- Email: [email protected]
Online real-time acquisition for transient temperature in blow molding
ARTICLE IN PRESS
POLYMER TESTING Polymer Testing 25 (2006) 839–845 www.elsevier.com/locate/polytest
Test Equipment
Online real-time acquisition for transient temperature in blow molding Han-Xiong Huang, Yu-Zhou Li, Yan-Hong Deng Center for Polymer Processing Equipment and Intellectualization, College of Industrial Equipment and Control Engineering, South China University of Technology, Guangzhou, PR China Received 23 February 2006; accepted 5 April 2006
Abstract In blow molding, the temperature is an important parameter which influences the process, cycle times, and part properties, etc. In the current work, a PC-based temperature acquisition system, including hardware and software, was developed to measure the transient temperatures of an extrusion blow-molded part during its cooling and solidification, and of a reheated preform in stretch blow molding (SBM). Two issues were addressed. Firstly, the thermocouples in the acquisition system were specially designed by the authors to allow for their penetration into the wall of the cooling part or reheated preform. Secondly, in order to measure the temperature of reheated preform as it rotates, a special brush mechanism was designed. The acquisition system was tested through a series of experiments on industrial blow-molding machines under different conditions, such as die temperature, blowing pressure, and blow mold material in extrusion blow molding, and the kind of heating lamps and their voltage settings in SBM. The ability of fast and repeatable online measurement of transient temperature profiles using the acquisition system should prove to be helpful to better understand the molding phenomena, to validate the numerical simulation results and to derive optimum processing parameters for blow molding. r 2006 Elsevier Ltd. All rights reserved. Keywords: Extrusion blow molding; Stretch blow molding; Temperature profiles; Online; Real time
1. Introduction In polymer processing, the properties of a finished part are dependent on both the material from which it is manufactured and the processing parameters during production. The temperature is an important processing parameter, which influences process features such as cycle times, crystallization rates, degree of crystallinity, melt-flow properties and Corresponding author. Tel./fax: +8620 2223 6799.
E-mail address: [email protected] (H.-X. Huang). 0142-9418/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2006.04.003
chemical stability. Study of the temperature profiles in polymer processing is of fundamental importance to a more complete understanding of many complicated phenomena such as heat transfer problems and molecular orientation, etc., which, in turn, can lead to the improved design of processing equipment and control for polymer products of specified dimensions. Moreover, the measurement of the temperature distribution during polymer processing is of great importance for the validation of numerical simulation results. So, many researches including both numerical simulations and experiments on the
ARTICLE IN PRESS 840
H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
temperature distributions in polymer processing, such as extrusion [1–5], injection molding [6–8], and blow molding [9–20] have been previously carried out. Blow molding is a major polymer processing technique for manufacturing a wide variety of hollow plastics parts. The blow molding is commonly subdivided into two main classes, i.e., extrusion blow molding and injection stretch blow molding (SBM). The former is widely used to produce containers of various sizes and shapes and is also adapted to make irregular complex hollow parts, such as those supplied for automobiles, office automation equipment and pharmaceutical sectors, etc. The latter technique is extensively used in the commercial production of bottles for the food, beverage, and pharmaceutical industries. Cooling and solidification is the final stage in the blow-molding process as well as many other plasticmolding operations. This stage represents 60% or more of the cycle time in the extrusion blowmolding process. Thus, the cooling time directly influences the productivity and cost of the process. Furthermore, the cooling and solidification also affect the properties, such as crystallinity, density, shrinkage, residual stresses, warpage, mechanical properties and permeability of blow-molded parts. Hence, the cooling rate or the cooling time should be at an optimal value, since excessive cooling time limits productivity, whereas short cooling time results in significant part deformation. Some researchers have devoted time to experimental and theoretical studies on the cooling and solidification of extrusion blow-molded parts [9–15]. However, the measurement of the temperature of the cooling part was generally only on its external surface in previous researches [10,15]. In the two-stage SBM process, tube-shaped preforms are first made by injection molding, cooled to room temperature, and stored until required. They are then reheated to an appropriate temperature distribution above the glass transition temperature of the material and stretch blow molded into bottles using a reheat SBM machine. Reheating produces temperature profiles, both through the thickness and along the length of the tube-shaped preform. The temperature and its distributions in the reheated preform have a strong effect on the stretching and inflation of the preform and the orientation, crystallinity, critical performance characteristics (the mechanical properties, barrier performance, and transparency), and thickness
