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Conference Proceedings

Process Window Identification for a Very Tight-Tolerance Injection Molded Part with Multiple Performance Criteria
Hamdi H. Demirci, May 2001

The injection molded part is for a very critical radar application and therefore its parabolic form has to be maintained through stringent application and environment conditions, while satisfying a number of other functional and quality requirements. A D-Optimal Design Of Experiments (DOE) analysis was run to identify an optimal process window in the four parameter design space, within which, ten very critical and tight-tolerance performance criteria were satisfied simultaneously. Prediction models generated based on the DOE analyses were shown to accurately represent the actual molding process. These models were then coded in a program to be utilized by molding engineers in process sensitivity analyses.

Innovations in Pad Printing - New Process Controls
John Marshall, Mike Learmouth, May 2001

Recent technical breakthroughs in pad printing machinery; such as automatic ink viscosity control, automatic pad cleaning, and compact automation friendly designs will assure a place for modernized pad printing well into the future. Gone are the old-school open inkwell systems that had their share of problems in production. Many modern machines have also been designed with an approach that requires only one (or two) nesting fixtures, giving many molding facilities ultimate flexibility without massive tooling costs. With these new process control innovations having been developed, the pad printing process now allows easy integration into automated systems. To help further bring pad print systems into modern molding facilities, the ink systems utilized have also made many technical leaps forward.

Free Radical Grafting of Maleic Anhydride on Polypropylene in the Presence of Supercritical Carbon Dioxide
Beth Dorscht, Costas Tzoganakis, May 2001

The functionalization of polypropylene (PP) with maleic anhydride in the presence of supercritical carbon dioxide was studied. Supercritical carbon dioxide was used in this reactive extrusion system to reduce the viscosity of the polypropylene melt phase by forming a polymer-gas solution in order to promote better mixing of the reactants. For that purpose, a reactive extrusion system was developed to facilitate grafting of maleic anhydride onto PP under supercritical pressures in a section of a twin screw extruder. Subsequently, the effect of supercritical carbon dioxide on the level of grafting, product homogeneity and molecular weight was evaluated. Analysis of the products revealed that the use of supercritical carbon dioxide led to improved grafting when high levels of maleic anhydride were used. The experimental results showed no evidence of an improvement in the homogeneity of the product while melt index measurements showed a reduction in the degradation of polypropylene during the grafting reaction when low levels of maleic anhydride were employed.

Development of Hollow Strand Plastic Foam
Slava Grinshpun, Michael Schaller, May 2001

We have developed a novel extruded foam structure that appears to have many advantages over current structures. The concept is a unique extension of the technology used to produce The Dow Chemical Company's STRANDFOAM* brand extruded polypropylene (PP) foam products. STRANDFOAM brand PP foam products are produced by extruding a gel made up of polymer and dissolved blowing agent through a die consisting of an array of holes. As the gel exits the die, it expands to form individual solid cylinders that coalesce into a solid plank. Hollow strand foam is produced in a similar fashion, except that the polymer gel is extruded through an array of annuli instead of an array of holes. This process produces hollow strands or tubes that expand and coalesce into a plank. The hollow strand structure gives the foam a host of interesting properties. For example, the hollow strand foam has excellent compressibility and recoverability compared to solid foam planks of similar composition. In addition, the new structure allows easier production of foam products with a low bulk density. Perhaps most intriguingly, it is possible to combine the hollow strand foam with solid strand or plank foam to produce products having two sets of performance attributes. There are numerous extensions of, and applications for, this technology. Examples include: impact energy absorbers; high impact packaging with built in drainage; low density hard to blow" foams like PET PC; leveling insulating board for concrete surfaces; combined thermal and acoustical insulation."

Advances in Understanding the Performance of Multilayer Films for Packaging Applications
Barry A. Morris, May 2001

A food package is called upon to perform a number of functions, including • providing a hermetic seal, • protecting against the environment (e.g., controlled moisture or oxygen ingress or egress, puncture resistance, impact resistance), • safeguarding the flavor of the food, • allowing the product to be packaged on high speed filling lines, and • conveying information to the consumer (e.g., advertising and product contents). A single material often cannot provide these functions in an economical way. Hence, multilayer structures are prevalent in the packaging industry. A number of examples are illustrated. Several processes are used to make multilayer packaging films including extrusion coating, lamination, coextrusion and various combinations. This paper will deal primarily with coextrusion. Designing and manufacturing multilayer films present special challenges beyond those encountered when making single layer structures. In this paper we will review recent progress made in understanding four such challenges: interlayer adhesion, the effect the coextrusion process itself may have on properties, stiffness and curl.

Prediction of Residual Deformation in Clamped NORYL GTX Plates after Thermal Cycles
Ihor D. Skrypnyk, Jan L. Spoormaker, May 2001

This paper is aimed on the development of a constitutive model for NORYL GTX with the purpose of Finite Element (FE) prediction of the residual deformation, caused by thermo-mechanical cycling of structural elements. This material is a blend, produced by General Electric Plastics and widely used in automotive industry. Two brands of this thermoplastic: NORYL GTX 964 and NORYL GTX 974 are specially developed for automotive parts for in-line painting. The technology of in-line painting includes thermo-cycle with maximum temperature ~ 170°C. Therefore, the aim of this study is related to prediction of performance of thermoplastic parts during and after the thermo-mechanical cycles (of painting). For this purpose an earlier developed non-linear visco-elasticity model of relaxation type is employed. The model calibrated using the experimental data on sagging of single-side-clamped thermoplastic plates under thermal cycles. The ability of the model to predict independent events was validated basing on the data from the tests of double-sides-clamped plates, subjected to a thermo-mechanical loading. Difference between the model prediction and the results of controlling tests is less than 10% that confirms applicability of the model proposed.

A Closer Look at the Long-Chain Branch Formation in Ethylene Polymerization Using Metallocenes
Daryoosh Beigzadeh, João B.P. Soares, Thomas A. Duever, May 2001

Polymerization of ethylene using metallocene catalysts, particularly the constrained geometry catalysts (CGC), was studied. The main focus of the paper is on the control of chain microstructure in olefin polymerization using metallocene catalysts, particularly long chain branching in ethylene polymerization. Combined metallocene catalysts, consisting of CGC and a conventional metallocene catalyst, which only produces linear chains (linear catalyst), were used to manipulate long chain branching degree. The feasibility of this technique was verified using a mathematical model developed for the polymerization of ethylene in a semi-batch reactor using combined catalyst systems. Polymerization experiments were performed to verify the validity of the proposed technique and some of the modeling results. It was shown that by choosing a proper catalyst system and polymerization conditions chain microstructure could be tailor-made. Monte Carlo simulation was also used to study the structure and length of the branches in metallocene catalyzed ethylene polymerization. This information is essential for making any correlations between LCB degree and rheological properties.

Determination of Comonomer Distribution in Ethylene/?-Olefin Copolymers
Daryoosh Beigzadeh, João B.P. Soares, Thomas A. Duever, May 2001

Estimation of chemical composition distribution in ethylene/?-olefin copolymers using crystallization techniques is studied in this paper. Monte Carlo simulation was used to model the fractionation process in crystallization analysis fractionation (CRYSTAF). Five poly(ethylene/1-octene) samples synthesized with a single-site-type catalyst were used to verify the simulation results. It was proposed that the fractionation mechanism be controlled by the crystallization of the longest ethylene sequence in each chain. Good agreement between experimental and simulation results verified the validity of the proposed fractionation mechanism.

Evaluation of Thermal Environment in Plastic Injection Mold
Feng Gao, Hiroshi Koresawa, Hiroyuki Narahara, Hiroshi Suzuki, May 2001

Thermal deformation is one of the major problems that affects a product's quality in plastic injection molding. It is very important to have an accurate evaluation of the thermal environment surrounding the injection mold, especially in the case of high precision or large product molding. This paper proposes an evaluation method of thermal environment with a consideration of both the effect of the resin solidification process and the product's geometric shape. With this method, the validity of the thermal environment in different cooling designs is discussed using numerical analysis.

Vibration Welding of Dissimilar Nylons
Valerie LeBlanc, Bobbye Baylis, Liying Qi, Dan Watt, May 2001

Tensile strengths of linear vibration welds of nylons with different melting temperatures and glass contents were determined. Two different geometries were investigated: T-welds and a cylinder welded to a plaque. The study involved weld strengths for both homogeneous" welds where both components being welded were the same and for "heterogeneous" welds where the two components were made of nylons of different melt temperatures. It was determined based on the T-weld and the cylindrical-weld analysis that there is potential for dissimilar material weld combinations using vibration welding as the joining process. Relatively high weld strengths were obtained when PA 6 (and PA 66) was welded to the 3 different PPA's. For the short-glass-fiber materials one of the factors influencing weld strength was the difference in melt temperature between the two resins: greater difference in melt temperature resulting in lower weld strength. The long glass-fiber reinforced material which is predominantly PA 66 exhibited approximately the same weld strength regardless of the difference in melt temperature between it and the other nylon to which it was welded."

