CLIAMS:We Claim:
1. A wire rod mill system adapted for selective generation of any of 7 mm or 8 mm wire rod without requiring stand changing comprising:
modified A strand involving a combination of finishing group strand and an intermediate group strand ahead of finishing group strand;
said A-strand comprising of roll pass standardized such as to be common for both 7mm & 8 mm rolling to suit a unified rolling scheme for keeping the same pass whereby so that stand changing could be avoided during the section changeover from 8mm to 7 mm and vice versa;

range of roller diameters maintained in said each stand to ensure desired metal size in each pass with commensurate speed/rpm at each stand to produce desired 7mm or 8 mm plain rod with desired profile and dimensional tolerance.

2. A wire rod mill system as claimed in claim 1 wherein said intermediate strand comprises four roll stands (16-19) and finishing group comprises another four (20-23) roll stands and wherein the intermediate stand and the finishing group stand have standardized pass common for both 7mm and 8mm rolling.
3. A wire rod mill system as claimed in anyone of claims 1 or 2 wherein the pass of the said intermediate group rollers enable generation of both 7mm and 8mm rods with only finishing group stands requiring change.
4. A wire rod mill system as claimed in anyone of claims 1 to 3 comprising speed control means for selecting different speed for 2nd intermediate group rollers and the finsihsing group rolers.
5. A wire rod mill system as claimed in anyone of claims 1 to 4 wherein stand 16,17,18,19,21 and 32 have said modified passes and pass of stand 22 suitable for 8mm rod is maintained also for stand 20.
6. A wire rod mill system as claimed in anyone of claims 1 to 5 adapted for adjusting the roll gap in said second intermediate group stand (16,17,18 and 19) for roling 7mm and 8 mm rods and for finishing group for rolling 8 and 7 mm all the starnds (20,21,22 and 23) are only changeable which together provide for maintaining desired diameter.

7. A wire rod mill system as claimed in anyone of claims 1 to 6 comprising means for adjusting the roll gaps for desired metal sixe for 7mm and 8 mm rod generation.

8. A wire rod mill system as claimed in anyone of claims 1 to 7 including the following strand specifications:

Stand No. Pass Width (mm) Rolling Schedule for Ø 8 mm Rolling Schedule for Ø 7 mm –
`A’ Strand at 5.74 m/s
Pass width Metal size
16 27 9.8x20 27 8.8x22.5
17 13 14.5x12.5 13 14.0x12.5
18 18.5 8.8x18 18.5 6.1x18.5
19 10.6 12.3x10.8 10.6 10.8x9.5
20 16.5 7.1x15 13.5 6.0x13
21 9.2 9.8x8.9 9.2 8.6x8.0
22 13.5 6.1 x 13 13.5 5.1x11
23 8.4 8.1 x 8.1 7.4 7.1x6.9

9. A wire rod mill system as claimed in anyone of claims 1 to 8 wherein the minimum and maximum roll diameters for generating 8mm and 7mm rods comprise:
8 mm 7mm
StandNo. Diameter Min. Diameter Max. StandNo. Diameter Min. Diameter Max.
16 295 320 16 295 320
17 295 320 17 295 320
18 295 320 18 295 320
19 295 320 19 295 320
20 245 270 20 265 280
21 245 270 21 265 280
22 245 270 22 270 280
23 245 270 23 270 280

10.A wire rod mill system as claimed in anyone of claims 1 to 9 comprising roll cooling arrangement based control of stand speed from involving preferably a banana type cooling pipe with nozzles for desired results.

11.A wire rod mill system as claimed in anyone of claims 1 to 10 comprising roller bearing to allow maximum speed to go up to 2500 rpm.

12. A method for producing Ø7mm plain rod in A-strand of wire rod milladapted for Ø 8mm plain/TMT rolling using the system as claimed in claims 1 to 11, comprising the steps of

using modified A strand involving a combination of finishing group strand and an intermediate group strand ahead of finishing group strand;
involving said A-strand with roll pass standardized such as to be common for both 7mm & 8 mm rolling to suit a unified rolling scheme for keeping the same pass whereby so that stand changing could be avoided during the section changeover from 8mm to 7 mm and vice versa;

maintaining range of roller diameters in said each stand to ensure desired metal size in each pass with commensurate speed/rpm at each stand to produce desired 7mm or 8 mm plain rod with desired profile and dimensional tolerance.

13. A method as claimed in claim 12 comprising:

(i) implementing the roll pass design by roll turning to achieve desired rolling schedule;

(ii) selecting the diameter of rolls in each stand vis a vis the speed/rpm to ensure achieving desired metal size by rolling in each stand;

(iii) decreasing mill speed from 5.95 m/s to 5.85 m/s, thereby ensuring that final speed at 23A remained below limiting levels;

(iv) implementing a unified rollingscheme for keeping the same pass design so that stand changing is avoided during the section changeover;

(v) implementingregular monitoring of metal size, proper cobble analysis and introducing guides with close tolerances to achieve proper rolled section within tolerance.

14. A method as claimed in anyone of claims13 or 14 wherein said roll design comprising modifying stand 16,17, 18, 19,21& 23 passes and utilizing Pass of stand 22 in stand 20.