distribution in the bottle. The regions with higher temperature will stretch and blow out faster and thin out more than the regions with lower temperature. The stretching temperature also determines the amount of orientation induced by stretching, which, in turn, affects the properties of the bottle. So, reheating is a decisive factor for the production of high quality bottles in the two-stage SBM process, and it is very important to investigate the temperature evolution within the preform during its reheating. A few efforts have been made to represent the heat transfer inside an infrared oven [16–20] but, because of the complexity of the radiative transfer in a transparent preform, the problem still remains open. Moreover, to the knowledge of the authors, in the previous researches on the reheating stage of the two-stage SBM process, the predicted temperature profiles were verified only by measuring the preform surface temperatures [16–18]. The current work describes the development of a PC-based temperature acquisition system which was used to measure the transient temperature profiles of an extrusion blow-molded part during its cooling and solidification, and of a reheated preform in SBM. For the former, the temperatures at different locations across the thickness of the cooling part were measured. For the latter, the temperature measurements were carried out at different locations both across the thickness and along the length of the preform. 2. Description of temperature acquisition system and experiments 2.1. Temperature acquisition system The temperature acquisition system consists of a PC, a data acquisition card (model PCL-818HG, manufactured by Advantech Ltd) and copperconstantan thermocouples (Type T). The data acquisition card used can provide 16 bit analog input. The thermocouples were specially designed by the authors to allow for their penetration into the wall of the cooling part or the reheated preform. The thermocouples were calibrated prior to the actual measurement. During measurement, the data from the data acquisition card were temporarily stored in RAM (random access memory) through DMA (direct memory access) channel. DMA is a technique for transferring data between a device and RAM without the intervention of the CPU (central processor unit). Finally, all data of every
ARTICLE IN PRESS H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
measurement in RAM were read to the hard disk of the PC. The test results showed that the delay time for the acquisition system is less than 0.2 s. The data were then processed using MATLAB software and transferred to the temperature profile curves.
2.2. Transient temperature measurement during cooling and solidification in extrusion blow molding Fig. 1 schematically illustrates the experimental setup for measuring the transient temperatures of the cooling part in extrusion blow molding. The experimental work was carried out using an extrusion blow-molding machine (model TDL-5L/1, manufactured by Tongda Plastics Machinery Co. Ltd). The machine has a screw diameter of 55 mm and a length–diameter ratio of 25:1. The annular die used to extrude the parison is a convergent one with an outer diameter of 20 mm. The mold with a circular cross-section was used to blow mold a 100 ml bottle. A hole, where is near the middle of the height of the mold, was drilled through the mold wall. Then a portion of the hole was screwed. The thermocouple tip, which has a diameter of 1.5 mm, protruded from the mold cavity through the hole and so penetrated into the wall of the cooling part. The protruding length of the thermocouple tip was adjusted to allow for its penetration into different locations across the wall of the cooling part. The material used was a PP (F401, Petrochina Guangzhou Petrochemical Co.) with a melt index of 2.5 g/10 min and a solid density of 0.91 g/cm3. During the experiments, the die gap opening was adjusted to make the blow-molded part have a 3 mm thickness. Three different die temperatures, 190,
Fig. 1. Schematic of the experimental setup for measuring the transient temperature during cooling and solidification in extrusion blow molding.
841
210, and 230 1C, and three different blowing pressures, 0.3, 0.5, and 0.7 MPa, were employed. Two materials, steel and aluminum, were used to manufacture the mold body. The overall cooling time was set at 30 s. The transient temperature profiles were continuously recorded during the entire cooling and solidification stage. 2.3. Transient temperature measurement during reheating of preform in SBM Fig. 2 schematically shows the experimental setup for measuring the transient temperatures of the reheated preform in two-stage SBM. Experiments were conducted on a reheat SBM machine (model WL-A03, manufactured by WeiLi Plastics Machinery Co. Ltd). Its oven has eight heating lamps. In order to obtain a uniform temperature distribution around the circumference of the preform, the temperature measurement should be carried out as it rotated. Therefore, a special brush mechanism (as schematically shown in Fig. 2) was designed. The support and rotating shaft in the brush mechanism were made of bakelite. The shaft rotated together with the preform and so the measurement could be made as the preform rotated. The thermocouples, with a wire diameter of 0.3 mm, were specially designed by authors to allow for their penetration into the preform. The preform used in the experiments was 55 g, 125 mm long, with a diameter of 28.6 mm and a thickness of 4.3 mm. The material used to injection mold the preform was an industrial grade PET (grade CB-602) manufactured by Far Eastern Industries (Shanghai) Ltd. It has an intrinsic viscosity of about 0.8. Two kinds of heating lamps, transparent far infrared tungsten lamps and far infrared quartz lamps, were used in this work. Three different
Fig. 2. Schematic of the experimental setup for measuring the transient temperature during reheating of preform in SBM.
