Highly elastic epdm article and curing method

Abstract

The application relates to the technical field of rubber material processing, and discloses a high-elasticity EPDM product and a vulcanization method. The method comprises the following steps: placing a blank in a vulcanization mold, applying a mold closing pressure and vacuumizing, heating to an initial temperature and keeping, injecting a vulcanization system composed of peroxide and an auxiliary crosslinking agent, increasing the pressure and heating to a first vulcanization temperature at a faster heating rate, immediately applying mechanical oscillation after reaching the first vulcanization temperature, stopping the oscillation, decreasing the pressure, cooling to a second vulcanization temperature and keeping, applying a constant magnetic field during the period, increasing the pressure after removing the magnetic field, heating to a third vulcanization temperature and keeping, cooling to room temperature again, opening the mold and taking out the product. The temperature, pressure, heating and cooling rate, oscillation parameters and magnetic field strength of each stage are controlled according to preset values, and specific proportional relationships are followed among the main parameters. Through the synergistic effect of multi-stage temperature and pressure time sequence, mechanical oscillation and magnetic field assistance, the elasticity of the vulcanized product can be improved without changing the formula of the rubber material.

Description

Technical Field

[0001] This invention relates to the field of rubber material processing technology, specifically to a high-elasticity EPDM rubber product and a vulcanization method. Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber, due to its saturated main chain structure, possesses excellent resistance to ozone aging, weathering, and chemical media, while also exhibiting a wide service temperature range. It is widely used in automotive sealing strips, wire and cable sheathing, waterproof membranes, and various shock-absorbing and cushioning components. With the continuous increasing demands for the performance of rubber elastic components from industries such as high-end equipment and new energy vehicles, how to further improve the elastic recovery capability and dynamic fatigue life of EPDM vulcanized products while maintaining its inherent aging resistance advantages has become a research hotspot in the field of materials processing.

[0003] Currently, the vulcanization process for EPDM products mainly follows the traditional hot vulcanization model. This involves filling the mold cavity with the pre-mixed vulcanization compound, then using an external heat source to raise the mold temperature to the vulcanization temperature and maintaining it for a certain period to induce a cross-linking reaction using peroxides or sulfur. While this process is mature and simple to operate, it reveals several shortcomings when dealing with products requiring high elasticity. First, in conventional vulcanization, heat is conducted from the mold surface to the interior of the compound. For thicker products, the internal heating rate lags behind the surface, causing the surface compound to reach the cross-linking activation energy first, while the internal cross-linking degree is insufficient, resulting in a non-uniform vulcanization structure of "externally matured, internally underdeveloped." This structural defect easily induces stress concentration under dynamic stress, degrading the overall resilience of the product. Second, existing vulcanization processes mostly employ a single-temperature range isothermal holding strategy. The cross-linking reaction rate exhibits a monotonous evolution characteristic of "fast-slow-to-stop" throughout the vulcanization cycle, lacking active control over the cross-linking network topology, making it difficult to promote a more uniform spatial distribution of cross-links. Furthermore, after the peroxide vulcanization system decomposes to generate free radicals, the crosslinking reaction process is highly dependent on the historical path of the temperature field. The unadjustable temperature curve in traditional processes limits the decoupling optimization space between crosslinking density and crosslinking bond type.

[0004] In recent years, a few studies have attempted to introduce ultrasonic or magnetic fields into the rubber vulcanization process. However, their application has mostly been limited to auxiliary dispersion treatment before vulcanization or post-treatment annealing after vulcanization, failing to systematically couple the external field effect with the multivariate time sequence of temperature, pressure, and time throughout the vulcanization cycle. Especially in the mid-temperature range, the crosslinking reaction is in the transition phase between the induction and rapid growth phases. Applying mechanical oscillations of specific frequency and amplitude at this time could theoretically promote molecular chain segment movement and adjust the spatial orientation of crosslinking precursors. However, current technology lacks a process parameter design scheme for applying oscillations to EPDM within this temperature window. Furthermore, the synergistic effect of pressure control and magnetic field intervention during the cooling phase also lacks systematic research, resulting in high residual stress and excessive elastic hysteresis loss in the finished product after vulcanization.

[0005] On the other hand, existing publicly available EPDM vulcanization patents mostly focus on improving the formulation system, such as by introducing plasticizers or modified fillers to improve the flowability or reinforcing effect of the rubber compound. However, the elasticity improvement brought about by formulation optimization often comes at the cost of sacrificing some heat resistance or processing safety. From a process perspective, without changing the basic rubber compound formulation, there is currently a lack of mature technical solutions to achieve a leap in elastic performance simply by reconstructing the vulcanization curve stepwise and using external field assistance. Especially for high-elasticity applications, the permanent deformation rate and dynamic stiffness stability of the product in repeated compression-recovery cycles are the core indicators for evaluating the quality of the process, and existing vulcanization methods have significant shortcomings in controlling these indicators. Summary of the Invention

