What is the hot pressing process for silicone products?

1.Basic principles
Hot pressing is an important process in the processing of silicone products. Silicone itself is made from silicone rubber raw material, which is a polymer with high elasticity. During the hot pressing process, silicone rubber is placed in a specific mold, and by heating and applying pressure, the silicone rubber flows inside the mold and fills various parts of the mold, thereby forming the desired shape of the silicone product. The main principle is to use thermal energy to make the molecular chains of silicone rubber more active, reduce their viscosity, and make them more fluid. At the same time, pressure helps silicone rubber better fill the gaps in the mold, ensuring that the molded product is dense and complete.
 

2.Process steps
Preparation stage
Firstly, it is necessary to choose suitable silicone rubber raw materials. Select the appropriate silicone rubber formula based on different product requirements, such as hardness, temperature resistance, color, etc. For example, for silicone products that require high hardness, silicone rubber with higher cross-linking density will be selected; For products that require high temperature resistance, corresponding high temperature resistant additives will be added.
At the same time, the mold should be cleaned and preheated. Molds are usually made of metal (such as aluminum alloy, steel, etc.), and cleaning is to remove impurities, oil stains, etc. on the surface of the mold to prevent affecting the forming quality. Preheating the mold can accelerate the vulcanization speed of silicone rubber and reduce the molding time. The preheating temperature is generally around 100-200 ℃, depending on the type of silicone rubber and the characteristics of the product.
Forming stage
Place an appropriate amount of silicone rubber into the mold cavity. This' appropriate amount 'is precisely calculated to ensure that the mold cavity can be completely filled without causing excessive overflow. Then close the mold and place it into a hot pressing equipment (such as a flat vulcanizing machine).
Then start heating and pressurizing. The heating temperature is usually between 150-250 ℃, and the pressure is generally around 5-20mpa. Under high temperature and pressure, silicone rubber undergoes vulcanization reaction. The vulcanization reaction is the process of forming cross-linking bonds between the molecular chains of silicone rubber through cross-linking agents, transforming the silicone rubber from a plastic state to a highly elastic solid state. This process usually lasts from a few minutes to several tens of minutes, depending on factors such as the formula of the silicone rubber, the size of the mold, and the thickness of the product.
Post processing stage
When the predetermined molding time is reached, stop heating and pressurization, open the mold, and remove the molded silicone product. At this point, silicone products may still have some burrs or excess silicone rubber parts that need to be trimmed. The trimming methods include manual trimming, mechanical cutting, etc.
Sometimes it is necessary to perform post vulcanization treatment on silicone products. Post vulcanization can further improve the performance of silicone products, such as enhancing their heat resistance and mechanical strength. Post vulcanization is usually carried out in an oven at a temperature of around 200-250 ℃ for a duration of about 2-4 hours. If silicone products are not post vulcanized and used directly, their performance may decrease over time during subsequent use.
 

3.Equipment and materials
Equipment: The main equipment for hot press forming is a hot press forming machine, commonly known as a flat vulcanizing machine. This machine has two heating plates on top and bottom, which can evenly heat the mold. It is also equipped with a pressure system that can precisely control the pressure applied to the mold. At the same time, the control system can set and adjust parameters such as temperature, pressure, and time to meet different molding requirements.
Materials: In addition to silicone rubber raw materials, some auxiliary materials will also be used. For example, release agents can prevent silicone rubber from adhering to the mold, making it easier to remove after molding. Release agents are generally organic silicon or wax substances, which are evenly applied to the surface of the mold during use. In addition, various additives such as crosslinking agents, reinforcing agents, pigments, etc. will be added to improve the performance of silicone rubber. Crosslinking agents are used to promote the vulcanization crosslinking reaction of silicone rubber; Reinforcing agents (such as white carbon black, etc.) can improve the mechanical strength of silicone rubber; Pigments are used to color silicone products.
The hot pressing process can produce various complex shaped and high-performance silicone products, which are widely used in electronics, medical, automotive, home and other fields, such as silicone seals, silicone buttons, silicone toys, etc.