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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EFFECT OF FILLERS SHAPE FACTOR ON THE PERFORMANCE OF THERMALLY CONDUCTIVE POLYMER COMPOSITES
As electronic devices tend to slimmer and more integrated, management of heat transfer in devices become a big task for device design. Metallic materials are widely used for heat dissipation materials, but, there re many attempts to replace the metallic materials with highly thermal conductive thermoplastic composites due to their lightweight and economic manufacturing cost. Intrinsically polymers are thermally and electrically insulator, but they can turn into thermally conductive material by compounding with thermally conductive fillers such as graphite, ceramic filler, carbon black, carbon fiber, or carbon nanotube (CNT). In this research, strong correlation of shape of graphite on thermal conductivity was investigated in polymer/graphite composites.
THE MICROSTRUCTURE OF MICRO-INJECTION MOLDED HIGH DENSITY POLYETHYLENE
Micro-injection moldings were obtained for high density polyethylene (HDPE), to study the effects of processing conditions on the microstructural characteristics and mechanical properties of the moldings. Various microstructural features, such as skin-core structure, skin layer thickness fraction, and distribution of crystalline shape and size, were observed under different processing conditions and analyzed and compared to observations made with poly(oxymethylene) (POM). Process-structure-Youngƒ??s modulus relationships were analyzed by considering the effects of skin layer thickness, average plunger velocity. Suggestions for mold design were proposed on the basis of polymer melt flow behaviour.
HIGH FLOW PP/EPR BLENDS FOR THE AUTOMOTIVE INDUSTRY: BASIC CORRELATIONS BETWEEN EPR COMPOSITIONAND APPLICATION PROPERTIES
Injection molded automotive parts usually feature high flow length to wall thickness ratios. In order to ensure low cycle times, tooling costs and scrap rates, the respective material formulations should have a high flowability. Reducing the viscosity, however, also affects the materials' morphology and mechanical properties, especially the impact strength. To quantify this effect high impact reactor-thermoplastic polyolefins (rTPOs) consisting of polypropylene (PP) blended with in-reactor made ethylene-propylene rubber (EPR) were prepared and tested. Particular attention was paid to the influence of the ethylene-propylene rubber's composition, i.e. comonomer ratio and molecular weight, on application properties of such rTPOs like toughness, surface gloss and scratch resistance.
PT CONTROL METHOD BY CAVITY TEMPERATURE FOR INJECTION MOLDING
It would be of great value to develop dependable strategies for the control of part weight. Based on the Pƒ??Vƒ??T (pressureƒ??volumeƒ??temperature) behavior of the polymer, a Pƒ??T (pressureƒ??temperature) control method by cavity temperature was presented in this study. In the present control method, the total injection time is controlled by cavity temperature instead of time, the relationship between pressure and temperature can be controlled. The experimental results revealed that the Pƒ??T control method by cavity temperature yields a much better part quality and uniform part weight than conventional control method.
LIFETIME PREDICTION OF POLYETHYLENE PIPES BASED ON AN ACCELERATED EXTRAPOLATION CONCEPT FOR CREEP CRACK GROWTH WITH FATIGUE TESTS ON CRACKED ROUND BAR SPECIMENS
Fracture mechanics lifetime and safety assessment of pressurized polyethylene (PE) pipes is based on the knowledge of material specific creep crack growth (CCG). However, with common test methods the investigation of this failure mechanism is not possible in modern PE-pipe materials in a feasible time. For an accelerated generation of CCG an extrapolation concept based on fatigue tests with cracked round bar (CRB) specimens was developed. In the present work this concept was applied to a common PE-pipe material to generate the material specific CCG data within a few weeks. To evaluate these data a fracture mechanics lifetime prediction of the CRB test was compared to results from static tests. With the integration of the data into a lifetime prediction model for pressurized pipes a simulation of a real pipe was possible.
HEATING AND PLASTICIZING THERMOPLASTICS WITH ULTRASOUND FOR MICRO INJECTION MOLDING
Ultrasonic plasticizing allows the melting of very small amounts of polymers for micro injection molding. The ability to plasticize polymers with ultrasound arises from the effect that they heat up under cyclic deformation due to inner and outer frictional losses. This paper presents investigations on the course of heating during plasticization. The heating rate as well as the corresponding process data of the ultrasonic equipment is analyzed in dependence on the parameter settings. Example micro parts being molded show the possibility to use ultrasonic plasticizing as a production technology.
EFFECT OF CARBON NANO FIBERS ON THE PERMEABILITY OF FIBER REINFORCED POLYMERIC NANOCOMPOSITES
One of the most attractive environmentally friendly energy generation methods is wind power. In order for this technology to compete favorably with the cost of traditional energy generation methods, the wingspan needs to be greatly increased from current dimensions. For this to occur, we need to take advantage of new material developments such as nano-composites.In order to manufacture such large parts, we need to understand factors affecting flow. In the case of flow through porous media, the material properties are permeability and viscosity. In this work we present preliminary results on the effect of carbon nano fibers on permeability.
