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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Design Optimization of the Layout of the Heating/Cooling Pipes in Rapid Heat Cycle Molding of a LED TV Shell
Compared to conventional injection molding, the rapid heat cycle molding (RHCM) mold design must meet higher requirements. Taking the average temperature, the quadratic sum of the temperature deviation, the average stress, the average maximum stress, and the average life as test indexes, the orthogonal test was done. Employing the math optimizing analysis software, 1stOpt, response surface models and regression equations of different indexes were obtained by analyzing the results of the orthogonal test. The optimization model of the heating/cooling pipe layout for a LED TV shell RHCM mold was established. Finally, the optimization design of the heating/cooling pipe layout was realized by employing nonlinear programming. The heating/cooling efficiency and lifetime of the optimized RHCM mold was ensured, and the molding cycle could be done in 62 seconds.
The Ultimate Thermal Transitions and Isothermal Curing Behaviors of a Two-Part Epoxy-Amine Adhesive System: Effects of Different Mixers
Various raw mixture samples of a two-part epoxy adhesive system were prepared using different mixers, including a series of commercially-available static mixers and a dual asymmetric centrifugal mixer. The total reaction enthalpies and ultimate glass transitions of the mixtures were measured using nonisothermal differential scanning calorimetry (DSC). The isothermal cure behaviors of the mixtures at selected temperatures were kinetically monitored as the time-resolved viscoelastic material functions by means of small-amplitude oscillatory shear rheometry (SAOS) and then, the characteristic physical transformation events including gelation and vitrification were determined. Based on these DSC and SAOS studies, it has been found that the ultimate glass transition temperatures and the occurrences of physical transitions during isothermal curing for different adhesive mixture samples may exhibit strong correlations to mixing tools. Hence, to attain optimum material properties at the cured states, it is important to choose and use a proper mixer for a two-part epoxy-amine adhesive system.
Determination of Stress Concentrations in Orthotropic Composites Using Mapping Collocation Techniques
This paper demonstrates the ability to determine the individual components of stresses by processing isopharic stress (sum of the normal stresses, sometimes it is called stress invariant or the trace of the stress tensor) with a series representation of the Airy stress function in complex analysis for orthotropic materials. The present case of a loaded plate containing an elliptical hole uses simulated experimental input from exact solution. The method presented here, which is based on equilibrium and compatibility, used complex-variable formulation involving conformal mappings, analytic continuation and numerical techniques. The technique utilized complex variables and mapping, and satisfies the traction-free condition analytically at the hole. The method is applicable for both isotropic and orthotropic materials.
Environmental Stress Cracking of Medical Thermoplastics: Assessing Lifetime of High Performance Amorphous Resins in Presence of Hospital Cleaners
There is a critical need to quantify and predict the likelihood of Environmental Stress Cracking (ESC) in medical devices, due to the expanding use of medical cleaners in hospitals to prevent infection as well as increased FDA documentation requirements. This paper performs constant flexural strain ESC experiments on two high performance resins, Noryl 20%gf and Ultem 20%gf, using three common hospital cleaners (bleach, quaternary amine with isopropanol, and hydrogen peroxide). ESC testing was performed using a 7-day soak followed by tensile testing to assess residual stress-strain performance.
From strain-at-break results for this 7-day soak method, ratings were obtained for each resin-cleaner combination. These results can be fed into mechanical models of components to quantify likely failure locations and safety factors.
Using time-to-crack datasets, an initial estimate of the n exponent for the ESC dependence on stress was obtained. Also, it was found that the use of Hansen Solubility Parameters could, with reasonably accuracy, predict trends in ESC damage.
