Railway switches and signals – Crossings – frogs – and mates
Reexamination Certificate
1999-06-14
2002-01-22
Morano, S. Joseph (Department: 3617)
Railway switches and signals
Crossings, frogs, and mates
C246S458000, C246S468000, C246S274000, C246S275000, C246S382000
Reexamination Certificate
active
06340140
ABSTRACT:
The invention pertains to a railroad frog for switch points and crossings. This type of frog is known from EP 0,282,796. As in all known frogs, the wing rails are separated from the frog point by filling plates in order to ensure the proper flange groove width. To guarantee a certain elasticity of the individual components of this frog, a bushing is passed through the frog with play, where this bushing is supported on both sides by the spacer element on the filling plates, which in turn lie on the fishplate seating surfaces of the wing rails. The wing rails are tightened together with a bolt, so that the filling plate, the spacer element, and the bushing thus together form a rigid unit. Only the frog point can move horizontally and vertically relative to the two wing rails with the stipulated amount of play. The two wing rails and the frog lie on a ribbed plate, which has vertically protruding ribs that serve as stops for the feet of the wing rails and the frog point for horizontal movement and permit the desired horizontal mobility based on the stipulated horizonal.
WO 94/02683 discloses a frog that is assembled from two unwelded rail sections screwed together via filling plates and a bolt that passes through the connector of the wing rails and the frog. To keep both unwelded rail parts of the frog point in a defined position relative to each other, the rail sections of the frog are penetrated without play by a bushing, or the opposing surfaces of the frog section are joined by a profile or indentation running in the longitudinal direction whose tooth flanks lie against each other without play.
A frog similar to EP 0,282,796 is also known from EP 0,281,880 B1 and DE 37,08,233 A1.
Simple, rigid frogs are generally arranged in switch points at the places where the inner wheel flange intersects the two treads in the crossing region for problem-free traversal. The wheel rims are so wide that they cover the groove width and the width of the still load-bearing point of the frog point. During the free passage of the flange, the wheel rims that transfer the wheel load must allow problem-free traversal over intersecting treads without destruction of the narrow frog point.
The rigid, simple frogs assembled from rails with the three main parts (i.e., the two wing rails and the single frog point) are bolted together via filling plates, which is also intended to prevent longitudinal shifting due to temperature fluctuations and braking. These threaded joints of the rigid, simple frogs now designed as HB (high-strength, bolted) threaded joints exhibit significant technical deficiencies, as well as very high manufacturing and maintenance costs, which adversely affects service life. The very high manufacturing costs are primarily attributed to the fact that filled section rails of the corresponding rail profile are used for the point instead of the standard rails otherwise common on the track at switch points. In order to be able to weld the welding cross section of the two points consisting of filled section rails, both the main point and the wing rail must be machined generally up to at most halfway in the critical region. Before welding these two cross sections into a single frog point, the area being welded must be preheated to about 400-500° C. so that no cracks form during welding of the highly carburized rail steel. This temperature must be maintained throughout welding. However, it is generally not held at this level, so that martensite formation occurs in the welding area and the welds crack, even after a short time, or the point rails break, which today is still, unfortunately, very often the case.
Moreover, the region of transfer of the wheel from the wing rail to the point or vice versa is often hardened or pearlitized in order to reduce wear. Decarburizations that lead to lower strength of this area, however, develop in the initial and end region during hardening or pearlitization, which in practice leads to increased maintenance costs due to so-called switch dents after brief operation.
It is also known from DE 33,39,442 C1 that the frog point can be provided with a recess in the region of the greatest wear, especially in the initial region, into which a frog insert made of high-carbon manganese steel is firmly fitted. The high-carbon manganese steel is secured by a press-fit produced by a low-temperature shrinkage process. This process does lengthen the service life of the frog point, but is very complicated and expensive and creates an almost inelastic frog point.
Holes can be drilled through both the frog block and the wing rails, which, on the one hand, entails high costs and, on the other, leads to rail breaks if the hole edges are not properly deburred. Joining of the filling plate support surfaces with the fishplate seating surfaces of the wing rails as free from play as possible requires high manufacturing costs. The main cause of high wear, and thus relatively short service life, is the unduly high rigidity of the transitional region of the wheel from the wing rail to the point and vice versa because of the unduly compact cross section, i.e., the total moments of inertia about the X axis, the combination of wing rail, frog points and filling plates. It was already recognized in EP 0,282,796 that these problems could be solved by greater elasticity than before, i.e., by a relative vertical displaceability between the frog point and wing rail so as to support only limited forces in the weak region of the frog point and high forces in the regions of greater rail cross section. Owing to the fact that both wing rails are still rigidly coupled via the frog point, their moments of inertia are still relatively high. The frog point is also mounted there to achieve a bending rod function, like a jib, i.e., its free end can be deflected vertically, whereas the rear region is rigidly fixed. The front region of the frog point thus bends downward when traversed and the tread is stressed in the region where the train is located, which has led to rail breaks even after a short period of operation.
If one compares the inertia, i.e., the moment of inertia of the transitional region of two wing rails, two filling plates and, if necessary, the filled section rail points, it can easily be seen that this type of transitional region acts like a rigid block that causes compressive deformation in the impact region because of its rigidity. If we further consider that railroad wheels are not perfectly round, which is caused possibly by the high rigidity of the impact point and pointlike or even bluntly run-over single frogs, it becomes clear that this is an additional major cause of wear. To eliminate this wear due to orthogonal compressive deformation on the frog point and the wing rails during operation, both the point and the wing rails are resurfaced by welding under practical conditions on the track. This resurfacing by welding is often not carried out skillfully, especially if the weld is not sufficiently preheated, which results in the frog breaking by martensite formation after a short time and its replacement.
The horizontal rigidity, which corresponds to a multiple of that for a single rail because of the very high moment of inertia of the entire rim frog about the Y axis, also excessively loads the guardrails. In order to reduce wear on the guardrails, the wing rails should be designed to be horizontally elastic, especially on contact with the rear wheel sets of the wheels.
The greatest tracking defect of current frogs lies in the fact that the wing rails are not cambered in accordance with the conicity of the form of the running wheel. Thus, during traversal of the point the axle of the wheelset at the equal height wing rails is significantly lowered vertically and thus strongly accelerated vertically. The wheel contact surface point then wanders farther from the running edge to the smaller diameters of the rim, which results in significantly lower circumferential velocity of the wheel on the frog side, whereas the wheel of the wheelset on the inner curve runs on a larger diameter of
Jules Frantz F.
Morano S. Joseph
Senniger Powers Leavitt & Roedel
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