bluuebunny/crossref_metadata_2025 huggingface dataset:
The Metallographer's Role in Damage Analysis
Authors: Weilnhammer G.
Published: December 2013

The metallographer's role is of extraordinary importance when clarifying cases of damage. This statement is documented by means of an example of corrosion damage on a brewery pipe.

Several different methods have been applied in order to provide for a final result, such as emission spectroscopy analysis, examination of damage areas under the scanning electron microscope including an examination of coatings by means of EDX analysis and examination of the metallographic section.

The comprehensive formation of a metallographer allows for a responsible examination and a summary of results that provides for an overall picture to clarify beyond doubt the cause of the damage.
Microstructures of Erbium Modified Aluminum-Copper Alloys
Authors: Berghof-Hasselbächer E. , Masset P.J. , Zhang L. , Liu L. , Jin Z. , Schmidt G. , Galetz M. , Schütze M.
Published: December 2013

Alloying with rare earth metals improves to the mechanical properties and corrosion resistance of aluminium base alloys at high temperatures. The rare earth metal erbium may be used for grain refinement. Within a project of computer-aided alloy development based on the CALPHAD (CALculation of PHAse Diagrams) method various alloys were melted on the Al-rich side of the ternary system Al-Cu-Er under argon atmosphere and their microstructures were characterized in the as-cast state or after long-term isothermal annealing (400°C/960 h) by means of different investigation techniques. As a result, the phases fcc(Al), τ1-Al8Cu4Er, θ-CuAl2, η-CuAl, and Al3Er were identified, their compositions and fractions were quantified, and their hardnesses were determined. The experimental obtained microstructures agree very well with the calculated solidification behaviors of the cast alloys. The knowledge gained from this work about the phase compositions and microstructures can also be utilized for the fine optimization of the phase diagram.
Fracture of a Compressor Stator Blade in a Gas Turbine Engine
Authors: Neidel A. , Matijasevic-Lux B.
Published: December 2013

On the occasion of the revision of a gas turbine power plant in Northern Germany, a surface crack was detected in one of the 44 stage 0 compressor stator blades during a routine non-destructive testing of the blades. By then the engine had completed more than 38,000 h of operation. The damaged blade was precision drop-forged and copy-milled of X20Cr13 and for some time was wearing a subsequently applied corrosion protection coating containing aluminium pigments. The blade's condition before the subsequent coating was applied is unknown.

The metallurgical investigation found that the cause of failure was corrosion fatigue.
„How exactly does this work?”
Authors: Reiter K. , Schnarr H.
Published: December 2013

In the course of the miniaturization and compaction of components and assemblies of components, the application of metallographic target preparation methods has seen a noticeable boost in recent years – not just in electronics industry but also in other industries and in the field of quality assurance in general. In this context, methods are as manifold and diverse as there are possible targets. Besides the classical method, that is progressive hand grinding accompanied by constant visual checks, more and more semi-automatic and automatic systems or aids are used, aiming at rendering the preparation process more user-independent, more effective, and more reproducible.

The replication “target preparation” of the DGM working group aims at illustrating common target preparation methods in the field of materialography and at comparing these methods in terms of preparation effort and accuracy by means of typical samples. Besides reaching the target levels, the focus was also on preparation quality. As samples of electronic components/assemblies usually provide all possibilities of combinations of materials and as such impose higher requirements in terms on the preparation as for homogenous materials, they were chosen as test material.

Evaluating the test results revealed the entire range of applied methods with comparable resulting accuracy, but partially differing qualitative results and different levels of effort. Procedures during these preparations resemble each other and as a result of the test, recommendations could be made for target preparation in general.
Characterization of some Lead-Free Bronzes
Authors: Živković D. , Mitovski A. , Novaković S. , Balanović Lj. , Marković D. , Marjanović B.
Published: December 2013

The results of some lead-free bronzes characterization are presented in this paper. Investigated samples, produced in the Company for production, processing and trade of non-ferrous, rare and noble metals “11. mart” AD Srebrenica (BiH), were examined using optic microscopy, hardness, microhardness and electric conductivity measurements in order to determine their structural, mechanical and electric characteristics.
Effect of Cu Addition on Surface Morphology of Bake Hardenable Galvannealed Steel Sheets
Authors: Hong M.-H. , Kim S.-I. , Yang H.-M.
Published: December 2013

The effect of chemical composition on the surface characteristics of the hot-dip galvannealed (GA) steel sheets with a carbon content as low as 15 ppm strengthened by Cu and/or Mn sulfides instead of Ti and/or Nb carbides has been studied. The most important goal for developing the new type of steel sheets is focused on the achievement of the extreme surface quality to fulfill the high aesthetical requirements for defect-free automotive outer panels. The shape and distribution of the surface enrichments of Cu, Mn, Al and O on the GA steel sheets were characterized by OM, SEM and TEM. Especially, formation mechanism of the narrow streaky mark with the width of 50–100 µ m occasionally observed on the surface of GA steel sheets will be presented.
Y2BaCuO5 Particle Distribution in YBa2Cu3O7-y Grains of Melt Growth Processed YBCO Oxides
Authors: Kim C.-J. , Park S.-D. , Park H.-W.
Published: December 2013