Cavity Effect on Core Penetration in Co-Injection Multi-Cavity Molding
Co-injection molding is commonly used in daily accessories, car parts, and structural-reinforcement product. However, there are too many combinations of designs, materials, core/skin ration, and process condition, how to have suitable control of co-injection is very challenge. Furthermore, co-injection with multi-cavity system is also utilized in some forks structure products. Due to the complicated nature, the inside mechanism of the multi-cavity co-injection system is still not fully understood yet. In this study, we have proposed three kinds of multi-cavity systems to investigate cavity design influence on the core material penetration behavior. In Model 1, it is a three separated cavities system. Although the flow rate can influence core penetration during early history through the runners, the separated cavity structure will restrict the core development in Cavity 1. Then it ends up with a non-uniform skin/core distribution in presence of different flow rates influence. Moreover, when it has a different thickness of connection between cavities in Model 2 (with 3.5 mm thick connector) and Model 3 (with 1.75 mm thick connector), during the early filling age (less than 90% of total volume filled), it is Branch 2 dominant in Model 3; while in Model 2 it has no preference for Branch 1 and 2. The flow rate conditions have no significant effects for core penetration in this period. However, as more melt keeps flowing into cavities till the end of filling, the core penetration behavior is dramatically different at low flow rate (say 10 cm3/s). These results show that in the presence of different thickness of connector, the penetration history and final shapes of core layer are significant different to that of separated cavity system (Model 1). Obviously, cavity design can alter the preference of core penetration from one side to the other. The results can help people for the management of skin/core distribution in co-injection molding.
Characterizing the Rheological Behavior of Liquid Silicone Rubber Using a High Pressure Capillary Rheometer
The injection molding process of liquid silicone rubber (LSR) imposes high demands on the injection molding machines and the tools due to the low viscosity of silicone rubber. There is very little data which describes the rheo-logical behavior of LSR and its influencing factors across a range of shear rates.
In this study, the rheological behaviors of different types of LSR were characterized using a high pressure capillary rheometer with an apparent shear rate that ranged from 350 to 4000 1/s. In order to identify the temperature-dependent behavior, the test temperatures were varied between 27 and 42 °C. The behavior of the material at a high pressure was evaluated by analyzing the pressure profile of each measurement.
All types of LSR displays a low level of viscosity from approx. 150 to 30 Pa s. As the shear rate and temperature rise, the viscosity of LSR decreases by at least 25 %. Ad-ditionally, we discover that the viscosity of LSR-materials with the same shore hardness differ strongly depending on which producers had made the materials. It was able to be shown that LSR displays homogenous material behavior across a wide range of shear rates.
The low viscosity of LSR makes it well-suited for applica-tions with complex structures, which require long flow paths in the injection molding process. If the viscosity sinks too low, the requirements for the tool construction increase, and, consequently, also the costs.
Using Ultrasonic Technology to Prepare Well-Dispersed Polycarbonate/Carbon Nanotubes Composites at High Flow Rate
Polycarbonate (PC)/carbon nanotubes (CNTs) composites were prepared using ultrasonic twin screw extruder at two different flow rates. During the extrusion of PC/CNTs composites, both the shearing and ultrasonic treatment helped dispersing CNTs into the polymer matrix. At low flow rate and longer residence time, CNTs can be well dispersed, but this may induce more degradation of polymer and low production throughput, which is not good for industrial production. At high flow rate, the dispersion of CNTs is worse than that in low flow rate and thus worse properties. Regarding to this problem, ultrasonic technology stands out and shows superior capability in improving the dispersion of CNTs and increase the throughput at the same time, which is especially beneficial for industrial production of polymer/nanofiller composites. The electrical, morphological, rheological and mechanical properties of the untreated and ultrasonically treated samples were investigated. The results supported the conclusion that ultrasonic technology is exceptionally efficient on improving the dispersion of CNTs and preparing welldispersed polymer composites at high flow rate.
Origin of Strain Hardening in Branched Metallocene Polyethylenes
The occurrence of strain hardening during extensional flow is known to be dependent on the molecular structure, in particular long-chain branching and molecular weight, based on studies on model polymer systems. However, commercial branched metallocene polyethylenes (BMPs) often present little or no strain hardening. The variety of molecular structures and distribution of molecular weight make it difficult to identify which species are needed for strain hardening to be observed in extension. We investigate a series of BMPs made by solution polymerization, in which the branching level vary in a systematic way, and in which only the most highly branched members of the series exhibit mild strain hardening. By use of polymerization and rheological models along with new data on the extensional flow behavior of the most highly-branched members of the set, we conclude that in spite of their very low concentration, tree-like molecules with branch-on-branch structures that provide a large number of deeply buried inner segments are essential for strain hardening in these polymers.
