Molding technology and research of the hottest hig

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The rapid development of science and technology has promoted the rapid development of the world economy, the mutual penetration of various technologies, and also promoted the development and progress of new industries. The world packaging industry is developing in the direction of new environmental protection materials, low cost, high quality, large-scale, specialization and intensive in the central laboratory. Only by reasonably and effectively introducing foreign advanced technology, timely digestion, absorption and innovative development, can China's packaging industry shorten the gap between China's packaging industry and that of developed countries, and continuously improve its product competitiveness and market share, In order to continuously improve the international competitiveness of China's packaging industry

in 1997, Hebei jinhoudun Plastic Co., Ltd. introduced the packing box production process of American technology, which filled the gap in the production of domestic rotational plastic packing boxes. The packing boxes produced by this rotational plastic technology are light in weight, strong and durable, and low in maintenance cost; Excellent sealing performance, waterproof, anti dust, anti pollution; Its impact resistance is particularly excellent, and it can be used as an airdrop packing box; The selection of good raw materials can make the product have good environmental adaptability and adapt to the harsh natural environment of ± 40 ℃. It is these incomparable advantages of this process product that have led to the rapid development of this packaging in the industry, such as 4x army field medical box group, Navy medical box group, logistics field equipment unit equipment box, etc. adopted by the medical and Health Department of our army. Its series of products are widely promoted by the land, sea and air forces of our country in the fields of drug packaging, medical equipment packaging, weapon packaging, logistics equipment packaging, etc, Moreover, it has been used by China's Aerospace Department as a shock box for aerospace measurement and control instruments. With the continuous improvement of scientific and technological level, its application will be more and more widely. In the research and production of rotational plastic packaging in the past 10 years, we have accumulated rich experience in the development, design and production of rotational plastic packaging boxes, and have a deeper understanding of rotational plastic production technology. Here we put forward some of our own arguments

I. rotational molding packaging molding process and its advantages

rotational molding is a process method for the molding of hollow plastic products, also known as rotational molding, rotational molding or rotational molding. The process of rotational molding is to add plastic powder into the mold, then heat the mold and make it rotate continuously along two mutually perpendicular axes. Under the action of gravity and heat, the resin in the mold is gradually and evenly coated, melted and adhered to the inner surface of the mold, so as to form the required shape, and then cool the mold and demould to get the product

rotational molding originated in Britain in the 1940s, developed greatly in Europe in the 1950s, and then spread to the United States, Japan and other places. With the maturity of rotational molding special material technology, it has increasingly become one of the most competitive molding methods in powder plastic molding process. In recent years, the rotational molding industry has continued to develop at an annual growth rate of 15% - 20%, and has become one of the best molding and processing methods for small batch production of medium, large or super large fully enclosed and semi enclosed hollow seamless containers. At present, the global consumption of resin for rotary molding has accounted for 8% - 9% of the total output of resin

compared with the traditional molding methods of hollow plastic products (such as injection molding, blow molding, thermal molding, etc.), the most remarkable feature of rotational molding process is that the resin heating, molding and cooling processes are carried out in the non pressure mold. Such characteristics make it show a series of advantages

1. It is suitable for large and extra large parts made of rotational molding. The vast majority of plastic molding processes, in the molding process, plastics and molds are under quite high pressure (pressure), such as injection molding, compression molding, extrusion, blow molding, etc., which are widely used. Therefore, when using these molding processes to produce large plastic parts, it is not only necessary to use molds that can withstand great pressure, making the molds cumbersome and complex, but also plastic molding equipment must be designed and manufactured very firmly, and the processing and manufacturing difficulty of machine molds increases correspondingly, and the cost increases. On the contrary, because the rotational molding process only requires the strength of the frame to be sufficient to support the weight of materials, molds and the frame itself, as well as the mold closing force to prevent material leakage, even large and oversized plastic parts do not need to use very heavy equipment and molds. The processing and manufacturing of machine molds are very convenient, with short manufacturing cycle and low cost. Theoretically, there is almost no upper limit on the size of parts formed by rotational molding process. It is impossible to produce such a large plastic container without expensive and huge blow molding equipment if blow molding is used

2. It is suitable for the production of plastic products with multiple varieties and small batches. Because the mold for rotational molding is not affected by external forces, the mold is simple, cheap and convenient to manufacture. In addition, the rotational molding equipment also has greater mobility. A rotational molding machine can install either a large mold or multiple small molds; It can not only mold parts with different sizes, but also shape products with very different sizes at the same time. As long as the raw materials used for rotational molding products are the same and the thickness of products is the same, they can be rotational molded at the same time. Therefore, the rotational molding process has greater flexibility than other molding methods

3. Rotational molding is easy to change the color of products. Each time of rotational molding, materials are directly added to the mold to make all the materials enter the products. After the products are taken out of the mold, the materials required for the next molding are added. Therefore, when we need to change the color of the products, we will not waste a little bit of raw materials, nor do we need to spend time cleaning the machine and mold. When we use multiple molds to roll mold the same plastic product, we can also add materials of different colors to different molds and roll plastic products of different colors at the same time

4. It is suitable for forming hollow parts with various complex shapes. In the process of rotational molding, materials are gradually coated and deposited on the inner surface of the mold, and the products have a strong ability to replicate the fine structures such as patterns on the mold cavity. At the same time, because the mold is not subject to external pressure in the molding process, the mold with fine structure and complex shape can be made directly by precision casting and other methods

5. Save raw materials. The wall thickness of rotational plastic products is relatively uniform and the chamfer is slightly thick, so it can give full play to the efficiency of materials and is conducive to saving raw materials. In addition, in the process of rotational molding, there is no waste such as runner and gate. Once debugged, there is almost no reheating material in the production process, so the utilization rate of materials in this process is very high. With simple mold and low cost, it is suitable for forming large plastic products

6. The products have no residual stress and are not easy to deform. As long as the structural design of rotational molding products is appropriate, the products will not be affected by external pressure during the molding process, and there will be no residual stress, and the products will not be easy to deform

in the past, there were only some simple swing type rotational molding machines in China that used the most primitive rotational molding process to produce toys, buckets, etc. Generally speaking, the equipment capacity and process level were relatively low. It was used to produce more refined rotational molding packaging boxes in recent years. As far as we know, only a few enterprises in China can produce rotational molding packaging boxes

II. Discussion on common quality problems of rotational molding packaging box

simplicity and practicality is a major advantage of rotational molding, but it also brings some congenital defects to the production process of this technology. For example, bubbles are easy to appear inside the products, while holes are easy to appear on the surface; Products are prone to bending, shrinkage, discoloration, etc. These phenomena not only affect the appearance of products, but also seriously damage the mechanical properties of products. In addition, the use function of roll plastic packaging box and the particularity of product aesthetic requirements cause structural stress in the design structure, resulting in product deformation and other process defects. Therefore, strengthening the research on the formation and disappearance of bubbles, the formation and disappearance of bending and shrinkage phenomena, the impact strength of products and enhancing the scientificity of product design are of great significance to improve the quality of rotational plastic packaging products

bubbles and pores:

bubbles are formed because air is entrained between powder particles when they melt and bond together. In industrial production, the method of increasing heating temperature is often used to reduce or eliminate bubbles in products. Because when the heating temperature is increased and the bubbles in the product are prolonged or eliminated, the viscosity of the material decreases and the bubbles diffuse easily. At the same time, because there is more time, the bubble can diffuse more thoroughly. Although this method is effective in eliminating bubbles in products, it also has side effects. For example, increasing the melting temperature will prolong the forming cycle, reduce the production efficiency and increase the product cost; Under high temperature, the material is oxidized, which reduces the mechanical properties of the products, especially the impact strength

impact strength:

there are many factors affecting the impact strength of products, such as heating temperature, heating time, cooling speed, particle size, mold, raw materials, etc., of which heating temperature and heating time are the main factors affecting the impact strength. The temperature is too low and the material is not melted enough, resulting in product impact. 12. Compactor: the strength of imported French Taikang is reduced; If the temperature is too high, the plastic will degrade, which will also reduce the impact strength of the products. The melt flow rate MFI is directly related to its impact strength, and MFI decreases with the decrease of impact strength. Therefore, MFI can be used as an indicator of impact strength of products

shrinkage and deformation:

shrinkage and deformation are also another major defect of plastic rotational molding products. On the one hand, shrinkage and deformation are caused by residual stress formed during cooling. Practice has proved that alternate cooling through different cooling methods can reduce the residual stress of the product, or fill the mold with compressed air during cooling, that is, the compressed air makes the cured plastic tightly stick to the inner wall of the mold to prevent it from breaking away from the mold wall or deformation, until the plastic is completely cooled, which plays a role in cooling and shaping. And because this method cools the inner surface of the cured plastic at the same time, the cooling mechanism is changed, so as to reduce the residual stress and inhibit the shrinkage and deformation of the product. In fact, when most plastic products are cooled, 0.11mpa compressed air is introduced, which basically eliminates the phenomenon of shrinkage and deformation; On the other hand, the design of the product structure and appearance also has a great impact on the products. Improper structural design may cause the long-term existence or generation of stress, so that the packaged products will return to the original state of shrinkage and deformation when subjected to external forces, resulting in the unsightly appearance of the packaged products and the poor quality stability of the finished products of rotational molding. We can use modern design technology, including computer aided design (CAD), and many enterprises from Chinese Mainland and Taiwan also participated in this exhibition, including computer simulation design, optimization design, reliability design, concurrent design and other technologies, to continuously improve the design level of packaging boxes

III. control of key elements in the process of rotational molding packaging box

thermal temperature control:

temperature is an indispensable element in the rotational molding process, especially the appropriate temperature control in the heating process is undoubtedly the most important means to improve product quality. Take polyethylene as an example to illustrate this problem. There is a special phenomenon in the rotational molding process of polyethylene: melting in powder

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