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 Effect of Cavity Pressure Transducers on the Overall Performance of a Multi-Cavity Hot Runner Injection Mold
Multi-cavity hot runner injection molds have historically had problems with unbalanced and/or unrepeatable filling patterns sometimes related to thermal variations in the manifold which can typically result in a number of processing issues. Typically, if a scientific approach to identifying optimal filling patterns is utilized, the overall performance of a multi-cavity hot runner tool can be improved. Scientific processing techniques in addition to cavity pressure transducers can be an advantageous approach to identifying optimal filling patterns and any variations that may exist in these types of injection molds. The purpose of this study is to identify the effect of cavity pressure transducers on the overall performance of a 32- cavity hot runner injection mold. Typical scientific processing techniques such as short shot studies and on-machine rheology curves were used as the foundation of the study. Once the preliminary molding conditions were identified and the cavity pressure transducers strategically placed, a design of experiments (DOE) was conducted to determine the effects of varying process conditions (injection velocity, hold pressure, and hold time) on specific cavity pressures in the 32-cavity hot runner injection mold. The short shot study provided an idea of the mold filling imbalances and allowed for the cavity pressure transducers to be strategically placed, an end of fill transducer in each quadrant of the mold. The results showed that an injection velocity ranging from 35 to 95% resulted in adequate material viscosities during the fill stage. The DOE indicated that injection velocity and hold pressure had the most significant effect on the cycle integrals. Also, the hold time tended to have a significant effect on the cycle integral when increased from 1 to 3 seconds. Additionally, increased injection velocity tended to increase flash and decrease warpage.
Criteria for Flow Instabilities in End-Gated Injection Molds
Jetting depends on material properties, the gate and cavity design in a mold, and injection molding parameters. Although various criteria define the limits between jetting and fountain flow, these rules are often contradictory. In this study, jetting flow instabilities were examined with a broad range of materials, molds, and processing conditions. The jetting depended on materials and gate and cavity dimensions, but was not eliminated or induced with increasing injection rates to ~200 cm3/s. Prediction of flow instabilities using extrudate swell-based criterion failed with some materials, particularly at high shear rates. Gate dimension design criteria also failed to predict jetting. Although not yet verified, a criterion incorporating melt elasticity and melt friction seems promising.
Composite Droplet Viscosity Ratio Effect on the Morphology of HDPE/PS/PMMA Ternary Blends
The influence of the sub-inclusion component viscosity on the composite droplet morphology was investigated in the melt state, using scanning electron microscopy. Based on previous work, a blend of high density polyethylene (HDPE), polystyrene (PS) and a low molecular weight poly(methyl methacrylate) (L-PMMA) is chosen as a model system. While it might be expected that a high engulfing-to-engulfed viscosity ratio could delay or even hinder the composite droplet formation, it is clearly demonstrated that the tendency for the dispersed components to combine to form PS-PMMA core-shell structures is only dependent on the spreading coefficients analysis.
Topological Characterization of Pultruded Rods Reinforced with Continuous Carbon Fibers
We describe the use of Large Area Automated Microscopy (LAAM) for the topological characterization of entire cross-sections of pultruded carbon fiber reinforced rods. This characterization is an essential step in developing currently unavailable quantitative correlations between processing conditions and component properties. Usage of LAAM involves the automated scanning of samples of relatively large area O(cm2), capturing of thousands of image frames, montaging of these frames, and extracting topological information for all inclusions in the sample. In this work we describe the use LAAM to obtain such data from large (~1cm2) cross-sections of unidirectional carbon fiber-reinforced rods, containing over 106 individual fibers. Analysis of this data for industrial-scale pultruded rods has revealed several mesostructural features (fiber clustering and fiber misalignment) that can be of assistance in identifying processing or sample preparation defects.
Optimization of Process Conditions in Gas Assisted Injection Molding
Gas-assisted injection molding has been widely used to provide promising solutions to problems in conventional molding. With additional process parametcrs introduced, optimization in gas-assisted injection molding is much more complex than that in conventional injection molding. This paper proposes an automated design methodology for gas-assisted injection molding with robustness in consideration. By introducing a definition of gas penetration cost, the optimization problems dealing with multiple quality issues can be modeled as constrained optimization problems, with the gas penetration cost as main objective function and other quality quantities as constraints. A direct search-based optimization procedure, the Complex method, is used to optimize the bounded single-criterion problem. To illustrate the methodology, a case study is carried out on simulation results.
Influence of Processing Conditions on the Formation of Birefringence of Optical Plastics Lens by Using 3D CAE
One of the factors delaying the applications of the plastics optical elements is the existence of birefringence in plastics lenses. It is generally recognized that the mechanism of birefringence generation is relevant to the resin behaviors during the injection molding process. If this mechanism is fully understood by the flow analysis, it may be a great contribution to the fabrication of plastics optical elements. However, the conventional two-dimensional flow analysis on injection molding fails to grasp the phenomena of birefringence. In this research the molding process of a plastics lens was analyzed by a true 3D CAE software package, called 3D TIMON. The generation of birefringence was successfully predicted. Analyzed results were successfully confirmed by experimental data. Several processing conditions were further studied to minimize the formation of birefringence.
