How to produce shell products with no melting marks, no flow marks, no streamlines, no sink marks, and a high-gloss surface is especially important for flat-panel TVs, computer LCD monitors, air conditioners, and automotive interior parts. Using high-gloss injection molding technology can solve this problem very well.

 

Mold is heated before and during mold closing process, and after mold closing is completed, injection is performed when temperature reaches set condition. During injection process, mold continues to maintain high temperature, so that rubber can maintain good fluidity in mold during injection. After injection is completed, when pressure is maintained and cooled, mold is cooled, which can greatly shorten cooling time of product, thereby improving production efficiency.

Technology is still an advanced production process in China at present. Because this technology greatly improves surface quality and surface strength of product, and can cancel subsequent spraying or painting processes, it not only protects environment and peprsonal health of operators, but also saves expensive secondary processing costs due to reduction of process flow, saves energy and materials while greatly reducing production costs.

Traditional method is to use a mold temperature machine to heat mold, but disadvantages of this method are as follows:
① It cannot meet needs of rapid heating and cooling in high-gloss injection molding;
② Temperature rise is small, and weld marks on the surface of product can only be reduced but not eliminated;
③ Because the higher hardness of plastic, the worse fluidity. Therefore, hardness of surface of product using this process can only reach HB level and cannot meet needs of actual use;
④ When mold heats up, it expands and shrinks when it cools down, making clamping force very unstable. It is easy to cause various defects such as underfilling, burning, and large internal stress of product.

Steam high-gloss injection molding technology developed on the basis of traditional technology has made improvements to above defects:
① This technology opens water pipe in mould, steam is passed when temperature needs to be raised, and cold water is passed when temperature needs to be lowered. After cooling is completed, residual moisture is blown out with compressed air to ensure rapid heating and cooling;
② To maximize elimination of various product failures such as weld line clips, water lines and lack of glue;
③ Due to large temperature rise, use of plastics with H or even 2H hardness levels greatly improves surface hardness of product;
④ Since only inner surface of mold is heated or cooled when pipeline is opened inside mold, the overall expansion of mold is small, thus reducing various product defects caused by instability of clamping force.
To produce high-quality high-gloss products, it is necessary to cooperate with injection molding machines, molds, temperature control equipment, special plastics for high-gloss products, boilers, and cooling devices.

① Rigidity of clamping mechanism is better; because temperature must be continuously raised and lowered during the entire production process. Therefore, it is required that clamping mechanism of injection molding machine must be rigid and strong to ensure accuracy and stability of clamping force. Thereby ensuring surface quality of product.
② Choose an injection molding machine with a large clamping mold: When using this process, gas-assisted injection can no longer be used, so clamping force required to produce product will be relatively large.
③ Choose a smaller injection volume according to situation: For example, when producing flat-panel TVs, LCD frames and other products, there is no need for a large injection volume. When selecting an injection molding machine, try to choose an injection molding machine with a small injection volume. Actual weight of product is best between 30% and 80% of theoretical injection volume of injection molding machine. If injection volume of machine is too large, rubber material stays in barrel for a long time and is easy to decompose separately, and defects such as silver threads will appear on the surface of product.
④ Equipped with a special screw to produce high-gloss products, plastic used in production of high-gloss products has high hardness and relatively low melt index, so plasticization of screw is required to be better. At the same time, shear of screw should not be too large, otherwise rubber material will be easily decomposed.

① Inner surface of mold requires a very high finish to ensure surface quality of product;
② Pipeline inside mold must be reasonable to ensure rapid heating and cooling;
③ Pipe inside mold should have good thermal conductivity;
④ Due to need for continuous heating and cooling during production process, steel used for mold is better;
⑤ Pay special attention to maintenance of mold during use to ensure dryness and dust-free.

① Temperature control should be very accurate, which is an important guarantee for product quality;
② Response of temperature control equipment should be very fast to ensure high production efficiency.

 

When producing products with high surface quality, commonly used plastics are ABS, PC+ABS or PMMA+ABS. Among them, ABS has the lowest hardness, and PMMA+ABS has the highest hardness, which can reach H or even 2H. But the higher hardness, the lower melt index. Fluidity will become poor, so appropriate plastics can be selected according to production needs.
With increasing application of plastic parts and people's increasing awareness of environmental protection and safety, steam traceless high-gloss injection molding has gradually become frontier and popular technology in the field of injection molding in the future.