Resumo:
The challenge
The customer was planning to produce a 5" angle in a rolling mill designed to roll up to the 4" size. Initial studies indicated that this product required a 160mm billet and the replacement of a gearbox of the roughing train. The customer informed the need of a roll pass design using 150mm billet, which is the current size of the Melt Shop, besides not replacing the gearbox, which would represent an extra investment and demand a long implantation time.
The mill's staff reported not having historic of breaking this gearbox and no overload on the heavier products.
The project
An innovative pass design was developed by the author, using the W Method, which increases the spread of the first four passes, thus reaching the desired angle leg dimension.
The project of this angle is usually done with eight passes. This design was done with eleven passes in order to have low section reductions and consequently generating torque and power compatible with the mill characteristics.
As this method is not used in any other known mill, thus not having a reference of its technical feasibility, a FES (Finite Element Simulation) and a FEM (Finite Element Modeling) was done through the Research and Development Department(R & D) of the customer that demonstrated the project viability.
It was done calculations for spread, temperature loss, separating force, torque and power.
The rolling mill team provided end-of-life rolls to machine the grooves, guides and accessories were manufactured and four months after the beginning of the project, it was possible to successfully test the first six passes in June/2018.
The results
From July 3 tests were done with the three angle thicknesses (5/16"- 3/8" - 1/2"), producing 700 ton of good quality products without difficulty of set-up. The rolling mill team carried out this project at a very low cost and in a very short time.
The torque of the motors was between 40 and 60%, without overload of the equipment. The calculated roll efforts were compared with the real data showing the correction of the methodology.
The shears, cooling bed, straightening machine and stacker processed the new product without problems.
For the new rolls to be machined the pass design was revised, mainly for the 1/2” thickness, whose leg widths was close to the maximum of the tolerance, the grooves weren´t completely filled and with very low section reductions. For this size, were reduced two passes and created four specific grooves with smaller width in order to have a better control of the leg sizes.
Conclusion
This innovative project proved to be fully feasible, with low implementation costs, generating good quality products and without equipment overload.
