日期：2021/11/11 8:43:17 / 閱讀： / 來源：本站
Synthetic vesiclesSynthetic foam (also called composite foam) is directly mixed with hollow spheres into plastic binder. Its cell is determined by the diameter of the hollow sphere. The binder is generally a low-molecular polymer (ie, polymer) at the initial stage of mixing. ), the degree is very low. After mixing, as the molecular chain grows and cross-links, the degree rises, and finally solidifies and sets. Therefore, its molding principle is different from that of other types of foams. It does not go through the nucleation and expansion stages of bubbles. The degree of foam depends on the quality and quantity of the hollow spheres added. The binder is mostly thermosetting plastic. The choice of binder should meet the following conditions.
①The initial mixing viscosity is low (prepolymer), which makes it easy to control the gel time.
②The exothermic reaction during curing is small, and the shrinkage rate during curing is small.
③Good adhesion and stickiness with hollow balls.
The binders are mostly epoxy resins, phenolic resins, poly, urea-formaldehyde resins, polyimines, and silicone resins.
The molding process is generally to mix the prepolymer of the binder and the hollow spheres uniformly, and more casting methods are used in casting, molding or extrusion molding. It can be slightly pressurized (0.5-2MPa) during casting to improve mold filling performance. Compression molding is more suitable for poor fluidity and high viscosity. It is very important to select appropriate process parameters for the molding process, such as temperature, mixing time, filling process, and the order and time of adding various additives, and they must be controlled as required. After the mixture is filled, the viscosity rises and finally solidifies and sets. The control gel time must be shorter than the stratification time. The amount of hollow balls added should not be too large. When the critical value is exceeded 67%, the flow will become worse, and cavitation is likely to occur between the hollow balls, which affects the quality of the foam. The hollow spheres should be evenly distributed during mixing, and a little vibration when injected into the mold cavity will help the hollow spheres to be evenly distributed in the binder; mixing under vacuum will not allow air to mix in and form small bubbles. The forming process of synthetic foam is easy to operate on site, so it has been used in submarines, various floating platforms, deep water operation platforms, etc.