Potakhov D. A.

Petersburg State Transport University, Russia

Cutting temperature as optimization criterion of the recovery of railway wheel sets

Usage of new grades of steel wheels with improved physical and mechanical properties in accordance with GOST 10781-2011 has a certain effect on the productivity in the recovery of profile of the running surface of wheel sets of rolling stock. Lack of data on the workability of new grades of steel wheels makes it difficult to assign rational modes for turning of wheel sets. The studies are conducted to determine the workability of new grades of steel wheels and recommendations on the choice of rational modes of recovery of wheels with increased hardness.

To restore the profile of the running surface of the wheel there is a wide variety of machine tools with a variety of technical and operational characteristics that affect the processing time of one single-piece wheel set, which in turn includes the engine, preparatory and auxiliary time. Analysis of the process of recovery of profile of the running surface of the wheel pairs [1] shows that the main reason for stopping treatment process and, as a consequence, increase the machine time for the restoration of a wheelset, is the premature failure of the cutting tool. The life of the tool is significantly affected by the state of the surface of riding profile, namely, the presence of not only the work surface defects such as melts, slides and defects with thermomechanical origin, which significantly increase the hardness of the metal surface layer, but also the variation of the hardness of the running surface, defined by GOST for each particular brand of wheel steel.

The science of cutting materials established the existence of the so-called optimal cutting temperature θ₀, with is a definite value for a particular pair of "instrumental material - the material being processed." The work on this optimal temperature ensures the greatest dimension stability for the tool, and the highest accuracy and the favorable properties of the metal of the surface soil for a processed detail. [2]

Based on the above the expediency of turning the roll surface profile of wheelset with an optimum temperature can be concluded, which will reduce the effect of the state of profile of riding surface during tool life, will give the finished surface the required accuracy and quality, and will improve the process of turning the wheel by increasing the efficiency of cutting tools.

Based on the thermophysical analysis of the recovery of riding surface of wheelsets of different hardness based on the recommendations [3], it was found that the effect of depth of cutting on the temperature for a single grade of steel is negligible. Moreover, with the increasing depth of the cutting temperature decreases slightly. For example, for steel with a hardness of 255 HB at cutting speed v = 20 m / min and feed s = 1,1 mm / rev temperature at a depth of cut t = 3 mm be θ = 770 ºC, with a depth of t = 5 mm – θ =766 ºC, and at a depth t = 7 mm – θ = 763 ºC. Were obtained depending on the influence of graphical wheel hardness steel cutting speed at different depths (Fig. 1), provided that the optimal cutting temperature, which for the pair of "wheel – cutting instrument" was taken to be 870 ºC [4].

Fig. 1 The effect of hardness of steel wheel on a rational cutting speed when

s = 1,1 mm / rev, γ = 0º

As can be seen from Fig. 1 for the effective recovery of wheelsets with increased hardness made of steels of grades T and A, GOST 10791-2011, repair shops will need to reduce the cutting modes of about 2 times compared to the processing modes for conventional rail wheels of grades 1 and 2 according to GOST 10791-2011.

References:

1. Bogdanov A. F. i dr. Vosstanovleniye profilya poverkhnosti kataniya kolesnykh par: Uchebnoye posobiye / A. F. Bogdanov, I. A. Ivanov, M. Sitazh. – SPb.: PGUPS, 2000. – p. 128.

2. Makarov A. D. Optimizatsiya protsessov rezaniya. – M.: Mashinostroyeniye, 1976. – p. 278.

3. Reznikov A. N. Teplofizika protsessov mekhanicheskoy obrabotki. – M.: Mashinostroyeniye, 1981. – p. 279.

4. Vorobiev A. A. i dr. Resurs i remontoprigodnost kolesnykh par podvizhnogo sostava zheleznykh dorog. Monografiya / Pod red. prof. I. A. Ivanova. – M.: INFRA-M, 2011. – p. 264. – (Nauchnaya mysl).