摘要:

AbstractAn automated rheometer is developed for an evaluation of the processability of rubber compounds at injection molding conditions. The rheometer utilizes a screw injection molding machine in order to push rubber compounds through a thermostated slit die at controlled flow rates. Three pressure transducers are flush‐mounted along the die length and a displacement transducer is installed to measure the screw motion. Signals generated by the pressure and displacement transducers and thermocouple are supplied to an A/D converted and the IBM PC/AT computer. Unsteady character of flow of rubber compounds is observed. The obtained data are compared with predictions from modeling of flow, using the viscoelastic plastic constitutive equatio

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractRotational molding grade polyethylene powders are classified according to sieve size, to typically–35 mesh, and by flowability, usually determined by pouring freeflowing powder from a funnel onto a fixed base cone. In the latter case, the static angle of repose is then measured. This study concentrates on general methods of characterizing powders and relating these methods of flowability of five selected commercial rotational molding grade polyethylene powders. The techniques described in this study include methods for measuring particle size distribution, particle shape characteristics, static and dynamic angles of repose, powder shear strength, and angle of internal friction. All powders examined had similar particle size distribution profiles, with distributions skewed to the coarser, −35 mesh size particles. The static and dynamic angles of repose were quite similar and the latter were essentially independent of the volume fraction of powder in the rotating cylinder and of the speed of rotation of the cylinder. All powders had shape parameters–elongational ratio, chunkiness, circularity, and roundness–that were essentially similar and independent of particle size, and the compressibilities of the bulk powders were not strongly dependent on powder bed

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIn a companion study,1it was found that five commercially available rotational molding grade polyethylenes had similar particle size distribution profiles and dynamic angles of repose. There were measurable differences in their general particle shapes. These powders were rotationally molded in an axisymmetric cylinder mold using time–temperature molding cycles recommended for these materials. Wall sections were then cut from the molded cylinders and tensile strengths, Young's moduli, elongations at break, and Izod impact strengths were measured. The resins were then injection molded and similar mechanical tests were performed. The rotationally molded samples exhibited porosity, the level of which depended strongly on the residence time in the isothermal oven. The rotationally molded samples showed greater strengths and moduli, but lower elongations at break and impact strengths. The rotationally molded samples also showed higher crystallinity levels and substantially larger spherulite dimensions. These observations support the mechanical property dat

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractSteady shear viscosity data of a polypropylene resin were obtained at two elevated temperatures using an Instron capillary rheometer. When the pressure drop across the capillary is small, the hydrostatic pressure in the barrel is low, and the data from the capillary rheometer follow a linear Bagley plot. For long capillary and under a high hydrostatic pressure, the pressure drop increases at a faster rate than the length. A. pressure‐dependent viscosity function is proposed to explain the deviation and a new method to evaluate the pressure coefficient is introduced in this study. The results indicate that there is a significant increase in viscosity at a typical injection molding pressure, e.g., above 108P

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractAn experimental study of the free‐radical‐induced crosslinking of linear‐low‐density polyethylene (LLDPE) in the melt phase has been carried out. Experiments have been performed both in a single‐screw plasticating extruder and in an extrusion plastometer using a peroxide as the free‐radical source. Concentration of the peroxide was in the range of 0.005–0.08 wt % for rheological investigation and was extended to 5 wt % for gel content examination. Results in the form of melt flow index (MFI) values, viscosity curves, extrudate swell, and gel content of the produced resins are p

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractSolid bed transport has an important effect on the over all performance of a plasticating extruder. The coefficient of friction and density are the properties of the solid bed that govern its transport in the feed section of the screw. These properties have been measured, as a function of temperature and pressure, for eight common thermoplastic materials in an apparatus that simulates solid bed motion and compaction in a plasticating extruder and the results have been interpreted phenomenologically.

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of the constituent material on the mechanical properties and on the overall crack propagation behavior of uniaxial graphite/epoxy composites was studied using two different types of graphite fibers, i.e., PAN precursor and pitch precursor fibers in combination with an epoxy known for its toughness. The tensile properties and interlaminar shear strength (ILSS) of composites with various fiber volume fraction were studied using an Instron Universal Testing Machine. The fracture surface of composites was studied using scanning electron microscopy (SEM). The surprising result from the tensile tests is that the percent elongation of AS4/epoxy composites was much higher than that of individual components, i.e., the epoxy and the fiber. The stress–strain curves of AS4 fiber/epoxy composites show yielding. The yielding is interpreted to result from shear stress concentration due to the fiber breakage. Two causes of failure mode were observed in this study: (1) ductile plastic deformation by the PAN‐based AS4/epoxy composites; (ii) brittle catastrophic failure shown by the pitch‐based VSB‐16/epoxy composites. The tensile strengths and moduli of the composites increased as the volume fraction of fibers increased. The principal fracture features of AS4/epoxy composites under tension were fiber pullout (bundles and single fibers) and very rough fracture surface due to the pullout of fiber bundles with epoxy, whereas VSB‐16/epoxy composites under tensile and bending loads showed only tensile (or compressive) failure. The composites of epoxy/PAN (polyacrylonitrile)‐based fibers (AS4) showed greater ILSS than those of the pitch‐based fiber (VSB‐16)/epoxy. The most characteristic features of the interlaminar shear failure surface of AS4/epoxy composites are delamination and forma

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe same base resin, a HDPE with vinyl–silane units grafted along the backbone, was subjected to three different types of crosslinking: (a) using peroxides and heat, (b) using a catalyst under high humidity, and (c) using high‐energy radiation. Macroscopic properties, such as tensile behavior‐at‐break, shear modulus, gel content, and crystallinity were measured for all three types of crosslinked material. Although the mechanical and rheological properties appear to indicate differences in distribution of crosslinks, the major differences are seen for the degree of crystallinity. These differences are rationalized on the basis of the mechanism of crosslinking and the resultant location of crosslin

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

ISSN:0730-6679    

DOI:10.1002/adv.1989.060090309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY