卷 46, 编号 2 (2017)

The article demonstrates the efficiency of vacuum carburization, which combines the rational process environment with advantages of automated process equipment. The equipment offers an opportunity to carry out carburization jointly with dry quenching in a high-pressure nitrogen flow. The advisability of building a specialized enterprise to produce domestic vacuum plants as a basis for modernizing the thermal process has been shown.

The features of different methods for the automatic assembly of components on two tape devices have been considered. The solution of this problems makes it possible to align the label on the cover tape with a molded container made of a carrier tape on automatic form–fill–seal packaging machines. It has been shown that the adjustable tape electric drive that tracks positions of marks on the cover material using a photosensor that makes it possible to ensure the steady positioning of the label on the molded container under changing properties of the cover material and technological process parameters.

An analysis of the temperature distribution in the tea-withering chamber has been carried out based on mathematical modeling. The revealed non-uniformity of the temperature distribution was adjusted due to the use of additional heat sources. The novelty of the work consists of applying additional heat sources in the areas where the conveyor belt that represents the modern energy-efficient elastic electric heaters are located.

The influence of the average value and amplitude of the transient internal pressure in the pipelines on the spatial vibrations of the latter has been assessed. The graphic dependences of the spatial vibrations, their phase patterns, Fourier spectra, and Poincare maps have been presented. The latter have been analyzed depending on the input parameters and time. Brief conclusions have been formulated.

This work is devoted to the evaluation of the influence of the curve shape of the ineradicable initial deflection of a two-span rotor with the residual imbalance on the transition vibration amplitudes at low critical speeds under the rundown. The model corresponds to a high-pressure rotor–combined mid-low-pressure rotor (HPR–MLPR) system of a turbine unit. It is assumed that rotors are connected by a rigid coupling and installed on anisotropic elastic damper supports. It is supposed that the resulting deflection (bend) of this system is formed as a result of the fact that a high-pressure rotor acquires the initial deflection during the operation or because of abnormal launch conditions, the curve shape of which for a load-free rotor is known. The influence of the mutual arrangement of the residual imbalances of rotors and the imbalances caused by the resulting deflection of shafting in a system on the amplitudes of its transition vibration under the rundown of a turbine unit has been studied for two shapes of the initial rotor deflection curve that have the highest and lowest values of the shape parameter. The values of the initial rotor bending deflection and the residual imbalance of both rotors have been set equal to the maximum acceptable values for the operation of a turbine unit. Amplitude calculations have been performed for rotors of a K-300-23.5 Leningrad Mechanical plant (LMZ) turbine.

The problem of the motion of a load at a constant velocity over an infinitely long beam that rests on a solid, nonlocally viscoelastic foundation is investigated. The load is considered to be a Gaussian random homogeneous function of the longitudinal coordinate with a constant mathematical expectation. The influence of the nonlocality and viscoelasticity characteristics of the foundation on the value of the critical velocity of the load and the root-mean-square variance in the deflection of the beam has been analyzed.

The ranges of the validity of power laws to describe the scale effect of the strength of machine parts and structural elements are evaluated based on the probabilistic-statistical approach to analyzing the scale effect. For small structures, it is necessary to refute the basic assumption of Weibull’s theory on the statistical independence of the values of local strength at various points of structures and transition to using the mathematical model of random field of local strength, which makes it possible to take into account the correlation of strength properties of material in closely spaced points of structure. The derived results underlay the creation of the combined probabilistic scaling law of strength.

The problem of calculating the lower confidence limit for the reliability function and the other main indices, such as the mean time to failure (mean lifetime) and the guaranteed (gamma-percentile) lifetime of a system based on the reliability test results has been considered. The problem is solved under the general nonparametric assumption of the monotonically increasing failure intensity function (aging) of a system. A series of expressions for the lower confidence limits of the aforementioned main reliability indices has been derived.

A number of problems in the reliability theory as applied to technical systems is considered for the case when the time-to-failure values are distributed as a mixture of two exponential distributions. This consists of finding a renewal function for a simple restorative (renewal) process, a comparison of three operating strategies according to the criterion of minimal cost intensity and using the method of moments to find point estimates for the parameters involved in the mixture. The choice of the mixture is caused by the fact that its failure rate has a running-in period that is characteristic within the initial operation period of technical systems, whereas afterwards, the failure rate is almost constant. This distinguishes the considered mixture from the exponential distribution with a constant failure rate widely used in the reliability theory.

The results of experimental studies of stress–strain behavior during hardening stages, as well as the stabilization and strength degradation of the rubber-cord casings during the static loading mode have been given. The influence of measurements of these characteristics on the drive dynamic loading has been shown. The physical processes of specific friction in the coupling flexible element have been considered. Dependence diagrams of the specific friction on dynamic torque, vibration frequency, torsion angles, and casing temperature have been made.

Mathematical model for assessing the strength robustness of oil-and-gas pipeline section under bending in the weak linear elastic soil (when ultimate tensile strength, loadings and dimensions are normally distributed) was obtained. Furthermore, the mathematical expectation of the normal bending stresses was found as a result of the differential equation solution of the bended pipe axis as a beam on a solid elastic foundation. Measures that decrease the variability of the project position of the oil-and-gas pipeline were developed based on the obtained data; this results in an increase in its robustness in the collapsible soils.