Vasily Yurevich Crete, Deputy Chief Designer "Experimental Design Bureau. Lyul’ko", A branch of OAO "UMPO" Alexey I. Zubko, Design Engineer "Experimental Design Bureau. Lyul’ko", A branch of OAO "UMPO", The competitor of the Moscow Aviation Institute (National Research University)
The problems associated with assessing the possibility of using ceramic bearings in the supports of gas turbine engines. The results of the experimental work.
The possibility of using of ceramic glade-bearings in the supports of gas-turbine engines is studied in this article. The results of the experimental works are presented.
Keywords: gas turbine engines, bearings, spectral (orbital) vibration analysis. Keywords: gas-turbine engines, bearings, spectral (orbital) vibration analysis.
From the equation of existence aircraft concluded that the solution to future problems of tomorrow in terms of the creation of aircraft with high efficiency requires an increase in specific thrust of the engine and a reduction in specific fuel consumption (which will, ceteris paribus reduce its stock on board). This causes the development of power plants include all higher values of gas dynamic parameters of the working cycle of the engine and, in particular, seek to reduce the aerodynamic drag elements gas-air line by reducing the number of working steps turbomachinery, a profiling of the elements, improve working rotors rotate and so. d.
However, at higher speed rotors dramatically increases the load on all parts of the engine, especially on the elements of the rotor system. This is due primarily dependent forces arising due to imbalances of the square of the rotational speed, increasing the pressure and velocity at the throat of the engine and, therefore, increase the reaction forces that are fully or partially transmitted to the motor casing through the bearings. loads are variable in size, intensity, and frequency of exposure to the applied forces. And, as a consequence, the bearing supports the rotor 6 are in a very difficult process, which significantly reduces their life.
Already today, mass-produced motor bearings close to the upper theoretical limit. This forces developers to seek new varib Antes design bearings rotors for use in advanced engines. From the current situation can be accessed in several ways, for example by increasing the manufacture of rolling bearings, or the use of other types.
Work on the improvement of rolling bearings are conducted in various areas of more than one year, providing a significant increase in their efficiency, while it is noted. The reason that many of the problems, quality of manufacturing materials for the production of finishing technological possibilities of production, does not achieve the desired results. Therefore, in the OKB. Lyul’ko attempt was made to evaluate the possibility of the use of ceramic bearings in the design supports gas turbine engines (GTE).
Plain bearings, which appeared much earlier rolling, gave way to last in many devices. This is due to reveal the advantages of rolling bearings is the low coefficient of friction, so these bearings characterized by lower losses of mechanical energy and higher efficiency However, along with these rolling bearings are inherent advantages and disadvantages, which include a high sensitivity for purity and quality of grease, a larger amount in their construction, and, accordingly, less reliable, less resistance to external vibration, etc.
Currently, new ceramic materials which can be used for manufacturing sliding bearings. In these bearings is possible to drastically reduce the friction in the working couple and get the value of the loss to the bearings. Thus, the application provides a slip better results when estimating parameters in a whole gas turbine engine.
The composition of the sintered material includes powder with addition of additives in the form of carbides, metals and non-metals in various proportions. Obtained by sintering at temperatures of about 1000 … 2000 ° C and pressures from vacuum to 7000 kg / cm2 or more, they are not composed of expensive tungsten. Ceramic materials can have a high, level microstructure, porosity (from 15 to 35%). With increasing porosity, the mechanical properties of the resulting materials and thus items made from them deteriorate. Therefore, to ensure the quality of ceramic materials it is necessary to search for compromise in the selection of the particle size structure elements included in the additives and their proportions.
It should be noted that under the same name materials may be produced tens of species having different compositions and properties. For comparison, the aggregated data on structural bearings.
