Quote:
On 2006-06-17 11:16, Speed3 wrote:
Crash, I believe that to be incorrect. A hard Anodized Aluminum sprocket will last almost as long as a steel one if properly maintained. I have a 45 T AFAM that has been on for almost 10,000 miles, and shows no wear.
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When you reach 50,000 miles come see me.
Hard anodizing is a surface process that in essence changes the chemical makeup of the aluminum a few microns deep- basically crystalizing the surface with aluminum oxide which is corrosion and abrasion resistant (Grinding disks are made of aluminum oxide for this reason). Colors can be added by introducing a dye during the process that gets trapped in the crystalline structure.
This is great for pretty sprockets that don't corrode, but it doesn't address the fundamental weakness of aluminum: i.e. it's both softer and more brittle than steel or stainless and breaks down under repeated use. Micro-fractures occur from repeated loading and unloading (fatigue) that eventually weaken the sprocket teeth. While you won't see surface erosion with anodizing, you still get fracturing and cracking- often hidden by the anodizing.
This is why when you bend your foot-peg in a crash and try to straighten it, it just breaks. Your sprocket may
look pristine, but there is damage that will eventually show up, perhaps catastrophically.
Note that the above is also true of steel and stainless steel, but they are far more resistant to such deterioration, and they are more likely to show early signs of this before a catastrophic failure.
This being known, I just don't think that it's worth it to use aluminum sprockets for non-race purposes. That's an opinion of course.
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