<p>The purpose of this thesis for Sapa Heat Transfer is to examine a furnace in which aluminium is pre-heated before hot rolling. The project is modeled in a computer environment in which the air flow in the furnace and the heat transfer to the aluminium solids are included. The computer environment and its governing equations, as well as boundary conditions and generalizations, are presented and explained.</p><p>The simulations are based on two models. The first model has an asymmetric solid placement, which is how it looks in today's ovens. It is validated against collected data. The second model has a symmetric solid placement, in which improvements are introduced and evaluated.</p><p>The results indicate that a symmetric positioning of metal solids in the oven is preferable in order to achieve a good airflow distribution. The use of plates has been proven useful for steering the air to critial areas and to get an even distribution of the airflow. Lastly the simulations indicate that an increased airflow can compensate the less optimal flow distribution that arises with asymmetric solid placements.</p>

The purpose of this thesis for Sapa Heat Transfer is to examine a furnace in which aluminium is pre-heated before hot rolling. The project is modeled in a computer environment in which the air flow in the furnace and the heat transfer to the aluminium solids are included. The computer environment and its governing equations, as well as boundary conditions and generalizations, are presented and explained. The simulations are based on two models. The first model has an asymmetric solid placement, which is how it looks in today's ovens. It is validated against collected data. The second model has a symmetric solid placement, in which improvements are introduced and evaluated. The results indicate that a symmetric positioning of metal solids in the oven is preferable in order to achieve a good airflow distribution. The use of plates has been proven useful for steering the air to critial areas and to get an even distribution of the airflow. Lastly the simulations indicate that an increased airflow can compensate the less optimal flow distribution that arises with asymmetric solid placements.

På Ovako i Hofors, framställs stål via götgjutning. Göten har ett kvadratiskt tvärsnitt som varierar mellan 300 och 700 mm. Dessa transporteras från stålverket, till valsverket för uppvärmning. Varpå de varmvalsas till färdiga ämnen. Under tiden i ugnen när göten värms upp, oxiderar järn och andra legeringar och bildar glödskal. Om glödskalet valsas in i ämnet ger det upphov till defekter, som föroreningar och sprickor, med kvalitetsproblem som följd. Därför var det en önskan från Ovako att ta fram en metod för att rensa glödskal på göt med varierande tvärsnitt.   Syftet med examensarbetet var att utreda möjligheterna att avlägsna glödskal från göt, med hjälp av vattentryck eller andra metoder.   Olika metoder har utvärderats utifrån tidigare forskning inom området, och utifrån olika värderingar, valdes högtrycksspolning med vatten som metod att gå vidare med. Under höga tryck och flöden sprutas vatten genom dysor, som bryter glödskalet och avlägsnar det från götet. Denna metod är den mest förekommande på de flesta valsverk. Problematiken hos Ovako är att deras göt har varierande tvärsnitt, och utrustningen måste anpassa sig efter dimensionerna.   Beräkningar gjordes med värden från befintliga valsverk, och med deras utrustning som klarar av att rensa glödskal på ett tillfredsställande sätt.   Ett systemtryck på 25 MPa, med ett totalflöde på nästan 130 l/s levereras genom 44 dysor fördelat på götets fyra sidor. Avståndet mellan dysor och göt är 150 mm, där dysornas stråle har en vinkel på 15 grader mot ytans normal. Detta system ger ett yttryck på 0,92 MPa. Varav yttrycket bör ligga mellan 0,5 och 1,0 MPa för att ge god rensning. Ackumulator bör användas, med en volym på ca 0,35 m3.   När götets tvärsnitt ändras vid rensningen, kommer dysramperna att justeras för att alltid ha samma avstånd från dysorna till götet. Slutsatsen av arbetet är att denna metod och utrustning kommer att rensa göt på ett tillfredsställande sätt. Däremot bör utrustningen optimeras, för att passa de olika typerna av stål som tillverkas på Ovako. / At Ovako in Hofors, steel is produced through ingot casting. These ingots have a square cross-section, which varies between 300 and 700 mm. These are transported from the steel plant, to a hot-rolling mill for reheating. Whereupon it then gets rolled into finished materials. During the time in the furnaces, when ingots are heated, iron and other alloys oxidize and form a scale. If this scale then is rolled into the material, defects, such as impurity and cracks are formed in the steel, with quality issues as a result. Therefore, it was a desire from Ovako to develop a method to clean the scale on ingots with varying cross-section.   The aim of this thesis was to investigate the possibility of removing scale from ingots using high-pressure water or other methods.   Various methods have been evaluated on the basis of previous research in the area, and based on different values, water was chosen as a method to proceed with. Under high pressure and flow, water is sprayed through nozzles, which breaks the scale and removes it from the ingot. This method is the most occurring in hot-rolling mills. The problem at Ovako is that their ingots have varying cross-section, and the equipment must adapt to the difference in the dimensions.   Calculations were made using values from existing rolling mills and with their equipment that is capable of descale in a satisfactory manner.   A system pressure of 25 MPa, with a total flow of almost 130 l/s are delivered through 44 nozzles distributed over the ingots four sides. The nozzle distance to the ingot is 150 mm, where the nozzles have a jet angle of 15 degrees to the surface normal. This system provides a surface pressure of 0,92 MPa. Which should be between 0,5 and 1,0 MPa to give a satisfactory result. Accumulator should be used, with a volume of 0,35 m3.   When the ingots cross-section changes during descaling, the spray headers will adapt to have the same distance between nozzles and the ingot. The conclusion of this work, is that this method and equipment will clean ingots in a satisfactory manner. However, the equipment should be optimized to suit the different types of steel, produced in Ovako.