GB2172234A - Method of explosive hardening a cast portion of acute angle frogs of railroad switches - Google Patents

Abstract

A method of explosive hardening a cast portion of acute angle railroad frogs of high-manganese steel residing in that a charge of sheet explosive is placed on the roll surface and side surfaces of a core 1 and guard rails 3 of this cast portion in the area where train wheels roll on the frog elements, and the charge is detonated to attack the surfaces by a slanted detonation wave front with a pressure of 50x10<8> to 250x10<8> Pa to act on said surfaces during 10<6> to 10<4> sec. <IMAGE>

Description

SPECIFICATION Method of explosive hardening a cast portion of acute angle frogs of railroad switches This invention relates generally to the art of railroad construction, and more particularly to a method of explosive hardening a cast portion of acute angle frogs of railroad switches.

The method of the invention can find application in the manufacture of such frogs to improve their resistance to wear due to impact loads exerted thereon.

The railroad frog is generally a unitized casting of a high-manganese steel which includes a frog point or core and guard or wing rails most susceptible to wear. When cast, this manganese steel is quite tough but has a rather low hardness of around 200 Brinell. Because of such properties during the initial period of survice under the action of heavy dynamic loads the frog is subjected to compression and fast wear, whereby surface irregularities appear and the core and guard rails of the frog tend to be reduced in height. The roll surface is understood to mean the surfaces of the core and guard rails to which train wheels exert impact pressure.

Railroad switches include obtuse angle frogs and acute angle frogs. The first are those in which the working edges of the guard rail define a right or blunt angle, whereas the second are railroad frogs with two guard rails defining a sharp angle by their working edges.

Acute angle railroad frogs are the most popular and they operate under heavy impact loads at high speed train passage (up to 120-160 kph). Therefore, their construction requires high resistance to wear and abrasion and high bearing strength to prevent impact fatigue.

Conversely, obtuse angle railroad frogs normally operate at low train speeds to require steels of much less hardness for their manufacture.

In order to provide for long life under severe service conditions, the cast portions of railroad frogs are work-hardened prior to installation.

To this date, methods of hardening railroad frog castings of high-manganese steel employed in this country and abroad failed to provide high resistance to wear and impact fatigue properties.

One known method of hardening railroad frog castings involves rolling their surfaces by shaped rolls (cf. article by N.N. Putri and V.P.

Mikhailova "Rezultaty ekspluatasionnykh ispytanii krestovin razlichnykh tipov i marok"-in Russian, Works of VNIIZhT MPS No. 431, the TRANSPORT Publishers, Moscow, 1971, pages 25 to 28).

The above method prescribes that a preservice bearing stress is imposed on the frog castings to result in an increase their surface hardness. A disadvantage of this method resides in that such a hardening produces a very hard surface or skin of only 5 to 7 mm, the underlying section remaining relatively soft. In addition, cracks tend to appear on the roll surface of the frogs in the course of hardening by rolling to lead to fatigue flaking and fast wear.

Also, this method requires much time and high energy expenditures.

Another method of hardening of a cast portion of railroad crossings cast from a highmanganese steel involves attacking the surfaces of such castings by explosive (cf. USA Pat No. 2,703,297, Cl. 148-4, published March 26, 1951).

This method increases the hardness of manganese steel castings to result in increased service life of the railroad crossing, the method being therefore quite adaptable for explosive hardening obtuse angle railroad frogs intended for low-speed train operations.

When applied for hardening acute angle railroad frogs operable at high train speeds of up to 100 to 160 kph and heavy impact loads, the method fails to provide the necessary degree of hardness and depth of hardness thereby failing to ensure high impact fatique resistance. As a result, service life of railroad frogs hardened according to the method is rather short.

Further, the above method of explosive hardening may result in cross-sectional deformation of frogs and a loss of required margin of plasticity and tenacity of the manganese steel subsequent to the explosive attack, whereby a repeated work-hardening may take place during frog service under heavy impact load accompanied by flaking and chipping of metal.

