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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An Advanced Cavity/Core System Mold for Ultra-Low Pressure Injection Molding-“ULPAC Mold”
An innovative injection mold system with a specific function has been developed for improving surface defects of molded articles. The system mold comprises an insulated thin metal cavity surface and a release-functioning core surface. Immediately after mold-filling under a low pressure such as one third of that in conventional molding, the cavity surface rapidly increases in temperature to develop wettability and adhering, while the resin on the core side is released and migrates toward cavity side to compensate the surface shrinkage. This will bring the merit to produce paint-free articles having accurate surface patterns in molding with downsized machines.
Heat Exchange in Molds for Injection Molding of Low-Viscous Epoxy Resins
The main aim of the research was to study the influence of adjustable process parameters on the breaking load of electrical insulating parts. Those insulating parts have been made by injection molding of low-viscous epoxy resins. Based on planned experiments and statistical analysis it has been concluded that the most influence on breaking load had two parameters: cavity wall temperature and reaction time. Thus, the additional aim of investigation was defined, which is to study the temperature field in molds and to establish the heat balance of molds for this procedure. Based on our own experience in this field, starting with heat exchange in molds for injection molding of thermoplastics, powder thermosets like phenolic and rubber compounds, one difference has been established. Due to long cycle time, some additional factors influence the heat exchange and temperature field in these molds.
The Optimized Design for Gates Location of Injection Molds Based on Filling Simulation and Industry Application
In injection molding process, gates design is of great importance to part quality and productivity. For a certain application, gate design includes selection of the gate number, location, type, and dimension, and it is dictated by the part and mold design. Numerical simulation of the molding process is an effective means that can be used to compare different effects of various gate designs. In this paper gate location design is studied, an industrially practical example illustrate how to use numerical simulation to optimize gate location.
Thin Wall Molding: Achieving Longer Flow Lengths and Decreased Internal Stress with Injection-Compression Molding
Different grades of PC and PC/ABS blends were molded at a wall thickness from 1.5mm to 0.5mm. A comparison was made between high-pressure, high-speed injection molding and injection-compression molding to evaluate flow length, fill pressure, and molded-in stress. In addition several factors specific to injection compression molding, such as mold gap and screw position at the start of compression were examined for their effect on flow length. It was seen that through the use of injection-compression molding longer flow lengths can be achieved and parts as thin as 0.5mm are possible.
Influence of Barium Sulphate on Rheological Behaviour and Mechanical Properties of Medical-Grade PVCs
Barium sulphate (BaSO4) is widely used as a radiopaque additive for medical grade PVC tubing in surgical procedures. The rheological characteristics and mechanical performance of two different medical grade PVCs containing BaSO4 (10-15 % w/w) having two different mean particle sizes (1 and 40 micron) was investigated. The results show significant change in melt viscosity, tensile properties and phase transitions (Tan ? max) with increase in BaSO4 concentration.
Polysulfone-Modified Epoxy Networks Prepared by Reaction Induced Phase Separation
The effect of epoxy/hydrogen-amine ratio and thermoplastic molecular weight on the curing process and final morphology of epoxy thermoset-polysulfone blend is presented. The cure kinetics was followed by differential scanning calorimetry, the beginning of phase separation by was determined by visual inspection and final morphology was analyzed by SEM.
Curing Kinetics and Thermo-Mechanical Properties Modelling of a General Purpose Unsaturated Polyester Resin (UPR)
Using a 3 mm thick mold trying to reproduce common industrial situations, a general purpose UPR was cured with styrene, methyl ethyl ketone peroxide (MEKP) and cobalt naphthenate. Modelling of the curing reaction (using a 2k with 5 central points design), tensile and impact strength and glass transition temperature was accomplished. To obtain close fitting, parameters interaction was considered for modelling.
On-Line Flow Rate and Pressure Analysis with Sensor Fusion
Plastics injection molding has been limited by the lack of observability and controllability, such that it has not been possible to know or control flow rates and pressures at multiple locations in a mold. An instrumentation and analysis method is presented that allows the estimation of flow rate and pressure at multiple points in an injection mold. While potential improvements are discussed, the presented methods will assist real time process and quality control.
Control of the Thermo-Mechanical Environment in Injection Molding
A special tool was designed to allow the injection molding of flat disc geometry under a wide window of thermo-mechanical conditions. This can be achieved by controlled mechanical actions of one of the cavity molding walls, which is able to rotate and move axially (in steady or oscillating modes) during the filling and holding stages. The movements are assured by two servo-actuated electric motors allowing for an accurate control of a previously defined moving sequence.This injection tool was used to mold polypropylene under different thermo-mechanical set-ups, including a filling stage under cavity wall movements (in rotation, compression or expansion modes).Polarized light transmission microscopy and small angle light scattering (SALS) were used to observe and assess the moldings microstructure, including the quantification of the core spherulite size.The results evidence a very large range of microstructural patterns, whose features can be associated to the specifically imposed thermo-mechanical conditions.Furthermore, the evolutions of the microstructure along the disc radius was also assessed.
Study on Mechanical Properties and Material Distribution of Sandwich Plaques Molded by Co-Injection
In the sandwich injection molding process (co-injection), two different polymer melts are sequentially injected into a mold forming a skin/core structure. Sandwich molding is a well established method for producing parts with tailored mechanical performance.In this study the mechanical properties of co-injected plaques have been investigated. Virgin and short glass fiber reinforced (10 and 40%) polypropylene were used in six different combinations of sandwiched layers.Flexural tests were carried out on co-injected samples both parallel and perpendicular to flow direction. Optical microscopy was used to determine the core/skin thickness ratio and to calculate the composite flexural modulus, which was compared to the experimentally measured modulus.
Application and Potentials of Injection Transfer Moulding for Processing Thermoplastics
Injection Transfer Moulding (ITM) is a combination of the well known injection moulding and transfer moulding processes. Although the ITM process provides many advantages compared to conventional injection moulding, ITM is up-to-now only used for the processing of crosslinkable plastics. Research work at the Institute of Plastics Processing (IKV) made the ITM-Process accessible for the processing of thermoplastic materials by use of a newly developed mould.This paper discusses the mould technology, the course of the ITM process as well as the resulting part qualities. Besides, a comparison of the ITM process to conventional moulds with hot runner systems is shown.
Processing Studies in Reactive In-Mold Coating for Thermoplastic Parts
In-Mold Coating (IMC) has been successfully used for many years with Sheet Molding Compound compression molded body panels for the automotive and heavy truck industries. The next logical step is to extend IMC technology to injection molded thermoplastic parts. The objective of this paper is to research the factors that affect IMC flow, cure, and final part appearance. We discuss the rheology of coating candidates for thermoplastic parts and show how it affects the coating process. We use 2D non-steady heat transfer computer code coupled with chemo-rheological analysis to predict cure time. Finally, we present a case study to demonstrate the effect of part thickness and initial molding conditions on cycle time.
Prediction of Production Yields in Injection Molding I
Plastics molders need to continuously improve production efficiency to remain competitive. With increasingly tight specifications driven by Six Sigma quality initiatives, however, such efficiency gains are more difficult to maintain. This paper investigates the use of process capability indices for linear and non-linear regression models based on observed shrinkage data for polypropylene molding parts. Statistical validation of the yield estimates is accomplished through Monte-Carlo analysis. The discrepancy among results indicates that current practices in industry are poor, and care should be taken when using yield prediction methods for process optimization or development.
Novel High Flow Polymers and Their Applications
Novel high flow, low crystallinity polyolefin polymers offer a wide variety of attributes in a broad range of applications. The basic characteristics of these polymers and their usefulness in applications such as hot melt adhesives, flow modification, masterbatches and color concentrates, thermoplastic polyolefins (TPOs), and thermoplastic road markings will be discussed.
A Review of Diffusion in Automotive Polymers
This paper reviews the research over the past number of years on diffusion of fuels and fuel components into polymers used in near engine fluid and fuel delivery systems. The areas investigated cover Fourier Transform Infra-Red (FTIR-ATR) spectrometry and standard immersion procedures to measure the migration of fuel components in a series of fluoropolymer, polyester and polyamide materials at various temperatures.
Composite Material Transmission Cross Member Feasibility
General Motors’ next generation full-size truck frames are currently 80 pounds over their targeted weight. By replacing the current steel transmission cross member on General Motors’ full-size trucks through the application of a composite material transmission cross member, a substantial weight reduction will be achieved. Reducing the weight of General Motors’ full-size trucks will consequently increase the fleet-wide fuel economy for the company’s truck line, allowing CAFE requirements to be met more easily.
Novel Polymer Modifier Improves the Flow Characteristics of TPO Compounds
The enhancement of one particular performance parameter in a Thermoplastic Polyolefin (TPO) is often tied to a decrease in another property. This trade-off is evident in the balance between compound viscosity and impact performance. While low melt index elastomers will result in higher impact performance, the increase in compound viscosity is undesired. This paper discloses the utility of adding ultra-low viscosity modifiers to a TPO to achieve high flow while retaining impact performance.
Thin-Wall Injection Molding Using Rapidly Heated Molds
While gains are achieved via cost reduction and increased portability, thinner and smaller parts encounter more difficulty in molding because of the frozen layer problem. Due to coupled filling and cooling involved in standard injection molding, the relative contribution of the frozen layer in the total part thickness drastically increases as the part thickness decreases, thus resulting in increased difficulty of flow. Resin providers recommend using high speed and high pressure to alleviate the increased molding difficulty. However, the high-speed and high-pressure strategy appears inadequate when molding ultra thin wall parts and microstructures and cannot be efficiently used for delicate structures due to localized high stresses. A thin-wall molding process, wherein the mold surface is rapidly heated during the filling stage, was investigated in this paper. By rapidly raising the mold temperature to above the polymer melting temperature, thin-wall cavities can be easily filled without frozen layer induced flow resistance. Characteristics of this molding process were studied and compared with those of standard injection molding with the aid of molding simulation. A thin-wall molding process for an electrical connector is used to demonstrate the advantages of the new molding strategy over the high-speed and high-pressure molding strategy.
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.
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