The compression set of rubber dust covers directly impacts their sealing performance and service life. Controlling this requires comprehensive optimization across multiple dimensions, including material formulation, vulcanization process, filler selection, and structural design. While material formulation is fundamental, the choice of raw rubber should be determined by the temperature and oil resistance requirements of the application. For example, fluororubber (FKM), due to its high-energy carbon-carbon crosslinks in its molecular structure, maintains low compression set even at high temperatures, making it suitable for high-temperature environments such as engine compartments. While nitrile rubber (NBR) exhibits excellent oil resistance, its polar side chains lead to high internal resistance, necessitating adjustments to the vulcanization system to mitigate deformation risk. The rubber content in the formulation must also be controlled, typically between 30% and 60%. A high rubber content results in large voids in the crosslink network, making it prone to collapse under stress. A low rubber content results in excessive filler, which, while cost-effective, can lead to filler aggregation and compromised crosslink uniformity, ultimately increasing deformation.
The vulcanization process is crucial, with vulcanization temperature and time directly impacting crosslink density. Too low a vulcanization temperature can lead to incomplete crosslinking, resulting in a loose network structure; too high a temperature can cause overcure, breaking crosslinks. Both can reduce rubber elasticity and increase compression set. For example, the vulcanization temperature for natural rubber is typically controlled between 160°C and 170°C for approximately 10-20 minutes to ensure a moderate crosslink density. The choice of vulcanization system is also crucial. Peroxide vulcanization systems (such as DCP) form high-energy carbon-carbon crosslinks. Compared to the polysulfide bonds in sulfur vulcanization systems, these have higher bond energies and shorter bond lengths. This makes them less susceptible to deformation under stress and allows for faster recovery from deformation, effectively reducing compression set. Furthermore, the addition of sulfur donors (such as TMTD) can reduce the free sulfur content, prevent embrittlement of the vulcanizate, and further optimize deformation properties.
The selection and treatment of fillers significantly influences compression set. Reinforcing fillers (such as carbon black) enhance the strength of the crosslinked network and reduce deformation by physically adsorbing or chemically bonding with rubber molecular chains. High-structure carbon black (such as HAF), due to its high surface roughness and numerous pores, forms more bonding points with rubber, resulting in superior compression set resistance compared to low-structure carbon black. While non-reinforcing fillers (such as calcium carbonate) can reduce costs, excessive use can disrupt crosslinking uniformity, so dosage must be controlled. Surface treatment of the filler is also crucial. Adding a silane coupling agent can improve the interfacial bonding between the filler and rubber, reduce agglomeration, and enhance crosslinking efficiency, thereby reducing deformation.
Structural design must balance sealing performance and deformation recovery. The compression of rubber product dust covers must be appropriately designed to avoid excessive compression that can lead to irreversible deformation. For example, in seal design, compression is typically controlled between 20% and 30% to ensure sealing effectiveness while minimizing permanent deformation. Furthermore, optimizing the wall thickness distribution of the dust cover to avoid localized stress concentration can further reduce deformation risk. For example, increasing the wall thickness in critical contact areas can disperse pressure and reduce deformation, while reducing the wall thickness in non-contact areas can reduce material usage while maintaining overall elasticity.
Process optimization is also crucial. Temperature and time must be strictly controlled during the mixing process to avoid uneven filler dispersion or local overheating that can lead to premature vulcanization. During molding, pressure must be uniform to avoid uneven pressure that can cause localized overcompression and increase the risk of deformation. Furthermore, post-vulcanization can eliminate internal stresses and further enhance the rubber's elastic recovery.
Environmentally adaptable design ensures long-term stability. Rubber products dust covers are susceptible to hydrolysis in hot and humid environments, damaging crosslinks and increasing compression set. Adding antioxidants, such as antioxidants and light stabilizers, can slow rubber aging and maintain crosslink network stability. For example, adding hindered phenolic antioxidants (such as 1010) can effectively inhibit oxidation and extend the service life of the rubber.
By optimizing material formulations, controlling the vulcanization process, selecting and treating fillers, improving structural design, optimizing processing, and designing for environmental adaptability, the compression set of rubber products dust covers can be systematically reduced, improving sealing performance and service life, thereby meeting the demand for high-reliability rubber products in the automotive and machinery industries.
