Summary: on the basis of an introduction to the application of mechanical sealing techniques in aviation engines, in particular the rationale, advantages and disadvantages of graphite ring sealing techniques and the problems of failure encountered in their application, and in conjunction with the failure of the graphite graphite-ring-sealed slipper in the graphite seal of a certain type of vortex engine, analysis of the reasons for the failure of graphite sealing by measuring and inspecting the sealing elements and wear marks, and recommendations for improvements to prevent the recurrence of failure。
Keywords: mechanical seals, graphite seals, wears, failure analysis
Introduction
Over the course of the development of aviation engine technology, the position of sealing technology in the factors affecting engine performance and lifetime has become increasingly critical. Aviation engine seals require deformation and placing caused by various factors, such as high relative rotation, high working temperature, high sealed pressure differentials and severe vibrations. As a result, the application of sealing technologies on engines has evolved to varying degrees in recent years, from traditional sealing to various new types of sealing, while graphite ring mechanical sealing techniques, as one of the commonly used sealing options, are becoming more sophisticated in repair controls。
I. Mechanical sealing
Mechanical seals are contact seals in a moving seal and are used mainly to seal media of various types of viscous, toxic, flammable, explosive, corrosive and corrosive solid particles with a life of up to 2,500 hours and generally not less than 800 hours. The following technical indicators have been achieved: axle diameter (5-2000) mm; pressure (10-6-45) mpa; temperature (200-450)°c; relative speed of 150 m/s。
Mechanical sealing is a sealing device consisting of two or more pairs or pairs of motion rings and flat frictions of silent rings. The side of smooth and flat motion rings and silent rings, which are combined relatively by the pressure of elastic components and sealed media, is usually in border lubricating condition, where a thin liquid membrane is maintained to achieve its purpose. The membrane is hydrodynamic and static and acts as a lubricating and balancing pressure. When the end of the seal is worn, the ring, together with the ring seal, is driven by a spring, resulting in a small shift along the axis to a certain compensatory capacity, known as the compensation ring. Through different structural designs, compensation rings can be carried out either by silent rings or by a moving ring. Components consisting of compensation rings, elastic elements and sub-sealed components are referred to as compensation ring components。
Mechanical seals consist mainly of graphite ring seals, magnetic ring seals, tooth seals, etc., and are analysed and studied below in conjunction with the graphite ring seals used by the aerodynamic brakers。
Ii. Aerodynamic graphite rings sealed
(i) speed-cutting works
As shown in figure 1, the speed-reducing units are specially designed for a certain type of russian vortex engine. When the air is driven to work, pressurizing the air impact on the air starter turbine, driving the turbine rotor to a high rate of rotation, passing the twist to the engine gas generator rotor through the brake and driving the engine to start. Air-mobilized brakes are planetary gears, with internal application of lubricating oils and, in order to prevent spills, graphite-ring sealing of turbine rotors at the turn-in end and external sealing of output-end elastic axes and external leather bowls。
The rate of the air starter is 8. 9 and the maximum speed of the turbine rotor can be as high as 50,000 r/min; within the brake, 926 aviation lubricants are used independently to lubricate and the temperature of the interior is about 120°c。
(ii) graphite ring seal
(b) air-motive turbine rotors are sealed externally with graphite rings, and mobile ring 4 is fixed to the end of turbine rotors 2, and rotates with turbine rotors; eight springs were installed on shell 1, with graphite rings on the top of the spring, with graphite rings on the surface of ring 3, with graphite rings on the surface of ring 3 and shell 1, sealed with a gel, and with a condensed structure on the lower part of ring 3, which can float up and down with spring 5, and do not move. While the brake works, the turbine rotor 2 drives together with the ring 4 and the silent ring 3 works with spring 5, pressing the graphite ring on the seal of the moving ring 4 to create friction by-products to prevent slips. The above, the ring 3 is the compensation ring; the ring 3, the spring 5 and the collide 6 together with the collage 6 form the compensation ring component, and when the graphite sealed end of the ring is worn, the ring 3 together with the ring seal tape 6 produce a small shift along the axis towards the spring 5 and achieves a certain capacity to compensate for the maintenance of the seal。
Iii. Graphite ring failure analysis
The graphite ring seal is not allowed to leak when the air is motivated to work. Anaerodynamic graphite ring leaking oil during tests or tests, some of which contained graphite powder in the spills. On the basis of the phenomenon of failure, the graphite sealing structure is used to analyse the cause of the failure in terms of the ring, the motion ring, the elastic element and the mass of the assembly。
(i) seal failure
A decomposition examination of the leaking brakes revealed a large amount of graphite powder in the slide at the failure point and a distortion of the surface of the decomposition graphite ring, such as figure 2. After the clean ring and the motion ring sealed surfaces, comparative and micrometric measurements revealed that both the silent ring and the motion ring surfaces were worn and severe. A combination of wear and tear marks of the ring and the ring can be seen to be complementary, resulting from an abnormal friction between the two. As shown in figure 2, figure 7. Further micro-observation of the graphite ring surface shows that the graphite ring surface is too rough and very low in plane level。
The friction surface produces ploughing ditches, and even if the friction substrates are the same material, they produce grinding particles in contact with the surface. When the friction surfaces are uneven, the wear microcrumbs are visible, and the contact of the silent ring with the motion ring surfaces under high-turn speed conditions will result in large quantities of grinding grains, which will be mixed into a new friction agent on the sealed surfaces. The roughness and peace of the surface of the graphite ring has a decisive impact on sealing performance。
When the graphite ring surface is rougher at work, there is an abnormal friction effect on grinding and sealing; failure to reach the required level results in the graphite ring not being closely bound to the moving ring 4 and the ski oil leaks during work。
The graphite ring damage can be repaired by grinding with a dedicated glass crystal plate, which generally requires a rough surface of up to ra0. 1 m and not more than 1 mm. Watch out for dust in grinding repairs and prevent impurities from being embedded in graphite seals。
A combination of static ring failure analysis shows that the motion ring seal surface is rough enough to reach less than a certain level of plane level, and that there is also a severe friction between the ring and the ring when the friction co-exposed speed is high. The slip oil from the malfunction contained large amounts of graphite powder and there was a severe friction on the surface of the decomposition kinetic ring. The roughness of the ring surface at work does not meet the requirements, which affects sealability; the lack of plane and parallelity does not close the ring to the graphite ring, resulting in leakage of the slide。
In the process of repairing the grinding platform, first of all, the grinding of the vortex with the ointment of the diamond and the turbo rotor, and the colouring of the measuring platform, so that the colouring of the co-opting surface is not less than 90 per cent and the paint is not broken around it; the second is the grinding of the ointment of diamonds, which is combined with the graphite ring, which is then washed by ultrasound, which is not allowed to be used to compress the air and to check the roughness and peace of the surface, while ensuring the parallelity of the upper and lower surfaces, and replacing the kinetic ring if the thickness of the grinding is lower than the assembly requirements。
(ii) resilient element ballistic control
The control of surface roughness, plane and parallel levels of the graphite rings and the kinetic rings met the requirements for use, the re-installation of the graphite ring seal was tested, and it was found that some of the subgraphite graphite ring seals were still leaking, fault trees were created, and each of the components of the sealed structures was checked for excavation。
As figure 3, flexing 8 springs of elastic elements for sealing devices that decompose the graphite ring surface with a "round" bias
The values of spring strength were found to be very poor. As shown in figure 1, the eight springs in the graphite ring seal structure are installed between shell 1 and ring 3, so that the graphite ring of ring 3 is attached to the surface of the moving ring 4 and, if the effect of spring 5 is too wide, the pressure is unevenly distributed on the graphite ring, which would result in tilting in the graphite ring during the operation and would also result in a graphite ring that is not closely bound to the moving ring 4 and would result in slippage. In the selection of springs, the strength of the eight springs should be controlled to meet elastic needs and to keep the composition within a more reasonable range, generally not greater than 0. 2 n, in order to ensure that the graphite rings (silent rings) are evenly applied in their work and that graphite seals are not offset by grinding。
(iii) quality impact of assembly
1. Turbo rotor installation face effects
