**2.3. RAS and RUB investigation**

558 Numerical Simulation – From Theory to Industry

ultimate broadening (RUB) were defined respectively as:

U is size of mold on the top entrance (mm); W is the measured width of the slab (mm); T is the ultimate width of the slab (in mm);

S is the width of the slab (in mm).

**2.2. Online measurements** 

at a preset frequency.

system is shown in Figure 1.

In order to measure slab broadening, the ratio of apparent shrinkage (RAS) and the ratio of

The value of the RAS, which denotes the degree of mold shrinkage, is positive when the top width exceeds the slab width. This index can be used to set the mold size. The value of the RUB, which denotes the degree of broadening, is positive when the slab width exceeds the

An online measurement system was designed to measure slab broadening at the exit of the caster.(FU JianXun et al. 2011(b)) The system comprises an optical lens, a digital camera, a data cable (IEEE 1394), and a computer. The system is controlled using the computer. The digital camera is used to take infrared images of the hot slab. Data is read from the camera

**Figure 1.** Online width measurement system for hot slabs.( FU JianXun et al. 2011(b))

Then, the graphics module creates images of the hot slab according to color aberration, and saves the images as files. The accuracy of the online system is 1 mm. A photograph of the

RAS U / W 1 100%, (1)

RUB S / T 1 100%, (2)

**2. Research method** 

**2.1. Index definition** 

where:

ultimate width.

Table 1 lists the RAS and RUB values obtained for five companies. The data in the right column is from a handbook (XIONG Yi-gang, 1994). The RAS values range from 0.47% to 2.16%, with most being higher than the handbook data. The linear shrinkage of carbon steel from the initial shell to the cooled slab is 2.5%. The RUB values range from 0.34% to 2.03%, which is the result that the linear shrinkage subtracting the RAS. In general, the width of a slab is smaller than the top width of a mold. Broadening may overcome shrinkage under certain operating conditions for some particular grades of steel.

The width of a cooled slab is larger than the ultimate width when broadening exists. To obtain a slab with the desired dimensions, the top and bottom widths of the mold must be reset. Therefore, the measured width (W) could replace the ultimate width (T). The RAS of a slab can thus be set by changing the values of the top and bottom widths of the mold. Then compare these values with the linear shrinkage of each steel grade, and it could consequently be found out whether the slab broadening exists and the approximate range of it could also be derived.


**Table 1.** RAS and RUB values at various manufactures (FU JianXun et al. 2010(a))

The data show that slab broadening is common in continuous casting. The slab width is the result of shrinkage and broadening. The linear shrinkage of a carbon steel is about 2.5%, which is slightly larger than the slab broadening.
