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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Melt Modification of PET with Reactive Glycidyl Compounds
Melt strength of polyesters for foam extrusion and extrusion blow molding is controlled by weight-average molecular weight, molecular weight distribution, and the degree of branching. This paper describes the chemical modification of polyethylene terephthalate (PET) as a technique to improve its melt strength using compounds containing the reactive glycidyl (epoxy) group. The effect of addition of di-, tri-, and tetra- functional epoxy compounds to the PET resin in the melt state was studied using a batch mixer. Changes in the torque and temperature in the mixer resulting from the addition of modifier(s) were followed in order to relate to the kinetics of the reactions.
Barrier Screws in Helically Grooved Barrels: Operating Characteristics and Implications for Simulation Models
Grooved feed zones in single screw extruders have been used in many variations over the years, mostly axial grooves in many sizes and shapes. The lesser known helically grooved feed zone permits, when properly designed, an operating mode where flow rate becomes a function of geometry only, practically independent of friction coefficients. Therefore, it has a linear behaviour with screw speed and is virtually independent of backpressure over a wide operating range, as shown by experimental evidence gathered over many years. The high flow rates obtained require barrier screws for adequate melting capacity. In the barrier zone, considerable pressure differentials are observed between the primary and secondary channel, where the melting occurs, at higher screw speeds. This effect is associated to the melting mechanism.
Effects of Material and Process Parameters on the Degree of Groove Replication in DVD Disks
Information storage devices such as re-writable DVD (DVDRW) disks require high degree of groove replication to achieve desired readability. Higher levels of replication are typically achieved by increasing mold temperature, packing pressure, and filling speed. These extreme molding conditions are often on the border of the material processing window. A simple groove forming process model is presented. The model is shown to predict well groove replication for wide ranges of mold and melt temperatures and two different radial locations. The model is useful in assessing replicability of new materials in new formats.
Predicting Shrinkage for Injection Molds
Shrinkage of plastics materials can be significantly affected by both process and flow induced orientation in a cavity. This paper presents a study of the factors that affect shrinkage in a variety of different types of thermoplastic materials. These include process, flow type (linear versus radial), material and material fillers. Sensitivity of shrinkage to these factors is established and can assist mold designers in more accurately sizing their cavities to account for in-mold shrinkage
Warpage Index for Mold Designers and CAE Analysis
This paper presents the results of study directed toward developing a simplified technique of classifying plastics materials relative to their sensitivity to warpage as caused by non-uniform cooling and flow induced stresses. The materials are then rated on a relative scale of 1 to 10. This information will allow mold designers and injection molding simulators analyst to realize the relative sensitivity of a material to warpage from these factors and therefore more strategically design their molds to address these issues.
Process Window as Effected by Shear Induced Flow Imbalance in Multicavity Molds
The paper presents a study on the sensitivity of shear induced mold filling imbalance, found in multi-cavity molds, to process variations. A variety of materials are molded in an eight-cavity test mold using a variety of different runner designs. The materials are molded at four different flow rates. Two different runner designs are used - a conventional geometrically balanced runner and a geometrical balanced runner including a melt rotation technology that eliminates shear induced mold-filling imbalances.
Effects of Aqueous Medium on Long Term Creep Properties
The determination of the physical properties of a polymer over time has long been a topic of speculation. It is not clear the effect of moisture on this mechanism. This research will attempt determine the interaction between percent humidity and the final creep properties, while the samples are completely immersed in an aqueous medium. This paper will attempt to bring together molecular interaction, secondary forces, and hydrolyzed components of them and how they interact with the final tensile, ultimately creep properties.
Design of Experiments to Optimize the Weldline Strength in Injection Molded Thermoplastics
The forming of weldlines wherever polymer flow fronts meet is one of the problems that confound the overall success of injection molding technology. An L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of injection molded thermoplastics. Experiments were carried out on an 80 ton injection-molding machine. A plate cavity with an obstacle at the center was used to create a weldline. After molding, the weldline strength of the parts was measured by a tensile tester. For the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of injection molded thermoplastics. In addition, weldline strengths of injection molded parts increase with the size of the obstacles.
Practical New Applications for an On-Line Rheometer
On-line rheometers have been around for over 30 years. They have been used in many different applications in R&D, polymerization processes, product development, and compounding. However, their main application has been in large volume resin production, mainly in the polyolefins industry. Applications in the processing and compounding industries have been almost non-existent because of the large size of the rheometers and the need to modify the extruders or compounders in order to use them. This paper discusses applications of a new rheometer, developed to address these problems, in the monitoring of a production PET sheet extrusion line. The real time" monitoring of viscosity and its application to the control of the resin moisture level and the consistency of a virgin/regrind blend is demonstrated and discussed."
A New Method of Rheological Analysis for Polymer QA and Product Development
For many years the capillary rheometer has served as an important tool in R&D and product development laboratories. It has even gained in popularity in the QA laboratory as a tool for assuring the processability of a resin. More recently two and even three barrels designs of the capillary rheometer have become more generally available. The main applications of these instruments have been for providing directly corrected viscosities and for doing measurements of extensional properties. However, very little has been said about the opportunity these rheometers provide for applications in QA and product development. This paper discusses the capabilities of the dual barrel rheometer for direct comparisons of materials in QA and for the fast and easy observation of changes in the flow properties of a new product, as it is modified in the development process.
