Würzburg, Germany — Oliver Franssen, global marketing director elastomers and transportation at Momentive Performance Materials in Leverkusen, Germany, presented a paper at the recent SKZ Silicone Elastomers conference about a new material, Silopren LSR 3366/50.
Franssen's paper, given with support from Momentive lead scientist Oliver Safarowsky noted that the 3 percent oil-content self-lubricating LSR has comparable mechanical properties as the established 2 percent oil-content LSR 3286/50, but it represents the most heat-resistant self-lubricating grade from Momentive.
The material does not rely on heat stabilizers or abrasive fillers, and customer trials have already resulted in positive feedback, Franssen said.
Automotive mat or frame seals for multicontact connectors, single wire seals and insulation are important application area for such LSR materials, especially with high temperature extremes in engine compartments.
"A cable harness can have as many as 200 connectors over a length of 3,000 meters," Franssen said.
Temperatures rise through downsizing with new vehicle designs, and there are many variants of the "same" connector, Franssen said. Electromobility raises challenges with high-voltage systems and reliability becomes vital with autonomous driving, Franssen observed.
He illustrated higher heat performance in ISO 815 (Method A) compression set tests (after post-curing for four hours at 200° C), for 22, 144 and 1,000 hours at 175° C. Tests in the past have been usually limited to 24 or 168 hours, seeking compression set below 40 percent.
LSR 3366/50 showed better compression set values of respectively 6 percent, 12 percent and 24 percent, compared with 10 percent, 23 percent and 62 percent for LSR 3286/50.
Better values of 15 percent, 29 percent and 38 percent were also obtained with LSR 3360/50 in the Volkswagen PV3307 compression set test over 22, 168 and 504 hours, compared with 31 percent, 54 percent and 58 percent with LSR 3286/50.
Compared with T5 class of -40 to 175° C under the 2013 Revision 6 of the SAE USCAR-2 standard, Franssen said of LSR 3360/50: "The limit has been shifted up now by more than 25° C, from 175° C to 200° C."
Franssen said lubrication or friction are not directly measurable. They are better characterized by oil sweating rate weight loss than oil percentage or friction coefficient measurement — and that hardness, type of LSR polymer, degree of cross-linking and the oil used all play important roles in achieving the required degree of lubrication.