Title of Invention

A DIFFERENTIAL COOLING METHOD FOR REDUCING CAMBER IN HOT ROLLED ANGLES IN ROLLING MILLS

Abstract

Improved cooling method for cooling of hot rolled angles in particular, to differential cooling method for reducing camber in hot rolled angles in rolling mills and to a system for carrying out such method of differential cooling. The method of differential cooling involving three stages cooling of angles comprising first stage water cooling of the hotter apex of the said angle to thereby minimise the temperature gradient between the apex and the flange followed by second stage air cooling and finally third stage rapid water spray cooling of the apex such that temperature gradient between apex and flange is reduced during cooling from plastic to elastic transformation of the angle and thereby reduce camber formation without affecting the usual roiling process. The improved method of cooling reduces camber in hot rolled angles in rolling mills by way of an online differential cooling method for hot rolled angles which would effectively minimise temperature difference between apex and flange at the transformation from plastic to elastic region.

Full Text

FIELD OF THE INVENTION This invention relates generally to cooling method in particular, to differential cooling method for reducing camber in hot rolled angles in rolling mills and to a system for carrying out such method of differential cooling. BACKGROUND OF THE INVENTION In roiling mills during angle rolling, there exists a temperature gradient between apex and flange of angle as it leaves the finishing rolling stand It is mainly due to initial thermal condition of input bar before rolling, difference in percentage reduction in the finishing stand, difference in thickness of angle section and rolling speed Angles cool in the air as it travels from finishing stand to cooling bed at the speed of 6-9 m/sec During air cooling, the temperature gradient between thicker apex and thinner flange increases The large temperature gradient during transformation temperature from plastic to elastic region, leads to generation of residual thermal stresses It causes camber in the angle Cambered angles gets, often, stuck in the cooling bed transfer table Sometimes, manual intervention is needed such as gas cutting etc it is very difficult to feed cambered angles into the inline straightening machine All these causes stoppage of rolling and delays and ultimately results in loss of production The existing method for controlling camber in angle on run out table involved single stage cooling and cooling has done after approximately 10 m from the finishing stand To provide some water spray from the bottom on the run out table, holes were provided in the run out table The methodology of single stage cooling was found to be not effective The water pressure and quantity was inadequate Spray orientation of water spray was improper Such cooling method could not effectively minimise temperature difference between apex and flange at the transformation temperature from plastic to elastic region hence camber always remained beyond undesirable limit OBJECT OF THE INVENTION The basic object of the present invention is to provide an improved method of cooling whereby it would be possible to reduce camber in hot rolled angles in rolling mills. 2 Another object of the present invention is to provide an online differential cooling method for hot rolled angles which would effectively minimise temperature difference between apex and flange at the transformation from plastic to elastic region and hence camber formation could be avoided/reduced Yet further object of the present invention is directed to provide a system wherein it would be possible to achieve the differential cooling in accordance with the present invention Thus according to one aspect of the present invention there is provided a differential cooling method for reducing camber in hot rolled angles in rolling mills comprising three stages cooling of angles comprising first stage water cooling of the hotter apex of the said angle to thereby minimise the temperature gradient between the apex and the flange followed by second stage air cooling and finally third stage rapid water spray cooling of the apex such that temperature gradient between apex and flange is reduced during cooling from plastic to elastic transformation of the angle and thereby reduce camber formation without affecting the usual rolling process The above disclosed online differential cooling method of the invention is adapted to cool hotter apex immediately after the finishing stand such that temperature gradient between apex and flange is minimum while cooling from plastic to elastic regime without hampering the existing rolling process In particular, the present online differential cooling method consists of three stages cooling of angle First stage cooling is an intense water spray cooling of angle apex immediately after the finishing rolling stand Immediately after the finishing stand, before first stage, apex has higher temperature than the flanges. At the end of first stage, temperature of apex surface is lower than the flanges of angle In the second stage air cooling is done where temperature of angle gets equalised with rise in apex temperature and slightly fell in flange temperature In the third stage, rapid water