EP0234204A2 - Method and apparatus for straightening a rail in a roller straightening machine - Google Patents

Abstract

In this method, the rail, during its passage through the top and bottom rollers arranged offset relative to one another, is repeatedly subjected to opposed bending deformations (maxima, minima) by alternate individual bending via head and foot. According to the invention, the rail is bent in such a way via the rail head during the passage and the maxima and minima are matched to one another in such a way that the rail runs with a constant end curvature having a radius of 15 to 60 m into the last straightening triangle in which this curvature is bent again into a straight line. This straightening method ensures that the rail is virtually free of longitudinal internal tensile stresses on the rail-foot side. The rail is thereby given better fracture resistance and fatigue strength. <IMAGE>

Description

The invention relates to a method for straightening a railroad track in a roller straightening machine according to the preamble of the main claim.

The invention further comprises a roller straightening machine suitable for carrying out the method.

Rails produced by hot rolling rail steels in appropriately calibrated rolls cool in air to room temperature after rolling on cooling beds. However, due to the different ratios of mass to surface at the rail head and foot, the rails bend when they cool down. In order to meet the high flatness requirements for the running surface, the rails must therefore be straightened.

When straightening in roller straightening machines, the rail is subjected to opposing bending deformations by means of alternating individual bends over head and foot as it passes through the staggered upper and lower rollers, which forces each cross-section of the rail to undergo a path that reverses several times in its incline, alternating maxima in contact of the rail foot with the lower rollers and minima when the rail head comes into contact with the upper rollers.

Two top rollers and the associated bottom roller and two bottom rollers or the associated center top roller are each referred to as a triangle.

In the last directional triangle on the outlet side, a bending deformation of the rail that deviates from the desired straight line is permanently eliminated. A roller leveling system of nine rollers is common worldwide today, with four upper rollers and three lower rollers effecting the actual straightening process, and the rail on the inlet and outlet sides is carried by another roller each. The axes of the lower rollers and the outfeed roller can be moved in the height direction parallel beyond the dimension that just allows the rail to pass freely. The amount of this shift is called employment. The axes of the top rollers cannot be adjusted. They are driven to cause the rail to pass. The maxima and minima that occur with the opposite bending deformations in the continuous path are brought about by positioning the lower rollers against the foot of the rail, with a lower roller adjustment decreasing towards the outlet side being provided according to the prior art. If a rail passes through the roller system with such a normal adjustment of the lower rollers, then it experiences alternating bends or curvatures up and down with maxima and minima until the desired flatness is finally achieved. Since the rail cross-section is plastically formed by the alternating opposing bending deformations when the rolls are straightened, but the shape changes are different over the cross-section, internal stresses arise in the rails oriented in this way. The residual stresses on the running surface and on the underside of the rails are positive in the longitudinal direction, ie they lie Tensile stresses that are opposed by residual compressive stresses in the web. The residual stresses increase with increasing strength of the rail material. The process for straightening rails in a 9-roll machine (seven straightening rolls plus entry and exit rolls) and the residual stresses that occur when straightening the rails are described in detail in DE-Z Stahl und Eisen 105 (1985), No. 25-26 , Pages 1451 - 1456, esp.pictures 9 and 10 on page 1455.

According to this reference, the longitudinal tensile stresses for a UIC 60 rail reach 90 A (strength: 950 N / mm ² ) in the head up to 200 N / mm ² and in the base up to 260 N / mm2, for a UIC 60 rail in the S grade 1200 (strength: 1250 N / mm ² ) in the head up to 250 N / mm ² and in the foot up to 400 N / mm2.

The high longitudinal tensile stresses in the rail head and foot are due to the fact that these areas of the rail are shortened by means of the roller straightening relative to the rail web, but these shortenings are compensated for by elastic expansions, since this requires the rail to remain together.

The elastic strains of the head and foot correspond to the tensile residual stresses to be measured there. The equilibrium is maintained by elastic compression of the web in accordance with the compressive residual stresses to be measured there.

