摘要:

AbstractA numerical model of mixing in single‐screw extrusion is developed which uses a two‐dimensional unsteady analogue to three‐dimensional continuous mixing. This two‐dimensional unsteady analogue uses the transverse and axial velocities to calculate an apparent tránsverse streamline velocity which is used to simulate mixing. The mixing calculations are rigorously correct for continuous mixing of well‐metered streams of equal‐viscosity Newtonian fluids in continuous mixers of constant envelope. This scheme is applied to the analysis of singlescrew extruders with stepwise varying cross‐section, particularly beginning and ending flights. The numerical simulation produces patterns qualitatively similar to those observed in mixing experiments and predicts behavior for unmodified extruders in close quantitative agreement wi

ISSN:0032-3888    

DOI:10.1002/pen.760230202

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractAn approach to predict the strain recovery behavior of polycarbonate (PC) and high impact polystyrene (HIPS) under isothermal and non‐isothermal conditions in a solid‐phase forming environment is presented in this paper. The constantsAandnof a power law relationship of the form ϵ(t) or δ(t) =Atn, fitted to isothermal creep and stress relaxation data, were determined over a wide range of temperatures for both materials. An expression for isothermal recovery was derived and compared to experimental data. Master curves and the resultant shift factors, obtained by superposing the stress relaxation and creep data (both in tension and compression) were used with the time‐temperature super position principle to numerically evaluate uniaxial strain recovery under a specific temperature history. The average temperature history obtained by numerically solving for the temperature distribution in a disc, at an initially high temperature and in contact with a cold metal surface, was used for the non‐isothermal case. The theoretical results were compared with recovery data obtained from non‐isothermal backward extrusion tests with a temperature history similar to the one described above. Reasonably good agreement w

ISSN:0032-3888    

DOI:10.1002/pen.760230203

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA model is proposed for the flow, reaction, and heat transfer during compression molding of thin, flat parts. The isothermal Newtonian version of the model is implemented using the finite element method, and is capable of handling arbitrary planar geometries. Automated mesh expansion and boundary condition modification allow the simulation to run without operator interaction. The model accurately predicts mold filling pattern for non‐Newtonian and non‐isothermal fl

ISSN:0032-3888    

DOI:10.1002/pen.760230204

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe effects of shearing conditions (i.e., shear temperature and shear rate) on the degree of orientation of polyethylene (Marlex 6006) and to what extent the induced orientation could be relaxed were examined in this study. Two types of samples were prepared: namely, SIC (shear‐induced crystallization) and non‐SIC samples. The SIC samples show induction times and possess a high degree ofc‐axis orientation along the shear direction. The induced orientation of SIC samples can be relaxed to a small extent but does not reach a steady value. Non‐SIC samples do not show induction times and they show low degrees ofc‐axis orientation. The induced orientation of non‐SIC samples can be relaxed to a steady state value with an activation energy of 90 kJ/mole. Our results also indicate that, when the shear temperature is at and above 145°C, polyethylene can be sheared up to 200X without introducing any significant molecular orientation even at very high

ISSN:0032-3888    

DOI:10.1002/pen.760230205

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractFrequently, the enhanced elevated‐temperature rigidity of engineering thermoplastics (ETPs) is a consequence of high glass‐transition temperature, and many ETPs contain aromatic ring structures in the backbone chain. These factors can lead to difficulty in melt processing, or fabrication, of parts. Thus, the definition of the melt rheology of such systems is of considerable technological, as well as scientific importance. The investigation reported here first defines the viscosity‐temperature dependence of five ETPs over a relatively narrow range of temperatures appropriate to melt processing in terms of superposition methodology. The five ETPs studied were bisphenol A polycarbonate, polysulfone, the condensation polymer of bisphenol A and mixed iso‐ and terephthalic acids, and two experimental condensation polymers: bisphenol A/isophthalic acid and 1,2 bis(4,4′‐hydroxy phenyl) ethane/isophthalic acid. Viscous flow energies of activation are examined in terms of polymer chain structure. In the second portion of the investigation it is shown that, for the latter two condensation polymers, the molecular weight, temperature, and shear rate dependence of the viscosity may be expressed in terms of a modified Carreau model. The Newtonian limiting low‐shear viscosity dependence on molecular weight and that of the shear rate shift factor (relaxation time) are found to be somewhat greater than that norm

ISSN:0032-3888    

DOI:10.1002/pen.760230206

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractSome of today's modern screws contain melt‐separating secondary (barrier) flights in the transition zone. With increasing utilization of barrier screws, the availability of proper and accurate design methods for the melting zone remains of paramount importance. A modified version of a mathematical model developed by the authors previously is applied to two most common types of barrier screws, viz.—The Mailefer screw (varying pitch and constant depth);—The Barr screw (constant pitch and varying depth). The present analysis provides valuable insight into the operating principles of these screws. A comparative study is presented demonstrating the possible advantages and disadvantages of the Maillefer and Barr screws in relation to conventional compression s

ISSN:0032-3888    

DOI:10.1002/pen.760230207

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractIn recent years the spinning speeds of poly(ethylene terephthalate) (PET) fiber have increased to the point that significant structural development is being observed in the spun yarn. At even higher speeds significant crystallization has been obtained. Data characterizing these yarns will be presented and discussed showing the development of crystals and that the onset of this phenomena is related to the stress at the “freeze point.” The “freeze point” rises from aroundTgat low speeds to the order of 200°C at high speeds. The spinline itself has been characterized by velocity and orientation profiles which show the crystallization process is extremely rapid, occurring over a few centimenters of the

ISSN:0032-3888    

DOI:10.1002/pen.760230208

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractPrediction of the screw horsepower requirement involves, among many others, the calculation of the shear stress (τs) between the solid polymer and the barrel surface during melting. Prediction of the solid bed down‐channel velocity also requires the calculation of τs. However, the pseudoplastic nature and strong temperature dependence of melt viscosity make the mathematics of calculating τsextremely difficult.As a first step of developing a reasonable mathematical model for calculating τs, experimental measurements of τswere made over a wide range of metal temperature and sliding speed for five commercial polymers using molded, block samples. Although dependences of τson metal temperature and sliding speed were found to have similar functionality to those of the dependences of melt viscosity on melt temperature and shear rate, this study showed that τscould not be expressed as a sole function of the melt rheological properties. Our subsequent study, to be reported in a follow up paper, will show that τsmust be expressed as a function of the thermodynamic properties and melt density of the polymer as well as the melt rheological properties and the melting c

ISSN:0032-3888    

DOI:10.1002/pen.760230209

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractIn general the monitoring and control of many industrial processes is so complicated by problems associated with the on‐line measurement of the desired objectives that they must be inferred from available measurements. This leads to a state estimation problem in which the selection and adaptation of the structure of the measurements plays an important role. In particular, in the reaction injection molding (RIM) process, an accurate on‐line estimate of the conversion field is highly desirable. Since conversions cannot be determined readily by direct measurements, and a thermocouple can provide reliable dynamic temperature data, we can predict the conversion field from the solution of a state estimation problem using temperature as the measured variable. In this article, we describe an algorithm for designing the optimal arrangement of measuring sensors and analyze the RIM process dynamics which influence the structure depending on the operating conditions. The search for the optimal measurement structure for the purpose of state estimation makes up the bulk of the results. No particular estimation‐control strategy is investigated in this paper. Work is underway to develop the on‐line corrective system, which will use the temperature measurements to correct model predictions. The results of that work will appear in part II of this

ISSN:0032-3888    

DOI:10.1002/pen.760230210

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760230201

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY