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.

In rotary-percussive drilling, axial forces are applied to ensure contact between the bit and the rock before the percussive impulse is applied to the bit. This property of the method was used in the investigations.One of the most important characteristics of percussive rock breaking is the efficiency of utilization of the energy of the percussive impulse. This impulse is characterized by the following parameters: shape, maximum amplitude, and effective duration (i.e., the duration of that part of the impulse which contains at least 95~o of the energy). Table 1, based on data from [1,2], gives the shapes and main formulae for the pulses generated by strikers of various different shapes (equal cross section with rod, absolutely rigid, cylindrical with greater cross section than rod, conical, and equal cross section with rod but with rounded end) for a pulse shape similar to that generated by the striker of the BU-1 rotary-percussive mechanism.According to the situation at the boundary between the bit cutting edge and the rock, part of the energy of the initial impulse will be converted to work expended on penetration of the bit into the rock, while the rest will be reflected back into the drilling rod in the form of the reflected pulse wave. The process of reflection of the pulse can occur throughout the time of action of the initial pulse, and therefore at any time we can distinguish the force and work associated with the initial pulse, Pi' Ai' with bit penetration, Py, Ay, and with reflection, Pg, Ag.Clearly the use factor (efficiency of utilization) of the pulse energy is given by the expression Ay(1)where ~ is the coefficient of transfer of pulse energy to the rock (CTE).It is convenient to compare pulses of different shapes by means of n with the condition that the masses and impact velocities of the strikers generating the various pulses are equal, i.e., that the pulses have equal energies. As the comparison standard we take the so called rectangular pulse generated by a striker with a cross section equal to that of the drill rod. If we denote the energy of this pulse by A 0 and assume that all the pulses being compared have equal energy, then we can write (1) in the form Ay'I t ~ ~ . AoIn an investigation [3] of the penetration of a bit into the rock under the action of a percussive pulse (see scheme in Fig, 1), we derived an expression for the wave process of displacement of the particles of the drill rod:

No abstract

The graph of rotary borehole drilling rate versus feed pressure has four sections ( Fig. 1): I) abrasion of the rock; II) transitional; III) bulk disintegration; IV) a zone where the rise of drilling rate fails off. The greatest effect is achieved in section HI, where the pressure shears off large rock fragments. In this section the rock is crushed with least expenditure of energy.The slope a of the linear part of section III on the V = F (Pf) curve varies with the rock strength. In most cases this section obeys the equation v = k (pz=po),where k is some coefficient of proportionality depending on tan c~, and P0 is the minimum feed pressure at which bulk fragmentation of the face begins.After analyzing numerous experimental results by many workers, the present authors have come to the conclusion that for optimum drill rotation rates k is constant for each rock, while P0 can be fairly accurately represented by the equation P0 = 35f, where f is the rock hardness coefficient on the Protod'yakonov scale.