It is to be noted that acute angle frogs have small cross-sections (between 15 and 40 mm) of the core and guard rails in the zone of train wheel rolling. Therefore, their elements subject to explosive hardening may be damaged, if the strength of explosive attack and the time of duration of this attack, as well as the thickness of sheet explosive and the amount of sheet explosive overhang on the side surfaces of the frog elements to be hardened are not properly calculated. The above method also fails to take into consideration a difference between specific pressure imparted by train wheels to the core and guard rails of acute angle railroad frogs, which results in non-uniform wear of said elements of railroad frogs and reduced service life thereof.

It is also to be noted that the above method fails to provide for the graduation of hardness from extremely hard at the surface through ranges of decreasing hardness to a condition of low hardness. In view of this fact, local surface irregularities may occur to adversely affect the interaction of train wheels with railroad frogs hardened as aforedes cribed, which is especially pronounced at high train speed operations. Such local surface irregularities will be hereinafter referred to as operational irregularities.

There is known a method of explosive hardening a railroad frog cast from a high-manganese steel used here as a prototype and residing in that a charge of explosive is placed on the roll surface and side surfaces of the core and guard rails of the frog in the zone where train wheels roll on said elements, whereafter this charge of explosive is detonated to attack these surfaces with very high pressure (cf. "Metal Treatment and Drop Forging" magazine, No. 292(29) in Great Britain in 1962, pages 285 to 287).

A charge of pentraerythritol tetranitrate 3 mm in thickness is used to effect the method.

A layer of this explosive is placed on the surface of the railroad frog to embrace it and extend approximately 20 mm beyond the end faces thereof. As a result of explosion, a detonation wave is produced with a pressure of the order of 155 kg/mm2. The method also prescribes that the surface of frog core be subjected to a single explosive hardening, while the surface of guard rails is subjected to a repeated explosive hardening.

However this method is likewise applicable to hardening obtuse angle frogs. The method is not adaptable for hardening acute angle frogs for the following reasons.

Firstly, the degree to which obtuse angle frogs are hardened is not sufficient for hardening acute angle frogs, since, as has already been noted, the obtuse angle frogs have more solid guard rails and are adapted for low train speeds.

Also, the method specifies only one discrete value of pressure at the shock wave front without defining its borders and the time of duration of the wave front acting on the surfaces being hardened, which make optimization of hardening impossible when using different explosives. The method also fails to specify variations in the thickness of the sheet explosive (the ratio between these thicknesses) in the horizontal portion and the overhang over the side surfaces of the frog core and guard rails and in the length of the surface to be hardened, whereby deformation and damage of the hardened elements of the frog may occur.

The invention is directed toward the provision of such a method of explosive hardening a cast portion of acute angle railroad frogs wherein due to the selection of duration of explosive attack and pressure of the slanted detonation wave front durability of frogs would improve as a result of increased resitance to wear along with a higher resistance to impact fatigue under heavy impact loads.

The aim of the invention is attained in a method of explosive hardening a cast portion of acute angle railroad frogs of high-manganese steel residing in that a charge of sheet explosive is placed on the roll surface and side surfaces of a core and guard rails of this casting in the areas thereof where train wheels roll on the elements of the frog to be hardened and the charge is detonated to attack these surfaces by a slanted detonation wave front with a pressure of 50108 to 250108 Pa during 110-6 to 1 10-4 sec.

The method ensures a required steel hardness at the roll surface prior to frog installation without surface deficiencies, which improves the durability of the thus hardened frog elements.

It should be noted that the graduation of hardness from the surface toward the underlying sections of the elements being hardened depends on the duration of the explosive attack impulse, the longer is this impulse, the more gradual is the change from extreme hardness at the surface to less hardened metal in the underlying sections.

The duration of the explosive pressure pulse acting on the surface being hardened is determined by the thickness of sheet explosive and the speed with which sound is propagated in the product of explosion, which may be calculated by: k6 T=-, where c k is the coefficient depending on the type of explosive employed (k=2-4); os is the thickness of sheet explosive in mm; and c is the speed of sound in the explosion product in km/sec (c=3-4 km/sec).

When duration of the explosive attack is less than 1106 sec., sheet explosive is required of not more than 2 mm in thickness, whereby use must be made of explosives with a detonation speed of between 8,000 and 9,000 m/sec. The use of such explosives will result in that in the case of small variations in the thickness of sheet explosive or deviations from the explosive hardening procedure cracks or other deficiencies appear preventing the application of the thus hardened casting as a railroad frog. In addition, the above duration of explosive attack and the use of explosives having high detonation speeds will fail to ensure a gradual decrease in the hardness of steel from the surface of the hardened casing toward its underlying sections.

When the duration of explosive attack is more than 1 10-4 sec., a sheet explosive of greater thickness (over 75 mm) is required.

Accordingly, at such a thickness of sheet explosive in order to prevent damage of the cast portion of railroad frogs, it is necessary to apply explosives having a rather low detonation speed, which explosives fail to obtain steel hardness of over 300 Brinell and suffici ent durability of the hardened elements.

With the explosive attack pressure below 50.108 Pa steel hardness is below 300 Brinell.

When pressure developed by the explosive attack is more than 250108 Pa, steel hardness may amount to over 400 Brinell, although surface damage may take place.

Preferably, the thickness of sheet explosive charge is gradually reduced lengthwise of the frog core toward the point thereof to a value close to the critical detonation thickness of the explosive employed.

This enables to attain a uniform hardening effect along the length of the frog core portion being hardened the cross-sectional width of which diminishes in said direction by virtue of reduced explosion pressure produced during detonation.

The ciritcal detonation thickness is understood to mean such a thickness a further reduction of which may fail to initiate an explosion.

Advisably, the thickness of sheet explosive on the roll surface of the frog core is less than the thickness of sheet explosive applied to the roll surface of the guard rails.

Such a reduction in the thickness of the sheet explosive charge provides for a uniform wear resistance of the frog elements being hardened. At equal sheet explosive thickness both on the frog core and guard rails having a greater cross-sectional width than that of the core the hardness of guard rails subsequent to explosive attack is about 25% less than the hardness of the frog core. This in turn results in reduced durability of the railroad frog, since the allowable wear of the guard rails is the same as that of the frog core.

Preferably, the thickness of sheet explosive on the side surfaces of the frog core and guard rails equals to one third the thickness of sheet explosive on the roll surfaces thereof to be close to the critical detonation thickness of the explosive employed.

Thanks to the above ratio between sheet explosive thicknesses, roll surface hardening is optimized and damage to side surfaces of the frog elements being hardened is prevented, this damage being otherwise liable to occur due to the action of relief waves, that is waves that follow the compression waves produced as a result of explosion.

Advisably, the height of sheet explosive on the side surfaces of the frog core and guard rails is selected depending on the thickness of sheet explosive applied to the roll surfaces of the elements, the height of sheet explosive on the side surfaces of the frog core being gradually reduced toward the point thereof the between 0.2 and 0.3 the thickness of sheet explosive on its roll surface. This maximizes the effect of hardening on the roll surface and makes it possible to preserve the cross-sectional geometry of the frog core and guard rails subsequent to hardening, since such a ratio provides for obtaining the required hardness of steel and prevents such defects as cracks, chipping and transverse deformation of the frog elements being hardened.

When the height of sheet explosive on the side surfaces of the frog core is in excess of 0.3 the thickness of sheet explosive on its roll surface, cracks and chips tend to appear in the areas of small cross-sectional width of the frog core subsequent to the action of the explosion wave.

When the height of sheet explosive on the side surfaces of the frog core is less than 0.2 the thickness of sheet explosive on its roll surface, the hardness of steel subsequent to explosive attack is below 300 Brinell resulting in insufficient resistance to wear of the frog core and reduced service life thereof.

Preferably, the charge of sheet explosive is placed on the roll surfaces of the frog core and guard rails such that it completely overlaps the area of operational irregularities, care being taken to ensure a gradual reduction in the thickness of sheet explosive charge on the roll surfaces at all end portions of the charge for a length of not less than 0.43 the width of the frog core at the end of its tail portion to a thickness of not less than the critical detonation thickness of the explosive used.

Thanks to such positioning of the charge of sheet explosive, a uniform wear lengthwise of the cast portion of the railroad frog its assured and the formation of local irregularities at the border between the hardened and nonhardened surface portions is prevented by virtue of a gradual variation in the hardness along the length of the railroad frog elements having been explosive hardened.

The invention will now be described in greater detail with reference to specific embodiments thereof taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic top view of a cast portion of an acute angle railroad frog to be explosive hardened; Figure 2 is a cross-section of the railroad frog casting illustrated in Fig. 1; and Figure 3 is a longitudinal sectional view of a frog core.

The method of explosive hardening a cast portion of acute angle railroad frogs resides in as follows.

The method of explosive hardening a cast portion of railroad frogs, which cast portion is a single unit casting comprising a core 1 with a point 2 and guard rails (Figs. 1 and 2) subject to the heaviest dynamic loads, comprises the steps of pretreatment of the cast portion of the frog, preparation of lower and upper layers of explosive charge indicated by 4 and 5, respectively, to provide for predetermined dimensions thereof, placement of these layers 4 and 5 onto the surface of the frog elements to be hardened (i.e., roll surface and side surfaces of the core and guard rails), detonation of the charge to produce an oblique shock wave front with a pressure of up to 50103-250108 Pa to act on the surfaces to be hardened for 1-10-3X-1-10-4 seconds.

Pretreatment of the cast portion of the railroad frog includes drying, removing particles of loam mold and other impurities therefrom by metal brushes or compressed air, elimination of irregularities from the surfaces to be hardened, and placing on the surfaces a layer of adhesive.

Concurrently, the layers 4 and 5 of explosive are prepared. Plastic explosives, such as those based on hexogen, are used for the purpose.

To obtain sheets of explosive of a preselected thickness, the explosive is rolled by bronze, brass or aluminium rolls. The thus produced sheets of explosive are cut to patterns to thus obtain the lower and upper layers 4 and 5 of explosive.

The lower explosive layer 4 is first cut out to a pattern, whereafter to provide for a better contact with the surfaces to be hardened, i.e. the roll and side surfaces of the core 1 and guard rails 3, it is die-stamped to conform to the configuration of the frog surfaces to be hardened. Subsequent to stamping, while the punch is still in the die, the excess overhang of the explosive layer 4 is trimmed to ensure the overhangs h1, h2 and h3 (Figs. 2 and 3) of the layer 4 of the explosive on the side surfaces of the frog elements to be hardened and the required thickness of the lower explosive layer 4. To preserve the thus obtained configuration of the layers, the die for stamping the layer 4 of explosive serves both as a base plate and as a template to stabilize dimensions of the sheet explosive layer 4 on the roll surface and on the side surfaces of the frog elements to be hardened.The lower explosive layer 4 is then turned over together with the die to fit on the surfaces of the core 1 and guard rails 3 covered with a film of adhesive and pressed thereagainst to provide for a tight contact with the metal surface of the railroad frog to thereby drive out air bubbles between the sheet explosive and the surfaces of the frog. Thereafter, the die is withdrawn and the lower layer 4 of explosive is smoothed manually, to be followed by checking the accuracy of placing the layer 4 and varifyng the amount of overhangs h1, h2 and h3 of the explosive sheet on the side surfaces of the frog elements to be hardened.

Another film of adhesive is applied to the sheet explosive layer 4, whereupon the upper explosive layer 5 is placed thereon. Care should be taken to observe that the upper layer is placed symmetrically in terms of the width of the core and guard rails of the frog.

To reduce the likelihood of defects, spacings of modifying material may be interposed between the charge of sheet explosive and the surfaces of the railroad frog to be hardened.

The lower and upper layers 4 and 5 of explosive charge form a total thickness h on the roll surface of the frog core, the total thickness of these two explosive layers on the roll surface of the guard rails being indicated by H (Figs. 2 and 3).

