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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
16.04.2004, Faculty of Mechanical Engineering
mr. sc. Mustafa Imamović
prof. dr. Ahmet Hadžipašić

Thesis title:

Designing Aspects For Selection And Calculation Of Reliability Of The Rolling Stand Basic Parts

Limitations and goals in the designing process are numerous. Minimum mass and volume of the system parts, minimum prices, maximum reliability and other are requested. Development of efficient methodology of designing process along with fulfilment of these requirements represents a big chalenge in the field of designing methods and process development.
Reliability of the system as one of its characteristics has a special importance for the system in use as well as for systems which are in the process of development. Complexity of the procedure of determination and prediction of the reliability level is connected with a complex calculation and long-lasting research of the same or similar systems.
Previous deterministic (classiacl) calculation of the parts, which understood invariability of designing parameters is not adequate, and continuous attempts to apply more acurate probabilistic (stochastic) calculation, which considers variability of parameters. An attachment how such calculating concept based on reliability can be applied to basic parts of rolling stands in the designing process, and thus to the complete system also is given in this paper .
This paper consists of ten chapters. Theoretical and experimental researches of parameters which are necessary for introduction of methodology and calculation of the rolling stand parts on the basis of reliability are presented in the paper.
Description of the problem, goals and limitations in the research are given in the first chapter of this paper.
Second and third chapter work out the theoretical considerations of reliability as well as methods to build the reliability into the parts in the designing process. Numerical method to determine the probability of parts failure in the different distribution of working and critical loads is proposed.
In the fourth and fifth chapter a way to determine the relevant loads during rolling process, occurrences which influence the level of loads, and method of forming the working loads spectrum in the variable flow of the loads are defined.
In the six chapter the analysis of critical loads of the parts (working dynamic strength), and its basic elements as scattering interval, distribution of working strength and distribution profile are given.
Through seventh chapter the experimental researches are presented. By tracking the behaviour of rolling stands system and its basic parts the reliability functions are determined, and criterions for reliability and intensity of failure in the designing process are defined. Working loads for rolling stands are researched in different rolling conditions and method for determination of relevant spectrum of loads for life-time are proposed. Then, working dynamic strenghts of steel P-18A and Č.4732, as materials being used to manufacture the basic parts of rolling stand, are researched by experimental method. Determined elements of probabilistic calculation through these experimental researches were tested on the rolls of the Medium section rolling mill stand. Result of research in this paper is one new principle to track the remaining reliability, which can be applied in use of such systems. Through researches in this paper the assumed hypotheses are proved and one different concept of rooling stands parts calculation in the designing process is defined. Concept is more realistic since it takes into account the variability of working and critical loads and their influence on the level of reliability.

Key words :
reliability, rolling mill, calculation, working loads, critical loads

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