Evaluación de la sustitución de la estructura de protección de palas cargadoras mediante el análisis de elementos finitos

Abstract

The greatest works of mining and civil engineering are based on the existence of developed extracting and transport elements which reach high displacement and extraction ratios. Nowadays, the use of load machinery is greatly extended in multitude of labour scopes due to its adaptability and versatility. Models for almost specific work exist, but unfortunately sometimes are not easy to find the appropriate option. Specifically, on underground hydrothermal metallic vein mining, the operation becomes in non firedamp atmospheres and requires the extraction of great amounts of material, but not in the middle of massive cameras as in the case of limestone mines, but in narrow galleries. In this case the roads used to move the loads have great restrictions on cross section, mainly in overall height, due to the necessity of optimizing and reducing the galleries’ occupied spaces. The use of small loaders make the operation non-viable because the so low extraction ratios. The development of specific models is not possible because small unit amounts are demanded. Consequently it is only possible to make modifications on current models to adapt them to this particular working environment. In order to diminish the overall height of the machine, owners usually make modifications on rollover protective structure, by means of the partial or total substitution of the cab elements. These modifications demand tests series and verifications, guaranteed by the effective norm, EN 13510: “Earth-moving machinery–Roll over protective structures- Laboratory tests and performance requirements. (ISO 3471:1994 including amendment 1:1997 modified)” and EN 13627: “Earth-moving machinery–Falling object protective structures- Laboratory tests and performance requirements (ISO 3449:1992 modified)”, which causes enormous costs that make required changes so difficult to be developed. One way to cut costs for the accomplishment of the tests series is the mathematical simulation of the modified cab behaviour by a finite element computer model. The model is constituted not only by the geometric characteristics of the parts of the new cab, but also by the manufacturing physical and mechanical material properties. Starting on the mathematical model and the contour conditions, the computer analysis allows obtaining stresses and deformations in all finite elements of the structure. Comparing the results with the norm restrictions, the analyst is capable of carrying out a project in which a favourable or unfavourable judgement on the changes of the protective structure is included.