WHEELSET AXLE WITH THE CAVITY OF UNIFORM CROSS

Planning and Design Technological Office, Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (056) 371 51 12, e-mail blaze777@inbox.ru, ORCID 0000-0002-0487-9257$ Planning and Design Technological Office, Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (056) 371 51 12, e-mail romaniuha.nikolay@gmail.com, ORCID 0000-0002-9514-6365 Planning and Design Technological Office, Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel. +38 (056) 371 51 12, e-mail spyhernter-08@mail.ru, ORCID 0000-0002-8408-8294


Introduction
One of the most popular and large-capacity rail purposed metal products is the production of wheelsets for rolling stock.
The scale assessment of the global market for railway wheelsets made by All Russian Market Research Institute based on data for the production of cars (about 100 thousand per year) and their park (more than 4 million pieces), taking into ac-count the needs in repair and modernization of the fleet, shows that each year about 1.500 thousand of wheelsets are produced worldwide.According to assessment of All Russian Market Research Institute based on the statistics of UN and UNECE, and data of national statistics in several countries [4], the total physical volume of production of these products in the world at the moment is about 1.5 million tons per year.
Due to operation in complex loading conditions, the wheelsets should provide high reliability [9, p. 3], since the train traffic safety largely depends on them.Therefore the special, high standardization requirements are imposed on them.They are regulated by the Rules of Technical Operation of the Railways, the Specifications on the inspection, repair and forming of car wheelsets and other regulations for the design, construction and maintenance.
The issues of the design, construction, manufacturing, quality control and maintenance of the wheelset axles abroad are clearly regulated by the European standardization documents.High-speed train traffic, increase in the number of passenger and freight transportations and other factors required the creation of new standards for the wheelsets of solid and hollow shafts of rolling stock too: At the same time F. Murawa in his research emphasizes that the constant striving to increase the environmentally safe and cost-efficient railway transportations involves not only the strict adherence to technical standards, but also the opportunities for innovations and new solutions [13].
Design and technical condition of wheelsets affect the smoothness, intensity of forces generated by the interaction between the car and track, and the motion resistance.These issues are discussed by scientists and practitioners from different countries.Thus, M. Novosad, R. Fajkos, B. Reha and R. Reznicek [12], S. Myamlin, V. Horobets and A. Bondarev [6] in their articles emphasize the importance of testing for fatigue failure of the wheelset axle metal.S. Beretta, M. Carbonia and other researchers [11], developing the given subject, research, corrosion-fatigue failure of steels.D. Dani-lov and A. Andreyev [2] study the stress-strain state of the car wheelset when driving on the straight and curved track sections, taking into account the impact of wind load by means of PC ANSYS.L. Lubenskaya [5] describes a method for increasing the performance properties of wheelset axles due to the hardening of their surface.At the same time, in spite of the number of studies on this issue, the problem of significant increase in performance properties of wheelset axles up to this day is still unresolved.

Purpose
The purpose of the work is to create a design of wheelset axle that will satisfy a number of basic requirements.The requirements are: 1) the availability of sufficient strength with minimum unsprung weight that is dictated by the need to reduce the empty weight of the rolling stock and reduce the direct impact on the rail track and the car elements during the passage of rail track irregularities; 2) provision (together with axle boxes) of the lesser resistance during the car moving and the greater resistance to the wear of elements undergoing the wear during operation.

