With the market demand for its products, blow molding will have the following development trends in materials, machinery, auxiliary equipment, control systems, software and other aspects.
(1), raw materials In order to meet the function and performance of blow molding products (medicine, food packaging) requirements, blow molding grade raw materials will be more abundant, better processing performance. Such as PEN materials, not only high strength, good heat resistance, strong gas barrier, transparent, ultraviolet radiation resistance, can be used for blowing a variety of plastic bottles, and high filling temperature, good carbon dioxide gas, oxygen barrier performance, and chemical resistance.
(2), product packaging containers, industrial products will have a greater growth, and injection blow molding, multi-layer blow molding, hollow blow molding will have rapid development.
(3) Precision and efficiency of blow molding machinery and equipment; Automation of auxiliary production (operation) equipment. "Precision and high efficiency" not only refers to the mechanical equipment in the production molding process has a higher speed and higher pressure, but also requires the production of products in the appearance of size fluctuations and weight fluctuations can achieve high stability, that is to say, the production of various parts of the size and shape of the geometry of high precision, deformation and reduction. The appearance and internal quality of products and production efficiency and other indicators should reach a higher level. Auxiliary operations include flash removal, cutting, weighing, drilling, leak detection, etc. The process automation is one of the developing trends.
(4) The research on the blowing mechanism of blow molding simulation is more in-depth, the reasonable construction of the mathematical model of blow molding simulation, the fast and accurate numerical algorithm is the key to the simulation, and blow molding simulation will play an increasingly important role in the prediction and control of product quality.
The following is an analysis of the molding parameters at each stage of the blow molding process. The blow molding process can be divided into four stages:
(1) The forming stage of the billet polymer in the extruder transport, melting, mixing, pumping molding is the forming stage of the billet; At this stage, the main process parameters that affect the wall thickness distribution are:
① Molecular weight distribution and average molecular weight of the material;
(2) The temperature control system and screw speed of the blow molding machine, including the temperature of the hopper, the temperature of the barrel 1 zone, 2 zone, 3 zone, 4 zone, flange temperature, and the storage die head; Shanghai blow molding processing
(2) blanking stage Blanking stage is extruded from the gap between the die lip and the die core. At this time, the two phenomena of mold expansion and vertical elongation of the billet affect the forming of the billet. The main process parameters affecting the wall thickness distribution are the die head diameter and wall thickness control system of the blow molding machine, wherein the air control system includes the axial wall thickness control system and the circumferential wall thickness control system to adjust the gap between the die lip and the die core.
(3) In order to avoid the contact and adhesion of the inner surface of the billet and improve the uniformity of the wall thickness of the product, the billet should be pre-blown. In the pre-blowing stage of the billet, air is injected from the bottom of the billet to protect the billet and reduce its sag. At this stage, the main process parameters that affect the wall thickness distribution are: pre-blowing pressure and pre-blowing time.
(4) High pressure blowing stage high pressure blowing billet, make it close to the mold cavity, to achieve the product plastic forming stage. At this stage, what affects the forming of the product is the deformation of the billet by high pressure blowing and the contact deformation between the billet and the mold cavity. The main process parameters that affect the wall thickness distribution are: the shrinkage rate of the material; Blowing pressure, time; Mold material, structure, mold exhaust system and mold cooling system, such as cooling water distribution, cooling water inlet temperature, etc. Although there are many factors affecting the quality of blow molding products, when the production conditions and product requirements are determined, adjusting the blow molding process parameters can effectively improve the quality of products. Optimized process parameters can improve production efficiency, reduce raw material consumption, and optimize the overall performance of products.
