103

515

500

Tilt 90

2

Barrel

76

100

523

320

3

Barrel

66

104

523

310

4

Rd32/40

78

76

20

425

315

5

Barrel

52

92

523

300

Tilt 90

6

Rd 32- 36

62

62

6

405

330

7

Barrel

38

75

436

380

8

Rd 32-36

50

48

12

398

420

9

Barrel

33

59

-

395

450

Tilt 90

10

Rd-36

43

40

4

385

370

11

Rd-32

31

46

9

360

420

12

TMT-32

32

32

3

375

540

Note: Where H and В are the size of metal in the respective passes t is the roll gap Dc is the collar dia. of the roll, Nr is the motor rpm

Rd 36 mm Pass for Stand-10 for TMT Rolling

Fig. 6.23 Rd 36 mm Pass for Stand-10 for TMT Rolling.

9 ROLLING DEFECTS AND ITS SOLUTION 9.1 Ovality

Ovality

Fig. 6.24 Ovality.

The sides of pass are not completely filled up. This is due to less metal from previous stand, when height of metal is correct. If the height is more then the top roll of finishing stand should be pressed. Metal from previous stand should be increased if metal height is conect. If, there is one side fin and at other side oval, then entry box of finishing stand should be shifted towards the oval side.

Diagonal Difference

Diagonal Difference

Fig. 6.25 Diagonal Difference.

Right or left diagonal may be more than the allowable tolerance. Reasons for this cause are the improper setting of the entry guide or rolls. The guide is to be shifted against the opposite direction of the higher shoulder, if it is not adjusted by the shifting of guide, then rolls may be adjusted.

Fin

Fin

Fig. 6.26 Fin.

Under-Filled

Under-filled

Fig. 6.27 Under-filled.

Under filling is normally caused by

Fish-tail

Fish-tail at the end of bar causes jamming inside the delivery rolling tackles or in the cooling pipe of TMT rolling system. Causes are:

Lap

Avoid overfilling of the pre-finishing oval pass and finishing round pass

Worn out Mark

Worn out mark

Fig. 6.28 Worn out mark.

It indicates when diagonals are more than height and width of the pass. Then pass should be immediately changed.

Pipe Formation in TMT

Different Types of Pipe

Fig. 6.29 Different Types of Pipe.

Pipe formation is mainly due to faulty steel making practices and can be reduced either by proper cutting of crop ends of bloom/billet at the shear of the blooming or billet mill or by strict inspection of billets at Billet yard, to avoid charging of pipy billets.

Pass Mark

It is mainly due to the use of worn out pass of pre-finishing or finishing stand or due to wrong setting of pass or guide. If, it is not eliminated by setting, then pass is to be immediately changed.

For good mill setting, the roller and its concerned staff should know about the special features of rolling technologies such as:

Mill Setting of Rounds/TMTS

Twisting

1. If rolls are cross.

Twisting depends upon the type of pass

(a) Box passes with height more than the width-If the top roll is axially displaced to the right, the bar shall twist clockwise and the roll is to be taken to the left i.e., to the opposite to the direction of the twist. It is because lateral deformation is more than the normal deformation.

Fig. 6.30.

(.b) Box passes with height less than the width- If the top roll is axially displaced to the right, the bar will twist anticlockwise and the top roll is to be taken to the left i.e., to the direction of the twist. It is because lateral deformation is less than the normal deformation.

Fig. 6.31.

 
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