In the production of silicone two-color straps, precise control of vulcanization time is crucial for ensuring the bonding strength between the two colors. The vulcanization process transforms silicone molecular chains into a three-dimensional network structure through a cross-linking reaction. Since two-color straps involve the co-vulcanization of two different colors or materials of silicone, the interfacial bonding strength is directly affected by the vulcanization time. Insufficient vulcanization time may lead to delamination or peeling at the two-color interface due to inadequate cross-linking; excessive vulcanization time may cause material degradation and abnormally increased hardness, thus weakening the bonding strength. Therefore, comprehensive optimization from multiple dimensions, including vulcanization mechanism, process parameters, and equipment control, is necessary to achieve high-quality production of silicone two-color straps.
The setting of the vulcanization time must be based on the characteristics of the silicone material and the selection of the vulcanization system. Silicone two-color straps typically use liquid silicone rubber (LSR) or solid silicone rubber, which have different vulcanization temperature ranges. Liquid silicone rubber commonly uses a vulcanization temperature of 150-200℃, while solid silicone rubber typically uses 160-190℃. The type of vulcanizing agent (such as platinum vulcanization system or peroxide vulcanization system) also affects the reaction rate: platinum systems can react rapidly above 150℃, while peroxide systems (such as DCP) require temperatures above 170℃ to decompose and initiate cross-linking. During production, the "temperature-time-torque curve" of the target material needs to be measured using a vulcanizer to obtain key parameters such as scorch time (T10, safe operating window) and optimal vulcanization time (T90, performance peak), providing a theoretical basis for setting the vulcanization time.
The structural complexity of two-color watch straps places higher demands on vulcanization time. Silicone two-color straps are typically formed through secondary injection molding or multi-color co-extrusion processes, and the contact interfaces of different colored silicones need to reach the optimal vulcanization state simultaneously. If the vulcanization rates of the two materials differ significantly, one material may be over-vulcanized while the other is under-vulcanized at the interface, thus reducing the bonding strength. Therefore, simultaneous vulcanization needs to be achieved through formulation adjustments: for example, adding accelerators to slow-curing materials, or using a staged heating process for fast-curing materials, first pre-curing at a low temperature and then main curing at a high temperature, ensuring that the two-color interfaces complete cross-linking at the same time point.
Mold temperature uniformity is a key factor in controlling vulcanization time. Silicone has poor thermal conductivity, and mold temperature fluctuations can lead to inconsistent vulcanization levels in different parts of the strap. For example, thick-walled areas may be under-cured due to slow heat transfer, while thin-walled areas may degrade due to overheating. Modern production lines use high-precision mold temperature controllers to control mold temperature fluctuations within ±2℃, and use zoned temperature control technology to set differentiated temperature profiles for areas with different wall thicknesses. For two-color straps, the flow channel layout also needs to be optimized in the mold design to ensure balanced pressure of the two rubber materials during filling, avoiding interface separation due to flow differences.
Dynamic monitoring and adjustment of vulcanization time is a necessary means to ensure bonding strength. During production, first-piece inspection is required to verify vulcanization parameters: testing strap hardness (Shore A hardness tester), tear strength (ASTM D624 Method B), and interfacial bonding strength. If under-vulcanization (sticky surface, low hardness) or over-vulcanization (brittle surface, white fold marks) is detected, temperature or time must be adjusted promptly. For example, for under-vulcanization, the temperature can be increased by 5-10℃ or the time extended by 10-30 seconds; for over-vulcanization, the temperature should be decreased or the time shortened. Simultaneously, periodic sampling inspections (e.g., 1-2 pieces per hour) can monitor parameter drift during production to ensure vulcanization stability.
Environmental factors and material management indirectly affect vulcanization time control. The production workshop temperature should be maintained at 23±3℃, and humidity below 50% to reduce the interference of environmental fluctuations on the vulcanization reaction. The compound should be stored according to the first-in, first-out principle. Once opened, the material should be used within 8 hours to avoid a decrease in vulcanizing agent activity leading to under-vulcanization. For rubber compounds requiring long-term storage, nitrogen-protected packaging and refrigeration are necessary. Process parameters must be retested and adjusted before use.
The application of intelligent equipment and digital technology can significantly improve the accuracy of vulcanization time control. Modern vulcanizing machines are equipped with real-time temperature recording systems and infrared thermal imaging technology, enabling rapid location of abnormal mold temperature areas. Online rheological monitoring devices can directly measure the actual vulcanization degree of the rubber compound in the mold cavity, achieving closed-loop control. Furthermore, by collecting key parameter data through Statistical Process Control (SPC) charts and calculating the process capability index (CPK), process deviations can be predicted in advance, avoiding batch quality problems.
Precise control of vulcanization time is a core challenge in the production of silicone two-color straps. Through material property analysis, mold temperature optimization, dynamic monitoring and adjustment, and the application of intelligent technologies, synchronous vulcanization and uniform bonding of the two-color interface can be achieved, thereby improving the structural strength and service life of the strap. In the future, with the popularization of intelligent manufacturing technology, vulcanization processes will further develop towards digitalization and refinement, providing a more reliable guarantee for the high-quality production of silicone two-color straps.
