The dynamics of parison development in blow molding

An experimental program was carried out to study the dynamics of parison swell and development in extrusion-blow molding. Two commercial blow molding grade polyethylene resins were employed in conjunction with an Impco, Model A13-R12 reciprocating screw blow molding machine equipped with a cylindrical bottle mold. Parison weight swell was measured with the aid of a parison pinch-off mold. In order to obtain more reliable and useful information regarding diameter and thickness swell of the parison and the dynamics of parison formation and development, high speed cinematography was employed. Data obtained by this technique are more reliable than results obtained with the pinch-off mold alone. They also give further insight into the phenomena of swell, sag, and parison spring back or recovery.     

Modeling parison formation in extrusion blow molding by neural networks

A series of experiments were carried out on the parison formation stage in extrusion blow molding of high‐density polyethylene (HDPE) under different die temperature, extrusion flow rate, and parison length. The drop time of parison when it reached a given length and its swells, including the diameter, thickness, and area swells, were determined by analyzing its video images. Two back‐propagation (BP) artificial neural network models, one for predicting the length evolution of parison with its drop time, the other predicting the swells along the parison, were constructed based on the experimental data. Some modifications to the original BP algorithm were carried out to speed it up. The comparison of the predicted parison swells using the trained BP network models with the experimentally determined ones showed quite a good agreement between the two. The sum of squared error for the predictions is within 0.001. The prediction of the parison diameter and thickness distributions can be made online at any parison length or any parison drop time within a given range using the trained models. The predicted parison swells were analyzed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2230–2239, 2005     

A comprehensive experimental study and numerical modeling of parison formation in extrusion blow molding

Parison dimensions in extrusion blow molding are affected by two phenomena, swell due to stress relaxation and sag drawdown due to gravity. It is well established that the parison swell and sag are strongly dependent on the die geometry and the operating conditions. The availability of a modeling technique ensures a more accurate prediction of the entire blow molding process, as the proper prediction of the parison formation is the input for the remaining process phases. This study considers both the simulated and the experimental effects of the die geometry, the operating conditions, and the resin properties on the parison dimensions using high density polyethylene. Parison programming with a moving mandrel and the flow rate evolution in intermittent extrusion are also considered. The parison dimensions are measured experimentally by using the pinch-off mold technique on two industrial scale machines. The finite element software BlowParison® developed at IMI is used to predict the parison formation, taking into account the swell, sag, and nonisothermal effects. The comparison between the predicted parison/part dimensions and the corresponding experimental data demonstrates the efficiency of numerical tools in the prediction of the final part thickness and weight distributions. POLYM. ENG. SCI., 47:1–13, 2007. © 2006 Society of Plastics Engineers     

A modeling approach to the effect of resin characteristics on parison formation in extrusion blow molding

The most critical stage in the extrusion blow‐molding process is the parison formation, as the dimensions of the blow‐molded part are directly related to the parison dimensions. The swelling due to stress relaxation and sagging due to gravity are strongly influenced by the resin characteristics, die geometry, and operating conditions. These factors significantly affect the parison dimensions. This could lead to a considerable amount of time and cost through trial and error experiments to get the desired parison dimensions based upon variations in the resin characteristics, die geometry, and operating conditions. The availability of a modeling technique ensures a more accurate prediction of the entire blow‐molding process, as the proper prediction of the parison formation is the input for the remaining process phases. This study considers both the simulated and the experimental effects of various high‐density polyethylene resin grades on parison dimensions. The resins were tested using three different sets of die geometries and operating conditions. The target parison length was achieved by adjusting the extrusion time for a preset die gap opening. The finite element software BlowParison® was used to predict the parison formation, taking into account the swell and sag. Good agreements were found between the predicted parison dimensions and the experimental data. POLYM. ENG. SCI., 2009. Published by Society of Plastics Engineers     

Noncontact measurement of parison thickness profiles affected by swell and sag in continuous extrusion blow molding

