For the purchasers, application engineers and supply chain managers of precision rubber products, the "three elements of vulcanization" are not merely process parameters, but the core variables that determine the "long-term reliability, adaptability to working conditions and compliance safety" of the products. From a professional perspective of "process influencing product performance", the following breaks down the deep roles of the three elements and provides a systematic solution in combination with waste cases to help you shift from "passive acceptance" to "active control of supply chain quality".
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The three elements of vulcanization: Building the "Golden Triangle" of Rubber Product Performance
The essence of rubber vulcanization is that "linear polymer chains form a three-dimensional network structure through cross-linking reactions", and the three elements of temperature, time and pressure respectively define the upper limit of product performance from the three dimensions of "reaction rate, cross-linking degree and structural density".
1. Vulcanization temperature: Regulates the rate of crosslinking reaction and determines the "working condition tolerance" of the product
Temperature serves as the "energy switch" for crosslinking reactions, and its control accuracy directly affects the "crosslinking density" of rubber - this is the core indicator that determines the product's heat resistance, wear resistance, and anti-aging performance.
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① Low-temperature risk (above 5℃ below the process set value) : Insufficient crosslinking reaction, low crosslinking density, and the product will exhibit the characteristics of "low elasticity and high permanent deformation". For instance, if the vulcanization temperature of the sealing ring of a vehicle engine (which needs to withstand a high temperature of 150℃) is insufficient, under long-term high-temperature working conditions, creep will occur due to "incomplete curing of the molecular chain", leading to oil leakage and engine lubrication failure. Medical silicone tubes (which need to be disinfected repeatedly) may precipitate due to "incomplete cross-linking of small molecule substances" if the cross-linking is not sufficient, which does not meet the ISO 10993 biocompatibility standard and poses safety and compliance risks.
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② High-temperature risk (above 5℃ above the process set value) : Excessive crosslinking accompanied by thermal oxidative aging leads to molecular chain breakage, resulting in the product presenting the characteristics of "high hardness and low toughness". For example:If the FKM sealing ring of the micro pump valve (which relies on elasticity to achieve dynamic sealing) is overly sulfurized at high temperatures, the sealing surface will crack due to the "brittleness of the elastic body", and the air tightness of the pump body will drop by more than 30%.Rubber products with metal skeletons (such as rubber-coated parts), when the temperature exceeds 180℃, will cause thermal degradation of the adhesive on the metal surface, the molecular chains will break, and the rubber film will lose its stickiness. At the same time, excessive high temperatures can cause "over-sulfurization aging" of rubber, and the bonding surface with the metal will separate due to "cracking of the rubber layer".
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③ Key coupling relationship = coordinated control of temperature and time
According to the Arrunius equation, for every 10℃ increase in temperature, the cross-linking reaction rate approximately doubles, and the corresponding vulcanization time is shortened by 50% (for example, 7.5 minutes at 150℃ and only 3.75 minutes at 160℃). However, it should be noted that for precision products with a thickness greater than 8mm, "step heating" or "constant temperature and pressure holding" should be adopted to ensure the "uniform cross-linking degree of the inner and outer layers". If the supplier only pursues efficiency and ignores the "uniformity of the temperature field", the product will have the "core defect" of "excessive sulfur on the surface layer and insufficient sulfur on the inner layer", laying the hidden danger of early failure.
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2. Vulcanization pressure: Ensures structural density and determines the "sealing reliability" of the product
The core function of vulcanization pressure is to "eliminate the internal voids of the rubber compound and promote the interface bonding between the rubber compound and the mold/frame", and its control accuracy directly affects the "density" and "interface bonding strength" of the product.
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① Low-pressure risk (above 10% of the process set value) : Insufficient fluidity of the rubber compound, unable to fully fill the mold cavity, and internal air bubbles cannot be discharged, resulting in: "pinhole defects" on the surface of the sealing parts, and "micro-leakage" is prone to occur in the hydraulic/pneumatic system. For example, if there are pinholes in the sealing ring of the vehicle braking system, it will cause a delay in braking response. The interface between the rubber and the metal skeleton (such as the threaded skeleton of the sensor sealing ring) is not tightly combined, and "interface peeling" occurs under vibration conditions, losing the sealing function.
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② High-pressure risk (more than 10% of the process set value) : Excessive extrusion of the rubber compound leads to "excessive flash", or deformation of the mold cavity, causing: precision dimensional parts (such as the sealing rings of micro pumps and valves, with a tolerance requirement of ±0.05mm) to have "dimensional out-of-tolerance", unable to fit the assembly clearance of the customer's equipment; Products with thin-walled structures (such as medical silicone valves) may experience "structural deformation", which affects the opening and closing accuracy of the valve and leads to fluid control failure.
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3. Vulcanization time: Ensures sufficient crosslinking and determines the "life stability" of the product
Vulcanization time is a necessary guarantee for "achieving the optimal degree of crosslinking reaction", and its core is to control the "optimum vulcanization point" - that is, the state where the physical and mechanical properties of the product (tensile strength, tear strength, elasticity) reach a balance.
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① Under-sulfurization risk (< 80% of the optimum vulcanization time) : The crosslinking reaction is not completed, and the product shows the characteristics of "low strength and high swelling property". For instance, if the sealing ring of a drinking water pipeline is short of sulfur, under the condition of long-term contact with water, it will swell due to "incomplete cross-linking of molecular chains", and the adhesion of the sealing surface will decrease, leading to pipeline leakage. If oil-resistant rubber parts (such as transmission oil seals) lack sulfur, they will expand in volume in the oil due to "insufficient oil resistance", resulting in "deformation of the oil seal lip" and loss of sealing ability.
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② Over-sulfurization risk (> 50% of the optimum vulcanization time) : Excessive crosslinking accompanied by molecular chain degradation, resulting in the product presenting the characteristics of "high hardness and low elasticity". For instance, if the shock-absorbing rubber pad is overly sulfurized, it will lose its shock-absorbing effect due to the "increase in elastic modulus", resulting in excessive vibration and noise of the equipment. If dynamic seals (such as the sealing rings of reciprocating cylinders) are over-sulfurized, they will wear out more rapidly due to the "increased coefficient of friction", and their service life will drop sharply from 3 million times to less than 1 million times.
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③ Red line of process discipline: The vulcanization time must not be adjusted at will
The optimum vulcanization time needs to be determined through the "vulcanization instrument test" (such as using a rotorless vulcanization instrument to measure the T90 value). It is recommended that you clearly stipulate in the quality agreement that "a vulcanization curve report must be provided for each batch" to ensure compliance with time control.
