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?