The forming principle of foam plastic
DATE：2021/8/31 8:34:48 / READ： / SOURCE：This station
The forming principle of foam plastic
There are many kinds of foam plastics, which are extremely versatile. Its molding method is similar to ordinary plastic molding methods. However, during the foam molding process, a large number of uniformly distributed bubbles will appear in the plastic melt or liquid, and the bubbles will also undergo expansion and The process of curing and shaping. It will be affected by the molding process. Any system in which gas and liquid coexist is often extremely unstable, and bubbles may swell or sink after they appear. There are many factors that affect the appearance of bubbles, expansion and collapse, and these influencing factors often interact with each other. Therefore, the molding difficulty of foamed plastics is much greater than that of non-foamed plastics. The mechanism is complex, and theoretical research often resorts to phenomenology, through experiments or practice, to observe and analyze a large number of macroscopic processes, find out the rules, and then make a theoretical analysis of the micro mechanism, explore the internal relationship, and propose mathematics that can express foaming behavior. Models. Most of the proposed models involve some multivariate variables and are difficult to directly apply, but they are still valuable as a theoretical basis for qualitative analysis. Limited to the above circumstances, this chapter can only introduce the relevant research situation and my understanding for readers to refer to when formulating raw material formulas, molding processes and equipment structures.
There are many types of foam plastics and various molding methods, but the molding and shaping process generally goes through three stages: the formation of bubble nuclei, the expansion of the bubble nucleus, and the solidification and shaping of the bubble. The forming mechanism of each stage is different, and the main influencing parameters are also different. The formation stage of the bubble nucleus plays a decisive role in the density and distribution of the cells in the bubble. Therefore, it is a key stage to control the performance and quality of the foam. The expansion stage of the bubble and the formation stage of the bubble nucleus are closely linked, especially for low-foam bodies, the expansion stage is extremely short, so it is more difficult to decisively separate. However, the situation is different for high foaming bodies. There is a big difference in the order of the parameters affecting the nucleation process and the parameters affecting the expansion process. The diffusion rate of gas in the polymer has little effect on the nucleation stage, but it has a great impact on the expansion stage, especially in the later stage of the expansion. The gas diffusion rate and permeation rate in the melt or liquid both control the bubble expansion rate. Important parameters.
In addition, the expansion stage of the bubble directly affects the geometry and structure of the bubble, such as the size of the bubble, open and closed cells, and the shape and distribution of the bubble are all determined by the conditions of the expansion stage. Whether the expansion result of the foam body can be solidified directly depends on the timing of the beginning of the solidification stage and the speed of solidification. There are many factors that affect the solidification speed of the foam body, and temperature plays a leading role. It is necessary to understand the dual relationship between temperature and expansion and solidification. In order to work out the appropriate temperature conditions for the foam molding and shaping process. Since there are different mechanisms and requirements at each stage of foam molding, the research and analysis of foam molding mechanism and influencing factors must be carried out in sections to find the best conditions, and then further analyze the relationship between each other, and conduct comprehensive considerations to formulate Develop the best overall plan. The following is an analysis of the mechanism of each foaming stage and its influencing factors.
Author：admin