Why flat vulcanization stage matters during the vulcanization process of silicone rubber?

From the vulcanization process diagram of the vulcanizing agent, it can be seen that during the flat vulcanization stage, the various physical and mechanical properties of the vulcanized rubber reach or approach the optimal point, or overall, they achieve the best comprehensive balance.

For natural rubber, its breaking strength and constant elongation increase to a certain maximum value with increasing vulcanization time, and then remain unchanged for a period of time. However, the elongation at break and permanent deformation are opposite, and the curve changes in the opposite direction after reaching a minimum value. This section of the crosslinking curve that maintains the highest value of certain indicators or the lowest value of another indicator is called a "vulcanization flat line" in production. The temperature and time taken for this period are respectively referred to as the positive vulcanization temperature and positive vulcanization time, collectively referred to as the positive vulcanization conditions.

Positive vulcanization, also known as the most suitable vulcanization, usually refers to the state when the performance of rubber products reaches the optimal value. The time required to reach the correct state is the positive vulcanization time, which corresponds to the vulcanization time of the "vulcanization flat line" section. In the early stage of positive vulcanization, it is called under sulfur, and in the later stage, it is over sulfur, which refers to the early and late stages outside the vulcanization flat line range.

Whether under sulfur or over sulfur, the physical and mechanical properties of the product are poor. The flattening stage of vulcanization is of great significance for selecting the correct conditions. For rubber materials with good flattening properties, it is difficult for products to experience under sulfur and over sulfur phenomena. Due to the optimal performance of the vulcanized rubber during the flat vulcanization stage, it is chosen as the range of positive vulcanization time. However, the vulcanization flat line is often very long, that is, the positive vulcanization time is a relatively long time interval. In actual production, a point in the first half of the flat line with tensile strength or constant elongation is often taken, or a turning point where the elongation at break or permanent deformation curve decreases. The corresponding vulcanization time on these curve points is called the positive vulcanization point, which is often used as a production process condition and is also considered as a weighted equilibrium time from the perspective of comprehensive equilibrium, It is a positive vulcanization point.

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