How can valve positioning films maintain dimensional stability and positioning accuracy under high-temperature conditions?
Publish Time: 2025-10-30
In modern industrial automation control systems, valve positioners, as core accessories of regulating valves, directly affect the control accuracy and operational stability of the system. The positioning film, as a key sensitive element within the positioner, plays a crucial role in converting pneumatic signals into mechanical displacement, driving the valve stem. Under high-temperature conditions, such as in petrochemical cracking units, combined heat and power systems, or high-temperature steam pipelines, ambient temperatures can reach 150°C or even higher, posing severe challenges to the material properties, structural design, and manufacturing process of the positioning film. To ensure that valves can accurately respond to control signals even under extreme temperatures, the positioning film must possess excellent dimensional stability and long-term positioning accuracy.1. Using High-Temperature Resistant Materials is FundamentalThe material of the positioning film directly determines its temperature resistance and dimensional stability. Traditional rubber diaphragms are prone to softening, aging, or hardening and cracking at high temperatures, leading to decreased elasticity and irreversible deformation, thus affecting positioning accuracy. Therefore, in high-temperature applications, positioning films commonly employ high-performance synthetic materials. Among them, FKM can operate stably within a temperature range of -20°C to 200°C, exhibiting excellent heat resistance and chemical inertness; FFKM can withstand extreme temperatures above 250°C and possesses strong creep resistance; while metal diaphragms achieve zero expansion deformation at high temperatures through cold working and precision stamping processes, making them particularly suitable for ultra-high temperature or high-cleanliness applications. These materials not only maintain a stable elastic modulus at high temperatures but also resist environmental degradation such as oxidation and sulfidation, fundamentally ensuring dimensional stability.2. Optimized Structural Design to Reduce the Impact of Thermal StressHigh temperatures not only cause material expansion but also generate thermal gradients in different areas of the diaphragm, leading to localized stress concentration and potentially causing warping or fatigue damage. To address this, positioning films often employ symmetrical corrugated structures or concentric annular pleated designs. This geometry effectively absorbs strain generated by thermal expansion and contraction, preventing tensile or compressive failure caused by linear expansion. Meanwhile, a well-designed thickness distribution enhances the uniformity of the diaphragm's stiffness, ensuring coordinated overall deformation under temperature changes and maintaining flatness and linearity of motion. Furthermore, multi-layered composite structures are widely used, further suppressing overall dimensional changes through the complementary thermal expansion coefficients of different materials.3. Precision Manufacturing and Pre-Aging Treatment Enhance ReliabilityTo ensure long-term stability at high temperatures, the positioning film undergoes rigorous process control during manufacturing. For example, CNC stamping or laser cutting technologies ensure dimensional tolerances within the micrometer range; vacuum vulcanization or plasma cleaning improves material density and surface cleanliness. More importantly, many high-end positioning films undergo pre-aging treatment before leaving the factory, i.e., prolonged thermal baking in an environment above the rated operating temperature, causing premature release of internal stress and completing the initial physical aging process. Diaphragms treated in this way exhibit minimal thermal deformation in actual use, significantly improving the ability to maintain initial accuracy.4. Synergistic Effect of System Integration and Heat Dissipation DesignBesides the diaphragm itself, the overall structural design of the positioner also significantly impacts high-temperature performance. For example, using heat-insulating brackets or extending the heat dissipation neck isolates the high-temperature valve body from the positioner body, preventing direct heat conduction to the diaphragm cavity; ventilation slots or reflective coatings are installed inside the diaphragm cover to enhance air convection and radiative heat dissipation; and using shell materials with low thermal conductivity further blocks heat flow. These measures effectively reduce the actual operating temperature of the positioning film and extend its service life.In summary, the dimensional stability and positioning accuracy of valve fitting positioning films under high-temperature conditions rely on the scientific selection of high-temperature resistant materials, structural optimization to resist thermal deformation, precise manufacturing processes, and system thermal management design. As industrial automation develops towards high temperature, high pressure, and high precision, positioning film technology will continue to advance, providing a solid guarantee for precise control under complex operating conditions.
