RU2691414C1 - Method of providing tightness of turbo-pump unit under conditions of high vibration loads - Google Patents

Abstract

FIELD: sealing equipment.SUBSTANCE: invention relates to sealing devices. Method of providing tightness of turbo-pump unit under conditions of high vibration loads consists in determining permissible radial play of shaft equal to 0.15–0.30 mm. At that, measurement of radial play of shaft is performed at completely selected gaps between parts located between shaft and housing of turbo-pump unit. For this purpose to turbine disc in plane of disc there is alternately applied in two opposite sides equal force in range 50–70 kgf.EFFECT: technical result of invention is tightness of turbo-pump unit and fuel system of aircraft engine before and after engine starting under conditions of high vibration loads.1 cl, 5 dwg

Description

The invention relates to the field of engineering, namely the sealing technique, and can be used to create turbopump units of aircraft (LA), operated in conditions of high vibration loads.

A known method of sealing rotating shafts with rubber cuffs [1. Basta, TM Hydraulic drives of aircraft. -M .: Mashinostroenie, 1967. - p. 443, 444, 447, 448, fig. 373a, b, 376.], in which to ensure tightness at speeds n≥2000 rpm, the shaft surface beating should not exceed 0.08 ÷ 0.10 mm, with n <2000 rpm, the beating should not exceed 0, 10 ÷ 0.15 mm. For large values of the beat between the cuffs and the shaft, a gap is formed, determined by the eccentricity and the angular velocity of the shaft.

A known method of sealing a turbopump assembly over a shaft with two lip seals to increase reliability [2. The design and design of liquid rocket engines: A textbook for aviats. universities / ed. G.G. Gahuna - M .: Mashinostroenie, 1989. - p. 230-232, fig. 10.29.], In which tightness is ensured when the shaft surface beats no more than 0.08 mm. At misalignment and shaft runout exceeding this value, the tightness of the seal is broken.

The disadvantage of these methods of shaft sealing [1., 2.] is the use of the shaft beat parameter as a criterion for tightness, which only applies to rotating shafts and does not characterize the fixed shaft tightness - a characteristic condition of the turbopump assembly before the engine starts when the fuel system is inhibited. In addition, the shaft beat characterizes the tightness is not fully. Tightness is determined not only by the shaft's beating, but by the full movement of the shaft in the radial direction when exposed to vibrations equal to the sum of the shaft's beating and all the gaps between the parts at which the rotor is installed in the unit housing.

The prototype of the claimed method for a combination of technical features selected a shaft sealing method with lip seals installed with tightness, leaks through which are at rest are absent both in the presence of pressure and without pressure, and can take place only during operation, increasing as the sealing parts wear [3. Makarov G.V. Sealing devices. - L .: Mechanical Engineering, 1973. -C. 95].

The method chosen as a prototype does not take into account the effects of vibrations on the sealed shaft, which is both mobile and stationary. In this case, when exposed to vibration, the tightness of the lip seals of the rotating shaft will be broken. Exposure to vibrations will also lead to seal failure of the lip seals in the state of rest of the shaft, both in the presence of pressure and without the pressure of fluid acting on the lip seals.

The problem to which the invention is directed, is to ensure reliable tightness of the turbopump unit and the fuel system of the aircraft engine under the influence of high vibration loads with a fixed and rotating rotor shaft, the presence and absence of fuel pressure in the unit.

In the proposed method of ensuring the tightness of a turbopump unit under high vibration loads, carried out by compressing the shaft with lip seals installed with tension, operating both under pressure and without fluid pressure, with a fixed and rotating shaft to be sealed, in order to ensure reliable tightness of the turbopump unit and fuel system of the engine under conditions of exposure to high vibration loads, determined the permissible radial play of the shaft, equal to 0.15 ÷ 0.30 mm.

Measurement of the radial play of the shaft is carried out with fully selected clearances between the parts located between the shaft and the casing of the turbopump unit, which is achieved by applying to the turbine disk in the disk plane alternately on two opposite sides of the same force in the range of 50 ÷ 70 kgf.

The invention coincides with the known method of sealing rotating shafts according to the following essential features: the method is carried out by compressing the shaft with lip seals installed with tension, both in the presence of pressure and without pressure acting on the lip seals. The main differences of the invention from the prototype are the introduction of the allowable range of the radial shaft play of the turbopump assembly, the magnitude and direction of the force applied to the turbine disk, when measuring the shaft shaft play.

