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Significance of Accurate Level 2 Force Prediction
Accurate prediction of roll separating force is
vital to the good shape
and properties of rolled flat products,
and to the mill yield and
productivity. See
Improvement on Level 2 Model
Force Prediction for the
work Metal Data can do for
you.
Force Error Causes
Center Buckle and Edge Wave
Roll
deflection, stand deflection and roll
flattening are all affected
by the roll separating force, so
force prediction error
causes the errors for all
those deformations. If the
force is estimated too much
lower than the real value,
the predicted roll
deflection is too much lower
than the anticipated one. An
equal draft has been planned
based on the predicted roll
deflection; but the actual
deflection is higher than
the planned one, so the
draft in the width center
region is actually smaller
than that in the edges and
consequently, an edge wave
could occur. On the other
hand, if the force is
predicted too much higher
than the true value, the
draft in the width middle
will be higher compared with
that in the strip/plate
edges. This would lead to
Center Buckle.
Force
Error Leads to Temperature
Error Related
Problems
In many
cases, temperature from pass to pass is calculated based on the measured force
(measured flow stress), so force prediction error also causes temperature
error. The temperature
error would further cause
numerous problems (see
Significance of Accurate
Temperature Prediction).
1%
Force Error Reduction = 1 Million US
Dollar Per Year !!!
Besides the shape and dimension problems, an inaccurate Level 2 force model may lead to poor mechanical properties of the rolled product. For a product order, the required properties (often, mechanical properties) of steel are specified. The steel plant usually designates a certain steel grade plus certain rolling procedures to produce the required steel. If the automation system is sufficiently accurate, the finish product should satisfy all the requirements. However, the automation system may have significant error, so the roll separating force, temperature and draft, etc. may be different from what are expected, and as
a result, the product quality may be below what is planed. To assure the satisfaction of the property requirements, the steel producer has to plan
a higher quality of the product than that is required by the customer. This
increases unnecessary expense for the steel plant. In addition, some plants conduct mill trials to select the proper rolling procedure for a new product; the cost of these trials is significant. A force error reduction by 10% for the Level 2 system
may have
an economic value
of over 10 million dollars per year for most plants, as estimated in the Table
1.
Table 1: Annual benefit for 10% force error reduction
[1]
|
Item |
Value |
Annual Total (US$) |
Annual Saving (US$) |
Assumption |
|
Investment Saving 1) 2) |
15% |
20,000,000 |
3,000,000 |
Equipment life span: 40 years |
|
Slab grade saving 3) |
1% |
400,000,000 |
4,000,000 |
50% of sales price |
|
Energy Saving 4) |
3% |
40,000,000 |
1,200,000 |
5% of sales price |
|
Yield increase |
1% |
800,000,000 |
8,000,000 |
1% yield increase |
|
Mill test saving for new products 5) |
45% |
4,000,000 |
1,800,000 |
0.5% of sales price |
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Total |
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18,000,000 |
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Notes
- Data in the table are based on a mill with US$800 million equipment
investment and US$800 million annual sales.
- The saving is based on the increase of equipment utilization of 10%, equivalent to 15% of investment.
- When significant force error occurs, higher grade of steel has to be scheduled for an order to guarantee the rolled steel properties.
Accurate Level 2 model reduces or eliminates this expense.
- The increase of energy consumption due to higher grade scheduled.
- Some plants conduct mill trial-and-errors for scheduling of new products.
Reference
[1] B. Li & J. Nauman, Metal Data LLC: MS&T
2008, October 5-9, 2008,
Pittsburgh, PA, USA.
Proceedings pp 1066-1077.
Metal Data Resources on
Level 2 Model Improvement
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