[0006] The purpose of this invention is to provide a highly elastic EPDM rubber product and a vulcanization method to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a highly elastic EPDM rubber product and a vulcanization method, the method comprising: Step 1: Place the EPDM rubber blank in the vulcanizing mold, apply the initial mold closing pressure P0, and evacuate the mold cavity to a vacuum degree V0. Then, raise the mold temperature to the initial temperature T0 at a heating rate H1 and hold it for a time t0. Step 2: Inject a vulcanization system containing peroxide and crosslinking agent into the mold cavity, while adjusting the mold closing pressure to P1 and heating it to the first vulcanization temperature T1 at a heating rate H2. Immediately after reaching T1, apply mechanical oscillation with frequency f1 and amplitude A1 for a duration of t1. Step 3: Stop the mechanical oscillation, reduce the mold closing pressure to P2, and cool it down to the second vulcanization temperature T2 at a cooling rate C1, holding it for time t2, during which a constant magnetic field strength B is applied to the mold; Step 4: Remove the magnetic field, increase the mold closing pressure to P3, and heat to the third vulcanization temperature T3 at a heating rate H3, hold for t3, and then cool to room temperature at a cooling rate C2. Open the mold and remove the product. Among them, P0, V0, H1, T0, t0, P1, H2, T1, f1, A1, t1, P2, C1, T2, t2, B, P3, H3, T3, t3, and C2 are all preset parameters, and P1=1.2×P0, H2=1.5×H1, t1=0.8×t0, P2=0.6×P1, T2=0.7×T1, P3=1.3×P2, T3=1.2×T2, and C2=2×C1.

[0008] Furthermore, in step one, the initial mold clamping pressure P0 ranges from 2.0 MPa to 4.0 MPa, the vacuum degree V0 ranges from -0.095 MPa to -0.099 MPa, the heating rate H1 ranges from 3℃ / min to 6℃ / min, the initial temperature T0 ranges from 60℃ to 80℃, and the time t0 ranges from 5 min to 10 min.

[0009] Furthermore, in step two, the vulcanization system is composed of dicumyl peroxide, triallyl isocyanurate, and zinc stearate in a mass ratio of 100:40:5. The injection amount of the vulcanization system is 2.5% to 4.5% of the mass of the EPDM rubber blank, the injection pressure is 8 MPa to 12 MPa, and the injection time is 3 to 8 seconds.

[0010] Furthermore, in step two, the mold clamping pressure P1 ranges from 2.4 MPa to 4.8 MPa, the heating rate H2 ranges from 4.5℃ / min to 9℃ / min, the first vulcanization temperature T1 ranges from 150℃ to 170℃, the mechanical oscillation frequency f1 ranges from 20 kHz to 40 kHz, the amplitude A1 ranges from 10 μm to 30 μm, and the duration t1 ranges from 4 min to 8 min.

[0011] Furthermore, in step three, the mold clamping pressure P2 ranges from 1.44 MPa to 2.88 MPa, the cooling rate C1 ranges from 2 °C / min to 5 °C / min, the second vulcanization temperature T2 ranges from 105 °C to 119 °C, the time t2 ranges from 15 min to 25 min, and the constant magnetic field strength B ranges from 0.3 T to 0.6 T.

[0012] Furthermore, in step three, the constant magnetic field strength B is generated by an electromagnetic coil embedded in the upper and lower templates of the mold. The electromagnetic coil has 200 to 400 turns, and the DC current flowing through it is 2A to 5A. The direction of the magnetic field is perpendicular to the mold closing direction.

[0013] Furthermore, in step four, the mold clamping pressure P3 ranges from 1.872 MPa to 3.744 MPa, the heating rate H3 ranges from 5℃ / min to 8℃ / min, the third vulcanization temperature T3 ranges from 126℃ to 143℃, and the time t3 ranges from 10 min to 18 min.

[0014] Furthermore, in step four, the cooling rate C2 ranges from 4℃ / min to 10℃ / min, and the cooling process uses circulating water to cool the outer wall of the mold. The initial temperature of the circulating water is 20℃ to 25℃, the flow rate is 5L / min to 10L / min, and the room temperature is defined as 20℃ to 30℃.

[0015] Furthermore, in step two, the mechanical oscillation is ultrasonic oscillation with a sine wave waveform. The ultrasonic oscillation is generated by a piezoelectric transducer connected to the upper mold. The input power of the piezoelectric transducer is 500W to 1000W. The ultrasonic oscillation is applied intermittently, stopping for 10 seconds after every 30 seconds of oscillation, until the cumulative effective oscillation time reaches t1.

[0016] Furthermore, the present invention also includes a highly elastic EPDM rubber product, which is prepared by the above-described vulcanization method.

[0017] Compared with the prior art, the beneficial effects of the present invention are: In step one of this invention, after placing the EPDM rubber blank in the vulcanizing mold, an initial mold-closing pressure is applied and a high vacuum is drawn. Then, the mold temperature is raised to the initial temperature at a set heating rate and maintained for a certain period. This initial stage preheating and venting pretreatment of the blank before the vulcanizing system is injected. The vacuuming operation effectively removes residual air from the blank and mold cavity, preventing the formation of bubbles or pore defects inside the product due to gas expansion under subsequent high pressure and high temperature conditions. Simultaneously, maintaining the initial temperature makes the overall temperature field of the blank more uniform, creating favorable temperature conditions for rapid dispersion after the vulcanizing system is injected. The application of the initial mold-closing pressure promotes moderate creep flow in the blank during preheating, making it more closely conform to the mold cavity surface, which is beneficial for improving the dimensional accuracy and surface quality of the final product.

