The forming principle of various foam plastics
DATE：2021/10/20 8:44:36 / READ： / SOURCE：This station
The forming principle of various foam plastics
One, structure bubble bodyThe structure of the structured foam is different from that of the free foam. The surface layer of the free foam is foamed the same as the core, while the skin layer of the structured foam is not foamed or less foamed. The core is foamed, which is similar to the free foam. In comparison, the surface layer of the structural foam is not only flat but also smooth, and has a greater hardness and rigidity of the skin layer. It is also called skinned foam. The mechanical properties are significantly better than those of free foam and molded structure foams, regardless of the extrusion method. Or injection method, its technical difficulty is greater than free foaming.
The skin layer and the core of the structural foam can use the same raw material formula or different raw material formulas. The latter belongs to composite molding. The raw material of the skin layer does not contain foaming agent. Generally, it is plasticized separately from the raw material of the core body, and is compounded only when it is molded and shaped, so the equipment is more complicated. The former skin layer and core body use the same raw material formula to contain foaming agent. In order to prepare structural foam, the skin layer and core part must be under different process conditions during the foaming molding and shaping process to form a non-staining foam. The foam skin and foam core.
There are generally two ways to form a non-foaming skin layer. One is to reduce the temperature of the skin melt to increase the viscosity of the melt and increase the resistance to bubble expansion. The low temperature also reduces the dynamics of bubble expansion, making it difficult for skin bubbles. Formation and expansion, the other is to increase the pressure on the skin layer to increase the solubility of the gas in the melt, so that the gas is not easy to separate from the melt to form bubbles.
The skin layer formed by the above two principles is very smooth, but there are certain technical difficulties. Another method is to foam the surface layer and the core at the initial stage of foaming, just like free foaming. The surface layer is heated and pressurized during shaping, so that the foamed surface layer bubbles are collapsed and become a smooth surface. At present, the first two molding principles are mostly used. For thin-walled foams, when the external pressure drops, the material temperature of the core is higher than that of the skin layer. Therefore, although the foaming and expansion resistance of the core is larger than that of the skin layer, the temperature difference of the material can compensate and reduce the material layer. The thickness can make the materials of the core and skin layer foam together. If the wall thickness is large, in order to fully foam the core material, it is ideal to use Celuka for extrusion foaming. This method is widely used in French patents. The principle is to depressurize the core of the material layer so that the material can be fully foamed. The specific method is to install a shunt shuttle at the die of the extruder, the front end of which extends straight into the foaming setting device, so that the plastic melt is first squeezed when passing through, and the cross-sectional area of the shunt shuttle is gradually reduced after exiting the die. The pressure of the core of the passing material flow is reduced, and the material in the core is foamed and expanded to form a foamed core.
The application of structural foam has been paid more and more attention, and the application range has become wider and wider.
Author：admin