Optimization of final part thickness distributions is crucial in the extrusion blow molding process in order to minimize resin usage. Prediction of part thickness distributions from basic process and material parameters would be ideal. However, attempts to do so have been unsuccessful, largely because of the inability to predict parison thickness profiles. One must therefore resort to measurement of the parison thickness profile and estimation of the final part thickness distribution by computational methods. This paper describes a new technique for the noncontact estimation of parison thickness profiles in continuous extrusion blow molding. The method accounts for sag and requires no previous knowledge of rheological data. It can be employed on-line for the purposes of process monitoring and control. The approach is based on the measurement of the parison length evolution with time during extrusion, the parison diameter profile, the flow rate, and the melt temperature gradient along the length of the parison. These parameters are utilized in conjunction with a theoretical approach that describes the extrusion of a parison under the effects of swell, sag, and extrusion into ambient conditions. Results are presented for three resins of various molecular weight distributions. The degree of sag is minimal at the top and bottom of the parison, and reaches a maximum near the center of the parison. Results are also presented to demonstrate the versatility of the method under other process conditions, such as varying flow rate, die temperature, and die gap.     

Parison formation and inflation behavior of polyamide-6 during extrusion blow molding

Parison formation and inflation behavior of three polyamide 6 resins during extrusion blow molding were investigated using cinematography, a transparent mold, a pinch-off mold and a modified blow pin, which allowed the pressure inside the parison to be determined during inflation. The glass fiber filled polyamide exhibited negligible extrudate swell and significant drawdown, whereas polyolefin modified polyamide exhibited appreciable extrudate swell and relatively small drawdown effects. The inflation behavior of the polyolefin modified polyamide was similar to the behavior of conventional blow molding grade polyolefins, whereas the unmodified and glass filled polyamides exhibited different inflation characteristics. Their inflation behavior at different internal pressures was characterized by decreasing and increasing Hencky strain rates with inflation time at high and low internal blow pressures, respectively. The characterized parison formation and inflation behavior of the polyamides emphasize the importance of rigorous blow moldability experiments and the difficulties associated with linking various rheological material functions to the blow moldability of modified polyamides.     

Three‐dimensional simulation on multilayer parison shape at pinch‐off stage in extrusion blow molding

We tried to predict the multilayer parison shape at pinch‐off stage in extrusion blow molding by nonisothermal and purely viscous non‐Newtonian flow simulation using the finite element method (FEM). We assumed the parison deformation as a flow problem. The Carreau model was used as the constitutive equation and FEM was used for calculation method. Multilayer parison used in this simulation was composed of high‐density polyethylene (HDPE) as inner and outer layers and low‐density polyethylene (LDPE) of which viscosity is five times lower than HDPE as a middle layer. We discussed multilayer parison shape in pinch‐off region. The results obtained are as follows; the parison shape of each layer was clearly visible in the pinch‐off during the mold closing. In addition, the distribution of parison thickness ratios for each layer was located for a large deformation near the pinch‐off region. The melt viscosity for each layer has an influence on the melt flow in the pinch‐off region. In a comparison with an experimental data of parison thickness ratios, the simulation results are larger than the experimental data. These simulation results obtained are in good agreement with the experimental data in consideration of the standard deviations. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

NPE 2009展示最新挤出和吹塑加工设备

1拉伸薄膜超高速收卷装置美国NPE2009上展示的最新挤出技术中,有2套新型拉伸薄膜收卷装置,其卷取LLDPE薄膜的速度可达到3000英尺/分或更快。目前,此前全球最快的拉伸薄膜收卷设备为戴维斯标准公司Converting Systems集团的4轴S4型装置,运行速度可达到2400英寸/分。在这一薄膜卷取速度以下,拉伸薄膜的产量主要受     

Fast online acquisition and analysis for parison swell and sag in blow molding

It is critical to quantitatively and reliably characterize the effects of swell and sag phenomena on the final parison dimensions in extrusion blow molding. To achieve this goal, an online image acquisition and analysis technique was developed. The successive images of parison were automatically taken using the online acquisition apparatus. These images were then analyzed by the combined use of the conventional digital image processing method and the new one developed by the authors. So the development of parison diameter and thickness swells with the extrusion time could be determined online. On the basis of the online obtained actual swell values, the pure swell and sag components were quantitatively determined. The developed technique was tested through a series of experiments using several resins under different processing parameters and die types. Shown in the present article were the results for a converging die under three different die gaps and a high‐density polyethylene. Some new phenomena were observed using the proposed technique. The results showed that the technique yields fast and accurate determination of the evolution of diameter, thickness, and length of parison during its extrusion. The technique can be employed as a part of the closed loop control for blow molded part thickness. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2399–2406, 2006     