Y2BaCuO5 (Y211) particle distribution within YBa2Cu3O7-y (Y123) grains of YBCO samples melt growth (MG) processed was examined. To understand the processing variables on the Y211 distribution, a cooling rate (R
C=1 K/h to R
C=20 K/h) through a peritectic temperature (T
p = 1010 °C), a precursor powder size and composition were changed. Two different Y211 distributions (a linear x-like track and planar butterfly-like pattern) were observed, depending on the processing variables. The linear x-like Y211 tracks were observed in the Y123 samples prepared using a stoichiometric Y123 precursor, whereas the planar butterfly-like Y211 patterns were observed in the Y1.8Ba2.4Cu3.4O7-d (Y1.8) samples prepared using an Y211-excess composition precursor. The track and planar Y211 patterns were clearer at lower R
C (slower growth rate of Y123 grains) and for the smaller Y211 particles. In contrast, the random Y211 distribution was dominant at the higher R
C and for the larger Y211 particles. The Y211 distribution patterns in the Y123 grains were explained in terms of the interfacial energy difference among growing Y123 fronts.
Lacunarity Term as a Basis of Multiscale Quantification of Structural Components Distribution Inhomogeneity of Multiphase Materials
Authors: Chmiela J. , Słota D. , Szala J.
Published: December 2013

The paper presents the quantification results of the inhomogeneity of phase distribution in intermetallic alloys from the Mg-Al-Sr system after die-casting and gravity casting, the quantification results of phase β of alloy Ti-6-4 after hydrogen treatment and cyclic heat treatment, and of intragranular regions of diverse crystallographic orientation in the copper microstructure in a state of strain and in a recrystallized state. The quantification of the distribution inhomogeneity, based on the concept of directional lacunarity, is effective and precisely detects the size of inhomogeneity and the degree of its intensity, irrespective of the morphology of microstructural components. An analytical description of inhomogeneity allows comparing the results of quantification, regardless of the size of the sets analyzed.
Preparing and Etching Titanium to Document Surface Effects
Authors: Gammon L. M. , Boyer R. R.
Published: December 2013

This paper is a follow-up and update of the article “Titanium and Its Alloys” in Volume 9 of the ASM Handbook, Metallography and Microstructures [1]. Because of its inherent characteristics, titanium is one of the more difficult metals to prepare for metallographic examination, as illustrated below. The challenge is to understand and minimize metallographic preparation artifacts through an understanding of their cause. They will be introduced if the wrong preparation steps and/or etching techniques are applied. For example, if one used the metallographic preparation process for a body centered cubic tempered martensitic steel, etching of Ti and its alloys would not reveal the true structure. This article covers the effect of etchant selection and etching time, the effect of remnant mechanical deformation and cold work produced during specimen preparation, the influence of interstitial contamination and enrichment on the microstructure, and the effect of these problems on heat affected zones.
Metallurgical Failure Investigation of Cracked Hook Nuts Used for Upending Gas Turbine Rotors on Site
Authors: Neidel A. , Fischer B.
Published: December 2013

Two types of non-metallic inclusion stringers were found in so-called upending hook nuts, in the vicinity of an indication on the bore wall's surface, first, manganese sulfides that can be expected in this material, and second, endogeneous oxidic inclusions from the steelmaking process. The latter ones, too, can be expected to an extend in the structural steel that was used to make the hook nuts from. However, they are present in an excessive amount and were causative for the decohesions that produced the reported MT indications. The forging process which was employed to produce the semifinished product used to machine the hook nuts from was unable to fragment and disperse the non-metallic inclusions sufficiently as is usually the case.
Metallurgical Failure Investigation of Overheated and Fractured Investment Cast Nickel-base Bolts Made of Inconel 939
Authors: Leggemann S. , Cagliyan E. , Riesenbeck S. , Neidel A.
Published: December 2013

A number of small investment cast nickel-base bolts used for fastening metallic heat shields in combustion chambers of large industrial gas turbine engines were found fractured upon a regular hot gas path inspection in one particular engine. No similar findings were reported from any other engine in the field. The fracture of a single-digit number of these fasteners in an individual engine did not cause the liberation of the respective heat shields, hence no secondary damage occurred. The subject bolts were fractured in the head region that is also used to apply the fastening torque upon assembly of the heat shields. No evidence of fatigue, creep or hot corrosion damage was found. From the results of the metallurgical failure investigation described in this paper it was concluded that the subject bolts failed by torsional and/or tensional overload. Severe embrittlement by precipitation of secondary phases due to long-term high temperature service exposure contributed to the failure. The bolts ran hotter than intended by design. It is likely that cracks were induced in the bolt heads by over-torquing them upon assembly. Those cracks later grew in service.
Metallographic Preparation of Aluminium-Titanium Composites
Authors: Romberg J. , Freudenberger J. , Scharnweber J. , Gaitzsch U. , Marr T. , Eschke A. , Kühn U. , Oertel C.-G. , Okulov I. , Petters R. , Skrotzki W. , Eckert J. , Schultz L.
Published: December 2013

