The prospects of creation of the draft gear with the polyurethane resin elastic element for the rolling stock

In article the main requirements of normative documents to characteristics of the draft gears are analysed. The principles of operation of the existing draft gears are considered, the main directions of perfecting of the existing designs are defined and in essence new solutions are proposed. Test data of a test piece which allow to draw the unique conclusion on prospects of the developed design are provided.


Introduction
Beside workloads, that are necessary for transportation of different types of cargo, railway wagons have a lot of parasite loads, that appear because of ups and downs of the way, acceleration, braking actions and collisions of wagons. These loads dominate in life limitation of railway wagons. To increase the life of wagons it is necessary to decrease level of parasite loads and as a consequence all loads, that appear. Such method is called amortization. One of the most powerful ways of amortization is changing of power characteristic of the whole machine or its certain line of action. For transport, civil and metallurgic machines main ways of influence are energy and deformation influence. For horizontal forces that appear in coupler, the main influence is made by energy, hit influence. In this case power characteristic of between wagons connections should ensure absence of above the level axial loads.

Problem
Nowadays railway wagons supplied with the draft gears, that terminate energy in case of axial coupling of wagons. Such set is called buffer and has two elements: first one is elastic element or energy accumulator and the second one is friction element or vibration damper. First one accumulates energy and second one dissipates it and converts it in heat. The draft gears are used by humanity for many years and they become better with wagon characteristics. At the same time the size of them is rather conservative and doesn't change for many years. Because of growth of weight and speed of wagons claims are grow too. Nowadays these claims are described In GOST 32913-2014 "Draft gears of the rolling stocks". Also there is no solution for the problem of developing of draft gear with strict measures (230x320x570 mm) and at the same time simple, reliable and maintainable device that will conform to energy intensity regulations from GOST 32913-2014.

Article's goals
In this article the vertical power line of the wagon, damping in wagons, axle buffer rod and other devices that decrease dynamic loadings on wheels of wagon are set aside. It is wanted to analyze horizontal loadings applied to the wagon and describe ways of horizontal parasite loads dropping. There is a task to develop draft gear for the rolling stock, where the energy intensity and damping facility will be increased and construction of the device will be simplified and the price will be reduced.

