bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical and Memory Properties of CuAlNi by Directional Solidification
Authors: Zhiping Liu , Woguang Li , Zhanhua Yin
Published: December 2013

Cu-Al-Ni shape memory alloy was fabricated under directional solidification in heated mold continuous casting equipment. The results show that it has distinct textures. Due to these strengthened textures, it has excellent mechanism, fatigue and memory performances.

The Ø 1.5 mm wire has a tensile strength of 910 MPa, elongation of 18.76%. Under 4% strain, the repeat tensile fatigue was up to 38560 circles and the recovery rate is 100%.
Wear/Friction Behaviour of FeB and FeB/h-BN Coatings Sprayed by Atmospheric Plasma Spraying
Authors: Ozdemir Ismail
Published: December 2013

The crushed and rounded ferroboron (FeB) powders of Fe-18.8B-0.2C-0.5Si-0.8Al (wt.%) were deposited onto an aluminum substrate by atmospheric DC plasma spraying to improve its tribological properties. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties similar to graphite were incorporated into the boride powders as a solid lubricant by a sintering process to obtain protective coatings with a low friction coefficient. As-sprayed coatings are composed of mainly FeB, iron matrix supersaturated with boron owing to the rapid solidification of molten droplets flattened on a substrate. The friction and wear behaviour of each coating were evaluated using a ring-on-disk type wear tester in paraffin based oil with an air atmosphere. It was found that sintering of iron boride powder with h-BN powder (5 wt.%) is an acceptable method for producing a protective composite coating against friction and wear. The evaluation of friction and wear results shows that iron boride coatings exhibit high seizure load and good anti-wear performance.
Metallographische Untersuchungen an Bauteilen
Authors: Stets Wolfram , Tschöpe Jörg
Published: December 2013

Kurzfassung

Im Zuge der immer schnelleren Verfügbarkeit von Maschinen und Anlagen steigt die Bedeutung der Bauteilmetallographie als Werkzeug der Schadensanalyse und Qualitätskontrolle. Das Institut für Gießereitechnik arbeitet auf diesem Gebiet mit einem tragbaren Auflichtmikroskop mit bis zu 500-facher Vergrößerung. Die Bilder werden mit Hilfe einer Digitalkamera aufgenommen. Anhand von verschiedenen Untersuchungsfällen wird die Leistungsfähigkeit des Systems demonstriert. Es wurden bis zu 37 t schwere Gussstücke aus Gusseisen mit Kugelgraphit sowie Pumpengehäuse aus Duplexstahl untersucht. Auf der Grundlage der Untersuchungsergebnisse konnten Expertisen für die weitere Verwendbarkeit der Gussstücke erstellt werden.
Boride Layer Growth Kinetics of the Borided Hypoeutectoid Plain Carbon Steels by the Powder-Pack Method
Authors: Çelik Osman Nuri , Aydinbeyli Nedret , Gasan Hakan
Published: December 2013

In the present work, kinetics of boriding of hypoeutectoid plain carbon steels has been studied. Boriding of the AISI 1010, 1020, 1040 and 1060 test materials has been performed by means of a powder-pack method using EKabor 2 ® powders. Boriding heat treatments were performed at 1173 K, 1223 K, 1273 K and 1323 K for 2, 4 and 6 h. The borided materials were characterised by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and optical microscopy in order to determine the phase contents (FeB and Fe2B). Boride layer thickness was determined by optical microscopy and hardness by microhardness testing. The thickness of borided layers measured ranged from 71 to 362 μm. It was found that the effect of boriding time and temperature on the increasing boride layer thickness was more significant than the effect of increasing the carbon content. The hardness of the boride layers ranged from 1243 to 1740 HV. The kinetics of the reactions, K=K0exp(-Q/RT), were determined by varying the boriding temperature and time for the materials. A correlation between the C content and activation energy has been established by this study.
Quantitative 3D-Gefügeanalyse — Stereologie oder Tomographie
Authors: Velichko Alexandra , Mücklich Frank
Published: December 2013

Kurzfassung

In der Materialforschung ist die dreidimensionale Ausprägung des Gefüges der Schlüssel zum Verständnis des Zusammenhanges zu den Herstellparametern einerseits und den Eigenschaften des Werkstoffs andererseits. Die prinzipielle Frage ist, ob es unbedingt nötig ist, alle Gefügemorphologien in 3D zu untersuchen, oder ob es ausreicht, bei den Gefügen die viel praktischere 2D-Bildanalyse zu nutzen und die 3D-Parameter nach stereologischen Beziehungen zu berechnen. Erwartungsgemäß gibt es bei der Vielfalt der Gefüge und den entsprechend komplexen Zusammenhängen keine generelle und einfache Antwort darauf. In diesem Beitrag wird am Beispiel der Korngrößenbeschreibung und damit verbundener Kennzahlen reflektiert, wann die 2D-Bildanalyse mit stereologischen Schätzungen zur 3D-Situation praktikable Ergebnisse liefert und wann die Gefügetomographie unbedingt nötig ist, um geeignete Informationen über das räumliche Gefüge zu gewinnen. Ausgehend von den bildfeldbezogenen vier Grundparametern des Gefüges wird dazu die Korngrößenbestimmung unter der Annahme von Kornformen mit zunehmender Komplexität (Kugel — äquiaxiale Polyeder — nichtäquiaxiale Polyeder — nichtkonvexe Kornformen) diskutiert. Es wird gezeigt, dass bei nicht konvexen unregelmäßigen Kornformen die 3D-Charakterisierung für sichere Klassifikationen und auch die Quantifizierung räumlicher Kenngrößen wie der Konnektivität oder der Teilchenzahl im Volumen unverzichtbar ist.
Properties of Alumina Coating Formed by Microarc Oxidation Technique on 6061 Aluminum Alloy
Authors: Polat Aytekin , Usta Metin , Makaraci Murat , Ata Ali , Tas Zakir
Published: December 2013

In this study, thick and hard alumina coatings were produced on 6061-T6 Al alloy substrates for different oxidation times and current densities by using of microarc oxidation (MAO) technique in an alkali-silicate electrolytic solution. The influence of oxidation time and current density on the kinetics, phase composition, hardness, surface roughness and structure of the coating were investigated. It is found that the kinetics of coating mainly depends on applied current density and oxidation time. The XRD results revealed that the coatings are composed of mainly α-Al2O3, γ-Al2O3 and mullite phase. The relative ratio of harder and denser α-Al2O3 phase increases with increasing current density and oxidation time. For the same coating time, the position of maximum hardness of coatings moves away from the substrate-coating interface to the coating surface with increasing current density. The surface roughness of coating is a function of coating thickness and increases with increasing deposition time and current density. The surface micro hardness of Al 6061-T6 alloy substrate was increased up to 2200 HV hardness after the coating.
Particle Distribution and Tool Wear in Friction Stir Processed Al-SiCp Coatings
Authors: Rao Kalvala Prasad , Patil Anand , Rangaraju RaghuRaj , Raja K.S. , Misra M.
Published: December 2013

Al-Mg alloy was friction stir processed (FSP) incorporating two different sized SiC particles. Reduction of particle size after FSP was very significant with coarser SiC particles than finer. The density of SiC particles in FSP nugget was found to be uniform from top to bottom with coarser SiC particles, whereas it was more at the bottom than the top with finer. Tool wear after FSP was found to be relatively more with coarser particles than finer.
A Procedure for in situ Identification of the Intermetallic AlTMSi Phase Precipitates in the Microstructure of the Aluminum Alloys
Authors: Warmuzek M. , Regulski K.
Published: December 2013

In this work, the results of the examinations of morphology and chemical composition of the primary AlTMSi intermetallic phases precipitates observed in the Al–Si cast alloys microstructure have been presented. A procedure for the treatment of EDS X-ray microanalysis results (selection and classification) using fuzzy logic concept has been developed and then tested in application for AlTMSi phase identification. Statistically significant differences in the chemical composition have been revealed between the analyzed groups of precipitates of both α- and β-AlTMSi phases formed in hypo- and eutectic Al-Si alloys with the same content of transition metals. The range of the measured Mn solubility in the precipitates of different crystal lattices has been statistically estimated.
Failure Analysis on a Ruptured Petrochemical Pipe
Authors: Harun M. , Shamsudin S. R. , Kamardin A.
Published: December 2013

The failure took place on a welded elbow pipe which exhibited a catastrophic transverse rupture. The failure was located on the welding HAZ region, parallel to the welding path. Branching cracks were detected at the edge of the rupture area. Deposits of corrosion products were also spotted. The optical microscope analysis showed the presence of transgranular failures which were related to the stress corrosion cracking (SCC) and were predominantly caused by the welding residual stress. The significant difference in hardness between the welded area and the pipe confirmed the findings. Moreover, the failure was also caused by the low Mo content in the stainless steel pipe which was detected by means of spark emission spectrometer.
Gefügecharakterisierung von Aluminium-Silicium Gusslegierungen
Authors: Kuhnke Katrin
Published: December 2013

Kurzfassung

Die Ausbildung des Gussgefüges hat einen signifikanten Einfluss auf die mechanischen Eigenschaften von Gussteilen. Durch eine gezielte Einstellung der Abkühlgeschwindigkeit wie z.B. durch die Wahl des Gießverfahrens und durch Schmelzebehandlungsmaßnahmen lassen sich positive Effekte erreichen.

Die vorliegende Arbeit gibt einen Überblick über die Gefügeausbildung von Aluminium-Silicium-Gusslegierungen und über den Einfluss verschiedener Parameter wie Abkühlgeschwindigkeit, Gießverfahren, Veredelung und Kornfeinung.
Microstructural Characteristic of Co-Cr-Mo Powder Alloy Coating on Stainless Steel by Plasma Transferred Arc Weld Surfacing
Authors: Somunkiran İlyas , Kurt Bulent , Buytoz Soner , Orhan Nuri
Published: December 2013

In this study, Co-Cr-Mo powder was coated on the surface of AISI 304 stainless steel by the plasma transfer arc (PTA) process at 80, 90 and 100 A current values and argon gas was used for both plasma and protective. Deposition layers were examined with optical microscopy, SEM, EDX, XRD analysis and microhardness test. The thickness of the coating increased with current density. No cracks or pores were detected in the interface and coating layer. Higher current levels resulted in higher dilution levels and also in melting/burning of the substrate.
EBSD-Gefügeuntersuchungen an Aluminiummatrix-Verbundwerkstoffen
Authors: Heimann Sebastian , Knyazeva Marina , Pohl Michael
Published: December 2013

Kurzfassung

Die Darstellung des Gefüges von Aluminiumlegierungen bereitet immer wieder Probleme. So kommt es z.B. häufig zu Fehlinterpretationen bei der Unterscheidung von Korngrenzen und Subkorngrenzen wegen deren unterschiedlichen Reaktionen auf die verschiedenen möglichen Ätzmittel. Aber auch die Vorbereitung durch Schleifen und Polieren kann bei nur wenig veränderten Randbedingungen zu unterschiedlichen Ergebnissen nach dem Ätzvorgang führen.