There is no method that allows the simultaneous preparation of titanium and aluminum, so that both phases can be investigated by means of scanning electron microscopy (SEM) at the same time. Especially local orientation measurements by electron back scatter diffraction (EBSD) are challenging as they require a very good surface quality. This study deals with the preparation of aluminum/titanium composites, produced by Accumulative Roll Bonding (ARB) as well as with their microstructural analysis emphasing on the metallographic sample preparation. Well established routes of metallographic preparation for aluminum and titanium are facing serious problems such as rounding of edges, arising of deformation layers, blurred layers and oxide layers. This is of particular concern when these routes are applied to Al/Ti multilayered samples without adaption. This study reveals a route for metallographic sample preparation that enables SEM including EBSD analyses of Al/Ti composites for both phases simultaneously.
Numerical Investigation of Hot Embossing Filling Characteristics
Authors: Kang T. G. , Kwon T. H.
Published: December 2013

In the present study, we aim to investigate the basic flow and filling characteristics in the hot embossing filling stage, which depend on the geometry and processing conditions. For this purpose, we have developed a numerical analysis to simulate hot embossing filling using the finite element method and verified the developed program using the existing experimental data. As s basic study to understand hot embossing filling we have chosen a simple rectangular cavity with repeating protruded parts as a computational domain. The filling pattern was found to be significantly influenced by the variation of thickness of polymer substrate for the same stamp geometry, thermal boundary condition, and the embossing time. Filling from the border of the cavity is clearly observed as the thickness of polymer substrate decreases under the equal wall temperature condition. As for the effect of unequal temperature at the stamp and solid base plate, we found that the filling pattern has been affected by the temperature difference between the two surfaces and embossing time. The localized uprising flow results from the thermal boundary condition and subsequent change in the effective thickness of polymer substrate having enough fluidity to deform.
Effect of Aerodynamics on Film Blowing Process
Authors: Zhang Z. , Lafleur P. G. , Bertrand F.
Published: December 2013

A Computational Fluid Dynamics (CFD) technique using a renormalization group (RNG) k –ε model and Fluent software was employed to analyze numerically the effects of aerodynamics on the air ring cooling system of a film blowing process. An in-line scanning camera system developed in our lab was used to study experimentally the detailed dynamics of bubble instabilities. An operation window for the heat transfer coefficient and the maximum air velocity function was established. The simulation results showed that it is adequate mainly at low BUR (Blow-Up-Ratio) outside of the air ring. The relationship between thermal inertia and cooling air aerodynamics for different bubble geometries was also explored. Different bubble shapes, for the same BUR, produced significant differences in the airflow pattern and heat transfer coefficient. The combination of experimental measurements and numerical simulations indicated that various cooling rates result in important variations in the dynamics of bubble instabilities for different BUR bubbles. It was observed that increasing the cooling rate can destabilize the lower BUR bubbles, but stabilize the higher ones due to the production of different bubble shapes. Finally, it is shown that the bubble instabilities depend on the static pressure distribution along the bubble surface, and that minimizing the pressure gradient can stabilize the bubbles.
A Study of Integration of LIGA and M-EDM Technology on the Micro Injection Molding of Super Thin Plates with Micro Through Holes
Authors: Tseng S.-C. , Chen Y.-C. , Lin C.-H. , Shew B.-Y. , Kuo C.-L.
Published: December 2013

There are still some difficulties in injection molding a super thin plate with micro through holes. Nozzle or filter plates are some examples of typical products. Conventional processes to manufacture nozzle plates of ink jet printer heads are electroplating or laser machining. In order to reduce the production cost and improve the performance of nozzle plates, a new approach, micro injection molding, is introduced to manufacture nozzle plates in this study. The micro mold was made by integration of the LIGA and M-EDM technology to improve the positioning and alignment accuracy. After assembling the micro mold, micro injection molding technique was applied to produce four nozzle plates in one shot. There are sixty micro through-holes on each plate and their diameters have been inspected and met the specification, 101 ± 1 microns, under a proposed vario-thermal molding process. The flow hesitation problem for molding a thin film of 50 microns was then solved. Experimental and simulation results indicated that the most significant factor for molding these nozzle plates is the initial mold temperature. This work recommends that the best initial mold temperature for molding such a thin film with the nozzle array is about 150°C for PP. The manufacturing procedures proposed here are believed to be more accurate and economical, and can be applied to mold similar micro parts.
Carbon Black Filled Polyester as Electrically Conductive Master Batch for Fibers
Authors: Jin X. , Xiao C. F. , An S. L. , Jia G. X. , Wang Y. Y.
Published: December 2013

Carbon black (CB) was added into a matrix of poly(ethylene terephthalate) (PET) by melt processing to prepare electrically conductive master batch (ECMB) for fiber applications. The amount of CB required to achieve a desired electrical property often results in poor mechanical properties of the final fibers. To solve this problem, a type of ECMB with a lower percolation threshold was designed by incorporating titanate coupling agent treated CB and using a matrix blend (adding polyethylene (PE) into PET). The effects of titanate coupling agent treatment and the matrix blend on the percolation threshold of ECMB are discussed and the effect of lower percolation threshold on the mechanical properties of final melt-spun fibers was investigated. The results indicated that titanate coupling agent treatment and a matrix blend are able to reduce the percolation threshold and thereby minimize problems with the mechanical properties of the final fibers, yet maintain the desirable electrical property.
Effect of the Chemical and Morphological Conditions of the Die Wall on the Extrusion of Linear Polyolefins
Authors: Larrazabal H. J. , Hrymak A. N. , Vlachopoulos J.
Published: December 2013

This study examines the effects of average surface roughness and composition of the die wall surface on the critical shear stress for the onset of instabilities in die extrusion. Increasing the average surface roughness of the die wall from 0.1 to 15m produced an increase of the critical shear stress for the onset of flow instabilities by as much as 20% during the extrusion of HDPE. The surface of the extrudates obtained with dies having an average surface roughness greater than 5lm showed lines and grooves along the direction of extrusion. Chrome-plated and nickel-plated dies showed an average 28% increase in the critical shear stress as compared to conventional steel dies. The chemical composition of uncoated steel dies wall surfaces, including the presence of iron oxide, did not affect the critical shear stress for the onset of sharkskin significantly regardless of the type of resin used.
Polymer Processing Extrusion Instabilities and Methods for their Elimination or Minimisation
Authors: Agassant J.-F. , Arda D. R. , Combeaud C. , Merten A. , Münstedt H. , Mackley M. R. , Robert L. , Vergnes B.
Published: December 2013

This paper presents and reviews findings in relation to three key areas where polymer processing instabilities occur. The paper also describes methods that can be utilised to reduce, or eliminate, the particular instability. Using previously published results in each of the three areas and work presented in the paper, physical insight into the three mechanisms is reviewed and compared. Extrusion instabilities develop with increasing extrusion rate and the onset of extrusion instability is often a key limitation to the maximum output of an extrusion line. The sharkskin instability is an exit effect instability that can be modified by changing exit geometries and eliminated using certain additives. The stick-spurt instability is intimately related to wall boundary conditions which can be influenced by certain wall and polymer formulations. Finally volume instabilities occur in the entry region of a die and result in a highly distorted product. The instabilities are related to viscoelastic effects within the die and can be minimised by appropriate die and polymer modification. The paper provides sufficient experimental background to identify the key physical aspects associated with each of the instabilities and this in turn provides insight into the different way each instability occurs and how they can be minimised.
PLLA Morphology Controlled by Dry-cast Process
Authors: Meng B. , Cui F. Z. , Cai Q. , Zhang Y.
Published: December 2013

The influence of solvent evaporation rate, in the dry-casting process, on crystallinity and morphology of crystallizable polymeric membrane was studied. Poly-l-lactic acid (PLLA) was taken as an example. The membranes were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). By controlling the solvent evaporation rate, samples with various crystallinities were prepared. From higher to lower crystallinity the membranes exhibit three types of surface morphology in sequence: granule, stripe and smooth.
Description of the Pressure/Throughput Behavior of a Single-screw Plasticating Unit in Consideration of Wall Slippage Effects for Non-Newtonian Material and 1-D flow
Authors: Potente H. , Timmermann K. , Kurte-Jardin M.
Published: December 2013

Up to now, existing mathematical models can only describe the throughput behaviour of compounding extruders assuming the condition of a wall adhering melt. However, there is a variety of polymer melts, as well as polymer suspensions, ceramic materials and food stuffs, which in the course of manufacturing are wall-slipping. A mathematical model describing the behaviour of the isothermal flow of non-Newtonian materials is developed. In addition to the development of the analytical model, which is based on Flumerfelt et al. [1] and Hirshberger [2], the flow behaviour of wall-slipping polymer melts is also analysed using Finite-Element-Simulations (FE). Comparison of the results for pressure, throughput and velocity profiles along the channel depth shows a very high degree of agreement.
The Reactive Extrusion of Thermoplastic Polyurethane and the Effect of the Depolymerization Reaction
Authors: Verhoeven V. W. A. , Padsalgikar A. D. , Ganzeveld K. J. , Janssen L. P. B. M.
Published: December 2013