15. A method as claimed in anyone of claims 13 to 14 wherein speed/RPM of roller based on diameter in stands comprising
Stand no. 16:for dia 327 rpm is 429 … to dia 295 rpm is 470; Stand no. 17:for dia 327 rpm is 554 … to dia 295 rpm is 614; Stand no. 18:for dia 327 rpm is 684 … todia 295 rpm is 758; Stand no. 19:for dia 327 rpm is 854 … to dia 295 rpm is 947; Stand no. 20:for dia 280 rpm is 1253 to for dia 261 rpm is 1344;
Stand no. 21:fordia 280 rpm is 1592 to for dia 261 rpm is 1708;
Stand no. 22: for dia 280 rpm is 1832 to for dia 261 rpm is 1965;
Stand no. 23: for dia 280 rpm is 2210 to for dia 261 rpm is 2371.
16. A method as claimed in anyone of claims 13to 15 wherein said rolling schedule for generating 7mm and 8mm rods comprised

Stand No. Pass Width (mm) Rolling Schedule for Ø 8 mm Rolling Schedule for Ø 7 mm –
`A’ Strand at 5.74 m/s
Pass width Metal size
16 27 9.8x20 27 8.8x22.5
17 13 14.5x12.5 13 14.0x12.5
18 18.5 8.8x18 18.5 6.1x18.5
19 10.6 12.3x10.8 10.6 10.8x9.5
20 16.5 7.1x15 13.5 6.0x13
21 9.2 9.8x8.9 9.2 8.6x8.0
22 13.5 6.1 x 13 13.5 5.1x11
23 8.4 8.1 x 8.1 7.4 7.1x6.9

Dated this the 10th day of July, 2015
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

,TagSPECI:FIELD OF THE INVENTION
The present invention relates to a system and method for producing 7mm diameter plain rod through intermediate group II and finishing rolling stand number 16-23 of wire rod mill. More particularly, the present invention is directed to a system for producing 7mm plain rod through A-strand comprising stand number 16-23 wherein roll pass design was standardized such that it was common for both 7mm & 8 mm rolling. Thus, mill stoppage due to section changeover was reduced from 8 hours to 3 hours and both 8mm plain/TMT and 7mm plain rods are rolled in the same strand avoiding stand changeover, by introducing/adjusting selective stand speeds, roll diameter, roll gaps and related parameters for respective wire rod section with enhanced productivity and quality.

BACKGROUND OF THE INVENTION

Operation of Wire Rod Mill in applicants’ Bhilai Steel Plant involves continuous planning & consultation, setting the Technological Parameters and put utmost efforts to fulfill the production targets coupled with optimizing the technological & quality parameters while carrying out rolling of wire rods of different sections in A,B,C & D strands of Wire Rod Mill. Keeping close monitoring of the Operational activities that encompasses production planning in co-ordination with CMO, M&BP , PPC and other units. Fulfillment of the monthly production plan of WRM , keeping the Operationaldelays within norms& developing A-strand for rolling TMT 7mm was a challenging job. It is only because of innovative idea , the applicant could succeed in overcoming the teething problems during the stabilization stage of rolling TMT - 7mm from A-strand & balancing it with modernized lines of B,C & D strands.

Evolution of idea of Rolling 7 mm plain from `A’ strand was originated by market demand trend projection by the Central Marketing Organisation of the applicant. Based on the market demand and also in view of the capacity of applicant’s competitors to produce 5.5mm & 7 mm wire rods, it was suggested to explore the possibility of production of these sections so that a positive impact in terms of quantity as well as marketability may be ensured.

Wire drawing units are the major customers of wire rods. Every extra mm in the diameter consumes contributed additionally tothe costof drawing tothe tune of Rs. 230/T. In view of acute power shortage and the added cost it was a pressing demand from the customers for thinner section of wire rods so that it will consume less power as well as time.

‘A’ strand of Wire Rod Mill was designed to roll wire rods of section 8 mm & 10 mm plain and 8 mm TMT bar.

The main constraint for the mill to roll out 7 mm from `A’ Strand was that of speed. After revamping of `C’ and `D’ Strand of Wire Rod Mill the speed of Stand No.15 is restricted to min. 5.88m/sec. And the maximum rpm of 23 A strand will be attained at 2140 rpm. For that rpm, only 8mm and 10 mm plain and ribbed bar section can be rolled. Subsequently, TMT rolling has been started through in house modification. Coiler speed is also under restriction. To increase productivity in the mill, stand no 15 speed is increased from 5.88 m/sec to 5.95m/sec . With this speed of Stand No. 15, to roll 7 mm from`A’ strand was not possible. In fact during C&D strand modernization, the equipment & technology supplier of the Mill’s `A’ Strand had ruled out any possibility of rolling out 7 mm wire rods from `A’ Strand of the mill.

Thus it was a challenging task before the applicant to provide system and method for producing 8mm and 7mm wire rods in A-strand to market demand as well as reduce stand change over time for section change over from 8mm to 7mm and vice versa.

It was realized that to roll 7 mm on ‘A’ Strand, Stand No 16 to 23 pass modification has to be carried out. If pass modifications is not done then in that case whenever section change over from 8mm to 7 mm or vice versa is to be done, all 8 stands (16-23) will have to be changed. It will take not less than 8 hours of mill stoppage in stand changing and mill setting. Stand no 23 speed has to be increased up to 2500 rpm at minimum dia of 245. Coiler speed should also be increased proportionally.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to provide a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of wire rod mill(WRM) with minimized stand change over and set up time while section change over from 8mm to 7mm or vice versa is undertaken.