ARTICLE IN PRESS H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
842 Table 1 Voltage settings of heating lamps Lamp no.
V1 (V)
V2 (V)
V3 (V)
#1 #2 #3 #4 #5 #6 #7 #8
80 70 60 60 60 60 40 20
70 60 50 50 50 50 30 15
60 50 45 45 45 45 25 10
voltage settings of heating lamps in the heat oven, which are denoted as V1, V2, and V3 and listed in Table 1, were used. The transient temperature profiles both through the thickness of the preform and along its length were measured (as shown in Fig. 3). For the former, the measurements were conducted at three locations, with a distance of 2, 3, and 4 mm from the external surface of the preform, respectively, around the circle (denoted as B) with a distance of 45 mm from the preform shoulder (denoted as A). The reheating was stopped when the temperature of the location at 2 mm from the external surface of the preform reached 110 1C. For the latter, the temperatures of three locations denoted as C, D, and E, at distances of 25, 45, and 65 mm from the preform shoulder, respectively, were measured. All measurements for these three locations were conducted at a distance of 2 mm from the external surface of the preform. The reheating was stopped when the temperature at C reached 110 1C. The wires of three thermocouples were inserted into different positions through the wall of the preform or along its length simultaneously prior to the measurement. The transient temperature profiles were continuously acquired during the entire reheating stage. 3. Results and discussion 3.1. Transient temperature distributions during cooling and solidification in extrusion blow molding
Fig. 3. Schematic of measurement locations during reheating of preform in SBM. All dimensions are in mm.
Fig. 4 shows the transient temperature vs. cooling time distributions at four locations across the wall thickness of the cooling part at die temperatures of 190 and 230 1C. It can be seen that the locations near the external surface of the part cool more rapidly, while the locations near the internal surface (within 1.5 mm from the internal surface) cool down at a slower rate. The cooling rate decreases with increase of the cooling time. Comparing the temperature distributions of the cooling part at two die temperatures, shows that the die temperature has more effect on the temperatures near the internal surface. This coincides with the simulation results carried out by Huang et al. [14]. Moreover, the resulting temperature difference under two die temperatures at the same location is larger at the beginning of cooling and then gradually decreases with increase of the cooling time, which is about 10 1C at the end of cooling. That means that the effect of the die temperature on the temperature
ARTICLE IN PRESS H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
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Fig. 4. Temperature profiles at different locations across the thickness of cooling part at die temperature of (a)190 and (b)230 1C. The blowing pressure is 0.5 MPa and the mold material is steel.
3.2. Transient temperature distributions during reheating of preform in stretch blow molding
Fig. 5. Comparison of temperature profiles at 2.0 mm from the external surface of part under three blowing pressures. The die temperature is 210 1C and the mold material is aluminum.
distribution of the part at the end of cooling is not very significant. Shown in Fig. 5 is the effect of the blowing pressure on the transient temperature distributions at 2.0 mm from the external surface of the cooling part. As expected, higher blowing pressure slightly improves the cooling. This is because higher blowing pressure favors tight contact between the mold cavity and the cooling part and so improves the heat transfer coefficient between the two.
Figs. 6 and 7 display the measured temperature evolution at circle B of the reheated preform as a function of reheating time using the transparent far infrared tungsten lamp and the far infrared quartz lamp, respectively. The results are shown for three different locations through the thickness of the preform under three voltage settings of lamps, as shown in Table 1. It can be seen that the voltage or the temperature of heating lamps has a strong effect on the heat up rate of the preform. Increasing the heating lamp temperature leads to a faster heat up rate, whereas the lamp temperature has little effect on the temperature difference through the wall of the preform at the end of reheating. The heat up rate decreases with increase of the distance from the external surface of the preform. A comparison between Figs. 6 and 7 shows that the transparent far infrared tungsten lamp leads to a higher heat up rate than the far infrared quartz lamp. Shown in Fig. 8 is the reheating time required for heating the location at a distance of 2 mm to a temperature of 110 1C. It can be seen that the reheating time required for the infrared quartz lamp is nearly twice as large as that for the transparent far infrared tungsten lamp. Fig. 9 shows the measured temperature distributions as a function of reheating time for three locations along the reheated preform using the transparent far infrared tungsten lamp and lamp voltage setting V2. Temperature difference along the
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Fig. 6. Temperature evolution at different locations through the preform thickness using transparent far infrared tungsten lamp for the lamp voltage setting of (a) V1, (b) V2, and (c) V3. The distance from external surface (mm): (&) 2, (J) 3, (n) 4.
preform exists under the lamp voltage settings used in the present work. In the next work, the acquired results will be used to verify the predicted temperature profiles for the reheated preform during two-stage SBM.
