Zhejiang Shifang Pipe Industry Co.,Ltd

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Performance Analysis of HDPE
- Dec 27, 2018 -

Chemical and physical properties

The high crystallinity of PE-HD results in its high density, tensile strength, high temperature distortion temperature, viscosity and chemical stability.

PE-HD has better penetration resistance than PE-LD. The impact strength of PE-HD is low. The properties of PH-HD are mainly controlled by density and molecular weight distribution. The molecular weight distribution of PE-HD suitable for injection moulds is very narrow. For density of 0.91-0.925g/cm3, we call it the first type PE-HD; for density of 0.926-0.94g/cm3, we call it the second type PE-HD; for density of 0.94-0.965g/cm3, we call it the third type PE-HD.

The material has good flow characteristics, MFR is between 0.1 and 28. The higher the molecular weight, the worse the flow characteristics of PH-LD, but the better the impact strength.

PE-LD is a semi-crystalline material with a high shrinkage of 1.5% to 4%.

PE-HD is prone to environmental stress cracking. The cracking phenomenon can be alleviated by using materials with very low flow characteristics to reduce internal stress. PE-HD is easy to dissolve in hydrocarbon solvents when the temperature is higher than 60C, but its solubility is better than PE-LD.

Injection Molding Process Conditions

Drying: If stored properly, no drying is required.

Melting temperature: 220 ~ 260C. For materials with larger molecule size, the melting temperature range is suggested to be between 200 and 250 C.

Mold temperature: 50 ~ 95C. The plastic parts with wall thickness less than 6 mm should use higher die temperature, while the plastic parts with wall thickness more than 6 mm should use lower die temperature. The cooling temperature of plastic parts should be uniform to reduce the difference of shrinkage. For the optimal processing cycle time, the diameter of the cooling channel should be no less than 8 mm, and the distance from the die surface should be within 1.3 days (where "d" is the diameter of the cooling channel).

Injection pressure: 700-1050 bar.

Injection speed: high-speed injection is recommended.

Runner and gate: The diameter of runner is between 4 and 7.5 mm, and the length of runner should be as short as possible. Various types of gate can be used, and the gate length should not exceed 0.75 mm. Especially suitable for the use of hot runner die.