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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New Uses for Electroless Nickel in Mold Building and Design
This paper describes electroless nickel and the scope for its many applications in mold making, maintenance and repair. While most mold builders are familiar with nickel solution for rust prevention in cooling water lines, many have remained unaware of the different formulations of electroless nickel plate and its capabilities as an engineering or functional coating applied by techniques firmly established in the electronics, fire-arms, automotive and other industries. Case histories of in-mold performance illustrate correct usage, proving that electroless nickel can offer properties equivalent to hard chrome plate, yet without the problems of thickness variation, anode deployment or the ever-rising environmental penalties and costs associated with chrome plating.
Designing with L-" and "U-" Shaped Snap Fits"
Snap-fit designs for assembly of thermoplastic-based products provide many benefits. However, when the strain caused by the deflection of a typical cantilever snap fit cannot be designed below the allowable strain of the intended material, conventional designs must give way to alternative snap-fit designs. In these cases, a U-" or "L-" shaped snap usually reduces the strain to an acceptable level without sacrificing the cost and performance benefits of the typical cantilever snap fit. These alternative designs can accommodate very large deflections without inducing high strains at the base of the snap-fit finger. Formulae for both the "L" and the "U" have been derived to allow for maximum deflection for a given geometry. Detailed examples of the application of these formulae which were confirmed using finite-element analysis are given in this paper."
Experimental Investigation of Fracture Toughness in Injection Molded Long Fiber Reinforced Thermoplastics
The variations of fracture toughness Kc in injection molded 50% E-glass long fiber reinforced polypropylene are investigated. Plaques at different sets of processing conditions have been produced and specimens have been obtained at preselected spatial locations, both in the in-flow and cross-flow directions. The effect of part morphology, which consists of through-thickness layers, was evaluated experimentally by measuring the fracture toughness at locations where a crack initiation is produced prior to the measurement. The results show a strong effect of processing conditions and spatial locations on the fracture toughness as a result of variations in the through-thickness layered structure.
The Effect of Ionic Strength Variation on Patterned Self-Assembled Monolayers Using Infrared Reflection Absorption Spectroscopy
The morphological properties of polymeric thin films deposited on self-assembled monolayers are closely related to the orientation of the macromolecular chains on the surface. In one such system where ionic polymers are involved, the orientation is highly influenced by the presence of an electrolyte and it depends in particular on the ionic content of the initial solutions. In the study presented here, infrared reflection absorption spectroscopy was used to elucidate the effect of salt concentration variation on the orientation of polymeric thin films of alternating bilayers of sulfonated polystyrene and poly (diallyl-dimethyl-ammonium chloride) (SPS/PDAC).
Viscoelastic Behavior of HDPE under Tensile Loading
The time dependent mechanical behaviour of high density polyethylene has been examined. Creep experiments with an endurance of eight weeks were performed. The creep strain can be described properly by the Leaderman model using engineering stresses and strains if the strain remains below approximately 2% strain. By expressing the Leaderman model in terms of true stress and true strain it is possible to improve the accuracy at higher strain levels. A good fit of the creep data up to approximately 5% strain can then be obtained. At strains above this value of 5% the creep strain gets an upward curvature, indicating the beginning of the secondary creep stage with plastic flow dominant. This can not be described yet. Results from tensile straining experiments show good agreement with the model predictions. Therefore the Leaderman model is capable of giving good predictions for the mechanical response of this HDPE for creep as well as for tensile straining conditions.
Time-Dependent Strain Distribution in Polymers under Complex Stress History: Experimental Study by Moire Fringe Method and Finite Element Predictions
A combination of experimental and computational methods are developed, for predictions of nonlinear viscoelastic creep of polymers in sheet form, subjected to inhomogeneous stress states and stress history. A recently proposed multiaxial constitutive model for glassy polymers was implemented in a commercial finite element (FE) package. The model was tested by means of creep experiments on PMMA at elevated temperature, using specimens with a central circular hole. The experiments were performed using a tensile creep machine, and the geometric Moire fringe method was employed for measuring strain distribution. The results obtained from the experiment and FE analysis were compared.