Fig. 7. Temperature evolution at different locations through the preform thickness using far infrared quartz lamp for the lamp voltage setting of (a) V1, (b) V2, and (c) V3. The distance from external surface (mm): (&) 2; (J) 3; (n) 4.
4. Conclusions The temperature measurements of the cooling part in extrusion blow molding and of the reheated preform in SBM were generally on surfaces in
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mination of temperature profiles and so assists the operators to quantitatively analyze the effects of the processing parameters and thermal properties of plastics and mold materials etc. Acknowledgements Financial support provided by the National Natural Science Foundation of China (20274012, 50390096) and Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE, P.R.C. is gratefully acknowledged. Fig. 8. Required reheating time for heating the location at a distance of 2 mm around circle B to the temperature of 110 1C.
References
Fig. 9. Temperature profiles for locations C (n), D (J), and E (&) along the preform using transparent far infrared tungsten lamp and lamp voltage setting of V2.
previous researches. Hence, a PC-based temperature acquisition system which can be used to measure the transient temperature profiles within the wall of the cooling part and the reheated preform was developed in this work. During cooling and solidification in extrusion blow-molding, measurements were conducted across the thickness of the cooling part at three die temperatures, three blowing pressures, and two kinds of blow-molding materials. During reheating of the preform in SBM, measurements were carried out at different locations both across the thickness and along the length of the preform. Two kinds of heating lamps and three lamp voltage settings were used during measurements. Some interesting phenomena were observed using the acquisition system. The results showed that the acquisition system yields fast and repeatable deter-
[1] A.J. Bur, S.C. Roth, D.W. Baugh, K.A. Koppi, M.A. Spalding, J. Gunderson, W.C. Buzanowski, SPE ANTEC Tech Papers 49 (2003) 3341. [2] A. Bendada, M. Lamontagne, Infrared Phys Technol 46 (2004) 11. [3] J. Keum, J.L. White, SPE ANTEC Tech Papers 50 (2004) 108. [4] K. Trivedi, D. Cuff, C.L. Thomas, SPE ANTEC Tech Papers 50 (2004) 1271. [5] A.L. Kelly, E.C. Brown, P.D. Coates, SPE ANTEC Tech Papers 51 (2005) 291. [6] V. Yang, C.T. Huang, P.C. Tsai, J. Perdikoulias, J. Vlcek, SPE ANTEC Tech Papers 50 (2004) 515. [7] N. Sombatsompop, W. Chaiwattanpipat, Adv Polym Technol 19 (2000) 79. [8] H. Yokoi, Y. Murata, W. Kim, in: P.D. Coates (Eds.), Polymer Process Engineering 2001, 2. [9] R. Bradean, D.B. Ingham, P.J. Heggs, Plast Rub Comp Proc Appl 27 (1998) 65. [10] T. Kakemura, N.R. Schott, SPE ANTEC Tech Papers 44 (1998) 789. [11] W. DiRaddo, R. Aubert, Plast Rub Comp Proc Appl 29 (2000) 168. [12] D. Laroche, K.K. Kabanemi, L. Pecora, Polym Eng Sci 39 (1999) 1223. [13] H. Masse´, P. Debergue, R.W. Diraddo, SPE ANTEC Tech Papers 50 (2004) 2. [14] H.X. Huang, Y.Z. Li, Y.F. Huang, SPE ANTEC Tech Papers 50 (2004) 27. [15] A. Bendada, F. Erchiqui, A. Kipping, NDT E Inter 38 (2005) 433. [16] M.D. Shelby, SPE ANTEC Tech Papers 37 (1991) 1420. [17] G. Venkateswaran, M.R. Cameron, S.A. Jabarin, Adv Polym Technol 17 (1998) 237. [18] L. Martin, D. Stracovsky, D. Laroche, A. Bardetti, R. BenYedder, R. DiRaddo, SPE ANTEC Tech Papers 45 (1999) 982. [19] C. Champin, M. Bellet, F.M. Schmidt, J.-F. Agassant, Y. Le Maoult, SPE ANTEC Tech Papers 51 (2005) 7. [20] H.X. Huang, Y.H. Deng, Y.F. Huang, SPE ANTEC Tech Papers 51 (2005) 12.
