Mold-metal reactions in magnesium investment castings

Mold-metal reactions can be encountered during the investment casting of magnesium alloys. This study was carried out for investigating the degree of reactions between the various refractory materials and the magnesium alloy AZ91E, and for finding new techniques to reduce these reactions. Investment casting molds containing multiple test pieces with the dimensions of 25x25x60mm in dimension were used. The wax pattern of each test piece was coated with a different ceramic face coat in mold fabrication and the resulting differences on cast metal surfaces were studied. The backup layers of the shell were the same for all test pieces. Fused alumina, fused silica, molochite, zircon, yttria, zirconia and fused magnesia were the ceramics studied as face coat materials. Digital pictures of the cast surfaces were taken and an image analyzer was used to a quantitatively assess the reacted areas. The results show that fused magnesia and yttria were the best face coat materials to resist molten magnesium. Fused alumina and zircon were the next best materials. Molochite and zirconia were ranked as moderate to poor in resisting reactions. Strong mold-metal reactions were seen in the case of fused silica. Shell permeability measurements suggest that the degree of reactivity is not related to the shell permeability. It can however be correlated to the free energy of formation of the refractory. The excellent reaction resistance of magnesia and yttria observed in the experiments can be explained by the strongly negative Gibb's free energy of formation and consequent stability of these materials. HSC software was used to calculate theoretically the free energy of formation for the refractories studied in this work. The obtained results were compared to experimental values. Analysis with EDS indicated that the reaction layers consisted mostly of oxides. Ceramic test bars coated with various refractories were dipped in magnesium melt to study for reactions. It was seen that none of the tested refractories reacted with magnesium as a result of the dipping operation. It was concluded that oxygen is required for the mold-metal reactions to be initiated. It was verified that the atmosphere surrounding the shell also influenced the observed reactions. In molds containing both normal and reduced permeability shells around the test pieces, the surfaces cast in reduced permeability shells showed large reductions in reactivity. It is suggested that reactions in investment casting molds occur in two stages: 1. During pouring and filling 2. After the filling is complete by the effect of external oxygen. The cooling curves of magnesia-coated test bars were compared with those of silica-coated test bars. Analysis shows that heat is released during the mold-metal reactions. An attempt was made to incorporate the inhibitor KBF4 in the mold structure in the form of first coat stucco. Rough cast surfaces were obtained, which indicated that the used high sintering temperature was not compatible with this inhibitor. Similarly, when the preheated investment-casting mold was placed in a bed of KBF4 before casting, only small reductions in reactivity were obtained. Reactivity was reduced in shells buried in a bed of Croning sand. Then, however, the cast pieces contained gas holes. NaBF4 produced better results as an inhibitor. It was first dissolved in water and then the sintered molds were dipped in this solution. Large reductions in reactivity were observed. The inhibiting effect of this chemical can be attributed to the liberation of BF3 gas during mold preheating.reviewe

Development and calibration of a 1D thermo-fluid dynamic model of ventilation in tunnels

In complex, large civil infrastructures where ventilation has a crucial role for the safety of users in both normal operation and hazardous scenarios, the correct prediction of flow and heat transfer parameters is of fundamental importance. While full 3D simulation is applicable only to a limited extent, and the resort to 1D modeling is a common practice in both design and evaluation phases, the limitation of such models lies in the choice of transfer parameters, such as friction loss coefficients and heat transfer coefficients. In this work, we present an original approach based on the Finite Volume integration of the 1D flow and energy equations on a network of ducts, representing the ventilation system in the 11.6 km long Mont Blanc Tunnel with a spatial resolution of 10 m. The calibration of a set of friction loss coefficients against a rich experimental dataset collected throughout a dedicated set of in situ tests is of particular concern here, as it is carried out by means of genetic optimization algorithms. Predictions of the flow field are in remarkable agreement with the experimental data, with an overall RMS error of ± 0.42 m/s. Further refinements and possible parameter choices are also discussed

