摘要:

AbstractThis note presents a coordinate frame representation for the conservation laws governing fluid motion in a helical configuration as suggested by a single‐screw extruder with deep flights and by the Kenics Static Mixer. This example demonstrates the care necessary in dealing with nonorthogonal coordinate systems. The conservation equations are also presented in terms of the proper physical components, as well as the physical components of the rate of deformation tensor. The paper closes with a brief statement of the boundary conditions for flow in a static mixe

ISSN:0032-3888    

DOI:10.1002/pen.760150602

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe work described herein was initiated in order to generate resin characterization data that could describe a B‐staged epoxy material via the viscosity‐time‐temperature interactions that are inherently related to the nature of thermoset processing. The technique of chemorheology is explored as a means of characterizing the viscosity‐time‐temperature behavior of the B‐staged epoxy resins. The resins studied are typical of those available as glass‐impregnated prepreg bonding sheets used to manufacture multilayer printed wiring boards. The B‐staged resins were characterized isothermally at various curing temperatures. Their isothermal behavior was correlated via an empirical viscosity expression in the form of a dual Arrhenius model. Experiments were then conducted in a nonisothermal temperature mode, measuring viscosity as a function of both time and temperature. The viscosity model was taken into the nonisothermal temperature mode by introducing a time‐temperature integral. Good correlations between measured and predicted dynamic viscosity profiles are presented. Deviations are explained in terms of resin chemistry. The generalizations of behavior are discused. Calculations are presented which allow the comparison of the various B‐staged resins in terms of their viscosity behavior under the influence of an actual laminat

ISSN:0032-3888    

DOI:10.1002/pen.760150603

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractPolybenzimidazole foams in the density range of 24 to 80 kg/m3have excellent thermophysical properties, fire resistance, and low smoke evolution when exposed to heat or flame; they also retain their mechanical properties up to 200°C without any significant degradation. In addition to superior thermal properties, the foams maintain a high degree of flexibility and a good modulus‐to‐weight ratio, as well as high strength‐to‐weight relationship at high temperatures. These properties make this foam an attractive candidate as a low‐weight, high‐temperature insulation for aerospace applications. This paper describes the relationship between prepolymer purity, processing parameters, and additives to the thermophysical and chemical properties of these foams. Foam properties are shown to be affected by differences in prepolymer purity, curing schedule, and the presence of additives in the foam. High‐temperature compressive properties were imporved by postcuring at 527°C. Surfactant additives were found to improve uniformity of cell size. Foams were characterized according to high‐temperature mechanical properties, density, porosity, thermal diffusivity, thermal conductivity,

ISSN:0032-3888    

DOI:10.1002/pen.760150604

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe environmental stress crack resistance of polyethylene is measured most conveniently by the bent‐strip method described in ASTM D‐1693‐70. The method has, however, suffered from poor reproducibility of test results. In this work we have carefully studied the effect of individual experimental variables that enter the test method. The effects considered are: the thermal history of test specimens; uncontrolled variations in the test procedures such as the sample holder width, the specimen thickness, and the stress relaxation occurring during the test; and the variability in the test results arising from the statistical nature of fracture process. It is concluded that each of the following four factors, when not properly controlled, could contribute an apparently random variation of a factor of two or more in the test results. These are (1) the aging of polyethylene specimens at room temperature, (2) the width of the specimen holder, (3) the dimensions of the tools employed for bending and transferring specimens, and (4) statistical fluctuations of the final results arising from the limited number of specimens tested and also from the stress relaxation occurring in the specimen during the test. By carefully controlling these and other variables, it should be possible to design a test procedure which is expected to yield results of a known precision and can serve even as a research