POLYMER TESTING Polymer Testing 25 (2006) 839–845 www.elsevier.com/locate/polytest
Test Equipment
Online real-time acquisition for transient temperature in blow molding Han-Xiong Huang, Yu-Zhou Li, Yan-Hong Deng Center for Polymer Processing Equipment and Intellectualization, College of Industrial Equipment and Control Engineering, South China University of Technology, Guangzhou, PR China Received 23 February 2006; accepted 5 April 2006
Abstract In blow molding, the temperature is an important parameter which influences the process, cycle times, and part properties, etc. In the current work, a PC-based temperature acquisition system, including hardware and software, was developed to measure the transient temperatures of an extrusion blow-molded part during its cooling and solidification, and of a reheated preform in stretch blow molding (SBM). Two issues were addressed. Firstly, the thermocouples in the acquisition system were specially designed by the authors to allow for their penetration into the wall of the cooling part or reheated preform. Secondly, in order to measure the temperature of reheated preform as it rotates, a special brush mechanism was designed. The acquisition system was tested through a series of experiments on industrial blow-molding machines under different conditions, such as die temperature, blowing pressure, and blow mold material in extrusion blow molding, and the kind of heating lamps and their voltage settings in SBM. The ability of fast and repeatable online measurement of transient temperature profiles using the acquisition system should prove to be helpful to better understand the molding phenomena, to validate the numerical simulation results and to derive optimum processing parameters for blow molding. r 2006 Elsevier Ltd. All rights reserved. Keywords: Extrusion blow molding; Stretch blow molding; Temperature profiles; Online; Real time
1. Introduction In polymer processing, the properties of a finished part are dependent on both the material from which it is manufactured and the processing parameters during production. The temperature is an important processing parameter, which influences process features such as cycle times, crystallization rates, degree of crystallinity, melt-flow properties and Corresponding author. Tel./fax: +8620 2223 6799.
E-mail address: [email protected] (H.-X. Huang). 0142-9418/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2006.04.003
chemical stability. Study of the temperature profiles in polymer processing is of fundamental importance to a more complete understanding of many complicated phenomena such as heat transfer problems and molecular orientation, etc., which, in turn, can lead to the improved design of processing equipment and control for polymer products of specified dimensions. Moreover, the measurement of the temperature distribution during polymer processing is of great importance for the validation of numerical simulation results. So, many researches including both numerical simulations and experiments on the
ARTICLE IN PRESS 840
H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
temperature distributions in polymer processing, such as extrusion [1–5], injection molding [6–8], and blow molding [9–20] have been previously carried out. Blow molding is a major polymer processing technique for manufacturing a wide variety of hollow plastics parts. The blow molding is commonly subdivided into two main classes, i.e., extrusion blow molding and injection stretch blow molding (SBM). The former is widely used to produce containers of various sizes and shapes and is also adapted to make irregular complex hollow parts, such as those supplied for automobiles, office automation equipment and pharmaceutical sectors, etc. The latter technique is extensively used in the commercial production of bottles for the food, beverage, and pharmaceutical industries. Cooling and solidification is the final stage in the blow-molding process as well as many other plasticmolding operations. This stage represents 60% or more of the cycle time in the extrusion blowmolding process. Thus, the cooling time directly influences the productivity and cost of the process. Furthermore, the cooling and solidification also affect the properties, such as crystallinity, density, shrinkage, residual stresses, warpage, mechanical properties and permeability of blow-molded parts. Hence, the cooling rate or the cooling time should be at an optimal value, since excessive cooling time limits productivity, whereas short cooling time results in significant part deformation. Some researchers have devoted time to experimental and theoretical studies on the cooling and solidification of extrusion blow-molded parts [9–15]. However, the measurement of the temperature of the cooling part was generally only on its external surface in previous researches [10,15]. In the two-stage SBM process, tube-shaped preforms are first made by injection molding, cooled to room temperature, and stored until required. They are then reheated to an appropriate temperature distribution above the glass transition temperature of the material and stretch blow molded into bottles using a reheat SBM machine. Reheating produces temperature profiles, both through the thickness and along the length of the tube-shaped preform. The temperature and its distributions in the reheated preform have a strong effect on the stretching and inflation of the preform and the orientation, crystallinity, critical performance characteristics (the mechanical properties, barrier performance, and transparency), and thickness
