摘要:

AbstractOptimization 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 ga

ISSN:0032-3888    

DOI:10.1002/pen.760321902

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractCo‐rotating, intermeshing twin screw extruders are widely used in polymer compounding and blending. Among the different modules of the co‐rotating twin screw extruder, the kneading discs are the dominant ones in determining mixing efficiency. The major difficulty in solving the flow problem in the kneading disc region arises from the complex geometry and the time‐dependent flow boundaries as the discs rotate. In this work, a fluid dynamics analysis package—FIDAP—using the finite element method was employed to simulate the flow patterns in the kneading disc region of a Werner&Pfleiderer ZSK‐30 co‐rotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter λ quantifying the elongational flow components. The last two parameters are the most important ones in analyzing mixing efficiency. The influence of design variables (stagger angle, right or left handed configuration) and processing conditions (rpm, axial pressure gradient) on the flow characteristic

ISSN:0032-3888    

DOI:10.1002/pen.760321903

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe rheological properties of polystyrene (PS) and poly(methyl methacrylate) (PMMA) composites filled with monodisperse sized crosslinked polymeric particles are sensitive to processing history and chemical composition. Particles compatible with the matrix, such as PMMA or copolystyrene‐vinylphenol in a PMMA matrix, are randomly dispersed on mixing, yielding (almost) Newtonian fluids. Particles incompatible with the matrix, such as PS or copolystyrene‐acetoxystyrene in PMMA, produce composites whose steady shear viscosities depend on shear rate and whose dynamic moduli are elevated at low frequency. Particles in incompatible composites tend to cluster, producing a structure that is destroyed at high shear rates and that reforms on aging at elevated temperatu

ISSN:0032-3888    

DOI:10.1002/pen.760321904

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe development of surface texture in biaxially deformed polypropylene is examined. Two polypropylenes formed into bottles under similar conditions by the injection stretch‐blow molding process exhibit different levels of clarity. Vertical cracks of light scattering dimensions are found by optical microscopy to be the source of haze. Rheological measurements indicate the resin that develops surface cracking has a much higher extensional viscosity and exhibits a significant increase above the linear case of its extensional stress growth function. Possible mechanisms for the formation of surface texture are discusse

ISSN:0032-3888    

DOI:10.1002/pen.760321905

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractLow density polyethylene (LDPE) is extruded, stretched, and photocrosslinked at different temperatures with different stretch rations in a continuous production line. Three different sequences are adopted: crosslinking before drawing, crosslinking after drawing, and crosslinking during drawing. The effect of drawing is studied by measuring the tensile properties. The increase of tensile strength and the decrease of elongation at break after stretching are related to chain orientation in crystalline morphology measured by X‐ray diffraction. Thermal analysis by differential scanning calorimetry (DSC) supports these results. Owing to chain relaxation, the effects of orientation by stretching are significant only when the samples are drawn at a temperature not much higher than the melting point. Annealing of the drawn samples at a temperature above the melting point shows that the orientation in a crosslinked sample is retained for a much longer time than in an uncrosslinked sample. For the crosslinked samples, it is found that crosslinking after or during drawing gives a material with lower shrinkage upon heating; however, crosslinking before drawing gives a heat‐shrinkable mater

ISSN:0032-3888    

DOI:10.1002/pen.760321906

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractA bulk‐molding compound made of unsaturated polyester resin, glass fiber, calcium carbonate fillers, and low profile additives is studied. The viscosity of the compound in the absence of cure reaction is measured by capillary rheometry. The compound exhibits a shear‐thinning behavior. Injection molding in a rectangular plaque equipped with pressure transducers shows that the crosslinking reaction can begin during mold filling for low flow rate or high mold temperature. Fiber orientation in the plaque is complex as the reinforcement appears under two aspects, bundles or filaments. Their lengths and orientations are different. A layered structure throughout the thickness is observed at the mold entrance, whereas the orientation becomes progressively unidirectional in the plaque. Two fiber‐free layers near the the mold walls are observed. A numerical simulation of mold filling assuming inelastic non‐Newtonian kinetic dependent behavior is presented. The results agree well with pressure measurements. A simplified decoupled fiber motion calculation is finally proposed. A qualitative explanation of the basic phenomena which induce fiber orientation is pr

ISSN:0032-3888    

DOI:10.1002/pen.760321907

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractDifferential scanning calorimetry (DSC) was used to study the effects of melt history on the isothermal crystallization kinetics of poly(phenylene sulfide) (PPS). Crystallization of the polymer was shown to be permanently altered by both the time and the temperature spent in the melt. Suggested explanations are nonequilibrium melting, chain scission, chain extension, and crosslinking. Molecular weight was also shown to affect the rates of these processes, PPS of lower molecular weight being more susceptible to the observed changes.

ISSN:0032-3888    

DOI:10.1002/pen.760321908

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760321901

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY