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Car Carpet Sheet Extruder
Commonly used molding methods for foam plastics include extrusion injection molding and compression molding. Among them, extrusion molding is one of the main methods of foam plastic molding and processing. Generally, foam products such as special-shaped sheets, pipes, diaphragms, cable insulation layers, etc. are made by this method. Foaming methods can be either physical foaming or chemical foaming. Physical foaming mainly uses some fluorocarbons and their mixtures, as well as their low-boiling point liquids.
The foaming process of foam plastics can generally be divided into two stages. The first is to form a large number of uniform and fine bubble nuclei in the plastic melt or liquid. The second is to continue to expand the plastic into the required foam structure, and finally solidify. The foam structure is fixed by shaping to obtain foam plastic.
The foaming system must undergo rapid nucleation and growth through the molding head. During this process, it is necessary to ensure that a greater supersaturation pressure and a faster supersaturation pressure drop are induced, so as to form a large amount of foam at the same time as much as possible. Bubble core, during the growth process, the appropriate machine head temperature is very critical for the stability of the growing bubbles and the control of the foaming ratio of the final product.
For the molding of polypropylene foam, according to the source of foaming power in foam molding, it can generally be divided into three types: mechanical foaming, physical foaming, and chemical foaming. Among them, mechanical foaming uses strong mechanical stirring to mix the gas evenly into the resin to form bubbles. Physical foaming relies on the change of the physical state of the foaming agent in the resin to form a large number of bubbles. Chemical foaming refers to relying on foaming. The gases produced when the agent undergoes chemical changes cause the resin to foam.
Foaming is mostly chemical foaming. The foaming agents used include azodicarbonamide diisopropyl azodicarboxylate, etc. Of course, nitrogen crop foaming agents can also be used for physical foaming.
In addition, the physical foaming method of directly injecting gas is also used in the extrusion molding process of foam plastics. The process parameters that affect extrusion molding foaming mainly include extrusion pressure, extrusion temperature, residence time of materials in the extruder, die axial pressure, etc. Generally speaking, as the extrusion pressure is higher, the cell size becomes smaller and the number of cells increases, and high-quality foam is only possible in a narrower temperature range. The higher the melt temperature, the lower the polymer melt strength, and the foaming pressure in the foam is likely to exceed the foam surface tension and cause the foam to rupture. Therefore, production must be optimized according to the specific polymer system to determine a suitable foaming temperature, thereby extending the residence time of the material in the extruder and increasing the number of bubbles.