distribution in the bottle. The regions with higher temperature will stretch and blow out faster and thin out more than the regions with lower temperature. The stretching temperature also determines the amount of orientation induced by stretching, which, in turn, affects the properties of the bottle. So, reheating is a decisive factor for the production of high quality bottles in the two-stage SBM process, and it is very important to investigate the temperature evolution within the preform during its reheating. A few efforts have been made to represent the heat transfer inside an infrared oven [16–20] but, because of the complexity of the radiative transfer in a transparent preform, the problem still remains open. Moreover, to the knowledge of the authors, in the previous researches on the reheating stage of the two-stage SBM process, the predicted temperature profiles were verified only by measuring the preform surface temperatures [16–18]. The current work describes the development of a PC-based temperature acquisition system which was used to measure the transient temperature profiles of an extrusion blow-molded part during its cooling and solidification, and of a reheated preform in SBM. For the former, the temperatures at different locations across the thickness of the cooling part were measured. For the latter, the temperature measurements were carried out at different locations both across the thickness and along the length of the preform. 2. Description of temperature acquisition system and experiments 2.1. Temperature acquisition system The temperature acquisition system consists of a PC, a data acquisition card (model PCL-818HG, manufactured by Advantech Ltd) and copperconstantan thermocouples (Type T). The data acquisition card used can provide 16 bit analog input. The thermocouples were specially designed by the authors to allow for their penetration into the wall of the cooling part or the reheated preform. The thermocouples were calibrated prior to the actual measurement. During measurement, the data from the data acquisition card were temporarily stored in RAM (random access memory) through DMA (direct memory access) channel. DMA is a technique for transferring data between a device and RAM without the intervention of the CPU (central processor unit). Finally, all data of every
ARTICLE IN PRESS H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
measurement in RAM were read to the hard disk of the PC. The test results showed that the delay time for the acquisition system is less than 0.2 s. The data were then processed using MATLAB software and transferred to the temperature profile curves.
2.2. Transient temperature measurement during cooling and solidification in extrusion blow molding Fig. 1 schematically illustrates the experimental setup for measuring the transient temperatures of the cooling part in extrusion blow molding. The experimental work was carried out using an extrusion blow-molding machine (model TDL-5L/1, manufactured by Tongda Plastics Machinery Co. Ltd). The machine has a screw diameter of 55 mm and a length–diameter ratio of 25:1. The annular die used to extrude the parison is a convergent one with an outer diameter of 20 mm. The mold with a circular cross-section was used to blow mold a 100 ml bottle. A hole, where is near the middle of the height of the mold, was drilled through the mold wall. Then a portion of the hole was screwed. The thermocouple tip, which has a diameter of 1.5 mm, protruded from the mold cavity through the hole and so penetrated into the wall of the cooling part. The protruding length of the thermocouple tip was adjusted to allow for its penetration into different locations across the wall of the cooling part. The material used was a PP (F401, Petrochina Guangzhou Petrochemical Co.) with a melt index of 2.5 g/10 min and a solid density of 0.91 g/cm3. During the experiments, the die gap opening was adjusted to make the blow-molded part have a 3 mm thickness. Three different die temperatures, 190,
Fig. 1. Schematic of the experimental setup for measuring the transient temperature during cooling and solidification in extrusion blow molding.
841
210, and 230 1C, and three different blowing pressures, 0.3, 0.5, and 0.7 MPa, were employed. Two materials, steel and aluminum, were used to manufacture the mold body. The overall cooling time was set at 30 s. The transient temperature profiles were continuously recorded during the entire cooling and solidification stage. 2.3. Transient temperature measurement during reheating of preform in SBM Fig. 2 schematically shows the experimental setup for measuring the transient temperatures of the reheated preform in two-stage SBM. Experiments were conducted on a reheat SBM machine (model WL-A03, manufactured by WeiLi Plastics Machinery Co. Ltd). Its oven has eight heating lamps. In order to obtain a uniform temperature distribution around the circumference of the preform, the temperature measurement should be carried out as it rotated. Therefore, a special brush mechanism (as schematically shown in Fig. 2) was designed. The support and rotating shaft in the brush mechanism were made of bakelite. The shaft rotated together with the preform and so the measurement could be made as the preform rotated. The thermocouples, with a wire diameter of 0.3 mm, were specially designed by authors to allow for their penetration into the preform. The preform used in the experiments was 55 g, 125 mm long, with a diameter of 28.6 mm and a thickness of 4.3 mm. The material used to injection mold the preform was an industrial grade PET (grade CB-602) manufactured by Far Eastern Industries (Shanghai) Ltd. It has an intrinsic viscosity of about 0.8. Two kinds of heating lamps, transparent far infrared tungsten lamps and far infrared quartz lamps, were used in this work. Three different
Fig. 2. Schematic of the experimental setup for measuring the transient temperature during reheating of preform in SBM.
