Reliability of the belt conveyor bed when restoring failed roller supports

The reliability of modern belt conveyors, whose length reaches tens of kilometers, is primarily determined by the reliability of the roller supports that support the belt and ensure its movement. As they wear out, some roller bearings fail and need to be repaired or replaced. The dynamics of the number of working roller supports is determined by the system of Kolmogorov equations. Their solution allows us to find the probabilities of finding the system in states with a different number of working elements. The article finds probabilities for two cases. In the first case, when restoring, only one roller support is repaired each time. In the second case, all roller supports are repaired or replaced. In the case of sequential recovery, the mathematical expectation of the number of properly working roller supports may be less than the total number by several units. There are always elements that need to be repaired. If the recovery rate of the elements is many times higher than the failure rate, the mathematical expectation of the number of properly operating roller supports is less than the total number of roller supports by less than one, during most of the time all roller supports are serviceable. In the case of simultaneous recovery of elements, an equally high level of reliability is achieved even with comparable failure and recovery rates. The results obtained can be used to determine the necessary reserve of spare structural elements and to plan the maintenance of conveyors.

Study on the Relationship between Chatter Mark Vibration and Rolling Skid for a Twenty-High Roll Mill Based on the Measured Torsional Strain of the Main Drive Shaft

The chatter mark vibration generated in the rolling process of the twenty-high roll mill not only significantly affects the mill performance, but also reduces surface quality of the strip steel. To identify the excitation source, the online monitor for the real time torsional strain of the main drive shaft is performed for a Sendzimir twenty-high roll mill. A corresponding relationship between the torsion variation of the main drive shaft and the period variation of the working roller is observed. The dynamic rolling skid model is further established and the torsion variation of the main drive shaft is simulated. The calculated results are compared with the measured torsion variation signal of the main drive shaft for without chatter mark vibration. The corresponding characteristics between the chatter mark vibration and the rolling skid is obtained. The results not only support the effective of the established model, but also reveal the relationship between the chatter mark vibration and the rolling skid, which provides for the development of monitoring method for the chatter mark vibration of the twenty-high roll mill.

Radiation pattern and seismic waves generated by a working roller‐cone drill bit

The seismic body wave radiation pattern of a working roller‐cone drill bit can be characterized by theoretical modeling and field data examples. Our model of drill‐bit signal generation is a pseudo‐random series of bit‐tooth impacts that create both axial forces and tangential torques about the borehole axis. Each drill tooth impact creates an extensional wave that travels up the drill string and body waves that radiate into the earth. The model predicts that P‐waves radiate primarily along the axis of the borehole, and shear waves radiate primarily perpendicular to the borehole axis. In a vertical hole, the largest P‐waves will be recorded directly above and below the drill bit; whereas, the largest shear waves will be recorded in a horizontal plane containing the drill bit. In a deviated borehole, the radiation patterns should be rotated by the inclination angle of the drill bit. This proposed seismic body wave radiation pattern is investigated with field data examples. The presence of the drill string in the borehole creates other wave modes that are not typically observed when conventional vertical seismic profiles (VSPs) are conducted in fluid‐filled wells. For example, the extensional wave traveling up the drill string creates a head wave traveling away from the drill string, provided the formation velocities adjacent to the borehole are less than the drill‐string velocity. Likewise, when the extensional wave traveling up the drill string reaches the drill rig, some of the energy continues through the drill rig structure, re‐enters the earth, and travels away from the rig as ground roll or shallow refractions. Secondary events are radiated at the drill bit after they travel up the drill string, reflect off drill‐string discontinuities, and travel back down the drill string to the bit. Each of these drill‐bit arrivals has a characteristic moveout as a function of wellhead offset and drill‐bit depth. A knowledge of the radiation patterns and the wave modes generated by the drill bit is essential to interpreting drill‐bit wavefields.