In den hier beschriebenen Untersuchungen wurden die Aluminiumlegierung EN AW-6061 und zwei Aluminiummatrix-Verbundwerkstoffe auf Basis von EN AW-6061 mittels Rückstreuelektronen-Kikuchi Beugung (EBSD; electron back scattering diffraction) untersucht.

Es konnte eine eindeutige Zuordnung von Groß- und Kleinwinkelkorngrenzen vorgenommen werden. So gelang eine genaue Analyse des Gefüges sowohl hinsichtlich des Einflusses der Fertigung als auch der Verstärkungsphase in den Verbundwerkstoffen.
SEM and TEM Investigations of Recovery and Recrystallization in Technically Pure Molybdenum
Authors: Primig Sophie , Leitner Harald , Lorich Alexander , Knabl Wolfram , Clemens Helmut , Stickler Roland
Published: December 2013

Beside traditional applications of refractory metals, e.g. in high temperature furnace construction, lighting or glass industry, one of the most important molybdenum products nowadays are large plates which are frequently used as targets for the sputtering of molybdenum layers in thin-film transistor liquid crystal displays. For the hot rolling of the sintered pre-material, the control over the recovery and recrystallization behavior is of particular importance. Molybdenum tends to a very recovery controlled behavior during hot deformation, at which the dislocations arrange into subcell boundaries instantaneously. These pronounced recovery processes seem to consume a large amount of the stored deformation energy for the actual recrystallization. On the other hand, recovery provides the future recrystallization nuclei. For a comprehensive characterization of these microstructural processes, electron microscopy appears to be the most proper means. The aim of this study is to evaluate the significance of electron channeling contrast imaging, electron back scatter diffraction and transmission electron microscopy with regard to recovery and recrystallization processes in molybdenum. Furthermore, appropriate specimen preparation procedures for scanning and transmission electron microscopy are described.
The Metallurgical Causes of Structural Inhomogeneities in Hot Rolled Bars of Martensitic 12% Chromium Steels
Authors: Neidel A. , Fischer B. , Leggemann S.
Published: December 2013

Signs of segregation found during the goods inwards inspection by the users of hot rolled bars of X20Cr13 turbine blade steel led to difficulties in the customer – supplier relationship, due to their unknown effect on the strength and reliability of the finished component. The aim of this investigation was to characterise the micro structural inhomogeneities metallographically, to discuss the metallurgical causes and possible consequences, and to suggest possible corrective of action.
A Step-By-Step Analysis of the Polishing Process for Tungsten Specimens
Authors: Manhard A. , Matern G. , Balden M.
Published: December 2013

The different stages of the polishing process of polycrystalline tungsten samples were investigated by scanning electron microscopy of both the sample surface and of cross-sections prepared with the help of a focused ion beam. It is shown that a distortion layer is present at the sample surface after mechanical fine grinding and even after polishing with diamond suspension, although the sample has a mirror-like finish. A sufficiently long chemo-mechanical polishing step using an alkaline colloidal silica suspension was able to remove this distortion layer. Although electropolishing produced an even smoother surface, the microstructure quality after chemo-mechanical polishing is comparable to that of an electropolished sample.
EBSD- und TEM-Investigations of the Deformation Induced Martensitic Transformation in the Austenitic Steel X6CrNiNb18–10 under Cyclic Loading
Authors: Soppa E. , Willer D. , Kuppler D. , Maile K.
Published: December 2013

As part of an existing research project [1] the fatigue behaviour at room temperature of the austenitic steel X6CrNiNb18–10 was investigated. From a combination of interrupted low cycle fatigue tests and EBSD-measurements in the scanning electron microscope (SEM) the deformation induced transformation of austenite into α'-martensite occurring was able to be observed over the life of the specimen. From TEM-investigations carried out on thin metal foils prepared from the fatigue specimens, the presence of body centred cubic (bcc) α'-martensite was confirmed within the austenitic matrix. This phase transformation affects the crack initiation mechanism. Fatigue cracks often form within the microstructure at the phase boundary between the austenite and the martensite and in the martensitic areas where they grow into the martensitic phase formed at the crack tip.
Microstructural Origins of Variability in the Tensile Ductility of Tilt-Pour Permanent Mold Cast Al Alloy at a Warm Temperature
Authors: Gokhale A. M. , Patel G. R.
Published: December 2013