ARTICLE IN PRESS H.-X. Huang et al. / Polymer Testing 25 (2006) 839–845
842 Table 1 Voltage settings of heating lamps Lamp no.
V1 (V)
V2 (V)
V3 (V)
#1 #2 #3 #4 #5 #6 #7 #8
80 70 60 60 60 60 40 20
70 60 50 50 50 50 30 15
60 50 45 45 45 45 25 10
voltage settings of heating lamps in the heat oven, which are denoted as V1, V2, and V3 and listed in Table 1, were used. The transient temperature profiles both through the thickness of the preform and along its length were measured (as shown in Fig. 3). For the former, the measurements were conducted at three locations, with a distance of 2, 3, and 4 mm from the external surface of the preform, respectively, around the circle (denoted as B) with a distance of 45 mm from the preform shoulder (denoted as A). The reheating was stopped when the temperature of the location at 2 mm from the external surface of the preform reached 110 1C. For the latter, the temperatures of three locations denoted as C, D, and E, at distances of 25, 45, and 65 mm from the preform shoulder, respectively, were measured. All measurements for these three locations were conducted at a distance of 2 mm from the external surface of the preform. The reheating was stopped when the temperature at C reached 110 1C. The wires of three thermocouples were inserted into different positions through the wall of the preform or along its length simultaneously prior to the measurement. The transient temperature profiles were continuously acquired during the entire reheating stage. 3. Results and discussion 3.1. Transient temperature distributions during cooling and solidification in extrusion blow molding
Fig. 3. Schematic of measurement locations during reheating of preform in SBM. All dimensions are in mm.
Fig. 4 shows the transient temperature vs. cooling time distributions at four locations across the wall thickness of the cooling part at die temperatures of 190 and 230 1C. It can be seen that the locations near the external surface of the part cool more rapidly, while the locations near the internal surface (within 1.5 mm from the internal surface) cool down at a slower rate. The cooling rate decreases with increase of the cooling time. Comparing the temperature distributions of the cooling part at two die temperatures, shows that the die temperature has more effect on the temperatures near the internal surface. This coincides with the simulation results carried out by Huang et al. [14]. Moreover, the resulting temperature difference under two die temperatures at the same location is larger at the beginning of cooling and then gradually decreases with increase of the cooling time, which is about 10 1C at the end of cooling. That means that the effect of the die temperature on the temperature
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843
Fig. 4. Temperature profiles at different locations across the thickness of cooling part at die temperature of (a)190 and (b)230 1C. The blowing pressure is 0.5 MPa and the mold material is steel.
3.2. Transient temperature distributions during reheating of preform in stretch blow molding
Fig. 5. Comparison of temperature profiles at 2.0 mm from the external surface of part under three blowing pressures. The die temperature is 210 1C and the mold material is aluminum.
distribution of the part at the end of cooling is not very significant. Shown in Fig. 5 is the effect of the blowing pressure on the transient temperature distributions at 2.0 mm from the external surface of the cooling part. As expected, higher blowing pressure slightly improves the cooling. This is because higher blowing pressure favors tight contact between the mold cavity and the cooling part and so improves the heat transfer coefficient between the two.
Figs. 6 and 7 display the measured temperature evolution at circle B of the reheated preform as a function of reheating time using the transparent far infrared tungsten lamp and the far infrared quartz lamp, respectively. The results are shown for three different locations through the thickness of the preform under three voltage settings of lamps, as shown in Table 1. It can be seen that the voltage or the temperature of heating lamps has a strong effect on the heat up rate of the preform. Increasing the heating lamp temperature leads to a faster heat up rate, whereas the lamp temperature has little effect on the temperature difference through the wall of the preform at the end of reheating. The heat up rate decreases with increase of the distance from the external surface of the preform. A comparison between Figs. 6 and 7 shows that the transparent far infrared tungsten lamp leads to a higher heat up rate than the far infrared quartz lamp. Shown in Fig. 8 is the reheating time required for heating the location at a distance of 2 mm to a temperature of 110 1C. It can be seen that the reheating time required for the infrared quartz lamp is nearly twice as large as that for the transparent far infrared tungsten lamp. Fig. 9 shows the measured temperature distributions as a function of reheating time for three locations along the reheated preform using the transparent far infrared tungsten lamp and lamp voltage setting V2. Temperature difference along the
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Fig. 6. Temperature evolution at different locations through the preform thickness using transparent far infrared tungsten lamp for the lamp voltage setting of (a) V1, (b) V2, and (c) V3. The distance from external surface (mm): (&) 2, (J) 3, (n) 4.
preform exists under the lamp voltage settings used in the present work. In the next work, the acquired results will be used to verify the predicted temperature profiles for the reheated preform during two-stage SBM.
