TPU seals, polyurethane seals, and oil seals are core products in the industrial sealing field, widely used in engineering machinery, automotive manufacturing, hydraulic equipment, electronics, and many other industries. Seal injection molds are the key tooling for achieving large-scale, high-precision production of these seals. These three types of seals have clear hierarchical and overlapping relationships in terms of material properties and functional positioning, while the mold, as the production carrier, connects the entire process from product design and development to mass production. This article will systematically explain the core characteristics, interrelationships, and technological development trends of these four types of products, based on industry-recognized technical parameters and actual production practices, providing professional reference for material selection, mold design, and product application in industrial production.
I. Polyurethane Seals vs. TPU Seals
Polyurethane seals are sealing elements made from polyurethane materials. TPU (thermoplastic polyurethane), as an important branch of polyurethane, makes TPU seals a core sub-category of polyurethane seals. While sharing similar material properties, they each have their own strengths and weaknesses, making them the preferred sealing solution for high-pressure and wear-resistant applications, accounting for approximately 35% of the industrial sealing market.
1. Material Properties and Core Parameters
Polyurethane seal materials include thermoplastic polyurethane (TPU) and cast polyurethane (CPU). TPU seals have an operating temperature range of -40 to +80℃, while CPU, after molecular chain cross-linking modification, can extend its temperature range to -45 to +120℃, exhibiting superior low-temperature resistance to brittleness. In terms of hardness, TPU sealing rings have a Shore hardness of 85±2, while CPU sealing rings have a Shore hardness of 90±3. Compared to traditional nitrile rubber seals, both exhibit a 40% reduction in elastic modulus decay at low temperatures and a compression set below 15% at 110℃, significantly improving wear resistance. Simultaneously, their tensile strength reaches 35~50MPa, and their elongation at break exceeds 500%, demonstrating fatigue resistance far superior to ordinary rubber materials under repeated dynamic sealing conditions.
2. Differences in Applicable Scenarios
TPU sealing rings, due to their excellent processing fluidity, are suitable for mass production of small to medium-sized, structurally regular seals. They are commonly used in CNC machine tool guideways, hydraulic valve groups, and other applications with pressures ≤10MPa, reducing equipment friction energy consumption by 18%. CPU sealing rings, due to their high pressure resistance and strong extrusion resistance, are mostly used in heavy-duty equipment with pressures ≤32MPa, such as engineering machinery cylinders and high-pressure oil pipe joints, extending seal life by 40%. Both exhibit good compatibility in common industrial media such as hydraulic oil, water-based liquids, and ethylene glycol, with a volume expansion rate of less than 5%. After immersion in aqueous media for 1000 hours, the tensile strength retention rate still exceeds 85%, making them suitable for the media requirements of most industrial scenarios.
II. Oil Seals
Oil seals are specialized sealing components categorized by function. Their core function is to prevent leakage of internal lubricating oil while isolating external dust and impurities. Material selection must be adapted to different operating conditions, and there is a clear cross-application relationship between them and polyurethane and TPU seals. They are key components ensuring the long-term operation of rotating shaft components.
1. Structural and Functional Characteristics
Oil seals typically employ a lip-type structure design. The elastic fit of the lip is crucial for achieving a sealing effect. In some high-pressure scenarios, a metal skeleton is used to enhance structural stability. The bonding strength between the metal skeleton and the rubber must be ≥3.5 N/mm. In terms of sealing performance, the reinforced lip design of the oil seal ring can control the leakage rate to within 0.1 mL/min under a test pressure of 21 MPa, meeting the dynamic sealing requirements of most industrial equipment and ensuring stable operation on rotating shafts with speeds ≤3000 r/min.
2. Material Selection and Industry Applications
The selection of materials for oil seal rings requires comprehensive consideration of operating temperature and media type. Polyurethane (including TPU) is the preferred material for high-speed, high-pressure equipment oil seals due to its strong wear resistance and high pressure resistance. In the automotive industry, nitrile rubber or fluororubber is often used for engine and transmission oil seals; polyurethane oil seals are widely used in the harsh conditions of construction machinery, as they can withstand sand and gravel impacts and severe friction; the food and pharmaceutical industries prioritize non-toxic and odorless silicone rubber oil seals, which meet food contact material safety standards. In the aerospace field, metal-framed composite structure oil seal rings can withstand pressures ≤70 MPa and temperature resistance exceeding 130℃, adapting to extreme operating conditions.
3. Quality Control Standards
Oil seal ring production must comply with ISO 3601-3 standards. Visually, the working surface must not have cracks or impurities greater than 0.2mm, and non-working surfaces are allowed defects ≤2mm, with a total number not exceeding 3. Regarding dimensional tolerances, industry-standard tolerances apply, with the core sealing surface dimensional tolerance controlled within ±0.15mm to ensure assembly accuracy and sealing fit. Furthermore, finished products must undergo a 100-hour high-temperature aging test, with the lip elasticity decay rate not exceeding 10% before shipment.
III. Injection Molds for Sealing Rings
Injection molds for sealing rings are core equipment for the industrial production of TPU sealing rings, polyurethane oil seals, and other products. The mold's structural design and precision control directly determine the performance and yield rate of the seals. In recent years, with the development of precision manufacturing technology, mold design and processing technology have been continuously upgraded, driving an increase in seal production efficiency of over 30%.
1. Mold Core Structure Design
Sealing ring injection molds typically employ a cavity mold structure. The cavity surface requires precision polishing, with a roughness controlled within Ra0.02~0.05μm to prevent burrs and scratches on the sealing surface from affecting the sealing effect. For thermoplastic materials such as TPU, the mold must be equipped with a precise temperature control system with a temperature control accuracy of ±1℃ to ensure uniform material melting and smooth mold filling. For oil seal molds with a metal skeleton, an insert positioning structure is used with a positioning accuracy ≤0.01mm to prevent skeleton misalignment during molding. Simultaneously, guide pillars and guide sleeves are incorporated to ensure the coaxiality of the mold opening and closing.
2. Key Process Technologies
Matching injection molding process parameters is crucial for mold production. During TPU sealing ring injection molding, the melt temperature is controlled at 170-190℃, the injection pressure at 80-120MPa, the holding time at 20-40s, and the cooling time at 15-25s to ensure uniform product density, no bubbles, and no shrinkage marks. The mold's ejection mechanism uses a flexible ejector pin design to avoid damage to weak parts such as the sealing lip. Simultaneously, the mold must have pre-reserved venting grooves, with a groove width of 0.01~0.02mm, to ensure sufficient gas discharge from the cavity, increasing the product qualification rate to over 99%.
3. Technological Development Trends
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