Domestic rotational molding process development
The rotomolding forming process is to add the plastic raw materials into the mold first, and then the mold rotates and heats along the two vertical axes. Under the action of gravity and heat energy, the plastic raw materials in the mold are gradually evenly coated, fused and adhered to the whole surface of the mold cavity, formed into the required shape, and then cooled and shaped into products. Since the roll forming process came out in the 1930s, after more than 60 years of development, its equipment and technology have become increasingly perfect, from small children's toys to common automotive plastic parts to huge engineering plastic products, especially super large and non-standard hollow plastic products. Due to the limitations of other plastic processing technology itself, now it can only rely on the roll forming process. It can be done. At present, rotomolding forming technology has become an important branch of plastic forming process.
The research and development of rotomolding technology in China started in 1960s. At that time, the toy industry in Shanghai began to produce soft PVC balls by the rotomolding method. Shanghai No.3 plastic product factory has successfully trial produced the rotomolding polyethylene containers with the volume of 200L and 1500L. In the mid-1970s, Beijing FRP Research Institute successfully developed the rotomolding nylon containers and applied them in forest fire extinguishers and other products. By 1992, although there were dozens of rotomolding plastic production plants in China, most of them belonged to the equipment and technology level of the 1950s and 1960s in the west, with an annual processing capacity of about 9000 tons, accounting for only 89% of the total resin consumption in China, 1% of the world average level, and about 28 kinds of products, 0.5% of the world quantity. Although some plastic enterprises are involved in the manufacturing of products with rotomolding technology, due to the constraints of key technology, there has been no major breakthrough, only some products without strict size and performance requirements are relatively rough. So that most practitioners do not know enough about the advanced nature of the rotational molding process and the strong market competitiveness. In the words of America's largest rotomolding plastic supplier: "China's rotomolding plastic industry has not yet started, and China's rotomolding plastic market has not yet been developed!"
In the middle and late 1990s, after some domestic enterprises introduced advanced rotomolding equipment and technology from abroad, they began the real large-scale industrial production. At present, domestic enterprises have been able to prepare large-scale plastic products such as chemical storage tanks with a capacity of more than 20000 L and high-speed all plastic yachts. In recent years, the rapid development of our country's rotomolding industry, the country's various rolling manufacturers have nearly hundreds, these manufacturers produce more and more types of rotomolding products, the application field is more and more extensive. But compared with the advanced level of foreign developed countries, the gap is still very obvious. In the early 1990s, there were more than 5000 kinds of rotomolding products registered with the American rotomolding Products Association, while there are only more than 40 kinds of rotomoldinmg products in China so far. Overseas rotomolding products have involved more than 30 industries, while China's rotomolding products only involve more than 10 industries. In terms of rotomolding forming raw materials, at present, in domestic rotomolding forming products, the proportion of polyethylene and its composite materials in the market accounts for about 75% of the total rotomolding forming products, and more than 99% of the rotomolding forming raw materials are PE, 95% of which are very suitable for rotomolding forming LLDPE, while the proportion of foreign rotomolding forming polyethylene materials is about 65%, xhdpe (cross-linked polyethylene) 2%, HDPE 10%, LDPE 5%.
With the continuous development of rotomolding forming technology, the types of rotomolding forming products are increasing, and the scope of application is also expanding. At present, the industries involved in rotomolding products at home and abroad include transportation, traffic safety facilities, entertainment industry, river channel dredging, construction industry, water treatment, medicine and food, electronics, chemical industry, aquaculture, textile printing and dyeing, etc.
1. Container type rotomolding plastic parts
This kind of plastic parts are widely used in storage and supply boxes, water tanks, storage and transportation containers for various industrial chemicals, such as acid, alkali, salt, chemical fertilizer, pesticide storage tanks, chemical enterprises, industrial coating, washing tanks, reaction tanks, turnover boxes, garbage bins, septic tanks, domestic water tanks, etc. For example, the Cross-linked polyethylene resin barrel made of maricxcl-100 by Philips company is comparable to the metal barrel, and it has good chemical corrosion resistance and low maintenance cost.
2. Rotomolding plastic parts for vehicles
It mainly uses polyethylene and PVC paste resin to rotomolding plastic various automotive parts, such as air conditioning elbow, vortex tube, backrest, handrail, oil tank, fender, door frame and gear lever cover, battery shell, fuel tank of snowmobile and motorcycle, aircraft oil tank, yacht and its water tank, small boat and buffer absorber between ship and dock, etc.
3. Sports equipment, toys and crafts
There are various parts made of PVC paste rotomolded, such as water polo, floating ball, small swimming pool, recreational boat and its water tank, bicycle seat cushion, rotomolded pallet, surfboard and so on. Rotomolding molds can be manufactured by precision casting, electroforming and other processes; the surface of rotomolded parts “replicates” the fine structure of the mold cavity surface is very effective, so rotomolding can make the product quite delicate and beautiful, so it is commonly For the production of products with greater ornamental value, especially toys such as pony, doll, toy sand box, fashion model, crafts and so on.
4. All kinds of large or non-standard rolling plastic parts
Rotational molding products are also widely used in various boxes, shells, large pipes and other products, such as rack, machine shell, protective cover, lampshade, agricultural sprayer, furniture, canoe, camping vehicle roof, playground device, planter, bathroom, toilet, telephone room, billboard, chair, road isolation pier, traffic cone, river sea buoy, anti-collision cylinder and building application. Work barrier, etc.
Rotomolding forming is the most economical and effective way to produce large hollow plastic products. In order to promote the application of roll forming in China, it is necessary to absorb foreign advanced technology, develop more and better roll forming materials, improve the automation level of rotomolding forming equipment, and shorten the mold design and manufacturing cycle. It is believed that with the continuous progress of modern material industry and machinery manufacturing and automation technology, the rotomolding forming process will have rapid development in China.