Study on surface quality optimization of microfoaming injection⁃molded products

doi:10.19491/j.issn.1001-9278.2022.02.004

Abstract

Abstract:

Micro?foaming injection molding experiments were carried out using two gas injection methods， i.e.， a high pressure short time method and a low pressure long time method， with polypropylene and high?purity nitrogen as raw materials. In the experiment with the low pressure and long time as the gas injection method， the relationship between the cooling time and the probability of large bubbles on the product surface was investigated under the conditions of different melt temperatures， injection pressure differences and storage lengths. The results indicated that the probability of large bubbles appearing on the surface of the products obtained from the high?pressure short?time gas injection was high. This seriously affects the quality of products. The probability of large bubbles on the product surface was reduced significantly by using the low?pressure and long?term gas injection. The large bubbles on the product surface could be eliminated completely by prolonging the cooling time. In a certain range， the higher the melt temperature， the greater the injection pressure difference and the longer the storage length， the longer cooling time is needed to eliminate the large bubbles.

Key words: microcellular injection molding, large bubble, gas injection way, cooling time, process parameter

CLC Number:

TQ328.06

ZHAI Yujiao, XIN Chunling, HE Yadong, YAN Baorui, QIAO Linjun. Study on surface quality optimization of microfoaming injection⁃molded products[J]. China Plastics, 2022, 36(2): 19-26.

Figures/Tables 18

Fig.1. Schematic diagram of microfoam injection technology

Fig.2. Schematic diagram of microfoam injection molding process

注气方式	注气时间/s	注气压差/MPa
注气方式	注气时间/s	水平1	水平2	水平3	水平4
高压短时	5.3	1.5	2.0	2.5	3.0
低压长时	20	0.9	1.0	1.1	1.2

Tab.1. Parameter of gas injection process

Fig.3. Schematic diagram of gas injection for microfoam injection molding

水平	熔体温度/℃	注气压差/MPa	储料长度/mm
1	180	0.7	90
2	190	0.8	97
3	200	0.9	104
4	210	1.0	111

Tab.2. Setting of process parameters

Fig.4. Microfoam injection molding products

Fig.5. Sampling position

注气方式	无声响	轻微声响	较大爆鸣声
高压短时	0	25	75
低压长时	50	25	25

Tab.3. Comparison of air injection sound

Fig.6. Comparison of probability of large bubbles

Fig.7. Pressure curve for different gas injection methods

熔体温度/℃	熔体压力/MPa
180	8.5
190	8.0
200	7.5
210	6.7

Tab.4. Melt pressure value

Fig.8. Influence of melt temperature on the relationship between the probability of large bubbles and cooling time

Fig.9. Relationship between the optimal cooling time and melt temperature

Fig.10. Influence of air pressure difference on the relationship between the probability of large bubbles and cooling time

Fig.11. Relationship between the optimal cooling time and air pressure difference

Fig.12. Influence of storage length on the relationship between the probability of large bubbles and cooling time

Fig.13. Relationship between the optimal cooling time and storage lengths

Fig.14. Change of PP section morphology with cooling time

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