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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Experimental Evaluation of Methods for Characterization of Power Output of High Power Ultrasonic Transducers
This paper reviews the evaluation of different techniques used to characterize the power output of high power ultrasonic transducers. Three laboratory measurement techniques were studied: 1) electrical, 2) calorimetric and 3) mechanical transmission line. The loads were theoretically modeled and their thermal, mechanical, and electrical losses were identified. It was found that the most accurate power measurement was based on multiplication of the measured voltage and current without the use of filters or methods that attempt to differentiate between stored and dissipated energy.
Experimental Studies in Gas-Assist Injection Molding to Investigate Residual Wall Thickness and Gloss Levels
Gas-assist injection molding allows designers the freedom to design plastic products that may be considered outside the realm of conventional injection molding. There are basically two design categories for the gas-assist injection molding technique: rod-shaped parts and panel-shaped parts. Rod-shaped parts have very thick cross-sections and include articles such as handles, armrests and structural components. Panel-shaped parts are large area moldings that utilize ribs with gas channels to improve part stiffness; automotive trim and business machine housings are in this category. This paper studies the residual wall thickness (RWT) of rod-shaped parts and gloss level variations of panel-shaped parts.
An Experimental Study of Antioxidants Effects on the Performance of Blow Molded HDPE Homopolymer Packagaing Containers
This research seeks to address the taste and odor problems that are currently being experienced in blow molded HDPE homopolymer packaging containers. Manufacturers of blow molded packaging containers have been experiencing odor and taste problems in their HDPE homopolymer products with antioxidant additives, especially in the water bottles. The scope of this research will be to determine the optimum idling time and antioxidant levels that will alleviate the taste and odor problems in water bottles. Odor and taste surveys as well as oxidative induction time tests will be used to characterize the performance of the tested blow molded products.
Experimental Study of Gas Penetration in the Gas-Assisted Injection Molding
Extensive studies were conducted to experimentally determine the effects of processing parameters on the gas penetration of the gas-assisted injection molding (GAIM) process. Experiments were performed in the mold having a standard tensile bar cavity with simultaneous measurements of the screw position, gas pressure, and pressures in the runner and cavity. Two Taguchi methods were applied in the study. The first method was used to determine the most important GAIM processing parameters affecting the gas penetration. In this case, various processing parameters, such as: shot size, gas delay and holding time, gas pressure, injection pressure, injection speed, mold and melt temperature were studied. The second method was used to elucidate a more detailed effect of the parameters on the gas penetration.
Experimental Study of LDPE Melting in a Twin Screw Extruder Using On-Line Visualization and Axial Pressure and Temperature Measurements
The melting of polymers in a twin-screw (T/S) extruder is an important operation in many industrial processes. Re-cent research by Shih, Gogos, Geng and others has identified the physical phenomena that take place during the phase transition. This paper describes an experimental study of Low Density Polyethylene (LDPE) melting in a co-rotating, intermeshing T/S extruder using on-line visualization and axial scanning of pressure and temperature techniques. The LDPE melting sequence observed included solid transport in a partially filled screw channel with conductive heating, compaction, pellet deformation, and viscous energy dissipation in the melt with un-melted solids. The effects of throughput (Q) and screw rotational speed (N) are examined. Low and high Q/N ratios have significantly different axial pressure profiles.
Experimental Study of Prepreg Bonded Single-Lap Composite Joint
Neat resin bonded single-lap composite joint has been extensively used in composite structures. Lower strength and longer fabrication time have been identified as technical barriers in practice. In order to increase the joint strength and reduce the fabrication time, two types of prepreg composites were used to bond composite single-lap joints. Test specimens were prepared per ASTM D 3165-95 standard. Accelerated conditioning was conducted to investigate the environmental resistance of specimens. The shear strength of various specimens was obtained using tension tests. Compared to control specimens, prepreg bonded samples exhibit higher tensile strength, higher environmental resistance, and shorter fabrication time.
Experiments and Simulations with Barrier Screws
Experiments were performed using four different industrial sized extruder barrier screws extruding two different polyethylene resins, 0.3 MI LDPE and 1.0 MI LLDPE, at two motor speeds. The data collected from these experiments consist of readings of pressure along the axis of the screw, exiting pressure, melt temperature, and output. The extruder motor load, screw speed and barrel temperature settings were also recorded. Experimental measurements are compared to computer simulation results from a flexible extrusion simulation approach which uses relatively simple models for pumping, heat transfer, and melting functions. The calculations are coupled through an iterative process, and are based on a number of assumptions. Reasonable agreement is found between experimental and predicted melt pressures.
Extensional and Shear Rheology of Reactively Extruded Polyethylenes
In this study, the rheological characterization in extension and in shear of melts of reactively extruded low-density and linear low-density polyethylenes was carried out. The polyethylenes were extruded with peroxide, in one case, and with peroxide and diethylmaleate, in the other, using a co-rotating twin-screw extruder. A capillary rheometer with cylindrical and converging dies was employed to obtain the shear and extensional viscosities at 200 °C. The Cogswell, Binding and Mackay-Astarita models were used to estimate the extensional viscosity of the materials. An increase in both the shear and extensional viscosities was obtained due to the presence of long branches produced by the modification processes.
Extensional Rheology of Polypropylene and its Effect on Foaming of Thermoplastic Elastomers
Extensional viscosity of several polypropylene polymers and their blends was measured and compared to the relative foamability of thermoplastic elastomers (TPEs) containing these polymers. Both linear isotactic polypropylenes and branched polypropylenes were considered for this work. The extensional viscosity is measured using an RME Extensional Rheometer at various strain rates. The TPE foam is characterized based on density and cell size distribution. A small amount of branched polymer substituted for linear polymer was found to lead to improved foamability of the TPE. Results of this study will aid in the understanding of the foaming process in TPEs.
Extruder Output-Pressure Relationships for Power Law Fluids Including Leakage Flow
In order to predict output for screw extruders it is useful to have relationships of output versus pressure for various degrees of shear thinning. These relationships can be determined using numerical techniques and are usually graphically presented in dimensionless form. Various workers have presented such dimensionless graphs.It is well know that leakage flow, the flow between the flight tip and barrel, can significantly affect output and power consumption. A finite difference program was developed that accurately calculates the effect of leakage flow on output and power consumption. When the flight clearance is made dimensionless with respect to the flight height the family of output-pressure- clearance curves can be used for extruders of any diameter; in fact, creating universal output-pressure- clearance curves. This paper will present data of two different size extruders on output vs. pressure and energy efficiency vs. pressure. The utility of the information presented will be demonstrated with actual examples.
Extrusion Blow Mold Simulation Software Verification of Pinch-Off Design Parameters
The design of the pinch-off in extrusion blow mold ing has relied on past experience, company recommendation guidelines, and material supplier guidelines. This experiment was implemented to determine if simulation software could be used effectively to design a functional pinch-off design before any steel is cut. Actual bottle measurements from a Design of Experiment (DOE) (1) were contrasted to the results of the simulation software to determine the accuracy of the simulation. The actual DOE that the software was compared to is a three level DOE. The DOE was used to determine the processing parameters and flash pocket depth that produces the strongest weld line strength. The specimens collected from the DOE were tested for tensile strength and impact strength.
Failure Analysis and Redesign of a Polycarbonate Spring
An integrated approach is advocated for failure prevention of plastic products by optimising: material selection, design, processing and mould construction. The redesign of a plastic spring for a positioning device, using a buckled strip, illustrates this approach.The initial design suffered from mistakes:A low molecular PC was selected for obtaining short cycle times.The transverse deflection of the spring was too high.The mould was not tapered and caused scratches on the surface.Unlocking the positioning device caused very high bending stresses.By combining mechanical engineering, polymer engineering and practical knowledge about mould design and injection moulding, a reliable spring was redesigned.
Failure Analysis of a Large Diameter Floating Marine Hose
Floating marine hoses are often used to transport oil products from tankers to offshore moorings and, as such, their structural integrity is of major importance. Marine hoses are typically composites of various rubber compounds, textile fibers and steel reinforcement, the interaction of which is quite complex, rendering analysis of the structure difficult. In this paper, we present a detailed forensic examination of a failed marine hose, including such techniques as rubber fractography, finite element analysis, mechanical testing, and chemical testing. The various test results are assimilated to deduce the actual cause of failure, which is shown to be fatigue induced from external change.
Failure Analysis of Automotive Assemblies - Part I
Failures occurred within assemblies used in a transportation application. The cracking was observed in a relatively high number of parts immediately after cyclic thermal shock testing of the components. The cracking was found at several locations within the overmolded resin in areas immediately adjacent to underlying metal components. The focus of this investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the failed components indicated that the cracking was the direct result of severe molecular degradation which occurred during the resin drying and molding operations, in conjunction with stresses induced through thermal shock testing of the parts. This paper will review some of the testing performed to characterize the failure mode and identify the cause of the cracking, while demonstrating the analytical procedure used in a failure investigation.
Failure Analysis of Automotive Assemblies - Part II
Failures occurred within assemblies used in a transportation application. The cracking was observed in a relatively high number of parts immediately after cyclic thermal shock testing of the components. The cracking was found at several locations within the overmolded resin in areas immediately adjacent to underlying metal components. The focus of the investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the field samples indicated that the cracking was the direct result of molecular degradation that occurred during resin drying and molding operations, in conjunction with stresses induced through thermal shock testing of the parts. This part of the paper reviews the various methods that were used to evaluate viscosity changes in the material during drying and molding. This study illustrates the various strengths and weaknesses of the methods available to determine the molecular weight of a polymer.
Failure Behavior of Fiber-Reinforced Toughened Polymers
In fiber-reinforced toughened polymers, the influence of matrix deformation needs to be properly considered in their failure processes. There is a transition from failure dominated by massive matrix plasticity to that dominated by fiber-related mechanisms as the fiber content increases. This paper addresses some experimental observations and physical rationalization of the complex events that lead to failure of short fiber reinforced toughened nylon 6,6. The toughening behavior was studied using fracture mechanics techniques. The essential work of fracture analysis shows that the inclusions of short glass fibers not only provided a stiffening effect but also a toughening influence.
Failure of TPE Washers in Central Heating Systems
Widespread failure of TPE washers in central heating systems led to a large claim against the manufacturers and suppliers. Initial blame had been placed on plumbers who fitted the washers, either for under - or over-tightening the joints to the radiators. The material had been chosen for its ease of manufacture by injection moulding and replaced fibre washers. Inspection of failed washers showed numerous radial brittle cracks suggesting a different explanation for the failures. Trial experiments with new washers exposed to water at 85°C for three weeks stiffened, with 90% permanent set, the polyester elastomer changing dramatically in properties at short exposure times. The washers could not seal the system and extensive leakage occurred.
Failures Due to Stress Concentrations
The majority of plastic products fail due to stress concentrations. This is often due to insufficient radii of curvature, but also due to manufacturing and the condition of moulds.The stress concentration factor (SCF) can easily be determined from Peterson's book of SCF and they give about the same values as linear Finite Element Method calculations.For plastic products the values of the SCF is not sufficient to predict failure. The temperature and the strain rate are very important. The manufacturing method of the stress concentration by mechanical machining or by injection moulding gives significant differences in failure behaviour.In fatigue the stress concentration will determine the crack initiation and because of that stress concentrations are more dangerous in fatigue then in static loading.
Fatigue - Temperature Resistance of Continuous Glass Fiber/Polypropylene Composites
The flexural fatigue resistance of a continuous fiber composite (CFC) of glass and polypropylene (PP) under a fabric form has been investigated. Stress-life curves at a temperature of -40°C, 23°C and 50°C were obtained. These S-N curves show that the very high fatigue resistance of the PP/CFC composite at 23°C, in terms of normalized maximum flexural stress in fatigue (with respect to the flexural strength), remains relatively high at a testing temperature of 50°C. These curves also show that the fatigue resistance is actually improved at -40°C, i.e. at a temperature below than the glass transition temperature of the PP matrix. Comparison with a thermoset composite of similar flexural strength indicates that the intrinsic toughness and ductility of the thermoplastic PP matrix provides improved fatigue resistance, especially below the glass transition temperature.
Fatigue and Creep Crack Propagation Kinetics in PVC Pipe Material
The kinetics and mechanisms of creep and fatigue crack growth in PVC pipe material were studied in order to develop a methodology for prediction of creep fracture. In this study, fatigue crack propagation was resolved into fatigue and creep components. The creep component became more prominent with increasing temperature or decreasing loading rate. By studying the dependence of fatigue crack growth rate on loading rate and temperature, the contributions of fatigue and creep components to the overall crack growth rate were determined. The creep crack growth rate of PVC was predicted at ambient temperature by taking the ratio of the fatigue and creep contributions.
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