SPE Library

As more molders face pressure to reduce costs of quality, many are turning to cavity pressure monitoring to automate part segregation. Here, abnormal parts are automatically rejected in real time using alarm levels placed around key cavity pressure measures. However, few techniques are available to determine which measures to monitor and what alarm levels to set for each of them. A new, systematic technique has been developed to assist molders in the selection of appropriate measures and alarm levels. Using data taken during a DOE based tryout, correlations are made between cavity pressures and key part characteristics. For metrics which show the best correlations, alarm limits are set based on part specifications. In this paper, a model study is presented to illustrate the application of these techniques.

Process conditions in injection molding can dramatically change the mechanical properties of glass filled PPS. The parameters studied included maximum cavity-fill pressure, packing pressure, injection velocity, and melt temperature. This study utilized advancements in cavity pressure measurement and switching by cavity pressure to control the injection fill stage. Also, an easy designed experiment was used that allows for practical, quick, and reliable testing of part properties that can be applied to future part performance studies. Due to many mechanical variables, this study focused on tensile properties.

For a resin to be successful in a blow moulding application, it has to comply with a set of characteristics known as a whole as the material's blow mouldability". This concept includes the parison swelling behaviour (both in diameter and thickness) and the resistance of the melt to extension (melt strength). This paper outlines a new methodology geared towards the establishment of relationships between relevant rheological properties and key processing material behaviour parameters (swell and sag) governing the blow moulding process. The technique has been applied to the intermittent extrusion of a PC/ABS blend (PULSE™
). Several processing parameters such as drop time extrusion temperature and die gap were studied."

PET plastic containers are mainly manufactured by the injection stretch blow moulding process. Their main advantages compared to glass containers, are their low cost of production, lighter weight and high impact resistance. However, the growing demands on beverage containers regarding barrier properties and hotfill ability have surpassed the PET limits in applications such as beer bottles, fruit juice containers, etc. The aim of this work is to examine if PET/LCP blends moulded on a one-step injection stretch blow moulding can produce bottles that fulfill the requirements of barrier and mechanical properties and hotfill ability. The results are interpreted based on the flow behaviour and microstructure characteristics of the materials.

For several years, plastics processors have been blending two or more generally incompatible materials in order to improve physical or mechanical properties. Depending on the degree of compatibility and thermomechanical history during processing, various goals may be attained: easier processing, improved mechanical (modulus, impact strength), thermal and barrier properties. Polyethylene terephthalate (PET) enjoys wide success in industrial applications because of its outstanding mechanical, optical and barrier properties. However, the growing demands of the electronics and automotive sectors have surpassed the PET performance limits. With its outstanding barrier properties as well as mechanical properties even at high temperatures, LCP's are potential candidates as a blend component.

Rovings are used in a variety of polymer processes such as filament winding and compression molding. In all these processes, impregnation of the roving monofilament bundle by the liquid polymer is essential. Modeling polymer impregnation requires an estimate of the transverse Darcy's Law permeability. This study measured the transverse permeability of 2400 tex glass rovings as a function of applied compressive stress, monofilament diameter, roving thickness, fluid velocity and viscosity. The permeability was observed to depend strongly on the compressive stress, and hence void fraction. The permeability was independent of the monofilament diameter, roving thickness, fluid velocity and viscosity. Results are presented using a simple model that accounts for roving void fraction inhomogeneities.

In the production of food packaging using the plug assisted pressure thermoforming process it is desirable to optimize costs and product properties through efficient distribution of material. Typically in industry conditions for forming are obtained by trial and error which can be very inefficient. In this paper the development of a finite element model of the process is described. Modeling was carried out using a commercial finite element package and the model encompasses both 2D axisymmetric and more complex 3D geometry. Material behavior is simulated using a viscoelastic model based on data obtained from various material tests.

In order to produce thermoformed products of consistent quality, an understanding of the effect of material and process parameters on end part performance is necessary. In this investigation the effect of pigment, nucleating agent, and recycling regrind on the nucleation of homopolymer isotactic polypropylene have been studied. Differential Scanning Calorimetry was used to reveal the effect of these additives on the crystallinity, type of crystals, crystallization and melting temperatures at different cooling rates. It has been found that percentage cystallinities were increased as the concentration of the nucleating agent and first and fifth generation regrinds increase up to the saturation level. Although more hexagonal ? crystals were formed by increasing the concentration of the pigment, the enthalpy of fusion was decreased.