[0018] In step two, a vulcanization system containing peroxide and a crosslinking agent is injected into the mold cavity. Simultaneously, the mold closing pressure is increased to 1.2 times the initial pressure, and the heating rate is increased to 1.5 times the initial heating rate, rapidly raising the temperature to the first vulcanization temperature. The synergistic increase in mold closing pressure and heating rate in this step has multiple effects: the higher injection pressure and rapid heating immediately promote the rapid decomposition of the peroxide initiator after the vulcanization system is injected, generating free radicals, shortening the induction period, and avoiding the ineffective consumption of free radicals in the low-temperature region; at the same time, the increased pressure helps the vulcanization system penetrate and disperse in the rubber compound, ensuring that the crosslinking initiation points are distributed as evenly as possible within the rubber compound volume. Applying mechanical oscillations of a specific frequency and amplitude immediately after the first vulcanization temperature is reached is crucial—introducing oscillatory energy at the initial moment when the crosslinking reaction has just entered its rapid growth phase allows the molecular chain segments to gain sufficient mobility before the formation of crosslinking points, thereby adjusting the chain segment conformation to tend towards a more energy-favorable arrangement. The specific proportional relationship between the duration of oscillation and the initial holding time ensures the overlap between the oscillation intervention window and the most active stage of the cross-linking reaction, so that the oscillation energy is effectively used for the spatial rearrangement of the cross-linking precursors, rather than being wasted in the later stage when the reaction is already saturated.

[0019] After stopping mechanical oscillation in step three, the mold closing pressure is reduced to the second pressure level, and the temperature is lowered to the second vulcanization temperature at a set cooling rate. This cooling and pressure reduction transition section breaks the fixed pattern of monotonous temperature rise or constant temperature in traditional vulcanization processes. With the crosslinking reaction having initially formed a network skeleton, appropriately reducing temperature and pressure can temporarily slow down the rate of crosslinking reaction, allowing the molecular chain segments between the formed crosslinking points to have a chance to relax stress and release the local internal stress frozen inside the network due to rapid crosslinking. The effect of applying a constant magnetic field to the mold at this stage is that the magnetic field generates orientation forces on the polar groups or conductive filler particles in the rubber matrix, guiding the molecular chain segments to rearrange along a specific direction during the relaxation process of the crosslinking network, promoting the spatial distribution of crosslinking points to tend towards isotropy or ordered according to the design direction. The intervention of the magnetic field and the cooling relaxation form a synergistic effect. The magnetic field assists the directionality of chain segment movement through weak physical interactions, while the cooling provides conditions to slow down the reaction rate and extend the relaxation time window. Together, they make the topological structure of the vulcanized network more uniform and reduce stress concentration points caused by local fluctuations in crosslinking density.

[0020] In step four, after removing the magnetic field, the mold clamping pressure is increased to the third pressure level, and the temperature is raised to the third vulcanization temperature at a set heating rate for post-vulcanization. Then, the temperature is lowered to room temperature at a set cooling rate. This post-vulcanization process of increasing pressure and temperature has a clear physical significance: based on the homogeneous cross-linked framework formed in the previous stage, increasing temperature and pressure reactivates the remaining unreacted cross-linking active sites, causing the already initially ordered network structure to further increase its cross-linking density while retaining its homogeneity advantage, making the cross-linked network more complete. The specific proportional relationship between the third vulcanization temperature and the second vulcanization temperature, and between the third mold clamping pressure and the second mold clamping pressure, ensures that the thermal driving force in the post-vulcanization stage is moderate—excessive temperature will destroy the formed homogeneous structure, while excessive pressure may inhibit chain segment movement. The parameter ratios set in this invention achieve a balance between continued cross-linking and maintaining an ordered structure. After post-vulcanization, cooling at a high rate quickly freezes the homogeneous cross-linked network structure formed at high temperature, avoiding the degradation of the ordered structure due to molecular chain relaxation during slow cooling. Attached Figure Description

[0021] Figure 1 This diagram illustrates the working steps of a high-elasticity EPDM rubber product and its vulcanization method according to the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The scope of protection of the present invention is not limited to the specific embodiments; simple substitutions and parameter adjustments made by those skilled in the art based on the core technical solution of the present invention all fall within the scope of protection of the present invention.

[0023] The EPDM rubber blanks used in the various embodiments and comparative examples of this invention were from the same batch of commercial EPDM raw rubber, with a Mooney viscosity ML(1+4) of 65 at 125°C, an ethylene content of 52 wt%, and a third monomer content of 4.2 wt% ethylene-bis(norbornene). The dicumyl peroxide, triallyl isocyanurate, and zinc stearate used were all industrial-grade high-purity raw materials. The vulcanizing molds used in the experiments were equipped with electromagnetic coils, piezoelectric ultrasonic transducers, vacuum pumping systems, temperature control systems, pressure regulation systems, and circulating water cooling systems. All testing equipment was calibrated.

[0024] The performance testing standards for the EPDM rubber products prepared by this invention are as follows: tensile strength and elongation at break are tested according to GB / T 528-2009 standard; elastic recovery rate is tested according to GB / T 1681-2019 standard; Shore A hardness is tested according to GB / T531.1-2008 standard; and permanent deformation is tested according to GB / T 7759.1-2015 standard. All performance tests are completed at room temperature of 25℃ and humidity of 55%. Each group of samples is tested in parallel 5 times, and the average value is taken as the final test result. Example

[0025] A vulcanization method for highly elastic EPDM rubber products includes the following specific steps: Step 1: Place the pretreated EPDM rubber blank in a special vulcanizing mold, apply an initial mold closing pressure P0=3.0MPa, evacuate the mold cavity to a vacuum degree V0=-0.097MPa, then uniformly raise the mold temperature to the initial temperature T0=70℃ at a heating rate H1=4.5℃ / min, and maintain the constant temperature and pressure for t0=7.5min to complete the preheating and shaping of the blank, expel the air inside the cavity and the residual moisture in the blank, and avoid the generation of bubble defects during the vulcanization process.

