Razvoj več funkcijskega jedra za ulitek iz sive litine s kroglastim grafitom

Mahkovic, Matic (avtor), Petrič, Mitja (mentor)

Krčilna poroznost se, zaradi krčenja taline med strjevanjem, običajno v ulitku pojavlja na delih ulitka, ki se strdijo zadnji, oz. na zadnjih območjih strjevanja. To so mesta z največjim geometrijskim modulom. V izogib nastanku krčilne poroznosti se uporabljajo napajalniki. Napajalniki morajo biti dimenzionirani tako, da se strdijo zadnji. Končno območje strjevanja in z njim krčilna poroznost se pomakne v napajalnik, ki ga kasneje odstranimo. V primerih, da območje, ki ga napaja napajalnik ni dovolj veliko, lahko povečamo s hladilno kokilo, oz. s hladilno kokilo zagotovimo usmerjeno strjevanje in pomaknemo strjevalno fronto proti napajalniku. Hladilne kokile so elementi, ki hladijo določene dele ulitka in premikajo končna območja strjevanja. Posledično se po ulitku premika krčilna poroznost. Predmet diplomskega dela je bil ulitek iz sive litine s kroglastim grafitom. V njem se je pojavljala krčilna poroznost na mnogih mestih zaradi kompleksne geometrije. Krčilno poroznost smo iz kritičnih mest poizkusili odstraniti s spremembo livarske tehnologije. V ta namen smo uporabili računalniški program za simulacijo livarskih procesov QuickCast, ki deluje na metodi končnih diferenc. Za simulacijo potrebujemo 3D model, na kateremu ustvarimo volumsko mrežo, določimo lastnosti materiala, robne pogoje, začetno temperaturo litja in parametre, ki definirajo prestop toplote, tako pa nam program prikaže problematična mesta, ki jih s spremembami odstranimo oz. napake omilimo. Problem krčilne poroznosti smo zmanjšali tako, da smo dodali v obstoječo livarsko tehnologijo tri nove hladilne kokile, spremenili vrat napajalnika na enem napajalniku, odstranili en eksotermni napajalnik in skupno dodali en napajalnik oblike prisekanega stožca. Na ta način se je krčilna poroznost v ulitku zmanjšala in premaknila na mesta, ki niso težavna.

• Jezik: Slovenski jezik
• Ključne besede: končna območja strjevanja, napajanje, hladilna kokila, strjevalna fronta, usmerjeno strjevanje
• Vrsta gradiva: Diplomsko delo/naloga
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Leto izida: 2018
• PID: 20.500.12556/RUL-103687
• COBISS.SI-ID: 1756767
• Datum objave v RUL: 21.09.2018

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Development of multifunctional core for casting from spheroidal cast iron

Izvleček

Shrinkage porosity usually occurs in parts of castings that solidify the last or so called final solidification zones or places with largest geometric modulus. Shrinkage porosity is a consequence of shrinkage of melt during solidification. In order to compensate the reduction in volume of melt the feeders can be used. Feeders must be dimensioned in order to solidify the last. The final solidification zone must end in the feeder, which is later removed. In cases where feeding area is not large enough, it can be increased by using chills. With chills we can provide directional solidification and move solidification front towards the feeder. Chills are objects that cool down certain parts of casting and move final solidification zones. Consequently shrinkage porosity moves across the casting or towards the feeders. For the simulation, we need a 3D model on which we create a volume net, determine the properties of the material, the boundary conditions, the initial casting temperature, and the parameters that define the heat transfer. Since the experiment with actual castings would be uneconomical, the areas where the shrinkage porosity was occurring were determined using the QuickCast simulation program, which operates on the end differential method. The aim of diploma work is to minimize amount of shrinkage porosity in a spheroidal cast iron casting. The shrinkage porosity was removed from the critical areas by the change of foundry technology. In order to achieve a goal a finite difference method simulation programme QuickCast was used. For the simulation, we need a 3D model on which we create a volume mesh, determine the properties of the material, the boundary conditions, the initial casting temperature, and the parameters that define the heat transfer. In this way a programme gives us a result of critical areas. The problem of shrinking porosity was solved by adding three chills, removing one exothermic feeder and adding a new conical feeder.The amount of shrinkage porosity was reduced and moved in areas which are not problematic.

• Ključne besede: final solidification zones, feeders, solidification front, directed solidification