The quality of extruded sheet for use in subsequent thermoforming operations may be defined in terms of its resistance to sag, low and consistent shrinkage, tensile properties and overall consistency of these properties with time. The sheet extrusion process has many variables such as melt temperature and output rate that may influence the properties of the sheet and it is the objective of this work to identify the critical variables in the process. To achieve this objective a series of experiments were conducted using a statistical design of experiments methodology. This investigated the effects of MFI, Melt Temperature, Chill Roll Temperature and Line Speed on the properties of the extruded polypropylene sheet which are of importance in the future thermoforming process. The sheet properties investigated included tensile properties, crystallinity, sheet sag and shrinkage. The main findings of the study were that melt temperature had the main effect on the shrinkage in the machine direction, while the chill roll temperature and line speed had the main effects on the tensile properties. Sheet sag was found to be greatest at the lower MFI value, which correlated to the lower levels of crystallinity of the as made sheet.

This paper relates the thermal decomposition behaviour of chemical blowing agents (CBAs) with the cell morphology of EPP (expanded polypropylene) produced using those blowing agents. Correlation between decomposition temperatures and rates of the various agents and the cell morphology of extruded, EPP are reported and discussed. The research has revealed relationships between the structure of an extruded PP foam and the thermal decomposition response of the chemical blowing agent used during production. The CBAs tested showed a very wide range of cellular structures under the same processing conditions. Those with a higher temperature and rate of gas evolution generally produced foams with the smallest cell sizes and highest cell densities.

Polymer density increases when it cools down in the cavity. In the injection molding process, without proper packing to provide extra material to fill the void due to the density change, parts will shrink and even warp. Reducing shrinkage and warpage of injection molded parts in order to improve quality is one of the top priorities in the manufacturing process. Part design, material properties and process conditions are factors that affect part quality most significantly. In this paper, the effects of process conditions on shrinkage and warpage will be discussed. They include packing pressure, packing time, fill time and mold wall temperature. Two tools, CAE software and design of experiment, will be used in this investigation. This paper will show that these two can be used together effectively to design the process window.

New PC-based software and peripherals are now available that allow the creation of a broadcast-quality animation and live-action video studio for under $2000. This opens up a valuable means for engineering and marketing to communicate design intent and performance via the readily accepted medium of video tape very early in the development cycle. These tools allow CAD data to be further leveraged through photorealistic computer animations of intended product usage. This paper surveys currently available software and hardware, including rendering and animation, video capture, video compositing, and video output, and discusses advantages and disadvantages of various approaches. Sample product demonstration videos will also be shown. The uses of desktop video are limited only by the imagination. However some of the more obvious possibilities include: • Animated fly-by • Product usage • Assembly procedure • Marketing and engineering evaluation • Corporate promotional video

Nowadays, many materials, pigments, additives, gas or reactants, are mixed to create new products combining the characteristics of different raw materials to obtain a specific product properties. The quality of the mixing, i.e. the uniformity of the mixture, is a key issue that will determine the morphology and the properties of the resulting compound [1, 2]. An insight into those features can now be obtained through the numerical simulation of flow in extruder components. 3-D transient numerical simulations of two twin screw extruder (TSE) sections are presented and their behavior compared. A new technique, the mesh superposition method (MST), accurately determines the part of the computational domain which is occupied by the fluid with respect to the current screws position; the Navier-Stokes equations are then solved without involving any remeshing. Through the calculation of trajectories of material points, statistical information (of the RTD, deformations, dispersion, etc.) can be obtained to compare both configurations in a synthetic and quantitative way.

The injection/compression molding process is a better choice than traditional injection molding process when large, thin or precision parts are produced. However, by introducing an independent press control to the polymer injection control, it becomes more difficult to find proper process conditions. In this paper two tools are discussed. The first tool is CAE software that has been developed to simulate injection/compression molding process. Second, a process window also has been developed to help the design of process conditions. This paper will show that both tools provide useful insight into the process that helps engineers make rational judgements.