[0026] Step two: Inject the vulcanizing system into the mold cavity at a ratio of 3.5% of the EPDM rubber blank mass. This vulcanizing system is composed of dicumyl peroxide, triallyl isocyanurate, and zinc stearate in a mass ratio of 100:40:5. The injection pressure of the vulcanizing system is controlled at 10 MPa, and the injection time is 5 seconds. Simultaneously, adjust the mold closing pressure to P1 = 1.2 × P0 = 3.6 MPa, and heat the mold at a uniform rate of H2 = 1.5 × H1 = 6.75℃ / min to the first vulcanization temperature T1 = 160℃. Once the preset temperature T1 is reached, intermittent ultrasonic mechanical oscillation is immediately applied through the piezoelectric transducer mounted on the upper mold. The oscillation waveform is a sine wave with an oscillation frequency of f1=30kHz, an amplitude of A1=20μm, and an input electrical power of 750W. The oscillation is applied in a manner of oscillation every 30s and stopping for 10s, with a cumulative effective oscillation duration of t1=0.8×t0=6min, which promotes the uniform penetration of the vulcanization system into the interior of the rubber blank and initially constructs a cross-linked network.

[0027] Step 3: Stop the ultrasonic mechanical oscillation and reduce the mold closing pressure to P2 = 0.6 × P1 = 2.16 MPa. Cool the mold at a uniform rate of C1 = 3.5℃ / min to the second vulcanization temperature T2 = 0.7 × T1 = 112℃, and maintain the constant temperature and pressure for t2 = 20 min. During the heat preservation process, a constant magnetic field is applied through an electromagnetic coil embedded inside the upper and lower mold plates. The magnetic field strength is B = 0.45T, the electromagnetic coil has 300 turns, and a DC current of 3.5A is applied. The direction of the magnetic field is perpendicular to the mold closing direction. The magnetic field is used to optimize the arrangement of rubber molecular chains and regulate the cross-linked network structure.

[0028] Step four: Remove the constant magnetic field from the mold, increase the mold closing pressure to P3 = 1.3 × P2 = 2.808 MPa, and heat to the third vulcanization temperature T3 = 1.2 × T2 = 134.4℃ at a heating rate H3 = 6.5℃ / min. Maintain the temperature and pressure at this time for t3 = 14 min to complete the deep cross-linking reaction. Then, cool the mold at a uniform rate C2 = 2 × C1 = 7℃ / min. During the cooling process, use circulating water to cool the outer wall of the mold. The initial temperature of the circulating water is 22℃, and the flow rate is 7.5 L / min, until the mold temperature drops to room temperature of 25℃. Open the mold and remove the molded EPDM rubber product to complete the vulcanization process. Example

[0029] A vulcanization method for highly elastic EPDM rubber products includes the following specific steps: Step 1: Place the same batch of EPDM rubber blanks into the vulcanizing mold, apply an initial mold closing pressure P0=2.0MPa, evacuate the mold cavity to a vacuum degree V0=-0.095MPa, and then uniformly raise the mold temperature to the initial temperature T0=60℃ at a heating rate H1=3℃ / min. Maintain constant temperature and pressure for t0=10min to fully preheat and soften the blanks and completely remove impurities and gases from inside the mold cavity.

[0030] Step two: Inject the vulcanization system into the mold cavity at a ratio of 2.5% of the EPDM rubber blank mass. The components and mass ratio of the vulcanization system are consistent with those in Example 1. The injection pressure is 8 MPa, and the injection time is 3 seconds. Simultaneously, adjust the mold closing pressure to P1 = 1.2 × P0 = 2.4 MPa, and uniformly raise the temperature to the first vulcanization temperature T1 = 150℃ at a heating rate H2 = 1.5 × H1 = 4.5℃ / min. After reaching the preset temperature, apply intermittent sinusoidal ultrasonic mechanical oscillation with an oscillation frequency f1 = 20 kHz, an amplitude A1 = 10 μm, and an input power of 500 W. The oscillation mode is 30 seconds of oscillation followed by a 10-second pause, with a cumulative effective oscillation duration t1 = 0.8 × t0 = 8 minutes, achieving low-speed and uniform penetration of the vulcanization system.

[0031] Step 3: Stop the ultrasonic mechanical oscillation and reduce the mold closing pressure to P2 = 0.6 × P1 = 1.44 MPa. Cool the mold at a uniform rate of C1 = 2℃ / min to the second vulcanization temperature T2 = 0.7 × T1 = 105℃, and maintain the constant temperature and pressure for t2 = 25 min. During the heat preservation process, a constant magnetic field with a magnetic field strength of B = 0.3T is applied through the electromagnetic coil built into the mold. The electromagnetic coil has 200 turns and a DC current of 2A is applied. The direction of the magnetic field is perpendicular to the mold closing direction, which slowly regulates the cross-linking structure of the rubber molecules.

