AA (steam locomotive)

 AA (Andrey Andreev) — an experienced Soviet steam locomotive. The only locomotive in the world with seven driving axles in one rigid frame (not to be confused with articulated locomotives).

Creation history

By the 1930s, Soviet railways had significantly increased the requirements for traction and speed of trains. The existing 0-5-0 (E series) and 1-5-0 steam locomotives, whose coupling weight did not exceed 85 tons, could no longer fully cope with the increased volume of traffic. Their replacement with significantly more powerful steam locomotives was urgently required.

Different groups of specialists offered different solutions. So, some suggested leaving five driving wheel pairs on the locomotive and only increasing the load from the axle to the rails, while strengthening the railway track. Others insisted on keeping the load from the driving wheelsets within 20 tons, while increasing their number. Both groups of specialists did not take into account that at that time the cars were mainly equipped with a screw harness (the automatic coupling on Soviet railways will be massively installed only from 1934), which could withstand a force not exceeding 20 tons.

A significant motivating factor in the creation of the Soviet 2-7-2 type steam locomotive was the experience of German and mainly North American steam locomotive construction, in the creation of steam locomotives with six driving axles in one rigid frame, respectively, types 1-6-0 and 2-6-1.

The technical specification issued in the spring of 1930 for an alternative preliminary design of a Soviet high-speed freight locomotive, with more than five driving axles in one rigid frame, provided for a maximum axial load on the rails of 20 tons, that is, the same as for the preliminary design of a Soviet 1-5-1 type steam locomotive (future FD), which significantly complicated the task for designers. If for the high-speed American type 2-6-1 with an average design axial load from the driving wheelset on the rail-26.9 tons-back in 1926, it was possible to successfully implement the specified traction and speed characteristics, then for the high — speed Soviet design version, taking into account the specified axial load-20 tons, the number of driving axles had to be increased to seven... Nevertheless, the acquisition of practical experience in solving such a complex technical problem was considered expedient for the young Soviet school of locomotive construction, in terms of implementing an unusually large — sized steam locomotive boiler and crew part with seven coupling axles-an absolute record in the practice of world locomotive construction.

Design and manufacture of steam locomotives

In 1931, a group of young graduate engineersMIITa has prepared a preliminary design of a steam locomotive with a 1-7-2 wheel formula and a rail load not exceeding 20 tons from the wheelset. In theory, such a locomotive was supposed to provide maximum carrying capacity and significantly reduce the cost of transportation due to the possibility of using low-grade coal and avoiding the use of articulated locomotives. At the same time, the load on the rails that does not go beyond the standards would allow such locomotives to be used without much reinforcement of the tracks. Driving wheels of a steam locomotive with a diameter of 1550 mm were located in one rigid frame. The coupling weight of the locomotive was 140 tons, the cylinder diameter was 735 mm, and the piston stroke was 812 mm. The grate area was 10 m2, and the evaporative heating surface of the boiler was 445 m2. Engineer K. P. Korolev, a future major specialist in the field of locomotive dynamics and the author of many books, did a lot of calculation work on the crew part.

Working drawings of the new locomotive were already being drawn up atVoroshilovgrad Locomotive Building Plant, which was assigned by the NKPS to produce two locomotives of this type. However, during the working design, it turned out that when using the 1-7-2 wheel formula, the weight restrictions could not be maintained, so it was decided to switch to the 2-7-2 type.. In addition to changing the wheel formula, the project has undergone a number of other changes. In particular, the cylinder diameter was increased from 735 to 740 mm, and the grate area was increased from 10 m2 to 12 m2. The steam pressure in the boiler should be 17 kgf / cm2. The locomotive received a radial boiler furnace, a bar frame and a superheater of the Chusov system.

The production of the locomotive at the plant was slow, and largely due to the fact that at the same time the plant mastered the mass production of FD type 1-5-1 locomotives. For the same reasons, it was decided to abandon the production of a second locomotive. The locomotive was ready only by the end of 1934. The new locomotive received the letter designation AA (in honor ofAndrey Andreyevich Andreev, who held the post of People's Commissar of the NKPS in 1931-1935) and the full designation of the steam locomotive AA20-1 (20 — the load from the driving wheelsets on the rails in tons).

Design features

The AA locomotive was the first and only locomotive in world history with seven driving axles in a single rigid frame. The steam locomotive boiler was one of the largest locomotive steam boilers in the world.Europe. Due to the huge size of the locomotive, a number of measures were taken to improve the fit of the locomotive in curves. In particular, the front bogie was able to deviate from the longitudinal axis of the locomotive in the range of ± 145 mm (at the extreme points), the rear — in the range of ± 265 mm. The running distance of the first and second wheel pairs was ± 27 mm, the seventh ± 35 mm. In addition, there were no ridges on the wheels of the third, fourth and fifth pairs, and the width of their bandages was 175 mm.

Also, the locomotive was distinguished by the original system of transmitting force from the piston rod of the steam engine to the driving wheel pairs. So, on a conventional steam locomotive, the tractive effort is transmitted to one of the axles (the driving wheelset), and from it through the drawbar directly to all the other driving axles. On the AA locomotive, the tractive effort was transmitted to the fourth driving axle, and from it the tractive effort was directly transmitted to the first three coupling axles. Also, this axis was connected to the fifth wheelset by a special drawbar, and the sixth and seventh were set in motion directly from the fifth driving axis.

Technical description of the locomotive

The boiler. A very developed "full" boiler, which is close in its parameters to the boiler of an American 2-6-1 type steam locomotive, provides an excess of the designed capacity of 3,500 hp.;

The length of the boiler when assembled is 17871 mm;

Weight of the boiler without fittings and fittings — 60 tons;

The boiler is supplied with water by two hot steam injectors with a capacity of 360÷380 l / min and two conventional hot steam injectors.

Heating of the boiler is stoker. In the 6-axle tender from the FD series steam locomotive (tender "type 17"), two mechanical carbon sensors of the "CLPB type" were installed — very unreliable in operation.

The furnace part of the boiler is of a radial type, with an afterburning chamber, of an all-welded design. In terms of structural and technological parameters, the furnace part of the boiler is similar to the FD steam locomotive, but differs in significantly larger overall dimensions. The furnace casing is connected by welds to the cylindrical casing of the afterburning chamber. The casing of the furnace, the casing of the afterburning chamber and the fire box passing into the afterburning chamber are reinforced with rigid and movable links.

Grate area — 12 m2;

The grates are made swinging, driven by a special piston machine, working with air or steam.

Length of firebox with afterburning chamber-7,3 m;

The volume of the firebox with the afterburning chamber is 24.5 m2;

Circulation (boiling) pipes are installed in the furnace, in order to increase the circulation of water in the boiler and to maintain the fire-resistant brick arch in the furnace.

Number of boiler pipes — 4;

The cylindrical part of the boiler designed from three drums is actually made from four drums, due to the impossibility of obtaining rolled products of the required width. The drums of the cylindrical part of the boiler are connected telescopically by two-row transverse rivet seams, and with the casing of the afterburning chamber — by four-row rivet seams. The front and rear pipe grilles are of welded construction.

Number of smoke pipes — 138;

number of fire pipes — 48;

Length of smoke and fire pipes between grilles-7000 mm;

Due to the large length of pipes between the grates, in order to prevent their deflection, blockage and reduce the resistance to the passage of flue gases, slightly increased diameter is made.

Diameter of fire pipes-163/173 mm;

Diameter of smoke pipes-65/70 mm;

Evaporative heating surface of the furnace — 38.56 m2;

Evaporative heating surface of the afterburning chamber — 11.81 m2;

Evaporative heating surface of boiler pipes — 4.85 m2;

Evaporative heating surface of fire pipes-180 m2;

Evaporative heating surface of smoke pipes — 212.3 m2;

Total evaporative heating surface (water) — 448.64 m2;

Working pressure of steam in the boiler — according to the pressure gauge) - 17 kg / cm2;

Superheater — Chusov systems, 6-pipe, single-turn with an increased diameter of elements (24/30) mm, in order to reduce the intensity of boiling of element tubes.

Pipe diameter of superheater elements-24/30 mm;

Superheater heating surface — 174.0 m2;

Total heating surface of the boiler — 662.04 m2;

Steam supply regulator-multi-valve type (seven valves are located in the manifold behind the superheater);

Steam engine. Two-cylinder single expansion with a cylinder diameter of 740 mm and a piston stroke of 810 mm, Walshart steam distribution. The spool valves are made with counterstocks, the spool diameter is 330 mm, the maximum stroke of the spool is 198 mm, the intake overlap is 50 mm, the exhaust overlap is 0 mm. The linear inlet displacement is 8 mm. Pistons are provided with O-rings of a Shtareva and are executed with countershocks.

The large weight of the moving parts of the machine (the leading drawbar — 730 kGf, the piston, rod and crosshead — 1127 kGf), as well as the high structural speed of the locomotive (90 km/h), made it necessary to carefully balance all the rotating parts, as well as the necessary part of the reciprocating masses. The balance of inertia of the horizontal forces of translationally moving masses was actually 57.77 %, the twitching amplitude was 4.32 mm, the balance of the moments of influence was 36.5 %, and the wobble amplitude was 0.00032. The calculations of the dynamic passport showed that the dynamic impact of the locomotive on the rail does not exceed the permissible limits. At the maximum (design) speed, the dynamic coefficient of the driving and other (coupling) driving axles corresponds to values from 1.5 to 1.6. However, this locomotive did not meet all the operating requirements, especially in terms of fitting into curves.

Driving mechanism. In order to reduce the diameter of the rolling pin (piston rod), the crosshead is made double. Rear-main crosshead-multi-tiered (Pennsylvania type), connected to the leading drawbar. Front-an additional crosshead that slides along a small parallel provides additional direction and connection to the piston rod. Without an additional crosshead, the diameter of the rolling pin, under the conditions of longitudinal bending, would have to be significantly increased, which in turn would lead to an increase in the weight of the reciprocating parts and to a deterioration in the working conditions of the oil seal on the rear cylinder cover. To ensure proper operation of the drawbar when moving the axles laterally during the passage of the locomotive in curves: The 1st and 2nd coupling drawbars are connected to each other by means of vertical and horizontal rollers; ball bearings are installed on the fingers of the 1st and 2nd coupling axes, which provide the possibility of turning the drawbar. All drawbars are made with round heads equipped with floating bushings adapted to both solid and liquid lubrication. The center neck of the crank pin of the 4th driving axis is connected by pairs with the crank pins of only the 3rd, 2nd and 1st driving axes. The cranks of the 6th and 7th driving axes are connected by pairs with the cranks of the 5th driving axis, which have fingers with a double neck (similar to the fingers of the 4th driving axis). The center finger necks of the cranks of the 5th driving axis are connected by pairs to the fingers of the cranks of the 4th and 6th driving axes, and the leading finger necks of the cranks of the 5th axis are connected to the leading necks of the 4th driving axis by a special, so-called tandem drawbar. The tandem drawbar greatly facilitates the working conditions of the driving pin, since only part of the force acting along the connecting rod is transmitted to the driving pin, which is necessary for rotation of the 4th, 3rd, 2nd and 1st axes, while the other part of the force acting along the connecting rod is transmitted through its fork-shaped crank head, through a stepped steel bushing pressed into its cheeks, directly to the front head of the tandem drawbar, for rotation of the 5th (driving tandem axis), 6th and 7th driving wheels.axes. The front head of the tandem drawbar enters the fork-shaped crank head of the connecting rod and rotates on the middle part of the stepped steel bushing, pressed with its extreme parts into the cheeks of the connecting rod head and put on together with the "floating" bronze bushing placed in it, on the finger of the 4th driving axis.

Steam distribution mechanism of the Walshart system. The installation of counter-cranks on the 5th driving axis caused a significant increase in the length of the spool rod, to prevent bending of which, an intermediate guide bronze bushing is installed. In addition, the design of the external steam distribution mechanism has become more complicated, due to the need to introduce an intermediate draft to the curtain rod and an additional rocker lever, with the formation of the so-called "tandem curtain rod" in order to shorten the eccentric draft and reduce its vibration level during the operation of the locomotive.

Crew part of the locomotive:

Main frame. Bar type, but unlike the FD series steam locomotive, its side panels are made not rolled, but cast. due to the lack of rental of the required size.

Devices that allow the locomotive to move and fit into curves:

Front 2-axle (runner) trolley. It consists of two longitudinal balancers that form axle boxes at the ends for the axle necks. The internal space of each balancer includes two springs that rest on the body of the balancer at the ends. On the middle part of each spring, a movable frame is supported by its protrusions-brackets, to the middle part of which a support frame is bolted — a lower roller plate having four inclined planes located in pairs, on each side of the middle of the cart. The right and left cylindrical rollers have the ability to roll over the corresponding pair of inclined planes of the lower roller plate. The upper roller plate, in its upper part, has a hemispherical recess, in which there is a movable pin that enters the guide attached to the lower part of the casting of the cylinder block. The weight load is transmitted sequentially: to the pin, to the upper roller plate, to the rollers, to the lower roller plate, to the movable frame and through its brackets — to the springs, balancers, axle boxes, and axle necks. The use of inclined support planes and rollers as a return device provides the limits of lateral deviation of the trolley (±145 mm) with a return force of 8250 kGf.

