The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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The Early Use of Process Simulation to Optimize the Wall Thickness of Blow Molded Plastic Parts
The variable method of extrusion blow molding is widely used for the production of plastic hollow bodies. The primary target of the paper is the early and complete use of computer aided techniques in advance for the development of new commodities. The use of the new tool PreBlow" for the calculation of realistic wall thickness distributions using machines under recognition of different wall thickness adjustment methods will show realistic simulations. Conclusions are provided together with industrial examples."
New Technology to Vary the Thickness of the Parison in Circumferential Direction during the Blow Molding Process
The complexity of blow molded parts grows steadily. Accordingly the technology must keep space with the raised requirements of the market. Thus to improve the thickness distribution of complicated blow molded parts such as tanks for cars it becomes necessary to alter the thickness distribution of the parison not only in axial direction but also in circumferential direction. Encouraged by the success of the introduction of Membrane Dies for film and sheet extrusion the idea was born to design also dies with an extreme flexible outer wall for blow molding machines. This flexible wall can be locally deformed by adjusting screws which are located around the circumference of the die. The basic steps to reach this goal and the possibilities of the new technology are described.
Rapid Tooling and Plastics - Where the RT Industry Stands in 2001 on Better Alternative Tooling Methods
Rapid tooling (RT) has been surveyed, talked about, praised and condemned by users, promoters and bystanders since the development of alternative tooling methods debuted. However, RT processes are improving, with newer direct metal deposition and spray metal methods addressing concerns by plastic molders about size, durability, and molded materials. This paper outlines the state of RT industry for users already familiar with prototyping and RT. Setting the group of commercialized RT products which can be used in standard injection molding machines against P20 CNC produced tooling standards for density, cosmetics, thermal conductivity, cost and lead-time, feature definition, and others shows the evolving technology and the gaps that persist. By and large, the RT industry has been redefining acceptable boundaries for rapid tooling, and listening more to customer concerns. Several experimental technologies and limited use technologies exist that may be used to produce molded plastic parts, but are not available for placement on a conventional injection molding machine. Experimental and noncommercial technologies are not covered in this paper, and discussion is limited to three commercialized processes that show more commercial and mainstream acceptance by custom molders, KelTool™, LaserForm™, and DMD™.
Metallocene Plastomer Based Thermoplastic Olefin Compounds Designed for Roof Membrane Applications
This paper discusses the use of ethylene octene (EO) copolymers made with metallocene catalysts in thermoplastic polyolefin (TPO) compounds designed for single-ply roofing. The performance of two neat EO copolymers is first compared with a polypropylene (PP) based Reactor TPO (RTPO) currently used in single-ply roofing. The more crystalline EO copolymer displays superior thermal and physical properties compared to RTPO. Formulations comprising the EO polymers were designed and optimized using mixture design of experiments. The optimal compounds contain about 50 % EO, 20 % PP and 30 % magnesium hydroxide (MH), a flame retardant additive.
Structure Performance of Thin-Wall Injection Molded Parts
Influence of processing conditions, part thickness and residual stress on the structure performance of 3C thin-wall injection molded parts were investigated. Thin-wall tensile test specimens were molded. A computer dictionary (CD), with 1.6 mm thick housings, was also used for structure evaluation of bending strength and drop-impact performance. It was found that as part becomes thinner, residual stress becomes higher and affects both part tensile strength and weld-line strength more significantly. Higher melt temperature and mold temperature, lower packing pressure and faster injection speed would reduce residual stresses, increase weld-line strength and improve associated properties. When CD housings were redesigned to 1 mm thick keeping sidewall 1.6 mm, both its bending strength and drop-impact performance were only slightly decreased.
Effect of Different Nucleating Agents on the Degassing Conditions as Measured by Ultrasonic Sensors
Ultra sonic sensors have proven to provide valuable information on the thermoplastic foaming process in polymers. Measurement of the attenuation of the ultrasonic signal can be easily related to the nucleation process, i.e. the onset of bubble formation in the foam matrix. The ultrasonic sensors can be installed in-line, on the extrusion line, and thus allow direct access to the prevailing processing conditions. In this work, the degassing conditions (pressure and temperature) of a mixture of polystyrene and a physical blowing agent, HCFC 142b, are determined for two different nucleating agents. The resulting cellular structure of the extruded foams is correlated to the degassing conditions determined by the ultrasounds. The results are discussed in light of other observations on the nucleation process.