[0032] Step four: Remove the constant magnetic field, increase the mold closing pressure to P3 = 1.3 × P2 = 1.872 MPa, and heat to the third vulcanization temperature T3 = 1.2 × T2 = 126℃ at a heating rate H3 = 5℃ / min. Maintain the temperature and pressure at this time for t3 = 18 min to complete deep cross-linking and curing. Then, cool down uniformly at a cooling rate C2 = 2 × C1 = 4℃ / min, with the circulating water initially at 20℃ and a flow rate of 5L / min. After cooling to room temperature (20℃), open the mold and remove the EPDM rubber product. Example

[0033] A vulcanization method for highly elastic EPDM rubber products includes the following specific steps: Step 1: Place the same batch of EPDM rubber blanks into the vulcanizing mold, apply an initial mold closing pressure P0=4.0MPa, evacuate the mold cavity to a vacuum degree V0=-0.099MPa, and then uniformly raise the mold temperature to the initial temperature T0=80℃ at a heating rate H1=6℃ / min. Maintain constant temperature and pressure for t0=5min to quickly complete the preheating and shaping of the blanks and efficiently expel the gas inside the mold cavity.

[0034] Step two: The vulcanization system is injected into the mold cavity at a ratio of 4.5% of the EPDM rubber blank mass. The components and mass ratio of the vulcanization system are consistent with those in Example 1. The injection pressure is 12 MPa, and the injection time is 8 seconds. Simultaneously, the mold closing pressure is adjusted to P1 = 1.2 × P0 = 4.8 MPa, and the temperature is uniformly increased to the first vulcanization temperature T1 = 170℃ at a heating rate H2 = 1.5 × H1 = 9℃ / min. After reaching the preset temperature, intermittent sinusoidal ultrasonic mechanical oscillation is applied. The oscillation frequency is f1 = 40 kHz, the amplitude is A1 = 30 μm, the input power is 1000 W, and the oscillation mode is 30 seconds of oscillation followed by a 10-second pause. The cumulative effective oscillation duration is t1 = 0.8 × t0 = 4 minutes, rapidly achieving full penetration and dispersion of the vulcanization system.

[0035] Step 3: Stop the ultrasonic mechanical oscillation and reduce the mold closing pressure to P2 = 0.6 × P1 = 2.88 MPa. Cool the mold at a uniform rate of C1 = 5℃ / min to the second vulcanization temperature T2 = 0.7 × T1 = 119℃, and maintain the constant temperature and pressure for t2 = 15 min. During the heat preservation process, a constant magnetic field with a magnetic field strength of B = 0.6T is applied through the electromagnetic coil built into the mold. The electromagnetic coil has 400 turns and a DC current of 5A is applied. The direction of the magnetic field is perpendicular to the mold closing direction, which optimizes the regularity of the cross-linked network.

[0036] Step four: Remove the constant magnetic field and increase the mold closing pressure to P3 = 1.3 × P2 = 3.744 MPa. Heat the mold at a rate of H3 = 8℃ / min to the third vulcanization temperature T3 = 1.2 × T2 = 143℃, and maintain the temperature and pressure at this rate for t3 = 10 min to rapidly complete the deep cross-linking reaction. Then, cool the mold at a uniform rate of C2 = 2 × C1 = 10℃ / min, using circulating water with an initial temperature of 25℃ and a flow rate of 10 L / min. After cooling to room temperature (30℃), open the mold and remove the EPDM rubber product.

[0037] This invention sets up three comparative examples, corresponding to traditional vulcanization methods that lack ultrasonic mechanical oscillation, lack constant magnetic field action, and do not use segmented gradient temperature and pressure vulcanization process. The other raw materials, billet specifications, and testing conditions are kept consistent with the examples to ensure the single variable of the experimental comparison.

[0038] Comparative Example 1: The traditional EPDM rubber vulcanization method omits the ultrasonic mechanical vibration step in step two, while the remaining process parameters are completely consistent with those in Example 1. The specific steps are as follows: Step 1: Place the EPDM rubber blank in the vulcanizing mold, apply an initial mold closing pressure P0=3.0MPa, evacuate to a vacuum degree V0=-0.097MPa, heat to 70℃ at a heating rate H1=4.5℃ / min, and hold at a constant temperature and pressure for 7.5min.

[0039] Step 2: Inject the same proportion of vulcanization system into the billet at 3.5% of the billet mass, with an injection pressure of 10 MPa and an injection time of 5 seconds; adjust the mold closing pressure to 3.6 MPa, heat to 160°C at 6.75°C / min, and hold for 6 minutes, without applying ultrasonic mechanical vibration throughout the process.

[0040] Step 3: After the heat preservation is completed, the pressure is reduced to 2.16 MPa, and the temperature is reduced to 112℃ at a rate of 3.5℃ / min. The temperature and pressure are kept constant for 20 minutes, and a vertical constant magnetic field of 0.45T is applied simultaneously.

[0041] Step 4: Remove the magnetic field, increase the pressure to 2.808 MPa, heat to 134.4℃ at 6.5℃ / min, hold the temperature for 14 minutes, cool to room temperature at 7℃ / min, open the mold and remove the product.

[0042] Comparative Example 2: The traditional EPDM rubber vulcanization method omits the constant magnetic field step in step three, while the remaining process parameters are completely consistent with those in Example 1. The specific steps are as follows: Step 1: Place the EPDM rubber blank in the vulcanizing mold, apply an initial mold closing pressure P0=3.0MPa, evacuate to a vacuum degree V0=-0.097MPa, heat to 70℃ at a heating rate H1=4.5℃ / min, and hold at a constant temperature and pressure for 7.5min.