A further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRMby introducingstandardized roll pass design for 16 -23 stands such that it was common for both 7mm & 8 mm rolling.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein mill stoppage due to section changeover was reduced from 8 hours to 3 hours.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein a unified rolling scheme has been developed for keeping the same pass design so that Stand change changing could be avoided during the section changeover from 8mm to 7 mm and vice versa.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM whereinspeeds of individual stands were corrected according to the modified metal sizes.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein speed of 15 was reduced with roll cooling arrangement and stand 23 of strand A is increased with provision of roller bearing to reduce bearing heating at high speed to suit rolling of 7mm wire rod.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein consistency in obtaining proper rolled section within tolerance is achieved by regular monitoring of metal size, proper cobble analysis and implementing guides with close tolerances.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein with pass modification which is common for both i.e. 7mm & 8 mm rolling, negative tolerance could be achieved while rolling 8 mm TMT rolling which was customer demand for a long time favouring reduction of weight per meter in 8mm TMT rolling.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein overall reduction in speed resulted into lesser coil height which in turn resulted in better handling of coil at the hook conveyor.

A still further object of the present invention is directed to a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of WRM wherein product profile shape is improved due to better filling of passes.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide a wire rod mill system adapted for selective generation of any of 7 mm or 8 mm wire rod without requiring stand changing comprising:

modified A-strand involving a combination of finishing group strand and an intermediate group strand ahead of finishing group strand;

said A-strand comprising of roll pass standardized such as to be common for both 7mm & 8 mm rolling to suit a unified rolling scheme for keeping the same pass whereby so that stand changing could be avoided during the section changeover from 8mm to 7 mm and vice versa;

range of roller diameters maintained in said each stand to ensure desired metal size in each pass with commensurate speed/rpm at each stand to produce desired 7mm or 8 mm plain rod with desired profile and dimensional tolerance.

A further aspect of the present invention is directed to a wire rod mill system wherein said intermediate strand comprises four roll stands (16-19) and finishing group comprises another four (20-23) roll stands and wherein the intermediate stand and the finishing group stand have standardized pass common for both 7mm and 8mm rolling.

A still further aspect of the present invention is directed to a wire rod mill system wherein the pass of the said intermediate group rollers enable generation of both 7mm and 8mm rods with only finishing group stands requiring change.

A still further aspect of the present invention is directed to a wire rod mill system comprising speed control means for selecting different speed for 2nd intermediate group rollers and the finishing group rollers.

A still further aspect of the present invention is directed to a wire rod mill system wherein stand 16,17,18,19,21 and 32 have said modified passes and pass of stand 22 suitable for 8mm rod is maintained also for stand 20.

A still further aspect of the present invention is directed to a wire rod mill system adapted for adjusting the roll gap in said second intermediate group stand (16,17,18 and 19) for rolling 7mm and 8 mm rods and for finishing group for rolling 8 and 7 mm all the strands (20,21,22 and 23) are only changeable which together provide for maintaining desired diameter.

Another aspect of the present invention is directed to a wire rod mill system comprising means for adjusting the roll gaps for desired metal sixe for 7mm and 8 mm rod generation.

Yet another aspect of the present invention is directed to a wire rod mill system including the following strand specifications:

Stand No. Pass Width (mm) Rolling Schedule for Ø 8 mm Rolling Schedule for Ø 7 mm –
`A’ Strand at 5.74 m/s
Pass width Metal size
16 27 9.8x20 27 8.8x22.5
17 13 14.5x12.5 13 14.0x12.5
18 18.5 8.8x18 18.5 6.1x18.5
19 10.6 12.3x10.8 10.6 10.8x9.5
20 16.5 7.1x15 13.5 6.0x13
21 9.2 9.8x8.9 9.2 8.6x8.0
22 13.5 6.1 x 13 13.5 5.1x11
23 8.4 8.1 x 8.1 7.4 7.1x6.9

A further aspect of the present invention is directed to a wire rod mill system wherein the minimum and maximum roll diameters for generating 8mm and 7mm rods comprise:
8 mm 7mm
StandNo. Diameter Min. Diameter Max. StandNo. Diameter Min. Diameter Max.
16 295 320 16 295 320
17 295 320 17 295 320
18 295 320 18 295 320
19 295 320 19 295 320
20 245 270 20 265 280
21 245 270 21 265 280
22 245 270 22 270 280
23 245 270 23 270 280

A still further aspect of the present invention is directed to a wire rod mill system comprising roll cooling arrangement based control of stand speed from involving preferably a banana type cooling pipe with nozzles for desired results.

Said wire rod mill system comprisesroller bearing to allow maximum speed to go up to 2500 rpm.