Modeling of complex parison formation in extrusion blow molding: Effect of medium to large die heads and fuel tank geometry

This work presents the effect of die geometry and die gap opening on the extrudate swell phenomenon, in complex parison formation using the vertical wall distribution system (VWDS) and partial wall distribution system (PWDS). The BlowParison^© software from IMI is used to predict the parison formation for a combined VWDS/PWDS system, accounting for swell, sag, and nonisothermal effects. This software couples a fluid mechanics approach to represent the die flow, with a solid mechanics approach to represent the parison behavior outside the die, and a mathematical swell model to account for the pronounced elongational and shear stresses at high Weissenberg numbers. The emphasis is placed on experimental validation of the predicted parison dimensions using four diverging die geometries and different sets of VWDS/PWDS profiles. The experimental and predicted weight profiles for a dissected fuel tank are also presented. Both experimental and simulation results suggest a strong dependence of extrudate swell to the die geometry in the die land zone. The results also demonstrate the validity of the numerical predictions for part design purposes given the multitude of experimental validations presented in this work. POLYM. ENG. SCI., 2009. Published by the Society of Plastics Engineers     

Overall numerical simulation of extrusion blow molding process

This paper focuses on the overall numerical simulation of the parison formation and inflation process of extrusion blow molding. The competing effects due to swell and drawdown in the parison formation process were analyzed by a Lagrangian Eulerian (LE) finite element method (FEM) using an automatic remeshing technique. The parison extruded through an annular die was modeled as an axisymmetric unsteady nonisothermal flow with free surfaces and its viscoelastic properties were described by a K‐BKZ integral constitutive equation. An unsteady die‐swell simulation was performed to predict the time course of the extrudate parison shape under the influence of gravity and the parison controller. In addition, an unsteady large deformation analysis of the parison inflation process was also carried out using a three‐dimensional membrane FEM for viscoelastic material. The inflation sequence for the parison molded into a complex‐shaped mold cavity was analyzed. The numerical results were verified using experimental data from each of the sub‐processes. The greatest advantage of the overall simulation is that the variation in the parison dimension caused by the swell and drawdown effect can be incorporated into the inflation analysis, and consequently, the accuracy of the numerical prediction can be enhanced. The overall simulation technique provides a rational means to assist the mold design and the determination of the optimal process conditions.     

Measurement and calculation of parison dimensions and bottle thickness distribution during blow molding

Experimental data are reported regarding the dynamics of the blow molding process, including parison formation, growth, and inflation. These data have been obtained with the aid of high speed cinematography and pinch mold experiments, in conjunction with two commercial blow molding polyethylene resins. It is shown that pinch mold experiments alone do not yield accurate data regarding thickness and diameter swell. Furthermore, the inflation process involves decreasing rates of inflation with time, as a result of the rise in viscosity due to the cooling of the parison during inflation. Mathematical procedures are proposed for a first-order estimation of parison length and swell as a function of time and the inflation behavior after clamping. In the absence of more dependable basic procedures, the proposed treatment is employed to estimate the effective transient swell functions for the parison using experimental data obtained under the specified conditions. The mathematical treatment is extended to determine the thickness distribution of the bottle. Good agreement is obtained between experimental and calculated results.     

An experimental investigation of capillary extrudate swell in relation to parison swell behavior in blow molding

An experimental study was carried out to study and characterize the capillary extrudate swell and parison swell behavior in extrusion blow molding of two commercial blow molding grade high density polyethylene resins. The capillary extrudate swell behavior of these resins were determined employing a capillary rheometer and a special thermostatting chamber. Parison swell behavior was determined using an Impco A13-R12 reciprocating screw blow molding machine in conjunction with cinematography and pinch-off. The experimental conditions under which capillary extrudate and parison swell data can be related are elucidated. Excellent agreement is found between the area swell values determined on the basis of capillary and parison swell experiments.     

