Comprehensive Guide to Silicone Injection Molding
Silicone Injection Molding
Details
Details:
Model
Material
Brand
Origin
Application
Booling-Injection-2
P20, 718, S136, 2738 etc
Booling
China
Automotive parts, industrial parts, medical parts, household
Silicone injection molding technology is a comprehensive molding process that uses certain air compression to inject liquid silicone into equipment, and then solidifies at high temperature to form an elastic body.
Advantages of Silicone Injection Molding：
- Excellent Electrical Performance
- Temperature Stability
- Weathering Resistance
- Simple Processing
- Excellent Mechanical Performance
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Silicone injection molding, as an advanced manufacturing process, has a wide range of applications, including but not limited to automotive parts, medical devices, household items, industrial equipment, etc. This custom injection molding technology mainly utilizes liquid silicone to be injected into the pre-tuned mold through an injection molding machine at high temperatures and pressure. It solidifies into the required product during the manufacturing process. This process combines computer-aided design to achieve 3D manufacturing from flat to three-dimensional.
Characteristics of Silicone Injection Molding
Compared to ordinary plastic injection molding, silicone injection molding has outstanding advantages, such as:
- Electrical Insulation Performance
Silicone still has strong insulation properties during injection molding, even under the influence of moisture, temperature rise, and frequency changes. The silicon dioxide generated after material combustion remains an insulator. In addition, the content of carbon atoms in the molecular structure of silicone is relatively low, and carbon black is not used as a filler. Therefore, silicone materials are not easily burnt during arc discharge and have high reliability and safety factors when used in high-pressure environments. In addition, it has excellent arc resistance and corona resistance, with an arc resistance life of 20 times that of fluoro rubber and a corona resistance life of 1000 times that of polytetrafluoroethylene.
- Wide Temperature Resistance Range
Among all rubber injection molding materials, silicone has the widest temperature range that can adapt and work, reaching -100 to 350 ℃. After processing at a high temperature of 350 ℃ for dozens of hours, low phenyl silicone vulcanizate can still maintain its elasticity. Its vulcanizate still has elasticity at temperatures ranging from -70 to 100 ℃, and its glass transition temperature can even be as low as -140 ℃. Ethylene-based silica gel or low phenyl silica gel that has been appropriately formulated can still maintain good elasticity and is not prone to age under the action of hot air at 250 ℃ for thousands of hours or 300 ℃ for hundreds of hours; Silicone material can withstand instantaneous high temperatures of thousands of degrees, which makes it suitable for use as a heat-resistant coating on the inner wall of rocket nozzles. This is also one of the biggest advantages of silicone injection molding.
- High Breathability
Compared with other polymer materials, silicone used in injection molding has good breathability. The permeability of oxygen, nitrogen, and air at room temperature is 30-40 times higher than that of NR. In addition, silicone materials have a certain selectivity for gas permeation, such as strong permeability for carbon dioxide, which is about 5 times the oxygen permeability.
- Special Surface Properties and Physiological Inertness
When silicone injection molding, its surface energy is smaller than most organic materials, and it has lower moisture absorption. Before use, it does not need to be dried, which improves the efficiency of injection molding. Manufacturers immerse it in water for a long time, with a water absorption rate of only about 1%, and its physical properties do not decrease, while also inhibiting the growth of mold. It does not bond with many materials and can be used as an isolation material. Injection-grade silicone material is non-toxic, odorless, highly compatible, and does not have adverse effects on the human body. It can be used in some medical devices with minimal reaction to body tissues. One major advantage of silicone materials is their excellent physiological inertness and aging resistance.
- Biomedical Performance
The molecular structure of silicone has excellent characteristics, which makes it have excellent biomedical properties. Silicone injection molding technology can be applied to a large number of animal and human experiments, promoting progress in the medical field.
- Aging Resistance
Silicone injection molded products have excellent resistance to oxygen aging, ozone aging, light aging, and weather aging, with long service life and good durability. Manufacturers expose silicone vulcanizing rubber to outdoor sunlight in a free state, and after several years, there is no significant change in performance, still maintaining strong reliability.
Sulfurization of Silicone Injection Molding Raw Materials
Compared to other raw materials, the vulcanization process is the most special step in silicone injection molding.
-Vulcanizing Agent
The vulcanizing agents used for hot vulcanized silicone mainly include aliphatic azo compounds, organic peroxides, high-energy radiation, and inorganic compounds, among which the most commonly used are organic peroxides. Through practice and testing, it has been proven that organic peroxides have relatively stable performance at room temperature. However, at higher vulcanization temperatures, they can rapidly decompose and produce free radicals, leading to cross-linking of silica gel.
Peroxide vulcanizing agents can be divided into two categories based on their activity:
- Universal Type: This type of vulcanizing agent has high activity and can produce sulfurization effects on various types of silicone gel;
- Vinyl-specific Type: This type of vulcanizing agent has low reactivity and is therefore only suitable for the vulcanization reaction of silicone-containing vinyl groups.
-Sulfurization Mechanism
In the process of silicone injection molding, when sulfurization is carried out with the help of peroxides, the crosslinking of silicone by peroxides occurs through free radical reactions between two activated methyl or vinyl groups.
In addition to the commonly used peroxide vulcanizing agents mentioned above, silicone materials can also undergo radiation vulcanization through high-energy radiation. The process of radiation vulcanization is also carried out according to the free radical mechanism. When the ethylene mole fraction in the raw rubber is high or used in combination with other rubbers, sulfur vulcanization can also be used, but the performance is extremely poor, and manufacturers choose this method in small quantities.
The Basic Process of Silicone Injection Molding
Compared to ordinary plastic injection molding, the special feature of silicone injection molding is that it first needs to be mixed and vulcanized.
- Mixing
The raw material for silicone injection molding is a two-component liquid material, divided into component A and component B. The A and B components are thoroughly mixed in a precise 1:1 ratio using a mixer.
- Color
Some special silicone products require color usage, so the mixer should be equipped with a color pump set and a color measurement part. After the additives, A+B components, colors, etc. are fully mixed, the material will enter the plasticizing system.
- Injection
The plasticizing screw has both homogenization and mixing functions. Manufacturers inject the mixture into the hot mold through the screw, and at a mold temperature below 170-200 ℃, the silicone undergoes a cyclic reaction.
- Cold Runner
When using a cold runner system, manufacturers need to note that the runner temperature should be sufficiently low. To avoid glue leakage, the needle valve is installed on the surface of the mold component. When the glue injection is completed, the needle valve immediately closes the injection nozzle.
Silicone injection molding is a process in which silicone material is melted by an injection molding machine and injected into a mold to solidify and form silicone parts. This is a precise manufacturing process.
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