Overview of the development of rotational molding technology in China

  The rotational molding process is to first add plastic raw materials into a mold, and then the mold rotates continuously along two vertical axes and heats it up. The plastic raw materials inside the mold are gradually and uniformly coated, melted, and adhered to the entire surface of the mold cavity under the action of gravity and heat energy, forming the desired shape, and then cooled and shaped into products. Since its emergence in the 1930s, the rotational molding process has undergone more than 60 years of development, and its equipment and technology have become increasingly sophisticated. From small children's toys to common automotive plastic parts, to large engineering plastic products, especially super large and non-standard shaped hollow plastic products, due to the limitations of other plastic processing processes, it can only be completed through rotational molding technology. At present, rotational molding technology has become an important branch of plastic molding processing technology.

  The development and research of rotational molding technology in China began in the 1960s. At that time, the toy industry in Shanghai began to use the rotational molding method to produce soft polyvinyl chloride balls; Shangsu No.3 Factory has successfully produced rolling plastic polyethylene containers with capacities of 200L and 1500L. In the mid-1970s, Beijing Fiberglass Research Institute successfully developed rotational molded nylon containers and applied them in products such as forest fire extinguishers. By 1992, although there were dozens of rotational molding production plants in China, the vast majority belonged to the equipment and technology level of the Western 1950s and 1960s. The annual processing of resin was about 9000 tons, accounting for only 0.89% of the total resin consumption in the country, which was 1% of the world average level. There were about 28 types of products, which was 0.5% of the world's quantity. Although some plastic companies are involved in the manufacturing of products using rotational molding technology, they have not made significant breakthroughs due to the constraints of key processes, and can only produce products with relatively rough requirements for size and performance. As a result, most employees do not fully realize the progressiveness of rotational molding process and strong market competitiveness. In the words of an American rotational molding company, "China's rotational molding has not yet started, and the Chinese rotational molding market has not yet been developed
 
  In the mid to late 1990s, some domestic enterprises began large-scale industrial production after introducing advanced rotational molding equipment and technology from abroad. At present, domestic enterprises are capable of preparing large plastic products such as chemical storage tanks with a container capacity of over 20000 liters and high-speed all plastic yachts. In recent years, China's rotational molding industry has developed rapidly, with nearly a hundred various rotational molding manufacturers across the country. These manufacturers produce an increasing variety of rotational molding products with a wider range of applications. However, compared with the advanced level of developed countries abroad, the gap is still very obvious. In the early 1990s, over 5000 types of rotational molding products were registered with the American Rotational Molding Association, while in China, there are currently only more than 40 types. Rotational molding products in foreign countries have involved more than 30 industries, while in China, they only involve more than ten industries. In terms of rotational molding raw materials, currently in China, the rotational molding of polyethylene and its composite materials accounts for about 75% of the total rotational molding products in the market. More than 99% of the rotational molding raw materials are PE, of which 95% are very suitable for rotational molding of rotational molding grade LLDPE. The proportion of rotational molding polyethylene materials abroad is roughly as follows: LLDPE is 65%, XHDPE (cross-linked polyethylene) is 2%, HDPE is 10%, and LDPE is 5%.

  With the continuous development of rotational molding technology, the types of rotational molding products are constantly increasing, and the application scope is also expanding. At present, the industries involved in rotational molding products at home and abroad include transportation vehicles, traffic safety facilities, entertainment industry, river and waterway dredging, construction industry, water treatment, medicine and food, electronics, chemical industry, aquaculture, textile printing and dyeing, and so on.