摘要:

AbstractDeterministic mathematical models of the Maddock melting mechanism based on analytical and finite‐difference solution methods are surveyed and classified according to the key assumptions involved. It has been concluded that the rigid solid bed concept coupled with a consistent non‐Newtonian analysis of the melt flow pattern, including cross‐channel circulation, leads to superior results. It is suggested that the development of the melting theory for the Maddock mechanism as an engineering analytical tool is virtually com

ISSN:0032-3888    

DOI:10.1002/pen.760251002

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe flow of polymer melts in a rotating disc extruder is analyzed with the development of a mathematical model for drag flow in a contoured rotating disc. The model assumes a fully melted material which exhibits Newtonian flow behavior under isothermal conditions. Flow is evaluated in successive sections of the flow path, and the drag flow component is calculated by assuming a zero pressure gradient by analogy to the analysis of single screw extruder performance. The final expression involves a computer‐assisted numerical solution. Results of the drag flow model are presented for three different disc geometries. A mathematical model of negative flow, and a comparison of the results with experimental data will be presented in followup paper

ISSN:0032-3888    

DOI:10.1002/pen.760251003

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe flow of polymer melts in a rotating disc extruder is analyzed with a mathematical model for pressure flow and leakage flow (termed neg ative flow). It is assumed that the material is fully melted and exhibits Newtonian flow behavior under isothermal conditions for each element. Flow is evaluated in successive sections of the flow path and the final expression involves a computer‐assisted numerical solution. Pressure flow, which is negative, is calculated by analyzing the situation in which the pressure gradient causes the extrudable material to flow back across the stationary disc. A simplified geometrical model is developed for numerical solution, assuming incompressible flow. Leakage flow is between the contours of the disc and the engaging interior face of the housing. The flow is also directed opposite to the drag component and is estimated by using parallel plate flow equation

ISSN:0032-3888    

DOI:10.1002/pen.760251004

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractIn practice, it happens very often that structural parts made of plastics are submitted to a long term loading which “jumps” periodically between a constant maximal value and a constant minimal one. The knowledge of the material response to such a kind of loading demands very laborious experimental investigations. Since generally the loading takes place in the nonlinear viscoelastic range of the material, an analysis based on linear superposition cannot be applied. In the present paper a computational method is proposed to predict the response of the polymer to a low frequency “jumping” load in the nonlinear viscoelastic range, This method is based on the knowledge of the long term behavior of the material under constant loading conditions, which is approximated by finite exponential series. Both cases, stress‐relaxation‐type and creep‐type loading histories are treated. Examples presented show a very good agreement between theoretical predictions and expe

ISSN:0032-3888    

DOI:10.1002/pen.760251005

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractSince the cure rate of injection molded thermosets is usually very sensitive to cavity surface temperature, spatial variations in these temperatures can lengthen the necessary cure time for the entire part and cause distortion and residual stress in the molded article. This problem is addressed in the present paper by combining an optimization algorithm with a quasi‐steady heat conduction analysis in the mold to determine the heating line positions and operating temperatures that minimize the spatial variation in cavity surface temperature. The method is applied to an example mold for a flat panel of uniform thickness, using two different gate locations. At a one‐minute cycle, the optimal designs for each gate location dramatically reduce the variation in cavity surface temperature compared with corresponding results using a conventional heating system. These results are made more significant by the fact that the optimal designs use considerably fewer heating lines. In spite of their simplicity, the optimal designs still have enough flexibility to adjust to a changing cycle without sacrificing uniformity in cavity surface temperat

ISSN:0032-3888    

DOI:10.1002/pen.760251006

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractReinforcement of polyester resin with jute cloth under constant load is studied, The pretreatment of jute cloth with tetrahydrofuran and the effect of binding properties of poly(vinyl acetate) and acrylic acid and their effect on the impact, tensile, and water absorptions of jute cloth polyester composites are reported and their chemical reactions are discussed.

ISSN:0032-3888    

DOI:10.1002/pen.760251007

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThis paper extends Petrie's work on film‐blowing to cover viscoelastic non‐isothermal flow for both the convected Maxwell and the Leonov models. Good agreement with experimental data is shown for the former. The calculations are highly unstable, however, and it is difficult to obtain convergence with arbitrary values of the film‐blowing parameters. The general effect of viscoelasticity is to stiffen the film and restrain the increase in bubble diameter. There is some difference between bubble shapes generated using the Maxwell and Leonov constitutive models but the temperature variation of properties is seen as the dominant effect, The Leonov model tends not to be stiff enough in its response to the present flow, which is purely extensional and good agreement with experiment was not obtained. For the Maxwell model the relevant mean relaxation time must be used for good agreement between experiment and calcul

ISSN:0032-3888    

DOI:10.1002/pen.760251008

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe melt flow behavior of thermoplastic polypropylenenatural rubber blends has been evaluated with specific reference to the effects of blend ratio, extent of dynamic crosslinking of the rubber phase and temperature, on viscosity, flow behavior index, and deformation of the extrudate. The proportion of rubber in the blend and the extent of dynamic crosslinking of the rubber phase were found to have profound influence on the viscosity of the blends at lower shear stresses. But at higher shear stresses, the effect of blend ratio on viscosity was comparatively less for the uncrosslinked blends than that for the crosslinked blends. At lower shear stress, the viscosity of the blend increased with increase in degree of crosslinking but at higher shear stress, the effect of crosslinking on viscosity was found to vary depending on the ratio of the plastic and rubber components in the blend. The deformation of the extrudates was also very much dependent on both blend ratio and degree of crosslinking.

ISSN:0032-3888    

DOI:10.1002/pen.760251009

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe kinetics of acetylene polymerization have been studied as a function of monomer pressure, catalyst aging and concentration,Al/Tiratio, and temperature. The rate constants of chain propagation and termination and their activation energies have been determined, TheMnof polyacetylene has been obtained using a radioquenching technique, and was found to vary from 500 to 250,000. Wide angle X‐ray diffraction showed the polymer to be highly crystalline but the crystallites are disordered. The crystal structures ofcisandtranspolyacetylene have been obtained from the fiber electron diffraction patterns. The c‐axis is the polymer chain axis which is along the fiber axis. The basic morphological entity is the microfibrils of 2 to 3 nm diameter which aggregate to form 20 to 30 nm fibr

ISSN:0032-3888    

DOI:10.1002/pen.760251010

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe tensile crazing and Charpy impact behavior of polypropylene modified with styrene‐butadiene copolymer (SBR) and ethylene‐propylene‐diene monomer (EPDM) was studied. Various rubber particle size distributions were obtained by varying the relative viscosities between rubbery phase and PP matrix. Transmission electron microscopy and computer‐aided image analysis were used to provide particle size information. In general, PP blends with smaller rubber particles are tougher and more ductile than those with larger particles, probably because the former represents a more efficient use of rubbery phase in promoting crazing and/or shear yielding. Samples with average particle diameter D̄ ≥ 0.5 μm were found to exhibit pronounced crazing. Within a given sample, no crazes appeared to develop around individual rubber particles with D<0.5 μm. The higher theD, the greater the propensity to form crazes. The behavior of samples with D̄ ≪ 0.5 μm appeared to be dominated by shear yielding; very few crazes could be found. That there exists a critical rubber particle size is explained by the requirement that sufficient stress concentration be maintained to a finite radial distance to permit the initiation and growth of a craze, which requires a finite volume. Small particles, inducing smaller stress‐enhanced zones, are therefore not effective in

ISSN:0032-3888    

DOI:10.1002/pen.760251011

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY