US3276924A

US3276924A - Method and apparatus for heattreating rail heads

Info

Publication number: US3276924A
Application number: US497389A
Authority: US
Inventors: Okamoto Tatsumi
Original assignee: Yawata Iron and Steel Co Ltd; Dai Ichi High Frequency Co Ltd
Current assignee: Yawata Iron and Steel Co Ltd; Dai Ichi High Frequency Co Ltd
Priority date: 1965-10-18
Filing date: 1965-10-18
Publication date: 1966-10-04
Anticipated expiration: 1983-10-04

Description

1966 TATSUMI OKAMOTO 3,276,924

METHOD AND APPARATUS FOR HEAT-TREATING RAIL HEADS Filed 001;. 18, 1965 4 Sheets-Sheet l FlG.2

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I N VENTOR Tafsum/ Okamo/o wwgz/ M M Get. 4, 1966 TATSUMI OKAMOTO METHOD AND APPARATUSFQR HEAT-TREATING RAIL HEADS 4 Sheets-Sheet 2 Filed Oct. 18, 1965 FIG.8

FIG. 6

Tem perufure INVENTOR O/ram 0/0 Tafsum/ 1966 TATSUMI OKAMOTO 3,276,924

METHOD AND APPARATUS FOR HEAT-TREATING RAIL HEADS Filed Oct. 18, 1965 4 Sheets-Sheet 5 9 FIG. no

INVENTOR Tafsumi Okamo/o amwpauzz v 1966 TATSL lMl OKAMOTO METHOD AND APPARATUS FOR HEAT-TREATING RAIL HEADS Filed Oct. 18, 1965 4 Sheets-Sheet 4 FIG. ll

a, n sf J 1 4 O 9 0 o 5 I 6 20 9 v a INVENTOR Tafsum/ O/ram f United States Patent O 3,276,924 METHOD AND APPARATUS FOR HEAT- TREATING RAIL HEADS Tatsumi Okarnoto, Kitakyushu, Japan, assignor to Yawata Iron & Steel Co., Ltd., Tokyo, Japan, and Dai-Ichi Koshuha Kogyo Kabushiki Kaisha, Kitakyushu, Japan,

both corporations of Japan Filed Oct. 18, 1965, Ser. No. 497,389 4 Claims. (Cl. 148146) This application is a continuation-in-part of my application Ser. No. 230,794, filed Oct. 10, 196-2, now abandoned, which in turn is a continuation in part of my application Ser. No. 840,636, filed Sept. 17, 1959, now abandoned.

This invention relates to a method and apparatus for heat-treating rails and more particularly it relates to a method and apparatus for hardening and tempering the heads of rails by induction heating.

Conventional heat-treated rails are subjected to such high surface pressure, repeated bending stress and shearing stress during their use that, when the hardened layer is thin, it will often peel off and make the rails unusable. Therefore, in order to prevent such peeling it is considered to be necessary that the depth of heat-treatment be more than 15 mm. 7

In the heat-treatment by a conventional flame heating method, since external heating by means of burners is employed, in order that the temperature be elevated above the transformation point where the hardened layer is deep, i.e., more than 15 mm. deep, the temperature of the surface part of the rail will become far higher than that and will reach a temperature above 1000 C. Therefore, when the rail is quenched from such a high temperature, there will often be defects such as the rail will be cracked by the quenching, the structure of the rail will become coarse, and the mechanical properties will be impaired.

Further, it is well known to harden only the part of the rail contacted by wheels, that is, only the surface layer of the head of the rails, so as to increase its wearresistance. However, in the actual heat-treatment for hardening and tempering the head of a rail so as to give a sorbite structure of the Shore hardness of about 50 and provide wear-resistance without sacrificing toughness, a great strain will be produced due to the peculiar shape of the rail. Therefore, the heat-treating operation is usually diflicult.

Moreover, in a conventional method of heat-treating rails wherein only the top face and the flanks or only the top face of a rail is hardened, after the hardening, the rail will largely curve with the head curved outside due to the combined action of the thermal expansion, the thermal contraction, the expansion due to the transformation stress, and the contraction due to the transformation stress. When the rail head is then tempered to a sorbite condition, the rail will this time largely curve with the head inside. For example, the curve may amount to more than 200 mm. per 10 meter of length of a rail or in an extreme case even to more than 1 m.

