DYNAMIC INSTABILITY AND ITS CAUSES DURING THE INTENSIFICATION OF THE DRILLING STATION OPERATION OF THE QUARRY DRILLING RIGS
The purpose of identifying the reasons for the insufficiently stable operation of drilling rigs of the SBSh-250 type (and other machines) when drilling blast holes. Development of design schemes and mathematical models describing the dynamic state of the tool, drill string, rotation drive and feed mechanisms. Substantiation of the reduction of dynamic loads and determination of the zones of stable operation of the drillstring and the entire rig as a whole.
Methods. To substantiate the real reasons for the dynamically unstable operation of the machine tool, we proceed from the fact that under the action of twisting and compressive force factors, the drilling string in the treated well takes the form of a helical line, which is "wound" onto the well. The helical line under the influence of continuously changing force factors is in a dynamically unbalanced state. On the basis of these ideas and the accepted design schemes, systems of differential equations have been compiled that describe the stable and unstable transient states of the working drill string before and after the loss of longitudinal and lateral stability.
Results. The studies carried out made it possible to establish that as a result of the action of technological force factors, the drilling string is deformed along the spatial curve. Under the influence of initially constant torque and feed force in the elastic system: drilling rod - cutting tool - drive, stable torsional buckling auto and parametric vibrations arise. These torsional frictional self-oscillations are induced due to alternating friction between the tool and the bottomhole, "winding" of the drillstring into the well, similar to a coil spring with a large pitch, as well as the presence of a motor with a rotational system of limited power. When analyzing the obtained systems of differential equations, it was found that due to significant longitudinal compliance during compression of the swirling rod, torsional impulses lead to longitudinal impact displacements of the tool relative to the bottom. Thus, becoming rods is involved in the process of joint torsional and bending vibrations, which are superimposed on each other during the operation of the drilling rig. In addition to these processes, there is a continuous rotation of the drill string, as a result of which the angular frequencies of rotation can coincide with the natural frequencies of the bending vibrations of the rod string. Such frequencies have been identified and are called critical angular frequencies of rotation of the shaft (rod set). These conditions during the operation of the stave lead to breakdowns and disturbances in the stable operation of the machine.
Originality. Based on the system of equations for the equilibrium of the drilling rod subjected to the action of axial compressive force and torque, the relationship between the dynamic torque and the dynamic longitudinal force is established. For the accepted design scheme, a system of differential equations of self-excited torsional vibrations of the stave with parametrically induced transverse vibrations of the stave in two planes is obtained. The solution of systems of two inhomogeneous equations is obtained in the first approximation. The conditions for the emergence of stable modes for parametric longitudinal-flexural vibrations are given.
Practical implications. In order to reduce the dynamic background when drilling wells with rotary drilling machines, it is proposed to limit the free movement of the feed mechanism by changing its design, which will ensure a decrease in the dynamic coefficient during longitudinal vibrations. In addition, to intensify the drilling process, it is proposed to additionally use the effect of pneumatic drilling, and the frequency of pulses of the hammer must exceed the natural frequency of oscillations of the stave, and the rate of application of pulses with the hammer must exceed the linear speed of drilling. In addition, the high-speed mode of rotation of the rod should be selected so that the angular frequency of rotation of the rod does not coincide with any of the lowest frequencies of bending vibrations of the rod string, or select the mode of operation when, when rotating, a dangerous frequency, called the critical one, has passed quickly, i.e. .e. the drill string must be operated at subcritical and supercritical speeds.
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