SPE Library
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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Conference Proceedings
New Intermeshing Pin Mixer for Injection Molding
It is well known that reorientation of interfaces is key to efficient distributive mixing. However, how to achieve reorientation is not well known. This paper describes how interfaces can be reoriented in screw extruders and which method leads to the most effective reorientation. A new mixing device was developed to achieve highly efficient reorientation. This mixer can produce excellent mixing quality over a short axial length, as short as one diameter.This makes it possible to incorporate this new mixer into the non-return valve of an injection molding screw. Results will be presented from injection molding studies that compare the mixing action of the new mixing non-return valve to other mixing devices.
Molding of Microstructures and High Aspect Ratio Features
The challenge of replication of microstructures by injection molding depends very much on the size and the aspect ratio of the features as well as the size of the area covered with such structures. The filling of the structure has to compete with the filling of the underlying thicker substrate. The degree of filling of structures with high aspect ratios is investigated in a mold with a single continuous thin wall section attached to a flow leader for a large number of thermoplastic polymers. The degree of filling of the thin wall part is found to depend very much on the distance from the gate. Materials with the smallest pressure drop in the flow leader tend to give the best filling. Processing conditions do not have a strong influence except for the injection speed which can change the filling picture even qualitatively. It is found that the degree of achieved filling depends mainly on the local ‘time-to-pressure’, which is inversely related to the slope of the pressure rise curve. Numerical simulation overpredicts the achieved filling of the thin section for all investigated polymers.
Effects of Mold Gating on Shrinkage and Warpage of Injection Molded Parts
A laser printer frame, which is one of the tightest tolerance injection-molded parts in a printer, was simulated using injection molding simulation software fromMoldflow® Corporation. The part was simulated with different types of gating, including multi-gate cold and hot runner systems. The simulations were used to predict the part deformation using the different gating options. The optimized gating was determined by minimizing the part’s shrinkage and warpage. The optimized gating was used in the production mold for the frame. The predicted part shrinkage and warparge was in good agreement with the actual frame deformation.
Method to Determine Screw Performance and Product Quality during Manufacturing Process
During the extrusion process, whether it is film, sheet or injection molding, the need to obtain consistent quality and output requires an extensive quality control program. Unfortunately, these operations are time consuming and wasteful, often requiring many pounds of extrudate be expended before the desired result is achieved.Also, as extrusion equipment becomes worn, output rates decline and product quality gradually falls, often going unnoticed, until significant problems occur.Thirdly, when a new screw purchase is required, time-consuming laboratory trials are normally set up to evaluate screws from different manufacturers before deciding the best one for that particular operation.To quickly assess changes in operation conditions, whether from day-to-day running, equipment performance or assessing new equipment, a concept has been developed for an extrusion product, which utilizes the principal of mixing two colors to achieve a homogeneous third color. Observing the homogeneity of the third color mix and the flow pattern it generates will indicate the screw performance and the quality of the product. This is a quick, efficient way to test the process without sacrificing product or running time.A series of experiments was performed to evaluate two different screw designs in an injection molding process. In addition, molded parts from the same mold but the different screw designs were evaluated for quality consistency. In a separate trial, the amount of wear on production screws and barrels in a color compounding process were evaluated.This paper is based on these experiments and prospective new products.
The Role of CAE in the Design of a TPV Weatherseal System
Computer aided engineering has impacted the design process of weatherseal systems by reducing the number of prototypes needed to create a part. Finite Element Analysis is useful in predicting compression load deflection and frictional forces. Advances in FEA include how forces change over time and loading; stress relaxation, cyclic loading, compression set, and elastic recovery. This paper follows the design and prototyping of a unique weatherseal system and highlights the role of CAE.
Materials and Design Trends in Exterior Automotive Plastic Applications
This paper examines material and design trends in exterior automotive plastic applications. Plastics are widely used in exterior automotive applications. With the many different exterior applications, this paper concentrates specifically on fascia, body side moldings/ claddings, rocker moldings, wheel flare, and cowl vent leaf catchers. Examination of the material and design trends for these exterior applications is accomplished by benchmarking a number of OEMs. Insight into future material and design trends is gained by identifying the drivers.
