The selection of characteristics for very large mechanical shovels

Abstract

622.271In working the Kansk-Achimk coalfield, which has variable seam and overburden thickness, it has been found inefficient to use mechanical shovels with normal characteristics. The bucket capacities necessary are 80-110 ms. In the Soviet Union there is as yet no experience in the construction and use of such machines. On the other hand, in (for example) the USA, one basic model may have various modifications to the characteristics of the bucket and the jib length, so that when the geological conditions vary it is only necessary to change the bucket and jib.In connection with the problems arising in working coal deposits Iike those in the Kausk-Achimk field, we shall, in this article, attempt I) tO find the relations between the basic characteristics of very large mechanical shovels, 2) to establish the relatlon between the bucket capacity and jib length for one basic model, and 3) to determine characteristics for mechanical shovels with bucket capacity 80-II0 m s, suitable for conditions like those of the Kausk-Achinsk field, Mechanical shovels are designed for working overburden rock lying above the excavator horizon. In selecting their principal operating Characteristics we use the theory of similarity and dimensions [I-3]. The material available from foreign journals [4-6] on this problem is given in Table 1.To dlsplay the relations between the main characteristics of mechanical shovels, the data from Table I qy where q is the nominal bucket capacity in m s, qy is the altered bucket capacity in m s, ! is the nominal jib length in m, and ! y is the altered jib length in m.In cons~uctlng the theoretlcal L-q curve for a basic model, we shah take an excavator with characteristics close to the mean value (curve a).In [3] it is remarked that "when the jib and arm lengths are increased by 20-25~ the bucket capacity is usually left unchanged. For a greater increase in the jib and arm lengths (up to 60-85ob), the bucket capacity is reduced roughly in proportion to the square root of the ratio of lengths q~. -. r q. c2)while the working weight of the excavator increases proportionally to the cube root of the jlb and arm lengths." Following [3], from (2) we construct curves b (see Fig. 1) for the basic models with q = 60, 90, and 120 m s and L = 55, 64, and 66 m, which show that with increasing jib length the bucket capacity also Increases for the same basic model. This is true for all the basic models.Mining Institute, Siberian Branch of the Academy of Sciences of the USSR Electrical Engineering Institute, Novosibirsk.