In home appliance industry, polypropylene plastics are used extensively in washing machines and dishwashers. Each washing machine uses an average of 4 kg of polyethylene and an average of 7 kg of polyethylene per dishwasher. Some data display that drying machine mainly uses engineering plastics (such as nylon and polyoxymethylene) as mechanical parts. Consumption growth rate of general-purpose thermoplastics in the field of home appliances exceeds the average growth rate of materials for home appliances.
Electronics Plastic Injection Molding
Appliance manufacturers are pursuing higher design flexibility in order to meet increasing aesthetic requirements of consumers. Since home appliance manufacturers can basically provide similar functions, design of home appliances especially electrical molding has become a major differentiation factor in the retail market. New environmental awareness and new regulations also have an impact on product specifications. Good function of plastics makes it possible to meet new requirements of home appliance industry.
Double-shot Injection Molding
Double-shot injection molding is a technology that can produce high gloss on surface and has two layers of different colors inside and outside. Application of this technology can greatly improve appearance of whole injection molded electronics. Compared with ordinary molds and small double-shot / two-component injection molding which has been widely used, large-scale two-shot injection molding have great differences in product characteristics, mold structure, action sequence, gate setting, flow path layout, etc. In continuous production, outer layer injection and inner layer injection are performed simultaneously, so molding cycle is substantially close to the conventional injection molding. Large-scale Double-shot injection molding technology can be combined with high-gloss non-fusion mark injection molding technology. High-temperature and high-pressure hot water or steam is used to heat the mold in the production, and cooling medium is quickly switched after injection is completed to quickly cool mold, and surface has no melt marks to improve the appearance of whole product. Large-scale double-shot injection molding adopts a rotary large-scale two shot injection molding machine. After the mold is clamped, outer plastic is injected first. After mold is opened, cavity with plastic part is rotated 180° with the rotary table, and mold is clamped again. After the inner layer of plastic is injected, mold is ejected.
Because inner and outer layers are separately injection molded, large double-shot injection molding requires two sets of cavities and two sets of cores, two of which are identical and interchangeable with two sets of cores; both sets of casting systems are located in core side, which is a reverse-loading structure; ejector is also placed on the core side, and is hydraulically ejected. Together with cooling system, complexity of entire core side structure is greatly increased.
In the optimization design of plastic parts, shape of outer layer formed for the first time needs to be as simple as possible. The inner layer of second molding can be designed with structures such as ribs and columns, but layout of gate and shape of flow must be fully considered. In order to make the appearance of plastic part have a color gradation effect, wall thickness of outer circumference can adopt a gradual design from thin to thick.
In the molding process, when large double-shot injection molding technology is formed for the second time, plastic flows along surface of the first molded plastic part, which is prone to injection defects such as bubbles, chromatic aberration, and running rubber. It is necessary to repeatedly debug and precisely control injection molding process parameters to achieve improvement and optimization of mold in combination with molding conditions.
After hard work and breakthrough, it broke through a series of key technologies and developed the first large two-color high-gloss injection mold that reached international advanced level in China. It was successfully applied to Hisense’s large-size LED-backlit LCD TV. Large-scale Doubt-shot high-gloss injection molding technology has high production efficiency and good surface quality. The inner and outer layers can be flexibly matched according to needs, which can greatly improve appearance and grade of the whole injection molded electronics. At present, this technology is getting more and more widely used in large-size LED-backlit LCD TVs. In the future, it also has broad market prospects in home appliance Industry such as high-end refrigerators, air conditioners and other home appliances.