The Use of EVOH in Automotive Applications
Regulations for automobile emissions are stiffening in the U.S., requiring reductions by 75 percent or more. Polymers used in automotive fuel systems are a source of evaporative fuel emissions as they have poor barrier properties to fuels. New barrier polyolefins containing EVOH have been developed for injection molded automotive applications so that evaporative emissions can be reduced. A new EVOH has been developed to allow for down gauging and reduced cycle time of the current plastic fuel tank. This new EVOH will allow for cost savings in fuel tank production.
Plastic Material Modeling for Vehicle Crash Simulation Using LS-DYNA
In commercial codes, the modeling of plastic materials lags behind compared to that of many other materials. As a result, engineers have been using material models developed for metal to model plastic materials. This paper discusses the stress-strain behavior of thermoplastics relevant to crash simulation, examines the plastic material modeling capability of a commercial code LS-DYNA and presents needed model enhancements.
Controlling Balanced Molding through New Hot Runner Manifold Designs
Shear induced variations created during flow results in variations between parts produced in many of today's conventional geometrically balanced hot manifold designs. Understanding of these shear imbalances has led to new design strategies which address these variations and provide both uniform filling and uniform material conditions to each cavity.
Prediction of the Impact Behavior of Injection Molded Plates
The falling-weight impact test in injection-molded plates is simulated in a finite element based computer code (FORGE2®). The effect of processing is introduced on the material constitutive model through the dependence of its coefficients upon the thermomechanical indices computed from mold filling simulations. Two plate-like moldings (a box and lateral gated disk) were injected with arbitrary sets of processing conditions. In the impact simulations, two extreme conditions of contact between the impactor and the plates are considered: frictionless and adhesive contacts. The simulated force-deflection curves are compared with the experimental ones. Good agreements are obtained providing the different strain-rate sensitivities of the microstructural parameters are taken into account The results also evidence the role of the viscoelastic coefficient on the initial deformation stages. Moreover, the contact conditions have a strong effect on the mode of rupture of the plates and consequently on the maximum sustained strength levels.
Effect of Compounding Conditions on the Wood Flour/Polyethylene Composites in Twin-Screw Extruders
The compounding of wood flour filled polyethylene is discussed with reference to co-rotating twin-screw extruders from two manufacturers. An acrylic acid-grafted polyethylene copolymer was used as the compatibilizer in high-density polyethylene-wood flour composite system. Special consideration was given to the compounding of the heat- and shear-sensitive wood flour. The relevant screw configuration was found to consist of short mixing elements with low intensity of shearing. A suitable combination of processing variables, including screw rotation speed, throughput rate, and barrel temperatures, was necessary for limiting the thermal degradation and the darkening of the wood filler. However, tensile properties of the composites were not affected much.
Effectiveness of Functionalized Polyolefins as Compatibilizers for Polyethylene/Wood Flour Composites
The effects of various types of compatibilizers on the mechanical properties of high-density polyethylene/wood flour (HDPE/WF) composite were investigated. Functionalized polyolefins such as maleated linear low-density polyethylene, polypropylene, and styrene-ethylene/butylene-styrene copolymer were incorporated to reduce the interfacial tension between polyethylene matrix and wood filler. It was found that LLDPE-g-MA gave maximum tensile and impact strength of the composite presumably due to better compatibility. Similar but less enhanced improvements in the mechanical properties, depending on the compatibilizer loading, were seen for SEBS-g-MA system. Whereas, notched impact strength decreased with increasing loadings of PP-g-MA. A scanning electron microscopy study was employed to reveal the interfacial region and confirm these findings.
