ADVANCED HNBR ELASTOMERIC COMPOUND FOR HEAT RESISTANT SEALING PROFILES PROCESSED BY CONTINUOUS HOT-AIR VULCANIZATION
Dr. A. Amash
Hydrogenated Nitrile Butadiene Rubber (HNBR) is one of the most interesting and expensive high-performance elastomers. It combines good physical and chemical properties including long-term temperature resistance. However, the thermal-mechanical behavior is a function of some factors, preliminary the chemical composition of the rubber compound. HNBR products are widely used in automotive and industrial applications and based on peroxide curing for better compression set and heat resistance. Therefore, HNBR is usually processed by compression/injection molding, i.e., vulcanized under pressure.
In this study, a new tailor-made HNBR compound was successfully developed to meet specific severe requirements regarding process and properties. The most important and challenging demands were: processability/suitability for extrusion of wide profiles, smooth and solid rubber profile for reliable sealing gaskets, workable peroxide cure system for continuous pressure-less hot-air vulcanization, extremely high temperature resistance and excellent compression set, lifetime at elevated temperatures >10 years, reasonable price of the final rubber compound. The post-cured product had to be tested and approved according to requirements based on international standards.
Different types of HNBR and other ingredients were used and tested regarding efficiency and dosage, in order to develop and optimize the unique rubber compound formulation. These components are crucial for consistent processing (e.g. mixing, extrusion, curing etc.) as well as for a reliable sealing application of the final product (e.g. good compression set and aging resistance at very high temperatures). We succeeded to develop the rubber compound and adjust the product features to fit all challenging requirements mentioned above. A thoroughly optimized post-cure stage at the end of an efficient profile production process was found to be necessary, in order to gain a perfect sealing capability at elevated temperatures. For example, an excellent compression set of maximum 20% at a very high temperature of 150°C could be clearly reached.