摘要:

AbstractRotational molding is a process by which powdered or liquid plastics are converted into hollow articles. This paper is devoted to the theoretical understanding of the process of rotational molding. There are seven sections:The Art, wherein we describe the process, discuss previous attempts at understanding the process, and mention processes that are similar in principle to rotational molding.Transient Heating of Mold Surface, wherein we show that the criterion for selection of mold materials is the ratio of the thermal diffusivity to the thermal conductivity, and present the heating curve for a mold in a rotational mold machine.Melting of Plastic Powder in a Rotating System, wherein we discuss in detail those physical powder characteristics that are necessary for good flow within the mold cavity.Fluid Flow During Rotational Molding, wherein we discuss the velocity profiles within the melt film, point out that there is very little bulk polymer flow possible within the mold cavity under normal processing conditions, and consider capillary flow forces and surface wetting.Sinter‐Melting, wherein we compare the Kuczynski‐Neuville empirical sintering model with the Lontz viscoelastic model, conclude that the latter is correct for the sintering of materials such as ABS, and apply the Frenkel glass densification theory to the prediction of void disappearance in sinter‐melt polymers.Degradation, wherein we compare our experimental tensile strengths of polystyrene, obtained at varying oven cycle times and oven set point temperatures, with values obtained from degradation models given in the literature.Laboratory Simulation of Rotational Molding, wherein we propose two series of experiments, the first series being carried out without using rotational molding equipment, and the second using rotational molding equipment with molds having relatively simple geome

ISSN:0032-3888    

DOI:10.1002/pen.760120402

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractMany industrial processes require that solids be transformed to the molten state, thus accurate correlations of heat transfer and melting rates are important in process design. The heat‐balance integral type of analysis is applied here to melter systems where phase change and convection effects are of equal importance, and the appropriate parameters that govern the thermal transport process are presented. Applications of the results to both Newtonian and non‐Newtonian, power‐law melts are discussed, and extensions to variable property situations are outlined. Although the results herein are directly applicable to contact melting systems, the governing parameters are useful in the correlation of other melting processes as well. Acomparison is made between the theory and some experimental data for a gravity‐feed contact melter. The results are directly applicable in practice to the melting of bulk and granular crystalline polymers on melting grids, tube bundles, and

ISSN:0032-3888    

DOI:10.1002/pen.760120403

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThis paper presents results obtained by the experimental technique of photoelastic stress analysis and by finite or discrete element analysis, applied to the case of buckling of a single, axially‐loaded metal fiber embedded in a plastic matrix. The program was conducted utilizing a mild steel fiber embedded in an epoxy resin system. The fiber was loaded axially with an increasing compressive force until buckling occurred. Along with determination of the critical load for the fiber, the maximum shearing stress at any point in the epoxy matrix was determined using two‐dimension photoelastic stress analysis. In the analytical study, the fiber was modeled by a series of bending elements and the matrix by an assemblage of constant‐strain triangular elements. The total system was thus modeled by the two types of elements connected at common nodal points. The instability was solved as a standard eigenvalue problem and the stress tensor was obtained by finite element stress ana

ISSN:0032-3888    

DOI:10.1002/pen.760120404

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe cup drawing process of thermoplastic sheet is analyzed on the basis of small deformation theory. The drawability of thermoplastic sheets is related to material parameters which may be investigated without performing an actual drawing process. Values for the drawability which are obtained by this method agree with values which are obtained by the Swift cup test.

