What are the requirements for extrusion equipment for multi-layer co-extrusion composite hollow blow molding products of float blow molding machine?
Multi-layer extrusion blow molding uses several single-screw extruders to provide different polymer melts. The task of the extrusion system is to provide well-plasticized melt to the parison head stably and evenly at the same time. Moreover, this method requires higher uniformity of materials for the functional layer and adhesive layer. Therefore, the requirements for the extrusion device are correspondingly higher. In order to ensure that the extrusion device for multi-layer extrusion blow molding has stable plasticizing performance, the following requirements should generally be met.
①Advanced structure screw and barrel. Proper design of the extrusion system (screw and barrel) can significantly improve extrusion stability. Screw design should fully consider the characteristics of various plastics under operating conditions. The screw length-to-diameter ratio is a major parameter that affects extrusion stability, and it is best to be above 25. In order to achieve good mixing effects, new screw structures (such as separation type, pin type, and corrugated screws, etc.) can also be used to ensure that various additives can be well dispersed and mixed, thereby improving the uniformity of the melt temperature. A slotted bushing should be installed in the barrel feed section to improve extrusion stability and ensure product quality.
② Set up a gear pump between the extruder and the machine head to improve the stability of the extrusion. That is, the melt extruded by the extruder will be pumped into the machine head after being pressurized by the gear pump. The gear pump is a forced displacement device that can discharge a fixed volume of melt per revolution, regardless of the properties of the extruded plastic. In this state, adjusting the screw speed can change the melting and mixing properties of the plastic to facilitate control of the thickness ratio of each layer.
③Use a metering feeding device to control the feeding amount of the extruder to improve the extrusion stability. Since the screw groove is not completely filled,
④The extrusion device used to process multi-layer recycled materials should consider the composition of the recycled materials and their heating history during processing. It is required that the screw can fully mix various resins at the lowest possible temperature rise, especially for resins containing heat-sensitive resins. The material layer, such as PVDC barrier layer, and the screw structure of the extrusion device must be properly selected to ensure good mixing performance at a lower temperature.
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Color Plastic Masterbatch
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