The uniformity of the vulcanization process for silicone watch straps directly affects their physical properties and lifespan, requiring a comprehensive approach encompassing multiple dimensions, including vulcanization system selection, temperature and time control, mold design optimization, and dynamic monitoring. Precise matching of the type and amount of vulcanizing agent is fundamental. Organic peroxide vulcanizing agents need to be added in proportions adjusted according to the thickness of the silicone watch strap to avoid blooming or under-vulcanization due to excessive dosage. For example, solid silicone watch straps commonly use DCP (benzoyl peroxide) as a vulcanizing agent, and its decomposition temperature must strictly correspond to the vulcanization temperature to ensure sufficient and uniform cross-linking reaction. Liquid silicone watch straps often employ a platinum vulcanization system, achieving low-temperature rapid vulcanization through a two-component catalysis, reducing localized insufficient cross-linking caused by temperature gradients.
The coordinated control of vulcanization temperature and time is crucial. During the vulcanization of solid silicone watch straps, if the temperature is too high, the surface layer may prematurely vulcanize, forming a hard shell that hinders internal heat transfer, leading to under-vulcanization in the central area; conversely, if the temperature is too low, the vulcanization time will be prolonged, potentially causing excessive degradation of the molecular chains. In practice, the "temperature-time-torque curve" of the target silicone needs to be measured using a vulcanizing apparatus to determine the optimal vulcanization time range. For example, the optimal vulcanization time for a certain medical-grade silicone watch strap at 180℃ is approximately 90 seconds. In actual production, a safety margin of 10%-20% is reserved to compensate for equipment errors or variations in the silicone compound. Liquid silicone watch straps, due to their good fluidity, can utilize higher temperatures to shorten the vulcanization cycle, but this requires a vacuum degassing process to prevent residual air bubbles from affecting uniformity.
Mold design plays a crucial role in achieving uniform vulcanization. For thick-walled silicone watch straps, the mold must employ a progressive heating structure, controlling the temperature difference between the cavity surface and center within ±2℃ using a mold temperature controller. For example, a 5mm thick sports watch strap mold will have multiple temperature control zones, gradually decreasing the temperature from the inlet to the distal end to compensate for heat loss during silicone flow. The parting surface design needs to optimize the venting groove layout to prevent trapped air from causing incomplete local vulcanization. For two-tone silicone watch straps, the mold must employ a two-stage pressing structure to ensure sufficient interface fusion of the two colored rubber materials during cross-linking, avoiding delamination or color difference.
Dynamic monitoring and parameter calibration are the last line of defense for ensuring uniformity. During the first-piece inspection, the hardness values of different parts of the strap must be tested using a Shore hardness tester, and the fluctuation range should be controlled within ±2A. If the hardness difference between the edge and the center exceeds the standard, the mold temperature must be adjusted or the holding time extended. During production, samples are taken every hour for tear strength testing. Under-cured samples show a sticky tear surface, while over-cured samples exhibit brittle fracture. Through real-time data feedback, vulcanization parameters can be dynamically corrected, for example, adjusting the vulcanization temperature from 180℃ to 175℃ and extending the holding time by 10 seconds to optimize the cross-linking density.
Post-processing plays a supplementary role in ensuring vulcanization uniformity. Secondary vulcanization can eliminate low-molecular-weight volatiles generated during primary vulcanization, stabilizing the physical properties of the strap. For example, medical silicone watch straps require a second vulcanization at 200℃ for 1 hour to increase tensile strength by 15% and reduce compression set by 30%. Surface treatments such as sandblasting or coating must be performed after uniform vulcanization; otherwise, inconsistent substrate hardness can lead to variations in coating adhesion.
Environmental control is an easily overlooked aspect. Temperature and humidity in the mixing workshop must be strictly controlled. Excessive temperature can cause premature decomposition of the vulcanizing agent, while excessive humidity can cause the rubber compound to absorb moisture and form bubbles. For example, the production workshop for liquid silicone watch straps needs to maintain 23℃±2℃ and relative humidity of 50%±5% to ensure that the mixing of components A and B does not cause localized curing abnormalities due to environmental differences.
The uniformity control of the silicone watch strap vulcanization process must be maintained throughout the entire process, from raw material preparation and mold design to production monitoring and post-processing. Through precise matching of the vulcanization system, dynamic optimization of temperature and time parameters, innovative mold structure, and real-time quality feedback, the consistency of the watch strap's physical properties can be achieved, meeting the stringent reliability requirements of high-end scenarios such as medical and sports applications.