Development of an Extrusion System for Fine-Celled Foaming of Wood-Fiber Composites Using a Physical Blowing Agent
H. Zhang, G.M. Rizvi, W.S. Lin, G. Guo, C.B. Park, May 2001

This paper presents an innovative design of a tandem extrusion system for fine-celled foaming of plastic/wood-fiber composites using a physical blowing agent (PBA). The plastic/wood-fiber composites utilize wood-fibers as reinforcing filler in the plastic matrix and are known to be advantageous over the neat plastics in terms of the materials cost and some improved mechanical properties such as stiffness and strength. However, these improvements are usually accompanied by sacrifices in the ductility and impact resistance. These shortcomings can be reduced by inducing fine-celled or microcellular foaming in these composites, thereby creating a new class of materials with unique properties. An innovative tandem extrusion system with continuous on-line moisture removal and PBA injection was successfully developed. The foamed composites, produced on the tandem extrusion system, were compared with those produced on a single extruder system, and demonstrated significant improvement in cell morphology, resulting from uniform mixing and effective moisture removal. The effects of both wood-fiber and PBA (CO2) content on the cell morphology and foam properties were studied. Increasing the CO2 content marginally improved the cell structure, whereas, increasing the wood-fiber content had an adverse affect. The effectiveness of a coupling agent was also evaluated. The cell morphology and foam properties showed improvement when the coupling agent was added.

An Experimental Investigation of the Plug Assist Thermoforming Process
G.W. Harron, E.M.A. Harkin-Jones, P.J. Martin, May 2001

This work investigates the influence of processing parameters on the properties of thermoformed polypropylene pots. Fourteen parameters were studied using a Design of Experiments methodology encompassing the polypropylene resin, extrusion parameters (Chill Roll Temperature and Line Speed) and thermoforming parameters including Plug Geometry, Plug Speed, Air Pressure and Sheet Temperature. The thermoformed pots were measured for wall thickness distribution, weight, and compression resistance. The force exerted on the plug during the forming cycle was also recorded, with a long-term goal of incorporating this data into a process control system for Plug Assist Thermoforming. Results show that the parameters associated with the plug have the greatest effect on the final pot quality.

Nonlinear Rheological Behavior of LDPE Melt during Capillary Extrusion under Vibration Force Field
Xiangfang Peng, Jinping Qu, Hui Zeng, May 2001

In order to study the rheological behavior of polymer on vibration force field, a new capillary dynamic rheometer has been successfully developed by us for the vibration extrusion experiments of polymer melts. In this paper the measuring principles for the capillary rheological behavior of polymer melts under vibration force field will be introduced. By the experiment study of low-density polyethylene (LDPE), it has been discovered that melt viscosity and extrusion swelling ratio nonlinearly changed with the frequency and amplitude of vibration sources. The viscosity of the LDPE melt, the swelling ratio and unstable flow of LDPE decreased during capillary extrusion under vibration force field, and had a minimum with vibration frequency's change. It has great significance to the researches on dynamic extrusion and injection processing of polymer materials.

A Robust Ultrasonic Mold Condition Monitor for Injection Molding
Charles L. Thomas, Russell Edwards, Rob Peterson, May 2001

An ultrasonic transducer was installed on an injection mold such that the sound pulse would strike the front surface of the mold cavity and reflect back to the transducer. Changes in the intensity of reflected echoes are shown to be sensitive to the presence of polymer in the mold. By monitoring this changing reflected echo a signal is produced that is sensitive to conditions in the mold during processing. The primary advantage of the transducer is that it can be mounted on the external surface of many molds, allowing an installation that requires no machining of the mold.

Rapid Prototype Tooling for Injection Molding Microfluidic Components Using Photodefinable SU-8 Epoxy
Thayne L. Edwards, Swomitra K. Mohanty, A. Bruno Frazier, Russell K. Edwards, Charles L. Thomas, May 2001

A rapid method for fabricating an injection molding tool using current MEMS processing is presented. The process was used to fabricate micro fluidic channels in a plastic substrate with depths of 27 µm. The tool was made using a photosensitive SU-8 epoxy on silicon. Two polymers were successfully used for injection molding the channels, clear rigid polycarbonate and opaque flexible polypropylene. Tool fabrication time was approximately 30 minutes and survived, 22 shots for polypropylene and 8 shots for polycarbonate. Deformities of the channels were observed in both plastics. Channel height was increased by 2-3 µm due to a ridge that was formed from shear forces generated between the walls. The channel width shrunk approximately 7.9% maximum for polypropylene.

