO2, the major advantage of this material although
lighter weight is also an asset. Oxides materials produce granular
debris whose melting temperature must be high enough for the
application to not become glazing paste. This whole problem
retarded disk development at the onset. Curbstone mechanics had
hole, slot and odd pad surfaces as solutions rather than
recognizing that it was a materials problem and that people skilled
in the art were working on it... with success.

Slotted disks scrape the glaze off and perhaps also create
channels for fumes and powder (or something-- whatever it is it
smells bad) to depart via thus preventing it from vitrifying.

Cross-drilling seems to be done for similar reasons-- to let
material of some kind escape (although the cheese-grater effect
seems to be an unwanted side-effect).

It's a materials problem and the appropriate people are developing
friction materials that makes this crude solutions go away, and
they have to a large degree except for those who like folklore.

Some of the F1 wear debris may be CO2, but some is just plain C, as
shown by the clouds of black stuff coming off when the wheels are
changed in the pits.

This first came to light years ago when hard disk drives began to use
sputtered Carbon as a wear layer. Using a ceramic slider in a test
chamber with a controlled atmosphere or vacuum, the production of
carbon wear debris in a nitrogen atmosphere was achieved and its
presence detected after which in an oxygen atmosphere all wear debris
became CO2. This was an early experiment I generated to show why much
harder oxides were damaging while carbon was benign. After that the
common wear layer changed to carbon coating. This work led to a PhD
for my summer student who verified my friction and wear theories.

friction and wear are not gas evolution jobst. but don't let that get
in the way of you trying to claim credit for someone else's research.



Any carbon dust you see coming off race car brake disks is a "don't
care" because it is not remaining in the interface and the interface
is purging itself of CO2, the only significant "gas" that occurs in
carbon disk brakes.

you're bull****ting jobst. the reaction rate of carbon and oxygen at
braking temperatures is so low, you'd have to wait months to achieve the
mass loss affected by just one hard brake application.


Tribology is a largely misunderstood subject.

by some, most evidently.


However, good publications were published about instantaneous flash
temperatures in sliding interfaces that were formerly considered to be
close to room temperature, the bulk temperature.


bull****ter.

Kerry Montgomery wrote:
wrote in message
...
Ben C wrote:

[...]
I find the defense of the gas theory, that arose from auto
mechanics, a form of religious faith. "I read it in Road & Track".
As I explained, in auto repair the cause of drum brake lockup was
not recognized as the same effect that caused total brake fade.
That disk brakes decouple application force and brake force, being
at right angles to one another, seems to elude many folks. When I
worked in brake development in F1 design in Europe, we were aware
of myth and lore that surrounded brakes.
Since you worked in brake development, do you know what causes pads
to glaze and what are the best solutions to the problem?
The occurrences I witnessed came from using drum brake friction
material hardly modified for disk use. The problem was that higher
temperatures developed with the pressure needed to make pads with
smaller area than drum shoes caused molten material to agglomerate on
the surface.

There is a basic rule in friction that when two materials slide over
one another, one or both must melt locally at asperity contacs in the
absence of a lubricant. Therefore, surface morphology will change if
the material is not suited for the operating temperature at the
interface, rather than the bulk temperature. As I mentioned
previously, brake friction material is an insulator, making its
surface extremely hot while the bulk remain far below that.
Matthauser didn't know that and put useless cooling fins on the back
of his brake pads.

Today's racing F1 brakes use carbon disks and pads whose wear debris
is CO2, the major advantage of this material although lighter weight
is also an asset. Oxides materials produce granular debris whose
melting temperature must be high enough for the application to not
become glazing paste. This whole problem retarded disk development at
the onset. Curbstone mechanics had hole, slot and odd pad surfaces as
solutions rather than recognizing that it was a materials problem and
that people skilled in the art were working on it... with success.

Slotted disks scrape the glaze off and perhaps also create channels
for fumes and powder (or something-- whatever it is it smells bad)
to depart via thus preventing it from vitrifying.
Cross-drilling seems to be done for similar reasons-- to let
material of some kind escape (although the cheese-grater effect
seems to be an unwanted side-effect).
It's a materials problem and the appropriate people are developing
friction materials that makes this crude solutions go away, and they
have to a large degree except for those who like folklore.

Jobst Brandt

Jobst,
Some of the F1 wear debris may be CO2, but some is just plain C, as shown by
the clouds of black stuff coming off when the wheels are changed in the
pits.
Kerry



of course. but jobst doesn't check facts, he just makes presumptions.

Michael Press wrote:
In article ,
jim beam wrote:

Michael Press wrote:
In article ,
clare at snyder dot ontario dot canada wrote:

On Sun, 04 May 2008 16:16:57 -0500, A Muzi
wrote:

Peter Cole wrote:
Cross-drilled seems to be more about looks than anything else. "Vented"
or "ventilated" rotors are another matter. They appear to be reasonably
effective, but it's not a *huge* effect (+40%, rather than 100%).
Robert Lorenzini wrote:
Vented (cross-drilled or slotted) rotors came from racing brakes
which use pads that boil gasses under heat. This is most noticeable
when bedding green pads and they act just like a tire hydroplaning
until most of the volatiles have disapated.
Michael Press wrote:
What is the chemical composition of the boiling gasses?
Do the boiling gasses come from the pads?
Counterintuitive, isn't it? This guy thinks it happens:
http://www.innerauto.com/Auto_Part/Brake_Disc/

I'm not convinced ('gas' goes in the little hole??) or that taking one's
foot off a brake can break it.

These guys just say 'ducted', which is what I thought this conversation
was about earlier:
http://www.lexus.com/models/IS/featu...sc_brakes.html
You don't need a scientific analasys to KNOW it happens. What happens
if you really brake hard, or just drag the brakes for a while?
Sniff - sniff- smell that strong, pungent smell of burning brakes?
What gas evolves?
What is its partial pressure?
or in your case, "what is its diffusion rate"? schmuck.

Partial pressure is exactly what I mean.


no you don't - not unless you're an idiot - you have no idea of
evolution rate. ah, but this is michael press!!!!!! schmuck.

On 2008-05-06, jim beam wrote:
Ben C wrote:
On 2008-05-05, wrote:
[...]
I find the defense of the gas theory, that arose from auto mechanics,
a form of religious faith. "I read it in Road & Track". As I
explained, in auto repair the cause of drum brake lockup was not
recognized as the same effect that caused total brake fade. That disk
brakes decouple application force and brake force, being at right
angles to one another, seems to elude many folks. When I worked in
brake development in F1 design in Europe, we were aware of myth and
lore that surrounded brakes.

Since you worked in brake development, do you know what causes pads to
glaze and what are the best solutions to the problem?

Slotted disks scrape the glaze off and perhaps also create channels for
fumes and powder (or something-- whatever it is it smells bad) to depart
via thus preventing it from vitrifying.

Cross-drilling seems to be done for similar reasons-- to let material of
some kind escape (although the cheese-grater effect seems to be an
unwanted side-effect).

so when is one of the knuckle-draggers going to mention the effect of
water on braking surfaces??? wet brakes can be spectacular for almost
total ineffectiveness. drilled/slotted brakes otoh are much more
effective in this situation.

I think the link Carl posted did mention that.

I don't think you want slotted disks on shopping cars because they wear
the pads too quickly.

I've not known wet brakes on modern cars (with plain vented disks) to be
a problem in practice. I suppose the pad just squeegees the water off,
which is why a gentle reapplication the other side of the ford is
recommended instead of waiting till the deer jumps out of the hedge
around the next corner.

On Mon, 05 May 2008 21:02:26 -0700, jim beam
wrote:

Ben C wrote:
On 2008-05-05, wrote:
[...]
I find the defense of the gas theory, that arose from auto mechanics,
a form of religious faith. "I read it in Road & Track". As I
explained, in auto repair the cause of drum brake lockup was not
recognized as the same effect that caused total brake fade. That disk
brakes decouple application force and brake force, being at right
angles to one another, seems to elude many folks. When I worked in
brake development in F1 design in Europe, we were aware of myth and
lore that surrounded brakes.

Since you worked in brake development, do you know what causes pads to
glaze and what are the best solutions to the problem?

Slotted disks scrape the glaze off and perhaps also create channels for
fumes and powder (or something-- whatever it is it smells bad) to depart
via thus preventing it from vitrifying.

Cross-drilling seems to be done for similar reasons-- to let material of
some kind escape (although the cheese-grater effect seems to be an
unwanted side-effect).

so when is one of the knuckle-draggers going to mention the effect of
water on braking surfaces??? wet brakes can be spectacular for almost
total ineffectiveness. drilled/slotted brakes otoh are much more
effective in this situation.

I've seen rotors SHATTER when they hit ice cold water when red hot
from heavy braking in my rally days.
** Posted from http://www.teranews.com **

clare at snyder dot ontario dot canada wrote:
On Mon, 05 May 2008 21:02:26 -0700, jim beam
wrote:

Ben C wrote:
On 2008-05-05, wrote:
[...]
I find the defense of the gas theory, that arose from auto mechanics,
a form of religious faith. "I read it in Road & Track". As I
explained, in auto repair the cause of drum brake lockup was not
recognized as the same effect that caused total brake fade. That disk
brakes decouple application force and brake force, being at right
angles to one another, seems to elude many folks. When I worked in
brake development in F1 design in Europe, we were aware of myth and
lore that surrounded brakes.
Since you worked in brake development, do you know what causes pads to
glaze and what are the best solutions to the problem?

Slotted disks scrape the glaze off and perhaps also create channels for
fumes and powder (or something-- whatever it is it smells bad) to depart
via thus preventing it from vitrifying.

Cross-drilling seems to be done for similar reasons-- to let material of
some kind escape (although the cheese-grater effect seems to be an
unwanted side-effect).
so when is one of the knuckle-draggers going to mention the effect of
water on braking surfaces??? wet brakes can be spectacular for almost
total ineffectiveness. drilled/slotted brakes otoh are much more
effective in this situation.

I've seen rotors SHATTER when they hit ice cold water when red hot
from heavy braking in my rally days.
** Posted from http://www.teranews.com **

sure! that would be exciting to watch. shouldn't really happen though
- depends of the quality of the casting. do you have any pics?

there's also the phenomenon, don't know what it's called, where water
splashed onto very hot metal never actually makes contact - it's held
off by an evaporative vapor layer. very cool. beads of water skip
about on the surface like mercury from a broken manometer in class when
the... well, when the manometer breaks.