As shown in figure 4, in the case of “two-point” grinding on the surface of the moving ring following the breakdown of the oil leak, the effects of silent rings, motion rings and elastic elements were removed from the analysis, the turbo rotor surface was tested, the installation surface was found to be uneven, the inner vortex core was symmetrically increased, and the installation of the motion ring support resonance was uneven, resulting in an oscillation with the static ring seal, which resulted in an abrasive grinding during the operation, resulting in oil spills。
When repaired, turbine rotors are placed in the grinder's plate, grinding the surface with grinders and polishing of diamonds, ensuring that the surface is rough and peaceful enough to meet the requirements, colouring checks are performed on the surface with the ring, and colouring is generally not less than 90 per cent and continues throughout the circle。
2. Turbo rotor beats very poorly
As shown in figure 5, there is a `interruptive' bias on the surface of the moving ring following breakdown of malfunctions, with a lower degree of friction, with a lower amount of ski oil leak, no major cause was detected following inspection of the cylindrical ring, the moving ring, the elastic element and the installation surface, and a seal covering was found between the disassembly and the installation surface
Uneven, affecting the parallels of the upper and lower surfaces, which, when installed, result in a slight slope of the moving ring-sealed surface, the parallels of the upper and lower surfaces of the moving rings, the verticality of the turbine rotor surfaces, the flatness of the axes, etc., resulting in intersevere grinding. The amount of beats can be guaranteed by applying evenly to the glue, moving the ring 4 against the turbine rotor 2。
In order to control the size of the post-installation dynamic ring surface, to prevent the installation of an oscillation or turbo axial error, the turbine rotor 2 will be required to measure the beat of the turbo 4 surface relative to the turbo 2 surface oscillation, which is generally not greater than 0. 01 mm。
3. Turbo rotor balance excess (figure 6)
Based on excavated repair experience, the turbine works at a very high rate and the parts should be installed with a moving balance, and the turbine rotor will be fitted with a kinetic ring, bearings, gears, and will require a check of the remaining imbalance not exceeding 0. 1 g cm. The balance affects the smoothness of the turbine rotor rotation, and if the balance is too poor, the ring is sharpened during the rotation, resulting in seepage of the slide oil。
The main factors affecting the balance are turbo rotors, uneven or processed gears and errors in assembly, which can be reduced through the use of balancing machines, relative angles of gears to turbine rotors, grinding turbine rotors, and meeting the requirements for remaining imbalances。
(iv) unusual wear of graphite rings
The graphite sealing ring of silicon ring 3 is attached to the surface of the moving ring 4 and forms the sealing side. If impurities enter between the sealed surfaces, they cause abnormal wear and tear of graphite rings and spill oil. The slipper from the malfunction contained large amounts of graphite powder, as shown in figure 7。
The main factors contributing to impurities are the graphite graphite ring of dust during grinding and the uncleaning of sealed surfaces during assembly. The grinding of graphite rings shall not be allowed using a grinding ointment or a platform containing ointment, after which it shall be kept clean of the seal surface and shall be assembled to check the cleanness of the seal surface. When assembled, a smooth ski oil is applied to the surface of the ring, so that a thin liquid membrane between the sides is maintained for the purpose of sealing, while acting as a lubrication and balancing pressure。
Concluding remarks
The graphite ring sealing is the usual method of sealing engines, but the pollution of the fluid is more demanding at the time of its use, and the graphite ring is more rapidly worn and prone to oil spills. The same graphite sealing is used for this type of russian vortex bearing bearing bearings, but the annual maintenance costs due to oil leaks are high due to the inherent shortcomings of graphite sealing。
Compared to the graphite ring seals described here, new sealing techniques with multiple structures, such as tooth seals, finger seals and gas membranes, have become areas of study with great potential. In the case of a three-generation vortex engine in a given country, the feeder seals are sealed in the form of tusk seals with magnetic seals. Soundly performing seals can effectively reduce fuel consumption and maintenance costs and increase engine life. While the air engine sealing technology is currently evolving in an innovative direction towards a high level of structural compactness, light quality, ease of assembly and broken safety, the domestic sealing technology is still in the use of traditional technologies, and it is hoped that the content of this paper will assist in the development of domestic sealing technologies in the future and inform innovation in new technologies。
