Wuhan Handern extrusion blow molding process
DATE：2020/6/10 8:43:00 / READ： / SOURCE：This station
Wuhan Handern extrusion blow molding process
1. Selection of raw materials
Taking polyethylene products as an example, the grade of raw materials must be selected according to the use of the products. The main parameters are density and melt index.
Softening temperature and rigidity are functions of density. The greater the density, the higher the softening temperature and rigidity. www.handern.com Hollow board equipment In order to maintain the structural shape of the product and develop thin-walled products, it is required to use resins with high density and low melt index. www.handern.com Hollow board equipment
Secondly, containers containing detergents and other chemical reagents and containers containing other materials have higher requirements on environmental stress cracking performance of products. The stress cracking is related to density, molecular weight and molecular weight distribution. Melt index is one of the molecular weight characteristics, so the environmental stress cracking resistance of polyethylene is related to the melt index. www.handern.com Hollow board equipment The melt index becomes smaller, the environmental stress crack resistance increases.
In addition, by observing the self-sag of the parison, we can find that when the mold extension reaches a certain length, the decline speed of the mold damage increases suddenly, and the length of the mold at this time is also called the critical length. The critical length can be used as a rough standard for parison sag. The droop of the type extension is closely related to the melt index. The greater the melt index, the faster the parison sag speed, that is, the shorter the critical length.
In order to improve the rigidity, impact strength, environmental stress cracking resistance and stability of the molding process of hollow products, resins with small Tingrong index and high density are suitable. www.handern.com Hollow board equipment Common high-density polyethylene often uses ethylene/butene or ethylene/ethylene copolymer. The melt index is 0, 2 to 0, 4. The melt index of the low-density polyethylene blended with it is generally from 03 to 1. When the blending ratio of low-density polyethylene is small, the melt index should not exceed 2.
2. Molding temperature
Each type of resin has a certain melting temperature, which should be strictly controlled during processing. www.handern.com Hollow board equipment Low or high temperature will produce rough surface of the product. In order to improve the appearance quality, the temperature at the mold lip should be slightly higher than the material temperature (about 5℃ higher). Extrusion temperature also directly affects the degree of parison sag, expansion ratio, cooling setting time, etc. Therefore, the melting temperature is an important parameter to control product quality and determine production efficiency.
3. Expansion ratio
The expansion ratio refers to the phenomenon that the extruded molten parison is larger than the die size. The expansion ratio typically shows the melt viscosity of polyethylene. Understanding the expansion ratio is of great significance for controlling the blow molding process, improving product quality, determining the die design size, and selecting the die. www.handern.com Hollow board equipment
Author：admin