RU2489499C1 - Heat treatment method of cast-iron friction wedges of freight-car truck, hardening device for its implementation, and friction wedge from cast-iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: cast-iron friction wedge is volume-heated up to 900-920°C, then, surface hardening of vertical and inclined walls is performed by means of the hardening device with water flow during 50-70 seconds at the speed of 0.5-2.0 m/s so that hardness on vertical wall surface of 45-50 HRC and on inclined wall surface of 30-35 HRC is provided. The hardening device is made in the form of ducts installed on the base with supply of cooling liquid, one of which is located vertically, and the other one is located at an angle relative to the base. Ratio of water amount is 3:1 to vertical and inclined surfaces respectively. Heat treatment involving water flow as hardening medium with its directed supply to working surfaces of the wedge and optimisation of geometrical dimensions provides the wedge life equal to more than 500,0 thousand kilometres of run-on operation.

EFFECT: improving strength properties of friction wedges and environmental conditions.

3 cl, 2 tbl, 6 dwg, 1 ex

Description

The invention relates to the field of heat treatment and to structural elements of railway freight trolleys, in particular to designs of cast friction wedges made of cast iron for perception and damping of vibrations of the pressure beam of a freight car trolley.

The “friction wedge - friction plate” assembly operates under severe conditions of dry friction. The performance of this unit and the nature of wear depends on the material of the rubbing surfaces. In trolleys of model 18-100, wedges made of cast iron Sch25 are used for planned repairs. The presence of a graphite component in cast iron works as a solid lubricant. [Rubin G.V. et al. Ways to increase the efficiency of the wedge vibration damper of the TsNII-KhZ 011 trolley // Improving the reliability and durability of parts of rolling stock in railway transport / Tr. MIIT. Issue 501. M .: MIIT Printing House, 1975, p.25-36.] - analogue.

The mileage of the car with wedges made of Sch25 cast iron is 160 thousand km. The need to increase the overhaul life of a freight wagon trolley created the conditions for the transition to the production of wedges from Sch35 cast iron - an analogue [Technical conditions: TU32TSV2459-2007].

The expected mileage in the general network conditions of the wedge from Sch35 should be 260 thousand km.

In promising freight carts, both in our country (OAO NPK Uralvagonzavod) and foreign models of carts (Company A. Staki) operating in the USA, friction wedges made of high-strength cast iron VCh 120 and subjected to isothermal hardening are used.

The closest analogue is the known method of heat treatment of the friction wedge of a freight car truck, made in the form of a hollow cast iron body having a base, side walls, a vertical and inclined wall, optionally with a removable removable polyurethane pad, including volumetric heating of the wedge to the austenization temperature and isothermal hardening in the salt bath. (Velikanov A.V., Borsch B.V., Friction wedges from ductile iron // Bulletin of the All-Russian Research Institute of Railway Transport. 2007 No. 2, pp. 18-22). The mileage of a car with wedges of ductile iron VCh120 with isothermal hardening is 500 thousand km

To eliminate the wear of the inclined surface of the nadressornoj beam and the inclined surface of the wedge in these wedges in the specified area, a polyurethane pad is installed.

A known installation for heat treatment of the friction wedge of a freight car truck, comprising a furnace for heating the wedge, a quenching device made in the form of a bath for volume cooling of the wedge, made in the form of a hollow cast iron body with a base, side walls, a vertical and inclined wall with a removable removable pad polyurethane. (Velikanov A.V., Borsch B.V., Friction wedges from ductile iron // Bulletin of the All-Russian Research Institute of Railway Transport. 2007 No. 2, pp. 18-22). Hardening of friction wedges is carried out by the method of isothermal hardening in salt baths.

A friction wedge of a freight wagon truck is known, comprising a hollow cast iron body subjected to heating and cooling, having a base, side walls, vertical and inclined walls, a removable polyurethane pad mounted on an inclined wall. (Velikanov A.V., Borsch B.V., Friction wedges from ductile iron // Bulletin of the All-Russian Research Institute of Railway Transport. 2007 No. 2, pp. 18-22). Known friction wedge is depicted in figure 1.

The technical result of the group of inventions is to increase the strength properties of friction wedges and improve the environment.

To achieve a technical result, it is proposed to use the technology of volume-surface hardening of wedges from gray cast iron, which provides hardening of the vertical and inclined friction surfaces of the wedge in one cycle of heating and quenching cooling. Moreover, the hardness of the inclined surface of the wedge, along with high wear resistance, should not lead to significant wear of the counter surface of the nadressorno beam, which is also provided by this technology by eliminating the setting.

In the known method of heat treatment of the friction wedge of a freight car truck made in the form of a hollow cast iron body having a base, side walls, a vertical and inclined wall, or an inclined wall, if necessary, with a removable removable polyurethane pad, including volumetric heating of the wedge to the austenization temperature and cooling volumetric heating of the wedge is carried out up to 900-920 ° C, then surface hardening of the vertical and inclined walls is carried out using a spray hardening device with a stream of water for 50-70s with a speed of 0.5-2.0 m / s and a ratio of the amount of water 3: 1, respectively, on the vertical and inclined surfaces, providing hardness on the surface of the vertical wall of 45-50 HRC and on the surface of the inclined wall of 30-35 HRC.

