1. Principle of formula design The rubber formula is ge […]
1. Principle of formula design
The rubber formula is generally composed of raw rubber, vulcanization antioxidant reinforcement system, protection system, reinforcement system and softening system. The purpose of the formula design is to seek the best combination of various components to obtain good comprehensive performance. The formula design should ultimately achieve the following objectives:
(1). Meet the performance requirements of seal ring.
(2). Good processing performance of rubber compound.
(3). On the premise of ensuring product quality, try to choose raw materials that are cheap, rich in source, non-toxic or low-toxic, and stable in performance.
Rubber formulas can be divided into test formulas and practical formulas according to their uses. The former is to study or identify the relationship between a certain raw material and the performance of vulcanized rubber and compounded rubber, and strive for simplicity in composition. The practical formula is mainly to study the relationship between the performance of the vulcanized rubber and the actual performance of the product and the performance of the rubber compound process. The process of formulating practical formulas is:
Environmental conditions and manufacturing process analysis of product use-à selection of rubber species and various compounding ingredients that make up the formula composition test formula-à performance evaluation test-à component adjustment and improvement-à expanded test to determine practical formula.
2. O-ring seal compound formula design
The working environment of O-shaped rubber seals is complex and diverse, which requires certain special properties of the rubber compound. In the hydraulic system, it is required to have good oil resistance, temperature resistance, low compression permanent deformation and a certain tensile strength. As a dynamic seal, in addition to the requirements, the rubber compound should also have good wear resistance and tear resistance. For the sealing of special media, the volume change and hardness change of the compound in the medium are small. In short, the formula design should be comprehensively considered according to the specific working conditions, medium type, use temperature, working pressure and application status.
3. O-ring seal material processing
At present, the manufacturing method of O-shaped rubber sealing ring is still mainly produced by over-molding method. Among them, the vulcanization methods of molded products mainly include plate molding, transfer molding and injection molding. Flat molding method has the longest history. Transfer molding was used around the 1950s, while injection molding has gradually moved from the plastics industry to the rubber industry since the 1960s. The current development trend is to gradually develop the injection method, but due to the different scope of adaptation. Coexistence and development of the three are still a reality. According to its characteristics, O-ring seals still use flat molding as the main molding method.
During the molding vulcanization process, the temperature, time and pressure of the vulcanization must be strictly and correctly grasped, and the changes of temperature and other parameters during the vulcanization process must be noted at all times, and corresponding treatments should be made, otherwise it will cause the product to be under-sulfur or over-sulfur. If an automatic control system is used, the entire vulcanization process will be automatically recorded and controlled to ensure that the product reaches the positive vulcanization level.
The vulcanization temperature is one of the basic conditions for the vulcanization reaction of rubber O-rings, which directly affects the vulcanization speed and product quality. High vulcanization temperature, fast vulcanization speed and high production efficiency; low vulcanization temperature and slow vulcanization speed. The vulcanization temperature depends on the formulation, the most important of which depends on the type of rubber and the vulcanization system used. The most suitable vulcanization temperature for natural rubber is generally 143℃-150℃, and synthetic rubber is generally 150℃～180℃. The vulcanization time is usually determined according to the determined vulcanization temperature through experiments.
Rubber products are pressurized during the vulcanization process, the purpose of which is to make the rubber easy to flow and fill the cavity, prevent air bubbles during the vulcanization process, and improve the density of the product. The size of the vulcanization pressure depends on the hardness of the compound and the size of the mold. When the hardness of the rubber is high and the size of the mold is large, the pressure can be larger, otherwise the pressure should be appropriately reduced.