Before the advent of composite ceramic materials generation silicon carbide, titanium carbonitride, etc., which have a low coefficient of friction, the use of bearings in turbine engine rotor support structure palates were possible because of a strained their working conditions. For example, the calculated values of the specific load for sliding support high pressure turbine TBG should be up to 17 kgf / cm2 at a peripheral velocity in the contact area of the sliding surfaces 40 m / s. For structural materials previously sliding bearings, which used a pair of friction cast bronze, at the specific load of 20 kgf / cm2, the speed limit does not exceed 1 m / s. This is less than the required parameters.
Results comparing values of indicators characterize the properties of materials that are traditionally used in the construction of the slide bearings (cast iron, bronze, babbit, nylon, etc.) and ceramics to enable a new generation, that the latter have higher hardness and heat transfer, lower specific gravity, entom thermal expansion close to that of steel, and, most importantly, significantly lower coefficient of friction.
By varying the composition of the components and properties of ceramic materials is possible to obtain not only workable in a GTD ceramic sleeve bearing, but also get a better performance compared with similar characteristics of metal and hybrid rolling bearings: extended operating temperature range (limited to the characteristics of lubricating materials); high vibration resistance; chemical resistance to aggressive media; noiseless operation; saving efficiency when working with insufficient lubrication or its complete absence; the gradual development of bearing failure, making it easy to diagnose in its early stages of development.
Sliding bearings wear out most strongly when working without lubrication (at the beginning of rotation of the support during the startup phase) or in its lack of quantity, ie, under boundary lubrication, when the roughness of the details relating roughness other parts. Therefore, the value of the coefficient of friction is the principal criterion for evaluating the performance of the bearing, because it depends on the magnitude of losses in the node. To ensure the operability of the bearing must have a lower coefficient of friction pairs, and the heat in the friction zone, should be easily discharged to the details of construction and support therethrough into the environment. The high thermal conductivity of the ceramic components allows to realize all the above requirements.
Ceramic structural materials allow producing part of several layers with different properties, which makes it possible to integrate the bearing assemblies and subassemblies of the individual modules of gas turbine engines. For example, Fig. 1 shows a fragment of a sample of the multilayer structural panels, developed by "Diaprom" (Moscow). Kazhdyyiz layers has its own, set designer designs unique properties. Such a solution, by an appropriate choice of material properties, depending on the magnitude of the stresses in each section, can significantly reduce the weight of parts while improving their strength properties.
At the same time, the bearings have disadvantages that must be considered in a comprehensive assessment of all the factors at the stage of deciding on their use, and in particular: increased demands on the alignment of bearing components; insufficiently investigated tendency to oscillate in certain modes of operation of the motor and bearings.
In order to assess the feasibility of design Rob tori poles GTE bearings from a new generation of ceramic materials by our specialists were tested options for smooth hydrodynamic journal bearings. Their geometric characteristics are selected so that the possibility of return of the roller rolling bearing employed in one of the engines.
The studies were conducted on the test bench bearings FSUE "CIAM. PI Baranova"Where for receiving and analyzing the parameters of the bearing temperature sensors were installed on the outside of the inner sleeve and sliding bearing oil inlet and outlet in the experimental assembly. In the course of the monitored bearing vibration state. For this purpose, use a spectrum analyzer and a set of software "Sirius" DeweSoft company with vibration sensors Tib PA firms in 4513&K. Means vibrodiagnostics determines the mode in which appeared the boundary friction. Also, orbital analysis" the centers of the shafts that visualize the nature of the motion of the rotor, its vibration precession, etc. General view of the assembled experimental unit of the stand shown in Fig. 2.
As one of the criteria for comparison was selected bearing calculated loss ratio in the working pair. As is known, the effectiveness of any mechanical device to evaluate the value of loss. In this case, a loss of the quantity of mechanical energy is removed, passed into heat. By measuring the temperature difference between the rings and the coolant temperature (oils) at the outlet and inlet into the bearing assembly, the quantity (determined by the flow rate per unit time), and the coefficient reference table of its heat capacity, it is possible to calculate the amount of released and before the heat of the oil.
It should be noted that the loss ratio calculated in this way has an error due to lack of consideration the amount of heat transferred to the colder parts of the stand, as well as the amount of heat by friction rained bench and gave the details to the oil. But since all bearings were tested on the same stand, the amount of errors can be assumed constant, and to simplify the calculations ignored.
During the experiments yielded the following dependence characterizing performance ceramic slip: the temperature dependence of the parts bearing on the magnitude of the radial load; dependence of the temperature difference and the oil bearing parts at its input at different speeds; dependence of the temperature difference at the outlet and the oil inlet of the bearing on the natural frequency of rotation of the bearing.
The best performance achieved performance sliding bearing using a pair of friction new generation (based composite carbide kremniyana titanium based carbonitride).
The studies evaluated the sliding performance at low oil consumption. Compared to today realized oil flow in rolling bearings supports the turbine products "96FP" and "99" it decreased by 60 times.
The temperatures measured at the surface of the ceramic bearing parts of the new generation, depending on the axial load are presented in Fig. 3. We note that the obtained dependence should be analyzed taking into account the features of the stand and the data acquisition system, contributing their own error.
After the start of the test oil at a rate of 1 liter / min. held burn-bearing surfaces, so the amount of heat generated was larger, and the temperature obtained above (blue line) than at a flow rate of 0.3 l / min. (light green line).
To simulate the operating conditions of the engine mount oil temperature in the test bearing (by heating or cooling systems stand) was maintained at 80 … 100 ° C. The amount of heat due to frictional losses hydro layers in the oil wedge and friction between the parts can be estimated by measuring the temperature difference of the bearing and oil on its input (Fig. 4).
Absence of the graph plots the high positive gradient and temperature values indicative of performance of the pilot bearing on modes Rusby oil moves up to 0.1 l / min.
Temperatures measured at the outer surface of the bearing, had a maximum value of 34 ° C temperature of oil entering the bearing uzel.Ddopustimaya calculated temperature difference data was taken to be 80 ° C. The test results recorded more than double the stock of this criterion.
In tests with oil flow 0.1 l / min., A load of 500 kg and sliding velocity of about 40 m / s in the loss factor sintered bearing defined by calculation 0.018. Roller bearing under the same loads and operating speeds of parts, but the oil flow 1 L / min., The calculated BER loss coefficient was 0.02. Received over the calculated loss factor at cermet slide bearing compared with the metal clip of the rolling bearings indicates its greater efficiency by reducing energy losses due to friction and increased efficiency
The marked tendency in the literature smooth sliding bearings to the emergence of self-oscillation "on the oil wedge" during a series of experiments it is not apparent. Perhaps the conditions of their origin has not been fully simulated on a test bench. It is also possible that the bearings in the course of experiments in other modes for the area of occurrence of oscillation.
With the passage of the rotor critical modes marked a short-term burst of vibration, does not lead to the development of oscillatory processes, indicating that the prevalence of damping forces of the forces. But in the regions close to the critical conditions of the nature of the distribution of loads and modes of interaction between the contacting surfaces, there was some increase in heat, causing the displacement of some points regarding the settlement (Fig. 4).
In areas far from the critical conditions there are low rotor vibration activity. "Orbit" the center of the rotor shaft on one of these modes is shown in Fig. 5. Move the center of the rotor shaft is uniform around the circumference close to the first, inclined orbits in the vertical plane. This path indicates the absence of vibration process in the system and there is no manifestation of the nonlinear characteristics of the stiffness of supports study of the rotors.
Smooth hydrodynamic design of the sliding bearing of a new generation of ceramic materials performance under operation in the bearing of the turbine rotor turbine engine with reduced oil consumption to 0.1 l / min. and radial loads up to 500 kg.
Established design not only equal, but the parameters superior characteristics similar metal roller bearing, previously studied in the same conditions at this stand.
The investigated metal-bearing confirmed the performance in conditions typical for mezhrotornyh GTE bearings. 71
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