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Ⅰ.What Is Post-Curing? In the production workshop, the process of heating, pressurizing, and shaping the finished product in a mold is called “first-stage curing” (also known as primary curing or initial curing). “Secondary vulcanization” (commonly referred to in the workshop as “second-stage vulcanization” or “post-cure”) refers to the process of neatly stacking rubber products that have already been demolded and shaped into a large industrial oven equipped with forced-circulation hot air, and continuing to bake them at atmospheric pressure for several hours at a specific temperature (typically 150–200°C). Ⅱ.Which Rubbers Require Secondary Vulcanization? Not all rubbers require secondary vulcanization. Common types such as natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR) are generally fully cured after the initial vulcanization stage in the mold and are shipped directly from the factory. Those requiring secondary vulcanization are often “high-end specialty rubbers” that are expensive, subject to extremely strict performance requirements, or made with special vulcanizing agents:   Ⅱ.Which Rubbers Require Secondary Vulcanization? Not all rubbers require secondary vulcanization. Common types such as natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR) are generally fully cured after the initial vulcanization stage in the mold and are shipped directly from the factory. Those requiring secondary vulcanization are often “high-end specialty rubbers” that are expensive, subject to extremely strict performance requirements, or made with special vulcanizing agents: 1.Silicone Rubber (MVQ / Silicone) — Over 95% require secondary vulcanization Reason: During compression molding or injection molding, silicone rubber uses peroxide-based curing agents (such as Di-25, Di-24, and odorless Di-25 curing agents). After these curing agents complete their reaction in the mold, they produce large amounts of acidic byproducts and volatile substances. Unless these are removed through a secondary curing process in an oven, silicone products will become brittle, yellow, or even develop a white bloom on the surface after just a few days. 2.Fluorocarbon Rubber (FKM / Viton) — 100% mandatory Reason: Fluorocarbon rubber reacts relatively slowly. During the brief few minutes spent in the mold (the first stage of curing), it actually forms only about 70% of its chemical cross-linking network. The remaining 30% must be transferred to a high-end oven set at 200–230°C and thoroughly cured for 8 to 24 hours to fully transform into its ultimate “oil- and heat-resistant” state. 3.Acrylate Rubber (ACM) and Hydrogenated Nitrile Rubber (HNBR) Reason: These two types of rubber are commonly used in high-end automotive oil seals and engine gaskets. Similar to fluorocarbon rubber, their reactions within the mold rarely reach full saturation. To achieve extremely low compression set, they must undergo secondary post-curing in an oven. 4.Automotive interior rubber parts with ultra-low odor and low VOC requirements (e.g., EPDM pedal covers, gaskets) Reason: Automakers enforce extremely strict standards for in-cabin air quality (odor testing per VDA 270). Ordinary EPDM products retain pungent amine and mercaptan odors after vulcanization, so they must be placed in an oven where high-intensity hot air is used to “squeeze out and bake away” the odors in a single pass. III. What Are the Core Benefits of Secondary Vulcanization? Given that it is labor-intensive and energy-consuming, secondary vulcanization must offer four irreplaceable, miraculous benefits:   The Four Core Benefits of Secondary Vulcanization 1.Fills the cross-linking network (eliminates under-vulcanization, doubling rebound and tensile strength) 2.Evaporates small molecules (removes residual cross-linking agents through heating, completely eliminating odors and white bloom) 3.Eliminating Internal Stress (Prevents later issues such as curling edges, distortion, and deformation) 4.Enhancing Durability (Maximizing resistance to pressure changes at high and low temperatures)   1.Making the Cross-Linked Network More Dense: Truly “Baking” the Rubber Through Many specialty rubbers are in a “half-baked” or “barely passable” state after the first stage of compression molding. Secondary vulcanization is like placing rice in a rice cooker for the final “steaming” process. Effect: It allows unreacted molecular chains within the rubber to continue linking together, exponentially increasing the cross-linking density. The resulting cured rubber experiences a qualitative leap in tear strength, tensile strength, and resilience. 2.Eliminate low-molecular-weight volatiles: Purify the product, eliminate odors, and remove bloom Toxins and odors generated by curing agents inside the mold are forcibly vaporized and extracted by the high-temperature hot air in the oven. Effect: Completely removes the fishy, kerosene, and pungent VOC odors from new products; simultaneously, it prevents curing agent residues from migrating to the surface, thoroughly eliminating the problem of “blooming” or “whitening” on the surface. For products such as medical-grade silicone and baby pacifiers, secondary vulcanization is a mandatory requirement for obtaining food-grade certification (FDA). 3.Stabilizing Product Dimensions: Eliminating “Trapped Internal Stress” When rubber compound is forced into the mold under high pressure, its molecular chains accumulate “internal stress” from being constrained. If shipped directly from the factory, the products will gradually shrink, deform, and warp over time. Effect: The high temperature in the oven allows the molecular chains to relax freely, releasing all the pent-up tension (eliminating internal stress). As a result, the finished products maintain extremely stable dimensions and will not lose their shape no matter how they are positioned. 4.Quality Enhancement: Pushing Compression Set (Creep Resistance) to the Limit High-end oil seals and O-rings, in particular, are most vulnerable to failing to rebound after being compressed. Effect: Secondary vulcanization creates a seamless chemical network, reducing the high- and low-temperature compression set of EPDM, fluorocarbon rubber, and hydrogenated nitrile rubber to half or even one-third of their original values. This not only extends the service life of the seals but also prevents premature oil and gas leaks.