A still further aspect of the present invention is directed to a method for producing Ø7mm plain rod in A-strand of wire rod mill adapted for Ø 8mm plain/TMT rolling using the system comprising the steps of

using modified A strand involving a combination of finishing group strand and an intermediate group strand ahead of finishing group strand;
involving said A-strand with roll pass standardized such as to be common for both 7mm & 8 mm rolling to suit a unified rolling scheme for keeping the same pass whereby so that stand changing could be avoided during the section changeover from 8mm to 7 mm and vice versa;

maintaining range of roller diameters in said each stand to ensure desired metal size in each pass with commensurate speed/rpm at each stand to produce desired 7mm or 8 mm plain rod with desired profile and dimensional tolerance.

Yet another aspect of the present invention is directed toa method comprising:

(i) implementing the roll pass design by roll turning to achieve desired rolling schedule;
(ii) selecting the diameter of rolls in each stand vis a vis the speed/rpm to ensure achieving desired metal size by rolling in each stand;
(iii) decreasing mill speed from 5.95 m/s to 5.85 m/s, thereby ensuring that final speed at 23A remained below limiting levels;
(iv) implementing a unified rollingscheme for keeping the same pass design so that stand changing is avoided during the section changeover;
(v) implementingregular monitoring of metal size, proper cobble analysis and introducing guides with close tolerances to achieve proper rolled section within tolerance.
A further aspect of the present invention is directed to a method wherein said roll design comprising modifying stand 16,17, 18, 19,21& 23 passes and utilizing Pass of stand 22 in stand 20.
A still further aspect of the present invention is directed to a method wherein speed/RPM of roller based on diameter in stands comprising
Stand no. 16:for dia 327 rpm is 429 …to dia 295 rpm is 470; Stand no. 17:for dia 327 rpm is 554 … to dia 295 rpm is 614; Stand no. 18:for dia 327 rpm is 684 … todia 295 rpm is 758; Stand no. 19:for dia 327 rpm is 854 … todia 295 rpm is 947; Stand no. 20:for dia 280 rpm is 1253 to for dia 261 rpm is 1344;
Stand no. 21:fordia 280rpm is 1592 to for dia 261 rpm is 1708;
Stand no. 22: for dia 280rpm is 1832 tofor dia261 rpm is 1965;
Stand no. 23: for dia 280 rpm is 2210 to for dia 261 rpm is 2371;

A still further aspect of the present invention is directed to a method wherein said rolling schedule for generating 7mm and 8mm rods comprised
Stand No. Pass Width (mm) Rolling Schedule for Ø 8 mm Rolling Schedule for Ø 7 mm –
`A’ Strand at 5.74 m/s
Pass width Metal size
16 27 9.8x20 27 8.8x22.5
17 13 14.5x12.5 13 14.0x12.5
18 18.5 8.8x18 18.5 6.1x18.5
19 10.6 12.3x10.8 10.6 10.8x9.5
20 16.5 7.1x15 13.5 6.0x13
21 9.2 9.8x8.9 9.2 8.6x8.0
22 13.5 6.1 x 13 13.5 5.1x11
23 8.4 8.1 x 8.1 7.4 7.1x6.9

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPNAYING DRAWINGS

Figure 1: shows the schematic layout of the wire rod mill showing the location of A, B, C & D strands and the respective rolling stands wherein 7mm wire rod rolling according to the present invention is implemented in A strand with roll pass modification in 16-23 stands.

Figure 2a-h: shows the schematic drawings of roll pass design modification and standardization implemented in the rolling stands 16-23 which is common for both i.e. 7mm & 8 mm rolling to enable an unified scheme of rolling to avoid stand change over during section change over with reduced section changeover time.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to provide a system and method for producing 7mm plain wire rods by rolling of 7 mm plain wire rod on `A’ Strand of wire rod mill(WRM) avoiding stand change over and minimized section change over time and set up time while section change over from 8mm to 7mm or vice versa is undertaken. Importantly, an unified rolling scheme is implemented with standardized roll pass design for stands numbered 16-23,which is common for both 7mm & 8 mm rolling. The stand speeds, roller diameter, roll gap and the related parameters are selected to achieve desired metal size in each pass and the final dimension of rolled product with desired dimensional tolerance, including specially negative tolerance on rolling 8mm which is much sought for by the end users.

`A’ strand of Wire Rod Mill was designed to roll wire rods of section 8 mm & 10 mm plain and 8 mm TMT bar. The main constraint for the mill to roll out 7 mm from `A’ Strand was that of speed.

Accompanying Figure 1 shows the schematic layout of the wire rod mill showing the location of A, B, C & D strands and the respective rolling stands wherein 7mm wire rod rolling according to the present invention is implemented in A strand with roll pass modification in 16-23 stands.

The objective was to undertake rolling of 7mm plain rod in the same ‘A’ strand with minimum change over time and avoiding stand change over whenever there was requirement of section change over from 8mmplain/8mmTMT to 7mm plain rod and vice versa. The product quality and section dimensional tolerance within allowable limits to satisfy users’ requirement was also a critical requirement.

To implement these objectives following limitations were required to be overcome based on trials:

1. The maximum rpm of 23 A strand will be attained at 2140 rpm. For that rpm, only 8mm and 10 mm plain and ribbed bar section can be rolled. Coiler speed is also under restriction.

2. To increase productivity in the mill stand no 15 speed was increased to 5.95m/sec.

3. With this speed of Stand No. 15, to roll 7 mm from`A’ strand was not possible.
4. To roll 7 mm on ‘A’ Strand, Stand No 16 to 23 pass modification was to be carried out.

a) If pass modificationsis not done then in that case whenever section change over from 8mm to 7 mm or vice versa is to be done, all 8 stands (16-23) will have to be changed. It will take not less than 8 hours of mill stoppage in stand changing and mill setting.
b) Trial was to be taken to roll 7 mm with minimum disturbance in pass design by modifying the few passes .
c) Procurement of new rolls were needed for “A” strand.
d) Stand no 23 speed has to be increased up to 2500 rpm at minimum dia of 245.
e) Coiler speed should also be increased proportionally.

Thus trials were undertaken by setting various parameters to understand the specific requirement of pass modification and standardization for the stand nos. 16-23. The result of the trials are presented in the following Tables 1-3:

Table 1:

Rolling Schedule for Ø 7 mm - `A' Strand at 5.88m/set (359 rpm) -1st set of trials
Stand No. Pass Width (mm) Metal Size Collar Gap (mm) Area (metal) Ø Working Dia rpm (motor) Gear Ratio
16 27 9.3x24.5 2.8 185.26 320 315.93 434.5 1
17 15 14.5x11.9 2.5 176.5 320 308.2 466.8 1
18 20.00 6.7x16.5 1.7 101.19 320 316.8 792.2 1
19 10.6 10.8x10.6 3.2 92.8 320 314.25 870.86 1
20 13.5 6.1x13.2 3.1 68.00 270 266.84 1399.62 1
21 9.2 8.8x9.2 1.5 63.78 270 264.56 1505 1
22 13.5 5.1x11.5 2.1 47.46 270 268.87 1990.1 1
23 7.4 7.1x6.9 1.5 40.28 270 265.67 2372.9 1

Table 2:

Rolling Schedule for Ø 7 mm - `A' Strand at 5.88m/set (359 rpm) –2nd set of trials
Stand No. Pass Width (mm) Metal Size Collar Gap (mm) Area (metal) Ø Working Dia rpm (motor) Gear Ratio
16 27 9.5X22 2.8 185.26 320 315.93 438 1
17 15 14.5X12.2 2.5 176.5 320 308.2 566 1
18 20.00 7.5X18.5 1.7 101.19 320 316.8 666 1
19 10.6 11.1X11.3 3.2 92.8 320 314.25 858 1
20 13.5 6.7X13 1.2 68.00 270 266.84 1279 1
21 9.2 9.1X9 1.2 63.78 270 264.56 1599 1
22 13.5 5.1X11.8 1.2 47.46 270 268.87 1869 1
23 7.4 7.25X8.4 1.2 40.28 270 265.67 2300 1

Table 3:

Rolling Schedule for Ø 7 mm - A Strand at 5.88m/set (359 rpm) – 3rd set of trials
Stand No. Pass Width (mm) Metal Size Area (metal) Ø Working Dia rpm (motor) Gear Ratio
16 27 9x22.5 185.26 320 315.93 450 1
17 15 13.5x12.5 176.5 320 308.2 570 1
18 20.00 7.5X18.5 101.19 320 316.8 711 1
19 10.6 10.7x11.3 92.8 320 314.25 903 1
20 13.5 6.1x13.5 68.00 270 266.84 1320 1
21 9.2 8.6x10.1 63.78 270 264.56 1630 1
22 13.5 5.1X12.5 47.46 270 268.87 1880 1
23 7.4 7.25x7.5 40.28 270 265.67 2280 1

Based on the above trials, exact requirement of pass modification was decided and Pass design for stands 16-23 was made. The new standardized pass designs for stand number 16 to 23 are illustrated in the Figures 2(a) to 2(h).

Reduced metal size through modification of pass as presented in following table 4, resulted in lowering of final speed of stand 23 of A strand and coilers.

Table 4:
STAND
No. 16 17 18 19 20 21 22 23
OLD F8mm
10.0x20.0 14.5x14.0 8.0x18.0 12.0x11.5 7.1x15.6 10.2x10.2 6.1x13.0 8.2x8.0
NEW F7mm
9.3x21.5 13.7x13.0 6.3x19.5 10.9x11.2 6.0x13.5 9.0x8.8 5.1x11.5 7.1x6.97
NEW F8mm
9.8x21.5 14.5x13.5 7.6x18.5 11.2x10.5 7.0x15.2 9.8x7.9 6.1x12.6 8.0x8.0

