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Silicone Rubber Molds Using Rapid Prototyping Methods Precautions

1. Be careful when lifting the mold
When the prototype structure has a draft, a groove, and a protrusion, the mold is generally smoothly molded as long as it does not exceed the deformation within the range of the silicone rubber tear strength, but lift the mold to be very careful to avoid damage to silicone rubber molds and parts.

2. Prototype parts should meet certain performance requirements
The prototype should have a good rigidity and certain strength, so as not to deformation in the mold. And, the prototype must have the correct shape, precise size and high finish.
Mold steel

3. Choose a reasonable way of casting
During the pouring process, if the pouring method and the pouring position are not proper, the air bubble inside the cavity will be wrapped into the cavity, which will make the mold leave the defect after curing. The solution is to gradually pour in batches in the pouring process, that is, the first thin layer of the surface of the prototype casting, until the surface of silicone rubber semi-cured state, and then pour the remaining material, so that the silicone rubber and prototype can fully contact to make the bubbles can be discharged relatively easily.

4. Mold must be placed flat
Pouring silicone rubber molds should try to make silicone rubber mold upper and lower flattened to avoid end uneven. Otherwise, at the use of silicone rubber molds casting parts, due to uneven placement of the mold, easy to cause deformation of the casting parts.

5. The bubble problem
(Mold steel) Whether the atmospheric pressure, pressure or reduced pressure method of manufacturing silicone rubber mold, the mold may be mixed with bubbles. Bubble can cause defects in the mold, there may have shrinkage in the casting mold parts, and sometimes there may be protruding point, affecting the quality of parts and silicone rubber mold due to stress concentration and lower strength, resulting in damage. The reason for the generation of the bubble and the solution are as follows.
  • Silicone rubber viscosity is high, mixing easily into different degrees of bubbles. The solution is to stir under vacuum conditions, or appropriate to reduce the amount of cross-linking agent and accelerator to extend the curing time in order to have a longer time for bubbles to free out: the other approach is to reduce the temperature of silicone rubber mixture and after casting.
  • Pouring methods and pouring position are inappropriate, and the solution is to gradual casting in batches in the pouring process. It also can be poured in the vacuum after the completion of the vacuum device for negative pressure exhaust.
  • Crosslinking of silicone rubber is the dealcoholation reaction, if the reaction is too fast, especially in the case of heating, the alcohol will leave a lot of holes after it escapes. In 40 to 60 ℃ different temperature curing, there will have different conditions of small pores, the higher the temperature, the more holes. When the temperature is less than 25 ℃, this phenomenon does not occur. Based on this, the initial curing of silicone rubber is best carried out at about 25 ℃ until the basic curing, and then after high temperature curing.

6. Sticky mold problems
The reasons for stick mold:
  • After pouring into the silicone rubber, curing temperature is too high or too long, there is the possibility of sticky mode. Suitable silicone rubber curing process is the first initial curing for 4-8h under the temperature of 25 ℃, and then remove model, and then at 120 ~ 150 ℃ for 2-4h curing, so you can avoid sticky mode.
  • The amount of cross-linking agent is too much or stirring is not uniform, local silicone rubber containing a lot of discretion, will also stick mold.
  • After silicone rubber at room temperature curing, without heat treatment, this time to reduce the strength of silicone rubber mold, often also cause sticky phenomenon.
  • Molds produce small bubbles, especially in the mold sidewall the small pitting and notch is too much, so that the mechanical strength of silicone rubber decreased accordingly, but also prone to stick mold.
Silicone rubber mold

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