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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Predicting Molding Forces in SMC Compression Molding
Much attention is now being given to improving the economy of Sheet Molding Compound (SMC) compression molding by reducing the cycle time required to produce acceptable parts in steady production. The longest stage of the molding cycle is the cure cycle. However, the filling stage does play an important role. The shorter the filling time, the more reactive an SMC can be used and thus the shorter the cure time. In particular for truck parts, due to their large size, being able to predict the press force needed to close the mold at a given speed is extremely important. The long-term goal of our research is to develop a model to predict closing forces as a function of raw material parameters - paste rheology, glass length and concentration - without the need to make the SMC. Here we present a simple model describing our approach and propose a preliminary procedure that can be used to obtain the closing force. This preliminary procedure still requires measurements to be obtained from the already made SMC. The results from this approach are compared to experimental results for a typical automotive grade SMC.
Comparison of DOE Methods on Hot-Plate Welding of Polypropylene
Design of experiments (DOEs) are a valuable tool for optimizing manufacturing processes and ensuring product quality. There are a wide variety of DOEs available, all having their own advantages and disadvantages and unique characteristics. In terms of plastic joining manufacturing processes, hot-plate welding of polypropylene was chosen as a platform for comparing three of the more common DOEs: full-factorial, Box-Behnken, and central composite. A complete analysis of the process was not sought, but within the field of factors studied, hot-plate welding of polypropylene appears to be a robust process. All three DOEs resulted in slightly different model equations, but very similar response surface contour plots.
New Thermoplastic Adhesive and Barrier Resins
BLOX™ Adhesive and Barrier Resins are the first commercialized polymers from a new family of thermoplastics, namely polyhydroxyaminoethers (PHAE). These resins offer a unique property set, including excellent adhesion to a variety of substrates, high gas barrier, superior clarity, and good mechanical strength and toughness. In addition, these resins are amorphous and can be easily processed using conventional thermoplastic processing techniques. Some commercial applications to-date utilizing PHAE resins include barrier packaging, starch-based foam packaging, and powder coatings. contributes to their relatively high selling price (typically between $3.00 - $5.00/lb), thus relegating their use to low volume applications such as resin modifiers and specialty coatings.
Factors Affecting Shot Size Variation in Injection Molding Processes
Many molders transfer from a velocity-controlled fill to a pressure-controlled pack and hold when the part is approximately 95% full. It is commonly known that changes in injection velocity affect the position of the melt front in the cavity at this transfer point. It is less commonly known that many other sources of process variation can have the same effect. This paper investigates the root sources of variation in fill-only part size. Three factors are considered: inertia of the injection unit, check ring leakage, and melt compressibility. While the common explanation in the industry has focused on inertia, deformation of the melt, check ring leakage, and the machine's hydraulic response play even more significant roles.
A Study of the Effects of Process Conditions on the Shrinkage of Plastic Parts in Injection Molding by the Taguchi Method
The shrinkage behavior of a plastic plays a critical role in determining the final dimensions of an injection-molded part. It is well known that process conditions affect many properties of plastic parts including shrinkage. This study applies the Taguchi method to systematically investigate the effects of process conditions on the shrinkage (along and across the flow directions) of three plastics; high-density polyethylene, general-purpose polystyrene, and acrylonitrile-butadiene- styrene. The most important processing variables affecting the shrinkage behavior of each plastic are identified. The optimization conditions to reduce the shrinkage identified by the Taguchi method are experimentally verified.
Modeling of Sink Mark Formation in Cross-Rib-Reinforced Injection-Molded Plastic Parts by Localized Finite Element Shrinkage Analysis
The sink mark formation in cross-rib-reinforced plastic parts has been modeled by a three-dimensional localized finite element shrinkage analysis. Using Abaqus software, sink mark formation is simulated by the localized thermal and structural finite element analyses near a cross-rib base. Initial conditions and boundary conditions for the Abaqus thermal analysis are determined from a molding analysis using C-Mold. Effects of packing pressure and cross-rib thickness on sink mark depth are analyzed. The predicted sink mark depth is compared with the experimental data from the literature.
Viscosity Effects in Rigid PVC
The viscosity of PVC is better understood if it is treated as a fluid which contains filler. Anomalous effects such as die swell increasing with increasing melt temperature and melting history causing changes to the viscosity can be explained if the PVC primary particles are viewed as filler which disappears during melting. The fusion torque peak is well described by this approach. The compaction minimum is a free flowing powder which transitions to a filler-containing viscous liquid. If another viscous liquid is added to a PVC compound then the fusion peak will be at a lower torque because the effective level of filler is reduced. This helps to explain the fusion curve of PVC compounds that contain CPE impact modifier.
TTIR Welding of Aliphatic Polyketone
This paper reviews the evaluation of through transmission infrared (TTIr) welding of aliphatic polyketone (Carilon Polymer). The paper reviews the effects of operating parameters, such as power density, weld time and pressure on weld strength. It was found that with proper operating conditions, parent material strength could be achieved. It was shown that thickness' as high as 6 mm were weldable using power densities in the range of 30 to 40 W/cm. Thickness' above 8 mm will be difficult to weld with TTIr (?=800-900 nm) due to surface heating and high power requirements (45W/cm). A transparent pressure foot may help remove heat and reduce marking.
Poly(phenylene ether) Engineering Thermoplastic Provides Creep Resistance, Toughness and Fire Resistance Required for High Performance Pallets
The first all-plastic pallets to meet high mechanical performance standards, and satisfy Underwriters Laboratories fire requirements have been developed. The foam injection molded top and bottom decks of the assembled pallets are made of a low specific gravity, flame retarded high performance (Poly(2,6 dimethyl 1,4-phenylene ether)/high impact Polystyrene) blend, Noryl® engineering resin. The pallet comer posts are made of injection molded high performance (Polycarbonate/Poly(butylene terephthalate) blend, Xenoy® engineering resin. Both of the resins' intrinsic properties, molding (processing) method, and design geometry meet the requirements for Grocery Market Association pallets. The resulting pallet is an all-plastic pallet with exceptionally high mechanical performance and flame resistance that is rated equal to or better than comparable wooden pallets.
On-Line Viscosity Measurement during Poly(ethylene terephthalate) Extrusion
The effects of various processing parameters (temperature, pressure and drying time) during extrusion of poly(ethylene terephthalate) (PET) were examined using a commercial on-line process control rheometer mounted on a twin-screw extruder. Particular attention was addressed to the effect of the moisture content. Moisture left in the resin pellets due to an incomplete drying reacts with the polyester to break down the molecular weight, which is reflected by a significant decrease of the viscosity. Since the PET resin is highly hygroscopic, off-line melt viscosity characterization may yield erroneous estimates of the rheological behavior. As in-line drying is recommended to achieve optimal properties, on-line viscosity characterization is required to provide an unbiased viscosity measurement and a true estimate of the performance of the drying step.
Nondestructive Study of Temperature-Property Correlations during the Curing of Rubberized Fabric
During the production of waterproof fabric for use as convertible car roofs, fabric and rubber are co-extruded and cured. Temperature control and residence time in the curing oven are key to the final properties. The manufacturer desires a nondestructive instrumented technique to replace the current pressure test used for quality control. Thermal conductivity of these fabrics has been measured nondestructively to relate to the degree of cross-linking. Thermal behaviors and compositions of this material have been evaluated both DSC. Combining thermal analysis techniques with thermal conductivity correlation's, may be an appropriate quality check of such product.
Analytical Methodologies Employed in a Comprehensive FDA Food Contact Compliance Investigation: Analyses for Residual Monomers, Resin Oligomers, Additives and Modifiers in Several Food Simulating Solv
FDA mandates and product stewardship concerns have given rise to challenging analytical problems. This is evident when considering the potential migration of constituents of a polymer formulation intended for food contact applications. Residual monomers, resin oligomers, additives and modifiers must all be considered in the evaluation of potential human health impact. In this paper we present a series of analytical methodologies that address these concerns. Liquid and gas chromatography and mass spectroscopy are used to quantitate the migration of a number of representative compounds from polymeric formulations intended for food contact applications.
