Study of longitudinal vibrations of stab knife refiners

The subject of research is the longitudinal vibrations of stab knife refiners. A model of the fibrous layer between the rotor and stator is developed. It is shown that it is advisable to use the Maxwell-Thomson model for liquid friction of the rotor and stator, and the Hooke elastic model for boundary friction. The formula for determining the dynamic stiffness of the fibrous layer is obtained. Dynamic and mathematical models of the refiner in the longitudinal direction are developed. The mathematical model is a system of linear differential equations with periodically varying coefficients (Mathieu-Hill equations). A method for calculating the amplitude of oscillations of the refiner rotor and stator is developed. According to this technique, Andritz 54-60-1c stab refiner was designed. Oscillation parameters of the refiner rotor and stator are determined theoretically and experimentally. The stator oscillation amplitude is 1.6-2.3 times smaller than the rotor oscillation one. In case of boundary friction, the amplitude of oscillations of the stator and rotor increases by 2-3 times in comparison with liquid friction. The oscillation amplitude of the rotor and stator in the longitudinal direction is comparable with the gap between these elements. Therefore, it is recommended while designing refiners, to develop methods and means of vibration protection, and during operation, to prevent boundary friction between headsets. The developed calculation procedure can be used in other industries, for example, mining and metallurgy. © Published under licence by IOP Publishing Ltd

Rationing and vibration monitoring of knife refiners

The subject of the research is rationing and monitoring of the vibration of knife refiners. GOST 26493-85, specifying the permissible values of the vibration amplitude of the mills, is outdated. This standard does not take into account new designs of knife refiners and the requirements of national and international standards. It is proposed to establish two criteria for assessing the vibration state of the refiners. The first criterion normalizes the amplitude of vibration in octave strips of frequencies, while the second criterion specifies the vibration trend on the general level. It is proposed to use the vibration velocity as the measured parameter. The necessity of separating the refiners into two groups was revealed: with a disc or cone diameter up to 1000 mm and with a diameter over 1000 mm. The boundaries of zones and vibration trends are determined: good; satisfactorily; need improvement and unacceptable. After that, a decision is made to limit the functioning of these machines (prevention and stop). The introduction of standards and vibration monitoring will accelerate the transition to repairs of machines on the technical condition. Methods of rationing and monitoring can be used in other industries, for example, in the mining and metallurgical industries. © Published under licence by IOP Publishing Ltd

Flexural fluctuations of the rotors of knife refiners

The subject of the study is the flexural fluctuations of the rotors of knife refiners. The dynamic and mathematical models of rotors of disk mills are developed. As a result of research, a method for vibration calculation of rotors is proposed and tested. Research was also conducted using the Ansys software package. The error in determining the lower frequencies of free fluctuations of the mill rotors does not exceed 9%. Failure to take into account the elastic compliance of the rotor bearings leads to an error in determining the frequencies of free flexural fluctuations by no more than 15%, and the gyroscopic moment increases the above frequencies by no more than 25%. The cantilever arrangement of the disk reduces the frequencies of free fluctuations of the mill rotor by 1.1 - 1.4 times in comparison with the inter-support arrangement. The developed calculation procedure can be used in other industries, for example, mining and metallurgy. © Published under licence by IOP Publishing Ltd

Research of the drawing of bars plate in the refiners

Object of research of article is the drawing of bars plate in the refiners at refining of chips and wood pulp. On the basis of the theory of contact interaction of bars influence of the drawing of plate on characteristics of contact processes is investigated. The friction coefficient between plate decreases at increase in density of contact of bars. At increase in an angle of crossing of bars rotor and stator and refining of pulp with concentration up to 6% the coefficient of friction decreases. At increase in an angle of crossing of bars chips and pulp with concentration over 10% the coefficient of friction increases. Therefore it is recommended to increase the angle of crossing of bars rotor and stator at refining of pulp of low concentration, and at refining of pulp of concentration over 10% and chips - to reduce, up to a radial arrangement. © 2021 Institute of Physics Publishing. All rights reserved

Analysis on compressor blading conditions of helicopter’s gas-Turbine engine working in polluted environment

© Research India Publications.Working in the dusty air pollution the air-gas channel of the engine is polluted. This results in deterioration of engine power plants. In this paper we present the results of studies of mass, density, thickness and microstructure of deposits on the rotor blades of a helicopter gas-turbine engine compressor having a nominal capacity of 883 kW after working 1500 h. The researches were conducted on ten blades of each stage. The blades were weighed before and after treatment, and then the averaged sludge mass was calculated. The results show that at the latter stages of the compressor deposit density was greater than at the first ones. Mode with full manifestation of roughness for a given engine is implemented in the first six stages of the compressor. It is concluded that the characteristics of the boundary layer and the value of the coefficient of friction on the surface of the blades are mostly influenced by the size of the arithmetic average height of irregularities Rz. The resulting data is used to develop methods of purifying of the compressor flow path

Observation of large arrays of plasma filaments in air breakdown by 1.5-MW 110-GHz gyrotron pulses

We report the observation of two-dimensional plasma filamentary arrays with more than 100 elements generated during breakdown of air at atmospheric pressure by a focused Gaussian beam from a 1.5-MW, 110-GHz gyrotron operating in 3-mu s pulses. Each element is a plasma filament elongated in the electric field direction and regularly spaced about one-quarter wavelength apart in the plane perpendicular to the electric field. The development of the array is explained as a result of diffraction of the beam around the filaments, leading to the sequential generation of high intensity spots, at which new filaments are created, about a quarter wavelength upstream from each existing filament. Electromagnetic wave simulations corroborate this explanation and show very good correlation to the observed pattern of filaments.open424

Investigation of the Millimeter-Wave Plasma Assisted CVD Reactor

A polycrystalline diamond grown by the chemical vapor deposition (CVD) technique is recognized as a unique material for high power electronic devices owing to unrivaled combination of properties such as ultra-low microwave absorption, high thermal conductivity, high mechanical strength and chemical stability. Microwave vacuum windows for modern high power sources and transmission lines operating at the megawatt power level require high quality diamond disks with a diameter of several centimeters and a thickness of a few millimeters. The microwave plasma-assisted CVD technique exploited today to produce such disks has low deposition rate, which limits the availability of large size diamond disk windows. High-electron-density plasma generated by the millimeter-wave power was suggested for enhanced-growth-rate CVD. In this paper a general description of the 30 GHz gyrotron-based facility is presented. The output radiation of the gyrotron is converted into four wave-beams. Free localized plasma in the shape of a disk with diameter much larger than the wavelength of the radiation is formed in the intersection area of the wave-beams. The results of investigation of the plasma parameters, as well as the first results of diamond film deposition are presented. The prospects for commercially producing vacuum window diamond disks for high power microwave devices at much lower costs and processing times than currently available are outlined

Plasma structures observed in gas breakdown using a 1.5 MW, 110 GHz pulsed gyrotron

Regular two-dimensional plasma filamentary arrays have been observed in gas breakdown experiments using a pulsed 1.5 MW, 110 GHz gyrotron. The gyrotron Gaussian output beam is focused to an intensity of up to 4 MW/ cm2. The plasma filaments develop in an array with a spacing of about one quarter wavelength, elongated in the electric field direction. The array was imaged using photodiodes, a slow camera, which captures the entire breakdown event, and a fast camera with a 6 ns window. These diagnostics demonstrate the sequential development of the array propagating back toward the source. Gases studied included air, nitrogen, SF6, and helium at various pressures. A discrete plasma array structure is observed at high pressure, while a diffuse plasma is observed at lower pressure. The propagation speed of the ionization front for air and nitrogen at atmospheric pressure for 3 MW/ cm2 was found to be of the order of 10 km/s.open322