Various methods have been suggested for preventing such great curving of the rails caused by the hardening of the heads. For example, there have been adopted a method wherein, simultaneously with the hardening of the surface layer of the head, the surface layer of the flange, which need not be hardened for strength reasons, is also hardened so that the curving of the rail being prevented by compensating the stresses in the two hardened parts each other; a method wherein the rail is curved 3,276,924 .Patented Oct. 4, 1966 ice previously in a same extent in an opposite direction of curving after heat-treatment; and a method wherein the flange of the rail is further heated after hardening the rail head.

In general, the thermal capacity of the flange of a rail is larger than that of the head. Thus there has been a case where, when both head and flange of a rail are hardened, the contraction of the flange having a larger thermal capacity will overcome that of the head and will cause curving and the degree of curving will be equal to that produced by hardening of only the head. For the above mentioned reasons, though head-hardened rails are superior in wear-resistance, they have not been extensively produced due to the complexity of correcting the curvature thereof.

Further, when rails have been laid, there are defects therein which will cause considerable wear to the under surface of the rail heads of the plates joining the rails due to vibration caused by tthe passage of trains and therefore damage will be caused by the disarrangement of the rail surfaces.

Therefore, it is an object of the present invention to provide a head-hardened rail having high Wear-resistance and toughness.

Other object of this invention is to provide a method and an apparatus for producing a head-hardened rail of which curving is prevented.

Still other object of this invention is to provide a method and an apparatus for continuously producing headhardened rails. v

According to the present invention, the above mentioned defects are corrected by adopting an induction heating hardening method instead of a flame heating hardening method and carrying out the heat-treatment as follows. That is, in this invention, heating and quenching of the flange of a rail that have hitherto been conducted in order to prevent curving of the rail are not carried out at all in the induction heating hardening method, that is to say, the treatment of the opposite surfaces for preventing curving is not carried out. Instead, not only the top surface and flanks of a rail head but also the underside thereof is hardened so that the curving of the hardened part of the underside may oppose the curving of the hardened part of the top face to prevent curving, and at the same time the angle of inclination of the second conveyor surface for conveying the rail directly after hardening is adjusted to prevent the formation of curving strain of rail. Thus, by the present invention the hardening operation for rails can be easily conducted and products having no curving and having a high wear-resistance for effectively preventing the Wear of the hardened parts of the underside of the rail due to the plates joining the rails.

The above and further objects'of this invention will be easily understood by the following detailed explanation of this invention referring to the accompanying drawings in which:

FIG. 1 is a side view showing an embodiment of this invention utilizing high frequency generator-type (M-G type) high frequency induction heating as a heating means for hardening and tempering rails,

FIG. 2 is a plane view of the apparatus shown in FIG. 1,

FIG. 3 is a perspective view showing the relation of the induction heating elements in the apparatus of this invention and rails,

FIG. 4 is a cross-sectional view taken on line AA of FIG. 3,

FIG. 5 is a cross-sectional view taken on line BB of FIG. 3,

FIG. 6 is a cross-sectional view taken on line C-C of FIG. 1.

FIG. 7 is a graph showing the relation of temperatures and volume changes when a rail is hardened and tempered according to the present invention,

FIG. 8 is a graph of the curved state and curved extent after applying the heat-treatment of this invention to rails of 12 m. in length and 50 kg./m. in weight,-

FIG. 9 is hardness distribution diagrams of the head of a rail heat-treated by the present invention,

FIG. 10 is a cross-sectional view of a rail heat-treated according to the present invention and equipped with joining plates,

FIG. 11 is a side view showing another embodiment of this invention,

FIG. 12 is a plane view of the apparatus shown in FIG. 11, and

FIG. 13 is a cross-sectional view taken on line D-D of 'FIG. 11.

In the figures, a hardening means 4 consists of a heating section and a cooling section. First of all, a high frequency current (SOD-10,000 cycles) generated by rotating a high frequency generator 3 by an electric motor-or other prime mover 2 is introduced to an induction heating coil 4 through a bus bar. The shape of the induction heating coil 4 is, as shown in FIG. 4, almost the same as that of the head of a rail 1.. That is, the clearance between the rail 1 and the coil 4 is almost the same at the top face, flanks, and undersides of the head of the rail. A water jacket 6 connected to a water pipe is placed adjacent the outlet side of said coil 4.

Adjacent the above-mentioned hardening means 4 is placed a tempering means 7. The tempering means 7 is almost the same as the hardening means 4 except the shape of a tempering coil 7'. That is, as shown in FIG. 5, the clearance between the head of a rail 1 and the induction heating coil 7 for tempering is narrow at the top face of the rail where the accepting heat capacity is large, broad at the flanks where the accepting heat capacity is small, and broader at the corners of the flanks and the undersides, since it is necessary to maintain the head of the rail at uniform temperatures lower than a red-heat temperature. The reason for adopting such a shape of the tempering coil 7' is that in the case of a high frequency heating treatment, the maintenance of the head .of the rail in a uniform temperature distribution lower than a red-heat temperature is not easy and the temperature of the head is liable to become higher than a transformation.

temperature.

In this case, a good result is obtained when the clearanoe between the flank and the tempering coil 7 is selected to be about 2-3 times as large as that between the top face of the head and the tempering coil and the clearance at the corners mentioned above is about 4 times as large as that between the top face and the coil 7'.

As mentioned above, the difference-in shape between the hardening coil and the tempering coil is one of the main features of this invention.

Further, other main feature of this invention is that the above-mentioned tempering coil 7' is positioned at a downwardly inclined position along the rail "1 disformed by the hardening-treatment, which will be mentioned below in detail.

In the embodiments of this invention shown in the accompanying drawings, the hardening coil 4' and the tempering coil 7' are energized by

separate generators

2 and 2, but they may be connected in series or in parallel, in each case it being convenient to adopt a reactor for controlling electric power. As illustrated in FIG. 1, the

depth, and the temperature increase in a range higher than the A transformation point is very slow, the temperature gradient in the head of a rail is very gentle in a deeper part from the top face of the head as compared with the case of using a flame heating hardening method. This makes the structure of the rail after heat-treating dine and uniform and hence. not only the strength is increased but also the heat strain is less, which are very convenient therefore in the .case where the thickness of the hardened layer is more than 15 mm.

According to the process of this invention, the thickness of the part converted into a sorbite structure, that is, the depth of the hardened layer reaches 15-25, mm. or more from the top face and flanks of the rail. The electric power required by the heat-treatment is about 200- 220 kw. when a high frequency induction heating of 3,000 cycles/sec. is used while moving rails of 50 kg./m. each at a speed of 250 mm./min. In general, for heating rails in this invention, induction heating by a high frequency current of SOD-10,000 cycles/sec. may be utilized.

Now, the inclination of the conveyor surface which is one of the main features of this invention will be explained.

In this invention, in order to conduct the heat-treatment continuously, the rails are joined to each other at both ends. That is, if rails are heat-treated separately without joining the. rails to each other, there remain insufliciently hardened portions at both ends of the rails and hence in order to overcome such a trouble and to reduce the losses in operation time and operation powers all the rails are joined by means of rail-joining metal members -14 utilizing rail-joining holes as shown in FIG. 6. Thereafter the rails are subjected to the hardeningtreatment in the hardening means of this invention and transferred into the tempering means by a below-mentioned conveyer means.

As shown in FIG. 1 and FIG. 2, the first conveyer system placed at the front of the heat-treating apparatus is constructed by supporting

rollers

9, 9, supporting

means

9, 9, for said supporting rollers; a motor 15'; a reduction gear system 15;, guide

rollers

19, 19, and pinch rollers 10 and the second conveyer system placed behind the heat-treatment meansis constructed by supporting

rollers

12, 12, In addition, the numeral 23. indicates a floor for introducing rails and the numeral 24 indicates members for placing the heat treated rails. The supporting

rollers

12, 12, are supported movably by supporting members 12-1, 12-1, that can be raised ,up or laid down by means of oil pressure cylinders. That is to say, by the action of the oil pressure cylinders the height of the supporting

rollers

12, 12, may be changed desirably.

The pinch roller 10 is rotated through the reducing gear system 20 by means of the motor 16 and supply rails to be heat treated into the hardening coil 4' and the temper- 7 ing coil 7'.