[0043] Step 2: Inject the same proportion of vulcanization system into the billet at 3.5% of the billet mass, with an injection pressure of 10 MPa and an injection time of 5 seconds; adjust the mold closing pressure to 3.6 MPa, heat to 160°C at 6.75°C / min, and apply 30 kHz, 20 μm intermittent ultrasonic oscillation for 6 minutes.

[0044] Step 3: Stop the oscillation, reduce the pressure to 2.16 MPa, and cool down to 112°C at a rate of 3.5°C / min. Maintain the temperature and pressure for 20 minutes without applying a constant magnetic field.

[0045] Step 4: Increase the pressure to 2.808 MPa, heat to 134.4℃ at 6.5℃ / min, hold the temperature for 14 minutes, cool to room temperature at 7℃ / min, open the mold and remove the product.

[0046] Comparative Example 3: The traditional one-step vulcanization process eliminates the segmented gradient heating, depressurization, cooling, and auxiliary field processes of this invention, and adopts conventional isothermal and isothermal vulcanization. The specific steps are as follows: The same batch of EPDM rubber blanks were placed in a vulcanization mold. The mold closing pressure was kept constant at 3.0 MPa. The cavity was evacuated to -0.097 MPa. The temperature was increased to 160°C at 4.5°C / min. The same vulcanization system with a mass ratio of 3.5% was injected at one time. The mold was continuously vulcanized at constant temperature and pressure for 40 minutes. Then it was cooled to room temperature at 7°C / min. The mold was opened and the product was taken out. There was no ultrasonic oscillation or constant magnetic field auxiliary treatment throughout the process.

[0047] Table 1: Summary of core process parameters for each embodiment and comparative example Example 1 30kHz, 20μm, intermittent oscillation for 6 minutes 0.45T vertical constant magnetic field, heat preservation for 20 minutes Four-stage gradient temperature and pressure vulcanization Preheating to 70℃ → First vulcanization at 160℃ → Constant temperature conditioning at 112℃ → Deep vulcanization at 134.4℃ Example 2 20kHz, 10μm, intermittent oscillation for 8 minutes 0.3T vertical constant magnetic field, heat preservation for 25 minutes Four-stage gradient temperature and pressure vulcanization Preheating to 60℃ → First vulcanization at 150℃ → Constant temperature conditioning at 105℃ → Deep vulcanization at 126℃ Example 3 40kHz, 30μm, intermittent oscillation for 4min 0.6T vertical constant magnetic field, heat preservation for 15 minutes Four-stage gradient temperature and pressure vulcanization Preheating to 80℃ → First vulcanization at 170℃ → Constant temperature conditioning at 119℃ → Deep vulcanization at 143℃ Comparative Example 1 No ultrasonic oscillation 0.45T vertical constant magnetic field, heat preservation for 20 minutes Four-stage gradient temperature and pressure vulcanization The gradient temperature and pressure parameters are consistent with those in Example 1. Comparative Example 2 30kHz, 20μm, intermittent oscillation for 6 minutes No constant magnetic field Four-stage gradient temperature and pressure vulcanization The gradient temperature and pressure parameters are consistent with those in Example 1. Comparative Example 3 No ultrasonic oscillation No constant magnetic field Traditional one-step constant temperature and pressure vulcanization Single temperature 160℃, constant pressure 3.0MPa As shown in Table 1, all three embodiments of this invention employ a unique four-stage gradient temperature-pressure coupled ultrasonic oscillation and constant magnetic field assisted vulcanization process. Each process parameter strictly adheres to the numerical ratios defined in this invention, exhibiting uniform parameter gradient changes and strong adaptability. Comparative Example 1 omits only the ultrasonic oscillation step, retaining the magnetic field assisted and gradient temperature-pressure processes; Comparative Example 2 omits only the constant magnetic field assisted step, retaining the ultrasonic oscillation and gradient temperature-pressure processes; Comparative Example 3 completely abandons the core auxiliary process and gradient vulcanization mode of this invention, employing a traditional single vulcanization process. The differences in single variables among the groups are clear, allowing for precise differentiation of the influence mechanisms of each core process step on rubber vulcanization performance, providing a rigorous experimental basis for performance difference analysis. Furthermore, Examples 1, 2, and 3 employ gradient configurations of medium, low, and high parameters, respectively, comprehensively verifying the universality and superiority of the process parameter range of this invention. The parameters cover the entire defined value range of this invention, and the experimental data possess sufficient representativeness.

[0048] Table 2: Test Results of Mechanical Properties of Rubber Products in Each Example and Comparative Example

[0049] As shown in Table 2, the EPDM rubber products prepared in Examples 1-3 of this invention exhibit superior mechanical properties compared to the three comparative examples, demonstrating excellent overall performance with high strength, high elongation, and low deformation. Example 3 shows the best overall performance, with a tensile strength of 23.6 MPa, an elongation at break of 710%, and a permanent deformation of only 2.9%, representing the best performance among all groups. Example 1, using a medium-parameter process, exhibits balanced and stable performance. Example 2, even with a low-parameter process, maintains performance indicators far exceeding those of traditional processes, proving that the parameter range of this invention has good adaptability.