Light-alloy castings often exhibit variability in the fracture sensitive properties such as ductility that does not necessarily correlate to the global average microstructural parameters such as dendrite cell size and porosity volume fraction in the three-dimensional microstructure. Nonetheless, in numerous such cases, the variability in the fracture sensitive properties does correlate to the variability in the local distributions of microstructural features and processing defects because the fracture path preferentially goes through the regions containing large concentrations of the defects and/or microstructural extrema. This paper presents the results of a detailed quantitative metallography and quantitative fractography based investigation of the relationships between microstructure and variability in uniaxial tensile ductility of the tensile test specimens drawn from very large size Al alloy automotive component castings fabricated using tilt-pour permanent-mold casting process. The percent tensile ductility e shows strong quantitative correlation with the area fraction of the porosity f in the corresponding fracture surfaces, which can be represented by the following power-law relationship, where e0 and n are empirical constants.
Measuring the Grain Size of Specimens with Non-Equiaxed Grains
Authors: Voort G. F. Vander
Published: December 2013

If a specimen has been cold worked, or it did not recrystallize after hot working, the grains will not be equiaxed and extra care must be taken when assessing the specimen's grain size. Always test a longitudinally oriented plane first to determine if the grains are, or are not, equiaxed. In this work, a low-carbon sheet steel was tested in the as-received condition (reportedly annealed), and after cold reductions in thickness of 12, 30 and 70 %. Above 70 % reduction, it can be quite difficult to reveal the ferrite grain boundaries well enough to get a precise measurement. Measurements were made on the three principal planes using the Jeffries planimetric method, the Abrams three-circle intercept method and the intercept method using directed parallel test lines. Grain elongation was assessed using the simple anisotropy ratio and the Saltykov degree of orientation method.
Microstructure Evolution and Mechanical Properties Investigation of Al-6 %Cu Alloy Laser and GTA Welds
Authors: Talari M. K. , Babu N. Kishore
Published: December 2013

Microstructural development, post-weld ageing response and mechanical properties of gas tungsten arc and CO2 laser welded Al-6 %Cu (AA2219) alloy were investigated in the present study. The fusion zone of laser weld consists of three parts: the fine grains in the middle part, the columnar zone and equiaxed zone adjacent to fusion boundary. In contrast, fusion zone of gas tungsten arc weld consists of two parts: the columnar zone in the middle part and the equiaxed zone adjacent to fusion boundary. The size of the equiaxed grains in the fusion zone was the least in the laser welds when compared to gas tungsten arc welds. Laser welds have exhibited higher hardness, post weld ageing response, yield strength, ductility and fatigue strength when compared with gas tungsten arc welds. Fine equiaxed grain morphology and discontinues eutectic distribution in the laser weld fusion zone could be attributed to the improved tensile and fatigue properties of laser welded samples. ‘Thermal pinning effect’, due to non isothermal conditions, has arrested grain growth in heat affected zone in spite of temperatures close to the melting point of aluminum in heat affected zone.
Practical Limitations to Carrier Layer Formation on Inclined Planes
Authors: Ikin J. B. , Thompson H. M. , Gaskell P. H. , Noakes C. J.
Published: December 2013

Two important instabilities associated with carrier layer formation on the inclined plane of slide-fed coating processes are explored, with a two liquid layer prototype configuration employed to mimic the slide-bead process as used by industry. The work relates to both slide-bead and curtain coating methods. Experiments first reveal how broad diffuse bands, that destroy the quality of the final coating, are formed as the carrier layer flow rate is reduced. The bands are found to be exacerbated by either decreasing the viscosity or flow rate of the carrier layer or by increasing the viscosity of the upper layer. As the flow rate of the carrier layer is reduced further, the upper layer begins to invade the carrier layer delivery slot. Flow visualisations reveal that a parallel sided delivery slot is superior to a chamfered one in terms of robustness against invasion of the interface and that reducing the slot width increases robustness further. Experiments and complementary numerical simulations confirm the existence of a recirculating eddy near the top of the downstream wall as the carrier layer flow rate is reduced and this insight is used to propose an instability mechanism for the onset of the bands. Further experiments expose the mechanism for the formation of cross bars. These can develop downstream of the carrier layer delivery slot and arise because the merging of the layers there becomes increasingly influenced by the flow, demonstrating that the sensitivity of cross bars to pump induced disturbances grows rapidly as the critical carrier layer flow rate for instability is approached and then collapses as the flow rate is reduced to a value where the layer is no longer effective in lubricating the flow of adjacent layers.
Simulation of Core Deflection in Powder Injection Molding
Authors: Ling D. , Gupta M. , Myers P. R. , Upadhyay R. K.
Published: December 2013

Core deflection in powder injection molding is one of the main causes of the structural defects in the molded part. Simulation of the core deflection in the injection molding process requires solution of the fluid-solid interaction problem, in which the fluid flow and solid deformation problems are coupled along the fluid-solid interface. A three-dimensional finite element program was developed in this work for a non-isothermal injection molding simulation including the fluid-solid interaction effects. With the assumption of small deformation in the solid structure, the fluid flow problem is formulated in an Eulerian frame-work, whereas the solid structure problem is formulated in a Lagrangian framework. Numerical simulation of the filling stage of injection molding for an airfoil-shaped part is presented and compared with the experimental data. The predicted melt-front advancement as well as the pressure is in good agreement with the corresponding experimental results. The predicted core deflection during the filling stage of the injection molding process is also compared with the measurements on a molded part.
Utilization of Rheology Control to Develop Wood-Grain Patterned PVC/Wood Flour Composites
Authors: Joo Yong Lak , Cho Myung Ho
Published: December 2013