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)

Standard O-ring sizes are defined by two core dimensions: inner diameter (d₁) and cross-section diameter (d₂, wire diameter). All major standards follow these two key parameters, together with matching tolerances and standardized series rules. The sizing principles and common standards are as follows: 1. Core Dimension Standards: All standards first establish a standard series for the cross-sectional diameter d2 (wire diameter) (e.g., 1.8, 2.4, 3.1, 5.7, 7.0 mm, etc.), and then match the wire diameter with standardized values for the inner diameter d1. Furthermore, d1 increases in fixed increments to avoid a chaotic array of specifications. 2. Dimensioning Rules: The general notation is d1×d2 (inner diameter × wire diameter). In some cases, the outer diameter (d1+2×d2) may be specified, but the standard core remains based on d1 and d2; 3. Tolerance Specifications: Different standards define upper and lower deviations for d1 and d2 based on size ranges (e.g., small inner diameter/large inner diameter, fine wire diameter/coarse wire diameter) to ensure interchangeability. Main Common Standards (Most Widely Used in Industry)： – GB/T 3452.1 (Chinese National Standard) The mainstream standard in China. It defines a narrow series (1.0–4.0 mm) and a wide series (5.7–12.0 mm) for crosssection diameters. Inner diameters are matched to each crosssection, covering most general industrial applications. – AS568 (American Standard) Widely used globally, especially in hydraulic and pneumatic systems. Each part number corresponds to a unique d₁×d₂ size (e.g., AS568010 = 1.78 × 1.78 mm). Key crosssections include 1.78, 2.62, 3.53, and 5.33 mm, widely compatible with American and European equipment. – JIS B 2401 (Japanese Standard) Divided into Type P (general) and Type G (precision). Its crosssection and inner diameter series differ slightly from GB and AS568, mainly for Japanese machinery. – ISO 3601 (International Standard) Highly aligned with GB/T 3452.1, serving as the unified global basic specification with consistent core dimension series. Key Notes: Standards clearly specify the matching rules for minimum groove dimensions. The Oring inner diameter d₁ and crosssection d₂ must be compatible with the bore and width of the installation groove (typical compression ratio: 10%–20%). This is also a necessary design requirement supporting size standardization.

