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Conference Proceedings

Correlation of Processing Temperature, Density Gradients, and Mechanical Properties in a Molded Polyurethane Foam System
Brendan O’Toole, Michelle Cameron Nelson, Michael Mullin, Dacia Jackovich, Robert Mohan, Linda Sapochak, Daniel Fogarty, Flocerfida Bennicasa, May 2002

Polyurethane foam is often molded directly in place as a thermal or vibration insulator, energy absorbing material, or core material for a sandwich structure. A smooth thin skin forms between the mold and the interior cellular structure of the foam. A non-uniform microstructure is often visible when foam cross-sections are examined, resulting in density variations throughout the foam. This paper investigates the effect of processing temperature on the average density, density gradient, compressive modulus, and compressive strength, for a free rise, water blown polyurethane foam system molded in aluminum cylinders. Resulting properties are also compared to reference samples that have a uniform density. It is shown that the processing temperature has a significant effect on the foam density and density gradient. This density gradient, as well as the presence of the skin, affect the compressive modulus but have minimal effect on the compressive strength.

The Cost of Tolerances in Injection Molded Parts
Anne Bernhardt, Mark P. Wolverton, May 2002

Specifying realistic tolerances that insure form, fit or function is one of the most overlooked areas in product development. All too often, tolerance specifications are missing, vague, and unrealistic. This and the subsequent 'variances' can lead to higher than necessary manufacturing costs, poor market acceptance and product liability exposure.This paper will examine the cost, quality and time-to-market implications of injection molded part tolerances and how to improve the tolerance specification and implementation process. The primary focus will be on the obvious - dimensional tolerances, but we will also look at the impact of visual specification tolerances and mechanical requirement tolerances.

Coupled Rheological and Mechanical Design of Stackable Spiral Dies
B. Rotter, W. Michaeli, May 2002

In recent years, the use of stackable spiral (pancake") dies in blown film extrusion has been continuously growing. One main disadvantage of this die design is the susceptibility to mechanical die deflections resulting from melt pressure which can lead to a poor melt distribution or leakage problems. In this paper a flow simulation model will be presented that is able to calculate the melt velocity and pressure distribution in the spiral section. Additionally a mechanical simulation model has been derived that can calculate the deflection of the die plates for a given pressure load. Because of the mutual influence of melt flow and die deflection the two models are coupled and iteratively solved. The impact of the die deflection on the melt distribution and experimental results will be shown."

Creep and Tensile Behavior of Polypropylene Nanocomposites
Alejandro Hernandez-Luna, Nandika Anne D’Souza, May 2002

Nonlinear creep in polypropylene has been previously explored. In the present work we examine the influence of montmorillonite on nonlinear creep. The issue is of paramount interest since long-term properties have never been explored in this nascent field. Creep-recovery measurements were done for nanocomposites containing 1, 2, 3 and 5 % of montmorillonite. Master curves and shift factors were determined based on horizontal and vertical shifts using Schapery's equation. The results show the influence of the reinforcement on the properties of polypropylene. Infrared images show differences in deformation mechanisms from one sample to another.

Crystallization and Melting Behavior of Poly(Ether Ketone Ketone)/Polyimide Blends
Yong Sung Chun, R.A. Weiss, May 2002

Poly(ether ketone ketone) (PEKK) is a relatively new engineering plastic with high temperature stability and excellent chemical and solvent resistance. The ratio of terephthaloyl (T) and isophthaloyl (I) moieties, see scheme 1, can be varied to control the crystallization rate and crystallinity of PEKK without substantially changing the end-use temperature [1,2].Sauer et al. [3,4] reported that PEKK and a thermoplastic polyimide (PI) synthesized from 4,4’-bis(3-aminophenoxy)-biphenyl and pyromellitic dianhydride were miscible in the amorphous phase. Both homopolymers are semi-crystalline, so the phase behavior of PEKK/PI blends can be complex. Crystallization of either or both components in the blends depends on the miscibility of the two polymers in the melt, the temperature history during cooling from the melt and the kinetics of crystallization of the two polymers. In this study, we investigated the effect of crystallization in PEKK/PI blends on the thermal transitions and crystalline structure using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and wide-angle X-ray diffraction (WAXD).

Cyclic-Olefinic Copolymers as Non-Migrating, Polymeric Slip Additives in LDPE Cast Films
David R. Constant, May 2002

Cyclic-olefinic copolymers (COC) are being used in flexible packaging as a blend component or as a discreet layer in multi-layer polyolefin films. They are typically used to enhance stiffness and heat resistance in food packaging. As a core layer in laminated or coextruded multilayer films, they provide high moisture barrier and exceptional clarity and stiffness.In place of commonly used organic slip additives, they can decrease film to film coefficient of friction (C.O.F.) to levels of commercial interest. Performance as a slip additive, however, is related to a number of variables, including viscosity of the matrix, type and add level of the COC and the film process melt temperature. Various microscopy techniques investigated support the findings.