spray cooling of apex is done with high flow rate of water In both the stages of water cooling, hotter apex is cooled from the bottom on the run out table After the third stage cooling, angle travels to the cooling bed During this 3 period final temperature equalisation of the angle takes place and the temperature gradient between apex and flange reduce as angle cools from plastic to elastic transformation temperature of steel The lower temperature gradients during transformation reduces camber on the cooling bed In accordance with yet further aspect of the present invention there is provided a system for use in differential cooling of hot rolled angles in rolling mills comprising means for three stages cooling of angles comprising a first stage water cooling means for water cooling of the hotter apex of the said angle to thereby minimise the temperature gradient between the apex and the flange ; means for second stage air cooling of said angle and means for third stage rapid water spray cooling of the apex such that temperature gradient between apex and flange is reduced during cooling from plastic to elastic transformation of the angle and thereby reduce camber formation without affecting the usual rolling process BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to the non-limiting exemplary embodiments as per the accompanying figures wherein Fig 1 shows the three stages of differential cooling of angle in accordance with the present invention, Fig 2 is a schematic layout of differential cooling method of the invention, Fig 3 is a detailed view of run out table used in the method of the invention, Fig 4 is a detailed view of cooling header used in the method of the invention, Fig 5 is a detailed view of conical guide (1) used in the method of the invention, Fig 6 is a detailed view of conical guide(2) and (3) used in the method DESCRIPTION OF THE INVENTION Reference is first invited to accompanying Fig. 1 which illustrates the three stages of the differential cooling of the hot rolled angles in accordance with the present invention As clearly illustrated in said figure, 1st stage water cooling comprise of cooling the apex of angle (1) by spraying of water (2) through nozzle (3) Thus 4 such first stage of cooling is an Intense water spray cooling of angle apex immediately after the finishing rolling stand. The 2nd stage of cooling involves air cooling whereby the temperature of apex and flange of the angle get equalised with nse in apex temperature and slight fall in flange temperature In the 3rd stage of cooling, rapid water spray cooling of apex is done with high flow rate of water, in both the stages of water cooling of the apex, the hotter apex is cooled from the bottom on the run out table Reference is now invited to Fig 2 which is a schematic layout of the differential cooling method involving the above three stage cooling of the present invention As shown in the Fig 2, after the hot rolled angles are out of the finishing rolling stand (1) the same is guided by the conical guide (9) to the 1st stage cooling unit In the first stage intense water cooling of apex immediately after the finishing rolling stand is effected The hot apex having thickness is selectively cooled by water spray from under the run out table through header pipes (6) supplied through pipeline (8) In second stage air cooling (3) is effected to thereby provide for conditions for substantial equalisation of the apex and flange temperature of the angle It also reduces temperature gradient between apex and flange Finally, by means of conical guide (10) the angles are directed on the table in the third stage cooling Under this third stage water cooling (4), it is a rapid cooling of apex with larger quantity of water and for longer duration. Hence all spray headers are well directed at the apex Since water flow rate is high in this stage, water discharge from the run out table should be efficient so that water does not accumulate on the table, otherwise angle flange will get quenched on the run out table which will increase the temperature gradient between apex and flange of the angle causing aggravation of camber to the angle As further illustrated in the figure, the method also consists of pump (5), cooling header of first stage (6) and cooling header of third stage (7) with connecting pipeline. The water is forced through the first and third stage headers at rate of 100 m3/hr and 80-90m3/hr respectively In accordance with a further aspect of the invention, the run out tables of first stage and third stage cooling have been modified for quick discharge of water 5 from the run out tables Run out table of first stage cooling have been modified with rectangular slots of water discharge in the base plate These slots are used also for cooling from the bottom The third stage cooling (Fig 3) run out tables have different bottom design to handle large flow rate of water The run out table base preferably has stationery rollers of diameter in the range of 50 to 60 mm and length 600 to 650 mm A gap of 12 to 16 mm preferably 14 mm is kept between two rollers In the 2nd stage cooling two run out tables are used of length 3000 to 3200 mm preferably 3150 mm and 1750 to1800 mm preferably 1800 mm Rollers are locked from the one side on the run out table side plate Roller type bottom surface does not allow any water accumulation