Frozen Layer Effect on Measuring the Internal Cavity Pressure during Injection Molding
Experimental and theoretical studies of internal cavity pressure during injection molding of a spiral tube cavity were carried out. The frozen layer thickness and the evolution of internal cavity pressure were calculated using a commercial software (C-MOLD). The evolution of the internal cavity pressure was recorded during injection molding of polystyrene into a spiral tube mold. To explain the differences observed between the calculated and measured internal cavity pressure, a pressure correction factor (PCF) was introduced based on the plane stress theory. This factor was determined by analyzing the stress state in the melt and calculating the frozen layer thickness near the mold wall. The corrected and experimental pressures have been compared to validate the applicability of the pressure correction factor.
Study of Cavity Pressure and its Prediction during Injection Molding
Cavity pressure is an important injection molding parameter. It is regarded as a good indicator of molded part quality and injection machine control performance. It not only indicates the material condition in the mold but also affects the microstructure and part quality. On the other hand, almost all users prefer better accuracy of CAE simulation. The discrepancy results from neglecting some important factors, such as the pressure-dependent viscosity, variable heat transfer coefficient, and variable material properties. The goal of the study is to understand how pressure-dependent viscosity, heat capacity, heat transfer coefficient, juncture pressure loss and pvT-data affect pressure prediction, and the importance of each parameter. Then the method to improve the prediction accuracy will also be discussed.
Cooling Versus Process Stability: Stable or Not, Here We Ship
The combination of increased quality standards and just in time (JIT) production has yielded a series of issues for injection molders. While striving to maintain high quality and a JIT posture they are often faced with the potential for scrap molded during start up procedures. An often-unseen contributor to start up scrap is the stabilization period required by the mold. Until the mold has reached temperature equilibrium, consistent production is questionable. Building process tolerance to this instability and accurately predicting the amount of time required for equilibrium are the two logical solutions to solve this problem. This research focused on the use of various injection mold core materials to determine their effect on process equilibrium.
A Comparison of Position, Cavity Pressure, and Ultrasound Sensors for Switch/Over Control in Injection Molding
A mold has been constructed with a continuous wave ultrasound transducer installed, along with post gate and end of fill cavity pressure transducers. Signals from these transducers and the position signal from the injection ram were used in turn to control the switch/over from injection to packing phase on a standard industrial injection molding machine. The accuracy with which this point was identified was measured for each sensor. The results show that cavity pressure and ultrasound are significantly more repeatable as switch/over sensors than the ram position sensor.
Micromoulding: Process Characteristics and Product Properties.
This paper describes the techniques employed to measure the dynamics of the micromoulding process and assess the influence of the processing parameters on the properties of the product. A number of sensors were fitted to a commercial micromoulding machine and a custom data acquisition system was assembled to record process data. Nano-indenting and Atomic Force Microscopy techniques were used to assess the mechanical properties and morphology of the micromoulded products. Results indicate that process conditions influence the morphology and mechanical properties of the product. Mould surface features of the order of ?ms were shown to be replicated on the surface of the product.
Flow and Heat Transfer Simulation of Thin-Wall Injection Molding with Microstructures
Injection molding has been used for mass production of polymer products with microstructures. Conventional 2.5D midplane simulation based on Hele- Shaw approximation was unable to describe the local flow pattern around the microstructures. This simulation tends to over predict the effects of microstructures on global flow pattern. A x-z 2D planar simulation was developed in our lab to achieve better accuracy and to retrieve more detailed flow and heat transfer information around the microstructures. For the unidirectional flow, it is able to obtain a good resolution, similar to that of Moldflow 3D simulation. The mold-melt heat transfer coefficient and injection speed are very important factors to determine the filling depth in microstructures. Since the velocity and stress fields vary significantly in the main flow and microstructure regions, the heat transfer coefficient and wall slip as a function of location need to be considered in the simulation.
Devulcanization of Recycled Tire Rubber Using Supercritical Carbon Dioxide
In this work, an extrusion process has been developed for the devulcanization of rubber crumb from recycled tires employing supercritical CO2. For that purpose supercritical CO2 has been injected in a twin screw extruder to swell the rubber crumb and to facilitate the otherwise impossible rubber extrusion process. As a consequence, waste rubber can be processed under mechanical shear and extensional forces at various operating conditions that may lead to different degrees of devulcanization.