After ascertaining the roll pass designs for stands 16-23, a new rolling scheme is implemented through steps as follows:
- New pass design of stand No. 17,18, 19, 21 & 23 done with the help of Roll Pass Design Bureau.
- New pass design is implemented and completed with the help of Roll Turning shop.Roll turning is dressing of Rolls according to the required pass design to obtain the desired section. It is also carried out when the pass is worn out.
- Stand No. 22 pass design has been used in Stand No. 20 also.
- To overcome the restriction in the maximum speed of 23A to below 2300 rpm which practically ruled out the possibility of rolling 7 mm,new speed chart preparedwith reference to new metal size and pass design. It was further modified by adjusting mill tension through visual inspection. In place of ball-bearing, roller bearing was provided in 23A stand which allowed maximum speed to go up to 2500 rpm. Further, mill speed was decreased from 5.95 m/s to 5.85 m/s, thereby ensuring that final speed at 23A remained below limiting levels.
- For Second Intermediate Group consisting of Stand No. 16, 17, 18 & 19 for rolling 8 mm Plain & 8 TMT and 7 mm Plain profile requires different type of rolling scheme and it requires three stand changing during section changeover from 8mm to 7 mm and vice versa.
- A unified rollingscheme has been developed for keeping the same pass design so that Stand changing could be avoided during the section changeover. The sectionchangeover time now has been reducedfrom 6 Hrs. to 3 Hrs.
- To achieve Consistency in obtaining proper rolled section within tolerance control of section profile/size and its successful implementation obtained through regular monitoring of metal size, proper cobble analysis and guides with close tolerances.
- As the reduced speed creates more contact of metal with pass leading to increased pass wear out , to increase pass life of rolls new cooling arrangement introduced for rolls. A banana type cooling pipe with nozzles introduced for better results than other conventional cooling arrangements.

The rolling schedule implemented in practice in regular and standardized rolling of 7mm section is presented in following Table 5A & B:
Table 5(A):
7mm Regular rolling
Stand No. Pass Collar
Gap
16 existing ok
17 modified 13.5 x 12
18 modified to be increased 6x18.5
19 modified ok 10.8x 9

20 22 pass ok 6 x13
21 modified to be increased 8.6 x 8
22 modified 5.1 x11
23 modified to be increased 7.1 x 6.9

Table 5(B)

Stand No. Rolling Schedule for Ø 7 mm - `A’ Strand at 5.74 m/s
Pass Width (mm) Metal size
16 27 8.8x22.5
17 13 14.0x12.5
18 18.5 6.1x18.5
19 10.6 10.8x9.5
20 13.5 6.0x13
21 9.2 8.6x8.0
22 13.5 5.1x11
23 7.4 7.1x6.9

The minimum and maximum diameter of rolls utilized in the modified pass implemented in stands 16-23 and the respective speed chart corresponding to different range of roll diameters are presented in the accompanying Table 6-10.

Table 6:

8 mm 7mm
StandNo. Diameter Min.(mm) Diameter Max.(mm) StandNo. Diameter Min.(mm) Diameter Max.(mm)
16 295 320 16 295 320
17 295 320 17 295 320
18 295 320 18 295 320
19 295 320 19 295 320
20 245 270 20 265 280
21 245 270 21 265 280
22 245 270 22 270 280
23 245 270 23 270 280

Table 7:
SPEED CHART FOR INTERMEDIATE GROUP II GROUP VOLTAGE 78 V
DIA 16 17 18 19
327 429 554 652 840
326 430 556 654 843
325 432 557 656 845
324 433 559 658 848
323 434 561 660 850
322 436 563 662 853
321 437 564 664 856
320 438 566 666 858
319 440 568 668 861
318 441 570 670 864
317 443 571 673 866
316 444 573 675 869
315 445 575 677 872
314 447 577 679 875
313 448 579 681 878
312 450 581 683 880
311 451 583 686 883
310 453 584 688 886
309 454 586 690 889
308 455 588 692 892
307 457 590 694 895
306 458 592 697 898
305 460 594 699 901
304 461 596 701 904
303 463 598 704 907
302 465 600 706 910
301 466 602 708 913
300 468 604 711 916
299 469 606 713 919
298 471 608 715 922
297 472 610 718 925
296 474 612 720 928
295 476 614 723 931

Table 8:

7 MM PLAIN ROLLING IN A STRAND
- SPEED CHART
DIA SPEED ( MOTOR RPM)
20 21 22 23
275 1256 1570 1835 2258
274 1261 1576 1842 2266

273 1265 1582 1848 2275
272 1270 1587 1855 2283
271 1275 1593 1862 2291
270 1279 1599 1869 2300
269 1284 1605 1876 2308
268 1289 1611 1883 2317
267 1294 1617 1890 2326
266 1298 1623 1897 2334
265 1303 1629 1904 2343
264 1308 1635 1911 2352
263 1313 1642 1919 2361
262 1318 1648 1926 2370
261 1323 1654 1933 2379
260 1328 1661 1941 2388
259 1334 1667 1948 2397
258 1339 1673 1956 2407
257 1344 1680 1964 2416
256 1349 1687 1971 2426
255 1355 1693 1979 2435
254 1360 1700 1987 2445
253 1365 1707 1995 2454
252 1371 1713 2002 2464
251 1376 1720 2010 2474
COILER SPEED - 1060 RPM

Table 9:
SPEED CHART FOR INTERMEDIATE GROUP II GROUP VOLTAGE 78 V
DIA 16 17 18 19
327 429 554 694 884
326 430 556 696 887
325 432 557 698 889
324 433 559 700 892
323 434 561 703 895
322 436 563 705 898
321 437 564 707 901
320 438 566 709 903
319 440 568 711 906
318 441 570 714 909
317 443 571 716 912
316 444 573 718 915
315 445 575 720 918
314 447 577 723 921
313 448 579 725 924
312 450 581 727 927
311 451 583 730 929
310 453 584 732 932
309 454 586 734 935
308 455 588 737 939
307 457 590 739 942
306 458 592 742 945
305 460 594 744 948
304 461 596 747 951
303 463 598 749 954
302 465 600 751 957
301 466 602 754 960
300 468 604 756 964
299 469 606 759 967
298 471 608 762 970
297 472 610 764 973
296 474 612 767 977
295 476 614 769 980

Table 10:
7 MM PLAIN ROLLING IN A STRAND - SPEED CHART
DIA SPEED ( MOTOR RPM)
20 21 22 23
280 1253 1592 1852 2258
279 1257 1598 1859 2266
278 1262 1603 1865 2274
277 1267 1609 1872 2282
276 1271 1615 1879 2291
275 1276 1621 1886 2299
274 1280 1627 1893 2307
273 1285 1633 1899 2316
272 1290 1639 1906 2324
271 1295 1645 1914 2333
270 1299 1651 1921 2342
269 1304 1657 1928 2350
268 1309 1663 1935 2359
267 1314 1670 1942 2368
266 1319 1676 1949 2377
265 1324 1682 1957 2386
264 1329 1688 1964 2395
263 1334 1695 1972 2404
262 1339 1701 1979 2413
261 1344 1708 1987 2422
260 1349 1714 1994 2432
259 1355 1721 2002 2441
258 1360 1728 2010 2451
257 1365 1734 2018 2460
256 1370 1741 2026 2470
255 1376 1748 2034 2479
254 1381 1755 2042 2489
253 1387 1762 2050 2499
252 1392 1769 2058 2509
251 1398 1776 2066 2519
250 1403 1783 2074 2529
COILER SPEED 1060 RPM

The Salient features of the major modifications which are done to implement the unified rolling scheme for 8mm and 7mm rods from the A-strand are as follows:

• Stand 16,17, 18, 19,21& 23 passes were modified.
• Pass of stand 22 utilized in stand 20. Minimum dia of roll was restricted to 265mm for 7mm and after re-turning, lower dia rolls were used for 8mm TMT rolling so that roll is fully utilized.
• Reduced metal size through modification of pass resulted in lowering of final speed of stand 23A and coilers.
• According to the modified metal sizes, speeds of individual stands were corrected.
• Reduction of stand 15 speed from 5.95 to 5.85 m/sec. by improved roll cooling arrangement was done.
• The new pass design was standardized such that it was common for both 7mm & 8 mm rolling. Thus, mill stoppage due to section changeover was reduced from 8 hours to 3 hours.
• Bearing of 23A main motor was changed from ball bearing to roller bearing to reduce bearing heating at high speed.

By developing a new profile 7mm plain to cater market demands, performance of the mill increased by reducing cost of production, increasing value addition of the product by innovative approaches.

The new profile has been rolled out to facilitate wire drawing units to draw thinner wire rods with less power consumption and in lesser time. Wire drawing units are important customers of wire rods and by rolling out this new profile, the Plant has fulfilled a customer demand.

We Claim:
1. A wire rod mill system adapted for selective generation of any of 7 mm or 8 mm wire rod without requiring stand changing comprising:
modified A strand involving a combination of finishing group strand and an intermediate group strand ahead of finishing group strand;
said A-strand comprising of roll pass standardized such as to be common for both 7mm & 8 mm rolling to suit a unified rolling scheme for keeping the same pass whereby so that stand changing could be avoided during the section changeover from 8mm to 7 mm and vice versa;

range of roller diameters maintained in said each stand to ensure desired metal size in each pass with commensurate speed/rpm at each stand to produce desired 7mm or 8 mm plain rod with desired profile and dimensional tolerance.

2. A wire rod mill system as claimed in claim 1 wherein said intermediate strand comprises four roll stands (16-19) and finishing group comprises another four (20-23) roll stands and wherein the intermediate stand and the finishing group stand have standardized pass common for both 7mm and 8mm rolling.
3. A wire rod mill system as claimed in anyone of claims 1 or 2 wherein the pass of the said intermediate group rollers enable generation of both 7mm and 8mm rods with only finishing group stands requiring change.
4. A wire rod mill system as claimed in anyone of claims 1 to 3 comprising speed control means for selecting different speed for 2nd intermediate group rollers and the finsihsing group rolers.
5. A wire rod mill system as claimed in anyone of claims 1 to 4 wherein stand 16,17,18,19,21 and 32 have said modified passes and pass of stand 22 suitable for 8mm rod is maintained also for stand 20.
6. A wire rod mill system as claimed in anyone of claims 1 to 5 adapted for adjusting the roll gap in said second intermediate group stand (16,17,18 and 19) for roling 7mm and 8 mm rods and for finishing group for rolling 8 and 7 mm all the starnds (20,21,22 and 23) are only changeable which together provide for maintaining desired diameter.

7. A wire rod mill system as claimed in anyone of claims 1 to 6 comprising means for adjusting the roll gaps for desired metal sixe for 7mm and 8 mm rod generation.

8. A wire rod mill system as claimed in anyone of claims 1 to 7 including the following strand specifications:

Stand No. Pass Width (mm) Rolling Schedule for Ø 8 mm Rolling Schedule for Ø 7 mm –
`A’ Strand at 5.74 m/s
Pass width Metal size
16 27 9.8x20 27 8.8x22.5
17 13 14.5x12.5 13 14.0x12.5
18 18.5 8.8x18 18.5 6.1x18.5
19 10.6 12.3x10.8 10.6 10.8x9.5
20 16.5 7.1x15 13.5 6.0x13
21 9.2 9.8x8.9 9.2 8.6x8.0
22 13.5 6.1 x 13 13.5 5.1x11
23 8.4 8.1 x 8.1 7.4 7.1x6.9

9. A wire rod mill system as claimed in anyone of claims 1 to 8 wherein the minimum and maximum roll diameters for generating 8mm and 7mm rods comprise:
8 mm 7mm
StandNo. Diameter Min. Diameter Max. StandNo. Diameter Min. Diameter Max.
16 295 320 16 295 320
17 295 320 17 295 320
18 295 320 18 295 320
19 295 320 19 295 320
20 245 270 20 265 280
21 245 270 21 265 280
22 245 270 22 270 280
23 245 270 23 270 280

10.A wire rod mill system as claimed in anyone of claims 1 to 9 comprising roll cooling arrangement based control of stand speed from involving preferably a banana type cooling pipe with nozzles for desired results.

11.A wire rod mill system as claimed in anyone of claims 1 to 10 comprising roller bearing to allow maximum speed to go up to 2500 rpm.

12. A method for producing Ø7mm plain rod in A-strand of wire rod milladapted for Ø 8mm plain/TMT rolling using the system as claimed in claims 1 to 11, comprising the steps of

using modified A strand involving a combination of finishing group strand and an intermediate group strand ahead of finishing group strand;
involving said A-strand with roll pass standardized such as to be common for both 7mm & 8 mm rolling to suit a unified rolling scheme for keeping the same pass whereby so that stand changing could be avoided during the section changeover from 8mm to 7 mm and vice versa;

maintaining range of roller diameters in said each stand to ensure desired metal size in each pass with commensurate speed/rpm at each stand to produce desired 7mm or 8 mm plain rod with desired profile and dimensional tolerance.

13. A method as claimed in claim 12 comprising:

(i) implementing the roll pass design by roll turning to achieve desired rolling schedule;

(ii) selecting the diameter of rolls in each stand vis a vis the speed/rpm to ensure achieving desired metal size by rolling in each stand;

(iii) decreasing mill speed from 5.95 m/s to 5.85 m/s, thereby ensuring that final speed at 23A remained below limiting levels;

(iv) implementing a unified rollingscheme for keeping the same pass design so that stand changing is avoided during the section changeover;

(v) implementingregular monitoring of metal size, proper cobble analysis and introducing guides with close tolerances to achieve proper rolled section within tolerance.

14. A method as claimed in anyone of claims13 or 14 wherein said roll design comprising modifying stand 16,17, 18, 19,21& 23 passes and utilizing Pass of stand 22 in stand 20.

15. A method as claimed in anyone of claims 13 to 14 wherein speed/RPM of roller based on diameter in stands comprising
Stand no. 16:for dia 327 rpm is 429 … to dia 295 rpm is 470; Stand no. 17:for dia 327 rpm is 554 … to dia 295 rpm is 614; Stand no. 18:for dia 327 rpm is 684 … todia 295 rpm is 758; Stand no. 19:for dia 327 rpm is 854 … to dia 295 rpm is 947; Stand no. 20:for dia 280 rpm is 1253 to for dia 261 rpm is 1344;
Stand no. 21:fordia 280 rpm is 1592 to for dia 261 rpm is 1708;
Stand no. 22: for dia 280 rpm is 1832 to for dia 261 rpm is 1965;
Stand no. 23: for dia 280 rpm is 2210 to for dia 261 rpm is 2371.
16. A method as claimed in anyone of claims 13to 15 wherein said rolling schedule for generating 7mm and 8mm rods comprised

Stand No. Pass Width (mm) Rolling Schedule for Ø 8 mm Rolling Schedule for Ø 7 mm –
`A’ Strand at 5.74 m/s
Pass width Metal size
16 27 9.8x20 27 8.8x22.5
17 13 14.5x12.5 13 14.0x12.5
18 18.5 8.8x18 18.5 6.1x18.5
19 10.6 12.3x10.8 10.6 10.8x9.5
20 16.5 7.1x15 13.5 6.0x13
21 9.2 9.8x8.9 9.2 8.6x8.0
22 13.5 6.1 x 13 13.5 5.1x11
23 8.4 8.1 x 8.1 7.4 7.1x6.9

Dated this the 10th day of July, 2015
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: A WIRE ROD MILL SYSTEM ADAPTED FOR SELECTIVE GENERATION OF ANY OF 7 MM OR 8 MM WIRE ROD WITHOUT REQUIRING STAND CHANGING.

The present invention relates to a system and method for producing 7mm diameter plain rod in wire rod mill. More particularly, the present invention is directed to a system for producing 7mm plain rod through A-strand comprising stand number 16-23 wherein roll pass design was standardized such that it was common for both 7mm & 8 mm rolling. Thus, mill stoppage due to section changeover was reduced from 8 hours to 3 hours and both 8mm plain/TMT and 7mm plain rods are rolled in the same strand avoiding stand changeover, by introducing/adjusting selective stand speeds, roll diameter, roll gaps and related parameters for respective wire rod section with enhanced productivity and quality.
(Figure 1)