摘要:

AbstractAn approximate analytical solution is obtained for the flow rate‐pressure drop relation for adiabatic capillary flow of a fluid with a pressure‐ and temperature‐dependent viscosity. Neglect of the pressure dependence can result in large errors in the usual range of injection molding practice. The approximate solution follows from an exact solution of capillary flow with a viscosity that depends only on pre

ISSN:0032-3888    

DOI:10.1002/pen.760210202

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractAn experimental and theoretical study was carried out to achieve a better understanding of bubble dynamics in foam extrusion through a converging die. For the experimental study, a number of converging channels were constructed of aluminum, with glass windows on both sides. Bubble dynamics in the flow channel were recorded on movie film as a gas‐charged molten polymer was extruded. The dies had various converging angles (30, 45, 60, 90, and 150 degrees), and the polymer was polystyrene. As blowing agent, sodium bicarbonate (generating CO2) was used. It was found that the gas bubbles moving along the centerline of the channel grow initially at the upstream end of the die, and then start to collapse as the gas‐charged molten polymer approaches the exit plane of the die. In order to help interpret the experimental results, a theoretical analysis was made of bubble dynamics in a converging channel, in which a thread‐like bubble was assumed to flow along the centerline of the converging channel and the Coleman‐Noll second‐order fluid model was assumed to describe the rheological behavior of the polymer melt. Some mathematically convenient simplifying assumptions not‐withstanding, the theoretical analysis corroborates the experimental observations. The practical significance of the present investigation is discussed in connection with controlling the cell structure in extruded fo

ISSN:0032-3888    

DOI:10.1002/pen.760210203

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe properties and processing characteristics of open‐celled foams produced by leaching small NaCl particles from high density polyethylene has been investigated. In a random dispersion of salt particles in the polymer matrix a minimum volume loading of 40 percent was required to produce an open‐celled foam. The time required to remove this quantity of salt with 50°C water was 100 min. The maximum porosity of the foam is limited to the maximum packing fraction of the salt. For randomly dispersed isotropic particles the maximum packing fraction is approximately 0.64. Because the composite rapidly loses melt strength as the filler content nears the maximum packing fraction, the practical upper limit of extruded foam porosity is approximately

ISSN:0032-3888    

DOI:10.1002/pen.760210204

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractSeveral rheological aspects of thermoplastic foam extrusion are described by a phenomenological model of the flow in an extrusion die. The macroscopic effects of the phase change, from a homogeneous polymer melt that contains a blowing agent, to a foam, are described in terms of two dimensionless parameters. α is defined as the ratio of the pressure gradient in the melt phase to the average pressure gradient in the foam phase. Θ represents the ratio of the pressure drop in the melt phase to the pressure drop in the foam phase. The position at which the phase change initiates, the exit contribution to the Bagley ends pressure correction, and the true wall shear stress in the melt phase are related to α and Θ. The quality of the foam produced is discussed in terms of the extrusion conditions and their effect on the foaming position in the die. It is demonstrated that the ends pressure correction cannot be neglected on the basis of a long die alone. Asymptotic conditions for which the phase change has negligible effect on the melt flow rate are predicted. α is calculated from the data of Han and Villamizar, who measured the pressure distribution in the die and observed the phase change directly. The prediction of α from theory is complicated by the lack of suitable constitutive relations for the foam phase. Since Θ only requires knowledge of the pressure at which the phase change initiates, it is relatively easy to ev

ISSN:0032-3888    

DOI:10.1002/pen.760210205

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractAn experimental investigation into the performance in general and the melting behavior in particular of a single screw extruder running with a low density polyethylene power has been carried out and the results compared with those for a granular feedstock of low density polyethylene having similar melt properties. It was found that the tendency was for the output rate, pressure generated and specific power consumption to be lower for the powders, and that the removal of barrel heating near the feed hopper increased these parameters. Two melting mechanisms were observed in powder extrusion; one being the classic “Maddock” type, and the other such that the solid bed and melt pool were in reversed positions relative to the Maddock case. There was a trend for this latter mechanism to operate with low screw speeds, shallow channels and full heating. Melt initiation occurred nearer the feed end and melting was completed much more quickly with powders. An explanation of the mechanisms is proposed which is based on the observation of early melt initiation, and the industrial practices of feed zone cooling and increasing feed pressure generation to improve the performance of extruders running with powders are seen to be consistent with this proposit

ISSN:0032-3888    

DOI:10.1002/pen.760210206

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA method is given for selecting the “effective viscosity” for isothermal flow of non‐Newtonian liquids in screw pumps or melt extruders. Effective viscosity is the Newtonian viscosity that would give the same screw‐pump performance with non‐Newtonian liquids at the same flow rate and speed. When effective viscosity is known, it can be inserted in performance equations for simple Newtonian flow. The analysis is restricted to shallow screw‐pump channels with large aspect ratios and to shear stress/shear rate curves with modest curvatures when shown in a double logarithmic plot. The shear stress/shear rate curve is replaced by a power‐law tangent to that curve in the domain of prevailing shear rates, but the analysis could be extended to more complex behavior. Curves are also included for calculating the efficiency of the screw‐pump channel, which can be used to estimate the energy dissipated in screw‐pumps. It is shown that efficiency decreases with decreasing p

ISSN:0032-3888    

DOI:10.1002/pen.760210207

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractFinite element solutions are presented for developed, isothermal, power‐law flow in an extruder channel, based on a variational formulation in helical co‐ordinates. The success of the method in handling non‐Newtonian flow in a deep, highly‐curved channel is tested by comparison with experimental results. Operating characteristics were determired under virtually isothermal conditions for a screw with depth to diameter ratio 0.25 pumping an aqueous glucose solution containing high molecular weight hydroxyethyl cellulose. Shear stress and first normal stress differences of this solution were determined in a rheogoniometer. It was both highly shear‐thinning and elastic. Computed and experimental screw operating characteristics agree well, except near closed discharge, where effects due to viscous heating and elasticity are tentatively

ISSN:0032-3888    

DOI:10.1002/pen.760210208

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA process of melting individual polymer granules and then combining them into a homogeneous molten mass is examined. The granules are introduced into a high temperature fluid bath, heated as they move due to the polymer‐fluid density difference and finally coalesce under the action of surface and gravity forces into a uniform polymer melt which can be used for extrusion, injection molding or other melt processing techniques. Theoretical models and analyses are presented to predict the time required to melt a granule in a particular polymer‐fluid system and to have the molten granule coalesce into the developing mass of molten polymer. This latter time includes the time for the continuous phase fluid to drain between the approaching granule and the molten polymer‐fluid interface and the time for the granule, once in contact with the interface, to be deposited to some specified depth in the bulk molten polymer. Design parameters for a particular embodiment of the process are presented. Experimental results obtained with a prototype device using mercury as the heat transfer medium are disc

ISSN:0032-3888    

DOI:10.1002/pen.760210209

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA new technique for the electrical monitoring of polymerization reactions such as resin cure is described. The technique is based on the charge‐flow transistor, which resembles a conventional metal‐oxide‐semiconductor field‐effect transistor (MOSFET), but with a portion of the metal gate replaced by the resin under study. Electrical signals obtained from several resins undergoing cure are presented, along with an electrical circuit model that can account for the principal features of these signals. The dramatic change in signal shape during cure can be related to corresponding changes in both the real and imaginary parts of the dielectric c

ISSN:0032-3888    

DOI:10.1002/pen.760210210

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760210201

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY