Reactive aircraft, which began to be created in the 1940s, demanded the development of a new type of engine.

The composite scapula of a large engine began with a small

Reactive aircraft, which began to be created in the 1940s, demanded the development of a new type of engine. The gas turbine jet engines that received the most widely used revolution in aviation equipment.

Science and life // Illustrations

The shoulder blades of the gas turbine of the reactive engine operate in very difficult conditions: they flow out the flow of hot gases from combustion chambers.

The cooling air, supplied from the side of the turbine axis into the canals of the shoulder blade, comes out of its end.

The rods are placed in the mold for casting the shoulder blade of the gas turbine. After cooling the workpiece, the rods are dissolved and channels remain in the finished shoulder blade to pass the cooling air.

The air that comes out of the holes in the side of the shoulder blades creates a thin air film that isolates the shoulder blade from hot gases (left). The channels leading to the holes have a rather complex geometry (on the right).

Metal of a cast blade freezes in the form of crystals of different sizes, linked not enough reliably (on the left). After the modifier’s metal was introduced, crystals became small and homogeneous, the strength of the product increased (on the right).

Thus, a directed crystallization of the material of the scapula is performed.

Having improved the technology of directed crystallization, it was possible to grow a shoulder blade in the form of a single monocristal.

In monocrystalline shoulder blades, a coolant of a complex shape is created. The latest developments of its configuration made it possible to increase the efficiency of cooling of the blades one and a half times.

Engines and materials

The power of any thermal engine is determined by the temperature of the working body – in the case of a reactive engine, this is the temperature of the gas arising from combustion chambers. The higher the gas temperature, the more powerful the engine, the greater its thrust, the higher the efficiency and better weight characteristics. In the gas turbine engine there is an air compressor. He is rotated by a gas turbine sitting with him in the same shaft. The compressor compresses the atmospheric air to 6-7 atmospheres and directs it into the combustion chambers, where fuel is injected-kerosene. The flow of red -hot gas flowing from the chambers – the combustion products of kerosene – rotates the turbine and, flying through the nozzle, creates jet traction, drives the plane. High temperatures arising in the combustion chambers required the creation of new technologies and the use of new materials for the construction of one of the most critical engine elements – stator and rotary blades of a gas turbine.They must, for many hours, without losing their mechanical strength, withstand the enormous temperature at which many steels and alloys already melt. First of all, this applies to turbine blades – they perceive the flow of hot gases heated to temperatures above 1600 K. Theoretically, the gas temperature in front of the turbine can reach 2200 K (1927oC). At the time of the birth of jet aviation – immediately after the war – materials from which it was possible to make blades that could withstand high mechanical loads for a long time did not exist in our country.

Shortly after the end of the Great Patriotic War, work on the creation of alloys for the manufacture of turbine blades was started by a special laboratory at VIAM. It was headed by Sergei Timofeevich Kishkin.

TO ENGLAND FOR METAL

Even before the war, the first domestic design of a turbojet engine was created in Leningrad by the designer of aircraft engines, Arkhip Mikhailovich Lyulka. In the late 1930s, he was repressed, but, probably anticipating his arrest, he managed to bury the drawings of the engine in the yard of the institute. During the war, the country's leadership learned that the Germans had already created jet aircraft (the first aircraft with a turbojet engine was the German Heinkel He-178, designed in 1939 as a flying laboratory; the twin-engine Messerschmit Me-262 became the first serial combat aircraft (entered service with the German troops in 1942. — Note. ed

.). Then Stalin called L.P. Beria, who was in charge of new military developments, and demanded to find those who are engaged in jet engines in our country. A. M. Lyulka was quickly released and given to him in Moscow on Galushkin Street a room for the first design bureau of jet engines. Arkhip Mikhailovich found and dug out his drawings, but the engine according to his project did not work out right away. Then they simply took a turbojet engine bought from the British and repeated it one by one. But the matter rested on materials that were absent in the Soviet Union, but were available in England, and their composition, of course, was classified. And yet it was possible to decipher it.

Arriving in England to get acquainted with the production of engines, S. T. Kishkin appeared everywhere in boots with thick microporous soles. And, having visited with a tour the plant where turbine blades were processed, near the machine, as if by chance, he stepped on the chips that had fallen from the part. A piece of metal crashed into soft rubber, got stuck in it, and then was taken out and already in Moscow subjected to a thorough analysis. The results of the analysis of the English metal and extensive own research carried out at VIAM made it possible to create the first heat-resistant nickel alloys for turbine blades and, most importantly, to develop the foundations of the theory of their structure and production.

It was found that the main carriers of the heat resistance of such alloys are submicroscopic particles of the intermetallic phase based on the Ni3Al compound.The spatulas from the first heat-resistant nickel alloys could work for a long time if the gas temperature in front of the turbine did not exceed 900-1000 K.

Casting instead of stamping

The shoulder blades of the first engines were stamped from an alloy cast in a bar to a form remotely resembling a finished product, and then for a long and carefully processed on the machines. But here there was an unexpected difficulty: in order to increase the working temperature of the material, alloying elements were added to it – tungsten, molybdenum, niobium. But they made the rafting so hard that it became impossible to stamp it – it did not succumb to form with hot deformation methods.

Then Kishkin suggested casting the shoulder blades. Motorist designers were indignant: firstly, after casting, the shoulder blade will still have to be processed on machines, and most importantly-how can you put a cast scapula in the engine? The metal of the stamped blades is very carny, its strength is high, and the cast metal remains more loose and obviously less durable than the stamped. But Kishkin managed to convince skeptics, and in Viam they created special foundry heat -resistant alloys and the technology of casting blades. Tests were carried out, after which almost all aviation turbojet engines began to be produced with cast turbine blades.

The first shoulder blades were continuous and could not withstand high temperatures for a long time. It was required to create a system of cooling. To do this, we decided to make longitudinal channels in the shoulder blades to supply cooling air from the compressor. This idea was not so hot: the more air from the compressor goes for cooling, the less it will go into the combustion chambers. But there was nowhere to go – the turbine resource must be increased at all costs.

They began to construct blades with several through cooling channels, located along the axis of the shoulder blade. However, it soon became clear that this design is ineffective: the air flows through the channel too quickly, the area of the cooled surface is small, the heat is not enough. They tried to change the configuration of the inner cavity of the scapula, inserting the deflector there, which rejects and delays the flow of air, or make the channels of a more complex shape. At some point, a tempting idea took possession of the specialists in aviation engines-to create a whole ceramic spatula: ceramics withstands a very high temperature, and it is not necessary to cool it. Almost fifty years have passed since then, but so far no one has made ceramic shoulder blades in the world, although attempts are ongoing.

How to make a cast scapula

The manufacturing technology of turbine blades is called casting models. First, they make a wax model of the future shoulder blade, casting it in a press form, in which quartz cylinders are previously put into the place of future cooling channels (then they began to use other materials). The model is covered with liquid ceramic mass.After its drying, the wax is expelled with hot water, and the ceramic mass is burned. It turns out a form that can withstand the temperature of the molten metal from 1450 to 1500 ° C, depending on the brand of the alloy. Metal is poured into the mold, which freezes in the form of a finished shoulder blade, but with quartz rods instead of channels inside. The rods are removed, dissolving in smelter. This operation is carried out in a hermetically sealed room, an employee in a spacesuit with an air supply hose. The technology is uncomfortable, dangerous and harmful.

To exclude this operation, in VIAM they began to make rods from aluminum oxide with an addition of 10-15% silicon oxide, which dissolves into alkali. The material of the shoulder blades with alkali does not react, and the remaining aluminum oxide is removed with a strong stream of water. Our laboratory was engaged in the manufacture of rods, and I myself began to study casting technology, materials for ceramic shapes, alloys and protective coatings of finished products and now I head this area of research.

In everyday life, we are used to counting cast products very rough and rough. But we managed to choose such ceramic compositions that the form of them is completely smooth and the casting of machining is almost not required. This greatly simplifies the work: the shoulder blades have a very complex shape, and processing them is not easy.

New materials demanded new technologies. No matter how convenient the additives of silicon oxide in the material of the rods were, it had to be abandoned. The melting temperature of aluminum oxide AL2O3 is 2050 OS, and SIO2 silicon oxide – only about 1700 OS, and new heat -resistant alloys destroyed the rods already during the filling.

In order for aluminum oxide the shape to remain strength, it is burned at a temperature higher than the temperature of the liquid metal, which is poured into it. In addition, the internal geometry of the form when filling should not change: the walls of the shoulder blades are very thin, and the dimensions should accurately correspond to the calculated ones. Therefore, the permissible value of the shrinkage of the form should not exceed 1%.

Why refused stamped shoulder blades

As already mentioned, after stamping, the shoulder blade had to be processed on machines. At the same time, 90% of the metal went into the chips. The task was set: to create such a technology of accurate casting so that the specified profile of the scapula would be immediately obtained, and the finished product would only have to be polished and applied to it the heat -cross coating. No less important is the design that is formed in the body of the scapula and performs the task of cooling it.

Thus, it is very important to make a scapula that is effectively cooled without reducing the temperature of the working gas, and has high prolonged strength. This problem was solved by combining the channels in the body of the scapula and the output holes from it so that a thin air film occurs around the shoulder blade. At the same time, two birds with one stone are killed at once: hot gases with the material of the shoulder blades do not contact, and therefore, they do not heat it and do not cool.

Here there is some analogy with the thermal protection of a space rocket. When a rocket enters the dense layers of the atmosphere at high speed, the so-called sacrificial coating that covers the head begins to evaporate and burn. It takes on the main heat flow, and the products of its combustion form a kind of protective cushion. The design of the turbine blade is based on the same principle, only air is used instead of a sacrificial coating. True, the blades must also be protected from erosion and corrosion. But for more on this, see page 54.

The procedure for making a blade is as follows. First, a nickel alloy is created with specified parameters for mechanical strength and heat resistance, for which alloying additives are introduced into nickel: 6% aluminum, 6-10% tungsten, tantalum, rhenium and a little ruthenium. They allow for maximum high temperature performance for cast nickel based alloys (there is a temptation to increase them further by using more rhenium, but it is insanely expensive). A promising direction is the use of niobium silicide, but this is a matter of the distant future.

But here the alloy is poured into a mold at a temperature of 1450 ° C and cools along with it. The cooling metal crystallizes, forming separate equiaxed, that is, approximately the same size in all directions, grains. The grains themselves can be both large and small. They adhere unreliably, and the working blades collapsed along the grain boundaries and shattered to smithereens. Not a single blade could last longer than 50 hours. Then we proposed to introduce a modifier into the casting mold material – cobalt aluminate crystals. They serve as centers, nuclei of crystallization, accelerating the process of grain formation. The grains are uniform and fine. New blades began to work for 500 hours. This technology, which was developed by E. N. Kablov, is still working, and it works well. And we at VIAM produce tons of cobalt aluminate and supply it to factories.

The power of jet engines grew, the temperature and pressure of the gas jet increased. And it became clear that the multi-grain structure of the blade metal would not be able to work under the new conditions. Other ideas were needed. They were found, brought to the stage of technological development and became known as directed crystallization. This means that the metal, when solidified, does not form equiaxed grains, but long columnar crystals elongated strictly along the axis of the blade. A blade with such a structure will resist fracture very well. I immediately recall the old parable about a broom that cannot be broken, although all its twigs individually break without difficulty.

HOW DIRECTIONAL CRYSTALLIZATION IS PERFORMED

In order for the crystals forming the blade to grow properly, the molten metal mold is slowly removed from the heating zone.At the same time, the shape with liquid metal is on a massive copper disk, cooled by water. The growth of crystals begins from below and goes up at a speed, almost equal to the flow rate of the form from the heater. When creating a technology of directed crystallization, I had to measure and calculate many parameters – the crystallization rate, the temperature of the heater, the temperature gradient between the heater and the refrigerator, etc. It was necessary to choose such a speed of the form that the columnous crystals germinate over the entire length of the scapula. Subject to all these conditions, 5-7 long column crystals grow for each square centimeter of the cross section of the shoulder blade. This technology made it possible to create a new generation of aircraft engines. But we went even further.

Having studied with radiographic methods, grown chopped crystals, we realized that the entire spatula can be made entirely from one crystal that will not have inter -seamless boundaries – the weakest elements of the structure along which the destruction begins. To do this, they made a seed, which allowed only one crystal to grow in a given direction (the crystallographic formula for such a seed is 0-0-1; this means that in the direction of the axis Z

The crystal is growing, and in the direction
X
—
Y
– No). The seed was put in the lower part of the shape and flooded the metal, intensively cooling it from below. The growing monocrystal acquired the shape of the scapula. By the way, the first publication about this technology appeared in the journal Science and Life back in 1971, in No. 1.

American engineers used a copper water -cooled crystallizer for cooling. And after several experiments, we replaced it with a bathroom with a molten tin at a temperature of 600-700 K. This allowed us to more accurately select the necessary temperature gradient and receive high-quality products. In Viam, installations with baths were built for growing monocrystalline blades – very advanced machines with computer control.

In the 1990s, when the USSR collapsed, Soviet aircraft remained on the territory of East Germany, mainly miG fighters. They had the shoulder blades of our production in their engines. The Americans examined the metal of the shoulder blades, after which quite soon their experts arrived in VIAM and asked to show who created it and how. It turned out that they were given the task of making monocrystalline meter -length shoulder blades that they could not solve. We designed the installation for highly gradient casting of large -sized blades for energy turbines and tried to offer their technology to Gazprom and RAO UES of Russia, but they did not show interest. Nevertheless, we are almost ready for an industrial installation for casting meter blades, and we will try to convince the management of these companies in the need for its implementation.

By the way, turbines for energy are another interesting task that Viam solved.Aircraft engines that have exhausted their service life began to be used at gas pipeline compressor stations and in power plants that feed oil pipeline pumps (see Science and Life, No. 2, 1999). Now the task has become urgent to create for these needs special engines that would operate at much lower temperatures and pressure of the working gas, but much longer. If the resource of an aircraft engine is about 500 hours, then the turbines on the oil and gas pipeline should work 20-50 thousand hours. One of the first to deal with them was the Samara design bureau under the leadership of Nikolai Dmitrievich Kaznetsov.

HEAT RESISTANT ALLOYS

A single-crystal blade does not grow solid – inside it has a cavity of complex shape for cooling. Together with CIAM, we have developed a cavity configuration that provides a cooling efficiency coefficient (the ratio of the temperatures of the blade metal and working gas) equal to 0.8, almost one and a half times higher than that of serial products.

These are the blades we offer for new generation engines. Now the gas temperature in front of the turbine barely reaches 1950 K, and in new engines it will reach 2000-2200 K. For them, we have already developed high-temperature alloys containing up to fifteen elements of the periodic table, including rhenium and ruthenium, and heat-shielding coatings, in which include nickel, chromium, aluminum and yttrium, and in the future – ceramic from zirconium oxide stabilized with yttrium oxide.

In the first generation alloys, a small amount of carbon was present in the form of titanium or tantalum carbides. Carbides are located along the boundaries of the crystals and reduce the strength of the alloy. We got rid of carbide and replaced it with rhenium, increasing its concentration from 3% in the first samples to 12% in the last ones. There are few reserves of rhenium in our country; there are deposits in Kazakhstan, but after the collapse of the Soviet Union, it was completely bought up by the Americans; remains the island of Iturup, which is claimed by the Japanese. But we have a lot of ruthenium, and in new alloys we have successfully replaced rhenium with it.

The uniqueness of VIAM lies in the fact that we are able to develop both alloys, and the technology for their production, and the method of casting the finished product. Huge work and knowledge of all employees of VIAM has been invested in all the blades.

See in a room on the same topic

E. KABLOV – VIAM is a national treasure.

A. ZHIRNOV — Winged metals and alloys.

M. BRONFIN – Testers – researchers and controllers.

Academicians give permission for a non-stop flight of N. S. Khrushchev to New York on an ultra-long-range aircraft TU-114.

I. FRIDLANDER — Aging is not always bad.

B. SHETANOV — The thermal protection of the Buran began with a sheet of tracing paper.

S. MUBOYAJYAN – Plasma versus steam: victory for a clear advantage.

BUREAU OF SCIENTIFIC AND TECHNICAL INFORMATION.

E. KONDRASHOV — Planes do not fly without non-metal parts.

I. KOVALEV – In science – from school.

S. KARIMOV — Corrosion is the main enemy of aviation c.

BUT.PETROVA – Put on glue.

Application and types of blade mechanisms

Blade mechanisms are widely used in machines for various purposes. They are most often used in turbines and compressors.

A turbine is a rotary engine operating under the influence of significant centrifugal forces. The main working body of the machine is the rotor, on which the blades are fixed along the entire diameter. All elements are placed in a common body of a special shape in the form of injection and supply pipes or nozzles. A working medium (steam, gas or water) is supplied to the blades, setting the rotor in motion.

Thus, the kinetic energy of the moving stream is converted into mechanical energy on the shaft.