Accuracy of Desktop Injection Molding Simulation for Part Design
The reliability of a commercially available injection molding simulation program for part designers, Moldflow Part Advisor, is examined with a set of molding trials. Break-outs and thin tab features, part geometries typically seen with electrical applications, are studied. An instrumented test mold is built to model the geometric features of break-outs and thin tabs. Molding trials are conducted with two resins. The molding trial results are used to validate the melt front advancement predicted by the simulation. Process conditions are varied to yield short shot moldings as well as completely filled parts. Results show that the filling patterns in parts with thin tabs are fairly well predicted. Filling patterns through break-out features are not well predicted. Molding situations that yield short shots are seen to be predicted in some cases.
Melting Phenomena and Mechanism in Co-Rotating Twin Screw Extruder
The heating and melting phenomena in co-rotating twin screw extruders is quite complex and awfully difficult to analyze it. The main difficulties are not only complexity in the rotor geometry but also the variation of operating conditions. It has been observed the variation of both screw configuration and the operating conditions gave rise to the different melting phenomena and the processing values such as percent torque and melt temperature. In the recent years, some attention has been paid to the research of polymer melting in co-rotating twin-screw extrusion in systematic way(1,2,3). The vehicle to understand and analyze these complex phenomena was invented. In this study, based on the previous experimental results(1,2,4,5,6) and the systematic experiments to illuminate each distinct heat generation terms (1,2,3) were used to elucidate the complex polymer melting progressing in co-rotating twin-screw extrusion.
The Energy Dissipation Mechanism in the Viscoelastic Material: The Plastic Energy Dissipation
In this paper, the main emphasis and focus will be to study and illuminate the nature of Plastic Energy Dissipation (PED) in a variety of polymers and relate it to the relevant polymer solid state material properties. This PED term represents the heat generated during deforming a polymer solid. Polymer solids are viscoelastic and their viscous nature generates heat. A series of experiments for various polymers have been conducted in 'direct measurement method' and 'indirect evaluation method'. The experimental evidence to relate the stress relaxation and the sensible temperature rise were revealed by the series of direct method experiments. A number of PED experiments were conducted as functions of strain rate, strain and temp erature and the iso-temperature rise plots were obtained in temperature-strain space for commercial amorphous and semicrystalline polymers.
Manufacture and Rehabilitation of Guardrail Posts Using Composite Fabrics for Superior Performance
Many in-service structural components (underwater piles, railroad ties, utility posts, guardrail posts, and others) require strength and stiffness increases either to overcome structural defects, or to enhance the inherent material structural properties. The objective for this research is to develop procedures to wrap structural components using fiber/fabric-reinforced composites to enhance strength, serviceability, and durability. To accomplish the above objective, research will include the following aspects: • Selection of primer and resin combination that is compatible to the original substrate. • Type of fiber/fabric-reinforced composite that enhances mechanical, thermal, and chemical resistance. • Type of manufacturing/installation process to develop a FRP composite stiffened base material resulting in higher strength and stiffness ratios compared to the original substrate.
Development of PP-Based Nanocomposites via In-Situ Copolymerization and Melt Intercalation with the Power Ultrasonic Wave
Thermoplastic nanocomposites based on the copolymers of polypropylene (PP) - polystyrene (PS) and organically-modified montmorillonite (org-MMT) were produced by using power ultrasonic wave in an intensive mixer. Owing to the unique action of the ultrasonic wave, free radicals of styrene monomers and macroradicals of PP were generated, by which copolymers of PP and PS were polymerized. Another important aspect of using ultrasonic wave during the mixing process was to enhance nano-scale dispersion of org-MMT by destructing the agglomerates of org-MMT in the polymer matrix. Optimum conditions for the in-situ copolymerization and melt intercalation were studied with various concentrations of styrene monomer, sonication time and different kinds of clay. It was found that a novel attempt carried out in this study yielded further improvement in the mechanical performance of the nanocomposites compared to those produced by the conventional melt mixing process.
The Properties of Injection Molded, Short and Long Carbon Fiber Reinforced Polyamide 6,6 Composites
Injection molding the dry blend of fibers and matrix granules usually results in composite materials with poor surface finishes, high mould shrinkage and variable strength. Therefore, the process usually involved two stages, i.e. compounding and molding. This process however, is associated with the problem of fiber breakage. In this work, short and long carbon fiber reinforced polyamide 6,6 composites, prepared by extrusion and pultrusion compounding respectively, were injection molded. Test pieces were then subjected to the fiber length distribution characterization and mechanical test. It was found that pultrusion compounded composites showed superior fiber characteristics compared to the extrusion compounded composites counterpart. Number average fiber length (Ln) and weight average fiber length (Lw) supports this behavior. These fiber length characteristics were also in agreement with the improved tensile strength and tensile modulus of long fiber composites over the short fiber composites, despite the reduction in their fracture strain.
