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12-27-2009, 08:52 PM | #1 |
Scooby Newbie
Member#: 163259
Join Date: Nov 2007
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Location: 7L Autosport
Vehicle:2007 UGM STI 307 hp / 317 tq |
Titanium Brake Shim Coloration
I've been running the StopTech Ti brake shims in my STI Brembos for a few months, and recently pulled the pad / backing plate assembly out of the caliper to take a look at it. The caliper piston side of the shim looked like it was brand new, but the pad side of the shim was mostly straw / yellow with some streaks of light to vivid blue through it.
My question is this: is there any kind of titanium coloration to max temperature scale? I've done a fair amount of research and everything I can find discusses welding, which so far as I can gather has more to do with weld purity and oxidization, or anodizing, which only gives colors in terms of the electrode voltage. I ask because I'm curious what temperatures the shims have seen so I have an idea of how hot the overall system is getting. I know I haven't boiled the brake fluid so I know the shims are insulating well, but I'd like to know just how hot the pads and rotors are getting under load when I can't go at them with an IR pyrometer and figured this would be a good place to start. I do know the rotors have almost certainly seen temps upwards of 1200 - 1300 deg F based on ~950 deg F pyrometer measurements once the car is stopped, if that's of any help. It's probably worth mentioning I'm developing a ducting system to get these temps way down - will post a thread on that when I have more progress. If any of you can bust out the mat sci skills I'd really appreciate it
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12-28-2009, 01:33 AM | #2 |
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No, there's not a direct correlation. There's many, many factors involved in determining how thick the oxide layer is. However, the color scale for head-induced oxidization is the same as for electrically-induced oxidization. So yellow is "not that hot". Well, depends some on which yellow/gold/straw color.
Lemme tell you, reliably oxidizing titanium to the same color is a PITA. |
12-28-2009, 06:52 AM | #3 |
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Titanium has a lower heat handling capability than stainless. Depending on the alloy, you may be operating in a range that is very near the limit of whatever those shims are made of.
Jay |
12-28-2009, 12:47 PM | #4 |
Scooby Guru
Member#: 71092
Join Date: Sep 2004
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MWSOC
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No, if he's only getting to yellow, he has A LOT of thermal headroom.
The important point is that Ti has a lower thermal conductivity. You're not going to melt either the Ti or the SS in a car. The Ti is just going to keep your fluid cooler. |
12-28-2009, 12:48 PM | #5 | ||
Scooby Newbie
Member#: 163259
Join Date: Nov 2007
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Location: 7L Autosport
Vehicle:2007 UGM STI 307 hp / 317 tq |
Quote:
Quote:
I would assume the shims are 6AL-4V, which I've read is generally used up to 750 F. Question is, what happens if it's exposed to twice that temperature? What little I've read seems to suggest that most hot working is done around 1,200 F and that almost half the yield strength is lost by 800 F. I'm not sure this is all that crucial however, but I also don't know what kind of pressure the shims are exposed to from the pistons. Given that they could likely see 1,400+ F, this may be a bit of a worry. It's also possible they are a higher temperature alloy - I would hope StopTech used something much more thermally resistant given the extreme temperatures where their shims will be used. I will try to get in contact with them and find out the specific alloy they use. |
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