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Author: MULAN -Plastic Molding Manufacturer
Control elements of blow molding process Extrusion of hollow blow molding products is one of the main molding methods of hollow plastic products. In the molding process of blow molding products, the following points need to be met: 1. Processing temperature and screw speed On the premise that smooth and uniform plastic parisons can be extruded without overloading the screw system, lower processing temperature and faster screw speed should be adopted as much as possible to increase the efficiency. 2. Molding air pressure Extruded hollow blow molding products are generally within the range of 0.2MPa~1.5MPa, and the size is mainly determined according to the melt viscosity of the plastic. Those with low viscosity, such as nylon and polyethylene, are easy to flow and blow, and the molding air pressure can be lower; those with high viscosity, such as polyoxymethylene and polycarbonate, have poor flow and blowability, so higher pressure is necessary. Molding pressure is also related to the size and thickness of blow molded products. Generally, a container with a large wall thickness requires a higher molding pressure, and a container with a thinner wall requires a lower molding pressure. The specific situation needs to be adjusted step by step after practical operation, with the method of increasing by 0.1MPa or decreasing by 0.1MPa until the product is tested. 3. Inflation ratio The ratio of the size of the blow molded product to the size of the parison is called the inflation ratio. When the parison size and quality are constant, the larger the product size, the greater the parison inflation ratio. Increasing the inflation ratio can save materials, but the wall thickness of the product will become thinner, difficult to form, and the strength and rigidity of the product will decrease; if the inflation ratio is too small, the effective volume of the product will decrease, and the flash will increase; the wall thickness, cooling time will be prolonged, and the cost will increase. Generally, the inflation ratio is 2 to 4 times, and it is more suitable for 1:2, and the wall thickness is relatively uniform at this time. For some special blow molding products, the inflation ratio will be small, and the determination of the inflation ratio needs to be carried out according to the blow molding product. Good results. 4. Mold temperature and cooling time The plastic parison of extrusion blow molding has a high temperature during molding, and a certain pressure holding and cooling cycle is required in the mold. If the mold temperature is too low, the cooling of the plastic will be premature, and the blow molding product will be difficult to form and the surface will not be glossy; when the mold temperature is too high, the cooling time will be longer and the production cycle will be longer; if the cooling degree of the parison is not enough, the product will be demoulded and deformed , Unfavorable conditions such as large shrinkage. Therefore, the determination of parameters such as mold structure, mold exhaust, cooling and temperature control are very important factors in the extrusion of hollow blow molding products, which will directly affect the quality of blow molding products. Proficient in mould|blow molding products| Started in 1998, trustworthy.