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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WARPAGE MANAGEMENT USING THREE DIMENSIONAL THICKNESS CONTROL METHOD IN INJECTION MOLDING
Warpage is one of the most crucial problems in injection molding quality control. Since many factors will cause shrinkage and warpage, it is very difficult to distinguish which factor always dominates warpage. In this study, we have developed Three Dimensional Thickness Control Method (3DTCM) to manage the warpage of the injected parts. Using this method, we will specify the geometry of parts with non-uniform three dimensional structures. After integrated with special gate design, material selection, various operation conditions, warpage of injected parts can be managed significantly. Also, to verify our results, both numerical and experimental investigation will be performed in this study.
CYCLE TIME OPTIMIZATION AND PART QUALITY IMPROVEMENT USING NOVEL COOLING CHANNELS IN PLASTIC INJECTION MOULDING
Cooling channel design in injection moulding is very important as it greatly affects the cycle time as well as the shrinkage and warpage of the plastic part. Traditionally, cooling channels have been machined into mould components with gun-barrel drilling, with that only straight channels were possible to manufacture. An advanced method of cooling system that 'conforms' to the shape of the part in the mould can be made possible with free form fabrication technique such as DMD (direct metal deposition). This paper presents an investigation on the optimization of mould design of conformal cooling channels of different cross sections for plastic injection moulding. Comparative study has been done with the conventional straight cooling channels. ANSYS thermal simulation software has been used to get comparative temperature profile on the mould and Moldflow simulation software has been used to compare shrinkage, warpage and temperature profile of the part itself during moulding process . Comparative results are presented based on temperature distribution and cooling time for the mould and warpage deflection, volumetric shrinkage and temperature profile of the part. The results provide a uniform temperature distribution with reduced shrinkage and warpage and reduction in cycle time for the plastic part.
DYNAMIC MOLD SURFACE TEMPERATURE CONTROL FOR MOLDING HIGH GLOSS, PAINTING FREE PART SURFACE ACHIEVING CYCLE TIME AND COST REDUCTION
The study shows the molding of a high gloss surface notebook computer (NB) display support without painting using dynamic mold temperature control. The required mass production rate is 300,000 pieces per month. Both water heating/cooling and induction heating/water cooling were employed to investigate the cycle time, mold and machine requirements. The former requires 60s cycle time whereas the later needs only 36s to achieve a weld line free surface. The associated cost reduction in energy consumption is US $23,700 per month, injection machine operation is US $52,800 per month, mold making cost is US $75,000 and painting cost saving is US $190,500. Annual savings could reach US $3,237,900.
A DIMENSIONAL ANALYSIS OF VISCOUS HEATING IN RUNNER SYSTEMS USING THE RADIAL FUNCTIONS METHOD
Polymer flow through circular tubes is a common occurrence in injection molding runner systems. Viscous dissipation affects the temperature distribution of the melt as it enters the cavity. The Radial Functions Method was used to model the flow and heat transfer inside runner systems in dimensionless form. Temperature increases are obtained from simple expressions as a function of the dimensionless Brinkman and Graetz numbers. This eliminates the necessity of simulation or experimental test of such flows when predicting temperature increments as a function of processing conditions.
EVALUATION OF THE CRACK INITIATION CHARACTERISTICS OF PIPE GRADE POLYETHYLENE UNDER FATIGUE LOADS
Recently, a circular notched specimen (CNS) is selected for studying the crack initiation characteristics of pipe grade polyethylene as a part of understanding quasibrittle failure. In this study, four types of pipe grade polyethylene were chosen and tested under variable fatigue loading conditions using CNS with various notch depths. The fatigue characteristics of four polyethylenes were evaluated, and the fracture surface of CNS after failure is analyzed by optical microscope and scanning electron microscope (SEM) to evaluate the fracture mechanism of pipe grade polyethylenes. In addition, the technical issues with CNS during tests were also investigated by finite element analysis.
CHALLENGE TO THE FOAMING OF A THIN-WALL INJECTION MOLDED PART- INFLUENCE OF INJECTION SPEED AND GATE GEOMETRY
Foaming of a thin-wall part during injection molding is challenging. Cell nucleation and growth are significantly constrained by rapid cooling from the mold by limited cavity space and by high mold cavity pressure generated by the viscous polymer melt. In this paper we study the influence of injection speed and gate geometry on the cell size uniformity and void fraction control of a foamed thinwall part. Real-time mold cavity pressures were recorded using pressure transducers and a computer system. It was found that high injection speed and proper gate design can minimize cooling from the mold maximize shear thinning at the gate and thus making possible uniform foaming throughout the part volume.
POLYMER-GRAPHITE AND POLYMER-CARBON NANOTUBE NANOCOMPOSITES:PROCESSING VIA SOLID-STATE SHEAR PULVERIZATION
A continuous, industrially scalable process method called solid-state shear pulverization is shown to be effective in producing well-dispersed polypropylene/ carbon nanotube and polypropylene/ as-received graphite nanocomposites that cannot be obtained by conventional melt processing alone. Major improvements in Young's modulus (> 100% increase) and yield strength (65% increase) are obtained in the nanocomposites made by SSSP, with the maximum increases being observed in samples containing the highest concentrations of nanofiller that are well-dispersed. In contrast, electrical conductivity is correlated to dispersion of carbon-based nanofiller in a different manner, with conductivity increasing with increasing nanofiller content even when an increase in nanofiller content results in less effective dispersion or exfoliation.
POLYLACTIDE COMPOSITES FILLED WITH MICROCRYSTALLINE CELLULOSE, NANOCRYSTALLINE CELLULOSE AND CELLULOSE NANOFIBERS
Polylactide (PLA) nanocomposites based on microcrystalline cellulose (MCC), nanocrystalline cellulose (NCC) and cellulose nanofibers (CNF) were prepared in the molten state by microextrusion. The dispersion was investigated by optical and electron microscopy. The mechanical properties of the nanocomposites were analyzed by dynamic mechanical analysis (DMA). The thermal properties were analyzed by differential scanning calorimetry (DSC). The effect of the addition of a proper coupling agent on dispersion and mechanical properties was analyzed.
MORPHOLOGY DEVELOPMENT IN THE PELLET DURING COMPOUNDING OF RECYCLED POLY(ETHYLENE TEREPHTHALATE) (RPET)/POLYPROPYLENE (PP) BLENDS
The morphology of RPET and PP pellets has been shown to have a profound effect on the properties of injection moldings. The size of PP dispersed phase is critical as it dictates the ductility of the blend. It has been shown that the size of a dispersed phase could grow by either coalescence or relaxation during and immediately after extrusion where temperatures are high. This study focuses on the chronological development of PP dispersed phase throughout the extrusion line during RPET/PP blending prior to pelletizing. The effect of compatibilizer content will be correlated to the growth rate of PP phase and also on the mechanical properties of subsequent injection moldings.
ASSESSING AND IMPROVING NANOMATERIALS HANDLING IN EXTRUSION
The compounding of polymer nanocomposites involves the handling, feeding and cleaning of high volumes of potentially low bulk density powders. The Nanorisk Framework document  guides practitioners in how to assess the effectiveness of operations and engineering controls designed to contain nanomaterials and minimize the risk of exposure or environmental release. This paper reviews a new approach for measuring and evaluating the effectiveness of engineering controls and operating procedures when feeding nanofiller powders into a compounding extruder. A method will be described that uses the extruder itself as an effective means to reduce dust generation from the feed system.
IN SITU PRODUCTION OF SLIGHTLY BRANCHED POLY(ETHYLENE TEREPHTHALATE) BY SOLID-STATE SHEAR PULVERIZATION: A POTENTIAL SOLUTION TO IMPROVED RECYCLABILITY AND SUSTAINABILITY
Using solid-state shear pulverization (SSSP) to process poly(ethylene terephthalate) (PET) without addition of chemical agents, we demonstrate that linear PET can be transformed into lightly branched PET, with resulting improvements in physical and mechanical properties. Rheological characterization demonstrates an increase in the melt viscosity of the pulverized PET while intrinsic viscosity characterization yields data consistent with no increase in linear chain length. These results indicate that branching occurs in situ during SSSP via mechanochemistry involving the production of polymeric radicals that result from low levels of chain scission accompanying SSSP. A hypothetical mechanism for this mechanochemical transformation is discussed. The lightly branched PET resulting from SSSP yields a dramatic increase in the crystallization rate of the PET, improving its processability. The ability to increase the melt viscosity of PET by SSSP may contribute to sustainable engineering of PET; a long-standing issue with recycling PET for high-value applications is the fact that melt processingof PET results in reduction of molecular weight and thereby melt viscosity, making the recycled material often unusable for the original application for which it was made.
PROCESS MONITORING AND CONTROL FOR MICROCELLULAR INJECTION MOLDING
The current study tests cavity pressure sensors and in-mold temperature sensors to determine their effectiveness for the process monitoring of microcellular foam injection molding. Piezoelectric pressure transducers were placed behind ejector pins. Exposed junction, microbead thermocouples were installed in the ends of ejector pins, with direct exposure to the melt. Sensors were located near the gate and near the end of fill in a two cavity production mold. Cavity pressure and melt temperature profiles, peak pressures and peak melt temperatures at each position were logged as well as the time to reach these peak values. These process data were then analyzed relative to part weights and part dimensions.
FINITE ELEMENT ANALYSIS OF HEAT STAKING DESIGN
Staking is a common joining method to assemble similar and dissimilar materials. Ultrasonic staking, hot air cold staking, heat staking, and infrared staking are common techniques used in the industry. Recently, impulse staking and laser staking are also reported. Regardless of the different staking techniques, the concept of staking is to deform a stud or hollow boss to form a button (or mushroom) to mechanically hold two materials together. The varieties of staking design guidelines developed by equipment suppliers possess significant discrepancies. This work utilized finite element (FE) modeling to study the effect of stake geometry on pull strength on a TPO material. Both 2-D axial symmetric and 3-D solid models were constructed to simulate the stake under tensile load. Geometric parameters such as button radius and button height were studied. It was found that mushroom height is the most critical parameter in achieving high retention force. Tall and large button provides highest retention force. However, tall and standard radius button provides compatible retention force and manufacturing advantages.
IMPROVE COOLING EFFECT OF INJECTION MOLDING BY PULSED-COOLING METHOD
In recent years, the variotherm molding technologies is more and more popular; and the pulsed cooling approach is one of the variotherm processing. However, the complicated cooling control system and the transient behavior of the mold made it difficult to optimize the process. In this study, through applying the comprehensive consideration with various operation specifications in simulation method, including pulsed time, coolant temperature, mold open and mold close temperatures, the cycle time can be dramatically reduced comparing to that of conventional method. In addition, experimental study will also perform to verify and realize the core issues in the near future.
COMPARISION OF FLOW STRIATIONS OF VARIOUS SSE MIXERS TO THE RECIRCULATOR AND ELONGATOR MIXERS
The Stratablend (trademark Newcastle), Energy Transfer, Variable Energy Transfer, and DM2 with Eagle mixer are well known single screw extruder (SSE) mixers. They have been diligently compared by mixing black ABS color concentrate pellets into a bright opaque ABS. This contrast reveals color striations and unmelts. The comparison is readily seen by eye. This paper compares a Recirculator screw and an Elongator screw using the same technique. Since no striations could be seen by eye, the extrudate was sectioned and examined by microscope at 100 and 200 times magnification showing no striations with the Elongator screw.
AN INVESTIGATION INTO THE MERITS OF USING NATURALLY DERIVED POLYURETHANES BASED ON CASTOR OIL AS A BARRIER MATERIAL IN SALINE AQUEOUS SOLUTIONS.
The sorption and diffusion properties of two castor oil polyurethanes based on an aromatic and an aliphatic isocyanate has been evaluated in various saline aqueous solutions whose pH varied from 4 to 10. These experiments are based on an immersion weight gain method and were conducted at 25 50 and 70 ?§C.Apparent diffusion coefficients have been calculated using Fickƒ??s equation. The results are discussed in terms of the nature of the isocyanate group and the long chain castor oil polyol structure. The changes in the diffusion and sorption experiments are evaluated using neutron activation analysis a technique that measures the amounts of the saline ions namely Na+ Ca2+ and Cl- into the polymer as a function of diffusion time.
FAILURE ANALYSIS OF HINGED HOUSING ASSEMBLIES
Failures occurred within medical housing assemblies. The cracking was observed in a significant number of parts that had been in service, and was found within the hinge bossesused on the various components of the assembly. The focus of this investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the cracked components indicated that the failures occurred through slow crack initiation via fatigue and creep rupture mechanisms. This paper will review the testing performed to characterize the failure mode and identify the cause of the cracking, while demonstrating the analytical procedures used in the investigation.
ASSESSING AND IMPROVING NANOMATERIALS HANDLING IN EXTRUSION
The compounding of polymer nanocomposites involves the handling, feeding and cleaning of high volumes of potentially low bulk density powders. The Nanorisk Framework document guides practitioners in how to assess the effectiveness of operations and engineering controls designed to contain nanomaterials and minimize the risk of exposure or environmental release. This paper reviews a new approach for measuring and evaluating the effectiveness of engineering controls and operating procedures when feeding nanofiller powders into a compounding extruder. A method will be described that uses the extruder itself as an effective means to reduce dust generation from the feed system.
IMPROVING SCRATCH PERFORMANCE OF TALC REINFORCED POLYPROPYLENE AND TPO COMPOUNDS
Rio Tinto Minerals has been actively studying scratch and mar performance of talc-reinforced polypropylene and TPO products for a number of years. A summary of major findings in these studies are provided and it is concluded that scratch performance of talc-PP and talc-TPO compounds varies with the type of resin or combination of resins used, and that using submicron talc products could improve the scratch performance. It is also shown that moderate improvement in scratch performance of softer TPO and impact copolymer PP compounds is achieved with Luzenac R7, a surface coated talc product that uses a proprietary additive. However, to maximize the scratch performance of these compounds, higher loadings of proper scratch additives are required. The performance of scratch additives is formulation dependent, and some loss of desired mechanical properties, e.g. flexural modulus, or heat distortion temperature (HDT) may be associated with using the additives especially if relatively high loadings are required. Using high performance submicron talc products along with the scratch additives allows the best combination of scratch and mechanical properties.
EXTRUSION FOAMING OF POLYSTYRENE/ACTIVATED CARBON/CARBON NANOPARTICLES USING CARBON DIOXIDE/WATER BLOWING AGENT
Extrusion foaming using supercritical carbon dioxide (CO2) is the most economic and environmentally benign process but it is difficult to control the foam density and maintain the thermal insulation performance. In this study, we added water as a co-blowing agent to better control foam density and introduced carbon nanoparticles/activated carbon (AC) to improve the thermal insulation performance of polystyrene (PS) foam. In order to understand this novel extrusion foaming process, the effects of various parameters such as particle style and content, extruder barrel and die temperatures on foam density, morphology and thermal insulation performance are investigated systematically.
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