The invention is illustrated graphic images. FIG. 1 shows the position of the shaft seal and the rotor support of the turbopump assembly; in fig. 2, 3 - the mechanism of occurrence of leakage of the turbopump assembly under the influence of vibrations; in fig. 4 is a graph of fuel leakage from the turbopump assembly from the radial shaft play when subjected to vibrations; in fig. 5 shows an example of a device for measuring the radial play of the shaft (in this application, the device is not considered).

The method is as follows. Collect turbopump assembly (Fig. 1) with lip seals 1, installed with tension on the shaft 2 of the rotor of the turbine 3. Measure the radial play δ of the shaft 2, folding from the gaps between the shaft 2, the sleeve 4, the bearing 5, the cup 6, the elastic ring 7, the case of the turbopump assembly 8, the radial play of the bearing 5 and the full radial stroke of the elastic ring 7, controlling the fulfillment of the condition for ensuring the allowable radial play of the shaft 0.15 ÷ 0.30 mm.

This range was obtained from the results of experimental studies [4. Act No. 11/18 of 09/07/2018 on the investigation of the causes of leakage of turbopump units of the aircraft engine according to lip seals installed with tension, when subjected to vibration loads. - [Orenburg]: AO PO Strela, 2018. - 2 p.]. To study the effect of the radial shaft play on the flow of fuel from the turbopump units and the fuel system, a bench was created to check the tightness of the units under the influence of vibrations. Simulation of the preservation of the fuel system of the engine was carried out using a pump that creates fuel pressure inside the unit. The unit was installed on a shaking table, and it was tested under high vibration loads without pressure and with fuel pressure in the unit (bench test circuits are not considered in this application). Studies have shown that the radial play of the rotor shaft, caused by vibrations, leads to depressurization of the unit not only when the shaft rotates, but also when the rotor shaft is stationary - a typical case for the canned fuel system of an LA engine, both without pressure and with the fuel pressure in the unit. In this case, the fuel flow increased with decreasing pressure in the unit, which is explained by the weakening of the compression of the shaft cuffs. It was found that the cause of the depressurization of the aggregates under high vibration loads is the effect of the shaft on the contact edges of the cuffs. FIG. 2, 3 shows the mechanism of occurrence of leakage of the turbopump assembly when exposed to vibrations. The frequency and amplitude of oscillation of the shaft 2 when exposed to vibrations are such that the elasticity of the cuffs 1 and the force created by the internal mounted springs 9 do not ensure continuous contact of the edges of the cuffs with the shaft. The contact edges of the cuffs do not keep up with the movements of the shaft, as a result a gap Δ is formed between the edges of the cuffs and the shaft - a leak appears.

The inertial effect of a non-rotating rotor shaft on the contact edges of the cuffs is possible only if there is a radial play of the shaft δ representing the total radial movement of the shaft from the free state to the stop on two opposite sides:

(1)

(one)

Radial play of the shaft consists of the amount of gaps between all parts located between the shaft and the housing of the unit, the radial play of the bearing and the full radial stroke of the elastic ring.

FIG. 4 shows a plot of the leakage of fuel from the turbopump assembly from the radial play of the shaft 8 under the influence of vibrations based on experimental data. The aggregates with radial shaft clearance δ from 0.14 to 0.76 mm were investigated. It has been established that the tightness of the aggregates is ensured with a radial shaft play δ≤0.35 mm, with δ> 0.35 mm a leak appears that increases in direct proportion to the increase in the shaft radial play. Knowing the value of the radial shaft play δ = 0.35 mm, above which a leak appears, the safety factor for the rotor play Δδ = 15% is established and the upper limit of the allowable radial play of the rotor is determined, equal to δ = 0.3 mm. The lower limit of the radial play of the rotor is determined based on the requirements of the strength and collectability of the design of the turbopump assembly, and is δ = 0.15 mm. Below this boundary δ <0.15 mm, the assembly of the aggregate is not permissible, since the detuning of the turbine rotor 3 by the elastic ring 7 from the resonant oscillations causing the destruction of the structure will not be realized. Also, compensation for misalignment of the turbine rotor 3 supports during assembly will not be provided; as a result, the unit will be assembled with mounting voltages, which will lead to a decrease in safety factors and destruction of the turbopump unit during operation. Thus, to simultaneously meet the conditions for ensuring tightness and structural strength, the radial play of the shaft of the turbopump units must be in the range of 0.15 ÷ 0.30 mm.