The high residual tensile stresses affect the structural strength and the break resistance of the rails. Although they are converted to residual compressive stresses on the running surface during operation, they remain on the underside of the foot.

The safety against breakage of rails can be increased by reducing the longitudinal tensile stresses in the rail foot. There are already various approaches to this. You can use the residual stresses e.g. B. reduce significantly by stress relieving. Also proposals are known to straighten rails by stretching with low residual stress (DE-OS 32 23 346). Finally, according to a not previously published proposal by the applicant, the internal stress condition during roller straightening can be changed in a favorable sense by suitable heating of the rail web. However, since roller straightening is the usual method by which rails are straightened in the production flow in order to meet high flatness requirements, the aim should be to achieve low longitudinal residual stresses in the rail foot alone with this method alone.

In e.g. Z. usual roller straightening machines for rails, z. B. a 9-roller straightener, only the lower rollers can be adjusted, d. H. only their axes can be moved vertically, but the top rollers cannot. Their axes lie on a line. The roll diameters are all the same.

The directional effect is achieved in such a way that the rail is first strongly bent with the head in the pull zone by appropriately adjusting the first lower roller. Starting from this state of curvature, the rail is then bent with decreasing amounts with decreasing amounts of the second and third lower rollers by successive action of upper and lower rollers (directional triangles) with the foot or head in the pull zone until it is straight. The common tangent to the top rollers specifies the desired trajectory in relation to the rail head. In this way, good results can be achieved with regard to the straightness of the rails, but only have very little influence on the longitudinal residual stresses in the foot. It is an object of the present invention to further develop the method of the type described above for the roller straightening of railroad tracks in such a way that the longitudinal tensile stresses in the rail foot, which determine the break resistance of the rail in operational use, are decisively reduced.

It is also an object of the invention to provide a device suitable for this.

The object is achieved in accordance with the characterizing part of the main claim in that the rail follows an overall curved continuous path with the center of curvature below the rail foot and is bent in such a way that the minima of the rail that each rail section in the straightening machine on its way to passes through the last directional triangle, is the corner point of an imaginary polyline that rises on the inlet side and falls to the last directional triangle and the maxima are above the polygonal line, and that each rail section with an end curvature to be removed by the last directional triangle with a radius of 15 - 60 m into the last directional triangle comes in.

The process is carried out so that, for. B. in the 9-roller straightening machine described at the beginning, the two upper rollers on the inlet and outlet sides keep their fixed axis, whereas the two middle upper rollers are shifted upwards. This means that a reference line for the adjustment for the path of the rail is no longer defined as a common tangent to the top rollers with respect to the rail head, but rather a polyline. The corner points of this polyline are given by the deepest points of the contact surfaces of the top rollers and the rail head.

These points of contact (= corner points of the polyline) represent the minima of the rail path. With the displacement of the respective lower rollers over the respective distances of the polyline, the adjustment against the rail foot necessary for the directional effect is achieved. The deflections that occur represent the maxima of the path of the rail.

When passing through the individual straightening triangles of the roller straightening machine, each section of the rail thus describes an arc directed upwards, limited by the pressure on the top rollers. This curve is modulated by the individual bends (maxima and minima) of the continuous path. The necessary adjustments of the middle upper rollers and the lower rollers are selected taking into account the spring back of the rail so that the rail receives a constant end curvature before the rail enters the last directional triangle. The radius of curvature is 15 - 60 m depending on the rail quality and the intended directional effect. This end curvature, which is constant on the last section of the polygon, is converted into a straight track of the rail in the last directional triangle, formed by the last upper roller, the last lower roller and the outfeed roller.

The arc of the rail continuous path curved toward the top rollers is preferably designed in such a way that the rail section with constant end curvature and the minima of the individual bends lie on a common circular arc. The middle top rollers are set an equal amount higher than the top and bottom rollers.

Alternatively, the upwardly curved arc of the rail pass can be designed such that the minima of the individual bends lie on a circular arc with a larger radius than the radius of the end curve. To the required end To achieve curvature, the last maximum of the individual bends must be set accordingly before the rail enters the last directional triangle. The setting is selected taking into account the springback so that the deflection of the upwardly curved rail in the range between this maximum and the last minimum corresponds to the desired constant end curvature.

In addition to the required flatness, rails oriented in accordance with the invention surprisingly have very low longitudinal tensile stresses on the underside of the foot, as will be explained in the examples below.

The curvature of the rail path that is essential for the method according to the invention, curved upward to modulate the individual deflections due to the adjustment of the lower rollers, with constant end curvature before entering the last directional triangle can also be achieved if a smaller diameter is provided for the two middle upper rollers than the diameter of the outer top rollers, with the axes of the top rollers lying in the same plane. With this measure, too, the rail receives the required curvature over the rail head, passing into a uniform end curvature before it is bent into the required straight line by the directional triangle on the outlet side. With this variant, in addition to the required flatness of the rail, very low longitudinal tensile stresses in the rail base are achieved.

Roller straightening machines with the features of claims 4 to 6 are suitable for carrying out the method according to the invention.

With the roller straightening machine according to claims 4 and 5, it is possible to set the respective curvature of the upward curved trajectory of the rail according to the desired tension conditions in the rail foot within certain limits. With a roller straightener with the features of claim 6, according to which the middle top rollers have a smaller diameter than the outer top rollers, the radius of curvature of the rail pass is determined by the diameter of the middle rollers binding. Such a machine can, however, be used advantageously where rails of constant quality and dimension are to be straightened. Then you can choose the diameter of the middle rollers from the outset so that the optimal judging result is guaranteed.

The invention is explained in more detail below with the aid of two examples and figures.

In Fig. I a 9-roll straightening machine is shown in which the two middle upper rolls are adjustable in height. This representation is associated with FIG. 2, a representation of the curved rail path over the individual directional triangles predetermined by the rollers.

3 shows a further 9-roll straightening machine in which the middle upper rolls have a smaller diameter than the two outer upper rolls.

FIG. 4 shows a representation of the upward curved path of the rail through the straightening machine according to FIG. 3.

In the case of Fig _. 1 schematically shown roller straightening machine R ₁ , four upper rollers 1, 3, 5 and 7 and a lower inlet roller E, three lower straightening rollers 2, 4 and 6 and a lower outlet roller A are mounted in a machine stand 8.

The middle top rollers 3 and 5 are height adjustable. In this example, all rollers have a diameter of 950 mm. The distance between the top rollers on the one hand and the bottom rollers on the other is 1,500 mm, based on the roller axes.

The lower rollers 2, 4 and 6 are each centered on the corresponding upper rollers 1, 3, 5 and 7.

The lower rollers 2, 4 and 6 as well as the inlet roller E and the outlet roller A are also adjustable in height.

All top rollers are driven by drive means, not shown.

A rail 9 is directed between the upper rollers and the lower rollers. The rail rests with its head 9a on the upper rollers and with its foot 9b on the lower rollers.

In the example, the middle upper rollers 3 and 5 are raised by an equal amount of 73 mm compared to the straight connection between the contact lines of the first upper roller 1 and the fourth upper roller 7 with the rail head 9a.

When the rail head 9a rests on the upper rollers 1, 3, 5 and 7, the continuous rail describes a (imaginary) polygon P with the corner points 1 ', 3', 5 ', 7'.

The lower rollers are positioned above the sides of the polyline P upwards. The lower roller 2 is set 22 mm higher, so that the (imaginary) polygon path 1'-3 'is bent upwards. This deflection gives the first maximum 2 'of the bending of the rail. The lower roller 4 is set 18 mm higher than the polygon segment 3'-5 '(maximum 4'), the lower roller 6 is 15 mm higher than the polygon segment 5'-7 '(maximum 6').

The result is an overall curved path of the rail 9 towards the upper rollers, whereby, as FIG. 2 shows, the minima 1 ', 3', 5 'and 7' assigned to the upper rollers, defined by the corner points of the imaginary polygon P, the same circular arc K with the radius r = 31 m as the rail section S with constant end curvature before entering the last triangle, the is formed by the top roller 7, the bottom roller 6 and the outfeed roller A.

The constant end curvature of the rail section S with the radius r = 31 m is eliminated by adjusting the runout roller A by 33 mm downwards.

The individual deflections (maxima, minima) of the rail selected in this example are adapted to a rail height of 172 mm (profile UIC 60) and, taking into account the springback before the rail enters the last directional triangle, result in the constant end curvature with a radius r = 31 m.

3 shows another roller straightening machine R ₂ . It corresponds essentially to the roller straightening machine R ₁ described in FIG. ₁ . The reference numerals, as mentioned in Fig. 1, are therefore retained. The difference to the roller straightener R ₁ is that in the roller straightener R ₂ the middle upper rollers 3 and 5 have fixed axles that are in line with the axes of the upper rollers 1 and 7. However, the diameter of the upper rollers 3 and 5 is smaller than the diameter of the outer upper rollers 1 and 7. In this example, it is 930 mm compared to 950 mm of the rollers 1 and 7. A UIC 60 rail with a height of 172 mm is straightened.

When the rail 9 rests with its head 9a on the upper rollers 1, 3, 5 and 7, there is also an imaginary polygon P 'with the corner points 1', 3 ', 5' and 7 ', which show the minimum of the rail bending when passing through Form the rail through the rollers.

The minima 1 ', 3', 5 'and 7' are here, as shown in FIG. 4, on a circular arc K 'with a larger radius r ₁ = 225 m than the radius r = 25 m of the rail section S with a constant end curvature Enema in the last direction triangle (rolls 7, 6, A). The lower roller 2 is set 22 mm higher than the polygon path 1'-3 '(maximum 2'). The lower roller 4 is raised by 8 mm (maximum 4 ') beyond the polygon path 3'-5'.

The lower roller 6 is raised by 20 mm beyond the polygon path 5'-7 '(maximum 6'). The deflection thereby given to the rail in the range between the maximum 6 'and the minimum 7' corresponds, taking into account the springback, to the desired constant end curvature of the rail section S with a radius r = 25 m. This end curvature is eliminated by moving roller A down by 10 mm.

With the method steps according to the invention, a longitudinal tensile internal stress of only 35 N / mm2, instead of otherwise 250 N / mm2, and z. B. in quality S 1200 of only 60 N / mm2, instead of up to 400 N / mm2 otherwise.

The range of the residual stresses achievable with the method according to the invention in rails with profile UIC 60 according to FIG. 5 is shown in the diagram according to FIG. 6.

While in the head 9a and web 9c the residual stress curve over the height of the rail 9 corresponds to that of the usual roller straightening (solid lines), lower longitudinal tensile to even compressive residual stresses arise in the foot 9b (tensile stress - plus values, compressive stress - minus values).

The dashed lines denote the spreading area according to the usual roller straightening, while the dash-dotted lines limit the spreading area which results in the footing area when straightening according to the invention.

The pre-curvature of the rail with a constant final curvature before entering the last directional triangle is of crucial importance for the method according to the invention.

In this pre-curved state, the splint still has the residual stress state with high longitudinal tensile stresses in the foot. The upward curved rail is then straightened in the last triangle and stretched so permanently in the foot that the total length of the rail foot is increased and the length of the almost undeformed rail web is adjusted again. When springing back after the rail has run out of the straightening machine, length compensation by means of elastic expansions or corresponding tensile residual stresses is no longer the same as in conventional roller straightening, so that the longitudinal tensile stresses in the foot are consequently zero or close to zero.

Due to the reduced longitudinal tensile stresses in the rail base, the behavior of rails directed according to the invention is changed significantly under stress.

The advantages of the residual stress distribution achieved in this way with low longitudinal tensile stresses on the underside of the rail foot could be demonstrated by continuous vibration tests on entire rails using a test arrangement as described in DE-Z Stahl und Eisen 105 (1985), page 1452, Figure 3, mentioned at the beginning .

The results of the fatigue tests are summarized in Fig. 7 for the UIC 60 rail profile in quality 90 A. Thereafter, the permanent structural strength is

the notched rails according to conventional roll straightening 100 N / mm ² , according to roll straightening according to the invention 150 N / mm ² .

The advantage in fatigue strength is then 50% in this example. It also applies proportionally to notched rails. Even if only half of it, i.e. 25%, can be continuously realized during the ongoing rail production, this advantage is considerable. In relation to the property of the rail as a carrier, this increases ent neither its load-bearing capacity by this percentage, or one can lower the section modulus of the rail and thus its meter mass with the same load. Instead of the UIC 60 profile with a section modulus of 335 cm ³ and a meter mass of 60 kg / m, in the case of the straightening method according to the invention, the profile S 49 with a section modulus of 240 cm ³ and a meter mass of 49 kg / m can be used without loss of long-term load-bearing capacity even in the event of corrosion and the notches made with it.

The advantages in terms of fracture safety according to fracture mechanical assessment are just as significant. The linear elastic fracture mechanics describes the conditions under which a component breaks brittle starting from an already existing crack. It can be used on rails. Thereafter, the safety against breakage of splints increases if a crack as deep as possible is borne before the breakage occurs with the same external stress. The usual roller-oriented UIC 60 rail in quality 90 A was subjected to a permanent crack of 9 mm in the fatigue test before it broke brittle at an upper tension of 205 N / mrn2.

In contrast, the roller-oriented splint according to the invention with 28 mm suffered a permanent tear three times as deep before the break occurred at the same upper tension.

Claims (6)

1.Procedure for straightening a railroad track in a roller straightening machine, the rail being subjected to opposing bending deformations as it passes through the top and bottom rollers, which form staggered triangles and are arranged one behind the other, by alternating individual bends over head and foot, which causes the rail to go into a multiple position Forcing the path reversing its slope, alternating maxima when the rail foot comes into contact with the lower rollers and minimums when the rail head comes into contact with the upper rollers, and in the last directional triangle on the exit side, a bending deformation curve of the rail still deviating from the desired straight line is eliminated,
characterized ,
that the rail follows an overall curved continuous path with the center of curvature below the rail foot and is bent such that the minima of the path that each rail section traverses in the straightening machine on its way to the last straightening triangle, corner points of an imaginary one, rising on the inlet side and the last Directional triangle sloping polygon and the maxima are above the polygon, and that each rail section with an end curvature to be removed by the last directional triangle with a radius of 15 to 60 m enters the last directional triangle. 2. The method according to claim 1,
characterized in that the rail section with the end curvature and the minima of the individual bends lie on a common circular arc. 3. The method according to claim 1,
characterized in that the minima of the individual bends lie on a circular arc with a larger radius than the radius of the end curvature, the last maximum of the individual bends being selected such that the constant end curvature is reached before the rail enters the last directional triangle. 4. roller straightening machine for performing the method according to claims 1 to 3,
Consisting of a machine stand and partially driven straightening rollers arranged in it, namely four top rollers and five adjustable bottom rollers arranged offset to the top rollers, of which the fourth top roller, together with the fourth and fifth bottom roller, form the last triangle when viewed from the inlet,
characterized in that in each case the lower contact line of the second and the third upper roller (3; 5) coming into contact with the rail head (9a) of a rail (9) to be straightened above the straight connection between the corresponding contact lines of the first and the fourth upper roller ( 1; 7). 5. roller straightening machine according to claim 4, wherein the top rollers have the same diameter among each other,
characterized in that the second and third top rollers (3; 5) are adjustably mounted in the machine stand (8). 6. roller straightening machine according to claim 4, characterized in
that the second and third top rollers (3; 5) each have a smaller diameter than the first and fourth top rollers (1; 7), which are identical in diameter to one another, the axes of the top rollers (1; 3; 5; 7) being in the same plane lie.

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