Effect of Layered Silicates on Thermal Characteristics of Polycarbonate Nanocomposites
Differential Scanning Calorimetry (DSC) and Thermo-Gravimetric Analysis (TGA) were used to investigate the thermal properties of polycarbonate (PC)-layered silicate nanocomposites. The type of clays used in this study include phosphonium exchanged montmorillonites as well as synthetic clays which contained C18-alkyl side chains with or without additional tethering amino- or epoxy-groups. Effects of clay contents on the glass transition temperature (Tg) and thermal stability of PC were determined. DSC results indicated that synthetic clays had little effect on the Tg of PC; however, a very slight decrease in Tg was noted in those nanocomposites filled with phosphonium exchanged montmorillonites compared to that of the pure PC. In addition to Tg, an endotherm at about 50°C was also evident in DSC obtained for the synthetic clay filled nanocomposites. TGA results revealed that the presence of synthetic clays caused a significant reduction in the thermal stability of PC. Nanocomposites filled with 7.5 and 10 % of C18-synthetic clay also exhibited a two-step thermal degradation. The second step occurred at a temperature slightly higher than the onset degradation temperature observed in pure PC. Phosphonium exchanged montmorillonites provided better thermal stability for PC than the synthetic clays; a slight increase in the onset temperature of thermal degradation over that of the pure PC was evidenced.
Mechanical Performance of Polyamides with Influence of Moisture and Temperature-Accurate Evaluation and Better Understanding
The wide use of thermoplastics has put higher demands on designers to conduct more accurate and increasingly sophisticated analysis of materials in order to ensure the performance of the molded parts under the end-use conditions characterized by varying humidity, temperature, and dynamic load or deformation. One of the key aspects in thermoplastic analysis is to apply correct material property parameters obtained using standard testing procedures and under end-use conditions. Previously we reported to SPE (AnTec'97, AnTec'98, and RETEC/ASTM'99) the short- and long-term mechanical properties of polyamides (nylon) with time and temperature effects under dry-as-molded conditions. The current paper focuses on the two of the most influential factors on polyamides' properties and performance - moisture and temperature. The tensile properties of conditioned polyamides were obtained from -40°C to 150°C, and the moisture content in the sample was examined immediately after test to ensure that the change in material properties is accurately reflected. The results provided critical understanding on the impact of moisture and temperature on polyamides strength and ductility. The findings in this investigation will enable engineers and product developers to successfully design and evaluate the performance of injection molded nylon parts under end-use conditions.
Defect Analysis and High Density Polyethylene Pipe Durability
Engineering thermoplastics, in particular polyolefins such as special grades of high density polyethylene, are gaining importance in high pressure pipe applications such as gas and water supply systems. To ensure proper performance of such pipes over the required lifetime, durability analyses are needed to adequately account for the effects of loading, time, temperature, and especially the occurrence of defect particles in the pipe, such as gel particles, contaminants, process residues etc. The objectives of this work are to characterize the defect particles in HDPE pipes, examine their origins, and correlate with the long-term performance of pipes. The results indicate that the lifetime of these pipes under hydrostatic test conditions may be more sensitive to the rigidity and interfacial adhesion of defect particles than purely the size of defect particles.
Automatic Cooling Channels Layout of Straight Cooling Pipes in Injection Molding
This paper deals with method of automatically arranging cooling channels, which are composed of linear-shaped cooling pipes, in an injection mold. For this study, an autonomous design methodology to automatically arrange curved cooling pipes was suggested and its efficacy was confirmed. This method will be expanded in this paper so as to be applied to a cooling channel with a combination of straight cooling pipes. Then, the method will be examined through a series of numerical experiments. In this study, straight cooling pipes are expressed by arranging in a straight line, lengthwise, a plural number of heat-absorbing elements. A cooling channel is composed of a combination of those pipes. To achieve the desired temperature distribution on the mold cavity surface, the arrangement of the cooling channel is searched through autonomous movement of cooling pipes. This movement will be achieved through translational motion, and expansion/contraction to satisfy the two constraints, the straight shape of cooling pipes and the maintenance of their interconnected relationship.