Using Co-Rotating Twin Screw Extruder for Fibre Reinforced Inorganics Extrusion
The extrusion of fibre reinforced inorganic cementitious materials combinations containing different fly ash contents and using a hybrid Polyether ether ketone (PEEK) and steel screws has been studied in this paper. Water flow rate was calibrated to achieve ideal viscosity for extrusion. Specific energy inputs, specific throughput rates, pressures within the die and torque measurements have been obtained during processing at constant screw speed set at 100 rpm. Apparent viscosity profiles of extrudates were measured immediately after extrusion and average wear loss was measured on both screws after the process. It has been shown that the incorporation of higher fly ash contents led to extrudates of lower apparent viscosities, which in turn yielded lower specific energy requirements, higher throughput rates and lower pressures within the die. Average diameter reductions of both PEEK and steel screws after extrusion were comparable, indicating good potential for using screws made out of PEEK when processing materials at low temperatures thus gaining notable energy savings.
Effects of Reactive Polymer as Modifier on Impact Strength and Hydrolytic Stability of PC/ABS Blend
PC/ABS blends have been widely used for specific applications such as in automotive interior & exterior parts and office automation equipment parts. In this study, effects of a reactive polymer as a modifier on the properties of PC/ABS blends were investigated. The reaction between PC and maleic anhydride group cannot be expected usually because the end hydroxyl group of PC is capped with end-capping agents such as t-butyl phenol to improve the properties of PC. However, we have found that a reactive polymer which has maleic anhydride group reacted with the end hydroxyl group of PC which was hydrolyzed with metal salts. From the results, the impact strength of PC/ABS was improved with the reactive polymer.
Ultrasonic Extrusion Technology for Recycling of Crosslinked Polyolefins
Among the many environmental problems which mankind faces in the XXI century is the problem of environmental sustainability and management of the tremendous amount of generated polymer waste. Among various polymer wastes, management of crosslinked plastics is a major environmental problem requiring a solution. This study was specifically directed toward the creation of a new, environmentally friendly and science-based technology for the recycling of crosslinked plastics. Uncrosslinked thermoplastics can be easily reprocessed and reused. However, managing crosslinked plastics is a very challenging problem. This is due to the presence of a three-dimensional network, which prevents flow and shaping of crosslinked plastics upon heating and shearing. Our laboratory developed ultrasonic decrosslinking technology for recycling of the crosslinked high density polyethylene (XHDPE) of different levels of crosslink densities and crosslinked LDPE (XLDPE). This is done by using ultrasonically aided single-screw extruder (SSE) operating at a frequency of 20 kHz and twinscrew extruder (TSE) operating at a frequency of 40 kHz at different levels of ultrasonic energy . The experimental studies on the ultrasonic decrosslinking of XHDPE and XLDPE have shown that the ultrasonic extrusion was capable to preferentially break crosslinks rather than main chains in XHDPE. Significant reduction of the extruder torque, die and barrel pressures with the ultrasonic amplitude was observed during decrosslinking of XHDPE and XLDPE. The specific ultrasonic energy decreased with the flow rate and increased with the ultrasonic amplitude, while die pressure increased with the flow rate and decreased with the ultrasonic amplitude [2-5]. Accordingly, application of ultrasonic treatment during extrusion enabled an increase of productivity.
Precision Micro Feature Moulding Using Vacuum Assisted Moulding Technique For Polymeric Microfluidic Chip Applications
In the precision moulding of polymeric microfluidic chips with designs of complicated channel structure, precision moulding of micro features with sizes down to microns and sub-micrometers are often required. In order to successfully fill these micro features on mould cavity during injection moulding, the management of cavity entrapped air is critical for minimizing the variation in melt pressure distribution during the injection phase and also avoids polymer degradation at the last filling zone. In this paper, an investigation study was conducted to evaluate the effects of vacuum assist moulding on chip flatness and the micro-feature replication accuracy of the polymeric microfluidic chips as compared to conventional injection moulding process. Process optimization with the Design of Experiment (DOE) method is used to optimize the processing conditions which defined a processing window for the vacuum assisted micro-injection moulding process. The replication accuracy of vacuum assisted moulded polymeric chips achieved less than 1% error compared to the actual insert dimension. The overall warpage was controlled within 15um, which is better than that achieved by conventional micro-moulding process.
Contribution to Warpage Analysis Using BlowView Software
Geometric tolerances are critical in the extrusion blow molding of plastic fuel tanks (PFTs) for automotive applications and therefore, part deformations due to solidification need to be controlled and optimized according to specific design criteria. Indeed, the shrinkage and warpage have been a focus for PFT manufacturers since dimensional changes can contribute to variation in the assembly of the fuel tank components as well as inconsistency with fuel indication during service. The complex design shapes of tank shells exacerbate these challenges that need to be resolved upfront in the early stages of product and tool design. Therefore, the development of an accurate simulation tool, well suited for industrial applications, able to predict thermoplastic part deformations due to solidification, has become essential for part designers to help achieve an efficient production.
The aim of this work is to show the latest advancements in predicting solidification and warpage of PFTs using NRC’s BlowView1 software. First, the importance of using the ideal geometry and an uniform mesh representing the mold cavity to perform the warpage analysis, rather than the distorted inflated parison mesh, is highlighted. Then, the capability of taking into account the in-plane part shrinkage of the cookie cavity geometry instead of the mold cavity geometry has been investigated and analyzed in depth. Finally, numerical warpage simulation results obtained using BlowView are presented based on an industrial case study. The simulation results, in terms of displacements, are also compared to the actual scanned part using the best fit technique in order to exemplify the accuracy and reliability of the proposed approach.
Automated Generation of Venting System in Plastic Injection Mold
Venting system plays an important role in injection mold, but the venting design process is very tedious especially for mold with complex parting surface. In this research, a systematic approach is adopted to finish the automated generation of venting system. Based on the geometric information of parting line, the main vent centerline is generated by a sequence of steps, including parting line offset and curve optimization. A recognition algorithm is proposed to find out the inlet vent and outlet vent centerline. A hybrid approach of extruding and thickening rather than sweeping is given to generate the vent feature. Finally, the prototype system has been developed and embedded into NX10.0.
Analysis on Mechanical Properties of Poly-lactic Acid Composites with Organic-Montmorillonite by Injection Molding
Biodegradable material enacts as an important role on reducing impacts in environment problem. This paper investigated the mechanical properties of Poly-lactic Acid (PLA) and PLA/nanocomposites by variant parameters of injection molding process. Effects on tensile strength between molecular orientation and density have been tested and discussed. The micron clay composites, organic-montmorillonite (OMMT) is used for filler materials in this study, and coupling agent, such as silane has been adopted to enhance polymer branches to catch OMMT and then improved both materials bonding. Effects on mechanical properties by different mixing ratio of pure PLA, PLA/M (PLA with OMMT) and PLA/S/M (PLA with silane and OMMT) clay composites have been prepared and the most significant factor for mechanical properties in tensile and impact strength with injection molding parameters have been obtained. The thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) have also been used to measure the thermal properties of such PLA and PLA clay composites. Results show that the tensile properties of PLA/S/M are superior to that of PLA/M and the PLA/S/M4 of 4wt% OMMT has the largest tensile strength as 84.85MPa as increases approximately 8.0% higher than that of pure PLA specimen. However, the impact strength of PLA/M is superior to that of PLA/S/M. The PLA/M4 has the best impact strength as 0.625J/cm2 as increasing 54.3% higher than that of pure PLA specimen. Results of this study can be applied to future applications of in-vivo medical assistive device or fixed scaffold products by injection molding processes.
Scale up of Abrasive Wear in Technical Compounding
A test was conducted to determine if a modified linear equation introduced in previous work has the capacity to accurately predict extruder screw wear during scale up. The equation significantly reduced the margin of error when compared to linear equations currently utilized in industry. The proposed equation was successfully utilized to extrapolate wear characteristics of a 30 mm tri-kneader from data collected in a 60 mm tri-kneader. The error obtained was found to be less than 45% for this set of tests.
An accelerated wear test proposed on preliminary work was utilized to conduct the experiment in an acceptable timetable. An item of concern was the repeatability of the test in smaller size extruders. The test proved reliable and repeatable. Further development is still necessary to relate the data from the accelerated wear test to that from industrial extruders.
Control of Rheological Resposes under Elongational Flow for Polyolefin Melts
Rheological responses under elongational flow play a crucial role in processability of a molten polymer at various processing operations. Therefore, the elongational viscosity has been evaluated. In industry, instead of elongational viscosity, the drawdown force, defined as the force required to stretch a molten polymer, is often evaluated, which is sometimes called melt tension or melt strength. In general, the drawdown force measurement is performed at non-isothermal condition, as similar to actual processing operations. Therefore, crystallization and/or glassification processes affect the value. Here, we proposed several methods to enhance the drawdown force for polyolefins with linear structure, such as isotactic polypropylene (PP) and high-density polyethylene (HDPE), considering the crystallization behavior. The results indicated that the drawdown force increases with the die length in the wide range of draw ratios and shear rates at die. Furthermore, this phenomenon was pronounced for a melt having long relaxation time at low extrusion temperature. The mechanism of the drawdown force enhancement was found to be attributed to rapid crystallization owing to the reduction in the density of entanglement couplings after passing through a long die. In fact, marked molecular orientation was confirmed by 2D-XRD measurements. Furthermore, the drawdown force of PP was enhanced by the addition of a nucleating agent. Blending with other polymeric materials such as high-density polyethylene (HDPE) and poly(methyl methacrylate) (PMMA) having low viscosity is also effective to enhance the drawdown force.
Process-Integrated Printing Technology for Plastic Parts during Injection Molding
In-Mold technologies, such as In-Mold Labeling or In-Mold Decoration, have been used for several years for the process integrated decoration of plastic surfaces. The additional handling and transport processes cause consi-derable costs and are a big disadvantage. The new in-mold printing, a process integrated printing technology offers an alternative and enables the decoration of plastic parts during injection molding. Here, the image is pad printed onto the surface of the mold and then transferred to the surface of the plastic part during injection molding. The feasibility of this method is demonstrated on PP and a process related phenomena of the ink transfer and the ink adhesion are identified. The mold temperature is conside-red to be particularly critical. This is due to the fact that the temperature of the ink is affected by the mold tempe-rature and liquid ink is necessary for a transfer of the ink to the polymer surface. In this study the thermal situation at the ink-plastic interface as well as the microscopic structure of the ink-plastic-interface are investigated. The goal of this paper is to show the influence of process para-meters and conditions and their influence on the ink adhe-sion of printed motives.
Environmental Stress Cracking Study of Alternative Welding Processes in Apparatus, Tank and Pipeline Construction
The infrared (IR) and vibration (VIB) welding processes are joining technologies established in series fabrication. They are characterized by their economically viable and efficient process management. These joining technologies are suitable for utilization in apparatus, tank and pipeline construction. However, they cannot be applied to this field. One reason for this is the lack of knowledge and proof in relation to the Environmental Stress Cracking (ESC). Within the framework of a research project promoted by AiF (Allianz industrieller Forschung), the vibration and infrared welding processes were investigated. Their potential for long-term applications was studied. The results show that minimum tensile creep welding factors of 0.8 are achieved by using the infrared (short-wave radiation emitter) and vibration welding processes. It was possible to obtain values which correspond to those of heated tool butt welding. Furthermore, the knowledge base of the mechanism of failure behavior of welded joints between plastics undergoing ESC was extended.
Effects of Clay Loading and Gascounter-Pressure on the Tensile/Foaming/Surface Roughness Properties of Microcellular Injection Molded PP/Claynano Composites
This study investigated the effects of the clay loading and gas counter-pressure technique (GCP) on the tensile/foaming/surface roughness properties of microcellular injection molded Polypropylene (PP)/clay nanocomposites. In the gas counter-pressure technique, nitrogen fills up the cavity during the injection molding process. This can delay the foaming process and affect the microcellular injection molding process. The results showed that the tensile strength decreases with the counter pressure and increases as holding time is increased, while the flow length decreases as the holding time increases. The cell size decreases as the holding time increases.
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