Materials and research results
In GOST 321913-2014-all draft gears are divided in three groups T1, T2, T3 by main technical characteristics. These properties are shown in Table 1. springs, polymer elements blocks are used, they are good for compression and work with loading near 300…400 kN instead 180 kN for steel springs. For frictional blocks there was testing with ceramic layers that have higher constant of friction. Typical design example of spring-frictional and polymer-frictional devices might be APM-110-K-01 and APM-120-T1, PMKP-110, RT-120. On these devices wanted properties for T1 class were reached, however, such devices have disadvantages [15]. 1. Wanted properies can be reached only after prework, at the beginning the maim characteristic (stress intensity) two times smaller. 2. Such devices have bend in (stiff) characteristic with force bounces. 3. Energy intensity Uн = 70 kJ and Umax = 90 kJ can be reached on ultimate loads Fн = 2.0 MN and Fm = 3.0 MN. Despite the fact that all requirments can be satisfied, these devices cannot be perspective. For efficiency assessment of draft gears priority properties should be introduced. The main task of improvement of draft gear is to increase durability of wagon. That's why the main property that should be controlled is the force that impact the wagon.
Nominal and maximal forces and stress intensity that are introduced in GOST 32913-2014 are conflicting, that makes it difficult to develop device that will meet requirments. When stiffness of draft gear will not be enough, reguired characteristics of stress intensity will not be reached even in with full device stroke, at the same time in condition of high stiffness compressing forces will reach requirments with slow device stroke and reguired characteristics of stress intensity will not be reached again.
Type of draft gear, that should be installed on the wagon is chosen depending on the cargo. Higher class can take higher impact energy and as a consequence impact on the wagon. During tests, when moving wagon with mass 100 tons kick standing one with the mass 94 tons normative axial loading 3.5 MN was got at next striking velocities  10-12 km/h class T1  13-15 km/h class T2  16-18 km/h class T3 Another important question that should be solved is quality assessment of the draft gear. Let's look at it on the example of the class 1 draft gear.
On the figure 1 there are two curves of T1 class draft gears. Both of these characteristics give us neccessary stress intensity E=90 kJ; the maximum compression was λ =120 mm. Both characteristics correspond to GOST 32913-2014. However, loading FM, when needes stress intenisity reached, differs a lot from each other; for the first curve it is FM =3.0 MN, for the second FM =1.5 MN.
Such a big difference leads to different strength of devices and different lifetime of wagons with such devices. At the same time, there is no information, which draft gear is more perspective. More perspective is such device, which better decrease parasite loadings. From the figure 1 we can see that better characteristic is curve number 2, soft characteristic. Its area (characteristic of stress intensity) might be calculated with: FМ and λмmaximal forces and compression of device (on the power characteristic they are overall dimensions): αcharacteristic charge ratio This coefficient may take the value (from theory) 0 ≤ α ≤ 1,0.
From reality this range is smaller. Analysis of modern draft gears gives us next range: 0.2 ≤ α ≤ 0.8. This coefficient is quality ratio of power characteristic. Smallest coefficients have springer-frictional draft gears. So draft gears AMP-120-T1 have quality ratio α = 0.25, at the FМ = 3.0 MN and compression λ = 120 mm. That is not enough for keeping good lifetime of the wagon. For hydraulic draft gears, for example Z73, this coefficient is three times higher, that allows to get higher stress intensity or decrease FМ , that allows to increase lifetime of the wagon.
Another big problem with draft gears is the price. Because elastomer (hydraulic) devices are very expensive and nonrepairable in engine houses. That's why the main task is to develop effective draft gear with quality ratio α ≥ 0.5 and price not higher than $500, that is two times chaeper than the hydraulic devices. It is possible if elastic element of such draft gear will not be liquid but solid, for example constructional polyurethan.
Solid elastomers are weakly compressible materials that is why roughness of detail, made from elastomer will increase, if loading will be like all-around compression [21,22]. Such stress state can be seen in places of elastic element where lateral strain embarrassed, for example in the zone of elaatomer contact with bearing area, where friction forces block free expansion of compressed elastomer or in the places of elastomer connection with more rough material.
Let's analyse loading scheme, during which elastomer loses shape in closed volume. As an example, we'll look at the device, where strike energy is taken up during all-around compression and that is put in robust body. Using Hook's law it is easy to show that body strength depends on filling. Even in condition of static loading Poisson's ratio's value of filling determines value of the pressure that impact on body's walls. When μ = 0, there is no pressure.
In condition of striking loading, value of the pressure depends on input energy and system's (that take strike) roughness values. Stiffness of such device defined by volume modulus of elasticity K of filling-elastomer, that connected with other constants by  Let's try to approximately take into account body's deformation. In case of using for body development high strengthened spring steel (Е = 210 5 MPa, v = 1600 MPa), then element's relative strain will be  = 0.008. Adjustment of element's cross-section area will be F = 0.016. So the deformation x will rise on the same value. Before deformation was x = 180/3000 = 0.06, so x = 6%. Extra deformation will be 1, 6 100% 26, 6% 6  Energy intensity will rise on the same value. Extreme pressure will be: * = 180√1.266 = 160MPa For the such scheme the most important is possibility of further increase of pressure (for example from 160MPa to 300MPa), that ideally increases energy intensity in 3.5 times. Solution of such problem allowed to develop our draft gear for the rolling stock.
Draft gear for the rolling stock consists of cylindrical body 1, where step-shaped plunger 2 is located (figure 2). Plunger is centered in plugs 3 and 4, press-fitted front 5 and back 6 covers. Elastic element is installed in body 1. Covers tightened with bolt pins 8 and screws 9. Plunger 2 gets inside elastic element 2 with bigger diameter and goes outside with smaller one.
Assembly of draft gear. Plugs 3 and 4 press-fited in covers 5 and 6. Then back cover should be installed horizontally, then bolt pins should be screwed in it. Then body 1, where elastic element 7 and step-shaped plunger 2 are located, should be installed on the cover 6. After this cover 5 should be installed on plunger 2, on the bolt pins screwes should be engaged. In such condition draft gear should be installed in press and be tighted, loading should be applied to the covers 5 and 6, then screws 9 should be tighted.
Work of draft gear. During compression and stretching of coupler, draft gear is compressed, forces are applied on he one side to the plunger 2 and from the other side to the back cover 6. Plunger 2 goes into elastic element 7 and compresses it. Elastic element at this moment is under all-around compression. Force of elastic stiffness, that impact plunger in axial direction, proportional to relative volume change, volume modulus of elasticity and difference between squares of plunger's 2 cross-sections in two sections-higher and lower its cone area. Aside from that, there are friction forces of elastomer that influnce plunger in axial direction. They are proportional to relative elastomer volume change, volume modulus of elasticity, friction ratio between plunger and elastomer and plunger's square, that is in contact with elastomer. By variation of device's parameters, it is possible to change relation between elastic force Fу and friction force Fт.    Computated pressure inside the body р* = 180 MPa Volume of elastic element 7300 sm 3 Working curve of tested device is shown on figure 6. Cover's tension bolts were made with cone head (cone ratio 1:20). Screws also were made with cone head (1:10). Cone ration was chosen with the result that during tightening screws, bolt was self stopped. Cone boltheads are in the back cover, in such way that way don't make the device bigger and doesn't engage its mounting on the stop shoulder. Cone ratio was chosen bigger to decrease frictional moment between screw and cone basement. Screws also are inside the front cover not to increase the measurements of the device. Cone ares of the screws lets better distribute loading in threaded assemblage.
Covers of the device are complicated, they stop the plugs. It provides plunger's plug's rail motion. Existence of different plugs provides an opportunity to change the diameter and plunger's configuration without changing the forms of basic details (covers, body, bolts). Cover's construction, that has cylindrical offsets, provides an opprtunity of preloading of the device, compressing it with two covers (without applying force to the plunger). Such way doesn't change the measurements of the device.
6. Conclusions 1. The absorbing devices of cars and locomotives by the principle of action represent the buffer devices perceiving external influence by energy and generating horizontal force. 2. Proceeding from need of increase in a resource of the car, the power characteristic of draft gear has to have bigger power consumption in the parameters «the maximum force-the maximum draught». Only devices of hydraulic type conform to this requirement. 3. The absorbing devices have to be economic in production and operation -devices of frictional type conform to this requirement. 4. The main objective of improvement of draft gear is development of devices with high quality of the power characteristic α ≥ 0,5 and low price (up to $500). To such requirements satisfy only the draft gear with an elastic element from solid constructional elastomer (polyurethane) can. 5. Tests of model and a prototype of draft gear of the autocoupling device of the rail vehicle have confirmed high loading of his details. Necessary power characteristics of the device are reached in that case when his steel details (in addition to elastomeric UE) carry out a role of springs, reserving elastic energy when loading. 6. Development of details of such form that distribution of tension in them was, whenever possible, more uniform was one of the main objectives. Then it is possible to count on the maximum power consumption of these details. The specified principle managed to be realized for two main details (the cylindrical case and coupling bolts). As a result of tests all calculated parameters have been reached. 7. Dynamic tests of a prototype have to become the following stage that will allow to draw more thorough conclusions on applicability of this design for the rolling stock demanding the draft gear's installation of the class T2.