How to produce shell products with no melt marks, no flow marks, no flow lines, no sink marks, and high gloss surface is particularly important for flat-panel TVs, computer LCD monitors, air conditioners, and automotive interior parts. Use of high-gloss injection molding technology can solve this problem well.

 

Mold is heated before and during mold clamping. After mold clamping is completed, injection will be performed when temperature reaches set conditions. Mold continues to maintain a high temperature during injection process, 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. Because this technology greatly improves surface quality and surface strength of product, can eliminate subsequent spraying or painting process, it not only protects environment and personal health of operators, but also reduces process flow and saves expensive secondary processing costs, while greatly reducing production costs, save energy and materials.

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

Steam high-gloss injection molding technology developed on the basis of traditional process has been improved for above defects:
① This technology opens water pipe in mold, passes steam when heating up, and cold water when cooling down. After cooling, compressed air is used to blow out residual moisture to ensure rapid heating and cooling;
② In order to eliminate defects of various products such as weld line clips, water lines and lack of glue to the greatest extent;
③ Due to large increase in temperature, use of H or even 2H hardness grade plastics greatly improves surface hardness of product;
④ Since only inner surface of mold is heated or cooled when pipe is opened inside mold, overall expansion of mold is small, so various product defects caused by instability of clamping force are reduced.
To produce high-quality high-gloss products, injection molding machines, molds, temperature control equipment, special plastics for high-gloss products, and boilers, cooling devices, etc. are required.

①Rigidity of clamping mechanism should be good; because temperature rises and falls continuously throughout production process. Therefore, clamping mechanism of injection molding machine must be rigid and strong to ensure accuracy and stability of clamping force. So as to ensure surface quality of product.
② Choose an injection molding machine with large clamping: 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 display frames and other products, you do not need a large injection volume. When choosing an injection molding machine, try to choose an injection molding machine with a small injection volume. Actual weight of product should be between 30% and 80% of theoretical injection volume of injection molding machine. If amount of glue injected by machine is too large, glue stays in barrel for a long time and is easy to decompose separately, defects such as silver wire will appear on the surface of product.
④ Plastic used in the production of high-gloss products with a special screw has a high hardness and a relatively low melt index, so screw is required to be plasticized. 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 Pipes inside mold must be reasonable to ensure that temperature can be raised and lowered quickly;
③ Pipe inside mold should have good thermal conductivity;
④ Since temperature needs to be continuously heated and cooled during production process, steel used for mold should be better;
⑤ Pay special attention to maintenance of mold during use to ensure that it is dry and dust-free.

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

When producing products with higher 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, up to H or even 2H. But the higher hardness, the lower melt index. Fluidity will become worse, so you can choose appropriate plastic according to production needs.
With increasing application of plastic parts, and people's awareness of environmental protection and safety gradually increasing, steam traceless high-gloss injection molding has gradually become frontier and popular technology in the future injection molding field.