塑料注射成型英文文献和中文翻译(7)
process. Mold temperature can be kept at high temperatures for a longer time than in water heating. Therefore, the filling and packing can be improved, making the contact between mold surface and melt improved.
Hardness is one of the most important properties of a material. It can be used as an indicator of the polymer product. When the other parameters are fixed, based on the standard of ISO 868, type D and resolution of 1%, Fig. 12 shows the Shore D hardness of the TV housing (measured at point P, Fig. 4) when the steam heating process with different mold target temperatures was used. It can be seen that the higher the target temperature, the higher the hardness of the TV housing. This can be explained by the effect of crystallinity in the product after molding. As mentioned above, by using steam heating, the mold temperature at the cavity surface can rise to a higher value, hence, after a filling period, the melt can be kept at high temperatures for a longer time. In this period, the crystals will continuously increase until
Fig. 11. Gloss of the TV housing with different target temperatures. Fig. 12. Hardness of the TV housing with different target temperatures.
melt temperature is lower than tg. This process shows that the heating time and target temperature are the important factors for hardness.
6. Conclusions
In this study, a steam heating system combined with water cooling to achieve rapid mold temperature control for injection molding was established. The effect of steam heating and the uniformity of mold temperature for simple plate mold were first evaluated. Then the effect of steam heating was applied for a TV housing mold and compared with water heating. By experiment and simulation, the temperature at the surface was observed and compared. In addition, the product quality was also compared between two types of heating. Based on the result, the following conclusions can be made:
• For the simple mold plate, steam can increase the mold surface from 50 °C to over 135 °C in 9 s (9 °C/s), and cool down to 50 °C in 44 s (2 °C/s). In this case, 5 periods of temperature history in each cycle can be observed clearly by experiment and simulation.
• For the real TV housing mold, steam system had shown a higher
efficiency in both heating and cooling. Compared with water heating, steam heating can reduce from 18 s to 8 s for the heating step and 16 s to 12 s for the cooling step. By changing the target temperature from 70 °C to 110 °C, the heating time varies from 7 s to 19 s, with the highest heating rate at about 3 °C/s.
• Part quality is also improved when the steam was used for heating.
Both hardness and groove were increased due to the high temperature maintained at the cavity surface in the filling and packing processes.
Acknowledgment
The authors would like to thank the financial support from The Center- of-Excellence Program on Membrane Technology from the Ministry of Education and the project of the specific research fields in the Chung Yuan Christian University, Taiwan, under grant CYCU-98-CR-ME.
References
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[2] D.G. Yao, B. Kim, Development of rapid heating and cooling system for injection molding applications, Polymer Engineering and Science 42 (12) (2002)
2471–2481.
[3] S.C. Chen, Y. Chang, Y.P. Chang, Y.C. Chen, C.Y. Tseng, Effect of cavity surface coating on mold temperature variation and the quality of injection molded parts, International Journal of Heat and Mass Transfer 36 (10) (2009) 1030–1035.
[4] S.C. Chen, H.M. Li, S.S. Hwang, H.H. Wang, Passive mold temperature control by a hybrid filming-microcellular injection molding processing, International Journal of Heat and Mass Transfer 35 (7) (2008) 822–827.
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