Little reading for everyone.....
I'm glad to hear that the rotors will be OK, but why does the Ferodo web site recommend the Sintergrip pads to be only used with stainless steel rotors and not with iron? Just wondering, Jeff.
It’s fairly simple really, we have to make recommendations that end up dealing with broad generalities, particularly when it is a safety issue. Historically, the majority of iron rotors manufactured over the past 20+ have been made from Gray iron, worse yet, individually molded Gray iron. This material has a relatively low threshold for thermal stress induced fracturing. Two main reasons, its molecular structure is of a coarse flake structure that is random in nature and as so often happens in the molding process, porosity is introduced during the cooling period creating even more random weak areas. The result is so often spider-web like cracks that can grow into catastrophic failure. As detailed below, ductile iron, particularly the high tensile strength variety from continuous cast bar (billet), exhibits neither of these failings.
DUCTILE VS. GRAY IRON SPECS:
The following specifications show our high grade Ductile iron from computer controlled continuous cast bar versus the best of Gray iron (also from bar). Be advised however, the actual strength values of individual mold castings are substantially lower by as much as 50%:
• Ductile Iron = 80,000 psi vs Gray iron at 40,000 psi
• Ductile Iron = 40,000 psi vs Gray iron at 20,000 psi
Fatigue strength is primarily influenced by the graphite size and shape and will also be affected by the matrix structure. The continuous casting process and strict metallurgical controls of our Ductile iron results in a uniformly dense, fine-grained microstructure essentially free of porosity, sand and other inclusions, that can affect the endurance ratio severely lowering fatigue life. The BrakeTech Ductile iron specification from billet has optimal strength in tension, compression and fatigue versus traditional castings (including individual mold Ductile iron castings). Ductile irons having nodular graphite will have the highest endurance ratio, and gray irons with coarse flake graphite will have the lowest.
Sintered metal friction material by design has an extremely high metal content, and at the friction couple, operate at a thermal interface level as much as 150 degrees (F) higher than most organic pads. This further stresses the already relatively weak Gray iron rotor. As a result, and anticipating the litigious climate with which we live, must make pad recommendations that fall squarely on the side of prudence. As an example; a person buys a used bike with iron rotors of unknown origin (high degree of probability they're Gray iron as it is more common being much cheaper to produce), jurisprudence dictates we must strongly recommend a friction material least likely to cause problems. Hence the blanket recommendation against using sintered pads generically on iron rotors.
Hope this sheds some light.