The reactive extrusion of thermoplastic polyurethane in a corotating twin-screw extruder was investigated. The polyurethane system consisted of a mixture of 2,4-diphenylmethane diisocyanate (2,4-MDI) and 4,4-MDI, methyl-propane-diol and a polyester polyol. An engineering extrusion model was designed and compared with experimental results. In this validation study the catalyst level, throughput, rotation speed and the barrel wall temperature was varied. A comparison of the experiments with the model showed that the model captured the polyurethane extrusion fairly well. Furthermore, the effect of the depolymerization reaction on the polyurethanes extrusion was investigated. It was found that the extruder operation is gravely affected by the depolymerization reaction: the depolymerization reaction limits the maximal obtainable conversion, stabilizes the extruder operation, and causes undesired post-extrusion curing of the polyurethane.
Numerical Simulation of the Effect of Processing Parameters on the Flow Behavior and Break-through Phenomenon in Co-Injection Molding
Authors: Ilinca F. , Hétu J.-F.
Published: December 2013

In this work, a three-dimensional finite element flow analysis code is used to study the flow behavior during sequential co-injection molding. Non-Newtonian, non-isothermal flow solutions are obtained by solving the momentum, continuity and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. Solutions are presented for the filling of a spiral-flow mould for which experimental measurements are available. The numerical approach is shown to predict the core advance stage during which the core flow front catches up on the skin flow front and the core expansion phase when the flow fronts of core and skin materials advance together without breakthrough. The breakthrough phenomenon is also predicted and the numerical solution is in good agreement with the experiment. Those phenomena are hard to predict numerically and to our knowledge this is the first attempt at simulating the three-dimensional melt behavior during core expansion and core breakthrough. The predicted flow front behavior is compared to the experimental observations for various skin/core melt temperature, skin/core viscosity ratio, and core injection delay. Simulation results are in good agreement with experimental data and indicate correctly the trends in solution change when processing parameters are changing.
Study of Shrinkage and Warpage in Microcellular Co-Injection Molding
Authors: Shen C. , Kramschuster A. , Ermer D. , Turng L.-S.
Published: December 2013

This study investigated the effects of processing conditions on the shrinkage and warpage behavior of a box-shaped, polypropylene part created using a special microcellular co-injection molding process. Results were compared to the shrinkage and warpage of conventional and microcellular injection molded parts. A preliminary study was performed to determine processing condition limits and the steady state conditions for each combination of molding parameters. A 26-1 fractional factorial design of experiments (DOE) was performed utilizing the previously determined processing conditions. The molded parts were measured using an optical coordinate measuring machine (OCMM), which had previously been examined with a repeatability and reproducibility (R&R) study. These measurements were analyzed to determine the processing parameters that had the greatest effect on the shrinkage and warpage (S&W). The results of this analysis indicated that the supercritical fluid content and core-to-skin volume ratio had the greatest effect on the shrinkage and warpage of microcellular co-injection molded parts. The results of the experiment were that a considerable reduction in shrinkage and warpage could be achieved by utilizing microcellular co-injection molding.
Experimental/Numerical Analysis of Chaotic Advection in a Three-dimensional Cavity Flow
Authors: Anderson P. D. , Ternet D. , Peters G. W. M. , Meijer H. E. H.
Published: December 2013

Advection of material volumes in a three-dimensional cavity flow is analyzed by using an experimental setup and a collection of computational tools. The experimental setup for the lid-driven cavity flow makes it possible to study the advection of drops for a wide range of flow parameters. The location of unmixed regions for a specific mixing protocol is predicted by means of the mapping method, which are then used to determine the initial location of the dyed drops in the experiments. Finally, an adaptive front tracking method is used to computationally follow the drops during flow in a precise way. In most cases, a qualitative comparison between the experiments and the simulations is found. In addition, the mapping method proves to be well suited to quickly predict unmixed regions in mixers.
Analysis of Necking Deformation Behavior in High-Speed In-line Drawing Process of PET by On-line Diameter and Velocity Measurements
Authors: Hahm W.-G. , Ito H. , Kikutani T.
Published: December 2013

