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Silicone Mold Products Molding Process Conditions

Silicone mold products molding is a forming process, which is feeding silicone raw materials mixed with vulcanizing agent in the mold, through a certain period of high temperature and high pressure vulcanization, to form the silicone mold products to a required shape. This process includes several factors that can directly impact the molding quality of silicone mold product, such as temperature, pressure, time, exhaust and other factors. Now for all the silicone mold products we will talk about the effect of product molding (vulcanizing) process parameters, and abnormal situations with improper setting.

1. Temperature
Also known as mold temperature, refers to the molding (vulcanizing) temperature of the silicone mold products, consists of upper mold and lower mold two sets of temperature.
Mold temperature can be divided into surface temperature and measured temperature. The surface temperature is the setting temperature on the vulcanizing machine. The measured temperature is the actual temperature measured by instrument. Due to the vulcanizing machine temperature control module error and the heat loss caused by heat transfer between the heater tube and forming mold, the measured temperature is about 5-10℃ lower than surface temperature, and the cavity setting temperature is 5℃ higher than the core setting temperature. Because most of time, the wind gun blows against the cavity mold while demolding, and the cavity mold is filled with more silicone raw material, more heat to be consumed. So we should pay attention to this when setting the molding (vulcanizing) temperature.
Generally, silicone molding (vulcanizing) temperature will be set at 160-200℃. The actual value is determined by product structure, volume, and demolding difficulty. If the setting value is too low, will lead to unqualified products, such as silicone products vulcanizing incomplete, have air bubbles, low load, long size. If the temperature is too high, will cause air bubbles, material shortage, the surface numbness, high load, short size.

2. Pressure
Molding (vulcanizing) pressure is also one of the important factors affecting the quality of silicone mold products.
It is the pressure value that vulcanizing machine applies to the mold when silicone mold products molding in the mold. 
This pressure value is determined by the tonnage of the vulcanizing agent and the forming mold size of the silicone mold product. For a 200T flat vulcanizing agent, for example, the 150mm×150mm forming mold set value is about 50kg/cm2, the 250mm×250mm forming mold setting value is about 100kg/cm2, the 350mm×350mm forming mold set value is about 150kg/cm2.
If the silicone molding (vulcanizing) pressure is too low, it will lead to silicone products lack of material, high load, thick base thickness, short length and other unqualified situations. And if the silicone molding (vulcanizing) pressure is too high, it will cause silicone mold low load, thin base thickness, long length, etc. If the pressure is far higher than required, it may even cause damage to the vulcanizing machine.

3. Time
It is the duration of silicone molding (vulcanizing) at high temperature and pressure conditions.
It depends on the structure and volume of the silicone mold product, the skill level of the operator, the adding proportion of the vulcanizing agent, the characteristics of the silicone raw material, the discharging way of the material in the mold, the exhausting parameters, and so on. The shortest can be tens of seconds. The longest will be five or six hundred seconds or even longer.
When the vulcanizing time is too short, the silicone products vulcanizing will be incomplete, air bubbles appearance and other unqualified situations. And vulcanizing time is too long, will lead to silicone products becoming brittle, difficult demolding and so on.

4. Exhaust
After silicone raw materials placed in the mold, a lot of air will be brought in the instant of clamping. Air can't be integrated into silicone raw materials, without air emission, it will lead to some bubbles on silicone mold products surface. For this we need to open the molding die after clamping and forcing, in order to release the air in the mold, this process is exhausting.
We need to set the mold opening distance and number of times according to different products, often call as exhaust stroke and number of exhaust times. Usually the exhaust stroke is setting at 0.6-1.2cm, and number of exhaust times is setting as 1-3 times. There is no fixed value, need to repeatedly test according to the structure and size of silicone mold products to achieve the best results.
Silicone mold products molding machine

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