Validating injection stretch‐blow molding simulation through free blow trials

A 2D isothermal finite element simulation of the injection stretch‐blow molding (ISBM) process for polyethylene terephthalate (PET) containers has been developed through the commercial finite element package ABAQUS/standard. In this work, the blowing air to inflate the PET preform was modeled through two different approaches: a direct pressure input (as measured in the blowing machine) and a constant mass flow rate input (based on a pressure–volume–time relationship). The results from these two approaches were validated against free blow and free stretch‐blow experiments, which were instrumented and monitored through high‐speed video. Results show that simulation using a constant mass flow rate approach gave a better prediction of volume vs. time curve and preform shape evolution when compared with the direct pressure approach and hence is more appropriate in modeling the preblowing stage in the injection stretch‐blow molding process. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

高透明度PP树脂为挤出吹塑扫清道路

匈牙利MOL集团开发了一种专为挤出吹塑(EBM)量身定做的新型无规共聚物聚丙烯(PP),据报道,该产品在透明度和光泽度方面具有优异的光学性能。根据MOL的说法,这一发展意味着当谈到EBM应用的透明度时,PP终于可以与PVC或PET竞争。MOL的Tipplen R 665 XClear使PP能够取代更贵,功能更少,或难以加工的材料,如PET、PVC和聚碳酸酯在各种吹塑中的应用.     

Tailored biodegradable films via extrusion blow molding using PBS,PBAT, and TPS

Research to replace synthetic polymers with biodegradable polymers is on the rise because common plastics have generated serious ecosystem problems. Films with thermoplastic starch (TPS), poly(butylene succinate) (PBS), poly(butylene adipate-co-butylene terephthalate (PBAT), and citric acid (CA) were produced by blown extrusion. They were characterized by blow-up ratio (BUR), water vapor permeability (WVP), soluble ratio (SR), water sorption isotherm, and thermogravimetric (TG) techniques. Films were uniform and showed BUR > 205%. The different proportions of PBS and PBAT significantly influenced the WVP of the films. All samples had WVP with an order of magnitude similar to other blends with high starch content (10⁻⁶ g m⁻¹ day⁻¹ Pa⁻¹). CA efficiently decreased the WVP of the PBS/PBAT/TPS formulations (15/15/70% and 20/10/70% by mass) by 25.2% and 24.7% compared to the acid-free formulations. There was no significant difference in SR (19.0%–20.1%). These materials were sensitive to moisture since the equilibrium moisture content increased pronouncedly from water activity of 0.5. Films showed good thermal stability, with a maximum decomposition temperature close to pure polyesters. CA did not increase the thermal stability of blends, probably because of the low content used (0.1%). Given the outcomes of this study, these films could be deemed appropriate for applications in food packaging.     

Confined parison inflation behavior of a high-density polyethylene

An analysis of the confined parison inflation step associated with the extrusion blowmolding of a high-density polyethylene is presented. Based upon simple geometrical considerations and material conservation principles, relationships describing the wall thickness variation have been obtained for various mold configurations. The experimentally measured part thickness distribution is found to be in good qualitative agreement and reasonable quantitative correspondence with the theoretical predictions. Furthermore, the expressions for the thickness variation have been utilized in order to estimate the confined inflation time for the case of a power-law constitutive equation. In addition, a brief discussion of some practical mold design considerations is given based upon the theoretical analysis.     

Numerical simulation of blow molding—prediction of parison diameter and thickness distributions in the parison formation process

In our previous study, we calculated the time course of parison length in the parison formation stage, but it could predict only the parison area swell. The next target in our study is to calculate the parison diameter and thickness swell. Annular extrudate swell simulation is necessary for the understanding of various kinds of swelling ratios in blow molding. We have examined three kinds of swells (outer diameter, thickness, and area swells) obtained from simulation results of annular extrudate swell, using the Giesekus model, and have developed a method of predicting parison outer diameter and thickness swell values. The predicted values of parison outer diameters are discussed in comparison with experimental data, and reasonable results are obtained by the proposed method. This prediction method could also be applied to the parison formation process using a parison controller. As a result, it is possible to predict approximately the whole process of parison formation by numerical simulation.     

Heat transfer in blow molding operations

A one-dimensional model of unsteady state heat conduction has been applied to the cooling and solidification of a polymer in a blow molding process. The approach includes a temperature-dependent specific heat term to account for latent heat effects during the phase change. The model is used to predict temperature profiles in a thick-walled component of high-density polyethylene. These profiles lead to a clearer understanding of the heat transfer process. It is further shown that these temperature distributions can be used to study the influence of the major process variables upon the cooling of the molded component.