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Vulcanized rubber is stronger and more elastic than natural rubber.
What is Vulcanization?
Vulcanization is the process of transforming raw rubber, which is like dough, into elastic, wear-resistant, and heat-resistant “cured rubber” through heating and the action of chemical agents (mainly sulfur).
In the rubber industry, raw rubber fresh out of the factory is called “raw rubber”. Although raw rubber has plasticity, it has extremely low strength and is very unstable: in the hot summer, it becomes sticky like chewing gum and may even run; in the cold winter, it freezes and becomes as hard as a rock.
Vulcanization is the process of heating and adding chemical additives (such as sulfur) to cause unstable raw rubber to undergo a chemical reaction, thereby transforming it into tough, elastic, heat- and cold-resistant “cured rubber”.
To help you understand better, let’s use a vivid analogy:
Before vulcanization (raw rubber): It’s like a bowl of cooked noodles. Each noodle is independent; if you pull hard, the noodles will slip, break, or clump together.
After vulcanization (cured rubber), it’s like a tightly woven net. The vulcanizing agent builds countless tiny “bridges” (chemical cross-links) between the noodles, connecting the individual noodles into a whole.
Commonly used additives include zinc oxide (activator), guanidines, thiazoles, xanthates, thiurams (accelerators), acetic acid, calcium chloride (coagulant), amines, phenols, and phosphites (antioxidants), pigments, oils, and defoamers.
Active vulcanization must be avoided during the mixing stage to prevent cracking of the rubber during molding or shaping.
The principle of the vulcanization process
Vulcanization is not merely a simple heating step but a precisely controlled physicochemical transformation process. It transforms a ductile rubber compound, constrained by a mold, into an elastic product with a fixed shape and high performance.
The entire process typically comprises the following three key stages:
1. Preparation and Filling (Physical Stage)
First, the rubber compound, containing vulcanizing agents, reinforcing agents, and antioxidants, is placed into a preheated mold. Under immense pressure, the rubber fills every tiny cavity of the mold, obtaining the initial shape of the product. At this point, heat transfer begins, and the rubber molecules gain energy and begin vigorous movement.
2. Crosslinking and Shaping (Chemical Reaction Stage)
As the temperature reaches the activation point of the vulcanizing agent, the chemical reaction officially begins. Crosslinking bonds are rapidly established between the rubber molecular chains, and the molecular structure changes from linear to a three-dimensional network.
In this stage, the properties of the rubber undergo a dramatic change: it gradually loses its plasticity, becomes hard and elastic, and is ultimately firmly “locked” in the shape of the mold.
3. Post-treatment and Stabilization (Cooling and Inspection)
When the crosslinking density reaches the optimal equilibrium point, the mold must be rapidly cooled to terminate the reaction and prevent “over-vulcanization,” which would cause the product to become brittle. After demolding, some precision products require secondary vulcanization (oven baking) to completely volatilize residual gases and further stabilize the molecular structure, ensuring the product’s performance remains stable and durable in future use.
Who invented rubber vulcanization technology?
Rubber vulcanization technology was accidentally discovered in 1839 by American inventor Charles Goodyear (1800-1860) and was granted a US patent in 1844 (patent number 3,633).
Key Aspects of Rubber Vulcanization:
- Discovery Opportunity: In 1839, a man accidentally dropped a sample of sulfur-laced rubber onto a hot furnace. He unexpectedly discovered that the material did not become sticky when heated and remained flexible after cooling, overcoming the thermal performance limitations of raw rubber—a breakthrough in the Lemelson-MIT Program.
- Technology Naming: After reverse engineering, British engineer Thomas Hancock named the process “vulcanization” in 1843, after the Roman god of fire, Vulcan.
- Industry Impact: Vulcanization technology laid the foundation for the modern rubber industry, and the Goodyear Tire Company was named after it in commemoration.
What are the uses and advantages of vulcanized rubber?
1. Four core advantages of vulcanized rubber
1. Exceptional elasticity
Features: Vulcanized rubber quickly returns to its original shape after being stretched, compressed, or bent.
Principle: The three-dimensional network structure acts like a spring, allowing deformation while limiting excessive slippage.
Value: This is rubber’s unique property, making it a preferred material for shock absorption and sealing.
2. Excellent physical and mechanical properties (strength & Durability)
Features: Significantly increased strength, wear-resistant, tear-resistant, and fatigue-resistant.
Comparison: Raw rubber breaks easily when torn, while vulcanized rubber can withstand enormous tensile and compressive forces.
Value: Adaptable to harsh mechanical friction environments (such as tires).
3. Good thermal stability
Features: Non-sticky when heated, non-brittle when cooled.
Comparison: Raw rubber melts and flows in summer and freezes solid in winter. Vulcanized rubber maintains stable performance over a wide temperature range (typically -50℃ to +150℃, with specialty rubbers having an even wider range).
Value: Suitable for all-weather, all-terrain applications.
4. Chemical stability and insulation
Features: Resistant to acid and alkali corrosion (depending on the formulation) and an excellent electrical insulator.
Value: Protects equipment from chemical corrosion or electrical damage.
2. Main uses of vulcanized rubber
1. Transportation (Largest Application Area)
Tires: Car, truck, and aircraft tires (utilizing their high wear resistance and elasticity).
Sealing Systems: Engine oil seals, O-rings, gaskets (preventing oil and water leaks).
Shock Absorbers: Suspension system shock absorbers and bump blocks (absorbing bumps).
2. Industrial manufacturing and machinery
Transmission belts and conveyor belts: Conveyor belts in factory assembly lines, automotive belts.
Seals: Sealing rings for various pipes and valves.
Rubber rollers: Rubber rollers for printing presses and papermaking machines.
3. Electronics and Electrical
Cable sheath: The outer sheath of wires and cables (utilizing its insulation and protective properties).
Buttons and casings: Remote control buttons, mobile phone protective cases.
4. Medical and Health
Medical gloves: Latex or nitrile gloves.
Catheters and balloons: Utilizing their biocompatibility and elasticity.
5. Daily life
Footwear materials: shoe soles and heels (wear-resistant and slip-resistant).
Daily necessities: Erasers, hot water bottles, sealing rings (thermos lids), and rain boots.
6. Architecture and Civil Engineering
Waterproofing materials: Rubber asphalt, waterproof membrane.
Bridge bearings: Used to cushion bridge vibrations and displacements.
Is vulcanized rubber environmentally friendly?
While vulcanized rubber is significantly tougher and more resistant to decomposition than natural rubber, studies show it is biodegradable in high-temperature composting environments. Its primary advantage lies in extreme durability, which actually facilitates refurbishment and reuse. This resilience allows products like old tires to be retreaded or repurposed into asphalt, landscaping mulch, turf infill, or livestock mats, in addition to being compounded into new materials.
Conclusion on Vulcanized Rubber
The vulcanization process significantly improves the mechanical properties and durability of rubber through cross-linking reactions. Based on technological breakthroughs by Hancock and Goodyear, this process enables low-cost, large-scale production, making rubber a stable material that can be reused for extended periods.
KODAO-type ring vulcanization
KODA possesses core in-house vulcanization capabilities and excels in custom O-rings. We employ a thermal cross-linking process to fuse rubber ropes, creating a seamless, high-strength connection that ensures superior product performance.
If you are a manufacturer or distributor and need sealing products, please contact us for a free quote or discuss your options with our knowledgeable and friendly staff.
