Sanluis Rassini’s new two-piece rotor comprised of a ductile iron hat and gray iron brake plates provides an up to 18% weight savings and better NVH characteristics than a conventional one-piece gray cast iron rotor.
With the physical separation between the hat and the braking surfaces, the dual cast iron rotor essentially acts as a floating disc to dissipate energy. In short, the interaction of the hat and the plates is akin to an internal friction system.
“The linkage between the hat and the plates provides an improvement in damping, which in turn enhances NVH,” Mauricio Gonzalez, Director of Engineering for Sanluis Rassini, told SAE Magazines.
The ductile iron/gray iron composite rotor also provides a more uniform heating surface in comparison to a traditional one-piece gray iron rotor.
“Our dual cast rotor’s capacity to withstand higher temperatures is due to the fact that the design inherently has almost zero thermal transient deformation. This design feature allows the rotor to maintain a higher degree of rotational perpendicularity relative to the caliper/friction materials, providing a more homogenous heating pattern,” explained Gonzalez.
The dual composite rotor has a unique I-beam cross-sectional shape where the body of the “I” is oriented in the circumferential direction, essentially being parallel to the brake plates. Small fins extend perpendicular from the body to the interior of each brake plate. According to Maureen Hayes, Sanluis Rassini’s Vice President Sales & Engineering, “The I-beam design promotes airflow through and around the extension, thereby mitigating the heat-sink effect.”
During the rotor’s development, the heat-sink phenomenon—an outgrowth of assembling the two pieces of the rotor—was a significant engineering challenge.
Noted Gonzalez, “We mitigated this unwanted effect by changing the design of the extension from a solid structure to a ventilated structure with an I-beam shape. Through a variety of analysis tools, including Dassault Systèmes’ Abaqus and Magma GmbH’s MagmaSoft, we determined that the heat-sink effect was created by the high mass of the solid extension of the hat into the braking surface.”
Going with an I-beam extension design also enabled Sanluis Rassini to meet General Motors’ specific brake system requirements for the 2014 Chevrolet Corvette Stingray. The two-piece composite rotor debuts on the Stingray’s Z51 high-performance package.
According to Hayes, although the parking brake application is the same as other Drum In Hat (DIH) rotors, “the distinguishing feature is this is the only composite brake rotor capable of being used as a DIH rotor. All other composite rotors used on current production passenger cars have aluminum hats. Aluminum composite rotors are not able to be used for DIH applications due to the tribological characteristics between the friction material on the brake shoe and the aluminum hat.”
The dual composite rotor will be produced in Sanluis Rassini’s Puebla, Mexico facility, which features an integrated foundry with machining, coating, stress relief, and ferritic nitro-carburizing processes.
“The most important part of the composite rotor manufacturing process is preparing the hat for the merger with the core. We are able to produce this new product utilizing our current process capabilities with minimal disruption to our overall manufacturing structure,” said Hayes.