TPU sealing rings, polyurethane sealing rings and oil seals are core products in the industrial sealing field, widely used in engineering machinery, automobile manufacturing, hydraulic equipment, electronic appliances and other industries. Injection molds for sealing rings are key equipment to realize large-scale and high-precision production of such seals. There are clear subordinate and intersecting relationships among the three in terms of material properties and functional positioning, while molds, as production carriers, connect the entire process from product design, R&D to mass production. Based on industry-recognized technical parameters and production practices, this paper systematically elaborates on the core characteristics, correlation logic and technological development trends of the four types of products, providing professional reference for material selection, mold design and product application in industrial production.
Polyurethane sealing rings are sealing components made of polyurethane materials. As an important branch of polyurethane, TPU (Thermoplastic Polyurethane) makes TPU sealing rings a core segment of polyurethane sealing rings. The two are interrelated yet distinctive in material properties, serving as the preferred sealing solution for high-pressure and wear-resistant scenarios, accounting for about 35% of the industrial sealing market.
1 Material Properties and Core ParametersPolyurethane sealing rings cover thermoplastic polyurethane (TPU), cast polyurethane (CPU) and other materials. The operating temperature range of TPU sealing rings is -40~+80℃, while CPU's temperature resistance range can be extended to -45~+120℃ through molecular chain cross-linking modification, with better low-temperature anti-brittle performance. In terms of hardness, the Shore hardness of TPU sealing rings is controlled at 85±2, and that of CPU sealing rings is 90±3. Compared with traditional nitrile rubber seals, the elastic modulus decay rate of both is reduced by 40% in low-temperature environments, and the compression set rate at 110℃ high temperature can be controlled below 15%, showing significantly improved wear resistance. Meanwhile, their tensile strength can reach 35~50MPa with elongation at break exceeding 500%, and their fatigue resistance in repeated dynamic sealing conditions is far superior to ordinary rubber materials.
2 Differences in Application ScenariosWith excellent processing fluidity, TPU sealing rings are suitable for mass production of small and medium-sized, structurally regular seals, and are often used in scenarios with pressure ≤10MPa such as CNC machine tool guideways and hydraulic valve groups, reducing equipment friction energy consumption by 18%. Due to high pressure resistance and strong extrusion resistance, CPU sealing rings are mostly applied in heavy-duty equipment with pressure ≤32MPa such as engineering machinery cylinders and high-pressure oil pipe joints, extending the service life of seals by 40%. Both have good compatibility with common industrial media such as hydraulic oil, water-based fluids and ethylene glycol, with volume expansion rate below 5%. After soaking in water-containing media for 1000 hours, the tensile strength retention rate remains over 85%, meeting the media requirements of most industrial scenarios.
Oil seals are functionally classified special seals, whose core function is to prevent leakage of lubricating oil inside equipment and isolate external dust and impurities. Their material selection must adapt to different working conditions, having clear material intersection with polyurethane sealing rings and TPU sealing rings, and they are key components to ensure long-term operation of rotating shaft parts.
1 Structural and Functional FeaturesOil seals usually adopt lip-type structure design, where the elastic fit of the lip is crucial for sealing effect. In some high-pressure scenarios, metal frameworks are used to enhance structural stability, and the bonding strength between metal frameworks and rubber shall be ≥3.5N/mm. In terms of sealing performance, oil seals with reinforced lip design can control the leakage rate within 0.1mL/min under a test pressure of 21MPa, meeting the dynamic sealing needs of most industrial equipment and working stably on rotating shafts with speed ≤3000r/min.
2 Material Selection and Industrial ApplicationsThe material selection of oil seals must be comprehensively determined based on operating temperature and medium type. Among them, polyurethane (including TPU) materials are preferred for oil seals in high-speed and high-pressure equipment due to their strong wear resistance and high pressure resistance. In the automotive industry, nitrile rubber or fluororubber are mostly used for oil seals in engines and gearboxes; in harsh working conditions of engineering machinery, polyurethane oil seals are widely applied, capable of withstanding gravel impact and severe friction; in the food and pharmaceutical industry, non-toxic and odorless silicone rubber oil seals are preferred, complying with food contact material safety standards. In the aerospace field, metal framework composite oil seals can withstand high pressure ≤70MPa with temperature resistance exceeding 130℃, adapting to extreme working conditions.
3 Quality Control StandardsThe production of oil seals must comply with ISO 3601 - 3 standard. In terms of appearance, no cracks or impurities larger than 0.2mm are allowed on the working surface, and no more than 3 defects of ≤2mm are permitted on the non-working surface. For dimensional tolerance, it shall be implemented in accordance with general industry standards, and the dimensional tolerance of the core sealing surface shall be controlled within ±0.15mm to ensure assembly accuracy and sealing fit. In addition, finished products must undergo 100-hour high-temperature aging test, and can only leave the factory if the lip elastic decay rate does not exceed 10%.
Injection molds for sealing rings are core equipment to realize industrial production of TPU sealing rings, polyurethane oil seals and other products. The structural design and precision control of molds directly determine the performance and qualification rate of seals. In recent years, with the development of precision manufacturing technology, mold design and processing technology have been continuously upgraded, increasing seal production efficiency by more than 30%.
1 Core Structural Design of MoldsInjection molds for sealing rings usually adopt cavity mold structure, and the cavity surface must undergo precision polishing treatment with roughness controlled at Ra0.02~0.05μm to avoid burrs and scratches on the seal surface that affect sealing effect. For thermoplastic materials such as TPU, molds need to be equipped with precise temperature control systems with temperature control accuracy of ±1℃ to ensure uniform melting and smooth filling of materials. For oil seal molds with metal frameworks, insert positioning structure is adopted with positioning accuracy ≤0.01mm to prevent framework deviation during molding. Meanwhile, guide pillar and bushing guiding mechanism is set to ensure the coaxiality of mold opening and closing.
2 Key Process Technology PointsThe matching of injection process parameters is crucial for mold production. When injection molding TPU sealing rings, the melt temperature is controlled at 170 - 190℃, injection pressure at 80 - 120MPa, holding time at 20 - 40s, and cooling time at 15 - 25s to ensure uniform product density without bubbles or shrinkage marks. The mold's ejection mechanism adopts elastic thimble design to avoid damage to vulnerable parts such as the seal lip. At the same time, the mold must be provided with exhaust grooves with width of 0.01~0.02mm to ensure full discharge of gas in the cavity, increasing the product qualification rate to over 99%.
3 Technological Development TrendsCurrently, injection molds for sealing rings are developing towards precision and intelligence. The adoption of integrated CAD/CAM/CAE design technology can realize simulation optimization of mold cavities, shortening the R&D cycle by 20%. In terms of mold materials, wear-resistant H13 hot work die steel is selected and subjected to nitriding treatment, with surface hardness reaching HRC55~60, extending the mold service life to over 500,000 cycles. In addition, modular mold design has become increasingly popular. By replacing cavity modules, different specifications of seals can be produced, significantly reducing production costs and adapting to small-batch and multi-variety production needs. Meanwhile, online mold monitoring technology is gradually applied, which can dynamically adjust the production process by real-time monitoring of mold temperature, pressure and other parameters through sensors, further ensuring product consistency.