The effects of wood flour and plasticizer on the rheology and extrusion of polyvinyl chloride (PVC) based wood—plastic composites are investigated. The intention of the study was to determine an optimal pair of PVC based wood—plastic composites that should exhibit substantially different rheological behaviors so that patterns similar to grain of wood can be developed inside and on the surface of the product when two selected wood—plastic compounds are extruded at once. The rheological study reveals that the shear viscosity and shear thinning behavior of the composites can be controlled by varying the contents of wood flour and plasticizer. It is also found that the depression of glass transition temperature due to the addition of plasticizer is substantially reduced by the loading of wood flour. In addition, various wood—plastic composites were compounded into different colors, and several pairs of the compounds with different rheological properties were extruded in single and twin screw extruders to see whether any wood-patterns are developed. When the differences in the shear viscosity and the glass transition temperature of the two compounds were too large, the incomplete plasticization of the higher viscosity component was observed due to the premature plasticization of the lower viscosity component. It is shown that distinct wood-patterns were developed both inside and on the surface of the extruded products only for the pairs of the composites with an optimal differences in both viscosity and plasticizer content.
Modeling Non-isothermal Mixing in a Rotor Mixer
Authors: Malkin A. Ya. , Baranov A. V. , Balinov A. I.
Published: December 2013

A mathematical model of the mixing process in a two-rotor mixer is proposed. The model developed takes into account the interrelations among the following essential features of the process: non-isothermal effects due to heat exchange and energy dissipation in flow, non-Newtonian behavior of a material and dependence of its properties on temperature and the degree of filler agglomerate destruction, kinetics of changing carbon agglomerate sizes due to mechanical distraction. The system of governing equations is formulated and the procedure of its solution is described.

The theoretical model is compared with experimental data obtained in real technological process of mixing of a rubber compound. In all cases quite satisfactory results of comparison were obtained. It means that the model proposed can be used for analysis of real technological processes of mixing and choice of optimal technological regime and geometrical sizes of a mixer (primarily size of the gap between a rotor and the wall of a chamber) as well.
Structure Development in Melt Spinning Polypropylene-EPM Blends and Dynamically Vulcanized Polyolefin TPEs
Authors: Yu Y. , White J. L.
Published: December 2013

Polypropylene blends, both mechanical blends and a dynamically vulcanized blend, have been melt spun into fibers. Melt spinning was carried out through air and in ice water. Melt spun filaments were characterized by wide angle x-ray diffraction (WAXS), birefringence and differential scanning calorimetry (DSC) measurements. Generally, the polypropylene crystalline orientation-spinline stress relationship is the same for the homoploymer, the blends and the dynamic vulcanizate. However, the blends and the dynamic vulcanizate have much lower birefringence apparently due to a lack of orientation in the rubber phase. It was shown that the PP contribution to the birefringence for all the systems is the same at the same spinline stress.
Compressive Squeeze Flow of Generalized Newtonian Fluids with Apparent Wall Slip
Authors: Lawal A. , Kalyon D. M.
Published: December 2013

The compressive squeeze flow is encountered in various processes like compression molding and in rheometry. It involves a complex deformation field driven by both shear and normal stresses. Here the flow and deformation field generated during the compressive squeeze flow of generalized Newtonian fluids, subject to wall slip, was analyzed using both numerical simulation based on the 2-D Finite Element Method and the 1-D analytical model, which is based on the lubrication assumption. The agreement between the analytical and numerical solutions deteriorates with increasing Navier's wall slip coefficient and the increasing yield stress value of the viscoplastic fluid. The lubrication assumption is valid under various squeeze flow conditions but numerical analysis in conjunction with experimental studies are necessary to determine the ranges of material parameters and operating conditions for which the lubrication assumption is valid.
Experimental and Numerical Study of Rhomboidal Mixing Sections
Authors: Rios A. C. , Gramann P. J. , Osswald T. A. , Noriega M. del P. , Estrada O. A.
Published: December 2013

The rhomboidal mixing section is becoming very popular among processors to provide distributive mixing. Currently, several different designs are used but the details of the flow behavior and mixing efficiency is not well understood. This information is needed to be able to design and find the most efficient rhomboid geometry. In this investigation nine different geometries with various pitches (helix of rhomboids) were analyzed using a 3-dimensional boundary element method (BEM). The geometries were compared according to mixing efficiency, pressure and energy consumption. The results were compared to experiments performed with a conventional single screw extruder that was fitted with three different rhomboidal mixing sections. The investigation led to the conclusion that the most effective distributive mixing sections were those with neutral rhomboids (pine-apple mixer). However, the neutral rhomboidal mixing section consumes the most pressure in the extruder. It was also concluded that rhomboidal mixing sections deform the material by shear, making them poor dispersive mixing sections.
Production of Pipe with Uniform Wall Thickness: How to Compensate for Gravity Sag
Authors: Pittman J. F. T. , Farah I. A.
Published: December 2013

A detailed simulation of the cooling process in the production of plastic pipes has been used to gain insights into the problem of gravity flow or sag, which can lead to troublesome wall thickness variations in thick walled pipes. It is shown how the simulation can be used in an iterative, forward-backward calculation, based on the time reversibility of the creeping gravity flow problem, to calculate the initial extru-date wall thickness profile that the die must deliver to precisely compensate for sag. For pipes with particularly thick walls, this calculation shows that no compensating initial profile exists whilst conventional cooling arrangements are used. Reduction of the cooling rate of the lower part of the pipe promotes wall thickness uniformity and the existence of a compensating profile. Means for achieving the required initial profiles are discussed, and the need for an integrated view of the design and operation of the die and cooling line in understanding and overcoming the effects of sag is emphasised.
A New Polymer Processing Technology for Polymer Blends with Unmatched Viscosity: Solid-State Shear Pulverization (S3P)
Authors: Khait K. , Torkelson J.M.
Published: December 2013

Solid-State Shear Pulverization (S3P) is a new polymer processing technology capable of efficient mixing blends with different component viscosities (which are unprocessable by conventional melt extrusion due to the phase separation). S3P sub ects polymers to compression and shear, resulting in fracture into a powder of various particle size and particle size distribution. S3P also allows modification of properties by compatibilization of ordinarily incompatible polymers without adding premade copolymers or conventional functional groups. Additionally, because S3P produces powder, it is suitable for a solid-state dispersion of pigments, curing agents, catalysts and other additives without melting (unlike conventional compounding).

After reviewing the S3P concept, this paper discusses recent experimental data. The research focuses on mixing like polymers such as virgin polypropylene (PP) with unmatched viscosity, resulting in blends with improved processability and a significant increase in elongation at break. A comparison with a conventional melt mixing by twin-screw extrusion is provided to demonstrate uniqueness of S3P processing. An additional example involves the mixing of dissimilar, ordinarily incompatible polymers such as recycled high-density polyethylene (PE-HD), low-density polyethylene (PE-LD), PP, polystyrene (PS), and polyvinyl chloride (PVC) with very different viscosities. Once again, the S3P-made material exhibited exceptionally high elongation at break as compared with that of the conventionally melt-mixed blend.
Polymerization of ∊-Caprolactone in a Twin Screw Extruder
Authors: Poulesquen A. , Vergnes B. , Cassagnau Ph. , Gimenez J. , Michel A.
Published: December 2013

The purpose of this work is to model the bulk polymerization of ∊-caprolactone in a corotating twin screw extruder. Starting from kinetic data and rheological laws previously defined, we use a twin screw flow modelling software to calculate the progress of the polymerization along the extruder. Experiments are performed to assess the influence of processing conditions (feed rate, screw speed, barrel temperature, initiator concentration) and to validate the model. They put in evidence the control of the polymerization process by the temperature and the residence time in the extruder. It is shown that a good correlation between theoretical and experimental results can only be obtained if accurate kinetic and rheological data are used in the model.
The Mapping Method for Mixing Optimization Part I: The Multiflux Static Mixer
Authors: Kruijt P. G. M. , Galaktionov O. S. , Peters G. W. M. , Meijer H. E. H.
Published: December 2013

The development of the mapping method [1, 2] and its application to viscous flow in a (multiflux) static mixer [3] is discussed. The mapping method describes the repeated transport of fluid from one domain to another and computes the concentration distribution, yielding a unique mixing measure, like e.g. the intensity and/or scale of segregation [4,5], the residence time distribution and structure parameters like e.g. the area tensor [6].

In the multiflux static mixer, the domain is a (two dimensional) cross-section of the flow channels at the beginning and end of a single element. Since static mixers are build of a sequence of similar elements, we only need to determine one mapping matrix (a computationally expensive operation). To simulate the complete mixer, the mapping matrix is repeatedly applied (a computationally cheap operation). Three different geometries are analyzed. It is shown that an approach like the mapping method is a prerequisite in order to obtain meaningful results after a number of mixer elements. Moreover, it enables optimization of industrial mixers.
Compatibilization of SBR/NBR Blends Using Chemically Modified Styrene Butadiene Rubber
Authors: Ramesan M. T. , Kuriakose Baby , Pradeep P. , Alex R. , Varghese S.
Published: December 2013

The effect of dichlorocarbene modified styrene butadiene rubber (DCSBR) as a compatibilizer in blends of acrylonitrile butadiene rubber and styrene butadiene rubber (SBR/NBR) has been studied. The cure characteristics, physical properties, crosslink density, FTIR studies and low temperature transitions of the blends were determined as a function of chlorine content of DCSBR. Compatibilizing efficiency depended on the chlorine content of DCSBR and composition of blend constituents. Effective compatibilization was achieved when chlorine content of compatibilizer was 25% and SBR content of blend was either 50% or lower. FTIR studies, glass transition behavior measured by DSC and DMA showed that an appreciable extent of molecular level miscibility has been achieved in SBR/NBR blends by using DCSBR as a compatibilizer. Improvement in mechanical properties such as tensile strength, tear strength, resilience, hardness and compression set were achieved both when DCSBR was added and chlorine content of DCSBR increased up to 25%. The resistance of the vulcanizate towards air and oil aging improved with compatibilization. The change in technological properties correlated with crosslink density of the blends assessed from swelling studies and stress-strain data.
PA612 Double Bubble Tubular Film Process – Processability and Structure Development
Authors: Rhee S. , White J. L.
Published: December 2013

Biaxially oriented Polyamide 612 (PA612) films made by double bubble tubular film extrusion were characterized. The processing characteristics of the polymer in the double bubble process were investigated. The development of crystallinity and orientation in the films was clearly considered. First bubble PA612 films showed a low level of crystallinity (X = 7.7%). Differential scanning calorimetry (DSC) indicated that the first bubble PA 612 films experienced a considerable increase in glass transition temperature (Tg), cold crystallization temperature (Tc) and crystallinity during aging at room conditions. The second bubble films were more highly crystalline (X = 22 to 28%) with poorly grown β unit cells. The WAXD and SAXS patterns showed that the crystallites of double bubble PA612 films became more perfect by annealing in a boiling 20% formic acid solution, resulting in a well-developed triclinic α crystals coexisting with minor proportion of β phase. The WAXD and SAXS patterns indicated that crystallography planes and lamellae in the second bubble films were oriented depending on SBUR × SDDR (second blow-up ratio x second draw down ratio). White-Spruiell biaxial orientation factors were calculated with the WAXD pole figure data. The hydrogen bonding (0k0) planes of biaxial double bubble films were found by WAXD to be aligned parallel to the sheet surface before and after annealing.
Flow Instabilities of Linear PE in Capillary Dies
Authors: Larrazabal H. J. , Hrymak A. N.
Published: December 2013

Flow instabilities of linear polyethylenes have been studied in capillary dies. The effects of shear stress, temperature, molecular weight and material of construction of the dies on both the critical shear stress for the onset of slip and slip velocities have been evaluated. Flow curves were obtained using capillary dies with constant L/D and different diameters. Slip velocities were calculated using the Mooney technique [1] as a function of shear stress. The onset of slip and slip velocity are affected by the material of construction of the capillary die. Flow instabilities were eliminated when brass dies were used under specific conditions. Instabilities persisted when naval brass and copper capillary dies were used.
Extrusion Coating with Metallocene-Catalysed Polyethylenes
Authors: Toft N. , Rigdahl M.
Published: December 2013

During recent years, the interest in metallocene-catalysed polyethylenes has been steadily increasing. These polymers are generally characterised by a narrow molecular weight distribution and a uniform comonomer distribution. In extrusion coating, the interest in these polymers is mainly related to the enhanced physical performance of the resulting film. However, from the processing point of view, the metallocene-catalysed polyethylenes can present problems. In this study, a number of metallocene-catalysed linear low-density polyethylenes (m-LLDPE) were characterised with regard to their viscous and elastic properties. Conventional grades of LDPE and LLDPE were included as references. The same grades were used in pilot scale extrusion coating experiments. The processability of the polymers was primarily expressed in terms of neck-in (NI), which describes the lateral reduction of the film width as the film is drawn down into the coating nip, and the draw-down ability (DD), which provides a measure of the ability of a thin film to be drawn into the nip at a high machine speed. A lower NI-value, which is desirable, was noted when the polymer melt exhibited a higher elasticity, expressed in terms of the steady state compliance, the extrudate swell and Trouton's ratio. Factors that had a positive effect on the NI-value tended in general to reduce the draw-down ability. A relation between NI and DD was established, which in principle makes it possible to optimise both NI and DD, based on finding the optimal values of the shear and the elongational viscosities. The results obtained indicate that a low shear viscosity and a high Trouton's ratio provide optimal processability with regard to NI and DD. It was noted that m-LLDPE-grades could be chosen to match the processability of more conventional polymers (expressed in terms of NI and DD). Rheology can be an important tool for such a selection.
Simultaneous Calculation of Roll Deformation and Polymer Flow in the Calendering Process
Authors: Mewes D. , Luther S. , Riest K.
Published: December 2013

Calender units with rotating rolls are used to produce foils or sheets from polymer material with viscous or elastomeric flow properties. Up to now, the design process of calender units, the calculation of flow and pressure fields in the calender gap and the calculation of resulting deformations of the rotating rolls are implemented with different computer programs. In this work a design concept that integrates design and calculation programs is being developed in order to achieve integrated design and calculation. With this concept, it is possible to design calenders and calculate flow fields and deformations. After designing the rolls with the Computer Aided Design program Pro/Engineer, the flow field in the calender gap is calculated with the Finite Volume Method program CFX4, and the deformation of the rolls is calculated with the Finite Element Method program ANSYS. The iterative process of design, calculation and modification of shape is continued until sheets or foils of constant thickness leave the calender gap. The design concept has an object-oriented operational structure. The data transfer between the programs takes place via a central data base in STEP format.