System of driving (coupling) wheel pairs. Lateral movements of the driving axes: 1st (±27 mm)and 2nd (±27 mm — - are provided by the presence of gaps between the axle boxes and platbands. Driving axes: the 3rd, 4th and 5th are made rigid, but without ribs with a band width of 175 mm; the 6th axis is ribbed, rigid. Lateral movement of the 7th driving axis (±35 mm) is provided by the presence of gaps between the axle boxes and platbands, and in addition, the axle boxes of the 7th axis are connected to the springs by two pairs of pendulum-type suspensions, which, as a return device, create a variable return force, from 1500 to 3000 kGf, depending on the magnitude of the transverse movement of the 7th axis. The return device of the 7th driving axis provides favorable conditions when the locomotive is moving in reverse and increases the resistance to "wagging".

Rear support trolley of the "2-axle Bissel" system. Structurally similar to the bogie of steam locomotives of type 1-5-2, Ta series and type 1-4-2 of the IS series, located under the furnace part of the boiler, equipped with a rocker return device that creates a constant return force of 1600 kGf, the minimum required when the locomotive is moving in reverse, without significantly worsening the conditions of forward travel, provides lateral deviations (±265 mm). Lateral movement of the 1st axis (±35 mm). The rocker return device includes a parent with two lower reference points.

Spring suspension of the locomotive. Made according to the scheme of three separate groups located at three points. The 1st separate group includes springs of the front bogie, and springs of the 1st, 2nd, 3rd and 4th coupling axles balanced with each other by longitudinal balancers giving one point; transverse balancers for the 1st group are: ball pin and upper roller plate of the front bogie. The 2nd and 3rd separate spring suspension groups are formed, respectively, by springs on the right and left sides of the 5th, 6th, and 7th driving axles and supporting axles of the rear bogie, connected on each side by longitudinal balancers. This spring suspension scheme provides a statically definable system. despite the increased pressure on the axle compared to the E-series locomotive (20 tons versus 16 tons). The static load on the springs of a 2-7-2 steam locomotive slightly exceeds the static load on the springs of an E-series steam locomotive (7700 kGf vs. 6770 kGf), due to the fact that the excess of axial pressure occurs due to the weight of the wheel pairs and the parts hung on them. In order to reduce the dynamic impact on the track, the stiffness of the springs of the leading 4-axis is reduced to 82 kg / mm; the spring stiffness of the other coupling axles is 97 kg/mm.

The braking system. The locomotive is equipped with a Kazantsev brake system. Taking into account the large transverse deviations (run-ups) of the axles, only the 3rd, 4th, 5th and 6th axles, as well as the 6-axle tender, are subject to braking.

Steam locomotive rating

The rating of the AA20-1 steam locomotive is ambiguous. L. B. Yanush is the most categorical in his judgments in his book" Russian Locomotives for 50 Years " of 1950. The machine owes its appearance to the creative impulse of young Soviet designers, who sought to create a machine capable of increasing the carrying capacity and reducing the cost of transportation on the main highways in the face of a number of technical limitations. As of 1934, the only section on the road network of the USSR where the AA-20 locomotive could compete with the FD locomotive, was an extremely heavy-duty carbon section " Krasny Liman-Osnova (Kharkiv)". The technical reconstruction of this section was carried out in full — heavy type "II-a" rails on crushed stone ballast, the embankment prism is designed for laying the second pair of tracks in its width, smoothed radius curves, elongated switches, auto-locking. However, to do this, it was necessary to put into operation at least ten such locomotives. U-turn for this locomotive was not required, when driving "pipe back" review was not much worse. Fan-shaped locomotive buildings They were short for both AA and FD, so by 1936, typical rectangular locomotive buildings were put into operation, suitable for both FD and AA. By its load capacity, as of 1936, this section occupied the first place on the road network of the USSR — 28 pairs of direct heavy trains per day. FD locomotives in this area were operated most intensively and literally at the limit of their capabilities.

On January 1 , 1935, the locomotive was sent to Moscow. On the ascent of 10 km, the 2,800-ton train reached a speed of 40 km/h. The power of the locomotive reached 3,700 hp, the traction force when starting from a place-up to 32,000 kgf. However, during operation, a number of design flaws of the locomotive were identified, in particular, in the steam distribution system.

A separate source of problems was the huge size of the locomotive. Despite the considerable run-ups of the bogies and wheelsets, the locomotive did not fit well into curves, upset the tracks and derailed on the arrows. In addition, the colossal machine did not fit on turning circles and in the stalls of locomotive depots.

For these reasons, in 1935, the locomotive made only a few test trips, after which it was finally suspended from train work. The next 25 years, the non-working locomotive stood "under the fence", until in 1960 it was cut up for scrap.