摘要:

AbstractThis study was aimed at comparing vented extruder geometries and identifying scale‐up parameters for melt devolatilization. Data are presented comparing single‐ and corotating twin‐screw extruders for devolatilization of methyl methacrylate from poly(methyl methacrylate), and parameters are identified which characterize dynamic similarity for potential use in design and scale‐up. These parameters include conventional process variables such as temperature, throughput, screw RPM, and degree

ISSN:0032-3888    

DOI:10.1002/pen.760302302

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA new capillary gas chromatography method to monitor a residual monomer in a polymer is described. A short (5 m) crosslinked methyl silicone fused silica capillary column with flame ionization detection gave good separation efficiency and parts‐per‐million detection limits. Capillary gas‐liquid chromatography was superior to packed column analysis (SP 1000) in terms of both analytical utility and ease of use. This technique may prove useful for monitoring other monomer/polymer sy

ISSN:0032-3888    

DOI:10.1002/pen.760302303

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThree polypropylene polymer samples possessing three different molecular weight distributions (MWD) ranging from narrow to broad, but having the same melt flow, were studied. The three resins were used to produce uniaxially oriented stretched tapes, which were evaluated for physical properties and morphological characteristics. In addition, five different drawing temperatures were used to investigate the effect of temperature on the physical properties and molecular morphology of the tape. As the MWD became broader, the tape modulus and tenacity increased slightly and the percent elongation and shrinkage decreased slightly. These effects were attributed to decreases in molecular mobility and increases in the number of tie molecules present in broad MWD resins. Morphological studies determined that the crystalline orientation was not affected by MWD. However, the amorphous orientation, at higher draw temperatures, demonstrated a small increase as the MWD became broader. MWD did not have a large effect on the percent crystallinity but the long period spacing (LPS) did exhibit a small decrease as the MWD broadened.

ISSN:0032-3888    

DOI:10.1002/pen.760302304

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractAn Iterative Boundary Pressure Reflection (IBPR) method has been developed to improve the accuracy of the flow front generation and transient mold filling simulation in injection molding. The method iteratively calculates the virtual pressure reflection, either positive or negative, at the impinging melt front nodes which are to be relocated subsequently according to the new pressure field. The scheme is formulated into a finite element program using a power‐law model and applied to the filling of polystyrene melts injected into an edge‐gated circular cavity and a variable‐gap‐thickness cavity with an insert. The calculated results show very good agreement with the experimental results of the previous study by others in the position of the advancing melt fronts at each time step, weldline location, and pressure distri

ISSN:0032-3888    

DOI:10.1002/pen.760302305

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractWarpage and global shrinkage of rotationally molded polyethylene parts can be a serious problem with resins of higher densities with rapid quenches and high mold wall thicknesses. It is shown that relatively low pressurization of molds substantially reduces the warpage of molded polyethylene parts. Samples cut out of parts produced in pressurized molds have the same density distributions, Izod Impact, and uniaxial stress‐strain characteristics as parts fabricated in unpressurized mold

ISSN:0032-3888    

DOI:10.1002/pen.760302306

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractMany scale‐up rules and theories have been presented in the area of extrusion. Until now all the theories concerned the single screw extruder. As the use of counter‐rotating twin screw extruders is increasing, it becomes important to propose scale‐up rules for this kind of extruder. Therefore a basic analysis of scale‐up in a twin screw extruder has been developed. It can be concluded that important factors scaling up a twin screw extruder are the fully filled length and the leakage flows of the extruder. So hydrodynamic similarity has to be assured in the scale‐up of most processes. However no serious constraints are put on the throughput of the extruder by this consideration. When the extruder is scaled up on the basis of thermal similarity the Brinkmann number is of importance. At low Brinkmann numbers the throughput is unfavorably affected by scale‐up. If the Brinkmann number is high the throughput is proportional to the diameter cubed. If the extruder is used as a chemical reactor for polymerization, an increasing area of research, the scale‐up rules are dependent on the Damköhler IV number. For low Damköhler IV numbers no consistent scale rules are found. However if the Damköhler IV number is high, useful rules for the scale

ISSN:0032-3888    

DOI:10.1002/pen.760302307

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe flow distribution in a coat‐hanger die is predicted using a three‐dimensional finite element technique. An iterative procedure is proposed for designing blow molding dies for a non‐axisymmetric parison to provide uniform outflow at the exit. A similar procedure is applicable to dies for film, sheet, or profile extrusion. Comparison with one‐dimensional models show significant differences. The effect of nonlinearity on the multiplicity of solutions and the effect of power law index have been con

ISSN:0032-3888    

DOI:10.1002/pen.760302308

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractPlastic profile die design is a complex task because of cross section area and shape changes occurring after die exit. Dimensions of the profile are increased by the extrudate swell phenomenon and decreased by drawdown and shrinkage. An experimental study on the effect of processing conditions on extrudate swell and on the shape of a rectangular profile was done for rigid poly(vinyl chloride), PVC, and high density polyethylene, HDPE, resins. Extrudate swell was found to be a strong decreasing function of residence time in the die and also, for short dies, of entrance geometry. For PVC, equilibrium swell increased with melt temperature. The differences in swelling for the two polymers are explained with the help of creep/recovery data obtained on a stress rheometer. Drawdown, die land length, and melt temperature were shown to have an important effect on the shape of a rectangular profile. Decreasing the die land and increasing the melt temperature had the effect of increasing preferably the thickness while drawdown, by inhibiting the swelling, decreased the thickness.

ISSN:0032-3888    

DOI:10.1002/pen.760302309

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of superimposing longitudinal and transverse oscillations on the die section at the exit of an extruder is examined. Longitudinal oscillations ranged from 0 to 30 mm in amplitude, and frequencies varied between 0 and 50 Hz. Transverse vibrations varied from 0 to 0.35 rad in amplitude and from 0 to 50 Hz in frequency. Experiments were performed in two types of extruders: a horizontal Brabender Plasticorder and a vertical Scamia both with similar characteristics of 7 Kw power output and 7.105Pa maximum pressure. The polymers used were high and low density polyethylene and polystyrene. The overall effect of the oscillations is to increase the mechanical properties of the extrudate as well as to reduce the pressure drop in the die section. This pressure reduction results in a considerable saving of the total power consumption per unit weight of extrudate. Within a given range of amplitude‐frequency of oscillations, overall power savings of up to 25% are possible with respect to the stationary mode. Furthermore, the total flow rate through the die is enhanced by the vibrations and the die swell is diminishe

ISSN:0032-3888    

DOI:10.1002/pen.760302310

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760302301

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY