REGARDING THE ISSUE OF A STUDY OF THE PECULIARITIES OF DEFORMING A CONTINUOUSLY CAST BILLET
The difference in shape between the original continuously cast billet and the square one [the ‘rhomboidity’ effect] may result in: (a) great difficulties when rolling the billet in break-down stands; (b) the breakdown bar dumping in a pass; and (c) errors in the billet’s design parameters after it has passed through a set of roughing stands. This, in turn, causes unstable rolling and heavy wear-out of the finishing stand rolls. In addition, as the experience of the rolling of distinct rhomboidity continuously cast billets shows, the latter has the effect of fully opening the internal and external corner cracks formed during its casting . The above-mentioned problems take on special significance under the conditions of integrating a section mill and a CC [continuous-caster] into a single casting and rolling unit.
To find out the peculiarities of changing the continuously cast billet shape as well as of the billet’s stressed and deformed state when rolling the billet in break-down stands, full-scale research has been done:
In the first stage of the pilot research has been done on lead sample billets simulating rolling a continuously cast billet in a break-down stand of the Rolling Mill 500/370, with the modeling scale being 1:5. To carry out the experiment, a special set of rolls has been produced for the Laboratory Rolling Mill 100 (see Fig. 1).
Figure 1: Roll view of the Laboratory Rolling Mill
When planning the experiment a second-order incomposite design has been used for three factors (see Table 1). The following values have been taken as the factors:
- Δh/Bo, where Δh is the absolute reduction, Bo is the original billet width;
- à=Âî/Âê, where a is a jamming ratio;
- Êð= D2–D1, where Êð is a ‘rhomboidity’ ratio; D1 and D2 are the greater and the smaller billet diagonals, respectively.
Table 1: Levels and Factor Ranges
|
Factor |
Factor Range |
Level |
||
|
Upper |
Major |
Lower |
||
|
Symmetric Pass |
||||
|
Δh/Bo |
0.15 |
0.34 |
0.19 |
0.04 |
|
à=Âî/Âê |
3.0 |
6.8 |
3.8 |
0.8 |
|
Êð |
0.03 |
1.06 |
1.03 |
1.0 |
|
Asymmetric Pass |
||||
|
Δh/Bo |
0.1 |
0.23 |
0.13 |
0.03 |
|
à=Âî/Âê |
2.0 |
4.6 |
2.6 |
0.6 |
|
Êð |
0.03 |
1.06 |
1.03 |
1.0 |
After giving the sample billet the necessary shape and dimensions, a net with a 2mm-mesh was printed on its lateral and contact surfaces. While being rolled, the sample billets stopped at the rolls, which resulted in the unfinished sections. On the sample billets, the change in the position of the net’s knots was captured with a digital camera. The measurement of the coordinate grid was carried out under the AutoCAD program.