Vulcanization is also known as crosslinking and curing.When vulcanizing agent and accelerator are added to the rubber, the linear macromolecules are transformed into a three-dimensional network structure under certain temperature and pressure conditions.As the first use of sulfur to achieve natural rubber crosslinking, it is called vulcanization.
The first factor affecting the vulcanization process of rubber: vulcanization temperature
Vulcanization temperature of rubber is the basic condition for vulcanization reaction (crosslinking reaction) of rubber, which directly affects vulcanization speed and quality of rubber products.Like all chemical reactions, the vulcanization reaction is accelerated with the increase of temperature, and it is easy to generate more low sulfur crosslinks.When the vulcanization temperature is low, the speed is slow and the formation efficiency is low.The vulcanization temperature is generally applicable to van't hoff's law, that is, for every 8~10 rise in temperature (approximately equivalent to a surface pressure of steam pressure), the reaction speed is approximately doubled;Or about half of the reaction time.
Two, the second factor affecting the vulcanization process of rubber: vulcanization pressure
Vulcanization pressure of rubber is an important factor to ensure the geometric size, structural density and physical and mechanical properties of rubber parts. At the same time, it can also ensure the smooth surface of parts without defects and meet the sealing requirements of rubber products.The main functions are as follows:
(1) to prevent bubbles in the vulcanization molding process of mixing rubber and improve the compactness of products;
(2) to provide the power of the filling flow of the glue, so that the glue can fill the whole mold cavity within the specified time;
(3) improve the adhesion of rubber and clamps (curtains, etc.) and the bending resistance of rubber products;
(4) improve the physical and mechanical properties of rubber products.
The selection of vulcanization pressure needs to consider such as the formula of the glue, the structure of the mold, the type of vulcanization equipment (plate vulcanizing machine, injection vulcanizing machine, injection vulcanizing machine, vacuum vulcanizing machine, etc.), the structure of the product characteristics and several other factors.
General principles for selection of vulcanization pressure:
(1) the glue hardness is low, pressure should choose small, high hardness choice;
(2) thin products choose small, thick products choose large;
(3) the product structure is simple to choose small, the structure is complex to choose large;
(4) mechanical properties require high choice, low choice;
(5) when the vulcanization temperature is higher, the pressure can be smaller; when the temperature is lower, the pressure should be higher.
The third factor affecting the vulcanization process of rubber: vulcanization time
Vulcanization time is closely related to the temperature of vulcanization, in the vulcanization process, the physical and mechanical properties of vulcanized rubber to reach or close to the best point, this degree of vulcanization is called positive vulcanization or the most suitable vulcanization.The vulcanization time required to achieve positive vulcanization at a certain temperature is called positive vulcanization time.When the rubber formula and vulcanization temperature is certain, vulcanization time determines the degree of vulcanization, different sizes and wall thickness of rubber products through the control of vulcanization time to control the degree of vulcanization, usually the size of the larger or thicker products, the longer the time required for vulcanization.