Surface Activation Systems for Optimizing Adhesion to Polymers
Many experiments have been performed globally to investigate ways of improving adhesion to polymers. This paper discusses current atmospheric surface activation systems, appropriate measurements of wettability and adhesion, over-treatment effects and surface analysis techniques relative to optimizing the adhesion of inks, paints, coatings and adhesives to polymer surfaces. Recommendations for improved activation by substrate and application are discussed.
Rapid Thermal Response Molding for Cycle Time Reduction
The idea of raising the mold temperature to enhance part quality is not new. However, its application is limited because of prolonged cycle time. The rapid thermal response (RTR) molding process can facilitate extremely rapid changes in the mold surface temperature, thus reducing the prolonged cycle time due to heating. While cycle time reduction via RTR molding is apparent for parts that need an elevated mold temperature, such as micro parts, ultra-thin parts and stress-free parts, it is not clear whether the process could also be used to reduce cycle time for standard parts. In this paper a RTR molding process for polycarbonate samples with varied thicknesses was simulated and the cycle times were compared with those in standard molding with the recommended mold temperature from the resin supplier. The simulation result indicated that, by application of RTR molding to standard parts, both quality improvement and cycle time reduction can be achieved especially for thick parts.
Evaluation of Pulsed Cooling in Injection Mould Tools
The use of a pulsed supply of a cooling medium to a mould tool has been shown to have benefits on the cycle time and energy consumption in the injection moulding process. Three papers at the ANTEC meeting last year reported on this technology. A definitive explanation for the effects reported was not submitted at that time. Since that meeting further experimental work has been carried out to compare direct cooling with the pulsed cooling technology. The results to be presented will also show the effects of thermally conductive additives on the injection moulding cycle time. Results from the first stage of a study to model the functions of pulsed cooling in injection moulding will also be discussed.
Electrically Conductive Nano-Composites in Powder Injection Molding
The objective of this paper was to study the effect of different process parameters on the conductivity of injection molded graphite samples and stainless steel samples. Different percentages of graphite powder and binder were mixed using a premixer. The mixture then was grinded into small granules; these granules were then injection molded to flexural bars. The injection molded flexural bars were then debinded at different times and temperatures. Conductivity testing was conducted on the bars and volume resistance was calculated for all samples. The effect of powder/binder concentration, debinding time and debinding temperature was studied on the conductivity of the samples. As the powder concentration was increased in the sample the volume resistance of the sample decreased. Also, with the increase in debinding time and temperature there was a considerable decrease in volume resistance.
Simulation of Optical Media Molding
A hybrid finite element/finite difference method is employed to solve the temperature and pressure fields of an injection-compression molding process using a non-isothermal compressible flow model. The process simulation is coupled with a thermal viscoelastic material model to predict residual stress, warpage, and birefringence. A finite element analysis is formulated using axisymmetric plate elements to simulate the thermal stress and warpage. Flow and thermally induced birefringence is calculated by applying the stress-optical rule to the predicted residual stress. Experimental validation of injection-compression molded CD-R substrates shows that the simulation well predicts the process and part qualities under various processing conditions.
Flow Analysis of the In-Mold Coating (IMC) Process for Thermoplastic Parts
In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. The coating will then solidify and adhere to the substrate. IMC process is being integrated with conventional thermoplastic injection molding to improve the part surface quality and to protect it from outdoor exposure. This paper presents a Hele-Shaw based mathematical model to simulate the coating flow during the IMC process. Power-law viscosity model is employed to describe the rheological behavior of the coating material. The continuous deformation of the thermoplastic substrate caused by the coating injection is analyzed by means of the PVT relationship of the substrate. The corresponding computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow. The predicted results have been verified by experiments.
Accelerated Weathering Characteristics of Inorganic Pigments in Various Thermoplastic Applications Systems
Iron oxide pigments have been around as a coloring agent for thousands of years. Despite this amazing longevity the question is frequently asked, “What is the UV stability of your iron oxide?” This question has always been answered in a lighthearted if somewhat cynical fashion, “Has your car ever spontaneously unrusted while sitting in your driveway?”The goal of the work represented by this paper is to try to remove the comedic quality of the answer by establishing an experimental set of parameters and providing a quantitative response to this question.
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