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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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.
Multi Functional Colorants for LDPE Articles
Functional performance of slip and release additives was investigated in low density polyethylene (LDPE) pigmented injection molded plaques. Coefficient of friction and adhesion studies were used to characterize migration of slip agents to the polymer surface and interaction between composition components. An attempt was made to combine different additives to achieve optimum slip performance while minimizing organoleptic impact of packaging material.
Is Trouble-Free Colored Wire and Cable Possible?
Color plays a critical role in the manufacture of wire and cable products. Colors are frequently created in wire and cable products through the use of color concentrates. There are some misunderstandings about how the concentrates affect the finished products. Because color accounts for a relatively tiny part of a compound, for example, some manufacturers neglect its potential influence on their products. Others make color concentrates their first suspect when problems occur.
Computer Simulation of 3D Short Fiber Orientation in Injection Molding
This paper develops a true three-dimensional numerical approach to simulating the melt filling and fiber orientation in injection-molded part of complex geometry. An efficient finite volume method is combined with VOF method to solve the melt flow during molding. The fiber orientation distribution is described by the second-order orientation tensors. The three-dimensional orientation of fibers is determined through the Folgar-Tucker equation, in which an interaction coefficient is introduced to account for the fiber-fiber interaction. Several example cases are simulated to verify the predicted melt front advancement and the corresponding fiber orientation. An industrial case with complex geometry is also studied to illustrate the capability of the proposed methodology.
Three-Dimensional Computer-Aided Mold Cooling Design for Injection Molding
Mold cooling system design in injection molding is of great importance because it is crucial not only to reduce molding cycle time but also to improve part quality. Traditional mold cooling analysis is based on the hybrid finite-difference/ boundary element (FD/BEM) approach. This approach was developed to accommodate the conventional 2.5D Hele-Shaw flow-based shell element model. In this paper, a true three-dimensional mold cooling analysis approach is developed. A fully tree-dimensional numerical analysis faithfully simulates the effects of part geometry, cooling system design, and ambient temperature on the solidification of the part. Finite volume method (FVM) is adopted as the numerical engine of the new approach. This developed approach is proved from numerical experiments to be a cost-effective method for true 3D simulation in injection mold cooling analysis.
Optimization of the Warpage of Fiber Reinforced Thermoplastics by Influencing the Fiber Orientation
This paper describes a new commercial simulation tool to simulate the injection molding process and the warpage of fiber reinforced thermoplastics considering the anisotropic behavior. A full 3D formulation of the Navier-Stokes equations with a VOF algorithm for the description of the free surface motion is used to simulate the filling process. The transport of the fiber orientation is calculated by the Folgar-Tucker equation using a hybrid closure approximation. The resulting fiber orientation tensor is used for the calculation of the anisotropic mechanical behavior. The Halpin-Tsai equations provide the anisotropic material data for the calculation. Through an real-life example it will be shown that the knowledge of the fiber orientation can be used to optimize the runner system in order to change the local fiber orientation and thereby to optimize the warpage of the part.
Effect of Colorant Carriers on Strength of Weld Lines in Polypropylene
In this study, the effects of polyethylene (PE) and polypropylene (PP) colorant carriers for various levels of loading on the short-term strength of weld lines in homopolymer polypropylene are quantified. Tensile bars (“dog bones”) were molded with an intentional weld line in the gauge length of the bars for a variety of material mixes. When tested at room temperature, the colorants with the polyethylene carrier drastically reduced the tensile elongation of the bars when compared with an unpigmented sample. The reduction was so severe that the PE-carrier specimens broke before yielding, thus exhibiting significant loss of strength. Samples of PP having the colorant with the PP carrier, while breaking at significantly lower elongation than their unpigmented counterparts, showed no reduction in weld-line strength because they yielded. Elevated temperature results are less dramatic, the unpigmented and PP-colorant samples yielded and stretched beyond 450%, while three-fifths of the PE-colorant specimens exhibited a yield. A PP co-polymer with PP-based colorant was also studied. In addition, slow strain-rate data is presented for a few compounds, and the rate / temperature dependence is discussed. Finally, several samples were aged at elevated temperature and subsequently tensile tested at room temperature. The results showed reductions in elongation but not weld-line strength.
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