Integrated Simulations of Gas Injection Molding Process and Part Structural Performance under a Unified CAE Model
Integrated simulations of gas injection molding process and part structural performance under a unified CAE model were carried out. An analysis algorithm based on DKT/VRT elements superimposed with beam elements representing gas channels of various section geometry was first developed to evaluate the structural reinforcement of gas channel in the design stage. During melt/gas filling process, a mixed control-volume/finite-element/finite-difference method combined with dual-filling-parameter technique was implemented to trace the advancements of melt and gas fronts. For the prediction of secondary gas penetration, flow model of isotropic-shrinkage origin was introduced. Mold cooling analysis was executed utilizing cycle-averaged boundary element method considering the cooling system. Both cooling channel and the hollowed core gas channel were modeled using line-source approach. Thermal residual stresses calculated from part temperature distribution were then combined with the structural analysis to predict part warpage. The monitor support was used as the case study. The analysis accuracy from this unified model of 2 1/2-D characteristics were examined experimentally. The only difference between process simulation and structure/warpage analyses is that different values of equivalent diameters assigned to a circular pipe representing gas channel should be used, respectively.
Waxs Modeling of the Liquid State of Polyethylenes: Implications for Phase Analysis, Glass Transition, and the WLF Constants in Thermoplastic Elastomers
Waxs studies of melts of branched copolymers with varying comonomer content revealed a temperature and branch dependence of the low angle amorphous halo (LAH). Numerous studies in real space suggested a semi-quantitative method for the deconvolution of the LAH. Two linear relations for the temperature dependence (low/high branch content) were observed. The WLF constant, C2, is derived from the slopes and the Tg° from the convergence temperature. The quantity fo of C2 is ca. 4.1x10-4/K. Proper representation of the liquid state scatter (and its temperature dependence) are crucial in quantitative phase analysis, including: interfacial content, latent heat, and crystal microstructure with increasing chain defects.
Elastomeric Polypropylenes from Unbridged Metallocenes
The present work describes properties of a series of experimental polypropylene polymers prepared with unbridged 2-arylindene group IV catalysts. Compositions span a broad range of isotactic content and have molecular weights typically used for extruded polypropylene films and fibers. Mechanical properties encompass elastomers with moderate recovery to highly ductile soft plastics. Compared to ethylene based copolymer elastomers with similar room temperature elastic modulus and tensile properties, these polypropylene elastomers have higher softening and melting temperatures but also higher glass transition temperature.
Traditional Xbar Charts for PET Preform and Bottle Manufacture Reduce the Effectiveness of the Industry's SPC Efforts - Issues and Solutions
Traditional Xbar charts, the most popular statistical process control charts in the PET preform and bottle manufacturing industry, are often counterproductive. The typical application ignores the fact that each mold cavity of an injection or blow mold potentially behaves differently due to characteristics of that mold cavity. This paper discusses effective control charting techniques for dealing with blow molding and injection processes. The techniques offer more accurate estimation of when it is necessary to intervene in the process, quicker forecasting of impending defective production, and better visibility of what's going on in individual molds or mold cavities.
In-Line Granulation - A Key to Reduced Edge Trim Recycle Costs
In-line granulation, the size reducing of plastic trim as it comes off an extruder, tenter, frame, slitter or other production machine has many advantages over conventional trim handling methods. Small granulator size is an inherent requirement because of the limited installation space around these production machines and sound pressure levels must be low because of the proximity of the granulator to the machine operator. Precision Cutters, Inc. (PCI), has developed a unique line of small, very efficient, high productivity in-line granulators that meet all size and operating requirements for use in this advanced, closed, one-step trim to granulate process. The engineering principles of film granulation and throughput rates in kgs/kw-hr (lbs/hp-hr) are covered.
SC Coupling System Enhances the Properties of Mica Filled Polypropylene and Mica/Glass Polypropylene Hybrid Systems
High aspect ratio mica improves the modulus and heat deflection temperature properties of thermoplastic polymers and reduces the shrink and warping of plastic composites. Tensile and flexural strength properties are usually maintained while impact properties decrease. Glass reinforced polypropylene composites offer good strength, impact and heat deflection properties; however, dimensional stability and warping of molded parts have always been a problem resulting in over engineered parts at premium costs. This study involves the development of the SC" coupled mica system to improve the bonding between the mica reinforcement and polymer matrix so as to enhance the traditional properties provided by mica to reinforce polymers."
Pressure-Volume-Temperature Relations of Polypropylene + Polymer Liquid Crystal Blends
Blends of polypropylene + polymer liquid crystal (PLC) were investigated by a pressure-volume-temperature (PVT) technique. The focus of the project was the determination of the characteristic parameters of the Hartmann equation of state, which are usable for the analytical representation of the time-temperature superposition principle. The necessary time-temperature shift factor can be calculated by the Williams-Landel-Ferry (WLF) equation. Since the WLF equation is limited in its temperature application, an equation was derived relating the time-temperature shift factor to the temperature via the reduced volume, which depends on the characteristic parameters of the Hartmann equation of state.
Thermoforming Behavior of Olefinic Instrument Panel Skins
Currently thermoplastic olefins (TPO) are being used for injection molded or extruded automotive exterior parts. Due to lack of melt strength of the polypropylene base resin, the thermoformable TPO are still under development for automotive interior skins. The advantages of TPO skins over the current PVC/ABS skins are long term aging, reduced fogging, and improved recycling. Laboratory evaluation for formability usually involves uncommon and tedious tasks. In this study, dynamic mechanical analysis in tension mode was used to predict the optimum temperature range for thermoforming, extent of network enhancement, as well as other mechanical properties.
Fourier Transform Infrared Micro Spectroscopy Mapping Studies of Weathered PVC Capstock Type Formulations. II: Outdoor Weathering in Pennsylvania
FT-IR micro spectroscopy coupled with mapping techniques is a powerful methodology to evaluate dimensionally dependent changes such as those encountered in PVC weathering processes. It is based on the complexity and specificity of the infrared spectrum and the dimensional resolution of the microscope. This presentation will outline a systematic FT-IR study of changes observed during outdoor photo degradation of PVC siding capstock formulations, as a function of exposure time and TiO2 level. The results will be compared with previously obtained accelerated QUV data. Profiles through the thickness dimension will be analyzed to identify degradation species and depth distribution.
Dispersion of Birefringence and its Influence on On-Line Measurement of Stresses in Polymer Films
Birefringence distribution in biaxially oriented polymer films is often used to assess non-uniformities in processing and in physical properties. Off-line characterization of this property can be performed by direct measurement of anisotropy in the refractive index, a process that is slow and not suitable for on-line use. By comparison, the spectral contents analysis (SCA) method is fast and easily adaptable for on-line process monitoring and real-time process control. However, implementation of this method requires accurate knowledge of the chromatic dispersion of birefringence. This paper discusses the contribution of birefringence dispersion to the precision of birefringence measurement by the SCA method, and it describes a new spectrometric procedure for accurate measurement of this material property.
The Effect of Shrinkage Induced Interface Gap on the Thermal Contact Resistance between the Mold and Plastic in Injection Molding
Accurate modeling of the heat transfer from the vitrifying plastic to the mold is essential to obtain accurate simulation of the injection molding process. The thermal contact resistance is one parameter that affects the heat transfer in injection molding and is difficult to measure from laboratory experiments. In injection molding the thermal contact resistance in the post filling stage is shown to depend on the gap formed between the part and the mold wall due to part shrinkage. It is shown from shrinkage calculations that the thermal contact resistance is a time and space (location on the part surface) dependent parameter and its value can vary by orders magnitude during each molding cycle. The effects of this variation on the molding process are discussed.
A Procedure for Determination of Thermal Properties of Polymers from Transient Temperature Data
Thermal properties are important parameters in both process and product design. In the case of plastics, the need for quick and accurate determination of thermal properties is gaining importance due to large variety of blends and recycled materials that are becoming available. A procedure based on an inverse method is presented for the determination of thermal conductivity and specific heat. The method makes use of transient temperature measurements. The temperature measurements are made in reference metal blocks and no temperature sensors are inserted in the plastic specimen. The method shows potential for obtaining the thermal properties over a wide range of materials and temperatures, and as a function of pressure. The method has been tested in simulation and results are presented.
Improving Economic Efficiency - Key for Market Penetration of Continuous Carbon Fibre Reinforced Thermoplastics
Due to its outstanding properties continuous carbon fibre reinforced thermoplastic is ideal for many industrial applications. But, insufficient economic efficiency has been clearly identified to be the main obstacle for future penetration of the targeted markets. A significant potential for cost saving has been identified by process optimisation. Additional cost reduction is expected from the announced introduction of low cost carbon fibres. Cost analysis shows that the level of processing cost will fall significantly in the future. However, the investigation indicates that a cost level acceptable for mass markets like the automotive industry will not be achieved in general.
An Integrated Adaptive Control for Injection Molding
The objective of the research project is to investigate the possibility and develop a methodology and associated system to control the quality of injection molded parts on-line and adaptively. The project makes use of rigorous process simulation programs first to determine the initial machine-setup condition and then to predict the part quality. Such simulation programs are incorporated in the feed-forward loop of a multi-level control architecture which also consists of three feedback loops involving the machine parameters, process variables, and part-quality levels, respectively. This paper describes the research plans and some results up to date.
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