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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Examination of Method for Diagnosing Mold Filling Imbalances in New Multi-Cavity Molds
During the startup and operation of new multicavity molds, it is expected that cavity-to-cavity filling variations will be found. This will occur despite the use of geometrically balanced runners. With cold runners, this imbalance is dominated by either steel variations in the mold, or shear induced variations developed in the runner. In order to correct the imbalances, it is important to be able to separate these two causes and to quantify their contribution. A method, here referred to as “The Five-Step Process” was developed for this purpose. This paper presents a study to determine how robust The Five Step-Process is in diagnosing steel variations in a mold.
The Effect of Runner Shape on Mold Filling and Product Variation
In the plastics industry today it is generally accepted that full round runners provide the most efficient flow channel. However, when full round runners are implemented it is common for misalignment of the two halves of the runner to occur. This paper presents the effect that this misalignment has on mold filling and the resultant product. It is also common, in many instances and for many reasons, for other cross-sectional designs to be used. This paper also examines how subtle variations in runner design dramatically affects filling pressure, resulting in variations in molded parts. This study finds that there is a direct predictable relationship between the pressure drop through a runner and the ratio of the perimeter of the runner geometry to the cross sectional area of the runner.
Relationship of Predicted Shear Stress to Molded Plastic Parts
Shear stresses developed during mold filling induce polymer orientation. This stress-induced orientation can be a significant contributor to a part’s residual stress, the development of anisotropic shrinkages and its tendency to warp. This paper presents a study that evaluates the relationship between the shear stress predicted from mold filling analysis software to its effects on a variety of different plastic materials. The study evaluates the impact of part wall thickness, melt temperature and fill rate. The study includes a variety of plastic materials, material fillers and reinforcements. Through a better understanding of the impact of predicted shear stress on different materials, a molder, or mold-filling analyst, will be able to minimize or avoid shear stress induced molding problems.
The Study of Process Stabilization and Consistency Using Pulse Cooling Compared to Cooling with a Thermolator
Injection molding requires a cooling phase within the cycle to cure the molten plastic that was just injected into a steel mold. The traditional method of cooling uses a mold cooling system to regulate the cooling. Pulse cooling, another method of cooling, is being studied to see how it compares in process stabilization and consistency to the traditional, constant flow, method of cooling.This study consists of an experiment using a constant flow cooling system to regulate cooling vs. using a pulse cooling system to regulate cooling. The data from the experiment is compared and the stabilization and consistency of the process using a pulse cooling system is compared to the standard cooling with constant flow.
Optimization of Extrusion Blow Molding Ovalized Tooling
Producing blow-molded bottles such as oval shaped cosmetics bottles requires the use of ovalized tooling. Currently the design of these dies is based the past experience. Simulation software can be used to eliminate extensive rework of the die, by allowing for the tooling design to be optimized without any steel being cut. The end result of this is a more uniform wall thickness distribution in the final product. 3D simulation software will be used to demonstrate its ability to construct and optimize the ovalizing of die and/or mandrel that could produce a parison for blowing oval shaped bottles. The results of this simulation can only be used with 3D simulation software.
Parison Verification of Parison Programming for Extrusion Blow-Molding Simulation Software
Using simulation software, a computer can help to gain a basic parison profile and in turn be an effective way to validate a design. When molding parts, by using parison programming, the operator has the ability to maintain a uniform wall thickness. The majority of users who do simulations assume a constant wall thickness and a uniform cylindrical shape for the parison. However, in real world applications this is not true, and two major occurrences, die swell and sag, are overlooked. The inability for the blow molding simulation software to recognize these factors, can lead to greater cost in terms of lost time.In an attempt to verify the accuracy of the software simulation programs, a 2D axisymmetric model of the parison was created and then compared actual parisons created on a blow-molding machine using parison programming. After completing this study, it is our hope that this will help the people who run the software to perform better simulations.
Evaluation of Geometric Effects for Extrusion Blow Mold Pinch-Off Design
This study looks at secondary design parameters that affect the strength of extrusion blow molded parts at the pinch-off. The effectiveness of secondary parameters on weld strength creates a greater understanding of pinch-off design. Pinch-off design is critical in extrusion blow molding since it welds the parison together in the mold. Weld strength is important because the part could fail in application if the weld strength is poor.This is a continuation of a prior experiment, which concluded flash pocket dimensions were the primary contributor to weld strength. This study focused on the secondary effects while keeping the flash pocket constant. The bottles for this experiment were made out of HDPE. A two-level Design of Experiment (DOE) was implemented to examine the effect of the parameters on weld line strength.