[0050] Comparing the data from Comparative Example 1 and Example 1, the absence of the ultrasonic oscillation process resulted in a 4.6 MPa decrease in tensile strength, a 139% decrease in elongation at break, and a 2.5% increase in permanent deformation. This indicates that intermittent ultrasonic mechanical oscillation can effectively break up agglomerated particles in the vulcanization system, promote uniform dispersion of the crosslinking agent, eliminate defects such as uneven local crosslinking and crosslinking blind zones within the rubber, and improve the overall integrity and mechanical stability of the rubber matrix. Comparing the data from Comparative Example 2 and Example 1, the absence of the constant magnetic field assistance resulted in a 3.3 MPa decrease in tensile strength, a 102% decrease in elongation at break, and a 1.7% increase in permanent deformation. This demonstrates that a vertical constant magnetic field can effectively regulate the arrangement of rubber molecular chains, inhibit disordered entanglement of molecular chains, optimize the density and uniformity of the three-dimensional crosslinking network, and reduce the probability of deformation in the vulcanized product.

[0051] Comparative Example 3 showed the worst performance in products manufactured using the traditional process. Compared to Example 1, the tensile strength decreased by 6.0 MPa, the elongation at break decreased by 190%, and the permanent deformation increased by 3.6%. This fully verifies that the four-stage gradient temperature-pressure coupled dual-auxiliary-field vulcanization process of this invention, compared to the traditional one-step isothermal vulcanization, can completely solve the problems of uneven vulcanization in the early stage, crosslinking defects in the middle stage, and residual stress in the later stage that exist in the traditional vulcanization process, thus improving the mechanical properties of rubber products. At the same time, the Shore A hardness of each group of products fluctuated less, indicating that the process of this invention can optimize elasticity and strength properties without changing the basic hardness characteristics of rubber, and adapt to the use requirements of high-elasticity rubber products.

[0052] Table 3: Test Results of Elasticity and Durability of Rubber Products in Each Example and Comparative Example

[0053] As shown in Table 3, the elasticity and durability data of the rubber products prepared in the embodiments of the present invention all exhibit elastic recovery rates higher than 95%, fatigue retention rates higher than 90%, vulcanization uniformity deviations lower than 2%, and internal defect rates lower than 0.6%. Their elasticity, durability, and product molding quality are significantly superior to those of the comparative examples. In Example 3, under the high-parameter process, the elastic recovery rate reaches 97.5%, the fatigue retention rate is 93.6%, the vulcanization uniformity deviation is only 0.9%, and there are almost no internal defects, resulting in the best molding quality.

[0054] Compared with Comparative Example 1 and Example 1, without ultrasonic oscillation assistance, the elastic recovery rate of the product decreased by 7.5%, the fatigue elasticity retention rate decreased by 9.1%, the vulcanization uniformity deviation increased by 3.3%, and the defect rate increased by 1.8%. The reason for this is that the micro-vibration effect of intermittent ultrasonic oscillation can achieve micron-level uniform dispersion of the vulcanization system, avoiding local over- or under-vulcanization, reducing defects such as internal porosity and uneven cross-linking from the source, while refining the cross-linking network structure, thus improving the rubber's elastic recovery ability and fatigue resistance.

[0055] Compared with Comparative Example 2 and Example 1, without the assistance of a constant magnetic field, the elastic recovery rate of the product decreased by 5.2%, the fatigue elasticity retention rate decreased by 5.6%, the vulcanization uniformity deviation increased by 2.0%, and the defect rate increased by 1.1%. A vertical constant magnetic field can induce the linear molecular chains of rubber to oriented and regularize, optimize the distribution of crosslinking nodes, reduce the elastic loss caused by disordered entanglement of molecular chains, and improve the stability of the crosslinking network, so that the product can still maintain excellent elastic properties under repeated tensile fatigue conditions.

[0056] Comparative Example 3 shows the most prominent drawbacks of the traditional process: an elastic recovery rate of only 85.7%, a fatigue retention rate of less than 80%, a vulcanization uniformity deviation as high as 6.8%, and a defect rate of 3.9%. The traditional one-step vulcanization process has a single heating rate and constant pressure. If the initial heating is too rapid, it will easily lead to premature vulcanization of the surface and delayed vulcanization of the interior, resulting in differences in internal and external cross-linking and generating a large number of internal defects. At the same time, without auxiliary field regularization and optimization, the molecular chain arrangement is chaotic, the cross-linking network has poor stability, and ultimately the product has poor elasticity, is prone to fatigue, and has low molding quality.

[0057] The data from the three sets of tables confirm that this invention, through precise control of four-stage gradient temperature and pressure, coupled with a dual-auxiliary process of ultrasonic oscillation dispersion and constant magnetic field regularization, with each process working in synergy and progressing step by step, first eliminates molding defects through preheating vacuum treatment, then achieves uniform dispersion of the vulcanization system through ultrasonic oscillation, regularizes the molecular structure with the help of magnetic field, and finally stabilizes the crosslinking network through deep vulcanization, effectively solving the technical pain points of uneven crosslinking, insufficient elasticity, poor fatigue performance, and high defect rate in traditional EPDM rubber vulcanization processes, thereby improving the elasticity, mechanical properties, and durability stability of rubber products.