Rapid tooling has allowed manufacturers to produce plastic injection-molded prototypes quickly and inexpensively. However, the mechanical properties of parts differ between rapid and conventional tools. The tensile and flexural properties of injection-molded parts produced in geometrically identical steel and composite molds were compared using atactic and syndiotactic polystyrene. When molded in the composite mold, both isomers exhibited an average of 17% lower ultimate tensile strength, similar Young's modulus, and 20% lower ultimate elongation than parts produced in the steel mold. The tensile stress-strain data for both isomers were found to be correlated. In flexural testing, both isomers molded in the composite mold exhibited an average of 19% higher flexural strength, 39% higher flexural modulus, and 27% lower ultimate flexural elongation than parts produced in the steel mold.

High conductivity carbon fiber was used to produce reinforced epoxy tools with unique thermal properties. When compared to epoxy and alloy backfilled stereolithography (SL) tools in identical heat conduction experiments, the fiber-reinforced epoxy tool showed an average of 17% greater conduction through the tool and 31% greater conduction across the tool's surface. These anisotropic thermal properties were speculated to be the result of preferential fiber orientation on the surface of the fiber-reinforced epoxy tool. Additionally, the fiber-reinforced epoxy tool exhibited 81% less total injection molding cycle time and 229% less production time than its backfilled SL counterpart.

In the compounding of polymers, static mixers are commonly used for distributive mixing. However, successful compounding generally requires both distributive and dispersive mixing; where the most difficult mixing involves the dispersion of materials having widely different viscosities. The best method to accomplish successful dispersive mixing is to expose the material to extensional flow. Furthermore, in terms of power consumption, extensional flows are far superior to the shear-type flows found in most mixing systems. This paper presents a new dispersive and distributive static mixer (DDSM), which exposes the fluid element to continual extensional flow for enhanced mixing.

A counter-rotating nonintermeshing twin screw extruder specifically designed to provide extensive backmixing was used to investigate the molecular weight distribution (MWD) occurring in the polymerization of Butyl Acrylate and the MWD and drift of copolymer content occurring in the copolymerizations of Butyl Acrylate/Styrene and Butyl Acrylate/Butyl Methacrylate. In contrast to almost plug flow characteristics observed in conventional single screw and twin screw extruders, this backmixed extruder has a residence time distribution comparable to a continuous stirred tank reactor, yet provides a positive drag flow regime for high viscosity fluids not available in stirred pots. The polydispersity (Mw/Mn) of chain addition polymerizations carried out in the backmixed extruder was cut in half when compared to those obtained in a conventional (plug flow) extruder, thus producing a more monodisperse polymer, and approached the theoretical value for a micromixed CSTR. The copolymer content of chain addition copolymerizations carried out in the backmixed extruder was demonstrated to be constant as a function of position in the reactor, whereas drift was observed in the conventional (plug flow) extruder. Acrylate/Styrene and Butyl Acrylate/Butyl Methacrylate produced in the backmixed reactor is contrasted with that from a conventional twin screw extruder, which exhibits virtual plug flow behavior. The copolymer composition is also contrasted at various locations in the extruder.

In recent years the rotational molding process for plastics has become more sophisticated in terms of equipment design and the complexity of the molded parts. One of the weaknesses that remain is the lack of precise control of the process variables. Molders can now monitor in real time the temperatures inside the mould but there is a lack of a model relating machine controls and the key temperatures in the process. This paper presents for the first time the use of neural network methods to develop models to assist in the design of control systems. In this first phase of the work, deterministic step changes were used to derive a model relating oven temperature and the mold internal air temperature.

As Metallocene Catalysed Polyethylenes ( mPE's ) become more commercially available they are finding ever increasing application in the blown film industry. However, it is becoming apparent that no two mPE resins behave in exactly the same manner. This paper examines the rheological properties of a range of mPE's with different densities and MFI's. These resins were then blended with a conventional low density polyethylene ( LDPE ) to form monolayer films. The mechanical properties of these films were compared to three layer coextruded films of A:B:A structure, where A is LDPE and B is mPE.