HDPE Blow-Molded Bottle Pinch-Off Weld Strength of High Density Polyethylene at Various Molecular Weights
This study focused on the weld strength of different materials in the pinch-off area of an extrusion blow-molded bottle. Various materials of different densities were run through an extrusion blow-molding machine. This study determined how weld strength at the pinch off was affected by the density of the material being processed. The pinch off is the portion of the mold that welds the ends, and at times the interior portions, of the parison as well as cut the excess flash to aid in removal. Having a strong weld was extremely crucial to overall bottle quality and was a direct result of pinch off design. The reason the pinch off has an effect on quality is due to the weld probably being the weakest part of the bottle and bottle strength is only as strong as its weakest point. Strength was a key issue in determining overall quality and the research performed allows for a direct correlation between strength and material grade.
Analysis of Weld Line Strength and Thickness for Extrusion Blowmolded HDPE Bottles
One objective of any blow molder is to create the strongest weld possible at the pinch-off region. In order to do this, a clear understanding of how the material’s viscosity interacts with processing variables to produce a weld line of certain thickness and strength is required. By varying mold closing time, mold temperature and relief angle on two melt viscosity variations of high density polyethylene (HDPE) this paper will show a clear relationship between these variables. Thus, allowing for the blow molder to produce the strongest and most optimum weld line for HDPE blow molded bottles. In doing so, this article will show that a slow mold closing time coupled with a high mold temperature will produce the strongest and thickest weld lines for both vicosity variations of HDPE.
Carboxylation of EVOH by Reactive Extrusion and its Blends with Polyamide 6,6
The carboxylation of poly(ethylene-co-vinyl alcohol) (EVOH) was carried out utilizing varying amounts of succinic anhydride in a reactive extrusion process. The functionalized EVOH was then melt blended with polyamide 6,6 to investigate the effect of carboxylation on blend miscibility and/or phase behavior. All functionalization reactions and melt blending procedures were carried out on a co-rotating twin-screw extruder. The effectiveness of the functionalization reaction was determined through infrared spectroscopy (IR) and titration while the thermal and mechanical properties of the blends were investigated using differential scanning calorimetry (DSC) and tensile testing. IR spectroscopy showed the presence of a carbonyl peak after functionalization, indicating the carboxylation reaction was successful. These findings were reinforced by titration data. While the blends were all immiscible, the mechanical properties of the blends all increased with the carboxylation of EVOH.
A Continuation of the Investigation of the Silane Crosslinking of Polyethylene Polymer Chains
Many hot water applications use crosslinked polyethylenes manufactured using methanol based silanes. Although ethanol based silanes are a higher cost material, the overall process using them would result in a lower cost alternative by removing an entire step of the manufacturing process. This experiment is a continuation of work performed on the silane crosslinking of polyethylene polymer chains. The experiment compares properties and manufacturability of methanol based silanes and ethanol based silanes. The results of this experiment are intended to aid in further research of the subject.
Mechanical Properties of Rotationally Molded Laminates of LLDPE and Foamed LLDPE
Part weight of plastic articles is reduced by use of foamed material or laminates that include a foamed layer. Traditionally rotationally molded parts may be filled with foam in a post-molding operation. The foam may, or may not, be the same material as the outer skin. It may, or may not, enhance properties. This paper describes the use of a two-step rotational molding process in which a LLDPE outer skin is molded followed by molding LLDPE with a blowing agent by opening a drop box containing the compound. Various ratios of skin-tofoam thickness were produced. ARM impact, tensile and flexural testing compare various ratios of laminate thickness. Results are compared to predictions from a laminate model.
Influence of Organo-Clay Type on the Thermal and Mechanical Properties of Poly(L-Lactide)/Clay Nanocomposites
Poly (l-lactide) (PLLA) has received considerable attention recently because it is environmentally friendly, derived from agricultural sources, and biodegradable. However, the mechanical properties of PLLA are typically low compared to other petroleum-based plastics. Recently, properties such as modulus and heat deflection temperature have been improved by creating polymer/clay nanocomposites. This study focuses on the effect of different organic modifiers for montmorrillonite clay on the thermal and mechanical properties of PLLA. Upon the addition of a small amount (1-10 wt %) of these modified clays, the storage modulus and Tg increases for all types of clays. The greatest increase in properties is found using quaternary ammonium ion having a pendant benzyl group.
Rheological and Chemical Modification of Polypropylene with Inorganic Clays
Polymer composites were produced by mixing an inorganic clay hydrotalcite (HT), stearate coated (HTC) and uncoated (HTU) at 5 and 30% by weight with polypropylene and modified polypropylene. Torque profiles from blending in a batch mixer indicated significant viscosity changes depending on the type of the particular clay/polymer components. FTIR, MFI, DSC and TGA data suggested corresponding structural changes in the composites. The results showed that coated hydrotalcite produced the highest melt viscosity when added in the modified polypropylene. Tests are underway on flammability and rheology to shed more light into the interactions of the clay and the polymers.
