How to precisely control the vulcanization process to reduce surface defects in the production of silicone watch bands?
Release Time : 2026-01-06
In the production of silicone watch bands, the vulcanization process is a crucial step determining product quality. Its precise control directly impacts the reduction of surface defects and the improvement of overall performance. The vulcanization process transforms linear silicone molecules into a three-dimensional network structure through a cross-linking reaction. The completeness of this transformation is affected by multiple factors, including temperature, time, pressure, and material properties. Fluctuations in any parameter can lead to surface defects such as wrinkles, bubbles, and cracks. Therefore, a comprehensive approach is needed, encompassing vulcanization system selection, temperature and time control, mold design optimization, pressure management, raw material and mixing processes, environmental control, and process monitoring, to achieve precise control of the vulcanization process.
The selection of the vulcanization system is fundamental. Different types of vulcanizing agents (such as platinum vulcanization systems and peroxide vulcanization systems) have different activation temperatures and reaction mechanisms. Platinum systems are suitable for medium- and low-temperature environments, and their reaction rates are temperature-sensitive; peroxide systems, on the other hand, require high temperatures to initiate decomposition. During production, a suitable vulcanization system must be selected based on the material characteristics and structural complexity of the silicone watch bands. It is crucial to ensure precise dosage and uniform dispersion of the vulcanizing agent to avoid surface defects caused by insufficient or excessive cross-linking.
Precise control of temperature and time is paramount. Excessive vulcanization temperature accelerates the vaporization of volatiles, causing premature surface crusting and preventing internal gas escape, resulting in bubbles. Insufficient temperature leads to incomplete cross-linking, resulting in a sticky surface. Insufficient vulcanization time results in incomplete curing, with residual low-molecular-weight substances precipitating during subsequent use; excessive time may cause over-vulcanization, leading to surface embrittlement. During production, the temperature-time-torque curve of the target silicone must be measured using a vulcanizing instrument to determine the scorch time, positive vulcanization time, and optimal vulcanization temperature, and these parameters are dynamically adjusted based on the thickness of the silicone watch bands. For example, thick-walled silicone watch bands require appropriately lower temperatures and longer times to avoid surface over-vulcanization and internal under-vulcanization; thin-walled silicone watch bands can benefit from higher temperatures and shorter times to improve efficiency.
Optimization of mold design is also critical. Mold temperature uniformity is crucial for vulcanization quality. Excessive temperature differences between mold areas can lead to significant variations in curing rate and shrinkage of the rubber compound, resulting in surface wrinkling or cracking. A high-precision mold temperature control system is necessary to minimize mold temperature fluctuations and implement zoned temperature control for complex silicone watch bands, setting differentiated temperature profiles for areas with different wall thicknesses. Furthermore, the mold venting channels must be rationally designed to ensure smooth gas discharge and prevent bubble formation due to poor venting.
Vulcanization pressure management is also critical. Appropriate vulcanization pressure promotes rubber compound filling of the mold cavity, improves density, and reduces defects such as incomplete filling and bubbles. However, excessive pressure may cause dimensional misalignment or internal stress concentration in the silicone watch bands, while insufficient pressure will result in insufficient rubber compound density, potentially leading to "false vulcanization" even with correct temperature and time. During production, the vulcanization pressure must be precisely set according to the silicone watch bands' structure and mold dimensions, ensuring pressure stability and avoiding fluctuations.
The stability of raw materials and the mixing process is a prerequisite. Fluctuations in raw material batches, moisture absorption during storage, or uneven mixing can increase the volatile content in silicone, creating a potential source of surface defects. During production, raw materials must be rigorously screened to ensure they meet performance requirements such as hardness and tensile strength. Mixing time and temperature must be controlled to ensure uniform dispersion of vulcanizing agents, colorants, and other additives. After mixing, the silicone should be allowed to stand to defoam, preventing air bubbles from forming during subsequent molding.
Environmental conditions are often overlooked but crucial. The temperature, humidity, and cleanliness of the production workshop affect the stability of the vulcanization process. For example, high temperatures may accelerate rubber aging, while high humidity may lead to moisture ingress and air bubbles. During production, the workshop temperature must be maintained within a suitable range, relative humidity must be kept low, and equipment and molds must be cleaned regularly to prevent contamination.
Process monitoring and dynamic adjustment are essential. During production, first-piece inspection and periodic sampling tests are necessary to monitor the hardness, elasticity, and appearance of silicone watch bands in real time to determine the degree of vulcanization. If under- or over-vulcanization is detected, temperature, time, or pressure parameters must be adjusted immediately. In addition, by using an online temperature recording system and infrared thermal imaging technology, abnormal temperature areas in the mold can be quickly detected, allowing for timely intervention and ensuring the stable operation of the vulcanization process.