magistrsko delo
Nik Kristjan Ceraj (Avtor), Primož Mrvar (Mentor)

Povzetek

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.

Ključne besede

siva litina z lamelnim grafitom;razpoke;zaostale notranje napetosti;ulivanje;neenakomerno ohlajanje;mikrostruktura;

Podatki

Jezik: Slovenski jezik
Leto izida:
Tipologija: 2.09 - Magistrsko delo
Organizacija: UL NTF - Naravoslovnotehniška fakulteta
Založnik: [N. K. Ceraj]
UDK: 669
COBISS: 245628931 Povezava se bo odprla v novem oknu
Št. ogledov: 113
Št. prenosov: 25
Ocena: 0 (0 glasov)
Metapodatki: JSON JSON-RDF JSON-LD TURTLE N-TRIPLES XML RDFA MICRODATA DC-XML DC-RDF RDF

Ostali podatki

Sekundarni jezik: Angleški jezik
Sekundarni naslov: master control of internal stresses and deformations on "pipe part" casting made of gray cast iron with lamellar graphite
Sekundarni povzetek: 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.
Sekundarne ključne besede: gray cast iron with lamellar graphite;cracks;residual internal stresses;casting;uneven cooling;microstructure;
Vrsta dela (COBISS): Magistrsko delo/naloga
Študijski program: 0
Komentar na gradivo: Univ. v Ljubljani, Naravoslovnotehniška fak. Oddelek za materiale in metalurgijo
Strani: XV, 52 f.
ID: 26809060