Cross-Linked LDPE as a Rheological Modifier for LLDPE
Melt strength tests were conducted for blends of linear low density polyethylene (LLDPE) with cross-linked low density polyethylene (xLDPE) to study the effect of rheological modification on the development of low density, LLDPE foam with improved processability during extrusion foaming. Blends of LLDPE containing various concentrations of xLDPE, cross-linked with peroxide, were prepared in a Brabender batch mixer. Melt strength tests of the prepared blends were conducted through a capillary rheometer. It was found that melt strength increased with respect to increasing concentrations of xLDPE, suggesting optimum foamability at specific xLDPE content.
On the Deformation of a Slender Bubble in a Carreau-Yasuda Liquid in an Extensional Flow
The deformation of a slender bubble in a Carreau-Yasuda liquid in a simple extensional and creeping flow has been theoretically studied. With the assumption of a constant pressure in the liquid, the deformation problem can be described by an ordinary differential equation, which was numerically solved. Analytical expressions for the local radius were obtained close to the center and the end of the bubble. The results for the shape of the bubble are presented as a function of four governing dimensionless numbers. The relevance of this work to polymer devolatilization and foam plastics is discussed.
Non-Reactive Process for Recycling of Cellular Phones
The use and production of cellular phones have skyrocketed within the last decade, with the average use lifetime between 1 and 3 years. So, the ability to dispose of and recycle the phones is a pressing issue. These phones are composed of a variety of materials, including thermoplastics (six different types), metals, rubber, and epoxy. This work pertains to the grinding of cell phones, separation of thermoplastics and epoxy from the bulk ground material, and subsequent compounding of the desired materials in an intermeshing, co-rotating, twin screw extruder. Tensile and Izod impact tests were performed on the immiscible blends, whereas SEM and AFM analyzed the fracture surfaces. Dynamic mechanical thermal analysis show how thermal properties of the blends change as a function of blend composition. A polyolefin elastomer (PE) was incorporated into the blend and was shown to improve impact properties.
Reactive Process for Recycling of Cellular Phone Housing
The front cover of the cellular phone housing was ground to be as the same size as the original particles before use using the knife mill and the undesired materials were separated with the sink-float process in water and salt. The unprinted glass fiber reinforced epoxy circuit boards were size reduced and pulverized using both the knife mill and the hammer mill. The separated epoxy powder and glycidyl methacrylate (GMA) were added as the additive and the reactive species for the reactive process using the batch mixer and the twin screw extruder, respectively. Izod impact strength at various temperatures, tensile test, particle size distribution analysis for the ground circuit board, SEM on the fracture surface, and dynamic mechanical spectroscopy were performed to characterize the reactive polymer alloys and mixtures compounded by the batch mixer and the twin screw extruder.
Morphology Development and Rheology of HDPE/PBT Blends
High density polyethylene and a small amount of poly (1,4-butylene terephthalate) (PBT) have been blended in a twin screw extruder, and its rheology as well as morphology has been investigated as a function of extrusion condition. When the blend was extruded slightly below the melting temperature (Tm) of PBT, the dispersed phase forms a curved sheet morphology, and turns into fibril and finally into droplet structure as more shear is applied. On the contrary, when the material was blended at the higher temperature, the dispersed phase forms only droplet structure.Even though the blend contains as small as 5wt% PBT, the moduli as well as shear viscosity of the blend with the sheet structure increases significantly. However, the droplet structure does not show enhancement of rheological properties unlike the case of curved sheet. This means that we can control the blend morphology as well as its rheology, and can enhance the rheological properties by inducing the microstructure like a curved sheet.
2D Composite Models of Modular Tangential Counter-Rotating Twin Screw Extruders
A new 2D composite model with hybrid FEM/FDM formulation was developed for simulating the fully filled and starved regions with the associated pressure profiles of a modular tangential counter-rotating twin screw extruder. 1D composite models combine the screw characteristic curve of individual element to analysis flow of an entire modular screw and the flow fields of the whole domain are not calculated again. Based on the linear relationship of the drag flow rate and the screw rotation speed under the single screw extrusion theory, the new mesh with artificial screw rotation speed boundary conditions was used to simulate the entire flow fields for the counter-rotating twin screw extrusion process in our 2D composite models.To demonstrate applicability, the predictions of individual screw elements via hybrid FEM/FDM agree well with Nichols's experimental studies. The pressure and filling factor profiles in a modular LSM34-34 extruder provided by 2D composite models show good agreements with those of 1D composite models.
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