From "a priori" to "a posteriori" static stability of the slewing superstructure of a bucket wheel excavator

Abstract

The complexity of the slewing superstructure (SS) balancing problem derives from the changeability of its geometric configuration, the complexity of working conditions as well as multiple limitations of the possible set of solutions. Having in mind the fact that the existing reference literature does not fully specify the procedure of static stability proof, the aforementioned procedure is presented in detail for the first time in this paper. A major contribution is represented in the classification of the slewing superstructure models into two groups which were named: the ‘a priori’ model (designed image of the SS) and the ‘a posteriori’ model (actual image of the SS). The fundamental stages of the ‘a posteriori’ model development method are presented in the paper. The transformation and validation of the calculation model ‘a priori’ to the calculation model ‘a posteriori’ was conducted on the basis of weighing results. A calculation of the basic parameters of the bucket wheel excavator (BWE) superstructure was conducted for both analyzed models by using the in-house developed software. The ‘a posteriori’ models provide a reliable calculation of the SS static stability and may be used not only for static stability proof of the machine as a whole, but also for load analysis of substructures and elements of BWE and related surface mining machines, such as spreaders. Besides that, the previously mentioned models are of extreme importance for a successful and reliable exploitation and maintenence of the machine since they present the basis for adjustment and control of limiting winch rope forces values, periodic control of mass and center of gravity position, as well as for a possible reconstruction which would be conducted in order to realize better customization of the machine versus operating conditions

Bucket wheel excavators with a kinematic breakdown system : identification and monitoring of the basic parameters of static stability of the slewing superstructure

“…However, the absolute values of the ordinates of the slewing superstructure CoG are still negligibly small (less than 3.5% of the radius of the calculating contour of the slewing superstructure leaning in the plane of the radiaxial slew bearing). In addition, it was proven in [3] that the impact of the lateral eccentricities of all forces acting upon the slewing superstructure on the safety factors against its overturning is negligibly small. Therefore, the CoG ordinate is excluded from the further analysis.…”

“…With all this in mind, it has been concluded that the synthesis of the results of analytical and experimental determination of the slewing superstructure BPSS is absent from the existing literature. The results of the pioneering research presented in papers [2,3] overcome this deficiency. Paper [2] presents an original concept of the corrective mass, based on the synthesis of the results obtained with analytical and experimental methods of determining the slewing superstructure BPSS.…”

“…Application of this concept allows for the formation of a model which can be successfully applied for the analysis of static stability, loading of the vital parts of the load-bearing structure of the slewing superstructure as well as the analysis of its dynamic response. Paper [3] emphasizes the extreme importance of harmonization of the technical documentation "...with all the changes made during the development of the project and the realization of the first erection procedure...". Fulfilment of this requirement makes it possible to form the 'a priori' [3] calculation model of the slewing superstructure, which has a degree of accuracy sufficient for a comparative analysis with the results of the initial weighing (the so-called 'zero weighing') of the BWE after it has been fully assembled [6].…”

“…Paper [3] emphasizes the extreme importance of harmonization of the technical documentation "...with all the changes made during the development of the project and the realization of the first erection procedure...". Fulfilment of this requirement makes it possible to form the 'a priori' [3] calculation model of the slewing superstructure, which has a degree of accuracy sufficient for a comparative analysis with the results of the initial weighing (the so-called 'zero weighing') of the BWE after it has been fully assembled [6]. Then, by applying the concept of the corrective mass [2], the 'a posteriori' [3] calculation model of the slewing superstructure is formed, representing a foundation for the accurate proof of static stability.…”

“…In order to develop the slewing superstructure 'a posteriori' model [3] using the concept of corrective mass [2], first it was necessary to remove the total designed counterweight mass (m CW,DES ) from the 'a priori' models (Table 1) and introduce the total counterweight mass (m CW,W0 ) at the zero weighing, expression (1). Having in mind that the counterweight belongs to the substructure 2 (Fig.…”