The method of controlling the wear of friction pairs under dynamic loads

 

(57) Abstract:

The invention relates to the field of engineering, namely the technology of induction welding durable powder alloys, for example, to friction and moving the pair of machines and equipment transport vehicles, including cars, locomotives, track and road cars, parts superstructure. The essence of the invention: method including induction and metallurgical cladding of wear resistant material and its dynamic recrystallization by contact of the friction surfaces, welding lead material of wear-resistant alloys undergoing contact austenitic transformation in the contact zone with the formation of finely dispersed carbide phase with a grain size of 2-8 μm and microhardness H0,9812000-17000 MPa and form in the contact zone of oxide film, and dynamic recrystallization ensure that the specific pressure at the contact does not exceed 1100 kg/cm2while maintaining the elastic-plastic properties of the deposited wear-resistant alloys. The thickness of the oxide film formed in a contact zone is 0.2-0.3 microns. The technical result of the invention is the ability to control the wear of friction pairs ness to technology induction welding durable powder alloys, for example, friction and mobile interfaces machinery and equipment transport equipment, including cars, locomotives, track and road cars, parts superstructure.

Currently, rail transport, there is the problem of rapid wear of friction pairs, working under high dynamic loads, such as vibration dampers, articulated swivel device, the shaft sleeve spring and walking beam suspensions, etc.

According to the existing technology wears these nodes eliminate arc method of welding with subsequent machining or technology Engineering center "Alloy" induction-metallurgical method.

Analyzing the optimization of friction pairs after induction welding, Engineering centre "Alloy" of the Ministry of Railways have discovered new opportunities recrystallization of the metal, not static, which is well known and dynamic that occurs in the contact zone of metal alloys at high loads or shocks cooperating friction surfaces, working in dry friction mode.

Working on reducing wear in friction pairs under dynamic loads allowed principianti friction pairs by several orders of magnitude.

The known method, which is implemented in the friction element managed tribological characteristics (see U.S. Pat. EN 2065098, CL F 16 F 3/08, B. I. 22, 1996), namely, that when the reciprocating movement of the friction pairs of speed change from V0=0 to Vmax=max by selecting the material, from which depend the friction coefficients from f1...fnand wear resistance j0...j0n.

However, this technical solution has addressed the issue of friction and wear, but did not dare question about the impact of a specific contact pressure, temperature fields and areas of contact of the friction pairs, operating without lubrication dry friction mode, and this in turn was not allowed to raise issues such as the influence of recrystallization phenomena in the contact friction pairs and control their durability in the process of their adaptability.

A prototype of the selected method of hardening of friction (see the book D. Buckley "Surface effects in adhesion and friction interaction), engineering, 1986, pp. 86-87), which describes the process of recrystallization during static loading of chemically pure iron.

The disadvantage of this method awseme loads, since the yield strength of such metals is significantly lower than permissible, which will lead to deformation and low wear.

In friction pairs usually work with a wear resistant steels or alloys, if steam is running in dynamic shock loads, the effect of recrystallization depends on the specific pressure and temperature of contact spots. Based on these circumstances, an important factor is the need to manage the phenomenon of recrystallization to improve wear resistance of the friction pairs.

The technical problem of the invention was to develop ways to control the wear of friction pairs under dynamic loads.

This object is achieved in that in the known method of controlling the wear of friction pairs under dynamic loads, including surfacing wear-resistant material and its dynamic recrystallization by contact of the friction surfaces, welding lead material of wear-resistant alloys undergoing contact austenitic transformation in the contact zone with the formation of finely dispersed carbide phase with a grain size of 2-8 μm and microhardness H0,9812000-17000 MPa and obrazuya contact does not exceed 1100 kg/cm2while maintaining the elastic-plastic properties of the deposited wear-resistant alloys.

In addition, the thickness of the oxide film formed in a contact zone is 0.2-0.3 microns.

In this case, the welding is conducted induction-metallurgical method.

In Fig. 1 shows a graph of wear of various materials depending on the load;

Fig.2 - surface friction contrapasso different pairs:

a) a pair of GL+FL

b) a pair of USC+FL

in a pair On 27+USC;

Fig. 3 - microstructure of the surface layer contrapasso in cross section thin section:

a) a pair of GL+FL

b) a pair of USC+GL;

Fig.4 - microstructure of weld metal on the surface of friction:

a) the surface of the deposited metal On 27 (with magnification of 250 times)

b) the surface of the deposited metal On 27 (with increased 800-fold).

Table of basic test results of friction pairs is given at the end of the description.

The proposed method is as follows.

The friction surface of the friction pairs, such as vibration dampers, articulated swivel device, the shaft sleeve spring and walking beam suspension, napravlyali durable pre-select materials, namely solid alloys that meet the following criteria.

First, wear-resistant surface friction pair must have the specific load not exceeding the plastic deformation of metal.

To improve wear resistance of friction pairs in the dynamic system of friction necessary to comply with the terms when specific load P(MC) is reduced to limits = 1100 kg/cm2while maintaining the elastic-plastic properties of metals.

Consider the static wear resistance, for example, a pair of friction in wheel-rail according to the formula Hertz-Belyaeva (see the book by A. F. Zolotarevsky "Thermally hardened rails), Transport, 1976, page 30).

< / BR>
wherearticle(J0) - static contact strength of the rail, kg/cm2;

MCspecific contact pressure, kg/cm2;

R is the wheel's radius, cm;

m - coefficient taking into account the area of contact; dependent on contact area of the interacting surfaces;

E - the modulus of elasticity young's modulus, taking into account the elastic-plastic properties of metals, kg/cm2.

The values of R and E are constant for these metals and of little significance. On this basis, considering the durability from the position on the wear of the friction pair can be expressed in the following dependencies:

< / BR>
where P is the actual load, kg;

S is the contact area, cm2.

Therefore, work must be done with alloys, in which the elastic-plastic properties is significantly higher than that of steel (see Fig.1).

Thus, the load contacts the friction must ensure that the plastic deformation of the projections of the metal, leading to their transformation.

Secondly, in thin surface layers in the process of friction generated temperature in the range 0.4 to 0.7 of the melting temperature alloys. This is because the temperature of the contact surfaces in friction pairs is significantly higher than that of pure metals. In this process the temperature reaches 1500-2000oC.

The temperature of recrystallization dynamic friction is greatly reduced, so in alloys, the temperature decreases with 1200-1300oWith up to 400-600oC.

Thirdly, a force in terms of wear causes in metastable structures structural transformations under the action of temperature. In the contact area due to local temperature flashes in the weld metal occurs vacation austenite with a selection of fine carbides with partial formation of Deuteronomy is PS.

As a result, the friction surface of the resulting finely dispersed carbide phase with a size of 2-8 microns with a microhardness H0,9812000-17000 MPa enshrined in the plastic matrix, which provides a significant improvement of wear resistance.

From the above we can conclude that as a result of dynamic recrystallization and oxidation of the contact surfaces of the tops of the protrusions are destroyed due to the transfer of the oxide film on the wear surface (softer), the number of contact points increases, the surface pressure at the contact points is reduced, which gives confidence to assert the possibility to control the wear of friction pairs under dynamic loading.

Example. Conducted research of various pairs of friction (three options), where the samples (II and III variants) were deposited induction smelting method of wear-resistant alloys, and then were tested for installation (not shown), while return plane-parallel movement.

Mode test: the load is 24.5 kg/cm2; cycle test - 2 hours.

Materials options: I pair - FL + FL; II para - USC + PL; III pair - On 27+USC.

ASD is used in the rolling stock of railway transport).

The tests showed.

Under load conditions of plastic deformation at the points of actual contact surfaces are activated by the adhesive forces between the atoms of the metals, which leads to adhesion on limited areas, leading to the setting of the first kind (see Fig. 2,a).

It is known that the friction of metal surfaces is formed oxide film, but in this case due to the low hardness of steel HF, the oxide film is destroyed, creating favorable conditions for structural transformations under the action of heat. On the sample surface are formed projections or scallops height of 1000 μm and a trench depth of up to 70 microns.

The microstructure was investigated in cross section (see Fig.3,a). In the surface layer due to navrachana metal prints microhardness fail. The depth of the deformed metal is about 200 μm, and the surface layer to a depth of about 40 microns, due to recrystallization takes place substructural strengthening. The latter happens when hot deformation at (0,4-0,7)TPL. Grain size less than 10 microns. When the friction pair FL on FL total depreciation per cycle was 28.5 g

Option II.

Spent tested ostonen alloy USC (TU 322-19-007-97), and the second is made of steel PL.

Tests showed that this pair of friction process setting is missing (see Fig.2,b), wear contrapasso of steel GF was 0,194 g or decreased by 70 times. Wear the deposited sample was 0,062 g or decreased to 240 times. This improved wear resistance due to the following factors.

First, the structural transformations on the surface of the alloy USC, in its surface layers is the collapse of the supersaturated solid solution or austenitic transformation with selection of the hardening phase - carbides of iron, chromium, manganese smaller than 10 microns (the original was 30-70 μm). This forms a finely dispersed carbide phase with a grain size of 2-8 μm and microhardness H0,9812000-17000 MPa, distributed in a plastic matrix (see Fig.4,a,b), providing good stability in conditions of friction.

Secondly, high elastic properties of all weld metal (structural components - carbides and grain solid solution) practically do not experience plastic deformation (see Fig. 3), which inevitably leads to decreasing pressure not exceeding 1100 kg/cm2as increases the actual contact area component of 0.2-0.3 μm. The latter is transferred from the deposited sample on steel contrapasso (see Fig. 3,b), increasing its durability.

The surface topography is almost flat.

Due to dynamic recrystallization plastic deformation extends to a depth of 50 μm, the substructure is formed to a depth of 30 μm.

Option III.

We investigated a pair of friction of the samples, the surfaces of which were deposited hard alloys On 27+USC.

Tests have shown that wear such a pair was 0,042-0,065 g per cycle, a pair of friction, both of the contacting surfaces of which are represented by solid alloys, wear 260 times higher than option I.

When a small film thickness, its hardness is almost the same with the micro-hardness of the carbides H0,9811700-12200 MPa, due to the high strength (see Fig.2,) and a good connection with the deposited metal.

Analyzing the results of tribological tests and physical metallurgy research has made the following conclusions.

1. When the friction pair HL+HL is "sticking" of the first kind, leading to significant wear - 13,5-15 g per cycle tests.

2. When surfacing the surfacing alloy USC one is 70 times;

alloy USC - 240 times.

3. The hardening of the two elements of the pair of friction increases the wear resistance of 270 times.

Based on comparison of experimental data it is possible to make such a conclusion (see Fig.1) that the dependence of the wear of materials from the loads as follows:

curve a shows: steel HB=150 when small loads are transferred from oxidative wear to be wrapped;

curve B shows: steel with hardness 40-50HRC - threshold setting is performed at much higher loads, due to thermal softening (leave a hardened structure in contact);

curve b shows: wear-resistant alloys with hardness 40-50HRC - setting wear-resistant alloys is carried out at very high loads, exceeding the contact strength of the material. High threshold setting due to the fact that as a result of dynamic recrystallization alloy surface and contrapasso become more smooth, and the contact patch is increased, which reduces the contact pressure that causes a temperature reduction of friction in the contact and a dramatic decrease wear.

The use of the proposed izobreteniya, which has a positive effect on the wear resistance of the friction surfaces, hardened alloys induction-metallurgical method. As a result, this allows to reduce the specific load twice, which leads to increased wear resistance of hardened friction pairs and above (12 times), thereby increasing the service life of parts of friction, which saves materials, energy and labor resources in the operation of machines and equipment in any branch of engineering.

1. The method of controlling the wear of friction pairs under dynamic loads, including surfacing wear-resistant material and its dynamic recrystallization by contact of the friction surfaces, characterized in that the welding of the lead material of wear-resistant alloys undergoing contact austenitic transformation in the contact zone with the formation of finely dispersed carbide phase with a grain size of 2-8 μm and microhardness H0,9812000-17000 MPa and form in the contact zone of oxide film, and dynamic recrystallization ensure that the specific pressure at the contact does not exceed 1100 kg/cm2while maintaining the elastic-plastic properties of the deposited wear-resistant alloys.

m

3. The method according to p. 1 or 2, characterized in that conduct induction-steel cladding.

 

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