Accuracy of Filling Analysis Program
In order to verify the accuracy of the filling analysis program (C-MOLD) for injection molding, pressure losses across four characteristic segments (Nozzle & Sprue, Runner, Gate, and Cavity) of the flow channel in the test mold were measured for the HDPE under various molding conditions regulated exactly. Without the additional assumptions in the simulation, the flow properties with the pressure-dependent viscosity and the juncture loss measured actually were added to the indispensable pvT-data, thermal conductivity, specific heat for simulation. After confirming good agreement between the observation and the simulation at the flow segment wherein thermal properties affected weakly on the pressure loss, the effects of the heat transfer coefficient between the polymer and the mold metal on the simulation were examined. By introducing the heat transfer coefficient of 1,200W/m2-K, instead of the default value of 25,000 W/m2-K, we found that the difference between the simulated and the observed pressure losses at the four segments were reduced to less than 20%.
Water Structure in Hydroxyethyl-Co-Glycerol Methacrylate Materials
Differential scanning calorimetry was used to analyze the state of water in crosslinked glycerol methacrylate and hydroxyethyl methacrylate hydrogel polymers. Glass transition temperatures were obtained for the dry materials and for the materials equilibrated at room temperature (23°C) and humidity (55% relative humidity). The total crystallization enthalpy was determined for these hydrogels equilibrated in water and at several states of partial hydration. The enthalpic information was used to quantitatively determine the fraction of nonfreezing water in the hydrogels. The integrated areas of the crystallization exotherms were reported to qualitatively access the freezing-bound and free water contents.
An Investigation of Part Variation in Multi-Cavity Injection Molds when Using Cavity Pressure Control
The use of cavity pressure to control velocity to pressure transfer during the injection phase of the molding process is generally considered to be the most repeatable method. However, for multi-cavity molds, it is believed that the part variation may actually be worse in non-controlling cavities than it would be if position transfer were used. This study will look at how the balance of conditions between cavities effects the part variation for both cavity pressure and position transfer methods.
Effects of Annealing on the Crystallization Behavior of Nylon 6,6 in the Presence of Nucleating Agents
Nucleating agents such as paraffin wax and MoS2 are known to vary the morphology and quality of crystals. Samples of unfilled Nylon 6,6, wax filled, and MoS2 filled were subjected to structured annealing conditions. Samples were then analyzed using Differential Scanning Calorimetry (DSC). Changes in tensile, flexural, and impact data were compared and correlated to the crystallinity data.
Orientation Effects on Thermoformed Parts at Different Temperatures
The orientation of a plastic part changes due to the processing temperature. The extent of these changes can be seen on thermoformed parts from the same mold, processed at different temperatures on a smooth surface.
Study of PVC Degradation Using a Fast Computer Scanning Procedure
A fast computer scanning procedure for the determination of total double bond concentration resulting from PVC thermal degradation is described. It allows the rapid estimation of rates of degradation and prediction of temperature and stabilizers effects on degradation.
Integrated Design Environment Enhancing Concurrent Engineering Approach in Plastic Injection Molds Design
As the injection mold market increases, Time and Costs Reduction will be important aspects for mold makers. A detailed analysis of todays workflow in the mold making industry has pointed out the need for tailored tools in an integrated environment. The COSMOS project, (a pre-competitive European Union founded project) wants to enhance CAE integration and data exchange in CAD-based mold design. A PDM-based (Product Data Management) environment is being tuned on the basis of a new Concurrent Engineering-based approach. The expected results will lead to a reduction in time-to-market by about 30% and cost of about 40% as compared to the traditional injection mold design and manufacturing paradigm.
A Physics Based Approach to Determining Filled Volumes within a Corotating Twin Screw Extruder
Determination of filled regions in extruders is important to the understanding of the operation of the extruder. This information can be useful to predict various performance measures for unit operations such as mean residence time and chemical conversion. A model is proposed that predicts the filled volume length for the extruder, based on the pressure drag flow model. This model is dependent on the system geometry in addition to the conveyed fluid's properties. Experiments have been performed that shows the ability of this model to predict the filled length in Co-rotating Twin-Screw Extruder (CoTSE) based upon a determined channel percent drag flow and specific throughput.
The Effect of Liquid Cooling of Gas Channel in the Gas-Assisted Injection Molding Process: Overview
In Gas-Assisted Injection Molding, gas channels are usually utilized as a gas transfer system. However, the gas channel can be considered to have dual purposes; it can be used as inner cooling channel to improve fast cooling and to reduce cycle time without losing part quality. In this study, a simple plastics part with an open gas channel is used for prediction of cooling effect when gas channel is acting as a cooling channel by introducing the mixture of gas and liquid. Results can be drawn on how fast the part cooling is and how much the fingering effect reduces. Most importantly, we can compare how the quality differs between the gas-injection molded part with and without internal cooling.
Cracks Prediction of Thin-Wall Injection Molded Part by CAE Simulation
Cracking in the injection-molded part is one of the problems which tooling engineer and/or design engineer often encounter in the molding process. This phenomenon originates from several factors. Among them are high-speed injection, high/long packing pressure/time, etc. In reality, the cracking may be recognized after long time, i.e. days or weeks after part production. In this study, CAE simulation helped to predict the potential cracking area in the plastics part and possible solution(s) to reduce or eliminate cracking by either redesign the part or changing plastics material or processing conditions through simulations. The part used in this study is from the thin-wall injection molded speaker grille product. In the analysis, this speaker grille would be 3-layer solid that is considered real 3D solid model.
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