Otpornost prema habanju i lomu reparaturno navarenih točkova kranskih dizalica

Abstract

Osnovni predmet ove disertacije je da se korišćenjem njenih rezultata omogući odvijanje proizvodnog procesa sa minimalnim troškovima održavanja uz minimalno učešće živog rada, što je inače svakodnevni zadatak savremene nauke i tehnike. Zahtevi pri reparaturi kranskih točkova su isključivo vezani za dimenzije i površinsku tvrdoću. Usled habanja točak/šina, točak gube dimenzije gazne površinne i venca, koje se repariraju navarivanjem. U cilju smanjenja zastoja na kranovima i produžetka veka kranskog točka, kao i smanjenja troškova, napravljena je multidisciplinarna analiza čiji je cilj razvoj i primena nove eksperimentalno-numeričke metode za prevcenciju pojave prslina i loma kranskih točkova. U cilju određivanja optimalne tehnologije navarivanja sprovedeno je iscrpno eksperimentalno istraživanje osobina i mikrostrukture navarenog sloja, uključujući ispitavanja svakog prolaza i optimizaciju broj prolaza i parametara navarivanja za svaki prolaz. Problem unosa toplote pri navarivanju, odnosno termomehanički problem određivanja temperature predgrevanja, je određen korišćenjem analitičkih izraza za prenos razmenu toplote, kao termovizijskom kamerom za eksperimentalno određivanje, odnosno merenje temperature. Dobijeni rezultati su upoređeni, a u dsikusiju naglašene razlike i problemi u analitičkom određivanju temperature. Numerička simulacija i procena integriteta na osnovu naponskog stanja točka u kontaktnom opterećenju sa šinom su dati korišćenjem analitičkih jednačina za Herzov pritisak (kontaktni napon), kao i odgovarajućim proračunom metodom konačnih elemenata, uključujući simulaciju uticaja prsline. Na kraju je data tehnoekonomska analiza postupka navaraivanja, odnosno procenjena njegova opravdanost (prednosti, mane) u odnosu na zamenu oštećenog točka. Pokazano je da se reparaturnim navarivanjem ostvaruju višestruke uštede, uz znatno kraće vreme poporavke.

The main goal of this dissertation is for its results to enable the performing of manufacturing products with minimal maintenance costs and human labor, which represents an everyday challenge for modern science and technology. Demands for crane wheel repairs are exclusively related to dimensions and surface hardness. Due to the rail/wheel wear, the wheel loses its drift and rim surface area, which can be repaired by welding. For the purpose of reducing downtime during exploitation of cranes and extending their life, along with reduction of costs, a multidisciplinary analysis was performed in order to develop and apply a new experimental-numerical method for prevention of crack initiation and crane wheel failure. In order to determine the optimal welding technology, extensive experimental testing of the welded layer’s properties and micro-structure was performed, including the testing of every pass and the optimization of welding parameters. The problem related to the heat input, i.e. the thermo-mechanical problem of determining the preheating temperature was analyzed using analytical expressions for heat transfer, using a thermography camera for experimental measuring of temperature. Obtained results were compared and differences and issues involved with analytical determining of the temperature were emphasized in the discussion. Numerical simulation and integrity assessment based on the stress state of the wheel due to the load caused by contact with the rail are given in form of analytical equations for Hertz’s pressure (contact stress), along with the corresponding finite element method calculation, including the simulation of the effects of a crack. Finally, a techno-economical analysis of the welding procedure, i.e. its justifiability (advantages, disadvantages), compared to damaged wheel replacement, was presented. It was shown that repair surface welding achieved significant savings, while greatly reducing the time needed for repairs.