The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs. / <p>QC 20111014</p>

Denna studie har undersökt om förvärmning av luft är en bra metod för att undvika frostbildning i motströmsplattvärmeväxlare i luftbehandlingsaggregat. Frostbildning i värmeväxlare för ventilation är ett problem i kalla klimat och sänker den återvunna energimängden när potentialen för energiåtervinning är som högst.   Tidigare forskning i området har utförts för att bland annat: 1) Definiera säkra förhållanden utan frostbildning i värmeväxlare med laminär luftströmning.  2) Jämföra olika frostkontrollstrategier. 3) Analysera frostbildningens egenskaper och effekt på värmeväxlare i ventilation. Att forskningen inte är entydig för vilken frostkontrollstrategi som är bäst belyser vikten av detta arbete.   I en fallstudie kvantifieras empiriska värmeöverföringskoefficienter som används i en analytisk modell som förutspår energianvändningen för luftvärmning under olika driftfall för ett luftbehandlingsaggregat. Värmeöverföringskoefficienterna tas fram genom mätningar i ett luftbehandlingsaggregat lokaliserat i ett flerbostadshus. Mätobjektet har ett installerat värmebatteri före värmeväxlaren vilket värmer inkommande uteluft till konstant lufttemperatur.  Tillverkaren proklamerar att det sker turbulent luftströmning i den studerade värmeväxlaren. Vid olika lufthastigheter ändras värmeöverföringskoefficienten mer vid turbulent strömning än vid laminär strömning. Att olika lufthastigheter har betydlig inverkan på värmeöverföringskoefficienten överensstämmer med resultatet från mätningarna. Effektiviteten av den aktuella styrningen av förvärmaren har granskats och brister har upptäckts. En ny optimerad styrning föreslås för frostfri drift och minimerad energianvändning. Den optimerade styrningen jämförs sedan med en vanlig avfrostningsmetod och utförs med hjälp av flödesbalansstatistik från ett aggregat med sektionsavfrostningsstyrning. Resultatet visar att förvärmning av luft för frostfri drift använder mindre energi än vid sektionsavfrostningsstyrning.  Den föreslagna styrningen innebär att bypass-spjället öppnas då förvärmaren går på full effekt. Detta för att förhindra påfrostning vid extrema utetemperaturer, då förvärmaren inte ger tillräcklig effekt för att undvika påfrostning. Den föreslagna styrningen regleras utifrån daggpunkten, temperaturen på tilluften innan värmeväxlaren och temperaturen på avluften. Den framtagna värmeöverföringskoefficienten i studien tar inte i beaktning ökad koefficient under fuktiga förhållanden då daggpunkten i frånluften är över fryspunkten och det sker kondens. En framtida studie kan hitta värmeöverföringskoefficienter som förutspår yttemperaturen under kondensutfällning då daggpunkten är över 0°C vilket ger medel för att ta fram en ännu mera energieffektiv styrning. Detta kan utföras genom mätning i ett luftbehandlingsaggregat med hög temperaturverkningsgrad placerat i en fuktig miljö. / This study has analysed if preheating of air is a good method to prevent frost formation in a counter flow plate heat exchanger used in Air Handling Units. Frosting in heat exchangers used in AHU-systems is a problem in cold climates and lowers the energy recovery when its potential is the highest.   Previous research has been done to 1) Define safe operating conditions without frost formation in heat exchangers with laminar flow. 2) Compare different frost control strategies. 3) Analyse frost formation properties and its effects on heat exchangers in AHU-systems. That the research is not unambiguous for which frost control method is the best highlights the importance of this work. Empirical heat transfer coefficients are quantified in this study and are used in the creation of an analytical model of a counter flow heat exchanger that predicts the energy use for heating the air at different operating modes. The heat transfer coefficients are produced by measurements in an AHU-systems located in an apartment building. The AHU has an installed air heater before the heat exchanger which heats the outdoor inlet air to constant temperature.   The manufacturer of the AHU-system proclaims turbulent flow in the heat exchanger. Change of airflow has greater impact on the heat transfer coefficients during turbulent flow compared to laminar flow conditions. This is also derived from the results of the measurements. The effectiveness of the current control system is analyzed, and flaws are discovered. A new control system is therefore proposed for frost free operation and higher energy efficiency. The proposed control system is compared to a frequently used frost control system which uses bypass-dampers to redirect the inlet air to the reheater, to let the warm air stream melt formed frost on the warm air side. This comparison is accomplished by analyzing the usage of the bypass-dampers during different outdoor temperatures in a comparable AHU-system that have the mentioned frost control method. The results show that preheating of inlet air for frost free operation uses less energy than usage of the bypass-dampers to melt formed frost on the warm air side. The proposed control system needs the bypass-dampers to be used when the preheater is on full operation to prevent frost formation at extreme outdoor temperatures when the preheating may not be enough. The proposed control system is regulated by the dewpoint and the temperatures of the exhaust air stream and the supply air stream. The derived heat transfer coefficient that is used to predict the plate-temperature take no account for condensation on the warm air side during humid conditions when the dew point is above the freezing point. Future studies can derive the heat transfer coefficient during condensation which will improve the prediction of the plate-temperature. This would make the system more energy efficient during humid air conditions. This can be done by measurements in an AHU-system with high temperature efficiency placed in a humid environment.

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

Aufgrund der stetig wachsenden Anforderungen hinsichtlich Gewichtsreduzierung und Funktionsintegration, besonders im Bereich des Automobilbaus, werden traditionell aus metallischen Werkstoffen gefertigte Komponenten immer häufiger durch Kunststoffbauteile substituiert. Dem entgegen steht derzeit die Tatsache, dass, trotz hohen Prozessverständnisses und des Wissens um die Prozess-Struktur-Eigenschafts-Beziehungen beim Vibrationsschweißen, die theoretisch erzielbaren Schweißnahtfestigkeiten, von 90 % bis 100 % des unverstärkten Grundmaterials, in der industriellen Serienfertigung bei weitem nicht erreicht werden. Die Komplexität eines industriell gefertigten Bauteils wird an Plattenprüfkörpern simuliert. Die Ergebnisse der Schweißversuche zeigen, dass unterschiedliche Wandstärken im Schweißnahtbereich, Bauteilverzug und unterschiedliche Schwingrichungen innerhalb einer Schweißnaht zu ungleichmäßigen lokalen Prozessbedingungen währenden des linearen Vibrationsschweißprozesses führen. Diese hinterlassen lokale Schwachstellen, welche das Gesamtbauteilversagen bestimmen. Durch alternative Prozessführungsstrategien, wie das Hochdruckanfahren und die IR-Vorwärmung, können diese Schwachstellen reduziert und die Gesamtbauteilfestigkeit angehoben werden. Dies wird am Beispiel des Bauteilverzugs veranschaulicht. / Due to the increasing demands for weight reduction and integration of function, especially in the field of automotive, components made of metallic materials are increasingly being substituted by components made of thermoplastic materials. In contrast to this there is currently the fact that, despite the high process understanding of the vibration welding and the knowledge of the process-structure-property relationships, the theoretically achievable weld strengths of 90 % to 100 % of the unreinforced base material strength are far to be achieved in industrial series production. The complexity of an industrially manufactured component is simulated by using plate test specimens. The results of the welding experiments show that different wall thicknesses in the weld area, component warpage and different friction angle within the weld leads to nonuniform local process conditions during linear vibration welding process. This results in local weak spots, which reduce the total component strength. These local weak spots can be reduced by using alternative process strategies, such as in-process pressure variation and IR preheating. So not only the local strengths but also the total component strength will be increased. This is shown on the example of component warpage.

In this study, the goal is to optimize the process and to reduce the clogging tendency during the continuous casting process. The focus is on clogging when the refractory base material (RBM) in the SEN is in contact with the liquid steel. It is difficult or impossible to avoid non-metallic inclusions in the liquid steel, but by a selection of a good RBM in the SEN clogging can be reduced.   Different process steps were evaluated during the casting process in order to reduce the clogging tendency. First, the preheating of the SEN was studied. The results showed that the SEN can be decarburized during the preheating process. In addition, decarburization of SEN causes a larger risk for clogging. Two types of plasma coatings were implemented to protect the RBM, to prevent reactions with the RBM, and to reduce the clogging tendency. Calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ) plasma coatings were tested in laboratory and pilot plant trials, for casting of aluminium-killed low-carbon steels. For casting of cerium alloyed stainless steels, YSZ plasma coatings were tested in laboratory, pilot plant and industrial trials. The results showed that the clogging tendency was reduced when implementing both coating materials.   It is also of importance to produce clean steel in order to reduce clogging. Therefore, the steel cleanliness in the tundish was studied experimentally. The result showed that inclusions originated from the slag, deoxidation products and tundish refractory and that they were present in the tundish as well as in the final steel product. / VINNOVA

Im Rahmen der vorliegenden Arbeit wird gezeigt, wie ein Gebäude- und Anlagensimulationsprogramm mit bekannten Optimierungsalgorithmen gekoppelt und zur theoretischen Lösung optimaler Steuer- und Regelprobleme in der Gebäudetechnik eingesetzt werden kann. Theoretische Optimallösungen erlauben im Sinne eines optimalen Vergleichsprozesses die Bewertung praktisch anderweitig umsetzbarer Steuerungs- und Regelungsmechanismen. Die im Hinblick auf ein gewähltes Gütekriterium erforderliche Notwendigkeit zur Verbesserung von vorhandenen Steuerungs- und Regelungsszenarien sowie die theoretisch maximal erreichbaren Extremwerte lassen sich leicht abschätzen.

Aufgrund der stetig wachsenden Anforderungen hinsichtlich Gewichtsreduzierung und Funktionsintegration, besonders im Bereich des Automobilbaus, werden traditionell aus metallischen Werkstoffen gefertigte Komponenten immer häufiger durch Kunststoffbauteile substituiert. Dem entgegen steht derzeit die Tatsache, dass, trotz hohen Prozessverständnisses und des Wissens um die Prozess-Struktur-Eigenschafts-Beziehungen beim Vibrationsschweißen, die theoretisch erzielbaren Schweißnahtfestigkeiten, von 90 % bis 100 % des unverstärkten Grundmaterials, in der industriellen Serienfertigung bei weitem nicht erreicht werden. Die Komplexität eines industriell gefertigten Bauteils wird an Plattenprüfkörpern simuliert. Die Ergebnisse der Schweißversuche zeigen, dass unterschiedliche Wandstärken im Schweißnahtbereich, Bauteilverzug und unterschiedliche Schwingrichungen innerhalb einer Schweißnaht zu ungleichmäßigen lokalen Prozessbedingungen währenden des linearen Vibrationsschweißprozesses führen. Diese hinterlassen lokale Schwachstellen, welche das Gesamtbauteilversagen bestimmen. Durch alternative Prozessführungsstrategien, wie das Hochdruckanfahren und die IR-Vorwärmung, können diese Schwachstellen reduziert und die Gesamtbauteilfestigkeit angehoben werden. Dies wird am Beispiel des Bauteilverzugs veranschaulicht. / Due to the increasing demands for weight reduction and integration of function, especially in the field of automotive, components made of metallic materials are increasingly being substituted by components made of thermoplastic materials. In contrast to this there is currently the fact that, despite the high process understanding of the vibration welding and the knowledge of the process-structure-property relationships, the theoretically achievable weld strengths of 90 % to 100 % of the unreinforced base material strength are far to be achieved in industrial series production. The complexity of an industrially manufactured component is simulated by using plate test specimens. The results of the welding experiments show that different wall thicknesses in the weld area, component warpage and different friction angle within the weld leads to nonuniform local process conditions during linear vibration welding process. This results in local weak spots, which reduce the total component strength. These local weak spots can be reduced by using alternative process strategies, such as in-process pressure variation and IR preheating. So not only the local strengths but also the total component strength will be increased. This is shown on the example of component warpage.