Among after-sales faults of hydraulic machinery, auto parts, and general equipment, oil leakage of rubber seals ranks the most frequent issue. Most customers initially attribute seal oil leaks to manufacturing defects of molds, including insufficient mold precision, dimensional tolerance errors, and flash blemishes. Nevertheless, based on years of supporting experience in sealing production for hydraulics, automotive, and industrial equipment, plus review of tens of thousands of after-sales leakage cases from rubber manufacturers, over 90% of seal oil leak failures root in improper rubber compound selection, while less than 10% stem from mold accuracy problems. Field practices verify that with identical molds, assembly structures, and operating conditions of equipment, simply switching to application-specific rubber compounds can eliminate oil leakage and extend the seal service life by 3 to 5 times. Ⅰ.Core Principle: Seal failure originates primarily from material compatibility rather than mold dimensional accuracy. The core sealing principle of rubber seals lies in the elastic deformation of rubber compounds: the material fills between mating metal surfaces, providing steady, uniform contact pressure to seal against oil, water, and gas leakage. Molds are designed to control product dimension, appearance, and tolerance compliance, whereas the inherent properties of rubber compounds govern seal stability under actual working conditions. Even with zero-tolerance, high-precision, and flash-free molds, persistent oil leakage will occur if the rubber formulation mismatches service requirements. Four major failure modes are listed below: High-temperature softening failure Standard rubber grades have inferior heat resistance. As equipment temperature rises, seals rapidly soften and creep, resulting in reduced structural support and a sharp decline in sealing contact pressure. Clearances can no longer be filled, leading to oil seepage and dripping. Low-temperature elasticity failure In cold environments, mismatched rubber hardens and embrittles with a sharp rise in elastic modulus. It loses conformability and cannot follow equipment vibration and pressure fluctuation to cling to mating surfaces, creating gaps and oil leaks. Medium-induced swelling/shrinkage failure Industrial lubricants contain chemical additives, including antioxidants, EP additives, and anticorrosives, rather than pure base oil. Incompatible rubber will swell or shrink drastically, crack or pulverize upon fluid contact, completely losing dimensional accuracy and triggering leakage. Long-term permanent compression set failure. Low-grade or mismatched rubber features high permanent compression set. After prolonged compressive loading, the seal fails to rebound and turns rigid, becoming the primary culprit of gradual oil leakage during long-term equipment operation. After-sales statistics indicate that 82% of oil leakage issues can be fully fixed simply by switching to application-specific rubber without mold revision or assembly modification. Ⅱ.Core Industry Comparison Table: Standard Selection of Specific Rubber Compounds for Various Oil Media Components, pH values, and additive formulations vary drastically among different industrial oils, so no single all-purpose oil-resistant rubber compound exists. Blind adoption of ordinary black general-purpose sealing rings accounts for 90% of material selection errors. In accordance with national industry standards and mass production specifications, below are the precise material selection comparison table and common pitfalls to avoid: Applicable Oil Type Optimal Rubber Grade Key Performance Requirements Common Selection Mistakes & Failure Consequences Conventional Mineral Hydraulic Oil NBR Mineral oil resistance, compression set ≤15%, service temperature: -30℃~100℃ Wrong selection of NR/SBR; severe swelling & cracking after oil immersion leading to rapid oil leakage High-Temp Engine Oil ACM Resistance to hot engine oil & oil oxidation, long-term stable at 120℃ Ordinary NBR misused; fast hardening & cracking under high temperature with total seal failure EP Additive Containing Gear Oil FKM Excellent chemical & EP additive resistance, stable oil resistance NBR misused; chemical erosion from gear oil additives causes material delamination and persistent leakage DOT Series Brake Fluid EPDM Resistance to polar solvents & brake fluid corrosion NBR/FKM misused; excessive swelling resulting in complete loss of sealing performance Lubricating Oil above 150℃ FVMQ Balanced high/low temp resistance, lube resistance and stable elasticity Conventional FKM misused; insufficient low-temp elasticity causes continuous oil seepage Core Selection Rule: Confirm 4 working parameters prior to custom seal ordering; reject empirical selection by appearance. Ⅲ.Objective Conclusion: Molds are not the root cause for oil leakage defects. We never deny the importance of mold precision. Mold defects such as misplaced parting lines, excessive flash, out-of-tolerance dimensions, and demolding deformation can indeed trigger short-term poor sealing and oil leakage. However, statistics from tens of thousands of failure cases show that less than 10% of oil leakage issues stem directly from inadequate mold manufacturing precision. A common industry misconception persists: when equipment leaks oil, companies blindly develop new molds, revise mold specifications, or switch mold suppliers, consuming substantial time and cost yet failing to resolve the trouble. The root cause lies in treating symptoms instead of the source: no matter how precise the mold dimension is, sealing performance becomes meaningless if the rubber compound fails to match actual service conditions. Numerous clients who spent repeated efforts on mold modification with no improvement have permanently eliminated oil leakage simply by switching to application-specific rubber grades, with no mold alteration or equipment adjustment required. Ⅳ.3-Step Operation Rules: Eliminate Seal Ring Oil Leakage Step 1: Verify actual service conditions precisely and reject ambiguous material selection Specified parameters shall be finalized material selection; vague descriptions, including “ambient temperature, ordinary engine oil, and standard pressure” are not acceptable. Temperature: Confirm maximum operating temperature, minimum ambient temperature, and continuous high-temperature duration; Medium: Specify exact oil grade, presence of EP additives/corrosion inhibitors, and mixed contaminants; Application type: Differentiate static sealing, reciprocating sealing, and rotary dynamic sealing. Pressure: Clarify normal working pressure and instantaneous peak pressure. Step 2: Require suppliers to supply complete batch material test reports Qualified seal manufacturers enable full traceability for every batch of rubber compound. Core performance test data must be requested to avoid inferior blended rubber and shoddy substitution: Basic indicators: Rubber hardness, tensile strength, and elongation at break. Oil resistance indicators: Volume change rate and weight change rate after oil immersion. Durability indicators: Permanent compression set (key index for sealing service life). Environmental indicators: Test data from high & low temperature aging tests. Step 3: Conduct small-batch installation verification before mass production launch For severe working conditions, including high temperature, dynamic movement, and special oil media, prioritize trial production, bench testing, and field installation verification with small lots. Optimal industrial workflow: Test oil leakage by switching to a matching rubber compound first. Proceed with mold optimization evaluation only after verifying satisfactory performance, to eliminate unnecessary mold revisions and redundant cost waste. Ⅴ.Conclusion Core sealing principle for rubber seals: Molds control dimensional accuracy, while rubber compounds determine sealing service life. 90% of oil leakage failures originate from mismatched rubber material against service conditions rather than inadequate mold precision. With properly selected application-specific rubber, qualified mold dimensions, and standard installation, the oil-tight reliability and overall service life of sealing rings can be improved 3 to 5 times, drastically cutting after-sales breakdown rates, maintenance expenses, and equipment downtime losses. The professional and cost-effective industry standard for seal selection follows this order: check rubber compound first, then inspect mold quality.  

Rubber sealing rings are vital components in numerous industrial manufacturing fields. Their high-temperature resistance directly determines whether equipment suffers liquid or gas leakage, or even shutdown failures. It is crucial to select suitable rubber sealing rings in advance, rather than trying to fix problems after malfunctions occur. Technically, high temperature resistance is closely linked to the thermal stability of rubber molecular chains. For instance, the carbon-fluorine bond energy of fluororubber reaches 485 kJ/mol, significantly higher than the carbon-hydrogen bond energy of common rubber, which is around 410 kJ/mol. The silicon-oxygen bond energy of silicone rubber stands at approximately 443kJ/mol, surpassing that of ordinary organic polymers (about 346kJ/mol). Accordingly, they boast excellent heat resistance and will not decompose or melt under high temperatures.   PART 01 High-temperature Resistance Comparison of Sealing Ring Materials FKM Usable temperature range -20℃ to 200℃. Withstands 250℃ briefly and 300℃ momentarily. Features oil, acid, alkali, and aging resistance. Ideal for engines, chemical facilities, fuel systems, and high-temperature valves. VMQ Wide temperature tolerance, long-term service at -60℃ to 200℃. Excellent cold and heat resistance. Special formulas endure over 250℃ temporarily. Suitable for home appliances, medical, and electronic applications. FVMQ Outstanding heat resistance. Stable from -50℃ to 250℃. High-grade variants sustain peak temperature up to 300℃ instantly. EPDM Good heat resistance, temperature range -55℃ to 150℃. Excellent resistance to steam and hot water, widely used in heating pipelines and cooling systems. NBR Working temperature -20℃ to 100℃, maintains stable sealing performance within the range. Rapid aging occurs above 120℃, which is not applicable for continuous high-temperature service. PTFE & Flexible Graphite Non-traditional rubber materials with superior extreme high-temperature performance. Filled PTFE dynamic seal withstands up to 265℃. Metal-clad flexible graphite static seal resists temperature up to 650℃. Applied to ultra-high temperature static sealing in oil refining and high-temperature furnaces.   PART 02 High-temperature Application of Sealing Rings Rubber materials retain elasticity, sealing performance, and mechanical strength within specific temperature ranges, enabling long-term service. Certain types can endure short-term high temperatures. Two critical temperature thresholds apply: Minimum operating temperature: Rubber turns brittle, loses elasticity, and may crack below this value. Maximum operating temperature: Excess heat causes softening, oxidation, hardening, and permanent deformation, resulting in loss of resilience and bearing capacity. The rated temperature range differs from the actual working temperature. Material formula, manufacturing process, contact medium, and dynamic/static working conditions all affect performance. A comprehensive assessment is required to guarantee a reliable sealing effect.

