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.
The main purpose of this study was to evaluate the efficiency of a injection family mold for produce security caps for pharmaceutical bottles using the computer aided design (CAD) and the computer aided engineer (CAE) tools. Such caps are made of two pieces: an internal and an external. A conventional four cavity mold with removable cores, as well as, an eight cavity family mold, both with an x" type distribution was evaluated. A manufacturing cost analysis for both molds was done finding the eight cavity mold as the cheapest one to be used for manufacturing such caps. The feasibility of these molds depends on the production cycle time the labor work shifts and the price of the injection mold."
This paper presents the work developed for last years in TIIP, Associate Unit to CSIC, in order to make easier and faster, the task of designing a thermoplastic injection mould. During a mold design, there is a great amount of repetitive tasks that makes the designer loose a lot of time.The work presented consists of a semiautomatic software that covers the complete generation of the mould, according to standard components. It also allows the most suitable orientation of the part into the mould, according to specified criteria, and the generation of its parting surface, and cavities.The software has a very easy and intuitive running, and it follows the methodology of mould design developed in TIIP.
Tooling has lived through substantial changes. The toolmaker has been, first of all, the designer and maker in one and the same person. Then, in the second part of the 20th century the division took place in the form of the increased specialization. Three function specialists: the mold designer, function makers of mold elements, and the assembling operators, toolmakers exist. The introduction of computers caused new redistribution of tasks. The mold designer activities (CAD) are followed by the mold manufacturing-planning phase (CAP), which includes also the software development for NC-equipment (CAM). The function element makers started to disappear they are materials machining-operators. A new reintegration, of part and mold designer functions will be discussed.
The main objective of this project consisted on the development of a measure container prototype and its mold, using Computer-Aided Design (CAD) / Computer Aided Engineer (CAE) / Computer Aided Manufacture (CAM) tools, through a 3D program and a simulation software of the thermoforming process, to determine the geometry corrections in the part design. The part prototype was carried out by using the material deposition rapid prototyping (RP) technique and the mold prototype was carried out for the machine technique. To evaluate both prototypes, the results obtained in a thermoforming machine and in a simulation software were compared.
This paper focuses on the study of the single-shot rotational foam molding technology for producing integral skin polyethylene foams. In this context, parametric studies over the mold rotational speed and in-mold temperature transition have been conducted. In conjunction with the utilization of the particle size difference between foamable and non-foamable resins, it has been found that increased mold rotational speeds can significantly improve the crucial separation of the time of formation of the skin layer from that of the foam layer. The proposed processing strategies secure the formation of a distinct layer of solid skin surrounding the high quality foamed polyethylene core.
The nature of powder flow and its effect on particle deposition in rotationally molded parts is studied in this work. Experiments were carried out to see the effects of various parameters such as powder characteristics and operating conditions on the deposition pattern. Models for cohesive forces were developed and their effects on particle movements were estimated. Results indicate that the polymeric powders are cohesive enough to prevent size segregation at room temperature. When heating, the particles become sticky and a relatively new phenomenon of cohesive segregation is seen.
The performance of a new generation of single site polyethylene resins is compared to that of conventional Ziegler-Natta (Z/N) resins. Results from rotational molding trials showed that under comparable molding conditions, the mechanical properties of parts produced from single-site resins superior to those of Z/N resins. Moreover, the densification of the single site resins is complete at significantly shorter residence time in the oven versus Z/N resins. The processing window is wider and shifted to lower temperatures for the single site resins compared to the Z/N resins. The enhanced densification arises from faster dissolution of bubbles formed during the heating cycle.
Polymer sintering is a formation of a homogenous melt through the coalescence of powder particles during the heating cycle of rotational molding. Although the importance of surface tension in rotational molding has been recognized as one of the most important controlling parameters, there is only limited information on the role of surface tension in rotational molding.The objective of this work was to develop an experimental technique for characterizing the surface tension of materials used in rotational molding. The effect of surface tension on sintering was investigated. This paper summarizes the results of the effect of surface tension on the rotomoldability of selected polyethylene copolymers and blends.
There is a consensus in the rotational molding and related industries that crosslinkable polyethylene (XLPE) is the choice material for gasoline-type reservoirs. Field failure of XLPE-based reservoirs is not common, and to resolve one such situation involving hydraulic fluid tanks, students of Pittsburg State University's plastics engineering technology program are utilizing the concepts of six sigma (DMAIC), define, measure, analyze, improve and control. In collaboration with the reservoir producing and user companies, the problem situation was defined; film products from the hydraulic fluid-XLPE tank interface clog up the fuel filter system and subsequently result in damaged pumps. Preliminary DSC (differential scanning calorimetry) measurements indicate similar thermal transition profiles for both film and tank materials, suggesting that the film is a plasticization rather than reaction product. Additional analysis of DSC, torque rheometry, rotational molding and solvent test data yield insightful information and the optimum processing parameters for improving and controlling XLPE hydraulic reservoir production.
Acetal copolymers can be rotationally molded into a wide variety of shapes and sizes, using conventional grinding and rotational molding equipment. Celcon® M15HP acetal copolymer is one such grade that was recently developed by Ticona to offer substantially improved physical, mechanical and thermal properties over general purpose grades of acetal copolymer. In particular, it exhibits higher tensile strength, flexural modulus, impact resistance, heat deflection, fatigue endurance, abrasion resistance and surface hardness.Because of its extremely low permeability to gasoline and alcohol, along with its excellent long-term chemical resistance and dimensional stability, acetal copolymer is currently being evaluated as a potential fuel permeation barrier to meet proposed CARB and EPA evaporative emissions regulations for small offroad engine and marine fuel tanks, which are found in numerous products manufactured by the Lawn & Garden, Outdoor Power Equipment, Recreation Vehicle and Marine industries. This paper will present some basic guidelines for the rotational molding of acetal copolymer, along with some techniques for data generation and analysis using six-sigma methodology, which have enabled us to optimize the rotational molding process around this material.
A new slip-flow model is developed to simplify and to overcome the current numerical difficulties of two-dimensional rotomolding model in predicting the internal air temperature inside the mold during the rotomolding process. The lumped-parameter system and coincident node technique have been incorporated with the Galerkin finite element method to address these rotomolding problems. This proposed methodology allows macroscopic multi-layered deposition" of heating polymer powder onto the mold surface in order to account for the complex thermal interactions between the internal air and its surroundings (mold and polymer). A semi-implicit method is applied to deal with the overall internal air temperature inside the mold. The predicted results agree with the available experimental data for rotomolded parts of cross sectional thicknesses up to 12 mm."
The analysis of heat transfer in the rotational molding (rotomolding) process is a non-linear multi-dimensional problem. Using the two-dimensional (2-D) model from Lim and Ianakiev the proposed phase-change algorithm, warpage formation, thermal distribution in the warped part, cycle time prediction and other key thermal properties have been investigated. The phase-change algorithm has decreased the computational non-linearity, while maintaining the level of accuracy. Additional useful observations and predictions are also presented from the warpage simulations.
In plug assist thermoforming, surface friction strongly affects the final part thickness distribution. This work investigates the effect of plug material, plug temperature, and sheet temperature on coefficient of friction between the plug and sheet. Three different plug materials (epoxy syntactic, engineering thermoplastic nonsyntactic and engineering thermoplastic syntactic) with a range of friction coefficients were investigated for thermoforming polypropylene sheet. The coefficient of friction was assessed using simulation software (T-SIM®). Coefficient of friction values were varied in the simulation software until the thickness distribution predicted by simulation was similar to that obtained experimentally.
For thermoforming simulation a measurement technique was developed to enable material characterization. A holistic approach was chosen to measure material parameters and the coefficient of friction. An improved “reverse-engineering” algorithm generates the material data.This paper explains the measurement devices and emphasizes the importance of the coefficient of friction. While static and dynamic friction occur in the thermoforming process, for simulation a “mixed” coefficient is used. As an example PET and ABS are investigated.
A new approach has been developed for modeling hot-drawing of semi-crystalline polypropylene (PP) under conditions similar to industrial thermoforming. The proposed model encompassed components derived from a combination of concepts including Buckley et. al. [i], DSGZ [ii], G'Sell-Jonas [iii], theory of linear elasticity and multi-dimensional stresses based on a biaxiality ratio. The resulting constitutive model precisely describes the yield, strain softening followed by flow and hardening observed in hot-drawing of polypropylene.
There is a need for high quality, high gloss, scratch resistant, weatherable Acrylonitrile-Butadiene-Styrene (ABS) sheet for exterior applications. This sheet can be obtained by co-extruding a thin capstock layer of a weather resistant and weather protective acrylic resin over an ABS substrate. This paper discusses the key parameters for the design of this sheet. It is intended to be an aid for sheet converters and those specifying weatherable coextruded sheet. The Dow Chemical Company and Atofina Chemicals, Inc. have combined their materials expertise to manufacture and test the sheet structures presented in this paper.
Although hot embossing is gaining popularity in the replication of micro-structures, it needs a breakthrough improvement on cycle time reduction before it can become a mass-production process. Previously, the authors developed a Rapid Thermal Response (RTR) molding process for enhancing the quality of conventionally molded parts. In the current study, this technology was adopted to hot embossing micro-structures. In the paper, RTR hot embossing machine setup and mold construction were described, and the results of fatigue test and RTR embossing were presented. Microstructures with characteristic dimension of 2?m were successfully replicated with substantially reduced cycle time. The fatigue test result indicated that this embossing technology is durable and reliable for microscale feature replication.
Recent progress in computer-aided polymer processing analysis demonstrates the need for accurate description of the material behavior under the conjugated effect of applied stress and temperature. In this work, we are interested in the characterization of circular thermoplastic membranes, ABS and HIPS thermoforming grade, under biaxial deformation using the bubble inflation technique. Hyperelastic (Mooney-Rivlin, Ogden) models are considered. First, the governing equations for the inflation of a flat circular membrane are solved using a dynamic finite element model (triangular membrane elements), and there after, a neuronal algorithm is employed to determine the materials constants. Moreover, the influence of the Mooney-Rivlin and Ogden constitutive models on the thickness and the stress distribution in the thermoforming sheet are analysed.
Hot embossing is an effective method for transferring micro-features in mold to plastic film or plates. Improving uniformity of pressure and reducing cycle time are constant challenges with MEMS or NEMS applications. This paper reports development of a rapid heating and uniformly pressing system for micro hot embossing. Direct fluids are used as working media. The seal film/mold/substrate stack is placed in a closed chamber. Then the fluid is introduced into the chamber for heating and pressing the stack. Micro patterns in the mold can be successfully replicated onto the substrate. Perfectly uniform embossing pressure throughout whole area can be achieved. The cycle time is less than 30 seconds.
Closed mold reactive liquid composite molding processes such as resin transfer molding (RTM) and any of its variations such as vacuum-assisted resin transfer molding (VARTM), Seemann Composite Resin Infusion Molding Process (SCRIMP), etc, are environmentally friendly alternatives to open mold processes, which have been traditionally employed to form large composite parts. However, in most cases, in order to improve and/or protect the part surfaces, gel coating is required. The gel coat is applied with the mold open, which releases harmful volatile organic compounds (VOCs) to the environment, partially compromising the benefits of the closed mold processes. In-mold coating (IMC) is an attractive alternative to gel coating to eliminate VOCs. IMC is a coating operation performed by injecting a coating material onto the surface of the substrate with the mold closed. The coating flows by compressing the substrate under pressure. In the present work, we develop mathematical models to predict the filling and packing stages of IMC for RTM substrates. These models include the effect of the compressibility of the substrate and mold.
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