Among other types of wagons, Ferrominera Orinoco Company uses 350 hopper type wagons for ore transportation. Each of these wagons has a mechanical linkage system, made up of nine mobile elements plus a frame to open and close two rotary discharge doors located at the bottom of the wagons. This paper presents the influence of clearances in the kinematic pairs of the operating mechanism for a tight sealing of the doors. For this purpose, a new mathematical model is developed to show how the positioning error of the doors — from its theoretical fully closed position — may be controlled via an adequate assignment of the clearances in the kinematic pairs. The results show that the positioning errors of each door due to clearances are independent from one another and may be obtained by modelling the kinematic cycle comprising each door as an equivalent five degree of freedom linkage as to obtain the maximum possible error of each door according to the combination of clearances in the kinematic pairs. This way, the most appropriate normalized fit may be assigned in order to limit a maximum positioning output error of each door.

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