Processing, Mechanics and Wear Resistance Performance of Nitrile Rubber Sealing Material for Main Drive of Shield Machine

Nitrile Butadiene Rubber (NBR) has polar nitrile group (-CN) and trans-1,4 structure in the molecular structure, with excellent oil resistance, heat resistance and wear resistance, widely used in aerospace, petrochemical, engineering machinery, pharmaceutical and vehicle equipment hydraulic seal, pneumatic seal and mechanical seal auxiliary sealing device. The severe working conditions of the main drive seal of large Shield Tunneling Machine are matched with the performance of NBR, and the wear resistance of NBR plays a crucial role in its sealing performance, and even directly determines the working life of the whole machine. The main drive seal material of Shield Tunneling Machine is a large special-shaped rubber seal, and the processing performance of rubber material plays an important role in its forming process its fine structure. The scorch time and Mooney viscosity are the key factors affecting the processing properties of rubber materials. According to the processing requirement of NBR for the main drive rubber seal of Shield Tunneling Machine, in this study, the compound plasticize was synthesized from pine tar, dibutyl sebacate and solid coumarone resin. The reinforcement system formed by high structure carbon black and low structure carbon black was used to control the processing performance, physical and mechanical properties and friction properties of NBR sealing materials. In this paper, the effects of different contents of pine oil in composite plasticizer on the processability, physical and mechanical properties and frictional properties of NBR composites were systematically studied. The results showed that pine oil could reduce the softening point of solid gumarone resin, and could effectively improve the elongation at break of rubber materials and enhance the flexibility of rubber materials due to the synergistic action of three components in the composite plasticizer. When the amount of pine oil used in the composite plasticizing system was 0.9 phr (parts per hundred parts of rubber), and the amount of high structure carbon black and low structure carbon black added in the reinforcing system was 45 phr and 15 phr, respectively, the high-performance NBR sealing material prepared in this study could not only meet the molding process requirements of special-shaped sealing ring for large shield tunneling machine, the scorch time T₁₀ of the compound could be as long as 168.6 s, and the Mooney viscosity M_L(1+4) could be as low as 46.95. It was also a self-lubricating rubber sealing material with high strength, high toughness, high-wearing feature, high recovery and high heat resistance. The tensile strength was as high as 22.51 MPa, while the elongation at break was 684.4%, the compression permanent deformation rate could be as low as 22.7% (100 ℃, 25% compression rate, 24 h), and the Akron wear value was as low as 0.1 cm³/1.61 km. The wear resistance of the material was also verified in the simulation test bench of the main drive of the shield machine, which could meet the requirements of the main drive system for sealing effectiveness and life. This study could provide support for the design and preparation of the main drive sealing material of large shield tunneling machine.