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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Compression Molding Tooling for Thermoplastic Composites
Tooling requirements for compression molding continuous glass mat, long fiber glass, or other types of reinforced thermoplastic composite products is presented along with critical tooling aspects. Emphasis is placed on the general tooling concepts associated with cooling lines, shear edges, guidance systems, ejectors and stop blocks. Basic product design issues that can lead to poor part performance i.e. weld lines, tabs and mounting holes, ribs and bosses, sink marks, multiple cavity molding, and venting are discussed. The relationship of prototype tooling and the requirements to go from design to production is discussed briefly.
A Physical-Mathematical Model for the Description of the Process Behavior of Mixing Elements
Tightly intermeshing, co-rotating twin screw extruders are commonly used for tasks requiring good mixing. The modular constitution of both barrel and screw makes it possible to optimize the extruder configuration for a given task. Physical-mathematical models enable the process engineer to predict the process behavior of a chosen extruder configuration and to optimize existing compounding processes. We will present physical-mathematical models for the prediction of the pressure-throughput relationship of grooved conveying and grooved reconveying elements. The models are based on an analytical approach for the description of the flow patterns within the investigated screw elements. Experimental investigations were performed with varying geometry, material and process parameters. Finally the developed model was compared to the experimental results.
Comparison of Results from a Simulated and Actual Design of Experiments
This study includes a design of experiments using a blow molding simulation software. An eight-run, four factor D.O.E. format was chosen. The response variable of interest is the variable wall thickness throughout an extrusion blow molded part. The simulation will help pinpoint the factors that have the largest effect on wall thickness variation throughout the part. The results will be implemented into an actual D.O.E. that will be completed in the future.
Study of Cast in Passages for Rotational Molds
This paper discusses the theoretical effect of cast in passages on the wall thickness of rotationally molded part. Finite element analysis was used to determine temperature differences for given passage geometry and dimensions. Testing was done to determine the relationship between surface temperatures and melt thickness versus time. This information provides a theoretical model for construction of rotational molds using cast in passages.
True 3D Flow Analysis for Designing Hot and Cold Runners in Injection Molds
The industry standard 1D beams used in current state of the art injection molding simulation software does not pick up the shear-induced imbalances created in branching runners. This imbalance requires the use of 3D simulation software, which is in its infancy, when used for injection molding. As none of the commercially available injection molding simulation programs currently provide the required solution, use of general purpose 3D flow analysis and 3D extrusion software is evaluated. This paper provides information on the accuracy of these 3D programs against actual molding.
Extrusion/Compression of Long Fiber Thermoplastic Composites
It is becoming common for long fiber-reinforced thermo-plastics (LFT) to replace existing GMT-type applications as well as to capture new applications. This is especially true in the European automotive industry, where the market for parts made from LFT is experiencing tremendous growth. The following paper discusses the available materials, the mechanical and physical properties, machine techniques and processing details of the LFT process. It will also discuss potential applications for LFT. The paper will cover different process techniques such as direct processing and make comparisons with other processes. An explanation on the effects that LFT has on properties and economics will be made. It will show how the economics can be improved by adding recycled material to the process. This paper will provide a better understanding of the LFT-process and how you could get benefits from this process.
Interaction in PC/ABS Blends Prepared in a Dynamic Melt Mixer
Polymer blends are more and more important materials in polymer technology. Their role increases due to the recycling processes of mixed plastic waste. One of the key problems of polymer blends is the interaction between the components as they determine the properties. Commercial polycarbonate (PC) and ABS were blended in a dynamic melt mixer in 80/20 and 70/30 ratios. Homogeneity of the blends was characterized by SEM method. Glass transitions of the blends and the pure materials were measured by calorimetric and dynamic mechanical analysis. The interaction and the partial miscibility between the components were determined from the shift of the glass transition temperatures. It was found that the homogeneity of the blends was uniform. The shifts of the glass transition temperatures show some interaction between the components.
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.
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