Corrosion-resistant sealing design and enhanced durability in humid environments for fastening systems
What are the core components of the anti-corrosion and sealing design of fastener systems?
The core components of the anti-corrosion and sealing design of fastener systems include elastic sealing washers, anti-corrosion coated fasteners and drainage-type fastener bases, which jointly realize the anti-corrosion and sealing function. The elastic sealing washers are made of nitrile rubber or fluororubber, installed between the bolt head and the pressure plate, with excellent elasticity and sealing performance, which can prevent rainwater, dust and salt spray from penetrating into the thread pair, and their anti-aging service life can reach more than 15 years. Anti-corrosion coated fasteners include dacromet-coated bolts and zinc-aluminum coated elastic bars, with a coating thickness of 8-12μm, which have sacrificial anode protection effect, and the corrosion resistance time in salt spray test is >=2000 hours. The bottom of the drainage-type fastener base is provided with drainage holes, which can discharge the infiltrated rainwater in time, avoid accumulation in the base, and prevent immersion corrosion of bolts and elastic bars. The design of these components needs to consider installation convenience, and the hardness of the sealing washer is controlled at Shore A60-70 to ensure that it is not easy to be damaged during installation.
, while meeting the requirements of sealing performance and durability. In humid and rainy inland areas, sealing washers can be selected. Nitrile rubber has good water resistance and wear resistance, with a service temperature range of -40℃-120℃, which can adapt to the climatic conditions of most inland areas, and its sealing performance can be maintained for more than 10 years. In coastal areas with high salt spray, sealing washers should be selected. Fluororubber has excellent salt spray corrosion resistance and chemical corrosion resistance, with a service temperature range of -20℃-200℃, which can resist salt spray erosion in coastal areas, and the salt spray resistance time is >=5000 hours. In alpine regions, sealing washers should be selected. Silicone rubber has good low-temperature toughness and can maintain elasticity even at a low temperature of -50℃, avoiding sealing failure caused by low-temperature embrittlement. Regardless of the material selected, the compression set rate of the sealing washer should be <=20% to ensure that the sealing performance can be maintained after long-term compression.
What are the key installation process points of the anti-corrosion and sealing design of fastener systems?
The key installation process points of the anti-corrosion and sealing design of fastener systems are concentrated on , which directly affect the sealing effect. Before installation, it is necessary to clean the contact surfaces of fasteners and fastener bases, remove rust, oil stains and debris to ensure that the sealing washers are closely attached to the contact surfaces without gaps. The installation of sealing washers must be accurately positioned to ensure that they completely cover the bolt holes and avoid sealing failure caused by offset. For circular washers, positioning grooves can be used for auxiliary installation, and the size of the positioning grooves is consistent with the outer diameter of the washers. The tightening of fasteners must follow the : first tighten the diagonal bolts, then tighten the remaining bolts. The tightening torque should be applied evenly. The tightening torque of fasteners for high-speed railway is 350-400N·m, and that for heavy-haul railway is 400-450N·m, ensuring that the sealing washers are compressed evenly, with the compression amount controlled at 30%-40% of the washer thickness. Insufficient compression will lead to poor sealing, and excessive compression will damage the washers. After installation, a sealing test should be carried out by water spraying to observe whether rainwater penetrates into the thread pair.
What are the differentiated requirements of the anti-corrosion and sealing design of fastener systems for different corrosive environments?
The differentiated requirements of the anti-corrosion and sealing design of fastener systems for different corrosive environments are mainly reflected in two aspects: anti-corrosion grade and sealing structure, which need to be optimized in a targeted manner. The coastal high-salt-spray environment has the highest corrosion degree, requiring the anti-corrosion grade to reach C5. The sealing structure should adopt the combination of fluororubber washers + dacromet-coated fasteners + drainage-type bases. The diameter of drainage holes should be >=5mm to ensure smooth drainage. At the same time, the coating thickness of fasteners should be increased to 12-15μm to enhance corrosion resistance. The humid and rainy inland environment has a moderate corrosion degree, requiring the anti-corrosion grade to reach C4. The sealing structure can adopt the combination of nitrile rubber washers + galvanized-coated fasteners, with the galvanized coating thickness >=85μm to meet the anti-corrosion needs of inland areas. The alpine and dry environment has a low corrosion degree, requiring the anti-corrosion grade to reach C3. The sealing structure can adopt the combination of silicone rubber washers + ordinary anti-corrosion coated fasteners, focusing on the low-temperature elasticity of the washers to ensure that they do not embrittle in low-temperature environments. In addition, in areas with frequent acid rain, the acid resistance of the coating needs to be additionally enhanced by using epoxy zinc-rich coating, with acid resistance time >=1000 hours.
What are the detection methods and acceptance standards for the anti-corrosion and sealing performance of fastener systems?
The detection methods for the anti-corrosion and sealing performance of fastener systems include , and the acceptance standards must comply with TB/T 3360-2016 and GB/T 2423.17-2008. The salt spray test is the core detection item. The assembled fastener system samples are placed in a salt spray test chamber with a salt spray concentration of 5% and a temperature of 35℃ for >=2000 hours. After the test, the coating of fasteners shall have no blistering or peeling, and the corrosion area of threads shall be <=5%. The sealing test adopts the : inject compressed air of 0.2MPa into the fastener system and soak it in water to observe whether bubbles emerge; no bubbles indicate qualification, ensuring that no rainwater penetrates. The durability test adopts the : apply a vibration load with a frequency of 50Hz for 1×10⁷ times. After the test, the sealing washers shall have no deformation or cracking, and the preload loss rate of fasteners shall be <=5%. The acceptance standard stipulates that products that pass all three tests can be judged as qualified. The sampling ratio is 5 groups of samples per batch. If one group is unqualified, double sampling shall be conducted; if it is still unqualified, the batch of products shall be judged as unqualified.