As a core component of valve positioners, the performance of the valve positioning film directly affects the accuracy and reliability of valve control. In low-temperature environments, traditional positioning films are prone to material embrittlement, leading to decreased flexibility and subsequent problems such as sealing failure and sluggish operation. To address this challenge, multi-dimensional improvements are needed, including material selection, structural design, process optimization, and environmental adaptability design, to achieve stable performance in low-temperature environments.
Material selection is fundamental to preventing low-temperature embrittlement of the positioning film. Traditional rubber or ordinary plastics tend to harden and become brittle at low temperatures due to reduced molecular chain mobility, losing their elasticity. Therefore, special materials with low-temperature toughness must be selected, such as ultra-high molecular weight polyethylene (UHMWPE), which maintains toughness and withstands impact without cracking even at extremely low temperatures of -269°C; or modified polytetrafluoroethylene (PTFE), which improves wear resistance by filling with carbon fiber or metal powder while maintaining elasticity at low temperatures. Furthermore, some novel plastics, such as Mylar-type polyester films, retain elasticity at liquid hydrogen temperatures (-253°C) and can be considered as candidate materials for positioning films. Material selection must balance low-temperature performance, chemical stability, and compatibility with the medium to avoid performance degradation due to immersion in the medium.
Structural design is key to improving the low-temperature adaptability of the positioning film. The positioning film needs to compensate for valve actuation errors through elastic deformation; however, the increased elastic modulus of the material at low temperatures leads to a decrease in deformation capacity. Therefore, a bellows structure or honeycomb reinforcing rib design can be used to distribute stress in local deformation areas, preventing brittle fracture due to concentrated stress. Simultaneously, optimizing the connection between the positioning film and the valve actuator, using flexible joints or ball joints, reduces additional stress caused by low-temperature shrinkage, ensuring operational flexibility. Furthermore, the thickness of the positioning film must be designed to balance low-temperature performance and response speed; excessive thickness reduces sensitivity, while excessive thinness easily leads to failure due to stress concentration.
Process optimization can significantly improve the low-temperature reliability of the positioning film. During material processing, low-temperature quenching or directional crystallization treatments are necessary to refine the grains, reduce internal defects, and improve resistance to brittle fracture. For example, nickel-based alloy or titanium alloy positioning films, after low-temperature quenching, can still maintain impact toughness at -50°C, preventing lattice fracture. For plastic positioning films, blending modification techniques can be employed, adding plasticizers or nanofillers to improve molecular chain flexibility and lower the glass transition temperature. Furthermore, surface treatment processes such as spraying wear-resistant coatings or metal plating can enhance the positioning film's wear resistance and anti-aging properties, extending its service life in low-temperature environments.
Environmental adaptability design is crucial for the low-temperature application of positioning films. In extreme low-temperature environments, the positioning film needs to be designed in conjunction with the overall valve system. For example, electric or steam heating systems can be used to maintain the operating temperature of the positioning film, preventing localized overcooling; or insulation layers can be used to reduce heat loss and mitigate the impact of ambient temperature fluctuations. For scenarios where active heating is not possible, such as deep-sea or polar regions, self-compensating positioning film structures should be selected, such as metal spring energy storage seal designs, using spring force to compensate for low-temperature contraction and maintain sealing pressure. Additionally, the installation location of the positioning film should avoid direct exposure to cold sources to reduce stress concentration caused by thermal gradients.
Material composite technology provides new insights for improving the low-temperature performance of positioning films. By combining metals and non-metals, both strength and flexibility can be achieved. For example, a composite positioning film with a metal skeleton encapsulated in modified PTFE utilizes both the deformation resistance of metal and the low-temperature elasticity of plastic. Alternatively, a multi-layer co-extrusion process can be used to stack materials with different properties, forming a gradient performance structure to adapt to complex stress states in low-temperature environments. Composite material design must address the interlayer bonding strength issue to avoid delamination due to differences in thermal expansion coefficients.
Low-temperature testing and verification are the final step in ensuring the reliability of the positioning film. Actual working conditions must be simulated in a dedicated low-temperature test chamber to test the elasticity, sealing performance, and durability of the positioning film within the range of -50℃ to -200℃. Impact tests, tensile tests, and fatigue tests are used to evaluate its resistance to brittle fracture and its lifespan. Simultaneously, finite element analysis (FEA) is used to optimize the structural design, predict stress distribution at low temperatures, and proactively mitigate failure risks. Test data can provide a basis for material selection and process improvement, forming a closed-loop optimization.
The prevention of embrittlement and maintenance of flexibility in valve positioning films at low temperatures require material innovation, structural optimization, process improvement, and system-wide collaborative design. From ultra-high molecular weight polyethylene to metal composites, from bellows structures to self-compensating seals, each technological breakthrough aims to improve the adaptability of positioning films under extreme conditions. In the future, with the expansion into fields such as deep-sea development and polar scientific research, the technological demand for cryogenic valve positioning films will continue to grow, driving materials science and manufacturing processes towards higher performance.