ISSN:0032-3888    

DOI:10.1002/pen.760120405

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractTorsional braid analysis has been explored as a means of providing a quantitative measure for the effectiveness of polymer additives. Quantitative determinations have been made of antioxidant activity of selected compounds when formulated with certain elastomers prone to oxidative crosslinking on heat aging. The torsional braid technique has been used to determine the time dependence of the sharp torsional modulus increase which corresponds to a change from a rubbery to a highly crosslinked state. This time dependence is taken as a measure of the rate of oxidative crosslinking in heat‐aged elastomer films coated on a Fiberglas braid. In this manner an assessment of antioxidant activity can be made. The effect of concentration and aging temperature on antioxidant activity can be made also. It has been also possible to use this technique to study the effect of structural changes in an antioxidant on its resultant activity. Feasibility studies have also been made on antiozonants in natural rubber andcis‐polybutadience at three temperatures. A value of 10.9 Kcal/mole was calculated for the activation energy for the oxidative crosslinking reaction ofcis‐polybuta

ISSN:0032-3888    

DOI:10.1002/pen.760120406

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe dimensional recovery of cold‐rolled polycarbonate was measured between 100 and 147°C, and compared to stress‐relaxation data. The strain‐recovery isotherms were superimposed to produce a master curve which could be represented by a distribution function,U(τ), termed the strain recovery spectrum.U(τ) is found to be nearly identical to the relaxation spectrum,H(τ), calculated from the stress‐relaxation master curve; and the shift inU(τ) as a function of temperature, WLF shift factor, is similar to that obtained from other viscoelastic measurements on polycarbonate. For the deformations studied, 25 and 50% reduction in thickness, the recovery behavior is found to be independent of strain (linear), suggesting that nonlinearity in a polymer glass results from large stresses, and not from l

ISSN:0032-3888    

DOI:10.1002/pen.760120407

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractA mathematical model is proposed for the quantitative treatment of the injection molding of thermoplastics as it relates to the behavior of polymer in the cavity. The model is based on setting up the equations of continuity, motion, and energy for the system during each of the stages of the injection molding cycle (filling, packing and cooling) and the coupling of these equations with practical boundary conditions. The treatment takes into consideration the non‐Newtonian behavior of the melt, the effect of temperature on density and viscosity, the latent heat of solidification, and the differences in thermal properties between the solid and the melt. In employing the model, it is necessary to know the pressure‐time variation at the cavity entrance. Numerical solutions have been obtained for the case of spreading radial flow in a semi‐circular cavity. The numerical results yield significant data on the progression of the melt front, the flow rate, and the velocity profiles at different times and positions in the cavity. They also yield temperature and pressure profiles throughout the packing and cooling s

ISSN:0032-3888    

DOI:10.1002/pen.760120408

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractExperimental studies have been conducted with a 2 1/3 oz reciprocating‐screw injection molding machine to check the validity of a proposed theoretical model for injection molding. A semi‐circular cavity has been employed in the study to achieve spreading radial flow during the filling stage. Both high speed photography and pressure transducer measurements have been employed to obtain data on polyethylene. The photographic studies confirm the existence of spreading radial flow throughout the filling stage, and are in very good agreement with data obtained with the transducer on the progression of the melt front in the cavity. The results show that the proposed theoretical model yields predictions which are in good agreement with experimental data for all stages of the injection molding cycle with polyethylene. The model also predicts a composite pressure‐time curve for the overall cycle which is similar to those reported in the literature and which satisfactorily represents the data obtained in this study. It is also possible to predict a short shot under selected molding conditions in agreement with observation. The main problems in the application of the model arise during the filling stage near the cavity entrance where viscoelastic and end effects are important and where some of the assumptions inherent in the model may not be

ISSN:0032-3888    

DOI:10.1002/pen.760120409

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractA criterion, based on the behavior of polymer solutions, is developed and applied for the prediction of the onset of flow anomalies observed at the capillary entrance for polymer melts. It is shown that a direct correspondence exists between the flow anomalies observed for polymer solutions and polymer melts. The onset of these anomalies can be correlated with a critical Weissenberg number which is consistent with the equality of the shear wave velocity and friction velocity. This critical condition can be employed to derive expressions useful for predicting the critical recoverable shear and critical shear stress for melt fracture.

ISSN:0032-3888    

DOI:10.1002/pen.760120410

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760120401

出版商:Society of Plastics Engineers, Inc.    

年代:1972

数据来源: WILEY