Methodology
Specificity of the axle operation consists in the fact that it undergoes the bending stresses under loading.These stresses are unevenly distributed along the cross-sectional area, reaching the highest values in the outer fibers and the minimal values in the internal ones.This aspect sets the problem of replacement of the uniform cross section by the hollow cross section without notable increase in the overall dimension.But it should promote the weight reduction as compared to the axle of uniform cross section.
It was found that the endurance limit in all parts of the hollow axles is not lower and the sensitivity to stress concentration is lesser than that of the standard solid axles [1, p. 94].The carrying capacity, which is estimated by the endurance limit product at the moment of the cross section resistance to the bending in the wheel seat of the hollow axle is 15% higher than this figure for the comparable solid axle.
Therefore the designs and technologies of the hollow axles manufacturing using the method of helical rolling [10] (Fig. 1) are developed.Technical and economic advantages of the wheelsets with hollow axes are defined by the following parameters [3]: 1) decrease in the metal consumption; 2) reduction of the empty weight ratio and increase of the car capacity (without changing the load from the wheel on the rail); 3) cost reduction for the non-productive transportation of the empty weight of cars; 4) reduction of forces of the dynamic interaction of rolling stock and track due to the reduction of the unsprung weight of cars.
The disadvantages of such structure should include significant manufacturing complexity of the cavity of variable cross-section.Internal configuration of the designed hollow axle is a longitudinal cylindrical hole with the same diameter in the middle part and wheel seat.It radially passes into the hole in the form of truncated cones in the prewheel seat with smaller bases to the openings of axle necks.
In turn, the openings in the necks of hollow axle are also in the form of truncated cones.The larger bases of these cones are directed to the butt ends of the axle or the cylindrical ones in case the necks forming in the black collar axle is made without a drawbar or mandrel.Smaller bases of the truncated cones of the wheel seat parts and the necks are mated together smoothly along the radius.Longitudinal holes in the necks at the butt are ended by the center holes with a protection cone.Through the holes all the internal surface of the blanks is descaled with the steel shot.As a result the surface layer from the inner side of the axle is somewhat strengthened due to work hardening.
Thus, the technical task, which would allow the efficient use of the hollow axles, is to develop the structure facilitating the manufacturing and machining of the inner cavity.
The specialists of Planning and Design Technological Office of the Rolling Stock, Track and the man-made structures of the Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan (Ukraine) have developed the hollow axle construction with internal longitudinal through cylindrical hole of the constant diameter throughout length (Fig. 2).
The item is made of steel seamless tube.The inner diameter of this tube should be a little smaller than the diameter of inner longitudinal through cylindrical hole, when the outer diameter of the is somewhat larger than the diameter of wheel seat part.The outer surface of the tube is welted to the diameters equal to the diameters of necks dor the bearings, prewheel seat, wheel seat and the hollow axle body.The inner surface of the tube is treated by mechanical means to remove the voltage concentrations in the internal longitudinal cylindrical through hole, which has a constant diameter along the entire length of the axle.Another use advantage of the hollow axle of this design is the absence of partial heterogeneity of the metal, which is inevitably, occurs during the solid axles blanking [8].Black collar solid axles are made of axle billet or directly from the steel ingots by forging, stamping, screw rolling or radial-rotational deformation [7].With such production method the metal heterogeneity often leads to the radial runout, which is corrected by the labor-consuming balancing on the special stands.Applying the same allrolled metal to produce the hollow axles eliminates this problem, when the manufacturing technology of the cavity with the same diameter throughout the length of the axle allows a conducting finishing cut of the surface with the exact accuracy that further improves the item balancing.
It should be also noted that due to the increase in the outer diameter of the axle neck, increases the inner diameter of the axle box bearings.Thus, to provide the necessary contact area for load transfer from the body car to the axle, the bearing width decreases.This prevents significant increase in weight and material costs for the axle box of the wheelset.

Findings
During the study the variants of wheelset axles were analyzed and the use advantages of the hollow axles were illustrated.The authors have developed the design of axle with the cavity of uniform cross-section, which would simplify the production of the item.

Originality and practical value
The authors have proved the need to improve the hollow axle of the wheelset and developed its new design.Production of wheelset axle with the cavity of uniform cross-section simplifies the hollow axles manufacturing.According to preliminary calculations, the use of the axle with the cavity of uniform cross-section would reduce the metal consumption by 100-110 kg.

Conclusions
As a result of the study the authors have found that for a significant increase in performance properties of the wheelset axles is necessary: 1) Creation of the wheelset design, having sufficient strength with minimum unsprung weight in order to reduce the empty weight of rolling stock and to reduce the direct impact on the rail track and the car elements during the passage of the rail track irregularities; 2) Ensuring (together with the axle boxes) the lesser motion resistance and larger wear resistance of the elements undergoing the wear during operation; 3) Application of the construction proposed by the authors, simplifies the manufacturing of the hollow axle and the machining of the inner longitudinal through-hole, while retaining all the use advantages of the hollow axle in the wheelsets of the rolling stock.