Separability Criteria for Entangled Polystyrene Solutions Using Flow Birefringence
Step shear strain experiments were performed using several entangled polystyrene (PS) solutions to investigate factorability requirements of the non-linear relaxation modulus, G(t,?) [? ?12(t,?)/?]. A phase modulated flow birefringence apparatus was used to measure optical equivalents of shear stress (n12) and first normal stress difference (n11-n22) in a plane-Couette shear flow geometry. For all polymers studied, a separability time ?k was identified beyond which the optical equivalent of G(t,?) [B(t,?) ? n12/? ? G(t,?)×C] could be factorized into separate strain and time dependent functions. In every case, ?k exceeded longest Rouse relaxation time ?R and found to be of the order of terminal relaxation time ?d0. These findings could help explain previous experimental observations of delayed factorability and non-factorable relaxation moduli in well entangled polymer solutions and melts.
Simulating the Cohesive Properties of Ultem and Related Molecules
The cohesive properties of many engineering plastics are difficult to determine experimentally, as the polymers are frequently insoluble, have high Tg's, and are sometimes poorly characterized. Molecular modeling can provide useful information of higher quality than might be obtained by other methods for these difficult polymers. A series of simulations on Ultem® and related molecules have been performed to evaluate the cohesive energy density of the polymer and determine interfacial interactions with small molecules. These methods yield a value near 22.0(MPa)½ for the solubility parameter of the polymer, and it is shown that benzyl alcohol has the most favorable interactions.
Adhesion of Polyethylene to Polypropylene in Multi-Layer Films
A distinct difference was found between metallocene and Ziegler-Natta catalyzed linear low density ethylene copolymers (LLDPE) in the coextrusion with polypropylene (PP). A layer of amorphous material was hypothesized to form between PP/Ziegler-Natta LLDPE interface and not in the PP/metallocene LLDPE system. The presence of a weak amorphous interfacial layer was supported by the results of the T-peel test where the metallocene LLDPE system showed significantly higher level of adhesion between PP and LLDPE than the Ziegler-Natta LLDPE systems.
Graphic Film Inserts for Molding
There are many methods to decorate plastic films. As an overview, I will highlight most of the methods used to decorate plastics in post mold operations and in mold operations.
Film Finishing Part II: Use of Multi-Layer Films in Finishing Technologies
Part I of this two part series addresses the background of film finishing, its status and the strategic potential for the technology. Part II is concerned with the materials and processes used in multilayer film production. Film application methods are reviewed from an overview perspective.
Micro-Photometric Inline Particle Monitoring in Flowing Melt (TSE)
A unique particle sensing system will be presented based on a special micro-photometric principle. The final objective is to achieve inline / realtime informations about developing and final stage of particle dimensions in flowing polymer melts. The performance of the new sensor prototytype PMP 690 adapted to a twin screw extruder (TSE, ZSK40-type) will be demonstrated by extrusion mixing of different model glass bead types (particle diameters and volume concentrations) into polystyrene melt.
Modeling the Melting Process of Polymer Pellets Caused by Friction
The melting of polymer caused by friction before the solid plug is formed is an important phenomenon in the plastic injection process. To analyze the melting process caused by solid particles sliding against the bellow, an analytical method that can simulate behavior of each particle during the calculation should be used. Particle element numerical method is hence adopted in the analysis for this research to take into consideration the behavior of each particle. In the review of literatures in this area, no publication has reported success in the analysis of the transient close-contact melting process caused by friction. In this paper an analytical expression for the transient melting process is derived by assuming friction against flight and screw as friction against adiabatic walls.
Modelling of the Effect of Slip in Plug-Assisted Thermoforming
In plug-assisted thermoforming, the interaction between the sheet and the plug strongly affects the final part thickness distribution due to sheet cooling and slippage on the plug surface. The type of plug material and surface finish has to be carefully selected. The amount of slip on the plug surface depends on the rheology of the polymer sheet and on the friction coefficient. Both properties are temperature dependent. In this work a non-isothermal friction coefficient model is evaluated for its potential in predicting the amount of slip in plug-assisted thermoforming. The model has been implemented in a finite element analysis software for predicting the consecutive steps of the thermoforming process. The model has been applied to simulate industrial scale plug-assisted thermoforming and the predictions are compared to experimental measurements.
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