SIMULATING THE DEFORMATION BEHAVIOR OF THERMOPLASTIC PARTS UNDER THERMAL AND MECHANICAL LOADS
During service, thermoplastic parts are often subject to a combination of thermal and mechanical loads. Especially the temperature has a great influence on the stiffness and the specific volume. Consequently the thermal exposure has to be considered during the design process of thermoplastic parts. This paper describes the modeling of the temperature-dependent viscoelastic material behavior. Because the determination of the required thermal and mechanical properties is cost- and time-intensive, a procedure is elaborated to depict the temperature-dependent long-term behavior on basis of short-time tensile tests. Finally the model is evaluated in a comparison with experimental results.
PREDICTING THE CYCLE TIME IN INJECTION MOLDING AS A FUNCTION OF THE FROZEN LAYER THICKNESS
In the current economic market, production efficiency is critical if manufacturers are to remain competitive. The largest part of the cycle in injection molding is the cooling time. Thus for injection molders, to be successful, it is extremely important that they minimize this part of the process without adversely affecting part quality. Predicting the minimum safe cycle time in injection molding is complicated by the cyclic nature of the process. The mold thermal state changes with continuous molding until a quasi steady state is achieved.In this work, we evaluate the minimum frozen layer thickness required before the part can be demolded and how the growth of this frozen layer is affected as the mold thermal state changes with continuous molding cycles. Experiments are used to relate the minimum frozen layer thickness to dimensional stability and to select an ejection criterion in order to obtain a minimum safe cooling time
A STUDY ON MATERIAL DISTRIBUTION AND MECHANICAL PROPERTIES IN CO-INJECTION MOLDING
In the co-injection molding process, sometimesreferred to as sandwich molding, two different polymermelts are either simultaneously or sequentially injectedinto a mold to form a part with a skin/core structure. Coinjectionmolding offers the flexibility of using the bestproperties of each material to reduce material cost andpart weight. Particularly, it allows, the use of recycledmaterial in the core without an adverse effect on surfacequality. The properties of a co-injection molded productdepend on the individual properties of the skin and corelayers, and the skin/core volume ratio. This paper presentsa study of the effect of molding parameters on materialdistribution and mechanical properties of co-injectionmolded plates. Two virgin materials were triedpolypropylene (PP), and thermoplastic polyolefin (TPO)as well as grinded TPO from plastic bumpers.
MODELLING THE STRUCTURAL PERFORMANCE OF STRETCH-BLOW MOULDED PET BOTTLES
The mechanical properties of PET bottles are significantly affected by the process. In order to precisely model the structural performance of these bottles, the wall thickness and the process dependent material properties have to be considered. This paper describes an approach to combine the structural analysis and the process simulation. The wall thickness distribution and the local stretch ratios of the blown bottle are calculated by a process simulation and are then transferred to the structural analysis. Thereby, the stretch ratios are correlated with stretch ratio dependent material properties. In cooperation with Nestl?? Waters M.T., Vittel, France, the approach is applied on an empty and filled 0.5 litre PET bottle. The investigations point out that the accuracy of the structural analysis is significantly improved by applying the integrative approach.
NUMERICAL SIMULATION OF THE FAILURE BEHAVIOR OF PE PRESSURE PIPES WITH ADDITIONAL LOADS
Using linear elastic fracture mechanics concepts a simulation methodology for the assessment of internally pressurized pipe lifetimes was developed. The concept is based on the numerical calculation of stress intensity factors for pipes under different loading conditions and on using experimentally generated creep crack growth kinetics for lifetime calculations. Comparison of simulated lifetimes with experimental data from tests with internally pressurized pipes proved the principal applicability of the concept but also identified major parameters affecting pipe lifetime.
NUMERICAL SIMULATION OF THE FAILURE BEHAVIOR OF PE PRESSURE PIPES WITH ADDITIONAL LOADS
Using linear elastic fracture mechanics concepts a simulation methodology for the assessment of internally pressurized pipe lifetimes was developed. The concept is based on the numerical calculation of stress intensity factors for pipes under different loading conditions and on using experimentally generated creep crack growth kinetics for lifetime calculations. Comparison of simulated lifetimes with experimental data from tests with internally pressurized pipes proved the principal applicability of the concept, but also identified major parameters affecting pipe lifetime.
DEVELOPMENT OF A PERMANENT PLASMA-INDUCED RELEASE COATING AS A SURROGATE FOR NON-PERMANENT RELEASE AGENTS
In the production of polyurethane parts the use of nonpermanent release agents is still inevitable. The regular mold-cleaning of residua of the release agent reduces the efficiency of the production process considerably. This paper describes the development of a permanent plasma-induced release coating with high durability for the series production of PU-parts as a surrogate for conventional non-permanent release agents. Basis of the project is a plasma-polymeric gradient layer with highly crosslinked siloxane-compounds for the mechanical strength of the coating and a high density of methyl groups towards the PU-sided surface for excellent release properties.
VALIDATION OF AN ACCELERATED FRACTURE MECHANICS EXTRAPOLATION TOOL FOR LIFETIME PREDICTION OF PE PRESSURE PIPES
For a fracture mechanics lifetime assessment of pressurized polyethylene (PE) pipes the knowledge of the material specific creep crack growth (CCG) kinetics is essential. As testing of CCG with common test methods is not possible in feasible times, an accelerated extrapolation procedure based on fatigue tests with cracked round bar (CRB) specimens was developed previously. Within the present work this test procedure was used to characterize CCG of a PE material at elevated temperatures of 60?øC. In combination with a numerical simulation model for pressurized pipes, lifetimes were predicted and correlated to real pipe failure times of the same material.
SAVING MONEY USING INTELLIGENT PROCESS OPTIMIZATION SOFTWARE
Looking at the increasing quality requirements and the potential for time and cost savings in almost all injection molding processes the classical way of optimizing a process has to be reviewed. New and innovative software solutions for process optimization and quality forecasting therefore plays an important role and helps to answer common questions to the shop floor managers: Is the current machine setting the best one in terms of cycle time and process capability? Is there a potential to save time material or energy? Which machine parameters have the highest influence on the quality? A new software solution using self generating neuronal networks now respond to these questions and supports users without requiring a deep mathematical background. It offers a pragmatic solution to be used by all participants on the shop floor level. Practical experience confirmed that on average 10% reduction in cycle time can be achieved.
SAVING MONEY USING INTELLIGENT PROCESS OPTIMIZATION SOFTWARE
Looking at the increasing quality requirements and the potential for time and cost savings in almost all injection molding processes the classical way of optimizing a process has to be reviewed. New and innovative software solutions for process optimization and quality forecasting therefore plays an important role and helps to answer common questions to the shop floor managers: Is the current machine setting the best one in terms of cycle time and process capability? Is there a potential to save time, material or energy? Which machine parameters have the highest influence on the quality? A new software solution using self generating neuronal networks now respond to these questions and supports users without requiring a deep mathematical background. It offers a pragmatic solution to be used by all participants on the shop floor level. Practical experience confirmed that on average 10% reduction in cycle time can be achieved.
STRUCTURAL ANALYSIS OF SEMI-CRYSTALLINE THERMOPLASTICS WITH REGARD TO THE LOCALLY DISTRIBUTED MATERIAL BEHAVIOR DUE TO VARYING INNER PROPERTIES
During its manufacturing cycle a thermoplastic injection-molded part can be exposed to heat at various times. This has an influence on the inner and therefore on the mechanical properties of the part. Regarding these effects an integrative simulation approach has been developed at the Institute of Plastics Processing at RWTH Aachen University. It includes the development of a user-defined non-linear material model which takes into account the local distribution of the inner properties depending on the processing conditions and heat treatment. This paper deals with the main aspects of the material model and with the linking of the process simulation and the structural analysis using a universal data format.
INVESTIGATIONS ON THE INTERACTION OF THERMOPLASTIC SURFACES AND PLASMA PROCESSES
Plasma processes constantly gain importance in the field of plastics processing. They are influenced by production parameters on one hand and the substrate itself on the other hand. The properties of polymers vary substantially depending on their processing conditions or their history. This paper describes investigations on the plasma modification of polyamide (PA6) and polypropylene (PP). This includes the examination of the influence of absorbed water in the surface near regions of the bulk material as well as the interaction with the polymeric microstructure. The knowledge of this interaction between plasma and thermoplastic surface can be used for the process development or quality assurance in terms of plasma-assisted modification of polymers.
PERFORMANCE OF A HELIBAR® EXTRUDER USING A GROOVED BARREL
A new type of single-screw extruder with grooved barrel in the feeding and the melting section called “HELIBAR®” was successfully introduced in recent years. The grooved feeding section is typically cooled passively by ambient air. The performance of a 35 mm D. 34 L/D HELIBAR was evaluated by running PP PC and ABS in pellet form HMW-HDPE in powder form and HDPE as a blend of pellet and regrind. One barrier-type single-stage screw was used for all resins. The output rates of this extruder were 3-4 times higher than those expected for the same size extruder with smooth barrel while the specific output rates (output rate per RPM) were more than twice and virtually independent of screw speed or head pressure. Furthermore this extruder had excellent stability of the output rate and the melt temperature.
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