A high-voltage detonator 6 is used to set off the charge of explosive in the lower and upper layers 4 and 5, care being taken that the explosive sheets 4 and 5 fit snugly against the generating surface of the detonator 6.

The thus prepared railroad frog is placed onto. a special carriage to be moved to an explosion chamber, the charge of explosive being thereafter set off from a remote control panel of this chamber.

For uniform workhardening lengthwise of the roll surface of the core 1, the sheet explosive must be placed such that its thickness would diminish in a direction toward the point 2 thereof to gradually reach the critical detonation thickness.

Uniform wear resistance of the frog elements to be hardened is attained through reducing the thickness of sheet explosive on the roll surface of the core 1 relative to sheet explosive thickness on the roll surface of the guard rails 3.

The thickness of the sheet explosive on the side surfaces of the core 1 and guard rails 3 is one third of the thickness h or H (Figs. 2 and 3) respectively of the sheet explosive charge on the roll surfaces, of these elements which is close to the critical thickness of detonation of the explosive employed.

Further, the height h, of the sheet explosive on the side surfaces of the core 1 and the heights h2 and h3 (Figs. 2 and 3) of the sheet explosive overhangs on the guard rails 3 is selected depending on the total thickness h of sheet explosive on the roll surface of the core 1 and the thickness H of sheet explosive on the roll surface of the guard rails 3, the height h, of the sheet explosive on the side surfaces of the core 1 being gradually diminished toward the point 2 to 0.2-0.3 the thickness h of sheet explosive on the roll surface thereof.

This affords to optimize the hardening effect and maintain the cross-sectional geometry of the core 1 and guard rails 3 after hardening, whereby the required steel hardness is ensured and defects are prevented both at the roll surface and in the underlying sections of the frog elements being hardened.

The charge of sheet explosive must be placed on the roll surface of the core 1 and guard rails 3 so that it would completely cover the area of operational irregularities, a gradual reduction in the thickness of the sheet charge being ensured at all end portions of the roll surfaces for a length of not less than 0.43 the width "a" of the core 1 at the end of its tail portion (Fig. 1) to a thickness of not less than the critical detonation thickness of the sheet explosive used.

Thanks to this, uniform wear of the length of the cast portion of the railroad frog will be ensured, while the formation of local irregularities at the border between the hardened and non-hardened surface of the frog will be prevented due to the gradual variation in the hardness lengthwise of the frog elements being hardened.

Subsequent to hardening the cast portion of acute angle railroad frogs is marked and tested for hardness.

Service tests have shown that railroad frogs hardened by the herein proposed method are 30 to 50% more durable in terms of average tonnage than non-hardened ones.

Described hereinbelow for the sake of a more complete understanding of the method of the invention are various preferred examples for effecting the method.

Example 1 A cast portion of a sharp railroad frog having a length 3,738 mm and a width a=231 mm at the end of the tail portion of the core 1 (Fig. 1) is admitted to an explosion chamber subsequent to drying and cleaning of the particles of loam mold and other impurities by compressed air. A layer of adhesive is applied to the surfaces of the core 1 and guard rails 3 to be hardened, whereafter the lower and upper sheets 4 and 5 of a hexogen-based explosive are placed thereon.

The lower sheet or layer 4 of explosive is pressed manually against the surfaces to be hardened to ensure a tight contact with the metal of the railroad frog and drive out air bubbles between the lower layer 4 and the surfaces of the frog to be hardened. The upper layer 5 of explosive is placed on the lower layer 4 subsequent to the application of adhesive to this lower layer 4 of sheet explosive. The upper layer 5 of explosive must be arranged symmetrically on the core 1 and guard rails 3.

The total thickness of sheet explosive on the roll surface of the core 1 is 9 mm, this thickness gradually diminishing toward the point 2 to 3 mm. The thickness of sheet explosive at the side surfaces of the core 1 is 3 mm, while the height h,=8 mm to be gradually reduced to 2 mm toward the point 2.

The overall thickness H of the sheet explosive charge on the roll surface of the guard rails 3 amounts to 12 mm, whereas the sheet explosive thickness at the side surfaces thereof is 4 mm with the height h2=h3=10 mm.

The layer of sheet explosive starts on the core 1 at a distance of 150 mm from its point 2 to be extended toward the tail portion thereof; the sheet explosive on the guard rails 3 starting at a distance of 140 mm from the point 2 of the core 1 to extend to the opposite direction. The sheet explosive is terminated on the core 1 at a distance of 600 mm from its point 2 toward the tail portion thereof, whereas on the guard rails 3 the sheet explosive terminates at a distance of 500 mm if measured in the same direction.

Gradual reduction in the total thickness h and H of sheet explosive on the roll surfaces of the elements being hardened for a length of not less than 100 mm before termination to a thickness of below the critical detonation thickness of the explosive employed. To set off the charge of sheet explosive between the lower and upper layers 4 and 5 thereof, the high-voltage detonator 6 is arranged, care being taken to assure a firm contact of the layers 4 and 5 with the generating surface of the detonator 6.

The thus prepared railroad frog is placed on a carriage and admitted to the explosion chamber, whereafter the charge of explosive is set off to result in a slanted detonation wave front with a pressure of 100.106 Pa within 6106 sec.

A hardness test is followed, the hardness thus attained being normally between 340 and 360 Brinell. Thereafter, the roll surface and side surface of the core 1 and guard rails 3 subjected to hardening are inspected visually for defects, which are normally absent.

The steel hardness attained and the absence of surface defects provide for the required operational toughness of the cast portion of the railroad frog subjected to explosive attack according to the method of the invention.

Example 2 The sequence of preparation procedure of the cast portion of the railroad frog to explosive hardening, the arrangement of the lower and upper sheets 4 and 5 of explosive and the high voltage detonator 6 thereon, as well as the manner in which the explosive charge is detonated are substantially similar to what has been described with reference to Example 1.

The total thickness h of the charge of sheet explosive on the roll surface of the core 1 is selected to be 7.5 mm; this thickness being gradually diminised toward the point 2 of the core 1 to 3 mm. The thickness of sheet explosive on the side surfaces of the core 1 is 2.5 mm; the height h,=7 mm with gradual reduction toward the point 2 to 2 mm. A charge of sheet explosive is applied to the roll surface of the guide rails with a thickness H=10 mm; the thickness of sheet explosive on the side surfaces of the guard rails 3 being 3 mm with a height of h2=h3=9 mm. The charge of sheet explosive layers 4 and 5 is applied to the railroad frog elements to be hardened in a manner essentially similar to the way it has been described with reference to Example 1.The charge of explosive is then set off to a pressure of slanted detonation wave of 140.106 Pa within 4.10-6 sec. After the explosive attack the hardness is normally between 360 and 380 Brinell to ensure the required toughness of the cast portion of the railroad frog with no defects on the roll surface and side surfaces of the core 1 and guard rails 3.

Example 3 The cast portion of a railroad frog is prepared, the layers 4 and 5 of sheet explosive and the detonator 6 are arranged, and explosion is initiated in a manner similar to the way it has been described with reference to Example 1.

The total thickness h of the charge of sheet explosive on the roll surface of the core 1 is selected to be 6 mm with a gradual reduction toward the point 2 to 2 mm. The thickness of the sheet explosive on the side surfaces of the core 1 is 2.5 mm, the height h, being 6 mm gradually diminishing to 4 mm toward the point 2 thereof. The overall thickness H of the sheet explosive on the roll surface of the guard rails 3 is 9 mm; the thickness of sheet explosive on the side surfaces of the guard rails 3 being 3 mm with a height h,=h2=4.5 mm.

The lower and upper layers 4 and 5 of sheet explosive on the elements of the railroad frog to be hardened are arranged substantially as described with reference to Example 1.

The charge of sheet explosive is detonated to provide a pressure of the slanted detonation wave amounting to 260108 Pa within 0.810 6 sec.

Steel hardness attained due to the explosive stack is 410 Brinell. Cracks are in evidence in the region of the point 2 of the core 1 and on the side surfaces of the guard rails 3, these cracks preventing the normal operation of the cast portion of the railroad frog.

Example 4 The cast portion of a railroad frog is first prepared as heretofore described. The layers 4 and 5 of sheet explosive are applied and the detonator 6 is arranged as specified in Example 1, the explosive charge being detonated in a likewise manner.

The total thickness h of the charge of sheet explosive here on the roll surface of the core 1 is 15 mm gradually diminishing toward the point 2 to 5 mm; the thickness of explosive charge on the side surfaces of the core 1 being 5 mm with the height h,=12 mm progressively reduced toward the point 2 to 3 mm.

The total thickness H of the sheet explosive on the roll surface of the guard rails 3 is 15 mm, while the thickness of explosive charge on the side surfaces thereof is 4 mm with the height h2=h3=15 mm.

The sheet explosive charge on the core 1 starts at a distance of 150 mm from its point 2 and extends toward the tail portion thereof, whereas on the guard rails 3 the charge extends 50 mm from the point 2 of the core 1 in the opposite direction. The sheet explosive charge terminates on the core 1 at a distance of 400 mm if measured from the point 2 toward the tail portion thereof; the charge on the guard rails 3 terminating a distance of 300 mm if measured in the same direction.

The charge of sheet explosive is set off to produce a pressure at the slanted detonation wave front equal to 40.108 Pa attacking the elements being hardened during 1.510-4 sec.

After subjecting to the explosive attack the hardness is from 270 to 280 Brinell.

The above hardness fails to ensure the necessary durability of the railroad frog. In addition, the hardened area is short of lapping over the zone of operational irregularities, which in turn will fail to provide for uniform wear lengthwise of the hardened elements of the railroad frog during service.

From the heretofore described examples 1 to 4 it is evident that when the parameters of explosive hardening as cited in the claims are conformed with, the required hardness of the cast portions of railroad frogs is attained without structural faults subsequent to the hardening. A failure to follow the prescribed parameters of the method of explosive hardening according to the invention will result in steel hardness below the required one.

Claims (7)

1. A method of explosive hardening a cast portion of acute angle railroad frogs of highmanganese steel residing in that a charge of sheet explosive is placed on the roll surface and side surfaces of a core and guard rails of this cast portion in the area where train wheels roll on said elements of the frog, and the charge is detonated to attack said surfaces by a slanted detonation wave front with a pressure of 50108 to 25010 8 Pa to act on said surfaces during 1-10-6 to 1.10 4 sec.

2. A method according to claim 1 wherein the thickness of the sheet explosive charge is gradually reduced lengthwise of the core toward the point thereof to a value close to the critical detonation thickness of the explosive employed.

3. A method according to claim 1 wherein the thickness of the sheet explosive charged on the roll surface of the core is reduced relative to the thickness of charge on the roll surface of the guard rails.

4. A method according to claim 1 wherein the thickness of the sheet explosive charge on the side surfaces of the core and guard rails equals to one third the thickness of the sheet explosive charge on the roll surfaces thereof to thereby be close to the critical detonation thickness of the explosive employed.

5. A method according to claim 1 wherein the height of the sheet explosive charge on the side surface of the core and guard rails is selected depending on the thickness of the sheet explosive charge on the roll surfaces of these elements, the height of this sheet explosive charge on the side surfaces of the core being gradually reduced toward the point thereof to between 0.2 and 0.3 the thickness of the sheet explosive charge on its roll surface.

6. A method according to claim 1 wherein the sheet explosive charge is placed on the roll surface of the core and guard rails such that it completely overlaps the area of operational irregularities, care being taken to ensure a gradual reduction in the thickness of the sheet explosive charge on the roll surfaces at all end portions of the charge for a length of not less than 0.43 the width of the core at the end of its tail portion to a thickness of not less than the critical detonation thickness of the explosive used.

7. A method of explosive hardening a cast portion of acute angle railroad frogs in accordance with any one of the foregoing claims substantially as disclosed in the description with reference to the accompanying examples and drawings.