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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 Pass 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

Total

18,000,000

Notes

  1. Data in the table are based on a mill with US$800 million equipment investment and US$800 million annual sales.
  2. The saving is based on the increase of equipment utilization of 10%, equivalent to 15% of investment.
  3. 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.
  4. The increase of energy consumption due to higher grade scheduled.
  5. Some plants conduct mill trial-and-errors for scheduling of new products.

Reference

 [1]  B. Li & J. Nauman, Metal Pass LLC: MS&T 2008, October 5-9, 2008, Pittsburgh, PA, USA. Proceedings pp 1066-1077.
 

Metal Pass Resources on Level 2 Model Improvement


See the profile for the primary consultant Dr. Benjamin Li. You may also view our company and personnel profiles. Please contact us via email admin@metalpass.com or by phone (001) 503 516 9625 for top quality consulting services.

 

 
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