I.Core Properties of Common Rubbers II.Differences and Applications of Common Rubbers Note: Practical rubber products often contain pigments, so color cannot be used as the sole basis for identification. The most reliable methods are: – Checking the material marking (e.g., markings on oil seals) – Consulting your supplier For simple identification, you can combine: – Oil resistance test (observe swelling after immersion) – Burning characteristics (e.g., CR is self-extinguishing) III.Advantages and Disadvantages of Common Rubbers Natural Rubber (NR) Main Advantages: Excellent elasticity, tensile strength, and tear resistance; good processability. Main Disadvantages: Poor resistance to oil, ozone, and heat aging; narrow operating temperature range. Styrene-Butadiene Rubber (SBR) Main Advantages: High abrasion resistance, heat resistance, low cost, and the highest production volume. Main Disadvantages: Slightly lower elasticity and cold resistance; poor resistance to oil. Butadiene Rubber (BR) Main Advantages: Outstanding elasticity, abrasion resistance, and cold resistance. Main Disadvantages: Poor tear resistance. Chloroprene Rubber (CR) Main Advantages: Good overall performance; resistant to oil, weathering, flame, and ozone aging. Main Disadvantages: High density, average low-temperature performance, and relatively expensive. Nitrile Rubber (NBR) Main Advantages: Excellent oil resistance (second only to fluorocarbon rubber, etc.), good abrasion resistance, and airtightness. Main Disadvantages: Poor cold resistance, ozone resistance, and electrical insulation. Ethylene Propylene Diene Monomer (EPDM) Main Advantages: Superior resistance to ozone, weathering, and aging; resistant to hot water and steam; good electrical insulation. Main Disadvantages: Poor oil resistance; slow vulcanization; poor self-adhesion. Butyl Rubber (IIR) Main Advantages: Best gas and water tightness; heat and aging resistance. Main Disadvantages: Poor tack, slow vulcanization, and poor oil resistance. Silicone Rubber (SI) Main Advantages: Widest temperature resistance range, non-toxic, insulating, and ozone-resistant. Main Disadvantages: Low mechanical strength, poor oil and solvent resistance, and high cost. Fluorocarbon Rubber (FKM) Main Advantages: High-temperature resistance, oil resistance, superior chemical resistance, and aging resistance. Main Disadvantages: Very expensive, poor processability, average cold resistance, and low elasticity. Chlorosulfonated Polyethylene (CSM) Main Advantages: Excellent abrasion resistance, weather resistance, ozone resistance, and good flame retardancy. Main Disadvantages: High cost, poor rebound, and compression set properties. IV. Quick Selection Guide Great elasticity → Choose Natural Rubber (NR) Great wear resistance & low cost → Choose Styrene-Butadiene Rubber (SBR) Oil resistance → Choose Nitrile Rubber (NBR) (general use) or Fluoro Rubber (FKM)(extreme conditions) Weather & aging resistance → Choose Ethylene Propylene Rubber (EPDM) Air & water tightness → Choose Butyl Rubber (IIR) Wide temperature resistance → Choose Silicone Rubber (SI) Super corrosion resistance → Choose Fluoro Rubber (FKM)