As examples, calenders with combinations of solid rolls are designed. The flow field in the calender gap is calculated for Newtonian and for viscoelastic fluids with use of an integral rheological equation of state. The flow field is compared to a measured flow field. The resulting deformations of the rolls are calculated and represented graphically. Furthermore, a design process for elastomer-coated rolls is implemented and their deformations as well as the interior stress fields are calculated.
Stress Induced Crystallization in Elongational Flow
Authors: Swartjes F. H. M. , Peters G. W. M. , Rastogi S. , Meijer H. E. H.
Published: December 2013

Stress-induced crystallization is studied in an extensional flow device (a cross-slot flow cell) for an isotactic Polypropylene (iPP) by measuring the micro-structure that develops after flow. Birefringence and Wide Angle X-ray experiments were performed. The birefringence experiments with flow below the melting temperature showed the occurrence of a fiber-like structure around the outflow centerline and, later in time, of ‘streamlines’. The latter are explained by the influence of shear gradients close to the optical windows. The WAXS experiments also showed the fiber-like structure around the outflow centerline, having orientations in the (110), (040) and (130) reflections, with a width of about 80 μm. This dominance of the elongational flow around the stagnation line could not be observed in experiments with flow above and subsequent crystallization below the melting temperature.

Structure development in this cell was numerically predicted using the Leonov and the extended Pompom (XPP) model. The oriented structures can be predicted. Moreover, process conditions are found with less influence of the (unwanted) shear gradients. Finally, it was concluded that the strain hardening behavior in the Leonov model over-estimates the first component of the Finger tensor, and thus the number of flow-induced nuclei. Therefore it is recommended to use the extended Pompom model as a more realistic basis for a quantitative flow-induced crystallization model.
Improved Spinnability of Metallocene Polyethylenes by Using Processing Aids
Authors: Vogel R. , Hatzikiriakos S. G. , Brünig H. , Tändler B. , Golzar M.
Published: December 2013

Melt spinning is a polymer processing technique that is strongly influenced by the extensional flow behaviour of polymer melts. Therefore only a few polymeric materials are usable for this kind of processing with sufficient take-up speeds. When approaching critical conditions of deformation most polymers show either fibre break in the molten state either by a brittle cohesive rupture or a ductile failure. During the melt spinning of pure and modified metallocene poylethylenes additional flow instabilities occur within the spinning die. Namely, wall slip, ‘sharkskin’ and pressure oscillations (gross fracture) may be obtained dependending on the volume flow rate. Pressure oscillations lead to diameter oscillations of the melt extrudate, which create local increase of tensile stress in the spin line. This effect immediately causes fiber break in the spinline.

Therefore, melt spinning of polyethylenes was only possible up to a critical molecular weight or its relating melt viscosity. The limitation of the molecular weight restricts the mechanical properties of the melt spun fibres. This paper reports on an attempt to find out appropriate processing aids for suppressing ‘sharkskin’ effects and pressure oscillations in an attempt to overcome the limitation of a critical molecular weight. At first, the critical conditions for the onset of flow instabilities for higher molecular weight polymers were analysed. Further experiments concerned with the use of processing aids for melt spinning of metallocene polyethylenes of higher molecular weights. A combination of boron nitride powder and a fluoroelastomer was found to be an effective processing aid for this process.
Effects of Zinc Fatty Acids on Improved Polymer Processing for Critical Extrusions
Authors: Kim K.-J. , VanderKooi J.
Published: December 2013

The processability of TESPD coupled silica-black-solution SBR with zinc fatty acids (EF and ZB) in an internal mixer and extruder was investigated. The processability, rheological property, and vulcanization property of their composite were measured as a function of storage conditions including time and humidity and as a function of mixing sequence (1P and 2P).

Processing through a single screw extruder, processing additive, zinc fatty acid, added compounds exhibited lower pressure build up than without-additive compound (Control) and their viscosities were lower than the Control. The EF-2P and the ZB-2P compounds exhibited lower pressure build up than the EF-1P and the ZB-1P ones, respectively. The Mooney viscosities of both the dry and the humid exposed ones increased as the storage time increased and the viscosities of the humid exposed compounds exhibited slightly higher than the dry ones.

The cure times of the humid exposed compounds were shorter than that of the dry ones, and as the storage time increases, the cure time of the dry ones were varied depending on mixing sequence; however that of the humid exposed ones were decreased.

The torque rises (MH-ML) of the humid exposed compounds were higher than that of the dry ones as the storage time increases, and while the torque rises of the dry compounds tend to remain constant that of the humid exposed ones increased.

Processing additive added compounds (EF-1P, EF-2P, ZB-1P and ZB-2P) exhibited lower modulus and longer cure time than the Control.
Investigation of Melting Phenomena in Modular Co-rotating Twin Screw Extrusion
Authors: Jung H. , White J. L.
Published: December 2013

An experimental investigation of the mechanisms of melting of polyolefins in a modular co-rotating twin screw extruder was carried out as a function of (i) barrel temperature including below the melting temperature (ii) screw speed and (iii) feed rate. The modular screws were removed from a twin screw extruder following experiments where pellets of linear low density polyethylene or isotactic polypropylene had been fed and processed under steady state conditions. The modular screws contained thermoplastic carcasses. These were sectioned and removed as well as inspected.

Three melting initiation regimes were identified. These were (i) melting initiated from barrel, (ii) melting initiated from screw, and (iii) melting initiated in the bulk. At high barrel temperatures mechanism (i) is observed, at lower barrel temperatures and slower screw speeds mechanism (ii) is found, and at lower barrel temperatures and higher screw speeds mechanism (iii) is observed. The propagation of the melting process was also investigated. Pellet bed instabilities are usually involved at higher screw speeds. We discuss modeling of these mechanisms.