Please use this identifier to cite or link to this item: https://repositorio.ufu.br/handle/123456789/19583
metadata.dc.type: Dissertação
metadata.dc.rights: Acesso Aberto
Title: Desenvolvimento e caracterização tribológica de materiais resistentes ao desgaste abrasivo para industria mineradora de cassiterita
Other Titles: Development and tribological evaluation of wear resistant materials for cassiterite mining industry
metadata.dc.creator: Máscia, Roberto
metadata.dc.contributor.advisor1: Sinésio Domingues Franco
metadata.dc.contributor.referee1: Mello, José Daniel Biasoli de
metadata.dc.contributor.referee2: Albertin, Eduardo
metadata.dc.description.resumo: Durante o processo de beneficiamento da cassiterita, minério do qual extrai o estanho, são utilizado a britagem, o bombeamento e a moagem, entre outros, de um minério contendo elevados teores de óxidos altamente abrasivos, e, em especial, o óxido de silício. Os componentes destes equipamentos apresentam, por esta razão, elevadas taxas de desgaste abrasivo e erosivo, gerando altos custos com reposição das peças. Como exemplo destes, temo-se impelidores de britadores, carcaça e rotores de bombas e revestimentos de moinhos. Os ferros fundidos brancos de alto cromo (FFBAC) têm sido empregados na confecção de componentes do britador e bombas, enquanto que os aço ferramentas contendo até 1%C e 12%Cr são comumente empregados em revestimentos de moinhos. Neste presente trabalho foram identificados os mecanismos de desgaste atuantes nestes componentes, com o objetivo de selecionar os ensaios de desgaste mais adequados para as ligas propostas. São apresentados também, resultados obtidos no desenvolvimento dos FFBAC contendo até 1,5%Nb e aços ferramentas com diferentes constituições e tratamentos térmicos. Para os FFBAC, o comportamento foi analisado utilizando um abrasômetro a dois corpos com lixa de Si02 80 mesh; pôde-se notar que, a taxa de desgaste é fortemente influenciada pela temperatura de austenitização e de revenimento. Além disso, para as condições tribológicas adotadas, a adição ótima de Nióbio está entre 0,5 a 1,0%. O comportamento dos aços testados em ensaio de desgaste abrasivo a três corpos com areia Normal Brasileira (150^mj mostrou diferenças insignificantes nas taxas de desgaste. Os resultados obtidos, mostraram ainda, que no ensaio utilizado, a taxa de desgaste decresce com o aumento da pressão nominal de teste. Por fim, foi desenvolvido, projetado e construído um hidroabrasômetro para simulação do desgaste do componentes de bombas. Foram avaliadas ligas ferrosas com diferentes teores de cromo e molibdênio no estado temperado e revenido a 200QC. Para amostras com maiores teores de cromo notou-se uma maior resistência ao desgaste erosivo, e a adição de Molibdênio, eleva significativamente a resistência a esse tipo de desgaste.
Abstract: During the cassiterite ore processing, a mixture containing mainly silicon oxide, cassiterite, iron oxides and water is guided through different crushing mills and pumps in order to reduce and separate it. These operations lead to large maintenance costs due to abrasive and erosive wear. To reduce wear in this field, the high chromium white cast irons are widely used in the crushing mills and pump parts. Tool steels, such those containing up to 1 wt. percent of carbon and 12 wt. percent of chromium have been used to protect the internal surface of bar mills. This work presents a set of different analysis, which were carried out to find out, first of all, the underlying wear mechanisms and so an appropriate wear laboratory test. The wear behaviour of hammer crushing mills was analyzed using an equipment based on the two body abrasion. High chromium white cast irons containing 15 wt. percent of chromium, 2 wt. percent of molybdenum and up to 1,5 wt. percent of niobium with different microstructures were produced, as an attempt to reduce the abrasive wear. The abrasive wear rate was measured using Si02 as abrasive and compared with the wear rate of commonly used white cast iron for hammer mills. It has been found the abrasive wear rate increased significantly with decreasing austenitizing temperature. The tempering temperatures also may considerably change the wear behaviour. A significant reduction on the wear rate was observed on the white cast irons with a niobium percentage between 0,5 and 1,0 percent. To simulate the wear behaviour of bar crushing mills, an equipment based on the lapping principle was used. Sand with an average grain diameter of 150 pm was selected as abrasive. The results showed that using a carbon steel as a counter-body and a nominal test pressure of 0,40 MPa, the abrasive particles are embedded in the carbon steel leading to a two body configuration. On the other hand, the use of a hard counter-body made of a high chromium white cast iron may lead to much less embedding and the three-body abrasive wear configuration predominates. Although, this situation can be modified during the test as consequence of the abrasive particle fragmentation. An increase of the wear test load may accelerate this change. Using the parameters which lead to a three-body abrasive wear no significant change could be observed between the studied steels. This suggests that the chromium content may be strongly reduced, and consequently the maintenance price of this kind of mills, without a marked reduction on the wear resistance. Finally to simulate the wear behaviour of pump parts a slurry pot were designed and constructed. A suspension of sand (5 % weight) was used and the impingement velocity was fixed at about 8 m/s. Different quenched and tempered high chromium white cast irons were tested. The wear mechanisms were analysed. The wear tests showed a positive influence of the M7C3 carbides and the addition of up to 1 weight percent of molybdenum considerably increased the wear resistance. Additionally, an analyses of the initial reduction of the wear rate was found to be mainly related to a reduction of the abrasive sharp cutting edges during the test.
Keywords: Desgaste mecânico
Ferro fundido - Branco-alto cromo
Aço - Ferramenta
Nióbio
Abrasão a dois e três corpos
Ferros fundidos brancos de alto cromo
Aços - ferramentas
Partículas abrasivas
Mecanismos de desgaste
Two and three body abrasive wear
High chromium white cast iron
Tool steels
Wear mechanisms
Niobium
metadata.dc.subject.cnpq: CNPQ::ENGENHARIAS::ENGENHARIA MECANICA
metadata.dc.language: por
metadata.dc.publisher.country: Brasil
Publisher: Universidade Federal de Uberlândia
metadata.dc.publisher.program: Programa de Pós-graduação em Engenharia Mecânica
Citation: MÁSCIA, Roberto. Desenvolvimento e caracterização tribológica de materiais resistentes ao desgaste abrasivo para a indústria mineradora de cassiterita. 2002. 141 f. Dissertação (Mestrado em Engenharia Mecânica) - Universidade Federal de Uberlândia, Uberlândia, 2002.
URI: https://repositorio.ufu.br/handle/123456789/19583
Issue Date: 22-May-2002
Appears in Collections:DISSERTAÇÃO - Engenharia Mecânica

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