To clarify the characteristic behavior of filament deformation in high-speed in-line drawing process of poly(ethylene terephthalate) (PET), on-line measurements of filament velocity and diameter were performed. In the process, velocity of the first godet roller was fixed at 2 km/min and the draw ratio was varied from 1.75 to 2.25 by changing the velocity of the second godet roller from 3.5 to 4.5 km/min. For comparison, on-line measurements were also performed for the high-speed melt spinning process at take-up velocities of 2 to 5 km/min. Diameter and velocity profiles of PET filament in the high-speed in-line drawing process indicated that the filament started to deform immediately after passing through the first godet roller (GR-1), and finished its deformation at 40 ~ 60 cm from the GR-1. The region of deformation became narrower and shifted toward the GR-1 with an increase in the draw ratio. Detailed analysis of necking deformation through simultaneous diameter measurements at two positions of close distance revealed that the position of necking deformation fluctuates along the drawing-line and its shape varies significantly depending on the direction of its movement. When the position of necking deformation was shifting toward the upstream, its shape was steeper than the one shifting toward the downstream. Results of the simultaneous on-line measurements of diameter and velocity supported this conclusion qualitatively. The analyzed maximum strain rate at the draw ratio of 2.0 reached a high value of 510 s– 1.
Process Optimization of Thermoforming PP/CaCO3 Composites
Authors: Liu S.-J.
Published: December 2013

Thermoforming of polypropylene/CaCO3 composite sheets has become an important process in industry because of their low cost and good formability. However there are some unsolved problems that confound the overall success of this technique. Nonuniform thickness distribution caused by inappropriate mold design and processing condition is one of them. An L'18 experimental matrix design based on the Taguchi method was conducted to optimize the thermoforming process of CaCO3 filled polypropylene composites. For the factors selected in the main experiment, the assist plug's displacement and velocity were found to be the principal factors affecting the thickness distribution of thermoformed composites.
A Comparative Study of Residence Time Distributions in a Kneader, Continuous Mixer, and Modular Intermeshing Co-Rotating and Counter-Rotating Twin Screw Extruders
Authors: Shon K. , Chang D. , White J. L.
Published: December 2013

Residence time distributions were measured for a Buss Kneader, Kobelco Nex-T continuous mixer as well as intermeshing co-rotating and counter-rotating twin screw extruders using polypropylene with aluminum flakes as a marker. Various modular screw configurations, screw speeds and feed rates were considered. Increasing feed rate and increasing screw speed the mean residence to shorter values and narrows the residence time distribution. Generally, in comparison of the different machines, the intermeshing counter-rotating twin screw extruder has the shortest mean residence time and narrowest distribution of residence times, while the Buss Kneader has the longest mean residence time and broadest residence time distribution.
Screw Drive Power of Single Screw Plasticating Units With Smooth Barrels
Authors: Potente H. , Obermann C.
Published: December 2013

In this contribution the computation of the drive power of single screw machines with smooth feed sections for extruders and injection molding machines will be presented. The drive power will be determined by means of the shear stresses at the barrel wall for the completely melt-filled channels as well as for the polymer melting section of the screw. In order to determine the shear stress and thus the power consumption the correct velocity profiles in the screw channels must be known, taking into account the non-Newtonian flow behavior of the polymer melt. For analytical solutions of this problem extreme simplifications are necessary. For this reason approximation equations are set up, which are based on numerical tests and by means of which a reliable determination of the screwdrive power is possible, knowing the throughput, the temperature development across the screwas well as the melting proile.
Design of Dispersive Mixing Devices
Authors: Rauwendaal C. , Osswald T. , Gramann P. , Davis B.
Published: December 2013

Mixing is one of the main functions of screw extruders. In the analysis of mixing, there are two mixing mechanisms that need to be considered: distributive and dispersive mixing. It is well known that single screw extruders generally have poor dispersive mixing capability, even when dispersive mixing elements are incorporated into the screw design. This paper will discuss the requirements for dispersive mixing, current dispersive mixing elements used in single screw extruders will be analyzed, and the lack of efficient dispersive mixing will be explained. A new generation of dispersive mixing elements will be introduced for use in both single and twin screw extruders and internal mixers. A two and three dimensional flow simulation will be used to analyze the mixing performance of these new mixers. Experimental work on the new mixing elements will be presented in a follow-up paper; the results demonstrate that it is possible to achieve dispersive mixing on single screw extruders that is as good as what can be achieved on twin screw extruders. The implications of these results on the compounding industry will be briefly discussed.
Using Computational Fluid Dynamics to Investigate the Flow of a Viscous Fluid in a Cavity with Oscillating Boundaries
Authors: Overd M. M. , Generalis S. C.
Published: December 2013

Many everyday engineering applications crucially depend on the mixing efficiency of the appropriate hardware. Chaotic mixing is pertained to be an effective way of attaining high levels of mixing. In this work we report on viscous fluid flow in a cavity, with oscillating boundaries, that exhibits such chaotic motion.

Using computational fluid dynamics we explain the transition from order to chaos which can be observed by a cascade of the trajectory orbit of particles as the time period of oscillation is increased. As the system moves from order into chaos it is shown that a particle will be displaced from ordered streamlines to the point where it moves throughout the whole low domain thus showing that good mixing is present. An attempt is also made to characterise the transition to aperiodicity, for the studied configuration.
Optimization of the Weldline Strength in Gas-assist Injection Molded Thermoplastic
Authors: Liu S.-J. , Ho C.-Y. , Chang J.-H. , Hung S.-W.
Published: December 2013

Gas assist injection molding has increasingly become an important process in industry because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that confound the overall success of this technique. Weldlines success of this technique. Weldlines form wherever polymer flow fronts meet is one of them. In this report, an L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of gas assist injection molded thermoplastics. Experiments were carried out on an 80-ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. A dumbbell-shape mold cavity was used. After molding, the weldline strength of the parts was measured by a tensile tester For the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of gas assist injection molded thermoplastics. Weld strength decreases with the length of gas penetration. In addition the weldline strength of gas assist injection molded parts was found to be generally weaker than that of conventional injection molded parts.
Wire Coating by Drawdown of an Extruded Annular Melt
Authors: Slattery J. C. , Giacomin A. J. , Ding F.
Published: December 2013

An analytical solution is presented for wire coating by drawdown of an extruded annular melt. The solution is developed with the assumption that the pressures inside and outside the film are equal; a process in which these pressures differ, such as a vacuum inside the film, is treated as a limiting case.
Simulation of Blown-Film Process Taking Account of Cooling-air Effect
Authors: Akaike O. , Tsuji T. , Nagano Y.
Published: December 2013

Numerical simulation of blown-film process of plastics provides a tool for air ring designs and suitable polymer properties. Although cooling-air plays a key role in the process ability and film properties, there have been few research works taking correct account of the cooling-air effect. Numerical analyses of heat transfer from the surface of molten polymer to cooling-air were conducted using precise turbulence models and then simulations of bubble shape of blown-film process were performed under the air pressure and the thermal boundary conditions estimated from the numerical analyses of cooling-air. The film bubble shape predicted has coincided well with experimental data and it is confirmed that the bubble stability is strongly dominated by characteristics of cooling-air flow and heat transfer near the bubble surface.
Fitting of K-BKZ Model Parameters for the Simulation of Thermoforming
Authors: Novotný P. , Sáha P. , Kouba K.
Published: December 2013

Thermoforming is characterized by large deformations of the polymeric material being processed. The simulation is complicated by the fact that an elastic material model cannot principally describe the thermoforming deformation precisely. In this respect non-linear and time-dependent viscoelastic behavior of the polymeric material has to be taken into account. In our research we used the K-BKZ model capable of describing viscoelasticity and large deformations. The parameters of this model were determined experimentally using a simple testing method. The method is derived from plug-assisted thermoforming. Computer analysis was used to evaluate the experiments: The tests performed were simulated using FEM (Finite Elements Method) repeatedly with different material parameters. The material parameters leading to a minimum sum of squares of differences between experimental and simulated values estimate the tested material behavior. It has been found that the final shape and the wall thickness distribution show a significant dependence on the material properties in case of deep thermoforming.
Weld Line Strength in PC/ABS Injection Moldings
Authors: Semba T. , Hamada H.
Published: December 2013

Polycarbonate(PC)/ABS is a very common immiscible polymer blend. The internal structure such as distribution of each component in the injection moldings of PC/ABS would be strongly affected by the processing parameters. Especially, the weld line formed by meeting two melt flows and the internal structure at the weld area would be a very complex form. By observing the etched samples of PC/ABS injection moldings using scanning electron microscopy, a weld part with fine dispersion of ABS was found in the area below V-notch. When tensile load was applied perpendicular to the weld line, the fracture initiated from the V-notch, but the crack propagated along the interface between the weld part with fine dispersion and the part behind the weld part. This leads to unique characteristics of the weld strength.
Capillary Flow of Hard-Metal Carbide Powder Compounds
Authors: Hausnerová B. , Sáha P. , Kubát J.
Published: December 2013

Experimental data relating to capillary flow of hard-metal carbide powders compounded with various polymeric binders are presented. Such powder—binder mixtures are used for the production of sintered hard-metal carbide components, mainly by injection moulding. In addition to measurements of their rheological behaviour in a capillary rheometer, the compounds were also subjected to thermo-gravimetric analysis in order to assess the ability of the binder to debind properly. The binder composition was varied from paraffin wax and its combinations with polyethyleneglycols to multi-component binders consisting of polyethyleneglycol, polyethylene, ethylene/vinyl acetate copolymer, and paraffin wax. Two kinds of hard-metal carbide powders differing in particle size distribution (uni-modal, bi-modal) were used. Although the compounds containing the simpler binder types had acceptable flow properties, their debinding behaviour was unsatisfactory. The multi-component compounds exhibited considerably better debinding; their flow was stable within a wide range of shear rates. Flow instabilities appearing at high solids loadings can limit the processability of the compounds used.
Computer Controlled Rotational Molding of a Hollow Femur for 3-D Photoelastic Analysis
Authors: Teoh S. H. , Lau C. Y.
Published: December 2013

The rotational molding technique was utilized in the fabrication of hollow femur models for the expressed purpose of photostress analysis. Advances in computer control coupled with the development of proper experimental protocols enabled the consistent and automated reproduction of the joint model. Such considerations proved to be critical in overcoming the limitations of prevailing rotational molding operations. The use of hollow rotation molded models was advantageous as it better represented the physiologic constitution of real bones, thereby, conferring a greater degree of accuracy in the photostress experiments. The fabrication of the hollow models entailed flow visualization studies, which assessed the variation in rotational speeds with time as well as the optimum relative rotation speeds to be adopted. The preferred mode of rotational motion was also determined through a series of simulated experiments to determine whether steady or repetitive cyclical rotational modes were more beneficial. The fabricated hip models were loaded and the stress profiles examined. Contour maps of the stress fringes manifested in the photoelastic analysis indicated several sites of stress concentrations. These sites coincided with physiologic patterns of hip fractures, verifying the validity of the hollow femoral models. Computer controlled rotational molding has proven to be a feasible manufacturing process in the development of hollow physiologically representative femur models.
Residual Stresses and Birefringence in Injection Molding of Semicrystalline Polymer
Authors: Guo X. , Isayev A.I.
Published: December 2013

The viscoelastic process simulation of the idealized injection molding process for various isotactic polypropylenes having different molecular weights are conducted by using the theoretical formulation developed in the first part of the present study. Molding experiments are performed under a variety of molding conditions, and birefringence measurements are carried out on the molded samples. Based upon the experimental and simulated results of the residual stresses and birefringence, the effects of molding conditions and molecular weights are studied. The influences of flow-induced crystallization kinetics on the buildup and relaxation of residual stresses and birefringence in the moldings are discussed. It has been found that, due to the absence of the flow-induced crystallization in the core region, the flow stresses and birefringence introduced in that region during the filling stage relax shortly after the cavity is filled. Moreover, the low stresses and birefringence get frozen-in due to the occurrence of the low-induced crystallization are relatively large and located within a very narrow region close to the mold wall. The main contribution to the overall residual stresses is found to be due by the residual thermal stresses that are introduced by the progression of crystallization during the postfilling stage. The distribution of the residual birefringence in the moldings is closely related to that of the crystalline microstructure pattern and less dependent upon the level of overall residual stresses.
Solidification Behaviour of PA6/iPP Blends at High Cooling Rates
Authors: Colletti C. , Piccarolo S. , Valenza A.
Published: December 2013

The non isothermal crystallization behaviour of two model blends of immiscible polymers (an isotactic polypropylene and a polyamide-6) was examined by a quenching procedure within a range of cooling rates from 0.1 to above 1000°C/s in order to emulate the solidification conditions arising during polymer processing. The final structure of the blends was analyzed by density and WAXD and the transition from stable to metastable phases in the blends and the pure homopolymers was compared examining their dependence on cooling rate. This shows that crystallization in the blends is always faster since the transitions move to larger cooling rates. Observation of morphological details suggests that this can be due to enhanced nucleation at the interface. The density variation in the case of the polyamide-6 rich blend is larger than expected from an additive volume contribution which may be ascribed to development of microvoids at the interface. In the case of the isotactic polypropylene rich blend the additive volume contribution is consistent with experimental observations.
A Network Analysis of a Screw Mixing Zone
Authors: Klason C. , Jinescu V. V. , Poştoacǎ I.
Published: December 2013

Starting from our previous results concerning the melt flow during the dispersive mixing zones of Maddock and Egan type, one establishes relations for the pressure variation, appropriate for incremental calculation. Because generally the melt flow along the mixing zone is non-isothermal, one establishes relations for the temperature variation along the mixing zone, namely: temperature variation caused by external heating, by internal friction, by external friction and due to melt compressibility.

By using the established relations one develops a network procedure for pressure and temperature variation calculation along the mixing zone. The computer program based on the network procedure was used to calculate a usual mixing zone for a 63.5 mm extruder-screw. The program gives the possibility to represent the pressure and temperature variation between the inlet and the outlet of the mixing zone. This is useful when we are interested in the optimum design of such mixing zones.
An Investigation of Venturi and Coanda Effects in Blown Film Cooling
Authors: Sidiropoulos V. , Vlachopoulos J.
Published: December 2013

Numerical simulation of turbulent air flow tangentially impinging on a blown film bubble has been carried out. The cooling air is assumed to originate from a dual orifice adjustable air-ring. The stream line pattern and heat flux are determined through a finite volume numerical technique using a version of the so called k-∊ modeling. It is shown that as the air flows through the air ring passage relatively large under-pressure is created (Venturi effect), which applies a suction to the bubble. Depending on the flow rates and geometrical configurations the air jet may attach itself (Coanda effect) to either the air ring surface and/or to the bubble. The Coanda effect has a significant influence on local heat flux. The numerical results suggest that the Venturi and Coanda effects influence significantly process stability, production rate and final film properties.