What’s the biggest complaint that seal manufacturers fear most? It’s definitely leakage. When you remove a leaking O-ring, you’ll often discover a heartbreaking sight: it’s no longer the smooth, plump O-ring it once was; its cross-section has turned square or flattened into a D-shape. If you squeeze it with your fingers, it feels rock-hard and completely lacks elasticity. In the rubber industry, this phenomenon has a technical term: compression set. When faced with this issue, many technicians’ first instinct is to say, “Use a higher-quality raw rubber!” or “Add more carbon black!” The result is often higher costs with little improvement. Today, Dr. will take you into the molecular world of rubber to see exactly how your seals “die.” Part 1: Understanding the Basics—What Is Compression Set? In simple terms, compression set refers to the percentage of height that rubber cannot recover after being compressed under a specific temperature for a period of time and then released. In laboratory testing, we use a precise scientific formula to calculate it:  C: Compression set value(The lower the value, the better the resilience and the longer the service life.)  h₀: Original height of the test specimen  h₁: Height of the specimen after recovery  h₈:Height of the spacer (limiter) For seals, CS is a critical indicator. When CS reaches 80% or even 100%, the rubber completely loses its elastic memory. Even the slightest vibration will cause fluids — oil or water — to leak through the gaps. Part 2: The Four Main Culprits — Who Killed Rubber’s Elasticity? Culprit 1: “Genetic Defects” in the Vulcanization System This is the most critical factor determining compression set! The common sulfur vulcanization system (CV) we typically use primarily produces polysulfide bonds (-S_x-). Fatal flaw: Although polysulfide bonds offer good tear resistance, their bond energy is extremely low. Under high temperatures and compression, these bonds will break. After breaking, the molecular chains slide into new, flattened positions and then re-crosslink (forming new chemical bonds). Result: When the pressure is removed, the newly formed chemical bonds tightly hold the molecular chains in place, preventing them from bouncing back. Your O-ring is thus “locked” in a flattened state. Culprit 2: Under-Curing & Lack of Post-Curing Phenomenon: To maximize production output, many factories push curing time to the limit (often not even reaching t90). Consequence: A large number of unreacted crosslinking agents and active sites remain inside the rubber compound. When the seal is compressed under high-temperature operating conditions, these unreacted substances undergo secondary crosslinking. Crosslinking while in a compressed state is like permanently “fixing” the flat shape into its structure. This is especially true for FKM and VMQ silicone: Without standard post-curing (typically oven curing at around 200°C for several hours) to remove volatile components and perfect the crosslinking network, their compression set values will be extremely poor. Culprit 3: Stress Relaxation and Molecular Chain Breakage at High Temperatures High temperatures are the arch-enemy of rubber. When subjected to prolonged pressure at 100°C or even 150°C: Physical relaxation: The thermal motion of the rubber’s polymer chains intensifies, causing irreversible slippage between chain segments. Chemical degradation: The main chain breaks down under the combined effects of heat and oxygen. Once the spring breaks, it naturally cannot spring back. Culprit 4: Escape of Plasticizers (Oil) If your formula contains large amounts of processing oil to reduce hardness or cost, these plasticizers will be extracted or evaporated when the seal is exposed to hot oil or chemical media. Volume shrinkage combined with stress loss causes the seal to degrade and collapse rapidly. Part 3: Doctor’s Prescription — How to Save Your Seals? Now that we’ve identified the culprits, we can target solutions effectively. If you want to produce high-end seals with ultra-low compression set, here is your practical prescription: 1.Overhaul the Vulcanization System (Top Priority) Abandon conventional sulfur systems: Switch to EV (Efficient Vulcanization) or SEV (Semi-Efficient Vulcanization) systems. By increasing accelerator dosage and reducing sulfur content, you form more stable monosulfide and disulfide bonds. Ultimate solution: Peroxide curing system (e.g., DCP, BIPB) Peroxide crosslinking creates carbon-carbon bonds (CC), which have extremely high bond energy and excellent heat resistance. These bonds rarely break under compression. For EPDM or NBR seals, whenever the customer requires low compression set, choose a peroxide system without hesitation. 2.Choose the Right Base Rubber For applications above 150°C, NBR will fail no matter how you adjust the formula. Upgrade directly to: – HNBR (Hydrogenated Nitrile Rubber) – EPDM (for water resistance, not oil resistance) – ACM (Acrylate Rubber) – FKM (Fluoroelastomer) 3.Strictly Implement Post-Curing For high-end FKM and silicone seals, never save on oven time! Post-curing is mandatory. It not only reduces compression set but also completely removes toxic or corrosive byproducts from the vulcanization process. 4. Optimize Fillers and Plasticizers Use carbon black with low structure and moderate particle size (such as N550, N774), or highly active silica (with coupling agents). High-structure carbon black tends to form a rigid network that restricts the recovery of molecular chains. Control the amount of liquid plasticizers, and choose low-volatility, extraction-resistant, eco-friendly oils or ester plasticizers. A compression set is essentially a microscopic war between destruction and reconstruction. The “failure” of a seal is not sudden death. It is the gradual compromise and rearrangement of the internal crosslinking network under high temperature and compression. As formulators and process engineers, our mission is to give rubber the strength to resist deformation —using the most stable chemical bonds (CC bonds, monosulfide bonds) and the most compact vulcanized network. Next time you face leakage issues, don’t blindly add more carbon black. Ask yourself: Is your vulcanization system correct?