The speed of the pinch roller 10 may be changed in response to the kind of rail to change desirably the hardened depth of thus head-hardened rail.

The guide rollers 19 are provided to maintain definite clearances between the rail. and the hardening coil 4' and the tempering coil .7 in the heat-treating system. The numeral 11 indicates a press roller.

One of the features of the above-mentioned rail conveying system is that the inclination of the secondconveyer surface can be controlled desirably and in order to incline the. second conveyer surface such that the surface be inclined downwardly from the end portion of the above-mentioned hardening means 4, the above-mentioned supporting

rollers

12, 12, are equipped at the behind section of the hardening means 4.

The reasonfor adopting such a construction of the conveyer system in this invention is as follows.

Since the railto be heat-treated in this invention has a specific shape consisting of a head section, a web section and flange section having a large heat capacity than the head section, the length is very long as compared with the height thereof, and further the rails are continuously heat treated by joining the rails by means of the joining members 14, the curving of the rail cannot completely be prevented though the rails are hardened at the underside surfaces.

When the head of a rail is hardened by the heat-treatment of this invention, the rail is curved with the head curved outside due to the thermal expansion in heating and the martensite transformation by quenching, and when the rail is then tempered into a sorbit structure, the rail 1s curved oppositely.

Now, the temperature and volume variations when a high carbon steel which is a material for a rail to be treated in this invention are shown in FIG. 7 wherein the solid line represents hardening, the dotted line represents tempering, the position (0) represents a state before hardening, the position (P) a martensite state after hardening, and the position (Q) a sorbite state after tempering.

According to the figure, there is little volume variation between (0) and (Q) and therefore there should substantially be no curving due to the variation of the structure by the heat-treatment of rails. However, as mentioned above, the head-hardened rail treated in the hardening means curves with the head concavely, the reason of which being as follows: Now, if the length of the rail is l, the expansion coefli-cient is d, and the heating temperation is t, the length It of the heated head part of the rail will be Due to the elongation of Al, the rail should curve in that amount, but if the rail is raised and heated in only the head part, the web and the flange of the rail will resist the expansion of the head. Further, due to the expansion of the head part, the rail will rise up from a supporting stand and hence the weight of the rail will greatly resist the expansion of the head part. That is, the heated part will be subjected to a great compressive force but, while the temperature is high, the yield point of the material of the rail will be so low that a permanent strain will be produced due to this compressive force. Accordingly, the length l t of the head part heated to temperaturet C. will be l t l-i-Al wherein AI AL Then, after the hardened material is tempered, as shown in FIG. 7, the volume will theoretically be at point (Q) and there will be substantially no difference from the initial point (0). That is to say, there will be substantially no volume variation due to the transformation. Therefore, after the head of the rail has been tempered, when the temperature becomes normal, the increased part Al due to thermal expansion will all be constant. Accordingly, the length of the head of the rail will be It will be equal to the length of the flange of the rail and hence the rail will not curve. However, in fact, the length of the rail becomes l t and then in this case the length after tempering and cooling will be as follows:

However, since Al Al, then l+l -Al l, that is, l l. Thus, the length of the head will become shorter than that of the flange and hence the rail will curve with the head inside. According to the above-described theory, if A1 is made equal to Al, 1 will become equal to l and therefor the curving of the rail will be able to eliminate.

It is a most important point in the present invention to make Al equal to Al. In FIG. 1, if the supporting

rollers

12, 12, after heat-treatment are placed on the same level as that of the supporting

rollers

9, 9, before heat-treatment, the rail 1 will be heated in only the head of it in the hardening coil 4 and will rise up from the supporting rollers near the hardening coil 4', whereby the rail will not be able to well curve in the hardening coil 4 and the length will become l+Al Therefore, if the supporting

rollers

12, 12, are vertically movable such that the load of the rail may not vary on the supporting rollers, I will be extended to l+Al and hence the rail will be prevented from curving. That is, the angle a is adjusted by vertically moving the supporting

rollers

12, 12, such that the rail 1 may not be separated from the supporting rollers, that is, the surface of the second conveyer system is inclined along the deformation direction of the rail 1, and the rail curved and inclined by heating for hardening treatment is supported on the conveyer surface as it is moved along the surface.

The angle a of the inclination of the second conveyer surface mentioned above is influenced by the kinds of rails, the shapes and dimensions of the hardening coil and tempering coil, heat-treatment rate, and the heating depth, but the angle is in general in a range of 1 30 to 15'.

That is, if the angle is less than 130, the inclination of the conveyer surface is ineffective and if the angle is larger than 15, the rail after hardened is not placed over the conveyer surface, which causes the formation of inside strains and hence reduces the effect of this invention.

Accordingly, the tempering means 7 is inclined along the rail 1 in the above-mentioned range.

Now, the invention will be explained about the mecha- First of all, the rail I placed on the rail-supplying floor 23 is moved to the central portion of the supporting roller 9, that is, a rail-passing line in the heat-treating apparatus by means of a rail-moving apparatus (not shown) consisting of hooks mounted to a wire rope, and the rail is then sent into the pinch rollers 10 by means of the supporting roller 9 having the reducing gear system 15. Thus, after separating from the rail-supplying floor 23, the end of the first rail is joined to a second rail at a rail-joining station 21 by means of a specific joining member 14 utilizing bolt holes at the ends of the rails. (Cf. FIG. 11 and FIG. 12.) Thus joined rails are moved by means of the pinch rollers 10 and only the head part of the rail enters the hardening coil 4'. The rail entered the hardening coil 4' is heated to about 800-900 C. therein and is completely converted into an austenite state. That is, a high frequency electric power (SOD-10,000 cycles/sec.) generated by the generator 3 is led to the hardening coil 4' through the high frequency reactor 18 and a high frequency modulator 17 whereby the above-mentioned rail is subjected to high-frequency induction heating. Where, the rail is curved in the definite angle a due to the thermal expansion and the weight of it and then the rail is, in that state, quenched by means of the cooling jackets placed just behind the hardening coil 4, whereby the structure of the rail is converted into a martensite structure. In this case, if the curving of the rail by the weight of the rail is insufficient according to the shape of the rail, the curvature is supplied by means of the compressing roller 11. Further, thus hardened rail is then continuously introduced into the tempering coil 7 placed just behind the hardening coil 4', wherein the rail maintained at 500 600 C. by high frequency induction heating. The thermal expansion in the tempering system is low due to the low temperature, and the yield point is high, and hence no permanent strain is formed. Thereafter, the rail is cooled by means of the water cooling jacket 6 positioned just be hind the temper-ing coil 7'.

The structure of the rail obtained by the process of this invention is a sorbite structure.

Further, the hardness of the head of the rail obtained by the hardening and tempering treatment of this invention is in a range of Hs 50:3 throughout the whole length of the rail.

In addition, the temperature control for the hardeningand-tempening-treatments may be conducted by automatic control systems inserted to the out put sides of the 7 high-frequency generators .and the temperature may be maintained in C. to a defined temperature by using such systems.

When the end of thusheat-treated rail is transferred by means of the supporting

rollers

12, 12, so adjusted that the angle of inclination of the second conveyer surface is in a range of 130'15 to a rail-discharging position 22, the rail joining member 14 is disengaged and the rail is transferred to the heat-treated rail placing station 24 by a rail-carrying means (not shown) or withdrawn by means of a crane.

Now, other embodiment of this invention will be explained referring FIG. 11 to FIG. 13. In this example, as the second conveying surface, a conveying trough 13 is used, which is supported on a supporting base 25. Since it is necessary to vary the angle a of conveying inclination according the kinds of rails and the conditions for heat-treatment, the supporting base 25 can be moved vertically.

In the embodiment shown in FIG. 13, an oil-pressure cylinder 26 is used for moving the supporting base 25-, but other means such as a screw means may be adopted. In this case, as shown in detail in FIG. 13, the conveying trough 13 is supported via bearings on the supporting base 25 rotatably mounted on the end of a rod of the 0il-pressure cylinder 26 whereby the inclination of the conveying trough can be smoothly adjusted.

When the heat-treatment is conducted by the process and the apparatus of this invention as mentioned above, the curved value of the rail is very low and in almost all the cases shown in the FIG. 8, the value is less than 20 mm. (The unit of the numbers in the FIG. 8 is a millimeter unit.) This shows that the inside stress after a correcting curving may be small, which gives good influences on the products as well as facilitates the heattreating operation, and therefore, it contributes to reduce the cost for correcting curving by heat-treatment.