Decisions, Judgment and Uncertainty: Psychology and Intuitive Probability
Geoffrey Engelstein, May 2002

Most decisions in business (and life) are made on the basis of incomplete or estimated information. A wide range of psychological studies conducted over the past thirty years have shown that when forced to deal with uncertainty people fall back on rules of thumb that more often than not violate basic rules of probability and lead to flawed results. By understanding the types of mistakes people typically make, one can avoid these traps and improve the quality of the decisions. This paper discusses several of these, including regression towards the mean, ignoring base rates, and linked events.

The Decrease in Strength of Polypropylene as a Direct Result of Thermal History and Oxidation
Matthew M. Jackson, Stephanie Bullard, May 2002

The strength of Polypropylene is influenced by the thermal history of the material and oxidation experienced during molding. As the material gains more thermal exposures and subject to more shear stress, the tensile strength of the material is going to be influenced. In this work, five trials of reground polypropylene will be compared to determine the effect of multiple processing on the strength of the material. The relationship between the elongation and tensile strength of the part will be compared.Five different trials will be compared in this paper with each gaining another cycle through the machine. What affect the thermal and physical processing parameters have on the material after five runs will be examined. All of the material being used has gone through the same number of cycles, and has been processed at the same parameters throughout the experiment.

Deeper Screw Flights Offer New Opportunities for Co-Rotating Twin Screw Extruders
Klaus Kapfer, Erwin Häring, May 2002

Co-rotating twin screws are the prime choice of machinery in the field of polymer compounding. Additional applications beyond that are the mixing, blending and homogenizing of viscous materials in the chemical industry where a self-wiping and thus self-cleaning profile is of the utmost interest for best performance.A great number of these processes e.g. filling with high loading of fillers, does not require extremely high powered twin screws since energy input for these materials and processing tasks is relatively low when comparing it to polymer compounding tasks such as alloying and reinforcing.It was therefore the challenge for design and process engineers to design a deep-flighted twin screw coping with these processes. The two key characteristic dimensions of a co-rotating twin screw diameter ratio" and "power-volume factor" were adapted such to meet the requirements of the low energy compounding tasks. At the same time mechanical constraints such as shaft and element interface shaft strength and gear box design had to be considered too."

Deformation Behavior of Rubber Blends Investigated by a New Real Time Spectral Birefringence System
Francesca Fiorentini, Miko Cakmak, May 2002

Rubber compounds used in tires usually contain blends of more than one rubber to synergistically combine the properties of these rubbers. These include styrene-butadiene (SBR) and butadiene (BR) rubber or blends of natural rubber (NR) and butadiene rubber.In this study we investigated the true-stress true-strain birefringence behavior of blend of SBR and BR with a new real time spectral birefringence system and obtained the stress optical constant for the SBR/BR blends covering 10-40% BR concentration. The stress optical constants were found to decrease with the increase of BR concentration.

Deformation Modelling of Glassy Polymers Incorporating Structural Change
J.J. Wu, C.P. Buckley, May 2002

To exploit fully the available software tools for Finite Element stress analysis of engineering polymers, there is a need for constitutive models that capture the complexity of material behaviour. Recent work has led to the development of such a model for glassy polymers, where glass structure evolves during deformation, causing strain-softening after yield. The new anisostructural model is an extension of the physically-based 3D Glass-Rubber" constitutive model proposed earlier by Buckley and Jones. To test the model further an experimental study has been made of plastic deformation in compression of a range of glassy atactic polystyrenes with varying molecular masses. The model gave good agreement with measured strain-softening in these polymers but in its present form over-predicted the dependence of yield stress on molecular mass."

Deformation of the Dispersed Phase in Polystyrene / High Density Polyethylene Blends Produced by Ribbon Extrusion
H. Padilla-López, M.O. Vázquez, R. González-Núñez, D. Rodrigue, May 2002

The deformation of the dispersed phase in polystyrene / high density polyethylene (PS/HDPE) blends produced by ribbon extrusion was studied numerically and experimentally. The analysis of the ribbon extrusion showed that parameters such as draw ratio (DR) and film-water contact length (X) influenced significantly the ribbon dimensions. A model was developed which enabled us to calculate the extensional stress (?xx) and the stretching force (Fo) as functions of extrusion conditions. As expected Fo, and hence ?xx, increased with increasing DR values. Furthermore, Fo not only depends on X, but also on the extrusion velocity (Vo) and the matrix viscosity (?m). The deformation of the dispersed phase and the stretching force were correlated theoretically by an uniaxial deformation analysis of the ribbon and the equilibrium shape of the particles determined by a balance between interfacial tension and extensional stresses. The results suggest that Fo is the most important parameter which determines the final shape of the particles. A comparison between the model and the experimental morphology produced a good agreement.

Degradation and Bond Strength Failure of New Dental Composite Resins
Gabriel Adusei, John W. Nicholson, Sanjukta Deb, May 2002

The studies on up-take of water and other fluids by dental composites have been important in the determining some of their properties and successful use in dentistry. Properties such as strength and adhesion using biaxial flexure strength (BFS) and shear bond strength (SBS) of one experimental and three commercial materials stored in different media, dry air, water, saline and artificial saliva were analyzed. Results subjected to one-way ANOVA (p< 0.05) showed that the strength of these materials increases in dry air but deteriorates significantly in wet conditions with time. Such observations are due to, water sorption, hydrolysis and degradation of bonds in the polymerized matrix.

