Many liquid silica gel liquid silica gel manufacturers in the manufacture of liquid silica gel mold or liquid silica gel products often encounter some problems, in general, the structure of the liquid silica gel mold and the structure of the thermoplastic mold are somewhat similar, but there are many significant differences. Liquid silicone products, for example, generally have a lower viscosity, so the filling time is shorter, even at very low injection pressure. In order to avoid air retention in the mold, a good exhaust device must be designed in the liquid silica gel mold.
In addition, liquid silica gel does not contract in the mold as thermoplastic compounds do. They tend to expand under heat and do not contract slightly as expected, so that their product does not remain on the convex surface of the mold as expected.
The following 2 points should be paid attention to in the manufacture of liquid silica gel molds:
1. The shrinkage rate
Although liquid silica gel does not shrink during molding, it typically shrinks by 2.5 to 3 percent after it is moulded and cooled. The precise degree of shrinkage depends in part on the formulation of the material. However, from a mold perspective, shrinkage can be affected by several factors, including the temperature of the mold, the temperature at which the material is demoulded, the pressure in the cavity, and so on.
The location of the injection point is also worth careful consideration because the contraction in the direction of the compound flow is usually greater than the contraction in the direction perpendicular to the compound. The size and shape of the product also have a certain impact on its shrinkage, thicker products generally smaller shrinkage rate.
2. Moulding line
The first step in the design of liquid injection mold of silica gel is to determine the position of the mold line. Exhaust design is mainly achieved through the groove located on the parting surface, the groove must be located in the injection liquid silicone final flow area, so as to avoid the formation of bubbles in the molding process, reduce the strength loss of the bonding joint.
Because the liquid silica gel viscosity is low, so in the design of the mold line must be accurate, so as not to overflow the raw material. Even so, the mold line is often seen on the product (this is inevitable, liquid silicone mold line is much thinner). Liquid silicone mold will be affected by the product geometry and parting surface position. A slightly chamfered liquid silicone product design helps ensure that the product has a consistent affinity with the desired half of the cavity.