Modelling of Bubble Formation in Rotational Molding
Polymer sintering and heat transfer are fundamental phenomena in rotational molding. In the heating stage of the molding cycle, the powder particles melt, adhere to each other and sinter. During this stage, pockets of air are entrapped between the particles and form bubbles. This work aims at determining the relative effects of material properties and molding temperature on the initial sintering and bubble formation in rotational molding. The molding temperature varies strongly with the oven temperature and molded part thickness, and is determined using a lumped parameters heat transfer model (Gogos et al., 1998). The initial sintering of powder is predicted using a two-particle sintering model (Pokluda et al, 1997). The sintering model is used together with the heat transfer model to predict the level of sintering reached when an additional powder layer adheres to the melt and thus entraps air pockets which in turn will form bubbles. Results show that the initial size of the bubbles formed does not vary significantly when changing molding conditions. The polymer rheological properties seem to dominate the bubble formation process. Further results will be compared with experimental work.
A Study of the Deterioration in the Mechanical Performance of Polymers Used in Multilayer Fuel Lines with Immersion in a Standard Automotive Test Fuel
Many multilayer fuel line structures are currently being developed for use in fuel handling systems in an effort to comply with pending legislation regarding reduced vapor emissions. This study examines the changes in the mechanical properties and glass transition temperatures (Tg) of the polymers used in multilayer tubes such as conductive Nylons, barrier layer materials including Fluoropolymers, and tie layers with immersion in the standard test fuel Fuel C at 25°C. The changes in Tg, percentage mass uptake, swelling, mechanical properties such as tensile, flexural and impact were determined for different immersion times. The results show that a significant deterioration in the mechanical performance of many of these polymers was recorded. A corresponding decrease in Tg with increasing immersion time in the test fuel was observed.
Pressure Build-Up in a Staggered Pin Compounding System
Pultrusion compounding is a widely used technique for mixing polymer with continuous reinforcement. It often involves pulling glass roving over staggered pins immersed in a pool of liquid polymer. This causes polymer pressure to build-up in a wedge-shaped region located between the roving and pin. This pressure drives polymer into the roving. To study this pressure build-up, roving was pulled over an instrumented pin placed in a silicon oil pool. A hole in the pin allows pressure to be measured at various locations in the wedge as a function of pulling speed, oil viscosity, and inlet tension. These parameters are lumped together with the roving width to form a dimensionless group called the lubrication number. Initial studies using impermeable tape showed that for lubrication values above 0.0001, the maximum pressure was equal to its theoretical value of tension divided by the product of tape width and pin radius. For permeable roving the maximum pressure was significantly less than that value. Models for pulling force as a function of process parameters have also been developed and validated.
Optimizing Welding Temperature of Semi-Crystalline Thermoplastics-Memory Effects of Nylon
Previously we reported*1 to SPE'99 on the basic principles for optimization of the vibration welding process and presented an analysis of the weld-melt temperature kinetics for linear vibration welding. For this investigation we used the advanced Thermovision 900® infrared measurement system*2 for comprehensive, real-time analysis and thermal imaging. Under optimized processing conditions for vibration (linear and orbital) and hot-plate welding technologies, the tensile strength of welded nylon 6 butt joints is equal to or 14% higher than the tensile strength of the base polymer (matrix). For optimized vibration welding conditions, the maximum temperatures of the weld-melt (in inter-phase) were significantly above (85 - 90 °C) the melt point of the welded nylon 6 and nylon 66 (Tm = 223 °C and 261 °C, respectively). For PP based plastics, J. Vetter and G. W. Ehrenstein observed*3 an increase in the maximum temperature in the weld-melt / in weld inter-phase of not more than 10 °C above the melting point ( Tmp ). In their report to SPE'99, the authors discussed the results of the physical modeling for semi-crystalline HDPE, showing the values of maximum temperatures in the weld inter-phase above 250 °C compared to melting point (Tmp = 126 °C). Ch. Bonten presented*4 to SPE'99 his analysis on the mechanisms active in weld interface of semi-crystalline thermoplastics (HDPE and cross-linked polyethylene PE-X). Mechanical performance of welded joints was affected by crystallization across the boundary layer and weld-melt temperature kinetics (above melting point Tmp). For a better understanding of the role and influence of the temperature of the melt (in injection molding) and weld-melt (in welding) on mechanical performance of semi-crystalline molded (welded) thermoplastics, we performed a comparative study for nylon 6 and nylon 66 (non-filled and fiber-glass reinforced) plastics. Mechanical performance of injection molded and welded nylon was evaluated using static (tens
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