塑料吹塑技術(shù)外文翻譯--- 用紅外熱像儀理解在吹塑冷卻階段的熱傳遞機(jī)制（英文）

1、Understanding heat transfer mechanisms during the cooling phase of blow molding using infrared thermographyA. Bendadaa,*, F. Erchiquib, A. KippingcaNational Research Council of Canada, Industrial Materials Institute, 75

2、De Mortgane, Boucherville, Que., Canada J4B 6Y4 bUniversity of Quebec in Abitibi-Temiscamingue, 445 Universite ´ Blvd., Rouyn-Noranda, Que., Canada J9X 5E4 cUniversity of Siegen, Paul-Bonatz Strasse 9-11, Siegen 570

3、68, GermanyReceived 15 June 2004; accepted 25 November 2004 Available online 24 February 2005AbstractThe cooling phase of the extrusion blow molding process has a large influence on the cycle time of the process as well

4、as on the properties and quality of the molded products. A better understanding of the heat transfer mechanisms occurring during the cooling phase will help in the optimization of both mold cooling channels and operating

5、 conditions. A continuous extrusion blow molding machine and a rectangular bottle (motor oil type) mold were used to produce bottles. A high density polyethylene (HDPE) and a metallocene polyethylene (mPE) having differe

6、nt rheological properties were tested. Melt and mold temperatures, cooling time, inflating pressure and die gap were varied systematically. An infrared camera was used to measure the temperature distribution of the plast

7、ic part just after mold opening as well as after part ejection. The wall thickness and dimensions of the bottles of the finished parts were measured in order to determine the shrinkage and warpage. Finally, the infrared

8、temperature fingerprints were used to explain what happens during the cooling phase and correlated with the final part characteristics. Crown Copyright q 2005 Published by Elsevier Ltd. All rights reserved.Keywords: Blow

9、 molding; Cooling; Infrared thermography; Polymer processing1. IntroductionIn the extrusion blow molding of medium size bottles, the cooling stage represents a substantial part of the overall cycle and has a profound eff

10、ect on the microstructure development and on the ultimate properties of the molded article. During the cooling of the blown part whilst in the mold, heat is removed both by forced convection (poly- mer/air interface at t

11、he internal wall) and conduction (polymer/metal interface at the mold wall). Once the mold opens, the part will continue to cool from both surfaces by natural convection. Several authors [1–4] have developed numerical al

12、gorithms for the predictions of the temperature profiles in the parts. Their efforts have been of limited value due to the uncertainty in the values of heat transfer coefficients used to represent the different heat tran

13、sfermechanisms. For these reasons infrared thermography presents itself as a complementary technique capable of mapping the thermal history of blow molded parts during the different stages of the cooling process [5–7].2.

14、 Experimental setupThe parametric study was done on a continuous extrusion blow molding machine (Battenfeld-Fischer FBZ1000), equipped with a motor oil type bottle mold. The mold is modular and has five interchangeable p

15、arts. The cavity is made of a top block, a middle block and a bottom block, each with its own cooling circuit. The three blocks are mounted onto a back plate and within the middle block an exchangeable insert is located

16、(Fig. 1). The mold cavity has a height of 220 mm, a width of 100 mm and a depth of 50 mm. In this study, a flat insert was used in the middle block to ensure a complete contact between plastic and mold. A diverging die (

17、fZ30 mm) was used in this study.0963-8695/$ - see front matter Crown Copyright q 2005 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2004.11.007NDT fax: C1 450 641 5106. E-mail address: akim.bendad

18、a@imi.cnrc-nrc.gc.ca (A. Bendada).(Dow/Polisur 70055L) and an enhanced polyethylene (mPE) produced using metallocene technology (Dow Elite 5100). The basic material properties are given in Table 1. Due to the different m

19、olecular structure of the materials, different parison swell and sagging behavior during extrusion is expected. A crude estimation of this behavior was obtained by measuring the diameter and thickness of the extruded par

20、isons, both close to the die and at the bottom of the parison. A comparison of the cross-section of the parisons (at the top and at the bottom) is shown in Fig. 3 for HDPE and mPE, respectively. HDPE swells considerably

21、and also appears to have low melt strength. This results in a parison having a wall thickness distribution along its length. On the other hand, the mPE exhibits lower swell and low melt strength, which results paradoxica

22、lly in a parisonhaving a more uniform thickness along its length. These differences will have a strong influence on the absolute and thickness distributions values in the blow part and consequently on its cooling behavio

23、r.4. Processing parametersA simple design of experiments scheme was used to vary the processing parameters. During the variation of one of the describedparameters,allotherparameterswerekeptconstant at their mean value. A

24、 summary of the range of parameter variation is given in Table 2. Due to the different material behavior, different melt temperatures and cooling times were chosen for the HDPE and the mPE. The temperature of the HDPE me

25、lt is varied between 220 and 240 8C, while for the mPE melt a 190–210 8C temperature range was used. In the case of the blowing times, these were varied as follows: HDPE—10, 15 and 20 s; mPE—5, 8 and 11 s. The lower temp

26、eratures and shorter cooling times were used in order to accommodate the shorter drop times of the mPE. The mold temperature is controlled through the variation of the flow rate and temperature of the cooling liquid. The

27、se tempera- tures were set at 4, 10 and 21 8C. The actual mold temperature was measuredbyusinga thermocoupleinsertedflushwiththe moldsurface.Thediegapisalsochangedwiththecontrolunit of the machine. By the use of a servo

28、cylinder, the mandrel within the die can be moved axially. Because the mandrel has a conical shape, the die gap changes by moving the mandrel, Fig.4.Aftereveryparameterchange,theprocesswasallowed toreachstableconditions.

29、 Thisstabilizationperiodappearsto be quite important when changing mold temperature and blowing pressure.5. ResultsMost of the studies that have been performed on the effect of cooling conditions on the final properties

30、of blow molded parts have not been careful in identifying the temperature distributions both in the parison and in the mold prior to blowing. These two conditions are crucial for a comprehensive interpretation of the mol

31、ding results. The bottom of the parison, although thicker in general, is exposed longer to the ambient air and therefore has a lower temperature. In our study, the HDPE parison exhibitsTable 1 Material propertiesHDPE mPE

32、Density (g/cm3) 0.951 0.92 MI (g/10 min) 0.14 0.85 Vicat softening point (8C) 129 105 Ultimate elongation (%) 600 650 Tensile strength (MPa) 27 53Fig. 3. (a) Cross-section of a HDPE-parison. (b) Cross-section of a mPE- p

33、arison.Table 2 Operating conditionsHDPE mPEDie gap (mm) 2–4 2–4 Tmelt (8C) 220–240 190–210 Tmold (8C) 9–21 9–21 Blowing pressure (bar) 3–7 3–7Cooling time (s) 10–20 8–11A. Bendada et al. / NDT&E International 38 (200