摘要:

AbstractResidual stress measurements and distortion analyses have been conducted on injection molded plaques made from polypropylene (PP) and a short glass‐fiber filled polypropylene (GFPP). The residual stress analyses include measurements both parallel and perpendicular to the direction of flow during mold filling. Residual stresses are very anisotropic in GFPP, but not in PP. The residual stress levels in PP fall on aging at room temperature, whereas in GFPP the proportion of stress relaxation is smaller, and significant stresses remain even after heating to elevated temperatures. A significant contribution to distortion has been linked to the ejection process, and the long‐ and short‐term distortion of moldings is discussed within the framework of the properties of the materials measured

ISSN:0032-3888    

DOI:10.1002/pen.760320302

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe standard spiral flow test is normally used to assess the “moldability” of thermosetting materials. It is proposed that such tests can be modified and analyzed to yield rheological information as from a viscometer. Specifically, a “parameter‐identification” scheme is developed to determine the constants in a viscosity model by minimizing the difference between the outcome of spiral flow tests and the results of numerical simulations of these tests. The proposed scheme is particularly applicable to fast‐reacting thermosets for which typical viscometers cannot be used. Successful application of the scheme is demonstrated for a particular encapsulating epoxy material, where constants are obtained for a modified WLF equation viscosity model. These constants are used to predict the outcome of spiral flow experiments not involved in the minimization procedure. A favorable comparison between experiment and simulation occurs at most operating conditions. The method requires no elaborate equipment or delicate inst

ISSN:0032-3888    

DOI:10.1002/pen.760320303

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractA study of simultaneous acoustic and rheometric (dynamic mechanical) measurements of the epoxy curing process is undertaken to assess the validity of using acoustic cure‐monitoring sensors for process control. Our results demonstrate that the acoustic technique provides a sensitive means for monitoring the cure of neat epoxy over the entire cure cycle. The acoustic modulus calculated from the shear velocity qualitatively tracks the mechanically measured dynamic modulus and correctly ranks the stiffness of two epoxy compositions. When the frequency difference is accounted for, using time‐temperature superposition of the dynamic mechanical measurements, quantitative agreement between the acoustic and mechanical moduli for fully cured epoxy resins is also quite g

ISSN:0032-3888    

DOI:10.1002/pen.760320304

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractEstimation of cooling time for a given injection molding part is becoming increasingly important, especially when a large number of parts are produced. In order to calculate the cooling time, the ejection temperature should be known. However, to date, there is no easy way to obtain the ejection temperature even though the material selected and part thickness are known. This study uses a combination of experimental, analytical, and statistical means to establish equations for calculating ejection temperature according to material properties, part thickness, and molding conditions such as injection and mold temperatures. Therefore the cooling time of a given injection molding part can be estimated in its early design stage.

ISSN:0032-3888    

DOI:10.1002/pen.760320305

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe emulsion polymerization of styrene in a continuous loop tubular reactor (CLTR) has been used to study the process kinetics under eigth levels of sodium lauryl sulfate (SLS) concentration, eight levels of potassium persulfate (KPS) concentration, and three levels of styrene monomer (St) concentration. A critical surfactant concentration for the overshoot phenomenon in the monomer conversion exists between 8.02 and 12.40 g‐SLS/1‐water. Overshoot was not eliminated by changing concentrations of the initiator and monomer. The overshoot in the number concentration of polymer particles was observed in all the polymerizations studied. The dependences of the rate of polymerization and the number concentration of particles in the steady state on the SLS and KPS concentrations are presented. The growth of the average cumulant diameter of particles shows a transient period followed by a steady state. The dependences of the volumetric growth rate of polymer particles on diameter are of the order of 1 for the lower SLS concentration and 0.5 for the higher SLS concentration, respectively. The steady state cumulant diameter depends on an order of −0.24 for the SLS concentr

ISSN:0032-3888    

DOI:10.1002/pen.760320306

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractCoat‐hanger dies are commonly used for the extrusion of plastic sheets and films. To describe the flow of a molten polymer through a coat‐hanger die, a two‐dimensional approach is necessary. Moreover, the thermal effects, which play an important role in the flow distribution, have to be taken into account. In this paper, two numerical models for the simulation of coat‐hanger dies are described and compared. These models differ mainly in the simplifying assumptions used and in the treatment of the thermal problem. The simulations obtained with the two models were compared with each other and with experimental data. The discrepancies between the two models can be explained by the different theoretical tre

ISSN:0032-3888    

DOI:10.1002/pen.760320307

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractA general computation of multilayer coextrusion flow in a flat die geometry is presented. For any given number of layers of different polymers, characterized by their thermal and rheological behaviors, the model permits computation of velocity and temperature fields along the flow in constant or slightly varying geometries. The influence of different operating parameters (wall regulation temperature, flow rate, initial temperatures) on the interface positions and temperature evolutions is evaluated. Theoretical predictions of interface positions are in agreement with experiments carried out on an industrial multimanifold flat die.

ISSN:0032-3888    

DOI:10.1002/pen.760320308

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760320301

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY