Ducati Sporting Club

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 26-May-2005, 11:24 AM
mikesps mikesps is offline
Registered Forum User
Mille
 
Posts: 235
Join Date: Jan 2005
Cast iron disk failure & Rotors

A friend's 916SP had a cast iron disk fail while braking into turn 15 at Sepang. Bike went straight on into the kitty litter and he managed to keep it up.

Those of us running CI disks may want to check them for cracks. The one which failed was not below minimum thickness, but had been used hard for many laps.

As the photo shows the caliper mount failed, presumably knocked off by the failing disk. There were no large pieces of the disk left.

Mike
Reply With Quote
  #2  
Old 26-May-2005, 11:42 AM
nelly's Avatar
DSC Member nelly nelly is offline
DSC Club Member
Ducati Corse
 
Posts: 3,133
Join Date: Jan 2002
Mood: Bloo and Yellow.. and Red now ;)
That is the main rason Brembo ceased making them a few years ago....
There were a couple of failures in the States, apparently, that cost them big time from the legal actions taken against them.

Hope your mate is OK.
Reply With Quote
  #3  
Old 26-May-2005, 12:00 PM
mikesps mikesps is offline
Registered Forum User
Mille
 
Posts: 235
Join Date: Jan 2005
He is fine thanks. Nothing that a new pair of underpants won't fix anyway.

Now I am thinking about taking the CI disks of my SP3.

Mike
Reply With Quote
  #4  
Old 26-May-2005, 03:25 PM
Shazaam!'s Avatar
DSC Member Shazaam! Shazaam! is offline
DSC Club Member
Big Twin
 
Posts: 1,167
Join Date: Nov 2001
Iron Brake Rotors

The main reason that iron brake rotors are used instead of the OEM stainless steel is that for a given brake pad material they offer a higher coefficient of friction and consequently more braking power, better heat management, and better brake force modulation (feel). But they also have drawbacks. Iron, as a material, is more brittle (less ductile) than stainless steel, it develops a coat of surface rust quickly, and unless it has a high carbon content will often squeal during a slow stop. High carbon cast iron rotors are used on over a hundred different car and commercial vehicles today.

The intrinsic brittle nature of the material, weight and the product liability issue is the main reason that manufacturers don’t use them as original equipment today. Improvement to brakes have been mainly concentrated in other areas such as pad material, caliper stiffness and multiple pads and pistons.

The shift to stainless has allowed brake performance improvements mainly by allowing the use of sintered pad materials that are more abrasive and produce excessive heating in iron rotors. If the temperature rise is not uniform in different regions of the rotor, the differential thermal expansion can lead to warping and cracks that can eventually lead to disc failure.

In recent years, improved foundry and cryo-treating material processes have resulted in a more ductile formulation of iron giving it a more uniform and finer grain structure that is less prone to rusting, and cracking from rapid thermal cycling and carrier interface loads.

So, don't confuse cast iron rotors (Brembo) with ductile iron (Brake Tech) rotors.

With this in mind, if you have a set of cast iron rotors you should inspect them for cracks regularly, especially after a crash, paying special attention to the cross-drilled cooling holes. If you’'re unsure, have the rotors inspected using a fluorescent liquid penetrant process like Zyglo.

WARNING - Do not use sintered pads with iron brake rotors

There are two classes of brake pad compounds: sintered and organic. Sintered pad compounds were developed specifically for use with stainless steel rotors and should not be used with cast iron brake rotors. They produce excessive temperatures in cast iron rotors that can lead to cracking during severe braking conditions. They also produce premature cast iron rotor wear when used hard.

Some European manufacturers of cast iron rotors, like Brembo, after first trying to warn against the use of sintered pads, have simply stopped offering cast iron rotors for liability reasons. The brake pad manufacturers simply tell you don’t use them with iron rotors, but some people do anyway. If someone tells you that they’ve used them with no problems, tell them about Jimmy Adamo's death at Daytona after his cast iron rotors shattered. This tendency to shatter under severe race conditions is the main reason why a number of race organizations ban the use of non-ductile iron discs.

Using sintered pads on ductile iron disks is less problematic, but still risky unless specific testing has been done by the manufacturers. For example, according to Jeff Gehrs (who runs Brake Tech and designed their rotors,) the Brake Tech Axis rotors have been tested by Ferodo and found to be compatible with their sintered pads. The Axis rotors are cryo-treated during manufacturing to get good fracture-resistant material properties, but other manufacturer’s rotors may not be as suitable.

Some sintered pads (EBH HH, for example) are claimed to be designed for use with both stainless steel or ductile iron rotors. Be skeptical. Compared to organic pads, you will experience accelerated wear and elevated heat levels which means more thermal expansion-induced stresses in the disc. This means that using sintered pads for moderate-braking street conditions could turn problematic at a hard-braking track.

One more point about pad selection. By matching the brake pad to the brake disc, feel can be greatly improved. The pads used by racers can be broken into two catagories; Free and Not-Free.

The Not-Free pads are the ones that win races. Not-Free pads include HRC pads, Brembo sintered pads and Performance Friction Carbon Metallic pads. All of these pads offer improved modulation as well as ultimate stopping power.



[Edited on 5-26-2005 by Shazaam!]
Reply With Quote
  #5  
Old 26-May-2005, 04:56 PM
Webcore Webcore is offline
Registered Forum User
Mille
 
Posts: 150
Join Date: Nov 2004
Excellent info as usual Shazaam! - Thank You! Is there a difference in the friction coefficient between cast iron and ductile iron? Do you still get better braking than with stainless discs?
Will be checking mine thoroughly when I fix all the damage next week.
Reply With Quote
  #6  
Old 26-May-2005, 07:30 PM
Felix Felix is offline
Registered Forum User
Ducati Meccanica
 
Posts: 2,468
Join Date: Dec 2001
Mood: Is 112 dB loud enough?? What??
Shazaam: What's the reason for the increased heat generation of cast iron rotors? Isn't the amount of heat generated by a brake system proportional to the amount of energy being dissipated? That is, the moving mass being decelerated regardless of what materials you use to do so?
Reply With Quote
  #7  
Old 26-May-2005, 11:39 PM
Dukerob's Avatar
Dukerob Dukerob is offline
Registered Forum User
500SD
Bikes: Diavel
 
Posts: 746
Join Date: Mar 2002
think I'll be checking mine too while its still at Nelly's for post-BMF tuning
Reply With Quote
  #8  
Old 27-May-2005, 03:57 AM
Shazaam!'s Avatar
DSC Member Shazaam! Shazaam! is offline
DSC Club Member
Big Twin
 
Posts: 1,167
Join Date: Nov 2001
Felix: What you say is true - for a given deceleration rate and moving mass the amount of kinetic energy converted to heat is the same for iron and steel rotors.

However when you use iron, the frictional force that is generated is higher for any applied piston force (F=uN). So, because of the higher maximum frictional force that can be generated with the maximum piston force available, the maximum heat that can be generated is higher.

Consequently, under maximum bike deceleration (which is higher for an iron rotor, i.e. better brakes) an iron rotor gets hotter than a stainless rotor does at its lower maximum deceleration rate.

Only when you get below the maximum deceleration rate achievable for stainless is when the rotor heat load is the same for both iron and stainless.
Reply With Quote
  #9  
Old 27-May-2005, 04:28 PM
adam adam is offline
Registered Forum User
Big Twin
 
Posts: 1,157
Join Date: Jun 2001
Mood: happy
I think ill stick to blakeys in the bottom of my boots for stopping.
Reply With Quote
  #10  
Old 27-May-2005, 06:06 PM
Felix Felix is offline
Registered Forum User
Ducati Meccanica
 
Posts: 2,468
Join Date: Dec 2001
Mood: Is 112 dB loud enough?? What??
Quote:
Originally posted by Shazaam!
Only when you get below the maximum deceleration rate achievable for stainless is when the rotor heat load is the same for both iron and stainless.

Which is true for the vast majority of the time, wouldn't you say? I don't disagree about cast iron rotors being more brittle, but I don't buy it that it's due to excessive heat. Age would seem to be a much more contributing factor, for instance.
Reply With Quote
Reply
  
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes
Postbit Selector
Switch to Vertical postbit Use Vertical Postbit

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Recent Posts - Contact Us - DSC Home - Archive - Top
Powered by vBulletin 3.5.4 - Copyright © 2000 - 2017, Jelsoft Enterprises Ltd. - © Ducati Sporting Club - All times are GMT +1. The time now is 06:39 AM.