Blow molding products mold cooling structure basic concept proficient in mold


Author: MULAN -Plastic Molding Manufacturer

Basic concept of mold cooling structure for blow molding products For almost all extrusion molding, injection molding, hollow blow molding and other methods, the productivity depends largely on the heating and cooling efficiency of the plastic. During the cooling process, the heat of the molten plastic is taken away by the mold, so that the blow molded product is cooled and shaped; The cooling time of blow molding products accounts for 60% to 80% of the molding cycle, and up to 90% for large and thick-walled products. Cooling times that are too short will result in product warping and significant shrinkage. In order to achieve high-speed blow molding, it is the best measure to improve the cooling efficiency of blow molded products, which can shorten the molding cycle and reduce energy consumption. However, the role of the cooling system is not only to increase productivity, a good cooling water system can improve Improve the surface quality of blown products and make them full. All in all, the quality of the cooling system is one of the important indicators to measure the blow mold. The cooling methods of blow molded products can be divided into three types: external cooling, internal cooling and post cooling. The main cooling system of the blow mold consists of external cooling and post cooling. 1. External cooling method External cooling refers to setting up a cooling system in the mold wall to cool the blow molded product through heat transfer through the outer wall. The common way to set up a cooling system in the mold wall is to drill cooling channels in the vertical and horizontal directions in the mold wall. The water channel of the cooling system in this way can be manufactured by machining, and the manufacture is simple, convenient and low in cost. The spiral copper sheet or stainless steel spiral sheet installed in the channel can divide the cooling water into two helical cooling water flows, increase the degree of turbulence of the fluid, and make the cooling water flow helically move along the outer wall of the cooling water hole, which can Accelerating the cooling rate also reduces the formation of scale in the cooling water channel. Drilled cooling channels are easy to clean and allow for easy modifications. 2. Internal cooling method During the cooling of blow molded products, the outer wall is cooled faster due to contact with the low-temperature mold cavity, and the inner wall is in contact with the inflation air, and the heat transfer is very small, so the cooling is slower. The difference in the cooling rate of the inner and outer walls may cause warping of blow molded products. One solution is to hold the pressure in the mold for a longer time, and let the product be completely shaped before taking it out. This will prolong the entire cycle and affect production efficiency. To this end, various internal cooling methods have been researched and developed, that is, water mist, liquid nitrogen or carbon dioxide, refrigerated air, circulating air or mixed media are injected into the inflated parison to rapidly cool the inner wall of the product. In internal cooling, liquid nitrogen and carbon dioxide are commonly used, because they are clean, non-chemical, and suitable for a variety of blow molding products. The internal cooling method is used to form blow molded products, and the production efficiency is high; however, it is necessary to control the temperature of the internal cooling medium. If the temperature is too low, defects such as strain and spots on the inner surface of the plastic will occur, which will affect certain dimensions (such as containers) Neck size) versus container volume shrinkage. The method of using liquid nitrogen for blow molding internal cooling is very effective in the extrusion blow molding process. It can be used as both a coolant and an inflation gas, which can shorten the production cycle by up to 50%. The length of time to shorten the cycle mainly depends on the performance of blow molded products, mainly related to The material, weight, wall thickness and shape of blow molded products are related. The liquid nitrogen blow molding process has good economic benefits when the blow molding products are shaped and held for longer than 20 s; in some large batches of blow molding products and places where liquid nitrogen supply is convenient Manufacturers of blow molding products may wish to try. When the internal cooling method is used, some special products need to be combined with compressed air blow molding, which can ensure good molding of products and improve production efficiency. 3. Post-cooling method Both internal and external cooling methods are for the parison in the blow mold. If at a higher temperature, the blow molding product is taken out of the mold as soon as possible, and placed in the rear station for cooling, the molding cycle of blow molding can be significantly shortened. This process is called post-cooling method. When demoulding, the temperature should not be too high. Generally, the mold can be opened after half of the normal cooling time to maintain The shape of blow molded products. Proficient in moulds|blow molding products| Started in 1998, trustworthy.

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