[0058] This invention employs a strictly proportioned and synergistically optimized vulcanization process, featuring a segmented design with gradient heating, depressurization, and cooling, adapted to the molecular reaction characteristics of the entire EPDM vulcanization process. The initial low-temperature preheating vacuum stage thoroughly removes gas from the blank and mold cavity, preventing vulcanization bubble defects and softening the rubber blank, providing a foundation for the vulcanization system's penetration. The medium-temperature ultrasonic oscillation vulcanization stage utilizes micro-vibration to enhance the dispersion effect of the vulcanization system, initiating the initial cross-linking reaction and constructing a uniform primary cross-linking network. The medium-low temperature magnetic field conditioning stage, under moderate cooling and depressurization, uses a magnetic field to correct the disordered molecular chain structure generated during cross-linking, refining the cross-linking network pores and improving structural regularity. The high-temperature deep vulcanization stage further refines the three-dimensional cross-linking network, eliminates residual internal stress, and stabilizes the product's structure and performance.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A vulcanization method for highly elastic EPDM rubber products, characterized in that, Includes the following steps: Step 1: Place the EPDM rubber blank in the vulcanizing mold, apply the initial mold closing pressure P0, and evacuate the mold cavity to a vacuum degree V0. Then, raise the mold temperature to the initial temperature T0 at a heating rate H1 and hold it for a time t0. Step 2: Inject a vulcanization system containing peroxide and crosslinking agent into the mold cavity, while adjusting the mold closing pressure to P1 and heating it to the first vulcanization temperature T1 at a heating rate H2. Immediately after reaching T1, apply mechanical oscillation with frequency f1 and amplitude A1 for a duration of t1. Step 3: Stop the mechanical oscillation, reduce the mold closing pressure to P2, and cool it down to the second vulcanization temperature T2 at a cooling rate C1, holding it for time t2, during which a constant magnetic field strength B is applied to the mold; Step 4: Remove the magnetic field, increase the mold closing pressure to P3, and heat to the third vulcanization temperature T3 at a heating rate H3, hold for t3, and then cool to room temperature at a cooling rate C2. Open the mold and remove the product. Among them, P0, V0, H1, T0, t0, P1, H2, T1, f1, A1, t1, P2, C1, T2, t2, B, P3, H3, T3, t3, and C2 are all preset parameters, and P1=1.2×P0, H2=1.5×H1, t1=0.8×t0, P2=0.6×P1, T2=0.7×T1, P3=1.3×P2, T3=1.2×T2, and C2=2×C1.

2. The vulcanization method for a high-elasticity EPDM rubber product according to claim 1, characterized in that, In step one, the initial mold clamping pressure P0 ranges from 2.0 MPa to 4.0 MPa, the vacuum degree V0 ranges from -0.095 MPa to -0.099 MPa, the heating rate H1 ranges from 3℃ / min to 6℃ / min, the initial temperature T0 ranges from 60℃ to 80℃, and the time t0 ranges from 5 min to 10 min.

3. The vulcanization method for a high-elasticity EPDM rubber product according to claim 1, characterized in that, In step two, the vulcanization system is composed of dicumyl peroxide, triallyl isocyanurate and zinc stearate in a mass ratio of 100:40:

5. The injection amount of the vulcanization system is 2.5% to 4.5% of the mass of the EPDM rubber blank, the injection pressure is 8 MPa to 12 MPa, and the injection time is 3s to 8s.

4. The vulcanization method for a high-elasticity EPDM rubber product according to claim 1, characterized in that, In step two, the mold clamping pressure P1 ranges from 2.4 MPa to 4.8 MPa, the heating rate H2 ranges from 4.5℃ / min to 9℃ / min, the first vulcanization temperature T1 ranges from 150℃ to 170℃, the mechanical oscillation frequency f1 ranges from 20 kHz to 40 kHz, the amplitude A1 ranges from 10 μm to 30 μm, and the duration t1 ranges from 4 min to 8 min.

5. The vulcanization method for a high-elasticity EPDM rubber product according to claim 1, characterized in that, In step three, the mold clamping pressure P2 ranges from 1.44 MPa to 2.88 MPa, the cooling rate C1 ranges from 2 °C / min to 5 °C / min, the second vulcanization temperature T2 ranges from 105 °C to 119 °C, the time t2 ranges from 15 min to 25 min, and the constant magnetic field strength B ranges from 0.3 T to 0.6 T.

6. The vulcanization method for a high-elasticity EPDM rubber product according to claim 5, characterized in that, In step three, the constant magnetic field strength B is generated by an electromagnetic coil embedded in the upper and lower mold templates. The electromagnetic coil has 200 to 400 turns and a DC current of 2A to 5A is applied. The direction of the magnetic field is perpendicular to the mold closing direction.

7. The vulcanization method for a high-elasticity EPDM rubber product according to claim 1, characterized in that, In step four, the mold closing pressure P3 ranges from 1.872 MPa to 3.744 MPa, the heating rate H3 ranges from 5℃ / min to 8℃ / min, the third vulcanization temperature T3 ranges from 126℃ to 143℃, and the time t3 ranges from 10 min to 18 min.

8. The vulcanization method for a high-elasticity EPDM rubber product according to claim 7, characterized in that, In step four, the cooling rate C2 ranges from 4℃ / min to 10℃ / min, and the cooling process uses circulating water to cool the outer wall of the mold. The initial temperature of the circulating water is 20℃ to 25℃, the flow rate is 5L / min to 10L / min, and the room temperature is defined as 20℃ to 30℃.

9. The vulcanization method for a high-elasticity EPDM rubber product according to claim 1, characterized in that, In step two, the mechanical oscillation is ultrasonic oscillation with a sine wave waveform. The ultrasonic oscillation is generated by a piezoelectric transducer connected to the upper mold. The input power of the piezoelectric transducer is 500W to 1000W. The ultrasonic oscillation is applied intermittently, with a 10-second pause after every 30 seconds of oscillation, until the cumulative effective oscillation time reaches t1.

10. A highly elastic EPDM rubber product, characterized in that, The product is prepared by the vulcanization method according to any one of claims 1 to 9.

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