The Effect of Injection Moulding Processing Conditions and ?-Olefin Co-Monomer Type on the Performance of Metallocene Catalysed Polyethylenes
A number of metallocene catalysed linear low density polyethylenes and a conventional LDPE, of different material properties, were injection moulded over different mould cooling conditions. An assessment of the effect of the cooling rate, density and the co-monomer type on the mechanical performance and crystallinity was then conducted in order to establish any underlying trends. The results obtained from this report show a direct correlation between the density and co-monomer type of the materials with the mechanical properties, and a less significant relationship with the mould temperatures.
Bulk Moduli from Enthalpy and Volume Data Obtained during Physical Aging Experiments
Sudden temperature change stimulated process of physical aging has been studied through enthalpy and volume relaxation. The investigated polymers were a-PMMA and its amorphous blends containing 6 and 14vol.% of PEO. Differential scanning calorimetry and mercury-in-glass dilatometry were employed. Based on , where Kubát at al. suggested the possibility of correlation of enthalpy and volume relaxation data, apparent bulk moduli, Ka, were calculated and compared with the moduli determined by direct compression. The correlation between computed and measured data was reasonably good.
The Use of Maleic Anhydride-Containing Concentrates to Effect Adhesion between Polyethylene and Ethylene-Vinyl Alcohol
Adhesion properties were determined on five-layer coextruded cast films that consisted of two high density polyethylene (HDPE) cap layers, two tie layers, and an ethylene-vinyl alcohol copolymer (EVOH) barrier layer (ABCBA configuration). The tie layers consisted of varying amounts of maleic anhydride-modified polyethylene-containing concentrates and various diluting resins. The extrusion temperature was also varied. Adhesion increased fairly uniformly as the film thickness and the concentrate level were increased. Adhesion was also affected by the choice of diluent and the ethylene content of the EVOH. Adhesion did not vary over our experimental temperature range.
Morphology Distribution of Injection Molded Polypropylene and its Dependence on Processing History
In this paper, the morphology distribution of injection molded ZMA 6170 polypropylene observed using polarized optical microscopy is reported. A three-region- multi-layer model is sufficient to describe the skin-core morphology of these injection-molded parts. In the fully developed flow regions, a clear three-layer structure composed of a surface skin layer, a transition layer, and an inner core layer is observed. The simulation software package Moldflow MPI is used to identify the thermal and shear histories of the polymer melt during injection molding process. The characterization of each layer and its dependence on the thermal and shear histories are discussed.
The Developing Behavior of Core Material and Breakthrough Phenomenon in Sandwich Injection Molding
The sandwich injection molding technique can be used in wide range of engineering applications. In this study, the developing behavior of core materials and break through phenomenon in the sandwich injection molding was investigated. The samples were preferred using a spiral-flow mold by changing the viscosity ratio and the melt temperature of skin and core materials. Developing behavior of the materials in sandwich injection moldings divided four regions, and it is noted that core material tends not to completely penetrate through the skin material at a stretch point, and it resulted in break through phenomenon. It is considered that break through phenomenon depends on the melt strength of the freezing layer of the skin material at flow front.
Mechanical Properties of Knitted PE Fiber Reinforced PE Injection Molding Composites
Interface construction is very important in the design of composite materials. Composites that consist of same materials but different shape such as fiber shape and matrix phase can create high interfacial strength. Call this composite Interface-less Composites". In this study knitted fabric was chosen as reinforcement configuration which has good drapability expandability and high productivity. Knitted polyethylene (PE) fiber reinforced PE film (PE/PE composite film) by film stacking method was prepared. Injection molding specimens were prepared by inserting this PE/PE composite film and PE was injected as matrix. Tensile properties of Interface-less composites by using injection-molding method were investigated."
Study of Damage Mechanisms in Uni-Weave/Satin-Weave Hybrid IM7/BMI Composites under Uniaxial Tensile Loading
The damage mechanisms in uni-weave/satin-weave hybrid IM7/BMI composites under uniaxial static tension loading have been investigated. The results reveal that hybridization effects on the damage mechanisms largely depend on the degree of waviness. For low waviness composites, the damage process is not affected significantly by hybridization. The damage patterns in the woven and hybrid composites are similar to those found in tape laminate. However, the large waviness composites exhibit complex damage behavior. Hybridization has a significant effect on the damage process.
Mechanical Properties of PP/PP Composites
The interfacial structure and mechanical properties of polypropylene (PP/PP) composites consisting of homo-PP fiber and propylene-ethylene random copolymer matrix were investigated. In PP/PP composites, the transcrystalline structure grows on PP fiber, which influences the mechanical properties. The two types of unidirectional PP/PP composite with different impregnating system were fabricated. In the well impregnated PP/PP composites, there were many transcrystalline layers, and the tensile modulus and strength were higher than those of badly impregnated PP/PP composite. Particularly in the transverse direction, well impregnated PP/PP composites had good adhesive properties. Therefore, it is supposed that the mechanical properties of PP/PP composites are influenced by trenscrystalline.
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