Estudo do comportamento tribológico de líquidos iônicos como fluidos lubrificantes em processos de estampagem

Embora o uso de óleos lubrificantes influencie na eficiência e na qualidade dos processos, quando usados ou contaminados, tornam-se resíduos perigosos para a saúde humana e meio ambiente. De acordo com o Sindicato Nacional da Indústria do Rerrefino de Óleos Minerais (SINDIRERREFINO), aproximadamente 1,4 bilhão de óleo lubrificante é consumido no Brasil, enquanto que apenas 405 milhões são coletados para reutilização. Atualmente, estudos indicam o uso de líquidos iônicos próticos (PILs) como lubrificantes alternativos devido às suas características intrínsecas quanto à lubrificação e por serem considerados biodegradáveis e ambientalmente corretos. Desta forma, o presente trabalho avaliou o uso dos líquidos iônicos próticos formiato de 2-hidroxietilamina (2HEAF) e pentanoato de 2-hidroxietilamina (2HEAPe) como fluidos lubrificantes, em um par tribológico formado por alumínio comercialmente puro e aço. Para isso, os sistemas lubrificados com PILs, foram analisados através de ensaio de desgaste, pelo método ball-on-plate, utilizando uma chapa de alumínio e uma esfera de aço. Após os testes, realizaram-se microscopias ópticas que permitiram estabelecer os mecanismos de desgaste. Como parâmetros delimitadores, os líquidos foram comparados com um sistema isento de lubrificação e com outro utilizando um lubrificante comercial. A aplicação dos PILs 2HEAF e 2HEAPe como fluidos lubrificantes, em processos de estampagem, foi analisada através do ensaio de dobramento sob tensão. Os resultados mostraram uma redução do coeficiente de atrito em duas vezes para o PIL 2HEAF e, em quatro vezes para o PIL 2HEAPe, quando comparado ao sistema a seco. Em relação ao desgaste, os PILs reduziram o contato entre as asperezas atenuando a perda de material. Todavia, para o sistema em que foi utilizado o PIL 2HEAF, como fluido lubrificante, constatou-se ineficiência quando submetido ao ensaio que simula a estampagem. Enquanto que, o líquido 2HEAPe apresentou resultados próximos aos encontrados para o lubrificante comercial. A eficiência do PIL 2HEAPe, como fluido lubrificante pode estar associada à estrutura molecular e polaridade, bem como à sua alta viscosidade.Although the use of lubricant oils influences on the processes efficiency and quality, after their usage or contamination, lubricant oils become hazardous substances for human health and the environment. According to the National Union of re-refining of mineral oils (SINDIRERREFINO), approximately 1.4 billion lubricating oil is consumed in Brazil, while only 405 million are collected for reuse. Recent studies point out the use of protic ionic liquids (PILs) as alternative lubricants due to their intrinsic lubricity, as well as biodegradability and being environmentally friendly. From here on, this work evaluated the use of the PILs 2-hydroxyethylammonium formiate (2HEAF) and 2-hydroxyethylammonium pentanoate (2HEAPe) as lubricant fluids for commercially pure aluminum – steel contacts. Therefore, wear test using ball-on-plate method were conducted for the PIL-lubricated systems. After the tests, optical micrographs of the plate and the ball were obtained and they allowed concluding the involved wear mechanisms. For comparison purposes, a dry test and another using a commercial lubricant were carried out. The PILs were also tested as lubricant fluids for metal forming processes through bending under tension (BUT) method. Results showed the reduction of the coefficient of friction in twice for the PIL 2HEAF and four times using the PIL 2HEAPe, related to the dry, non-lubricated system. Regarding the wear, PILs diminished the contact between the each surface roughness and, thus, reduced the material loss. However, BUT test demonstrated that the PIL 2HEAF was not efficient as lubricant fluid for the studied metal forming application. On the other hand, the PIL 2HEAPe displayed results close to the ones for the commercial lubricant. The 2HEAPe efficiency as lubricant fluid can be associated to its structure, polarity and high viscosity

Protic ionic liquids used as metal-forming green lubricants for aluminum : effect of anion chain length

Among the applications for protic ionic liquids (PILs), lubrication is one of the newest and the most promising. In this work, ammonium-based protic ionic liquids were tested as lubricant fluids for aluminum-steel contacts. PILs were synthesized with 2-hydroxyethylamine (2HEA) and a carboxylic acid (formic and pentanoic), aiming to understand the effect of two different anion chain lengths on the lubricant behavior. The synthesized PILs were characterized by RMN, FTIR and TGA. Wear tests, conducted using a ball-on-plate configuration, showed that the increase of the anion carbon chain length in the PIL structure reduced significantly the coefficient of friction value. Besides, after the wear tests, the PILs structural integrity was not affected. In the same way, bending under tension (BUT) tests evidenced that the performance for stamping conditions of the PIL with the longest anion carbon chain was similar to that of the commercial lubricant. Since, both formed a uniform tribofilm, developed the same lubrication regime and the drawing forces values were close and constant. Hence, the ionic liquid obtained with 2HEA and pentanoic acid (2HEAPe) is as suitable as the commercial lubricant for metal forming processes