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>Carpet sheet extruder
In the setting and solidification stage, a reasonable cooling rate has an important impact on the density and performance of the final product. Therefore, the processing equipment includes extruder type, screw configuration, pressure control device, foaming head. If a physical foaming agent is used, its injection and metering, as well as process parameters including temperature and pressure, etc., have an impact on the foam structure density mechanics of the final foamed material. Performance and thermal properties will have a significant impact.
The bubble 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 number of bubbles at the same time as much as possible. Core, during the growth process, the appropriate machine head temperature is very critical for the stability of the growth bubbles and the control of the foaming ratio of the final product.
In the four processes of extrusion foaming, we must first ensure that the polymer and foaming agent form a homogeneous solution, and establish a high enough extruder head pressure to prevent the foaming system from advancing near the extrusion die. Foam.
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, and 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.
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