Wuhan Handern Extrusion Blow Molding Process
DATE：2020/11/23 8:46:07 / READ： / SOURCE：This station
Wuhan Handern Extrusion Blow Molding Process
The main factors affecting the stability of hollow blow molding processing and product quality are raw materials, temperature, expansion ratio, inflation ratio, head weight size, blow molding pressure, mold cooling and molding shrinkage, which are described below. www.handern.com Hollow Board Equipment
1. Selection of raw materials
Taking polyethylene products as an example, the raw material grades must be selected according to the use of the products. The main parameters are density and melting index.
Softening temperature and stiffness are functions of density. The higher the density, the higher the softening temperature and rigidity. www.handern.com Hollow Board Equipment In order to maintain the structure and shape of products and develop thin-walled products, resins with high density and low melt index are required. www.handern.com Hollow Board Equipment
Secondly, containers containing detergents and other chemical reagents and containers with other materials have higher requirements on the environmental stress cracking performance of products. The stress cracking property is related to density, molecular weight and molecular weight distribution. Melt index is one of the characteristics of molecular weight, so the environmental stress cracking resistance of polyethylene is related to the melt index. www.handern.com Hollow Board Equipment As the melt index decreases, the environmental stress cracking resistance increases.
In addition, by observing the self-sagging phenomenon of the parison, it can be found that when the profile reaches a certain length, the falling speed of the mold breaks suddenly increases, 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. Type extension sag is closely related to melt index. The greater the melt index, the faster the parison sag, that is, the shorter the critical length.
In order to improve the rigidity, shock strength, environmental stress cracking resistance and stability of molding processing of hollow products, it is advisable to select resins with a small Tingrong index and high density. www.handern.com Hollow Board Equipment Commonly used high-density polyethylene often uses ethylene/butene or ethylene/ethylene copolymer. The melt index is 0,2～0,4. The melt index of the low density polyethylene blended with it is generally 03 to 1. When the blending ratio of low-density polyethylene is small, the melt index should not exceed 2.
2. Molding temperature
Each grade 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 cause rough surface of the product. In order to improve the appearance quality, the temperature at the die lip should be slightly higher than the material temperature (about 5°C higher). The extrusion temperature also directly affects the degree of parison sag, expansion ratio, cooling setting time and so on. Therefore, the melting temperature is an important parameter that controls product quality and determines production efficiency.
3. Expansion ratio
Expansion ratio refers to the phenomenon that the extruded molten parison is larger than the size of the die. 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 design size of the die and selecting the die. www.handern.com Hollow Board Equipment
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