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Conference Proceedings

Modelling of Bubble Formation in Rotational Molding
C.T. Bellehumeur, J.S. Tiang, May 2000

Polymer sintering and heat transfer are fundamental phenomena in rotational molding. In the heating stage of the molding cycle, the powder particles melt, adhere to each other and sinter. During this stage, pockets of air are entrapped between the particles and form bubbles. This work aims at determining the relative effects of material properties and molding temperature on the initial sintering and bubble formation in rotational molding. The molding temperature varies strongly with the oven temperature and molded part thickness, and is determined using a lumped parameters heat transfer model (Gogos et al., 1998). The initial sintering of powder is predicted using a two-particle sintering model (Pokluda et al, 1997). The sintering model is used together with the heat transfer model to predict the level of sintering reached when an additional powder layer adheres to the melt and thus entraps air pockets which in turn will form bubbles. Results show that the initial size of the bubbles formed does not vary significantly when changing molding conditions. The polymer rheological properties seem to dominate the bubble formation process. Further results will be compared with experimental work.

A Study of the Deterioration in the Mechanical Performance of Polymers Used in Multilayer Fuel Lines with Immersion in a Standard Automotive Test Fuel
M.P. McCourt, G.M. McNally, W.R. Murphy, T. McNally, May 2000

Many multilayer fuel line structures are currently being developed for use in fuel handling systems in an effort to comply with pending legislation regarding reduced vapor emissions. This study examines the changes in the mechanical properties and glass transition temperatures (Tg) of the polymers used in multilayer tubes such as conductive Nylons, barrier layer materials including Fluoropolymers, and tie layers with immersion in the standard test fuel Fuel C at 25°C. The changes in Tg, percentage mass uptake, swelling, mechanical properties such as tensile, flexural and impact were determined for different immersion times. The results show that a significant deterioration in the mechanical performance of many of these polymers was recorded. A corresponding decrease in Tg with increasing immersion time in the test fuel was observed.

Pressure Build-Up in a Staggered Pin Compounding System
P.J. Bates, J. Kendall, D. Taylor, M. Cunningham, May 2000

Pultrusion compounding is a widely used technique for mixing polymer with continuous reinforcement. It often involves pulling glass roving over staggered pins immersed in a pool of liquid polymer. This causes polymer pressure to build-up in a wedge-shaped region located between the roving and pin. This pressure drives polymer into the roving. To study this pressure build-up, roving was pulled over an instrumented pin placed in a silicon oil pool. A hole in the pin allows pressure to be measured at various locations in the wedge as a function of pulling speed, oil viscosity, and inlet tension. These parameters are lumped together with the roving width to form a dimensionless group called the lubrication number. Initial studies using impermeable tape showed that for lubrication values above 0.0001, the maximum pressure was equal to its theoretical value of tension divided by the product of tape width and pin radius. For permeable roving the maximum pressure was significantly less than that value. Models for pulling force as a function of process parameters have also been developed and validated.

Optimizing Welding Temperature of Semi-Crystalline Thermoplastics-Memory Effects of Nylon
Val A. Kagan, May 2000

Previously we reported*1 to SPE'99 on the basic principles for optimization of the vibration welding process and presented an analysis of the weld-melt temperature kinetics for linear vibration welding. For this investigation we used the advanced Thermovision 900® infrared measurement system*2 for comprehensive, real-time analysis and thermal imaging. Under optimized processing conditions for vibration (linear and orbital) and hot-plate welding technologies, the tensile strength of welded nylon 6 butt joints is equal to or 14% higher than the tensile strength of the base polymer (matrix). For optimized vibration welding conditions, the maximum temperatures of the weld-melt (in inter-phase) were significantly above (85 - 90 °C) the melt point of the welded nylon 6 and nylon 66 (Tm = 223 °C and 261 °C, respectively). For PP based plastics, J. Vetter and G. W. Ehrenstein observed*3 an increase in the maximum temperature in the weld-melt / in weld inter-phase of not more than 10 °C above the melting point ( Tmp ). In their report to SPE'99, the authors discussed the results of the physical modeling for semi-crystalline HDPE, showing the values of maximum temperatures in the weld inter-phase above 250 °C compared to melting point (Tmp = 126 °C). Ch. Bonten presented*4 to SPE'99 his analysis on the mechanisms active in weld interface of semi-crystalline thermoplastics (HDPE and cross-linked polyethylene PE-X). Mechanical performance of welded joints was affected by crystallization across the boundary layer and weld-melt temperature kinetics (above melting point Tmp). For a better understanding of the role and influence of the temperature of the melt (in injection molding) and weld-melt (in welding) on mechanical performance of semi-crystalline molded (welded) thermoplastics, we performed a comparative study for nylon 6 and nylon 66 (non-filled and fiber-glass reinforced) plastics. Mechanical performance of injection molded and welded nylon was evaluated using static (tens

Thermoforming Simulation and Experimental Validation on a Bass Boat Hull
D. Laroche, R. Connolly, C. Elie, M. Gundjian, May 2000

An integrated thermoforming simulation of a HDPE bass boat hull was performed. The part is fabricated by Pelican International. The sheet heating, forming and cooling stages were sequentially analysed in order to predict the sheet sag and temperature as well as the final part wall thickness distribution. Sheet heating includes radiation from the oven banks combined with air convection. The viscoelastic deformation of the polymer under gravity load was modelled in order to predict sheet sag in the oven. The effect of the sheet sag, for a long part (3 m), on the sheet deformation during the forming stage could then be predicted. The part thickness was measured with a magnetic sensor. These experimental values were then compared with the prediction. Good agreement between predicted and measured wall thickness distribution was found.

Orientation Recovery in Biaxially Oriented Amorphous Polymer Films
C.C. Chau, W. LaFollette, May 2000

The dimensional recovery of biaxially oriented polystyrene and high impact polystyrene films was found to follow dual second order kinetic processes that took place in parallel. The early stage of the recovery involved major dimensional changes with a high rate constant and is likely related to the recovery of main chain orientation. The later stage process gave smaller dimensional changes with a low rate constant and is not directly related to the main chain orientation. This study indicated that the orientation in amorphous polymer films could be examined by understanding the kinetics of thermal recovery.

Engine Cooling Performance Optimization Using a CFD Guided Design Modification of a Centrifugal Plastic Fan
L. Reinhardt, E. Homsi, May 2000

Large scale computational fluid dynamics (CFD) models, typically consisting of 100 thousands of cells, are used in the design process of plastic components. Readily available hardware and software have made it possible to simulate a system as a whole and determine the contribution and effect of each component onto the overall performance. The CFD tools are used primarily to guide making modifications to achieve better performance and to execute smarter validation test, thus eliminating unnecessary preliminary models. This paper presents a CFD guided case study on performance optimization, conducted on a centrifugal fan used in the cooling of a tractor engine.

Application of Internet and Web Technologies for Management of Molding Know-How
Lih-Sheng Turng, John Lottey, Manjunath Mahishi, Nur Yildirim, Mandar N. Damle, Bharat Gupta, May 2000

This paper presents the latest development of a Web-based Knowledge Management System (KMS) for injection molding. This system is aimed at helping any knowledge-intensive organization in the molding industry to create, capture, manage, and share engineering data and know-how related to plastics part design and manufacturing (Molding Intelligence"). The KMS is implemented within the framework of the Internet and Web technologies to facilitate ease of use global and instant information access and dissemination and collaboration among geographically dispersed team members."

Blow and Injection Molding Process Set-Ups Play a Key Role in Stress Crack Resistance for PET Bottles for Carbonated Beverages
Stephen W. Zagarola, May 2000

This paper discusses the role of injection and blow molding set-up in reducing the bottles' vulnerability to stress cracking; an aspect often ignored in traditional training on stress crack prevention. Case studies, involving process optimization for stress crack resistance, illustrate typical key process variables affecting stress cracking including interactions with injection molding variables. Examples show how to strike a balance between the demands of stress cracking performance and performance of other key areas. It comments on the relationship between stress crack resistance and properties such as material distribution and base clearance (the gap between the injection gate and the bottom of the bottle).

Understanding the Effects of Weathering Variables on Plastics Using Fractional Factorial Experiments
Henry K. Hardcastle III, May 2000

Sophistication of experimental designs for weathering research testing continues to evolve. The majority of current weathering experiments utilize simple designs which change few variables at a time. These types of weathering experiments require more trials and result in more cost and less information than approaches using Fractional Factorials." Conducting "Fractional Factorial" experiments before using traditional approaches focuses weathering research on the significant and important variables effecting material performance. This paper presents a methodology for applying "Screening Fractional Factorial" approaches to material performance research. This paper includes a case study and examples of weathering data."

Edge Effects in Film Casting of Molten Polymers
Kathleen Canning, Albert Co, May 2000

In most analyses of the film casting process, edge effects such as necking in and edge beading are usually neglected. In this work, we investigated the significance of these effects and their dependence on the rheological properties of the melts, the draw ratio, and the extrusion rate. Two linear low-density polyethylene melts and a low-density polyethylene melt were considered. The rheological behaviors of these melts were characterized under shear and elongational flows. Streamlines from the die exit to the chill roll, velocity profiles, film tension, neck-in profiles, thickness profile of the solidified film, and edge bead thickness profile were examined.

Solution of Inverse Thermoforming Problems Using Finite Element Simulation
Chao-Hsin Wang, Herman F. Nied, May 2000

Finite element simulation of thermoforming can provide highly accurate predictions of final part thickness. The majority of these simulations have been for isothermal situations. Similar calculations can also be performed for non-isothermal processing conditions, provided suitable temperature dependent material properties are available for the polymer of interest. For these simulations, it is assumed that the initial sheet temperature is known and does not change significantly during forming. In this paper sample results are presented for the so-called inverse thermoforming problem, where an initial temperature distribution is sought that will result in a specific final thickness distribution. Thus, a finite element simulation is combined with an iterative algorithm to obtain inverse solutions for a simple axisymmetric thermoformed part. In this example, the required initial temperature distributions that result in a uniform final thickness, are determined for a deeply drawn part. It is shown that the calculated results are quite sensitive to perturbations in the specified initial temperature profile and thus the practical application of optimal temperature distributions may require high precision thermal sensors and controls.

Effects of Various Fillers on the Coefficient of Thermal Expansion of Epoxy Resins
Glenn E. Lawson, May 2000

It has long been recognized that the predictive ability of the rule of mixtures for coefficient of thermal expansion (CTE) is less than desired. It ignores the elastic interaction and restraint between the matrix and the filler, hence yielding values that are too high. The predictive ability of the rule of mixtures and three other theories are compared to actual measured CTE values of over 90 particulate filled epoxy formulations. It has been found that the Kerner theory can predict the CTE within 8 ppm/°C at the 95% confidence interval for the epoxy systems evaluated.

Analysis of Adhesive Properties of Different Engineering Thermoplastics to Elastomers by a Two-Shot Injection Molding Process
Sandip Patel, Chetan Makadia, Qing Guan, Sanjay Mehta, Stephen P. McCarthy, May 2000

The objective of this research was to study the adhesion between a core (hard) material and skin (soft) material mainly used for the interior applications in automotive industry, using the two-shot injection molding process. Two different groups of materials were tested for the adhesive bond strength. In the first group, filled polypropylene (PP) and two thermoplastic polyolefins (TPO) were tested with two thermoplastic elastomers (TPE). In the second group, polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and PC+ABS alloy were tested with thermoplastic polyurethane (TPU). Since many current applications involve the use of an elastomeric material as a skin material for a hard material, this research will provide some guideline for materials to be used, part design, process parameters, adhesive joint design, and post conditioning.

Kinetic Welding of Plastic Parts
Judith A.H. Jones, Yogish Mahadevaiah, Balint Koroskenyi, Sanjay Mehta, Stephen P. McCarthy, May 2000

Typical consumer products cannot be produced as a single part. Most items require the manufacturing of multiple parts followed by an assembly procedure. Assembly methods vary depending on the nature of the parts and their end uses. Typical assembly methods utilize bosses with nuts and bolts, snap fits, ultrasonic or spin welding and press fits. This report addresses tests undertaken on a variety of plastics, to determine the viability of the patented kinetic weld process invented at Bell Labs, the research and development arm of Lucent Technologies. In order to develop design guidelines for kinetic welding it is necessary to test a wide range of materials with different pin and boss combinations. The first series of tests were performed with welds of three different materials at three different assembly pressures and two geometric configurations. It was found that materials with relatively higher impact strengths tend to perform better than less resilient ones. It was also found that numerical design guidelines were important in optimizing the dimensions of the pin, boss and weld so as to have equalized stress throughout the part.

Injection Molding Cycle Time Reduction Using an Advanced PC/ABS Blend
Cheryl L. Weckle, Dick P. Lauer, Blair S. Patty, Hoang T. Pham, May 2000

An advanced PC/ABS blend has been developed offering reduced cycle times for injection molding applications, and thus creating economic value for the molder. This material has improved flow as compared to traditional PC/ABS blends, yet it is designed for high toughness. The results of molding trials demonstrate injection pressure and melt temperature can be reduced, ultimately resulting in reduced cycle time and improved manufacturing cost. Physical properties and desired part performance criteria, such as heat resistance and low temperature ductility, are maintained.

Ultrasonic Heating and Hardening of Hot Melt Adhesive
Kin Ming Kwan, Avraham Benatar, May 2000

The application of hot melt adhesives is based on heating the adhesive from solid state to liquid state for wetting, and cooling back to its solid state to develop cohesive and adhesive strength. Conventional hot melt adhesive application methods use a separate heat source to melt the adhesive and apply it onto one of the substrates. Frequently, the adhesive cools while the second substrate is brought into contact with it resulting in inadequate wetting. With ultrasonic vibration, viscoelastic internal heating of the adhesive is used to melt it and to aid in wetting of the pre-placed hot melt adhesive film on the surfaces of both substrates. In this work, a conventional 40 kHz ultrasonic welder was used to heat a coated hot melt adhesive film in a laminate. The effects of the processing parameters of heating time, vibration amplitude, heating pressure, and hold pressure on bond performance were studied. It was found that the holding pressure plays an important role in sealing and bonding performance. Through the use of ultrasonic vibration it was possible to produce high quality seals in very short cycle times of less than 7 seconds.

Laser Transmission Welding of Semi-Crystalline Thermoplastics-Part I: Optical Characterization of Nylon-Based Plastics
V.A. Kagan, R.G. Bray, W.P. Kuhn, May 2000

Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.) The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties. In a following paper (Part II)a1 we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.

Comparative Study of Contact and Non-Contact Hot Plate Welding of HDPE
Bovornchok Poopat, Avraham Benatar, Joon B. Park, May 2000

Hot plate welding is one of the most popular plastics joining methods and it is employed in most industries. Traditionally, the hot plate is coated with a non-stick" surface usually polytetrafluoroethylene (PTFE) which is usable to temperatures not exceeding 260°C. To avoid sticking to the hot plate and to accommodate higher hot plate temperatures non-contact hot plate is used. This paper is concerned with determining the optimum process parameters for non-contact hot plate welding of high-density polyethylene. For a given welding pressure the melt layer thickness weld displacement and their ratios were used as control or reduced parameters. During heating the melt layer thickness of the high-density polyethylene samples was measured. An empirical relationship between melt layer thickness and hot plate temperature and heating time was developed and used to predict the melt layer thickness in future experiments. The effects of the reduced welding parameters on joint quality are presented and compared with contact hot plate welding. For both processes the maximum attainable joint strength is 100% of the bulk material strength with the optimum melt layer thickness of 3.5 mm (1.75 mm for each part). The energy at break was more dependent on the ratio of weld displacement to melt layer thickness. For non-contact hot plate the optimum weld displacement melt layer thickness ratio was 0.75 compared to a ratio of 0.4 for contact hot plate welding.

Non Destructive Evaluation of Plastic Parts Using 3D Computed Tomography
Bruce Davis, Jeff Hanson, May 2000

During the production of plastic parts the presence of voids, inclusions, fiber reinforcement and fillers can play a critical role in the structural integrity of the product. Although in recent years tremendous improvements have been made in the field of analysis and design software to predict such factors, their physical detection is more difficult to accomplish. Certainly, when considering quality assurance and quality control, the ability to accurately and efficiently determine internal structure in a non-destructive manner is beneficial. This paper presents a novel method of using Computed Tomography (CT) to detect and visualize internal structure in polymer articles.







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