Maksay Stefan

We suggest a mathematical interpretation of the influence of the main alloy elements over the mechanical characteristics (the hardness on the crust of the rolls) of this nodular irons, resulting the average values and average square aberration of the variables HB, and the main alloying elements (Cr, Ni, Mo), the equations of the hyper surface in the four dimensional space. For the statistical and mathematical analysis, there were used 23 industrial cases. This study analyses iron rolls cast in the simplex procedure, in combined forms (iron chill, for the crust and moulding sand, for the necks of the rolls). The research included rolls from the semihard class, with hardness, between 33...59 Shore units (219...347 Brinell units) for the 0 and 1 hardness class, measured on the crust, respectively 59...75 Shore units (347...550 Brinell units), for the class 2 of hardness. This study is required because of the numerous defects, which cause rejection, since the phase of elaboration of the...

The technical conditions, which are imposed to the cast iron rolls in the exploitation period, are very different and often contradictory. The obtaining of various physical and mechanical properties in the different points of the same foundry product meets difficult technological problems in the industrial condition. This supposes us to know many technological factors, which lead to this deformation equipment. The rolls must present high hardness at the crust of rolls and lower hardness in the core and on the necks, adequate with the mechanical resistance and in the high work temperatures. If in the crust the hardness is assured by the quantities of cementite from the structure of the irons, the core of the rolls must contain graphite to assure these properties. One of the parameters, which determine the structure of the irons destined for rolls casting, is the chemical composition. If we not respect this composition, which guaranties the exploitation properties of the each roll in ...

The present note tries to use the results of mathematic shaping to determine some probability density of polynomial forms. After the determination of a regression curve by a degree previously given, aided by the method of the smallest squares, it will be selected from this curve a domain of definition in which this function will satisfy the conditions of being a probability density.