Controlling Injection Phase/Packing Phase Switchover Using an Ultrasonic Sensor
Russell Edwards, Charles L. Thomas, Rob Peterson, May 2001

An ultrasonic transducer was installed on an injection mold such that a sound pulse would strike a surface of the mold cavity and reflect back to the transducer. A change in the intensity of reflected echoes indicates the presence of polymer at the point where the sound pulse strikes the cavity surface. Detection of the arrival of the polymer at a specific position in the mold cavity is then used to identify the end of the injection phase in a similar fashion to the current cavity pressure based technique. Two important advantages of this technique are that the transducer can be mounted on the external surface of many molds, allowing an installation that requires no machining of the mold and the technique directly senses the position of the polymer in the mold cavity.

Overmolding-Stack-Mold Technology - An Innovative Concept in Multi Component Injection Molding with Many Advantages for the Molder
Hermann Plank, May 2001

Turning a part of the mold is the classical, most widely used, method of transporting preforms in multiple component engineering molds. Up until now, turning was carried out exclusively with vertical turntables which were mounted on the moving machine platen and which have a horizontal turning axis. However, because the machine has to provide turning space according to the diagonals of the mold, the problem of a very large machine clamping unit is encountered. In addition to the turning space, a high clamping force is needed for the injection of preform and finished part in one cycle. This situation looks much more advantageous if the over-molding-stack mold system is linked with a horizontal turning device. This process has been developed by Ferromatik Milacron in close co-operation with Foboha GmbH Formenbau, Haslach.

Weathering Effects on Mechanical Properties of Recycled HDPE Based Plastic Lumber
Jennifer K. Lynch, Thomas J. Nosker, Richard W. Renfree, Prabhat Krishnaswamy, Robert Francini, May 2001

Commingled recycled plastic lumber (RPL) decking was exposed to the environment for eleven years. The weathering effect is examined by performing mechanical property tests on the full size deck boards before and after the exposure. Flexural tests on the weathered deck boards were conducted with the exposed side and the unexposed side tested in tension. The flexural properties after weathering are compared to the original flexural properties. These data show the effect of weathering on recycled high-density polyethylene based RPL. A life cycle cost analysis (LCCA) is also presented to compare the cost of a wood deck versus an all RPL deck. The purchase, maintenance, and disposal costs are included.

Investigation of the Change in Mechanical Properties of Concrete Mixed with Styrene Beads
Hyera Kim, May 2001

Judicial mixture of industrial material to produce new properties not inherent in each individual micro constituent has been the subject of an intense scientific and engineering investigation. One such material is a concrete based mixed with styrene (poly-concrete) to change a selected physical and mechanical properties with a reduction in weight. Poly-concrete not only can be used in the construction industries it is also used in plastics industries as well. The need to corrugated materials for production of thermoforming mold has been well sited in the technical literature. Such a material can provide thermoformer with the ability to produce a rapid prototype molds, or molds requires a deep draw ratio at a fraction of cost of more conventional materials. At the present time corrugated aluminum is considered the only material with such a property available in the market. The cost of the corrugated aluminum prohibits more common application of this material in thermoforming industry. The purpose of this study is to investigate the difference between selected properties of traditional concrete as compared to concrete mixed with various amount of expanded polystyrene beads. The investigation was involved with preparation of a concrete mixed with various amounts of expanded Styrofoam beads for evaluation. Five samples of each mixture were produced to the dimensions specified by a predesigned specification. Common concrete mixture as specified by the American Concrete Society was used. A proper curing-time was given to the samples to achieve the optimum mechanical properties. The verification of the uniformity and integrity of the sample was investigated using an imaging system and optical microscope. The result was evaluated using three-point- bending, compression, and impact tests. The expected result was used to establish a correlation between the selected mechanical properties and as a function of the physical composition of the material.

The Effect of Blend Ratio on the Properties of Syndiotactic and Isotactic Polymer Blends
Richard Goshgarian, Caitlin Orroth, Gregory Parthum, May 2001

Isotactic polypropylene and syndiotactic polypropylene were random blended and injection molded in various ratios. The blends produced mechanical properties that varied blend composition. Blends with increased i-PP content had higher crystallinity in the isotactic phase, and so exhibited higher moduli and yield strengths and elongation and lower impact properties. As the percent s-PP was increased, overall crystallinity decreased and the impact behavior improved. Since increasing the back pressure during molding enhanced isotactic crystallinity at the expense of syndiotactic, the blends became more rigid. Best clarity was observed in blends with high s-PP contents and lower back pressure.

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