ISSN:0032-3888    

DOI:10.1002/pen.760150605

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe mechanical properties are presented for a series of discontinuous fiber‐reinforced thermoplastic composites made with random‐in‐plane fiber orientation. The matrix and fiber materials were chosen to provide a wide range of strength, modulus, ductility and adhesive properties. In many cases strong, rigid, yet tough composites were fabricated. Strength levels of over 20,000 psi and modulus values over 1,000,000 psi were reached in several systems reinforced with short Kevlar‐49 and graphite fibers. A strong dependence of composite strength and modulus on fiber strength and modulus was noted indicating good transfer of load from matrix to reinforcement. Fiber efficiency factors for modulus and strength were calculated for the experimental composite systems and averaged 0.19 and 0.11 respectively. Data were analyzed using basic composite theory. Properties of the experimental composites could not be predicted from constituent pro

ISSN:0032-3888    

DOI:10.1002/pen.760150606

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractTwin screw extruders are finding increased usage in reacting and devolatilizing applications. Using self‐wiping profiles, the twin screws fulfill the requirement that there be no “dead” or “unmixed” zones. Agitator design must be chosen with care so that a reasonable balance can be obtained between forwarding rate, surface‐generation rate, vapor passageway, power, and axial mixing. Techniques have been developed for measuring residence time distributions and characterizing axial flow behavior. The method also permits direct determination of the holdup in starved barrel applications. Data on residence time distribution are presented for 4‐in. diameter twin screw equipment with a variety of rotor c

ISSN:0032-3888    

DOI:10.1002/pen.760150607

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe effect of screw wear on the performance of a 2.5 in. diameter extruder is studied with the aid of computer simulations. The effect of progressively increasing flight clearance on the extrusion of low density polyethylene, polypropylene and nylon 6/6 is presented. The remedial effect of increased screw speed and its side effects on melting behavior, solids content, extrudate temperature and power consumption are also described.

ISSN:0032-3888    

DOI:10.1002/pen.760150608

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractAn experimental method initiated by Williamson and Busse has been extended to produce veil‐free shish kebab structures in linear polyethylene without need for severe recovery treatments. The technique involves the dilution of polymer in a concentrated solution of low molecular weight paraffin followed by a simple isothermal shear. The resulting shish kebab structures are isolated from the wax matrix and subjected to electron microscopical and electron diffraction study. From the diffraction patterns, it is shown that the shish‐rich ordered structure is similar to the orthorhombic structure of crystalline linear polyethylene, but with certain significant deviations. The resolvable morphology of the shish appears to be characterized by a length‐to‐diameter ratio which is consistent with a prediction based upon Wulff's theorem utilizing certain relevant surface energy values which have been obtained by others for polymeric c

ISSN:0032-3888    

DOI:10.1002/pen.760150609

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe known generalized Newtonian fluid “power law” solution of the radial flow between parallel discus has been used to estimate the normal stress, the magnitude of inertia, and the temperature changes due to viscous dissipation. The flow near the wall has been found to be “nearly steady shear flow;” thus the three viscometric functions can be expected to describe the stress at the wall. Further away from the walls, however, the flow is very different from “steady shear flow.”The temperature field in the radial flow section depends on the dimensionless parameters Nahme number, Graetz number, and ratio of inner to outer radius, as well as on the thermal initial and boundary conditions.Experimentally the radial pressure profiles for flow of three different polyethylenes and of one polystyrene have been studied. The measured pressure profiles are about 20 percent lower than the calculated ones from the “power law” solution. This discrepancy cannot yet be explained; the effects of normal stresses, of inertia, or of viscous heating in these experiments are too small to give a me

ISSN:0032-3888    

DOI:10.1002/pen.760150610

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractA method of analysis is given by which the critical strain energy release rateGcfor impact tests may be deduced for both Charpy and Izod tests from normal energy measurements. Suitable calibration factors are determined and the method is applied to a range of polymers. Very close agreement is achieved between the Charpy and Izod results except for highly ductile materials for which it was necessary to use a fully plastic analysis. The method is extended to blunt notches and it is shown that the use of a strain energy per unit volume to yielding, together with a blunt notch stress analysis, gives a good description of the results.

ISSN:0032-3888    

DOI:10.1002/pen.760150611

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY