摘要:

AbstractAn experimental study was conducted with a plasticating single‐screw extruder, which had the following screw dimensions: (a) the diameter (D) of 6.35 cm; (b) the total extruder length of 24 D; (c) the length of the feed section of 3 D; (d) the length of the tapered section of 4 D; and (e) the length of the metering section of 17 D. The extruder had nine pressure transducers which were mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel, so that we could measure axial pressure profiles during extrusion. Also measured in our study were the solid‐bed width profiles in the screw channel by conducting tracer experiments (i.e., screw ‘pushout’ experiments). For the study, a high‐pressure low‐density polyethylene and a high‐density polyethylene were used. Experimental results were analyzed using the reported Lee‐Han melting model. Theoretical predictions of axial pressure profiles were found to be in good agreement with results. Of particular note are the theoretical predictions that for the particular screw configurations used, which has short feed and tapered sections, and extrusion conditions employed, there was considerable solid‐bed acceleration in the tapered sec

ISSN:0032-3888    

DOI:10.1002/pen.760302402

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA model relating molding force, compression speed, and part thickness, to material properties, part size, and processing conditions (mold and charge temperature) is necessary, to determine the ranges of closing speed feasible, when molding a predetermined part with a press of given capacity (tonnage). The faster we can close, in principle, the faster reacting systems we can run in a given press. A model has been developed to predict the force required for compression molding of SMC under non‐isothermal conditions. The model requires two material rheological parameters, namely, the material resistance to extension η and a friction coefficient λ. A method has been developed to measure these coefficients. Preheating the charge is an attractive way of decreasing the molding force required. Also higher molding temperatures would give lower friction and thus lower molding fo

ISSN:0032-3888    

DOI:10.1002/pen.760302403

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA sound wave extrusion system has been developed. This system includes a single screw extruder and an annular die having an internal surface oscillating in the sound frequency range. Oscillating shear flow has been imposed in the direction parallel to the main pressure flow. The die characteristics and average melt temperature at the exit from the die for several thermoplastics have been measured with and without imposition of oscillations. Modeling of parallel superposition of sound oscillations upon pressure flow has been performed using the Leonov viscoelastic constitutive equation. Three cases are considered: (i) the process is isothermal and the change in die pressure is only due to a nonlinear interaction of oscillatory and pressure flow; (ii) the process is nonisothermal and adiabatic, and pressure reduction is due to the nonlinear interaction and the dissipation of oscillatory energy leading to the temperature rise in polymer melts; (iii) the process is nonisothermal with heat transfer due to transient heat conduction and the dissipation of oscillatory energy. Pressure reduction occurs due to both nonlinear interaction and temperature rise. It is found that case (i) cannot explain the observed die pressure reduction, while case (ii) describes those data only at high flow rates. The theoretical results from case (iii) are found to be in qualitative agreement with experimental observations. Generally, the theoretical results of case (iii) are better than those of cases (i) and (ii).

ISSN:0032-3888    

DOI:10.1002/pen.760302404

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe morphologies and impact behavior of blends based on an unsaturated polyester matrix and different added rubbers were studied by scanning electron microscopy (SEM). These rubbers were prepared from a carboxy‐terminated acrylonitrile‐butadiene copolymer (CTBN). The introduction of an epoxy‐terminated triblock copolymer (ETON) by exchanging 10% by weight of the CTBN rubber compatibilizes the initial blend by reducing the interfacial tension between the components. Consequently, the morphology of dispersed phase was modified: decreasing of the particle size and reducing the number of large particles. For a blend with 5 phr of rubber, Charpy impact behavior was enhanced and the number of catastrophic failures was reduced. This study displays the existence of relationships between the interfacial tension between components and the morphology of the resulting mate

ISSN:0032-3888    

DOI:10.1002/pen.760302405

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe characterization of network segment density of elastomers is discussed. Normally equilibrium solvent swelling is used as long as the polymer‐solvent interaction parameter χ is available. However, χ is often not known or may be a function of the network segment density, or composition for a polymer whose structure is changed upon aging. The technique of measuring the modulus in tension or compression on solvent‐swollen samples allows the network segment density to be calculated from the theory of rubber elasticity. This circumvents the problems associated with the solvent swelling technique. The modification of a commercially available thermomechanical analyzer is described, to enable compression modulus measurements on solvent swollen elastomers to be perf

ISSN:0032-3888    

DOI:10.1002/pen.760302406

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractOven aged tensile bars of heat stabilized, glass reinforced nylon 66 material were studied by Fourier transform infrared (FTIR) spectroscopy using a photoacoustic detector. Flat weighed scrapings were removed from tensile bars whose tensile strength, elongation, impact, molecular weight, and thermal properties had previously been measured. Using the amide I band of nylon 66 as an internal standard, the thermal oxidation of nylon was followed using a commercially available photoacoustic detector. The infrared absorbance spectra demonstrate the formation of carbonyl stretching vibrations due to the thermal oxidation of nylon with a band center at 1713 cm−1whose width at half height is 40 cm−1. The difference infrared spectra support reaction mechanisms dealing with an Initial increase in the degree of polymerization followed by transamidation reactions with subsequent formation of an α, β unsaturated carbonyl species and chain scissioning. By using data related to the percent retention of certain physical properties which had also been measured on these tensile bars, subtractive infrared spectroscopy yielded additional fundamental information regarding nylon 66 degradation. Consequently, nylon products being used in underhood automotive applications are currently being investigated for thermal oxidative degradation using this rapid and relatively non‐destructive photoacoustic FTIR technique for durability conside

ISSN:0032-3888    

DOI:10.1002/pen.760302407

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper describes a method for obtaining the thermal contact resistance (TCR) between an injection molded part and its mold. Due to the absence of TCR the simulated cooling times obtained from Polycool II, a computer aided engineering (CAE) package for cooling simulation of injection molding, have compared poorly with both field and experimental data. This paper shows that an improvement in the accuracy of the simulated data results from making TCR an Input to Polycool II. TCR was obtained through a combination of experimental and analytical procedures. Experimental work was performed to obtain the part surface temperature distribution and the inside cavity pressure gradient. The part surface temperature distribution was then used as a boundary condition in the thermal analysis. The inside cavity pressure gradient was utilized as a basis for determining the inside cavity shrinkage. The results show that due to the thermal expansion of thermoplastics, the compressibility of the plastic melt, and the mold deformation, the inside cavity shrinkage is reduced as the thickness of the part is increased. Therefore, the TCR value of a thicker part is lower than that of a thinner part. The effects of both part thickness and process parameters, such as temperature and pressure, on TCR are also discussed.

ISSN:0032-3888    

DOI:10.1002/pen.760302408

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe flow analysis network (FAN) method developed in earlier work, for simulating the isothermal flow of a generalized Newtonian fluid in a narrow‐gap region has been refined to better account for irregularly shaped flow boundaries. The resulting equation, which involves only pressure as an unknown, is solved by successive relaxation; the velocity distribution is then back calculated from pressure values. For Newtonian fluids, overrelaxation with a relaxation factor of 1.75 gives the fastest numerical convergence. For power‐law fluids, it is suggested that one start with the associated Newtonian solution and then use under‐relaxation with a relaxation factor equal to the power‐law index. The FAN solutions for two test problems compared very well with analytical and finite element solutions. The rubber flow in a cavity was analyzed using the FAN program. Compared to a Newtonian fluid, a shear‐thinning fluid gave a larger velocity variation across the flow channel exit due to a stronger dependence of velocity on pressure gradient. Through iterations, the output ratio and velocity uniformity were improved without causing too long resid

ISSN:0032-3888    

DOI:10.1002/pen.760302409

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA crystallization rate coefficient (CRC) parameter is introduced which has allowed a direct comparison of the crystallization rates of various polymers on a single scale for the first time. Basically, CRC represents a change in cooling rate required to bring about 1°C change in the supercooling of the polymer melt. For the polymers studied, this value varies between 35 h−1(polyethylene terephthalate) and 155 h−1(poly(tetrafluoroethylene)) and jumps to 295 h−1for indium metal; the precision being better than ±5 percent. The reliability of CRC has been tested against the established trends e.g., (i) a large decrease in the crystallization rate of polyethylene terephthalate with increase in molecular weight, (ii) a lower crystallization rate of the “virgin” nylon 6 as compared to the processed nylon 6 resin, (iii) an increase in the crystallization rate of nylon 6 in the presence of nucleating agents, and (iv) a dramatic increase in crystallization rate as we go from poly(ethylene terephthalate) to poly(tetrafluoroethylene) and then from poly(tetrafluoroethylene) to the metals. The significance of the CRC barometer is discussed in the light of prior difficulties in directly comparing the crystallization rates

ISSN:0032-3888    

DOI:10.1002/pen.760302410

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe microstructure and fracture behavior of Injection molded samples of unfilled and filled grades of liquid crystalline polymers (Vectra® and Ultrax®) containing cold and warm knit lines have been studied by scanning electron microscopy, X‐ray scattering, and Instron tensile tests. Four process parameters—melt temperature, mold temperature, injection time, and holding pressure—have been varied in accordance with a 24factorial design experiment. In cold knit lines a 200 µm thick region with transverse orientation with Hermans orientation function f ≈ 0.12–0.18 is formed on both sides on the weld area. The strength of the cold knit lines is very low, 9.0–19.8 MPa corresponding to 15–20% of the full strength of the material. The strength of the warm knit lines increases markedly with increasing distance from the insert and is generally significantly greater (40–45 MPa, 48 mm from the insert) than in the cold welds. Annealing at 260–300°C of samples containing cold knit lines causes first a partial healing of the knit line and later extensive chemical degra

ISSN:0032-3888    

DOI:10.1002/pen.760302411

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY