20.500.12556/RUL-170690 Celovito obvladovanje notranjih napetosti in deformacij na ulitku »del cevi« iz sive litine z lamelnim grafitom magistrsko delo Master control of internal stresses and deformations on "pipe part" casting made of gray cast iron with lamellar graphite master's thesis V industrijski livarni Livarna Gorica. d. o. o. je pri končni manipulaciji ulitka »del cevi« prihajalo do razpok na vedno istem mestu. Ulitek je izdelan iz sive litine z lamelnim grafitom. Naša naloga je bila, da to napako odpravimo. Predvidevali smo, da so za nastanek razpok krive zaostale notranje napetosti. Najprej smo izvedli eksperimentalno litje problematičnega ulitka in izmerili robne pogoje. Nato smo naredili računalniško simulacijo livarskega procesa, meritev notranjih napetosti na kritičnem mestu ulitka in analizo mikrostrukture z metalurškim svetlobnim mikroskopom v bližini razpoke. Računalniška simulacija nam je pokazala, da se kritično mesto zadnje zapolni s talino, zato je ta takrat že zelo hladna in to mesto se ohladi bistveno hitreje v primerjavi z ostalimi deli ulitka. Neenakomerno ohlajanje in nakrčevanje ulitka na jedro povzročita zaostale notranje napetosti, ki so jih meritve tudi potrdile. Poleg tega velike ohlajevalne hitrosti na kritičnem mestu ulitka povzročijo trdo in krhko belo strjeno mikrostrukturo, kar je pokazala metalografska analiza. Ta skupaj z zaostalimi napetostmi tvori idealne pogoje za iniciacijo in propagacijo razpok. Problem smo rešili na način, da smo ulitek obrnili tako, da se med ulivanjem kritično mesto ne zapolni več zadnje. Zaradi tega je talina tam še veliko toplejša in ohlajanje je bolj enakomerno, kar zmanjša razvoj notranjih napetosti. Poleg tega se forma in jedro zaradi večjega toka taline v okolici kritičnega mesta bolj pregrejeta. Posledično je tudi ohlajevalna hitrost tam manjša, zaradi česar se izognemo trdemu in krhkemu belemu strjevanju. Ker je jedro bolj pregreto postane manj togo, kar še dodatno zmanjša zaostale notranje napetosti. Z ukrepom smo tako odpravili oba vzroka za iniciacijo in propagacijo razpok. In the industrial foundry Livarna Gorica. d. o. o, cracks were always occurring in the same place during the final manipulation of the cast "pipe part". The casting is made from gray cast iron with lamellar graphite. Our task was to eliminate this defect. We assumed that residual internal stresses were to blame for the formation of cracks. First, we performed an experimental casting of the problematic casting and measured the boundary conditions. Then, we performed a computer simulation of the casting process, measured internal stresses at the critical point of the casting, and analysed the microstructure with a metallurgical light microscope near the crack. The computer simulation showed us that the critical point is filled with the melt last, so it is already very cold at that time and this point cools down significantly faster compared to other parts of the casting. Uneven cooling and shrinkage of the casting onto the core cause residual internal stresses, which were also confirmed by measurements. In addition, high cooling rates at the critical point of the casting cause a hard and brittle white solidified microstructure, which was shown by metallographic analysis. This, together with the residual stresses, creates ideal conditions for the initiation and propagation of cracks. We solved the problem by turning the casting so that the critical point is no longer filled last during casting. As a result, the melt there is much warmer and the cooling is more uniform, which reduces the development of internal stresses. In addition, the mould and the core overheat more due to the greater flow of melt around the critical point. As a result, the cooling rate there is also lower, which avoids hard and brittle white solidification. Since the core is more overheated, it becomes less rigid, which further reduces residual internal stresses. With this measure, we have thus eliminated both causes of crack initiation and propagation. siva litina z lamelnim grafitom razpoke zaostale notranje napetosti ulivanje neenakomerno ohlajanje mikrostruktura gray cast iron with lamellar graphite cracks residual internal stresses casting uneven cooling microstructure true false false N. K. Ceraj Slovenski jezik Angleški jezik Magistrsko delo/naloga 2025-07-12 09:00:05 2025-07-12 09:00:10 2025-08-14 09:13:59 0000-00-00 00:00:00 2025 0 Ljubljana 0 Ljubljana XV, 52 f. 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 669 105381 245628931 25421.pdf 25421.pdf 1 7AF076687BED08E921819D8FBF6D62EE d92fd9c0cef4d2dda95231f50e2dfba5fc31f1ea231165d2121df658cb44b610 ed1ff4e0-5eeb-11f0-b232-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=212734 Naravoslovnotehniška fakulteta 0 0 0