An example of the depth of the hardened layer and the distribution of hardness in a cross-sectional plane of a 50 kg. rail subjected to the heat-treatment of this invention is shown in FIG. 9. 'In the figure, (a) represents a case where the, tempering temperature is high and (b) represents a case where the tempering temperature is low. The hardness is low in (a) or is Shore 45-4-8 while it is Shore 48-51 in (b). The depth of the hardened layer is 20-22 mm. in the top face of the head of the rail and 18-18.5 mm. in the back side of the head in both (a) and (b), which clearly shows practically valuable hardened state.

Further, in the case of practically using rails, rails 1 are joined by means of joining

plates

25, 25 and bolts 26 as shown'in FIG. and since the rail obtained by the present invention is hardened even in the portion contacted with the joining plates, the wear of that portion can be effectively prevented.

The invention is explained about several examples, but it should be understood that many corrections and changes may be done in the scope of this invention.

What is claimed is:

1. -In a method for heat-treating rails for railroads, said rail having a head, a web, and flanges, the improvement which comprises heating a rail by high-frequency induci tion heating in only the tread, the flank, and the underside of the head of the rail while the rail is conveyed in a state joined to other rail, whereby natural curving of the rail caused by the heating is effected sufliciently, followed immediately by quenching, conveying then the rail along a conveyer surface inclned to the curved direction of said rail, tempering the rail there by heating it by induction heating and then immediately quenching, and'disengag ing joining of the heat-treated rail whereby the rail in a normal and substantially straight state is obtained.

2. In an apparatus for heat-treating rails for railroads,

said rail having a head, a web, and flanges, the improvement comprising a hardening means having a first conveying surface and a tempering means having a second conveying system; said hardening means having a high frequency heating device having an induction heating coil in which the clearance between the coil and the rail to be hardened being substantially same at the tread, the flanks and the undersidesof the head of the rail and a cooling device; said tempering means having a high frequency heating device having an induction heating coil in which the clearance between the coil and the rail to be temperedbeing broader at the flanks than at the tread and being broadest at the corner of the tread and the flank and a cooling device; said tempering means being downwardly inclined along the second conveying surface; said first conveying surface consisting of supporting rollers for conveying the rail in a horizontal direction, a guide roller, and a pinch roller; and said second conveying surface consisting of supporting rollers movable freely in height for conveying the rail curved in the quenching, said second conveying surface being downwardly inclined from the end portion of said hardening means.

3. The apparatus as claimed in claim 2 wherein said second conveyer surface is composed of supporting rollers supported by vertically movable members, the height of said member being freely changed by means of a cylinder system or a screw system.

4. The apparatus as claimed in claim 2 wherein the angle of the inclination of the second conveying surface with the horizontal is from 130 to 15.

No references cited.

DAVID L. RECK, Primary Examiner.

C. N. LOVELL, Assistant Examiner.

Claims

1. IN A METHOD FOR HEAT-TREATING RAILS FOR RAILROADS, SAID RAIL HAVING A HEAD, A WEB, AND FLANGES, THE IMPROVEMENT WHICH COMPRISES HEATING A RAIL BY HIGH-FREQUENCY INDUCTION HEATING IN ONLY THE TREAD, THE FLANK, AND THE UNDERSIDE OF THE HEAD OF THE RAIL WHILE THE RAIL IS CONVEYED IN A STATE JOINED TO OTHER RAIL, WHEREBY NATURAL CURVING OF THE RAIL CAUSED BY THE HEATING IS EFFECTED SUFFICIENTLY, FOLLOWED IMMEDIATELY BY QUENCHING, CONVEYING THEN THE RAIL ALONG A CONVEYOR SURFACE INCLINED TO THE CURVED DIRECTION OF SAID RAIL, TEMPERING THE RAIL THERE BY HEATING IT BY INDUCTION HEATING AND THEN IMMEDIATELY QUENCHING, AND DISENGAGING JOINING OF THE HEAT-TREATED RAIL WHEREBY THE RAIL IN A NORMAL AND SUBSTANTIALLY STRAIGHT STATE IS OBTAINED.