Fig. 7. Temperature evolution at different locations through the preform thickness using far infrared quartz lamp for the lamp voltage setting of (a) V1, (b) V2, and (c) V3. The distance from external surface (mm): (&) 2; (J) 3; (n) 4.
4. Conclusions The temperature measurements of the cooling part in extrusion blow molding and of the reheated preform in SBM were generally on surfaces in
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mination of temperature profiles and so assists the operators to quantitatively analyze the effects of the processing parameters and thermal properties of plastics and mold materials etc. Acknowledgements Financial support provided by the National Natural Science Foundation of China (20274012, 50390096) and Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE, P.R.C. is gratefully acknowledged. Fig. 8. Required reheating time for heating the location at a distance of 2 mm around circle B to the temperature of 110 1C.
References
Fig. 9. Temperature profiles for locations C (n), D (J), and E (&) along the preform using transparent far infrared tungsten lamp and lamp voltage setting of V2.
previous researches. Hence, a PC-based temperature acquisition system which can be used to measure the transient temperature profiles within the wall of the cooling part and the reheated preform was developed in this work. During cooling and solidification in extrusion blow-molding, measurements were conducted across the thickness of the cooling part at three die temperatures, three blowing pressures, and two kinds of blow-molding materials. During reheating of the preform in SBM, measurements were carried out at different locations both across the thickness and along the length of the preform. Two kinds of heating lamps and three lamp voltage settings were used during measurements. Some interesting phenomena were observed using the acquisition system. The results showed that the acquisition system yields fast and repeatable deter-
[1] A.J. Bur, S.C. Roth, D.W. Baugh, K.A. Koppi, M.A. Spalding, J. Gunderson, W.C. Buzanowski, SPE ANTEC Tech Papers 49 (2003) 3341. [2] A. Bendada, M. Lamontagne, Infrared Phys Technol 46 (2004) 11. [3] J. Keum, J.L. White, SPE ANTEC Tech Papers 50 (2004) 108. [4] K. Trivedi, D. Cuff, C.L. Thomas, SPE ANTEC Tech Papers 50 (2004) 1271. [5] A.L. Kelly, E.C. Brown, P.D. Coates, SPE ANTEC Tech Papers 51 (2005) 291. [6] V. Yang, C.T. Huang, P.C. Tsai, J. Perdikoulias, J. Vlcek, SPE ANTEC Tech Papers 50 (2004) 515. [7] N. Sombatsompop, W. Chaiwattanpipat, Adv Polym Technol 19 (2000) 79. [8] H. Yokoi, Y. Murata, W. Kim, in: P.D. Coates (Eds.), Polymer Process Engineering 2001, 2. [9] R. Bradean, D.B. Ingham, P.J. Heggs, Plast Rub Comp Proc Appl 27 (1998) 65. [10] T. Kakemura, N.R. Schott, SPE ANTEC Tech Papers 44 (1998) 789. [11] W. DiRaddo, R. Aubert, Plast Rub Comp Proc Appl 29 (2000) 168. [12] D. Laroche, K.K. Kabanemi, L. Pecora, Polym Eng Sci 39 (1999) 1223. [13] H. Masse´, P. Debergue, R.W. Diraddo, SPE ANTEC Tech Papers 50 (2004) 2. [14] H.X. Huang, Y.Z. Li, Y.F. Huang, SPE ANTEC Tech Papers 50 (2004) 27. [15] A. Bendada, F. Erchiqui, A. Kipping, NDT E Inter 38 (2005) 433. [16] M.D. Shelby, SPE ANTEC Tech Papers 37 (1991) 1420. [17] G. Venkateswaran, M.R. Cameron, S.A. Jabarin, Adv Polym Technol 17 (1998) 237. [18] L. Martin, D. Stracovsky, D. Laroche, A. Bardetti, R. BenYedder, R. DiRaddo, SPE ANTEC Tech Papers 45 (1999) 982. [19] C. Champin, M. Bellet, F.M. Schmidt, J.-F. Agassant, Y. Le Maoult, SPE ANTEC Tech Papers 51 (2005) 7. [20] H.X. Huang, Y.H. Deng, Y.F. Huang, SPE ANTEC Tech Papers 51 (2005) 12.