Density Measurement of Thermoplastic Powders during Heating and Cooling Cycles Using Thermal Mechanical Analysis
G.M. McNally, M.P. McCourt, May 2002

The measurement of changes in polymer density during the heating and cooling cycles in rotational molding is important in terms of improved cycle times and improvement in product performance. This investigation uses Thermal Mechanical Analysis (TMA), to continuously measure density changes of a range of thermoplastic powders, during heating, curing and solidification during cooling. Small samples of a range of thermoplastic powders were carefully weighed into small aluminum pans of known dimensions, with the tip of the free moving, weightless TMA quartz probe positioned on the top surface of the pan. The probe displacement was continuously recorded during the various heating and cooling cycles. Compaction of the various powders during heating, followed by compaction of the melt at elevated temperatures were easily recorded for various heating rates, holding temperatures and cooling rates.

Description of the Transport Mechanisms in Planetary Roller Extruders
A. Limper, S. Seibel, May 2002

The compounding process gains importance in the plastic processing industry, due to the increasing demands on the quality and flexibility during the production. The planetary roller extruders (PREs) convinced in comparison with other compounding machines through the thermally careful compounding, the balanced ratio of shear and heat transfer and the narrow residence time distribution [2], [5]. Experimental investigations to analyse the process behaviour of PREs were carried out for the first time. For the experiments, process and material parameters were varied and different materials were used. To model the process both the essential geometric dimensions and the kinematic conditions are presented. It is shown, that the transport mechanisms in the PREs consist of a combination of forced conveying through the gearing, a pressure- drag-flow in the meltbank and flows through head and flank gaps.

Design and Optimization of Planar Automotive Blow Moulded Parts
F. Thibault, P. Debergue, D. Laroche, R. DiRaddo, M. Milliste, May 2002

The key quality requirements of automotive blow moulded parts include weight distribution, geometric tolerance and mechanical performance. This work deals with the optimization of an automotive filler panel used in a sports utility vehicle. The part is moulded with an insulating material (carpet) on one side, which renders the design of the part complex, due primarily to the non-uniform solidification of the part and the tight tolerance requirements of automotive OEM's. The proposed optimization consists of the manipulation of the die gap programming points and the mould temperature in order to optimize the part thickness distribution and to minimize the part warpage.

Design of a Tricycle Frame Using Topology Optimization Software
Christopher Yeagley, Amanda McKain, May 2002

This Project optimizes the design of a child's tricycle frame. This is done using a topology optimization software package. Using specified material properties, this software technique analyzes a simplified finite element model with assigned loads and boundary conditions and returns a model with maximum structural rigidity and a minimal amount of material. The software goes through an internal iterative process of removing material from the model and recalculates the model's structural characteristics until an optimized shape and material distribution are created. The suggested shape may require further refinement to address manufacturing feasibility for an intended process.

Design of Lab Scale Test to Determine Feeding Characteristics of Solid Antioxidants in Industrial Scale Configurations
Ivan Saenz, Elisabeth Papazoglou, John Mara, May 2002

State of the art methods based on mathematical models allow full characterization of the flow behavior of a solid material [1,2]. These methods draw their parameters from shear cell measurements and offer detailed analysis of the flow of the material and its potential problem [3]. Appropriate feeder design can then be implemented to avoid such problems.The following paper describes the use of a self-made shear cell for the measurement of critical flow properties of polymer stabilizers of various physical forms.This detailed analysis is then compared to Carr's empirical model previously employed [4], to characterize such materials.

Design of Software Solution for Setting Price of Flat Film Product
Sarka Vlckova, James Busby, Drahomira Pavelkova, May 2002

Economical analysis software, created as an additional feature to commercially available extrusion simulation software, is presented. The software allows calculating the price of a flat film, coextruded, product based on the structure, material price, equipment price and other economical variables. The link to the simulation software allows getting some values, such as energy consumption from the calculation rather than as an estimate. The simulation software can also indicate that the structure that is the most beneficial from the cost point of view may not be possible to be manufactured.

Design Sensitivity Analysis of Gas-Assisted Injection Molding
Florin Ilinca, Jean-François Hétu, May 2002

Gas-assisted injection molding is an increasingly used manufacturing process that allows production of parts with more uniform properties, reduced shrinkage, warpage and residual stresses. Getting the proper combination of different process parameters such as gas pressure, gas injection delay and melt temperature, makes gas-assisted injection molding more intricate than the traditional injection. Very often a successful design in gas-assisted injection comes at the end of a long trial and error process. Design Sensitivity Analysis (DSA) can help the processors improve the design and can produce substantial investment savings in both time and money. This paper compares two approaches to perform sensitivity analysis for the filling stage of the gas-assisted injection molding process. Solution of the gas-assisted process and the sensitivity of the solution with respect to different design parameters are computed in three-dimensions using a finite element method.







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