Development and calibration of a 1D thermo-fluid dynamic model of ventilation in tunnels

In complex, large civil infrastructures where ventilation has a crucial role for the safety of users in both normal operation and hazardous scenarios, the correct prediction of flow and heat transfer parameters is of fundamental importance. While full 3D simulation is applicable only to a limited extent, and the resort to 1D modeling is a common practice in both design and evaluation phases, the limitation of such models lies in the choice of transfer parameters, such as friction loss coefficients and heat transfer coefficients. In this work, an original approach based on the Finite Volume integration of the 1D flow and energy equations is presented. Such equations are to be solved on a network of ducts, representing the ventilation system in the 11.6 km long Mont Blanc Tunnel with a spatial resolution of 10 m. A preliminary calibration of a set of friction loss coefficients against a rich experimental dataset collected throughout a dedicated set of in situ tests is of particular concern here, as it is carried out by means of genetic optimization algorithms. Predictions of the flow field are in remarkable agreement with the experimental data, with an overall RMS error of - 0.42 m/s. Further refinements and possible parameter choices are also discussed

An integrated approach for the analysis and modeling of road tunnel ventilation. Part I: Continuous measurement of the longitudinal airflow profile

The knowledge of the flow field inside road tunnels under normal operation, let alone fire conditions, is only approximate and partial. The reason is that while the full three-dimensional, unsteady problem is out of reach of numerical methods, on the other hand accurate measurement of the airflow in road and railway tunnels constitutes an extremely demanding task. The present work, structured as a twofold study, takes up the challenge and proposes an original integrated experimental and numerical approach for the analysis and modeling of flow inside a road tunnel and its ventilation systems, aiming at defining a methodology for the creation of “digital twins” of the system itself, on which advanced ventilation and smoke control strategies can be tested and fine-tuned. In this first part, an innovative experimental facility for the continuous acquisition of the longitudinal velocity profile along the whole length of a road tunnel has been designed and built. The facility consists of a survey rake with five bidirectional vane anemometers, which is mounted on a small electric vehicle that can travel through the tunnel at constant speed. This paper reports the design procedure of the measurement facility, with particular focus on the conception and realization of the vehicle carrying the survey rake. Results of the first experimental campaign carried out under the 11611 meters long Mont Blanc road tunnel are presented to corroborate the validity of the approach adopted and the accuracy of the measurement chain

The Impact of Internet and Social Media on Kids’ and Parents’ Game Habits

Internet, already a part of our lives far surpassing its limits as a means of communication, seems to have shaped most fields in human life and changed most of our daily habits and as a consequence the digital natives are observed to be completely living in Internet culture. One of the reflections of this culture and arenas in the Internet, social media has substantial impacts on gaming habits of digital natives. Up to the period in which Internet has interfered in man’s life, the games played by parents were passed from older generations to the new ones as a tradition, so generations used to play the same games; when the children of a previous era became parents they described the games they used to play to their kids thus paving the way to the sustainability of this game tradition. While different generations used to play the same games, today with the dissemination of Internet and social media caused a change of format in the traditionally played games and street games started to give their places to those played on the computers. Therefore, children started to play games on the Internet, an endless space whether negative or positive. The fact that parents are alienated from this arena, enabled the children to play violent games without any boundaries and to take place in social media arenas that could have negative impact on children’s worldly and spiritual well-being. The study is highly important in the sense that it clarifies the extent to which Internet and social media, which is actually the agent of change in children’s gaming habits, environments changed parents’ gaming habits among themselves and with their children. Surveys are conducted to the parents of primary school students as a field work to identify the changes originating from Internet and social media. According to research results, social media and Internet are found to be altering gaming habits of parents with their children. It is identified that parents keep themselves away from online environments in which their kids take place thus possibly breaking off the communication relationships between kids and parents

Mukopolisakkaridoz hastalarındaki otolarengolojik bulgular

Bu derleme makalede MPS hastalarındaki otolarengolojik sorunları raporladık. Mukopolisakkaridozlar (MPS'ler) her biri mukopolisakkaritlerin parçalanmasında rol alan ve şimdilerde glikozaminoglikanlar denilen (GAG'ler) kalıtsal bir enzim eksikliği nedeniyle oluşan bir lizozom depo hastalıkları grubudur. Mukopolisakkaridozlar, mukopolisakkaridoz tip 1-VII diye bilinen 7 metabolizma hastalığı grubunu oluştururlar. Grupların tümünde klinik ve otolaringolojik belirtiler görülür. Mukopolisakkaridoz hastalarında sık görülen otolarengolojik bulgular olarak üst hava yolu obstrüksiyonu, obstrüktif uyku apnesi, ağız açmanın kısıtlanması, orta kulak efüzyonu, işitme ve soluma sorunları vb. bildirilmektedir. KBB uzmanları arasında MPS'ler konusunda farkındalığın artırılması çocuk doktorundan ziyade bir KBB uzmanına giden MPS'den kuşkulanılan hastalar için yaşam kurtarıcı bir çaba olacaktır. Mukopolisakkaridoz hastalarında kısa boyun nedeniyle trakeotomi yapmak zorlaşabilir. Ağız açmanın kısıtlanması nedeniyle tonsillektomi ve adsenoidektomi ameliyatlarından önce hastalar dikkatle değerlendirilmelidir. Anesteziden önce hava yolu sorunları değerlendirilmelidir. Tüm KBB uzmanlarının bu sorunların farkınnda olmaları konusunda dikkati çekilmelidir.In this review paper, we reported otolaryngological problems in patients with mucopolysaccharidoses (MPSs). Mucopolysaccharidoses are a group of lysosomal storage diseases, each of which is produced by an inherited deficiency of an enzyme involved in the degradation of acid mucopolysaccharides, now called glycosaminoglycans (GAGs). The mucopolysaccharidoses consist of a group of 7 metabolic disorders, known as mucopolysaccharidoses types I-VII. In all groups, there are clinical and otolaryngological manifestations. In MPS patients, upper airway obstruction, obstructive sleep apnea, restriction of mouth opening, middle ear effusion, hearing and breathing problems, etc. are reported as common otolaryngological findings. Increasing awareness of MPS's among ENT doctors will be a life saving attempt for MPS suspected patients who admit an ENT doctor rather than a pediatrician. In MPS patients, tracheotomy may be difficult due to short neck. Due to mouth opening restriction, patients should be evaluated carefully before tonsillectomy and adenoidectomy operations. Airway problems must be evaluated before anesthesia. All ENT doctors should be noticed to be aware of these problems

Fatigue behavior of Ti6Al7Nb titanium alloy

Titanyum ve alaşımları sahip oldukları üstün mekanik özellikleri, düşük yoğunlukları ve yüksek korozyon dirençleri sayesinde havacılık, otomotiv, kimya ve biyomedikal endüstrilerinde yaygın olarak kullanılmaktadırlar. Titanyum ve alaşımlarının yüksek sıcaklıkta oksijene olan yüksek afiniteleri kullanımları sınırlamaktadır. Titanyum ve alaşımlarının yüksek sıcaklıkta oksijene maruz tutulmaları yüzeyde oksit tabakasının ve hemen altında ise oksijen difüzyon bölgesinin oluşmasını sağlamaktadır. Bu işleme termal oksidasyon adı verilmektedir. Bu çalışmada aşınma ve korozyon direncinde önemli artışlar sağlayan termal oksidasyon işleminin Ti6Al7Nb alaşımının yorulma davranışı üzerine etkisinin incelenmesi amaçlanmıştır. Bu amaçla 600 C’de 60 saat tutulmasıyla gerçekleştirilen termal oksidasyon işlemi sonrasında numunelerin yüzey karakterizasyonu, kesit mikroyapısının incelemesi ve yüzey mikrosertlik değerinin ölçülmesi ile yapılmıştır. Numune yüzeylerinin mikrosertlik değerleri, termal oksidasyon öncesi ve sonrasında, numuneler çekme deneyine tabi tutularak, akma ve çekme dayanımı ile kopma uzaması ve kesit daralması değerleri belirlenmiştir. Dönel eğmeli yorulma deney düzeneği ile orijinal ve termal oksidasyon uygulanmış numuneler, 25 Hz frekansta farklı gerilme genliği değerlerinde yorulma deneylerine tabi tutularak S-N eğrileri elde edilmiştir. Dönel eğmeli yorulma deneyleri sonrasında, numunelerin kırık yüzeyleri stereo mikroskop ile incelenmiştir. Termal oksidasyon sonucunda Ti6Al7Nb alaşımının yüzeyinde ince bir oksit tabakası ve hemen altında oksijen difüzyon bölgesi oluşmuştur. Termal oksidasyon sonucu yüzey sertliğinin Ti6Al7Nb alaşımında % 170 gibi yüksek bir oranda arttığı belirlenmiştir. Termal oksidasyon işlemi sonrasında Ti6Al7Nb alaşımının mekanik özelliklerinde kayda değer bir değişiklik görülmemiştir. Termal oksidasyon sonrasında Ti6Al7Nb alaşımının yorulma dayanım sınırı düşmüştür. Anahtar Kelimeler: Oksidasyon, titanyum, yorulma.Musculoskeletal system diseases cost in the coun-tries around the globe a significant amount of money annually. The occurrence of bone fractures has also increased due to an increase of the number of traffic accidents and the increase of life expectancy almost twice as compared with past centuries. It is expected that one-third of European citizens will be soon over the age of 60. Hence, healthcare costs will be an increasing burden for society. Therefore, the need for economically feasible biomaterials for fracture healing will increase. For decades, researchers have focused on devoloping a viable and cost effective alternative materials for the dental applications instead of nickel-chromium and cobalt-chromium alloys which have been popular for the denture frameworks since 1970s. Usage of alloys containing nickel was limited due to doubts related with biological safety. Titanium, which eliminates persisting doubts as to biological safety of alloys containing nickel, was introduced in the 1970s. Titanium alloys are attractive materials for many engineering applications, which require excellent combination of mechanical properties, corrosion resistance and biocompatibility along with a low weight. Their excellent corrosion resistance and biocompatibility are assumed to be due to the formation of a dense and stable TiO2 layer, which rebuilds spontaneously after being damaged, even in solutions with low oxygen contents. Unfortunately, in applications where contacting motion of counterparts is maintained, titanium and its alloys have limited usage owing to their poor tribological performance. Poor wear resistances of titanium and its alloys can be enhanced by surface modification techniques. Among the surface modification techniques, thermal oxidation is one of the simplest and cheapest process and appears as it is very promising way to produce hard surfaces on titanium and its alloys. Surface modifications like surface roughening, oxidation or coating techniques also often improve the bioadhesion and the corrosion behaviors of titanium implants. Although many types of titanium alloys are commercially available, since when compared with commercially pure titanium Ti6Al4V alloys have superior physical and mechanical properties and almost same of nickel-chromium and cobalt-chromium alloys, alfa/beta alloy Ti6Al4V is the most commonly used in the biomedical applications. Sometimes usage of Ti6Al4V alloy can be problematic due to the toxicity of vanadium in the body. In order to eliminate this negative effect of vanadium, in the 1980s new vanadium-free alloy containing niboium Ti6Al7Nb was devoloped. The aim of this study was to examine the effect of thermal oxidation on rotating bending fatigue behavior Ti6Al7Nb alloy. Thermal oxidation was conducted at 600°C for 60 h in air. Characterization of the oxidized alloy was made by microstructure examinations, hardness measurements, tensile and fatigue tests. Micro-structure survey was conducted on the cross sections of the oxidized alloy by an optical light microscope after etching with 2% HF. Hardness measurements were made on the surfaces of the samples by a micro hardness tester in the unit of Vickers hardness under different indentation loads. Before and after thermal oxidation, tensile tests were performed in order to measure the yield and tensile strengths, percent elongation and reduction in area. Fatigue tests were performed under rotating bending condition at a frequency of 25 Hz. Fractured surfaces obtained from rotating bending fatigue tests were investigated utilizing a stereo microscope. In this study, the effect of thermal oxidation on the rotating bending fatigue behavior of Ti6Al7Nb alloy was investigated. Thermal oxidation, which was performed at 600 C for 60 h in an air furnace, resulted in the formation of 0.7 µm thick oxide layer with a 7 µm oxygen diffusion zone beneath it. Thermal oxidation con-siderably improved surface hardness to 929 HV0.1. Among the tensile properties only the yield strength was affected from the thermal oxidation. Yield strength of the examined alloy increased from 947 MPa to 1019 MPa, which corresponds to about 8 % improvement. Other tensile properties including tensile strength, elongation at fracture and reduction in area did not show any significant variation with thermal oxidation. Rotating bending endurance limit at 5x106 cycles decreased from about 560 MPa to about 500 MPa upon oxidation. The loss in fatigue resistance corresponds to 12%. Keywords: Fatigue, oxidation, titanium

Nasolacrimal duct obstruction: the relationship with nasal allergy

Abstract Nasolacrimal duct obstruction (NLDO) is a common event in clinical practice. The authors, all members of the Italian Society of Rhinology, analysed 100 cases from different ENT Departments. The causes of NLDO, according to the etiology, can be divided into two classes: idiopathic primary acquired nasolacrimal duct obstruction and secondary. The aim of the study was to describe an association between the sign and symptoms of chronic rhinosinusitis and a complaint of epiphora

An integrated approach for the analysis and modeling of road tunnel ventilation. Part II: Numerical model and its calibration

The present work represents the second and final part of a twofold study aiming at the definition and validation of an integrated methodology for the analysis and modeling of road tunnel ventilation systems. A numerical approach is presented, based on the Finite Volume integration of the 1D mechanical and thermal energy conservation equations on a network of ducts, representing the ventilation system of the 11.6 km long Mont Blanc Tunnel. The set of distributed and concentrated loss coefficients, representing dissipation of mechanical energy by friction in each part of the ventilation system, is calibrated against a rich experimental dataset, collected throughout a dedicated set of in situ tests and presented in the first part of the work. The calibration of the model is carried out by means of genetic optimization algorithms. Predictions of the flow field using the calibrated parameters are in remarkable agreement with the experimental data, with an overall RMS error of \ub1 0.27 m/s, i.e. of the same order of the accuracy of the measurement probes. Further validation against a selection of field data recorded by the tunnel monitoring and control system is brought forward, highlighting the robustness and potential general applicability of the proposed approach

Measurements and scaling of buoyancy-induced flows in ventilated tunnels

We investigate the ventilation conditions required to control the propagation of smoke, produced by a tunnel fire, in the presence of two inertial forcings: a transverse extraction system and a longitudinal flow. For that purpose, we performed a series of experiments in a reduced-scale tunnel, using a mixture of air and helium to simulate the release of hot smoke during a fire. Experiments were designed to focus on the ventilation flows that allow the buoyant release to be confined between two adjacent extraction vents. Different source conditions, in terms of density and velocity of the buoyant release, were analysed along with different vent configurations. Experiments allowed us to quantify the increase of the extraction velocity needed to confine the buoyant smoke, overcoming the effect of an imposed longitudinal velocity. Vents with a rectangular shape, and spanning over the whole tunnel width, provide the best performance. Finally, we studied the stratification conditions of the flow, individuating four regimes. Interestingly, when the stratification conditions fade out, as both the longitudinal flow and vertical extraction flows increase, the flow dynamics becomes almost independent of the forcing induced by the presence of buoyant smoke, which eventually acts as a passive scalar transported by the flow