摘要:

AbstractIt is pointed out that in viscoelastic fluid constitutive equations, non‐linear response to deformation rate and strain beyond the second order is usually interpreted in terms of the deformation rate or strain dependence of the memory function. These non‐linearities act to decrease the extent of the memory. The dependence may be characterized by one or more dimensionless material parameters. A new dimensionless group based on the primary material parameters describing the intensity of the deformation rate dependence of the memory function is introduced and its significance is discussed. This is called the Yamamoto number. The solutions of viscoelastic fluid mechanics problems are considered to depend upon both the Weissenberg and Yamamoto numbers. Such problems include topics of interest in polymer melt processing such as uniaxial elouigatioiial flow, fiber spinning and vortex development in extrusion through a die en

ISSN:0032-3888    

DOI:10.1002/pen.760211702

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe influence of several process parameters on the curing of multipurpose unsaturated polyesters with styrene, in heated molds, is discussed. The polymerization kinetics was studied in a quasi‐adiabatic reactor taking into account corrections for heat losses. The following expression resulted: dx/dt= k′[I](1 −x)3exp(−16.6/RT), wherexis the conversion of unsaturated bonds and [I] is the initial initiator concentration (benzoyl peroxide); cobalt octoate was used as an accelerator. Specimens were cured in two kinds of heated molds (one jacketed and the other electrically heated), and temperature profiles recorded. The temperature increase at the midplane showed a maximum when plotted as a function of the reaction rate (Arrhenius preexponential factor), in agreement with previous theoretical predictions. The temperature increase was enhanced for a thermally initiated r

ISSN:0032-3888    

DOI:10.1002/pen.760211703

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA theoretical study of non‐isothermal superimposed flow of two polymer melts in wire coating co‐extrusion dies has been carried out. Numerical methods have been employed to solve the coupled momentum‐ and energy‐balance equations. Various combinations of three polymers—namely, high density polyethylene (HDPE), polystyrene (PS) and low density polyethylene (LDPE) have been studied and least squares curve fitted quadratic polynomials have been used for constitutive equations for all three polymers in non‐Newtonian high shear rate regions. A multitude of thermal and mechanical boundary conditions can be treated by this algorithm. It was found that temperature and velocity profiles in the die depend significantly on the arrangement of the polymers. Maximum temperature rise has been noted to increase sharply with wire velocity but it can be reduced by increasing the die radius. When the thickness of the outer layer is increased from zero, the shear stress at the wall undergoes a dramatic change (if the viscosities of the polymers are different) at small values of the flow rate ratio and it reaches an asymptotic value at large values of flow rate ratio. It was also found that viscosity ratio at the interface can be reduced by changing the initial temperatures of the liquids. It was observed in some cases that large errors in the calculation of rheological and thermal variables for this problem can be made if temperature rise due to viscous dissipation is not

ISSN:0032-3888    

DOI:10.1002/pen.760211704

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractBecause heat is convected by the motion of material in the cavity of a compression mold, the time‐averaged heating load on the cavity surface is nonuniform. In rapid production of large, thin parts, this can lead to large variations in cavity surface temperature when the mold is heated by the usual uniform distribution of heating lines. In this paper, a new method is developed for optimizing the mold heating design so that this nonuniform heating requirement can be satisfied with a minimum variation in cavity surface temperature. Oil heating is considered specifically, but the method can also be used for stream or electric heat. The optimal position and power supply for each heating line in the mold is determined by combining mathematical programming techniques with an analysis of the steady temperature field in the mold. The nonuniform heating load on the cavity surface is represented by a time‐averaged steady heat transfer coefficient calculated from the transient temperature distribution in a polyester sheet molding compound as it fills the mold cavity. The design method is applied to an example mold for a large flat panel. At a one‐minute cycle, the optimal heating design dramatically reduces nonuniformity in cavity surface temperature compared with a conventional distribution of heating lines. The optimal design is remarkably simple, uses only conventional equipment, and involves only half the customary number of heating lines. Nevertheless, it still has sufficient flexibility to adjust for changes in cycle time without sacrificing uniformity in cavity surface temper

ISSN:0032-3888    

DOI:10.1002/pen.760211705

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractWeld regions are formed wherever polymer flow fronts meet. The present study examines the effects of melt temperature, mold temperature, mold cooling conditions, injection speed and annealing on the tensile properties and morphological structure of weld regions in four commercially available polypropylene resins. One of the resins contained nucleation particles. Scanning electron micrographs of the weld region revealed a wide range of morphologies from very strong welds which formed part of a stable neck to brittle failures at low elongation caused by the presence of large nucleation particles in the weld region. The melt temperature, mold temperature, and annealing had the greatest effect on the weld region's tensile properties.

ISSN:0032-3888    

DOI:10.1002/pen.760211706

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractIn the previous paper (1) the melting performance of a number of recent screw designs was analyzed, using a rather simple theory. A new screw design was proposed. Here the results of more elaborate calculations, are given in which the influence of the flight clearance and of a shear‐thinning temperature dependent viscosity are investigated. The former conclusions are not altered in essence by these effects. Experimental results with a prototype screw are presented, showing that melting capacity is increased. Up to 100 percent increase in throughput is possible in the high RPM range (in comparison with a much longer traditional compression screw), provided that the feed capacity is sufficient. This usually requires the use of a grooved, well‐cooled, feed section; the capacity of such a feed section depends, for a given screw geometry, on channel depth and granule dimensions. The melt leaves the melting section at a relatively low temperature. The melting section only melts the material and does not raise, its temperature unnecessarily. A further step towards separating distinct tasks of the extruder by functional screw design has been m

ISSN:0032-3888    

DOI:10.1002/pen.760211707

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractAn analysis is given of the pressure generation mechanism in the tapered channel of a single‐screw extruder. It is shown that when increasing the throughput the pressure build‐up capacity of the melting zone tends to decrease. As a result, severe pressure drops may occur in the tapered sections. A relationship between the pressure profile and the melting mechanism (solid bed/melt pool configuration) is described in terms of the cross‐channel melt circul

ISSN:0032-3888    

DOI:10.1002/pen.760211708

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe activation energy for sintering of poly(methyl methacrylate) particle pairs is shown to be similar to their activation energy for Newtonian flow. Sintering progress with time is in good agreement with the Frenkel's coalescence theory. Typical sintering shear rates are shown to be very low and potential energy change (two particles) is small in comparison with the surface energy change. These results lead to the conclusion that the coalescence sintering mechanism of amorphous polymers above their glass transition temperature is essentially a Newtonian viscous flow mechanism where surface tension is the major driving force. A periodical phenomenon associated with sintering progress with time is reported and a supporting mechanism is proposed.

ISSN:0032-3888    

DOI:10.1002/pen.760211709

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe viscosities of suspensions of glass fibers in an aqueous solution of sucrose have been studied by use of a capillary viscometer. In the aligned condition in the capillary, the viscosity depends little on shear rate within the range studied or on fiber length, but increases with increasing volume fraction of the fibers. The entrance effect was found to depend strongly on fiber volume fraction and fiber length: this indicates that the suspensions are relatively resistant to flow during the initial stages while alignment takes place.

ISSN:0032-3888    

DOI:10.1002/pen.760211710

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe tensile fatigue behavior of unnotched injection molded polysulfone specimens has been investigated. The effects of orientation and residual stress were studied by comparing asmolded specimens with annealed or annealed and quenched specimens with a known residual stress pattern. The treatments are shown to have differing effects at high stresses, where failure is by shear yielding and necking, and at intermediate stresses, where failure is by fatigue crack propagation. The geometries of fatigue cracks are described for each case. An attempt is made to separate the effects of crack and craze initiation from crack propagation, and cyclic loading from cumulative time under load.

ISSN:0032-3888    

DOI:10.1002/pen.760211711

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY