Attention points in design development and mold manufacturing
Since the liquid silica gel itself is a liquid material, and there is obvious shear thinning during the injection and shearing process of the material, the fluidity of the liquid silica gel is very good. In the structural design, it is necessary to strictly review all the bonding parts, and the mold processing technology should also choose the precision processing technology, such as precision grinding machine processing, so that the movable parts of the mold can minimize the probability of burrs.
On the other hand, due to the precise fit of the mold, it will have a greater impact on the exhaust, so the negative pressure system should be considered as much as possible. The most ideal setting position of the negative pressure system is at the end of the flow, to ensure that the material can flow to the end, and at the same time to avoid problems such as bubbles and weld lines.
The evaluation of the shrinkage rate of liquid silicone is also very important. Similar to ordinary injection molding, liquid silicone also has a shrinkage rate during cooling, usually 2%-3%, but factors such as secondary vulcanization will affect the shrinkage rate. Have a certain impact.
A more scientific approach is to first determine the molding process flow of the product, and then analyze it through finite element modeling, so that the shrinkage rate of the product and other potential problems, such as weld lines, deformation, etc., can be analyzed very accurately. The front can have an early warning effect.
Glue injection port design is also an important part of determining product quality in liquid silicone molding. It is usually recommended to use cold half mold for liquid silicone molding. The material still needs to be protected at low temperature in the glue inlet manifold, but the mold cavity is heated The rod is heated and solidified to form.
This requires heat insulation for the gate and the runner, and the runner plate needs to be cooled by water. This dynamic heat and cold balance is very important, otherwise it is easy to block the gate and the material will solidify in the runner. Some production abnormalities.
Finally, the ejection system also plays a vital role in liquid silicone molding. Because the liquid silicone material itself is very sticky to metal, it is necessary to select an easy-to-release formula in the material formula.
In addition, in the design of the ejection system, more consideration can be given to the overall ejection of the push plate, the profiling push block, and the gas assisted ejection. Minimize the use of ordinary ejector pins for ejection, because the liquid silicone is very soft and can easily form defects such as ejector marks on the surface.
Forming process introduction
In terms of molding process, it is necessary to control the ratio of A/B components. In addition, the static mixer needs to be cleaned regularly to ensure the effect of static mixing. The injection process is similar to the traditional process. It is necessary to control the injection time, pressure, speed, position and other parameters to avoid some burrs, short shots and other defects. At the same time, pay attention to the law of fluid flow to avoid melt fracture. Defects in appearance.
Baby pacifiers made of liquid silicone injection molding. Take the baby pacifier as an example. The weight of this product is 5g. The product’s glue inlet point is designed in the middle of the pacifier. The cold runner system is used. Both the cold runner and the cold gate are equipped with cooling water channels. The water channels on the gate can be very It is a good solution to the heat insulation problem between the glue inlet and the cavity.
The gate valve needle is pneumatically controlled, which can effectively control the valve needle in and out, and at the same time can avoid the problem of valve needle damage caused by the oil core pulling system. In terms of materials, materials with self-release formulations are used. After the mold is opened, a gas assist system is used to blow the product away from the parting surface. The feeding system should also use high-precision equipment to ensure that the A/B ratio is strictly controlled at 1:1. If the static mixing ratio is unstable, it will cause product quality fluctuations, product performance defects, incomplete curing or incomplete curing. Problems such as cracking.
The liquid silicone market has great potential
The excellent biocompatibility of liquid silica gel and the material's safety and non-toxic characteristics make liquid silica gel widely used in the medical field. In respiratory products such as medical laryngeal masks and face masks, liquid silicone has begun to be used more and more.
In addition, the hardness of liquid silicone can be less than 35°, so it is also widely used in the field of plastic surgery, such as breast augmentation and other operations. At the same time, liquid silicone is also widely used in baby products, such as baby pacifiers and baby spoons.
Liquid silica gel has excellent transparency. Compared with other optical materials, liquid silica gel has good high temperature yellowing resistance. Therefore, in the field of automotive lamp holders, high-end lamp holders have begun to use liquid silicone molding technology in recent years.
Because of the many excellent material properties of the liquid silica gel, it is determined that it can shine in many fields and has a promising future.