in the run out table The slots and gap between two rollers are utilised for water spray through nozzles. Nozzles on the cooling headers are decided on the basts of flow rate required in first and third stages of cooling The cooling headers are installed at the bottom of the run out table For correctly guiding the angles on the run out table, conical guides are installed before entry to the water cooling zone and after the cooling zone. To prevent accumulation of water on the run out table, slots at the base plate of first stage cooling and roller base in the third stage with gap between roller have been made The type of cooling header used are shown in Fig (4) To properly align the moving angles, speed 6-9 m/sec, at covered position of cooling water spray from the bottom, conical guides have been installed at the entry and exist of cooling segments The respective drawings of conical guide (9) and conical guides (10) are given in Fig (5) and Fig (6) respectively Positioning the angle above cooling header is very important since any misalignment of cooling spray aggravates intensity of camber. In accordance with further preferred aspect to check water splashing, covers are put over the run out table. It also works as a cover to water spray when there is no angle on the run out table Tests were carried out to ascertain the attainment of the objectives of the invention to reduce generation of camber in cooling bed and delay due to camber For the purpose, the camber and delay due to camber in use of differential cooling vis-a-vis control cooling (without differential cooling) was studied Under differential cooling selective cooling of apex was done in first stage and third stage of water cooling In the first stage apex cooling was done in such a way that 1/4 length of the flange is cooled from the bottom In the third 6 stages cooling, % length of the flange is cooled from the bottom The results obtained following differential cooling of the angles vis-a-vis conventional cooling (without three stages differential cooling) are detailed hereunder, Camber before straightening a) Camber in 90 mm angle before straightening without differential cooling • Height-170-380 mm b) Camber in 90 mm angle before straightening with differential cooling - Height 130-150 mm It would be clearly evident from the above that the differential cooling achieves the desired objective of reducing the camber DELAY The arrange delay, during 90 mm angle rolling, due to camber was 2.0 hours/day The delay due to camber has been eliminated after installation of differential cooling method as clearly represented in the results obtained as detailed hereunder. Type of cooling Camber on cooling bed (CB) Average delay per day due to camber Conventional cooling 170-380 mm 2 hours Differential cooling 130-150 mm Nil It is thus possibly by way of the differential cooling of the invention to reduce camber generation in angles to reduce delay and consequently increase in average rollers rate from 426 T/shift to 499 T/shift 7 We Claim A differential cooling method for reducing camber in hot rolled angles in rolling mills comprising three stages cooling of angles comprising first stage water cooling of the hotter apex of the said angle to thereby minimise the temperature gradient between the apex and the flange followed by second stage air cooling and finally third stage rapid water spray (2) cooling of the apex to subsequently effect final temperature equalisation of apex and flange by air cooling maintaining the temperature gradient between the apex and flange minimum near plastic to elastic transformation temperature of the angle 620-650°C to thereby reduce camber formation without affecting the usual rolling process 2 A method as claimed in claim 1 wherein said first stage cooling comprise an intense water spray cooling of angle apex immediately after the finishing rolling stand when the apex has higher temperature than the flanges such that at the end of first stage, temperature of apex surface is lower than the flanges of angle 3 A method as claimed in anyone of claims 1 or 2 wherein in said second stage air cooling the temperature of angle is substantially equalised with rise in apex temperature and slight fall in flange temperature 4 A method as claimed in anyone of claims 1 to 3 wherein in said third stage, rapid water spray cooling of apex is carried out with high flow rate of water 5 A method as claimed in anyone of claims 1 to 4 wherein in both the stages of water cooling, hotter apex is cooled from the bottom on the run out table 6 A method as claimed in anyone of claims 1 to 5 wherein after the third stage cooling, angle travels to the cooling bed and during this period final temperature equalisation of the angle takes place and the temperature gradient between apex and flange reduce as angle cools from plastic to elastic transformation temperature of steel 2 8 7 A method as claimed in anyone of claims 1 to 6 wherein the water is forced through the first and third stage headers at rate of 90 to100 m3/hr and 80-90m3/hr respectively 8 A system for use in differential cooling of hot rolled angles in rolling mills comprising means for three stages cooling of angles comprising a first stage water cooling means for water cooling of the hotter apex of the said angle to thereby minimise the temperature gradient between the apex and the flange ; P means for second stage air cooling of said angle and means for third stage rapid water spray cooling of the apex such that temperature gradient between apex and flange is reduced during cooling from plastic to elastic transformation of the angle and thereby reduce camber formation without affecting the usual rolling process. 9 A system as claimed in claim 8 wherein said means for first stage cooling comprise of means for spraying of water through nozzle said means for second stage cooling comprise means for supply of air for cooling and means for said third stage of cooling comprise means for rapid water spray cooling of apex 10 A system as claimed in anyone of claims 8 or 9 wherein both said first and third stage cooling means comprise means for water cooling of the apex, the hotter apex from the bottom of the run out table means 11 A system as claimed in anyone of claims 8 to 10 comprising guide means such that after the hot rolled angles are out of the finishing rolling stand the same are guided by conical guide means to the means for first stage cooling unit 12 A system as claimed in anyone of claims 8 to 11 comprising conical guide means whereby the cooled angles from said second stage cooling means are fed to said third stage cooling means 9 9 13 A system as claimed in anyone of claims 8 to 12 wherein said first and second stage cooling means comprise spray headers adapted to direct at the apex 14 A system as claimed in anyone of claims 8 to 13 wherein said run out tables are adapted to favour fast water discharge such that water does not accumulate on the table 15 A system as claimed in anyone of claims 8 to 14 comprising pump, cooling header of first stage and cooling header of third stage with connecting pipeline 16. A system as claimed in anyone of claims 8 to 15 wherein said run out tables of first stage and third stage cooling are adapted for quick discharge of water from the run out tables said run out table of first stage cooling provided with rectangular slots of water discharge in the base plate which are also used for cooling from the bottom with said the third stage cooling run out tables provided with different bottom design to handle large flow rate of water 17 A system as claimed in anyone of claims 8 to 16 wherein the run out table base preferably has stationery roller of diameter in the range of 50 to 60 mm and length 600 to 650 mm , a gap of 12 to 16 mm preferably 14 mm between two rollers, in the 2nd stage cooling two run out tables are used of length 3000 to 3200 mm preferably 3150 mm and 1750 to 1800 mm preferably 1800 mm, rollers being locked from the one side on the run out table side plate, said roller type bottom surface adapted not to allow any water accumulation in the run out table, the slots and gap between two rollers being utilised for water spray through nozzles 18 A system as claimed in anyone of claims 8 to17 wherein the nozzles on the cooling headers are selected based on the flow rate required in first and third stages of cooling and said cooling headers are installed at the bottom of the run out table 17 10 19 A system as claimed in anyone of claims 8 to 18 comprising covers means over the run out table 20 A differential cooling method for reducing camber in hot rolled angles in rolling mills and a system for use in such method substantially as herein described and illustrate with reference to the accompanying drawings Dated this 16th day of March 2001 Improved cooling method for cooling of hot rolled angles in particular, to differential cooling method for reducing camber in hot rolled angles in rolling mills and to a system for carrying out such method of differential cooling. The method of differential cooling involving three stages cooling of angles comprising first stage water cooling of the hotter apex of the said angle to thereby minimise the temperature gradient between the apex and the flange followed by second stage air cooling and finally third stage rapid water spray cooling of the apex such that temperature gradient between apex and flange is reduced during cooling from plastic to elastic transformation of the angle and thereby reduce camber formation without affecting the usual roiling process. The improved method of cooling reduces camber in hot rolled angles in rolling mills by way of an online differential cooling method for hot rolled angles which would effectively minimise temperature difference between apex and flange at the transformation from plastic to elastic region.

Documents:

00158-cal-2001-abstract.pdf

00158-cal-2001-claims.pdf

00158-cal-2001-correspondence.pdf

00158-cal-2001-description(complete).pdf

00158-cal-2001-drawings.pdf

00158-cal-2001-form-1.pdf

00158-cal-2001-form-18.pdf

00158-cal-2001-form-2.pdf

00158-cal-2001-form-3.pdf

00158-cal-2001-pa.pdf

158-cal-2001-granted-abstract.pdf

158-cal-2001-granted-claims.pdf

158-cal-2001-granted-correspondence.pdf

158-cal-2001-granted-description (complete).pdf

158-cal-2001-granted-drawings.pdf

158-cal-2001-granted-examination report.pdf

158-cal-2001-granted-form 1.pdf

158-cal-2001-granted-form 18.pdf

158-cal-2001-granted-form 2.pdf

158-cal-2001-granted-form 3.pdf

158-cal-2001-granted-letter patent.pdf

158-cal-2001-granted-pa.pdf

158-cal-2001-granted-reply to examination report.pdf

158-cal-2001-granted-specification.pdf