The apparatus for heat treatment of the friction wedge of a freight wagon truck contains a volumetric heating furnace, a quenching device for cooling a friction wedge heated to austenitization temperature, consisting of a hollow cast iron body having a base, side walls, vertical and inclined walls, if necessary with a removable removable cover made of polyurethane, made in the form of sprayers installed on the base with coolant inlets, one of which is located vertically and the other at an angle from relative to the base, while the sprayers have openings for supplying a flow of water with a given speed, respectively, to the vertical and inclined walls of the wedge housing for 50-70 s at a speed of 0.5-2.0 m / s and the ratio of the amount of water 3: 1, respectively vertical and inclined surfaces with providing surface hardening and obtaining hardness on the surface of the vertical wall of 45-50 HRC and on the surface of the inclined wall of 30-35 HRC.

A friction wedge of a freight car truck containing a heat-treated hollow cast-iron body having a base, side walls, vertical and inclined walls, optionally with a removable removable polyurethane pad, in which the vertical and inclined walls of the cast-iron body are subjected to volume-surface hardening, have the structure troostomartensite and hardness on the surface of the vertical wall 45-50 HRC and on the surface of the inclined wall 30-35 HRC, while the inclined wall is made in the form of a flat plane.

Figure 1 shows the basic version of the friction wedge;

In Fig.2 shows a friction wedge: side view and a cross section of a wedge with an inclined surface made in the form of a flat plane (with a single platform);

Figure 3 - shows a hardening device for hardening the vertical and inclined surfaces of the wedge;

Figure 4 - shows a top view of the quenching device.

The process of hardening wedges made of gray cast iron Sch25 by the technology of volume-surface hardening is environmentally friendly, unlike most traditional technologies of thermal hardening, including isothermal hardening.

As a result of hardening by the technology of volume-surface hardening, the surface hardness of the vertical surface of the wedge from SCh25 is 45-50 HRC, and the inclined 30-35 HRC (figure 5). There is also an increase in strength properties by more than 30%, compared with similar wedges in the basic version.

The friction wedge consists of a hollow body made of gray cast iron 1, containing a base 2, side walls 3, a vertical 4 and an inclined wall 5, in the form of a flat plane (platform) 6, which, if necessary, has a removable polyurethane pad. The main wear are exposed to the vertical 4 and inclined 5 walls of the cast-iron wedge body, which are subject to hardening.

The apparatus for heat treatment of the friction wedge of a freight wagon truck contains a heating furnace (not shown in the drawing) and a quenching device having a vertical duct sprayer 1, an inclined duct sprayer 2 placed at an angle to the horizontal base of the frame 3 and the vertical sprayer 1, both sprayers have holes for supplying a water flow at a speed of 0.5-2, m / s for 50-70s in an amount with a ratio of 3: 1, respectively, on the vertical and inclined walls of the wedge body and inlets 6, 7 of the coolant. The quenching device is mounted on the base using the support flange 8. An example implementation of the method.

The heat treatment of wedges from SCh25 using the technology of volume-surface hardening is characterized by the following parameters. A wedge of Sch25 cast iron is heated volumetricly in a gas or electric furnace to a temperature of 900-920 ° C. After volumetric heating, the wedge is placed in a quenching device for local volumetric-surface hardening of the wedge body: vertical and inclined walls of the wedge body. The wedge body with base 2 is installed on the horizontal frame 3 of the quenching device, the vertical wall 4 of the wedge is located opposite the holes of the vertical sprayer 1, and the inclined wall 5 of the wedge is located opposite the holes of the inclined sprayer 2. The vertical and inclined walls of the wedge body are cooled by the water flow supplied from the openings of the sprayers with the ratio the amount of water, respectively, 3: 1, at a speed of 0.5-2.0 m / s for 50-70 s. These modes provide (see Fig. 5) surface hardening with obtaining hardness on the surface of the vertical wall 45-50 HRC (Fig. 5a) and on the surface of the inclined wall 30-35 HRC (Fig. 5b).

Quenching cooling parameters are selected taking into account isothermal diagrams. An additional vacation operation does not apply.

Application of the method of volume-surface hardening allows for one technological cycle of heating and cooling to carry out surface hardening to a predetermined depth to obtain maximum hardness, the level of which mainly depends on the chemical composition of cast iron, as well as to harden the deep layers of the product on the structure of troostomartensite.

This combination provides a high level of mechanical properties, including an increase in strength properties of more than 30%, compared with standard wedges from SCh25 (see table 1)

Table 1 Mechanical properties of friction wedges made of cast iron Сч25 after standard production and volume-surface hardening Material, processing technology Temporary resistance,
σ _V , MPa Conditional yield strength, σ _0.2 MPa Elongation, δ,% Relative narrowing, Ψ,% MF25, standard technology 230 190 1.3 1.4 VCh120 1200 850 1,0 isothermal hardening SCh25, OPZ 300 255 3.9 4.1

In the table. the average values for the test results of six samples are given.

Given the pattern of cutting cylindrical samples, it should be borne in mind that this type of test evaluates the averaged values, since the hardened layer and the viscous core partially fall into the sample cross section during manufacture. This provision applies to wedges made of gray Sch25 cast iron after volume-surface hardening.

When implementing the process of volume-surface hardening of only the vertical surface of wedges made of cast iron Сч25. The inclined surface provides for the use of protection in the form of a polyurethane lining. The mode of heat treatment of wedges is similar to the main option.

The results of field tests of wedges from Sch25 hardened by the method of volume-surface hardening at the installation with hardening of vertical and inclined surfaces showed that the mileage of trolleys equipped with such

wedges is over 500 thousand km while maintaining operability. Damaged analysis of the base case of cast iron wedges from Sch25 to

operation shows that one of the causes of wedge failure in operation is the formation of cracks on an inclined surface due to the complex stress state arising in the wedge due to the action of a bending moment on it, which is possible while ensuring optimal running-in of the friction surfaces of the wedge with reciprocal contact surfaces.

A structural feature of the cast-iron friction wedge, which ensures its self-installation and optimal running-in, is the presence of protruding contact pads two millimeters above its inclined surface - a well-known friction wedge.

In addition to the above effects from the presence of these contact pads, it is necessary to note that they are stress concentrators on this surface at the entire stage of their existence. To eliminate this negative effect, a friction wedge design with an inclined surface made in the form of a flat plane (a single platform) was developed, which allowed us to perform an accurate analysis of the stress-strain state of the structure. The calculations were made based on the “Norms for the calculation and design of railroad cars of the MPS 1520 gauge (non-self-propelled)”, the estimated equivalent stresses according to Mises are summarized in table 2 and Fig.6: figa - equivalent stresses of the basic version of the friction wedge made according to . 1698.00.002; figb is a variant of the friction wedge with a single platform on the basis of the features. 1698.00.002.

table 2 Comparison of maximum values, stress state in different zones of the models of the friction wedge of the base case and the case with an inclined surface having a flat plane (in the form of a single platform) friction wedge Inclined surface Rear vertical surface technological windows Spring erase pad basic version Maximum equivalent stresses, MPa 89.5 17.4 31.7 27.9 single platform option 44.5 14.0 31.7 27.9 Percentage of maximum equivalent stresses, variant with a single platform to the base variant (%) fifty 19 0 0

As a result of the assessment, it was found that the maximum equivalent stresses in the basic version of the wedge operate in the lower zones of the contact pads. It was also found to reduce the maximum equivalent stresses in the version with an inclined surface made with a flat plane (single platform) in comparison with the basic version of the wedge by 50%.

Based on the results of the assessment, it follows that the current maximum equivalent stresses in the considered options do not exceed the permissible ones. In this case, the stress state of the base case is more unfavorable, which is probably not so significant in the absence of hardening of the inclined surface, since the wear of the contact pads occurs in a fairly short operational period.

When applying the method of hardening by the technology of surface-surface hardening, the operational period of existence of constructive contact pads increases several times, and therefore, the duration of the maximum equivalent stresses established for the basic version of the friction wedge also increases.

An analysis of the results shows that when choosing a structural change in the wedge to eliminate a high level of stress in the inclined surface of the wedge, the presence of two sites is eliminated and the supporting inclined surface of the wedge has a flat plane (a single area, surface) with a thickness increase of 2 mm.

Claims (3)

1. The method of heat treatment of the friction wedge of a freight car truck, made in the form of a hollow body made of gray cast iron, having a base, side walls, a vertical and inclined wall, including volume heating of the wedge and cooling, characterized in that the volume heating of the wedge is carried out up to 900-920 ° C, then volume-surface hardening of the vertical and inclined walls is carried out with a water stream for 50-70 s at a speed of 0.5-2.0 m / s and the ratio of the amount of water 3: 1, respectively, on the vertical and inclined surfaces, ensuring verdosti on the surface of a vertical wall 45-50 HRC and 30-35 HRC surface inclined wall. 2. Installation for heat treatment of the friction wedge of a freight car truck, comprising a heating furnace, a hardening device for cooling the wedge, made in the form of a hollow body of gray cast iron having a base, side walls, vertical and inclined walls, characterized in that the hardening device is made in the form of vertical and inclined sprayers mounted on a horizontal frame with coolant inlets, while the vertical sprayer is perpendicular to the frame opposite to the vertical flax wall of the wedge, and the inclined sprayer is at an angle relative to the frame opposite the inclined wall of the wedge, and the sprayers have openings for supplying a stream of water to the vertical and inclined walls of the wedge body for 50-70 s at a speed of 0.5-2.0 m / s and a ratio of the amount of water 3: 1, respectively. 3. Friction wedge of a freight car truck containing a heat-treated hollow body made of gray cast iron, having a base, side walls, vertical and inclined walls, characterized in that the vertical and inclined walls of the cast iron body are subjected to volume-surface hardening, have troostomartensite structure and hardness on the surface of the vertical wall 45-50 HRC and on the surface of the inclined wall 30-35 HRC, while the inclined wall is made in the form of a single platform with a flat plane.

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