Avaliação tribológica de novas modificações superficiais para cilindros de laminação a frio

The present work analyzed the tribological behavior of coatings/surface modifications traditionally used in cold rolling mill rolls and new coatings/surface modificationswith potential to replace the carcinogenic hard chrome. The study started with identification of wear mechanisms occurring in real coldrollingmill rolls. Due the high cost and dimensions of the rolls, thereplication technique was used. Replicas were obtained from 4 different rolling millBrazilian companies before and after a normal rolling campaign. Initial sliding tests were conducted using spherical and cylindrical counter bodies in order to verifywhichtribological conditions allowed to reproduce the wear mechanisms found in the replicas. These tests indicated the use of reciprocating sliding tests with cylindrical counter bodies (line contact), normal load of 100 N, and test times of and 1 h and 5 h. Different surface modifications were carried out on samples produced from a fragment of a rolling mill roll. The specimens were heat treated and ground on both sides. After, some specimens were surface textured by electrical discharge texturing (EDT). For both groups (ground and EDT), subsequent treatments of chromium plating, electroless NiP coating and plasma nitriding were carried out. The results of the reciprocating tests showed that specimens with electroless NiP coating presented the lowest friction coefficients, while plasma nitrided specimens showed the highest. In general, previous surface texturing before the coating/surface modification increased the wear of the counter bodies. Oneexceptionwas for EDT with subsequent electroless NiP coating, which presented the lowest counter bodies wear rate. The samples withelectroless NiP coating promoted a tribolayer consisting of Nickel, Phosphorus and Oxygen on both the specimens andthecounter bodies, which was apparently responsible for the reduction of friction coefficient and wear rate. The increase of the test time reduced the wear rate of the samples, apparently due the stability of the tribolayers formed, except for the nitrided samples. For the textured specimens, NiP coating showed the best performance in maintaining the surface topography of the specimens after the sliding tests.

Território, Criminalidade e tráfico de drogas ilícitas em Montes Claros/MG

Urban violence, manifestly public and free, has changed the standard of sociability of townspeople. The city is an increasingly private space of hopes of reducing the risk of victimization, due to the fear of violence that separates and distances the classes in expectation of concealing this behavior. However, violence has many facets and, in one way or another, will always be present as a product of social friction. It is in the urban context and using drug trafficking as a backdrop that this work raises questions about the territorial violence in Montes Claros - MG. The objective was to analyze the dynamics of illicit drug trafficking from the concepts of territory, observing to what extent the appropriation of space contributes to the use of violence, especially in interpersonal disputes. Methodologically, it seeks from quantitative and qualitative techniques make the spatial distribution of criminal indicators, defining and creating hierarchy territories of violence in urban areas. From the qualitative approach seeks to organize and analyze data together to the Civil and Military Police, Brazilian Institute of Geography and Statistics -IBGE, João Pinheiro Foundation and the System of the Ministry of Health Mortality Information - SIM. The opportunity of miscegenation between the knowledge of the survey respondents and the official data has introduced qualitative part. The city of Montes Claros has been taken as an object of observation due to a set of conditions, which stood its medium size, your importance in the regional context and their socioeconomic disparities. The results point to the existence of multiple territoriality of violence involving the trafficking of illicit drugs in urban space. Territorial disputes by the traffickers have victimized people with socioeconomic characteristics and urban spatial origin similar. The dynamism of the established boundaries from the cohesion and / or rupture of the interests of those involved creates and destroys territories in the power struggle.