Evaluation of large-scale load-carrying structures of machines with the application of the dynamic effects factor
(*) Tekst artykułu w polskiej wersji językowej dostępny w elektronicznym wydaniu kwartalnika na stronie www.ein.org.pl in the construction industry which are usually designed to transfer only static loads and thus only need to fulfill the ultimate strength requirement. Dynamic loads accelerate the progressing degradation of the load-carrying structure, which is manifested in an increasing number of fatigue cracks. Fig 1 shows an example of a fracture and its location. Such faults are difficult to spot and if the fracture is located in a critical area, it can grow uncontrollably and lead to a catastrophic failure. A fracture similar to the one in Fig. 1 caused the catastrophe of the KWK 1400 excavator (Fig. 2). Such load-carrying structures are most often found in the mining, rock processing or bulk material handling industry. The situation in this case is even more special because some of the basic technological processes (e.g. excavating, crushing) are very often subject to large dynamic loads [15, 16]. Due to the environment in which such machines most often operate, it is difficult to use solutions that are effective at reducing vibrations but are not susceptible to damage [2, 48]. In addition, the design of load-carrying structure can be prone to excitation [7,17] (e.g. long-span superstructures of surface mining machines). Such machines are still being designed in accordance with standards from the 1980s, which define the dynamic effects factor, which, in turn, is used in calculations of fatigue life. Both the definition of this factor and its assumed values, in accordance with the standards, do not reflect the actual operating conditions. This is manifested in the occurrence of numerous cracks in superstructures [1, 12, 37] and undercarriage structures[1, 4, 13, 46]. Over the years several studies have been carried out aimed at solving this problem
Spatial Reduced Dynamic Model of a Bucket Wheel Excavator with Two Masts
A holistic approach to analyzing the dynamic behaviour of a bucket wheel excavator (BWE) superstructure, which is practically neglected by technical regulations but nowadays widely used during their design and redesign, is presented in the paper. The procedure for determining the potential and kinetic energy and the vector of generalized non-potential forces of the system, leading to the development of a reduced spatial dynamic (RD) model of the BWE with two masts is presented in detail. Direct validation of the established model has been performed by comparing the values obtained for the first ten natural frequencies (NFs) of the finite element (FE) model to those obtained by the RD model. Percent deviations of values of the NFs obtained for the RD model are very low compared to those obtained by the FE model (~1% for three fundamental NFs). Indirect validation of the RD model used in this research i.e. validation of values of the NFs which have been obtained by calculation and the respective modal deflection shapes has been achieved by comparing them to the studies containing the results of numerical-experimental research on the dynamic characteristics of BWEs of the same design concept. The values of NFs are of the same order of magnitude and the corresponding deflection shapes are in full compliance with those of the experimentally-analyzed BWEs.
Materials Handling Handbook
Partial table of contents: Basic Materials Handling Concepts . UNIT MATERIALS HANDLING. Unit Load Concepts. Automatic Guided Vehicles. Conveyors. Containers. Positioning Equipment. BULK MATERIALS HANDLING. Properties of Bulk Solids. Design of Bins and Hoppers. Feeders. Bucket Elevators. Sampling and Weighing. Excavators. TRANSPORTATION INTERFACE. Rail and Water Transportation. Truck and Air Transportation. SAFETY, ENVIRONMENT, AND HUMAN FACTORS. Appendixes. Index.