CLIAMS:CLAIMS:

1. Method for controlling the toe radius of railroad rail in a conventional rail mill, the method comprising the steps of:-
providing first rolling a roughly rolled billet into a rail by rough rolling mill employing two high reversing rolls with 7 – passes;
providing subsequent rolling by intermediate stands employing a pair of three high stands coupled together with 3 passes in each stands;
providing final rolling by finishing stand for the final shaping and dimensional accuracy to the rolled profile; wherein the
the progress of the reciprocative rolling causing the corners of each of the head and foot of the rail to become unaffected is carried out during rolling in intermediate stands and the pass profiles are modified in intermediate stands in such a way that proper working is carried out on the material with subsequently formation of proper toe radii and throat radius, eliminating formation of sharp corners in the rail profile.

2. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the distribution of material during rolling in intermediate passes of conventional rail rolling is carried out for proper formation of toe radius of rail.

3. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the rolling in the rough rolling mill is carried out after reheating the billet at 1100-11500C and more preferably 10800C.

4. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein hat pass is given in first two passes of first Intermediate stand, whereby material is reduced by formation of rail parts.

5. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the final shaping and dimensional accuracy to the rolled profile is carried with finishing rolling temperature of 860-9400C.
6. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the top rolls of the said rolling mills are hydraulically balanced for reducing the mill spring along with high rigidity housings ensuring high degree of consistency in the dimensional accuracy of the rolled profile.

7. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the toe radius in first pass and finishing pass was increased from 5mm to 7-9 mm during rolling in the intermediate mill.

8. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the toe thickness of pass 4 close flange was altered as (i) Top part from 20 .7 mm to 21.0-22.0 mm, (ii) Bottom part from 16.3 mm to 17-19 mm.

9. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the throat radius of pass # 4 and pass # 5 is controlled increasing it by 2-3 mm.

10. A method for controlling the toe radius of railroad rail in a conventional rail mill as claimed in claim 1, wherein the rails possess R-60 profiles of 90 UTS & 110 UTS grade steels.

Dated: this 27th day of February, 2015
,TagSPECI:METHOD FOR CONTROLLING THE TOE RADIUS OF RAILROAD RAIL IN A CONVENTIONAL RAIL MILL

FIELD OF INVENTION
This invention relates to a method for controlling the shape of hot railroad rails during rolling thereof in a conventional rail mill, and more specifically, a method for controlling the shape of railroad rails including proper formation of toe radius during roll pass thereof in line with a rolling mill.

BACKGROUND ART
Generally, rolling of rails is done by the so-called rolling method of conventional rolling, wherein rolling is carried out with upper and lower horizontal rolls having pass designs. As annular slot turned in the body of a rolling mill roll is called the roll groove. A combination of the grooves in two mating rolls is termed the roll pass. However, this rolling method requires a high level of operation technique; the pass designs used for the method are difficult to design and manage; and proper distribution of material in different passes is essential.

The design of roll passes is based on the knowledge of the theory of plastic deformation of metal. Sizing of each rolled shape should be kept with the principles of the given metal rolling method and with the design features of the given rolling mill. The proper pass design provides for steady conditions of processing and ensures high quality of the rolled products, as well as the most favorable technical and economical characteristics of the production.

During rail rolling the metal is distributed between the elements of the section (head, web and base) dissimilarly. Stringent requirements for the quality, structure, strength and dimensional accuracy of rails dictate that a meticulous approach be taken in designing the roll passes for rails.
The difficulties which are met with in rolling rails are explained by the asymmetry of the rail section with respect to the vertical axis of the roll passes, this causes the development of considerable axial forces which act on the rolls and may affect the thickness of the base and the head of the rail in live flange.

When analyzing actual roll pass designs non uniformity of deformation, particularly in the first shaping passes becomes evident. Consequently, the metal flows from one part of the rolled section to another.

Therefore, by this method rejection/down gradation of the product is bit on the higher side as dimensional accuracy of the rails is essential.

In order to solve such problems as mentioned above, the universal rolling mill method is gaining popularity. The universal rolling method is fundamentally different from the above rolling method of the roll pass type. The former uses a universal rolling mill with the horizontal rolls and vertical rolls concentrating reduction on every part of the to-be-called material, particularly the upper surface and both sides of the part to be rolled into the head of the rail which will contact wheels, thus producing a rail having a head of good quality resulted from sufficient forging.

However, this method is so carried out that the material to be rolled into a rail in several passes subjected to the universal rolling mill and edging rolling mill. However, particularly in the case of rolling such products as rails that have the head and the foot reduced greatly differently, even the rolling operation by this method is impossible, for the following reason. When rolling the material to be rolled into a rail by using the universal rolling mill, part of the reduction power put on the head and the foot of the rail works so as to make them stretch in their respective directions, and moreover they are subjected to the reduction of the same rate, making the reduction of the head greater than that of the foot. This causes a great difference in the above stretched volume between the head and the foot. Even with respect to the head of the rail, the stretched volume varies top to bottom. Subsequent to the universal rolling mill, the rail is sent to the edging rolling mill which is equipped with the roll pass so designed as to put the same reduction rate to the head and the foot, but the passing of such to-be-rolled material as the rail having the head and the foot with greatly different stretched volumes causes different reduction rates between these parts, thus causing such troubles as bending of the so-called products, these troubles making any further reciprocal rolling impossible. Even if such rolling can be carried out, the corners of the head and of the foot of the so-rolled rail will form an acute angle, which constitutes a fatal shortcoming of the prior art method. Thus, it is believed to be difficult to develop an effective and economical universal rail rolling method.

Bhilai Steel Plant produces rails in R-52 & R-60 profiles of 90 UTS & 110 UTS grade steels. Rail rolling process consists of reheating the blooms, rolling into desired profile, roller straightening, inspection of the finished product and shipping of the product to the customer. Initially blooms are heated in reheating furnace at around 12500C-12800C. The blooms after reheating are first rolled in the 950mm roughing mill, having 2 high reversing rolls with 7-pass scheme. The roll gap for each pass is adjusted by top roll screw down and the blooms are guided into the passes by manipulators. Working roll tables and housing rollers on either side of the rolls provide the drive to the blooms while rolling.

After roughing stand stocks are rolled in Intermediate Mill, which are high. The Intermediate mill has two 3 high stands coupled together and driven by a single drive motor. The scheme employs 3 passes in each stands coupled together and driven by a single drive motor. Lifting tables lift the rolling bar upto the upper passes for reversal of direction.

The top rolls are hydraulically balanced for reducing the mill spring and along with the high rigidity housings ensure high degree of consistency in the dimensional accuracy of the rolled profile.
After rolling in 2 intermediate stands, finish rolling is carried out in 2 high finishing stands which provides the final shape and dimensional accuracy to the rolled profile. The rolling in finishing stand is very important as it controls the final dimensions of the rolled profile.

Rails of different shapes and dimensions are used in railroad transport and in industry. The rolling scheme for rails is designed to work the head and foot of the rails more to ensure a very fine surface finish.

In rail profile at flange radius are provided at the corners (fig. 1), but at times formation of radius is not perfect. As per Indian Railways specification formation of toe radius in rails is required. Formation of proper toe radius is essential for overall quality of rail profile and customer satisfaction, as sharp corners leads to stress concentration and corrosion.

SUMMARY OF INVENTION
An object of the present invention is to provide a method of rolling rails, whereby the conventional rolling of rails is made possible by modifying intermediate stand so as to not form a sharp corner. Modifications were carried out from pass no. 3 which is used as preparatory ones for providing better working of the rolled piece. Corners at flange are formed by using, in addition to the normal pass design, modification in third pass onwards that is hat pass with radii to cause the corners to be made larger than those of the abovementioned normal pass design, whereby a rail having a sufficiently forged head can be produced, thus solving the abovementioned problem.

By modification in the roll pass design for rails is meant the distribution of deformations among the metal passes in rolling and also the design of the shapes and calculation of dimensions of the roll passes, as well as the design of the rolled work piece sections.

Consecutive changes of the shapes and dimensions of the rolled metal sections in passes were carried out for filling of the roll passes with the metal.
The sizing of the rolled shapes consists in distribution of the shapes and dimensions of the roll passes, as well as of the work piece sections among the metal passing, while the roll pass design involves the arrangement of the passes on the rolls and this is determined by the draught scheduled, the method of rolling and effective use of the rolls.

Modification in roll pass was carried out with the aim for determination of optimum deformation in each passes and of the number of passes, as well as at the creation of rolling conditions necessary to obtain rolled section which will meet the prescribed requirements.

Another object of the present invention is to provide a method to produce rails having designed radii at the flange corners.

In order to attain these objects, the present invention is developed in relation to a method of rolling rails by using a conventional rolling mill train comprising a Roughing stand, two intermediate stands and one finishing stands. These stands have grooves in rolls for imparting desired deformation to the stock so that to get desired shape of rails. The shape of the roll pass determines the rolled metal structure, especially in the most critical element of the section.

In an exemplary embodiment of the invention the disclosed method enables formation of proper toe radius, toe thickness, throat radius in rail profile for overall improvement in rail quality. It also improves rail quality with respect to stress concentration and corrosion resistance.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates the R-60 Rail profile in accordance with the present invention;
Fig. 2 illustrates the Roll pass design of Pass No. 3 of Intermediate stand in accordance with the present invention;
Fig. 3 illustrates the Roll pass design of Pass No. 4 of Intermediate stand in accordance with the present invention;
Fig. 4 illustrates the Roll pass design of Pass No. 5 of Intermediate stand in accordance with the present invention;
Fig. 5 illustrates the Roll pass design of Pass No. 6 of Intermediate stand in accordance with the present invention;
Fig. 6 illustrates the Roll pass design of Pass No. 7 of finishing stand in accordance with the present invention.

DETAILED DESCRIPTION
In order to solve such problems as mentioned above taking place in rolling rails in the conventional rolling mill, the present invention provides, method to impart radius at the flange corners in the rails. This causes, at the latter stage of rolling operation, the prescribed radiuses for respective corners of the foot of the so-rolled rail to be formed by the subsequent roll pass.

As mentioned above, the present invention is characterized by using a modified rolling profile using the basic arrangement of a conventional rail mill in which drafting schedule and pass profiles are modified over roughing mill, intermediate mill and finishing mill such that material is worked overall so to form proper radius at the flange end without compromising of other sections of the rails. This method uses proper distribution of material in different pass profiles during rail rolling in such a way that overall working of the material results in better rail profile. This method also uses material properties and spread of the material in such a way that material flows in lateral direction so that proper filling of passes takes place.

950mm Roughing Mill
In 950mm Roughing Mill the rolls have an average diameter of 950mm and barrel length of 2300mm. The rolling in the roughing mill is carried out with rectangular blooms of material size: 330*335mm and 315*340mm, after reheating at 1100-11500C and more preferably 10800C, employing 2 high reversing rolls with 7-pass scheme. The roll gap for each pass is adjusted by top roll screw down and the blooms are guided into the passes by manipulators. Working roll tables and housing rollers on either side of the rolls provide the drive to the blooms while rolling.

In roughing stand initially drafting is provided to the stock/work piece for 5 passes. In pass No. 6 and 7 during roughing pass knifing pass is given in the bottom portion of the stock. Ideally in roughing passes as temperature of the stock/work piece is high, more draft is given to take advantage of the higher plasticity of the material at higher temperature.

800mm intermediate mill
The 800mm intermediate mill comprises of 3 high non reversing stands. These stands having a pair of 3 high stands coupled together and driven by a single drive motor. The scheme employs 3 passes in each stands coupled together and driven by a single drive motor. Lifting tables lift the rolling bar upto the upper passes for reversal of direction. The working rolls have an average diameter of 800mm and a barrel length of 1900 mm. The top rolls are hydraulically balanced for reducing the mill spring and along with the high rigidity housings ensure high degree of consistency in the dimensional accuracy of the rolled profile.

In intermediate passes rough shape of rail is imparted in the stock. In first two passes of first Intermediate stand, hat pass is given, whereby material is reduced by formation of rail parts i.e. head and flange does not take place. Basically from 3rd pass of first intermediate stand rough shape of rail start to take place. From pass 3 of the first intermediate stand material is distributed in flange and head portion and formation of rough shape of rail profile starts.

This is the stage from which process of formation of toe radius starts. For proper formation of toe radius sufficient material is to be provided at each pass so that working is done at toe portion of the rails. For formation of proper toe radius working of rolls at toe portion of the material is essential.

850mm FINISHING STAND
The 2 passes from high finishing stands provides the final shaping and dimensional accuracy to the rolled profile with finishing rolling temperature of 860-9400C. The working rolls are mounted on anti-friction bearing and have hydraulic roll balancing and a closed top structure to minimize mill spring and roll gap variations. The rolls have an average diameter of 850 mm and barrel length of 1200mm.

Final shape of toe radius is given at this stage. For that top open flange coming from intermediate stand is kept long but narrow and bottom closed pass is short but thicker. The formation of toe radius is depended on proper filling of passes. The modification in the toe radius was carried out from pass 3 of intermediate stand. Material was redistributed with modification in pass profile so that proper working is carried out in the rail profile. Cobble analysis from different passes and its comparison with roll pass design give exact situation of the pass filing. Based on these findings modification in pass profile was carried to get proper toe radius

The following is to explain the present invention concretely using the preferred examples shown in the drawings:

The issue of non-formation of toe radius was analyzed with Rail Mill and Roll Turning Shop. Toe radius of R-52 and R-60 rails was compared with respect to pass formation of leader and finishing pass in mating rolls. It was observed that as section at flange is thin and therefore it gets colder fast. This cold stock shears roll pass groove and subsequently sharp edges are observed in the flange.

Different roll passes profiles for rolling R-60 rails from pass no. 3 of intermediate stand to finishing stands (Fig. 2 to Fig. 6) were studied and reduction ratio at different location of rail profile was worked out. The third pass in rolling of rail called the web cutting pass or knifing pass. From pass 3 of the intermediate stand onward formation of rail from the previous hat passes begins. In conventional rolling of rails, the top flange is closed and the bottom flange is open to facilitate the working and sizing of the flange dimensions. Also top head is open and the bottom head is of close type so as to facilitate the working in the head portion of rail. Subsequently metal volume at different locations of rail profile was studied and analyzed.

The intermediate time schedule between the passes is as under:
Time taken from Furnace discharge to Roughing Stand: 25-40Sec
Time taken from Roughing to 1st Intermediate Stand: 20Sec
Time taken from 1st Intermediate to 2nd Intermediate Stand: 30Sec
Time taken from 2nd Intermediate to finishing stand: 20Sec

Based on analysis material was redistributed by modification in rail pass profile. Following actions were undertaken:
1. Toe radius of was compared with respect to pass formation of leader and finishing pass in mating rolls
2. Cobble analysis from pass # 3, 4, 5 & 6 with existing roll pass design and following points were observed:
• Length of close flange of pass 6 which is the bottom flange is short by 2 mm from design size.
• Due to shortness of close flange length of pass 6 open flange length of pass 7 (finishing pass) is not as per design and moreover the flange is not working on toes resulting in to a Sharp corner at the bottom of the toe.
• It was also found that the open flange length of pass 5 is also short by 2 to 3mm which is not feeling properly the close flange of pass 6.
• While checking the cobble of pass 4 it revealed that the close flange is running under fill by 3 mm from design size, which is not allowing making proper open flange length of pass 5.
• While checking the cobble of pass 3 of 1st inter stand which is being fed to pass 4 of second inter stand, the open flange length was found as per design but the toe thickness is 3 to 3.5mm more than the design which is restricting the flow of steel in to pass 4 close flange due to chocking.
3. Reduction ratio for different passes worked out.
Based on analysis the new Template was generated and rolls were turned and changes were incorporated in the roll pass design as follows:.
a. Toe radius in leader pass and finishing pass was increased from 5mm to 7-9mm.
b. Toe thickness of pass 4 close flange was altered as mentioned below
i. Top part from 20 .7 mm to 21.0-22.0 mm
ii. Bottom part from 16.3 mm to 17-19 mm
c. Throat radius of pass # 4 and pass # 5 by increasing it by 2-3 mm

Highlight of the Inventive steps:
1. Working out the modified pass profile for rail rolling in conventional mill.
2. Proper distribution of material during rail rolling.
3. Improvement in overall profile of R60 rails.
4. Formation of proper toe radius in R60 rails.
5. Reduction in stress concentration in rails.
6. Modification in roll pass to get proper toe radius has resulted in improvement in acceptance level of rails by 1.3%. In financial terms this results in bene3fit of around Rs.800 lakhs.
7. This modification was necessitated on account of strict specification of Indian Railways and formation of proper toe radius as specified in Indian Railways Specification is essential.
8. Toe radius formation starts taking place from pass no. 3 of intermediate stand. In subsequent passes working by rolls are done to form toe radius.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.