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
A General Method of Designing Injection Molds by Straightforward Solution Procedures
The design of injection molds can be accomplished by the state-of-the-art software available on the market. However, in daily practice where quick estimates of the parameters involved are needed, the application of sophisticated software can be time consuming and costly. This paper deals with straightforward solution procedures for optimizing the mold design by taking thermal, mechanical and rheological design criteria into account. Easily applicable analytical methods are given for calculating the heat transfer between the melt and the coolant. It is shown in these calculations how the geometrical layout of the cooling channels is related to the mechanical strength of the mold material. Furthermore, explicit relationships based on resin rheology are presented for balancing the melt flow in runner systems. These proven equations are illustrated by numerous worked-out examples.
Thermal Performance of Hybrid Injection Moulds with Epoxy Inserts
Hybrid injection molds with non-metallic components in the molding zone are being considered for short runs or pre-series. Cast resin tooling is one of the techniques for making the molding inserts. The nonmetallic materials being used have poor thermal properties that tend to increase substantially the molding cycle. In this study, the dependence of the thermal performance of hybrid molds with respect to the cooling layout was studied using epoxy inserts. Experimental data was gathered in terms of temperature at the polymer/mold interface and compared with simulation using the software C-MOLD. The thermal performance is discussed for different cooling layouts.
Medical Grade Copolyesters for Profile Extrusion
Resins used in profile extrusion require high viscosity at low shear rates to improve melt strength and low viscosity at high shear rates to prevent melt fracture. This paper discusses the development of copolyester resins with the desirable rheological properties, as well as good optical and physical properties. The processing, biocompatibility, and sterilization of these resins will also be discussed.
Modeling Polymer Balloons for Angioplasty: From Fabrication to Deployment
Postulating that arterial injury resulting from the angioplasty intervention is a possible predictor of restenosis, a three-dimensional finite element model is proposed to predict stresses during balloon angioplasty. The model simulates balloon folding, insertion and deployment into a diseased artery. This work focuses on the balloon material model and properties, using experimental characterization and inverse modelling. A numerical example, including balloon folding and deployment inside a stenosed artery is also presented.
The Design of the Small Punch Test and its Application to Testing Medical Polymers
The small punch test is a useful technique in the mechanical testing of polymers where limited material is available. This investigation focuses on the latest developments in the small punch test design, including integrated temperature control and environmental conditioning and its use in analysis of polymethyl methacrylate (PMMA) bone cement.
Plastic Medical Enclosures Made without Molds
It has never been easy, in the Medical Products Industry to design and build a custom plastic enclosure when the initial or lifetime quantities do not justify molds or tooling. In the last few years, a toolless technology has been commercialized to allow the manufacture of such enclosures, with minimal up front costs and broad design flexibility. This paper describes the technology, its application, strengths and limitations and provides an economic comparison to the other enclosure technologies used in the industry.
Sequential Injection Molding Using Fast-Response Valve Gate System
Due to the complication in operation mechanisms, commercial valve gate usually delays for about 0.3 to 0.5 seconds once the valve-opening command is given. This signal to operation delay limits its application to 3C thin-wall injection molded parts. In this study, a fast-response gas-driven unit developed for thin-wall gas-assisted injection molding was adopted to perform valve gate control. Verifications of valve-gate opening were monitored using CCD camera, cavity pressure transducers and accelerometer, respectively. All design parameters including gas-valve response characteristics, tolerance between inner piston and cylinder, gas pressure, melt temperature, etc., that would affect valve-gate opening were investigated. The delay time for vale-gate shaft movement in a non-melt environment can be reduced to about 50 milliseconds whereas it increases to about 80 milliseconds in a melt-filled environment. The improved system results in injection molded parts without weld line and good cosmetic quality.
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.
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