When performing measurements of the radial play of the shaft of the turbopump assembly, force is applied to the turbine disk in the disk plane to ensure accuracy and repeatability of measurement results. The magnitude of the applied force must be in the range of 50 ÷ 70 kgf and be constant when checking different units of the same design. This range is determined experimentally by applying a smoothly increasing force to the turbine disk in the plane of the disk and then the other side until the indicator arrow stops, indicating a complete choice of gaps between the parts of the unit, including the radial play of the bearing and the full radial stroke of the elastic ring. At the moment when the indicator hand stopped, the magnitude of the applied force was fixed. A complete choice of gaps is the main condition for measuring the true value of the radial shaft play. In order to accurately determine the forces at which the gaps will be completely selected, measurements have been made on several turbopump units of different designs.

The measurement of the radial play of the shaft of the turbopump units is carried out on the fixture (An example of the fixture is in Fig. 5, the device is not considered in this application), which is a welded frame 10 with a round cut-out for access to the turbine disk 11. The frame is fixed to the frame by screws. To measure the shaft radial play, a force is applied to the turbine disk in the disk plane by rotating the screw 12. The force is transmitted to the disk of the turbine 11 through the dynamometer 13 and the clamp 14. Using the dynamometer 13, an amount of force 50 ÷ 70 kgf is applied to the turbine disk and then the other way. The readings from the dynamometer 13 are displayed on the electronic board 15. The rotor shaft moves in one and the other direction are measured by the indicator 16, the measuring leg 17 of which rests directly on the rim of the turbine disk 11 through the hole in the collar 14. The radial clearance of the shaft is determined by summing the displacement data.

In case of failure to provide a radial clearance of the shaft of 0.15 ÷ 0.30 mm, the turbopump assembly is disassembled, and the dimensions of parts affecting the radial clearance of the shaft are checked. The identified part with the deviation of the geometry is replaced, the unit is assembled and re-checked the radial play of the shaft. If the test results are positive, the unit is assembled permanently.

Thus, the technical result of the invention is to ensure the tightness of the turbopump assembly and the fuel system of the aircraft engine before and after starting the engine under the conditions of high vibration loads.

The technical result is achieved by the fact that:

- permissible radial play of the shaft of the turbopump unit is 0.15 ÷ 0.30 mm;

- measurement of the radial play of the shaft is carried out with fully selected gaps between the parts located between the shaft and the casing of the turbopump unit, which is achieved by applying to the turbine disk in the disk plane alternately on two opposite sides of the same force in the range of 50 ÷ 70 kgf.

The application of this method solves the problem of ensuring the tightness of the turbo-pump unit and the fuel system of the engine during joint flight of the aircraft with the aircraft and increases the reliability of the aircraft in conditions of high vibration loads.

The proposed method can be performed using standard equipment and materials of domestic production. Thus, the claimed method meets the criterion of "industrial applicability".

Sources taken into account:

1. Bashta, T.M. Hydraulic drives of aircraft. -M .: Mashinostroenie, 1967. - 495 p.

2. Design and design of liquid rocket engines: Educational Edition / Ed. G.G. Gahuna - M .: Mashinostroenie, 1989. -424 p.

3. Makarov, G.V. Sealing devices. - L .: Mechanical Engineering, 1973.-232 p.

4. Act No. 11/18 of 09/07/2018 to investigate the causes of leakage of turbopump units of the aircraft engine using lip seals installed with tightness when exposed to high vibration loads. - [Orenburg]: JSC “PO“ Strela ”, 2018. - 2 p.

Claims (1)

The method of ensuring the tightness of the turbopump assembly under high vibration loads, carried out by shaft compression with lip seals installed with tension, operating both under pressure and without fluid pressure, with stationary and rotating shaft being sealed, which is equal to 0 , 15 ÷ 0.30 mm, and its measurement is carried out with fully selected gaps between the parts located between the shaft and the casing of the turbopump assembly, which is achieved by applying to the disk urbines in the plane of the disk alternately in two opposite sides of the same force in the range of 50 ÷ 70 kgf.

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