CZ305025B6 - Method of preventing press fit damages to wheelsets and apparatus for making the same - Google Patents

Abstract

The present invention relates to a method for preventing press fit damages to wheelsets, particularly to wheelsets of rail vehicles. To this end, the surface of a wheelset shaft is treated before subsequently joining of the wheelset. The aim of the invention is to develop a method, which cost-effectively protects the wheel seats from press damages by means of a special surface treatment, which is adapted to current maintenance technologies, and which avoids structural changes to existing wheelset designs. To this end, the invention provides that, first of all in at least one step, the wheelset shaft is longitudinally turned or longitudinally ground in its cylindrical and conical end area, and the resulting transition is smoothed and/or rounded whereby subsequently treating the surface of the wheelset shaft using a plasma ion implantation method. During this treatment, a finely distributed powder that reduces coefficients of friction, especially a powder containing sulfide, is applied to the rotating wheelset shaft under atmospheric pressure while using cold plasma that contains reactive gas serving as a carrier gas. The powder is applied in such a manner as to construct, on the nanometer and/or micrometer scale, a very hard metallic slide layer having a low adhesiveness. In the event of the highest contact pressures between the wheelset shaft and the wheel, a solid lubrication, which prevents press damages, is produced immediately after the lubricant film has been ruptured. Apparatus for making the above-described method is a lathe. The longitudinally turned or longitudinally ground wheelset shaft is further incorporated into a plasma ion implantation device wherein the plasma discharge is director onto the rotating wheelset shaft at an angle of 90 degrees.

Description

Technical field

BACKGROUND OF THE INVENTION The present invention relates to a method for preventing damage to a press fit of a wheel set, in particular a wheel set of a rail vehicle, in which the surface of the wheelset is treated and the wheelset is subsequently assembled. The invention further relates to an apparatus for carrying out this method.

BACKGROUND OF THE INVENTION

In the case of wheelsets of rail vehicles, the overwhelming majority of the connections between the wheelset shaft and the wheel are made as a longitudinal press fit. During the maintenance of the wheelset, several loosening and reconnection of the pressed joints is necessary. In this process, damage often occurs in the form of longitudinal grooves, cold welds and surface defects, which can lead to the wheelset shaft becoming unusable. In order to allow further use of the wheelset shafts, the wheel bearing recesses damaged during pressing must then be reprocessed. However, additional machining of the wheel bearing recesses causes an increase in production costs and reduces the shaft diameter. By reprocessing the wheel bearing shoulder the permissible diameter limit value is reached and the wheelset shaft becomes unusable prematurely.

With regard to the state of the art, it is disclosed in DD-PS 1 52 972 that molybdenum disulfide paste has been used to prevent the gradual corrosion formation of numerous steels in longitudinal pressed fitting joints. Molybdenum disulphide powder is also used to prevent the formation of rust due to the corrosion of black steel on the cross fitting but with little success. According to the patent, the mating surfaces of the shaft-hub connection are to be provided with non-metallic organic layers of a chemical compound of the base material. Temporary corrosion protection agents can also be added to these layers. This is to prevent the formation of rust due to the corrosion of the black steel and to increase the coefficient of adhesion between the mating surfaces.

Furthermore, a method in which shafts are provided with molybdenum coatings by spray coating has been known for some time. The advantage of better sliding is, however, redeemed by higher production costs and shaft weakening.

In practice, it has been shown that sprayed metal coatings often do not have sufficient adhesion and tend to peel due to operational stresses. In addition, there is corrosion of black steel in the cartridges.

In DE-OS 23 46 144, a light metal disc is connected to a steel tire by means of a conical bearing using a two-component adhesive. According to DE-OS 23 61 891, a sleeve is used which is softer than the shaft and is inserted into the hub by means of a hot insertion. This assembly is then mounted on the shaft again by inserting the heat.

DE-OS 23 54 206 discloses a hot-fitting adhesive connection. According to DE-OS 23 62 434, the ring-free wheels have a special shape, so that the heat supplied by the block brake, when the temperatures exceed even 300 ° C, does not cause any flange distances or wheel disks when pressed or hot-pressed.

In DE-OS 23 63 403, during normal compression, the hub protrudes over the shaft bearing so that an elastic mass can be placed at this point to protect the connection against the ingress of moisture.

. i.

EP 223 759 A1 discloses a method of forming surfaces for reusable longitudinal fitting connections.

The shafts of the hardenable steels have hardened surfaces running parallel in the axial direction, i.e. in the direction of application of the pressing force, in particular the surfaces formed by laser surface hardening and formed by a solid phase with a martensitic structure.

The hardened surfaces should reduce the friction in the axial direction to facilitate the pressing process, while the friction in the radial direction should be increased by slightly penetrating the hardened surfaces into the hub surface.

DE-OS 26 35 608 finally dispenses with the conventional press fit of the wheelset and moves to bolt fastening, even with other shaft components.

In these solutions, however, the disadvantages of corroding, i.e. considerable surface damage due to the effect of strong dry friction in the molded bearings, are largely retained. Lubrication has only limited efficiency at the high pressures exerted during the pressing process, since a thin film of lubricant tears.

Non-metallic organic layers are not intended to reduce friction during repeated bonding and release of longitudinal press fit connections.

Even when hardened surfaces are used, the steel or steel casting is still frictional, albeit partially, without the sliding layer being possible and without preventing the formation of rust due to the corrosion of the black steel.

In the case of conical bearings with the use of two-component adhesives, there is a risk of loosening the connection, especially at high heat input.

The use of an additional sleeve means increased production costs while avoiding the tendency to corrode.

For hot-seal bonded joints, there is a risk of extreme forces occurring when loosening the joints on the press with subsequent corroding.

It is known to optimize lubricated sliding surfaces and / or wear surfaces as well as surfaces subjected to static or dynamic pressures or solid surfaces which are separated by moving interfaces formed by solid, liquid or gaseous substances, while the chemical-physical structure The grid-shaped profile surfaces can be altered by the implantation of arbitrary ions (DE 30 22 826 A1). By bombarding the substrate with various metal ions, metal alloys or intermetallic compounds are formed. An example application of this method is directed to separately moving fixed surfaces. They are so-called plain bearings, the sliding movement being carried out on the liquid cushion. The relative speeds of both parts of these bearings are several orders of magnitude higher than in the case of the coupling of the shaft and the hub of the wheelset. On the other hand, the pressure in this application is several orders of magnitude lower due to completely different physical conditions than in the case of a shaft-hub connection. Moreover, the aim of this solution is to adapt the running-in behavior of the plain bearings in the region of the so-called mixed friction. The results are not comparable with those of the wheelsets.

DE 38 13 803 A1 discloses a laminate or a laminated workpiece and a process for its production in which a functional layer, in particular a sliding layer, is applied to the surface of the solid support layer. This layer is applied by a known method of spraying metal melted in an air-entrained plasma stream. It should be remembered that, when spraying metal melted in the plasma stream, in contrast to the plasma implant method, a wire or powder melts in the plasma flame, which subsequently solidifies on the workpiece surface. The coating layers have a thickness

-2E 305025 B6 do not enter chemical bonding with the base material in the range of several hundred micrometers.

Finally, DE 199 35 053 C2 discloses a process for forming a thin film of highly fine particles, in which a simple substrate layer is applied to the surface in a vacuum chamber. However, this method is definitely not functional under atmospheric conditions. There is no implantation of particles into the surface. Also in this method, the microtopography of the surface is not adjusted by mechanical machining.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method which, without adversely affecting the workplace, is environmentally friendly and energy-efficient and inexpensively protects the wheel bearings from damage during compression. This method should be able to be integrated into existing maintenance technology and be sufficient without altering the design of the gears (overhangs) and the coupling procedure according to UIC 813. Furthermore, the method should provide high safety against fatigue fractures as well as high force and torque transmission comparable to production processes and joining methods currently used. It is also an object of the invention to provide an apparatus for carrying out this method.

The object of the present invention is to provide a method for preventing damage to the press fit of a wheel set of a rolling stock, in which surface treatment of the wheelset shaft is made and the wheelset is subsequently assembled according to the invention. grinding or regrinding the step and smoothing and / or curving the resulting transition, after which the surface of the wheelset shaft is treated by the ion implantation method in plasma by cooling the rotating wheelset shaft through the cold plasma of ionizing reaction gas used as carrier gas at atmospheric pressure; Apply a finely divided powder containing sulphides to reduce the coefficient of friction.

The wheelset is joined by longitudinal pressing.

The powder applied to the surface of the wheelset by the ion implantation method in plasma, in particular the sulphide-containing powder, is applied as a sliding layer with a thickness in the order of micrometres, preferably from 50 nm to> 2 pm.

Longitudinal turning of the surface of the wheelset shaft achieves a maximum surface roughness R _a = 1.2 μιη.

The plasma treatment can be repeatedly performed during the maintenance process. The solid lubricant is applied to the rotating shaft of the wheelset at a feed speed of 5 to 50 mm / min, preferably 10 mm / min.

Surprisingly, it has been found that the two opposite feed directions during machining in the cylindrical and tapered end sections of the wheelset shaft result in a significantly better suppression of the formation of grooves after pressing.

In the first step, the cylindrical end section of the wheel bearing shoulder is turned or grinded from the inside to the outside at an optimized feed.

On the other hand, the conical end section of the wheel bearing shoulder is turned longitudinally or grinded from the inside out. The resulting transition area is smoothed and / or rounded.

The object of the present invention is to provide a method for preventing damage to the press fit of a rolling stock of wheelsets, wherein the axle of the wheelset is rotatably mounted in a jig according to the invention which is a lathe and longitudinally turned or ground

The wheelset shaft is further incorporated into the plasma ion ion implantation device, wherein the plasma discharge is directed at a 90 ° angle to the rotating shaft.

The plasma discharge is arranged at a distance of 20 to 80 mm, preferably 30 mm, from the wheelset shaft and is displaced relative to the surface of the wheelset shaft, so that the plasma stream can cover a larger area.

The plasma discharge generating device is preferably mounted on the support of a lathe or the like.

In the plasma treatment, the solid lubricant particles are implanted into the surface and provide solid phase lubrication at the point where the thin layer of the lubricant used as an auxiliary agent entrains during compression. The reaction gas used as the carrier gas diffuses, possibly in the form of inhibitors, into the surface of the wheel bearing recess and, in addition, by increasing the hardness, causes an increase in the material's resistance to scratches due to the pressing.

Implantation of solid lubricant particles and diffusion of the reaction gas into the surface takes place in the order of nanometers / micrometers. This does not reduce the fatigue limit of the wheelset.

The implantation of the ions in the plasma is then followed by a longitudinal compression method using the molybdenum disulfide paste as a compression aid.

When the molding process is achieved thanks to the pre-treatment values of the coefficient of friction acting against detachment in the lengthwise direction of at Vn max. 0.15 and values of the coefficient of friction acting against slippage in making _r i max. 0.12.

The ion implantation device can be integrated into the maintenance process and the manufacturing process due to the short technological times (in the range of minutes) as well as the small space and energy requirements. The implantation of ions in the plasma can be repeated at any time if necessary, for example when adjusting the shoulder diameter of the wheel bearing needs to be made in the maintenance process.

Thus, the process can be applied equally to new production and maintenance.

The use of non-toxic gases, the very low noise level and the fact that it can be operated without costly electrical protection measures and without special equipment to protect the industrial electrical distribution contribute to the favorable characterization of the plasma implant ion device according to the invention. 230/400 V.

Clarification of drawings

The invention will be explained in more detail below with reference to one embodiment of the drawings, in which FIG. 1 shows a longitudinal section of a plasma sliding device on a wheelset shaft and FIG. 2 shows the formation of adhesive trenches.

DETAILED DESCRIPTION OF THE INVENTION

The wheel bearing shafts of the wheelsets were modified by implantation of ions in the plasma, with the device for implanting the ions in the plasma mounted on the lathe support. Press-fit overhangs were selected so that one wheel recess is provided with a lower limit value and one wheel recess with an upper limit value of the permissible interference fit for UIC 813.

Between the anode 1 and the cathode 2 of the plasma discharge, the carrier gas is mixed with the solid lubricant particles 3 by means of a high-voltage voltage at a high frequency and transformed into a state of ionized cold plasma. The plasma 5 formed by the ionization of the reaction gas is directed to the wheel recess 6 on the rotating shaft 7 of the wheelset. In this way, the entire surface of the wheel support shoulder 6 is treated by a straight forward movement of the plasma discharge.

After the implantation of the ions in the plasma discharge, the wheels were pressed under operating conditions on a railway wheel press and withdrawn after 48 hours without adding and spreading the lubricating oil by pressing. Overall, the wheel bearings were thus connected and released eight times without the appearance of grooves due to pressing.

In order to demonstrate the fatigue limit, the wheelset was subjected to a rolling test bench of 10 million rolling cycles at a radial force of 170 kN and a transverse force of 60 kN. There were no cracks and no permanent displacement of the wheel during the test.

PATENT CLAIMS

Claims (10)

A method for preventing damage to a press fit in a wheel set of a rolling stock, in which a surface treatment of the wheelset shaft is carried out and the wheelset is subsequently assembled, characterized in that: - the wheelset shaft, in its cylindrical and conical end section, is first turned or reground in at least one step, and - the resulting transition is smoothed and / or rounded, whereupon - the surface treatment of the wheelset shaft is treated by a method of implantation of ions in the plasma by applying a finely divided powder containing sulphides reducing the coefficient of friction to the rotating wheelset shaft by means of the cold plasma produced by ionizing the reaction gas used as carrier gas at atmospheric pressure. Method according to claim 1, characterized in that the assembly of the wheelsets is carried out by longitudinal pressing. Method according to claims 1 and 2, characterized in that the plasma treatment is carried out repeatedly during the maintenance process of the wheelset shaft. Method according to claims 1 to 3, characterized in that the solid lubricant particles ionized by the plasma jet are applied to the surface of the rotating shaft of the wheelset at a feed rate of 5 to 50 mm / min, preferably 10 mm / min. Method according to Claims 1 to 4, characterized in that, in a first step, a cylindrical shoulder section for supporting the wheel from outside to inside is turned or grinded longitudinally at a slow traverse of 5 to 50 mm / min. Method according to one of Claims 1 to 5, characterized in that, in the second step, the tapered end section of the shoulder for receiving the wheel from the inside out is turned longitudinally or grinded at slow traverse. -5 CZ 305025 B6 Method according to one of Claims 1 to 6, characterized in that the transition between the cylindrical section of the wheel bearing shoulder and the conical end section is rounded as required. An apparatus for performing a method of preventing damage to a press fit in a wheel set of rail vehicles, wherein the wheel set shaft is rotatably mounted in a jig, characterized in that the lathe and the longitudinally turned or ground wheel set are further incorporated into the plasma ion ion implantation device; wherein the plasma discharge is directed at a 90 ° angle to the rotating shaft. Device according to claim 8, characterized in that the device for implantation of ions in the plasma is arranged at a distance of 20 to 80 mm, preferably 30 mm, from the wheelset shaft. Device according to claims 8 and 9, characterized in that it is provided with a displacement of the rotating shaft of the wheelset relative to the plasma discharge. Apparatus according to claims 8 to 10, characterized in that the plasma discharge device is mounted on the support of the used lathe.