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Hard-to-design roll passes Completed with Roll Design Software Suites

(Extended Summary)


Bingji Li,Ph,D
 Metal Pass LLC, Pittsburgh, PA, USA.
Email: bli@metalpass.com,
Phone (China): 13400064848

Hard-to-design roll passes contain large number of constrains, so the design requires many trial-and-error attempts. One example for the constrains is in the pass design for the POSCO Specialty Steel Ltd, in which a new breakdown mill was to be added into an existing plant. The constrains include: (1) Single stand reversing mill, with limited number of grooves cut on the roll; (2) Big ingot (700mm square) and bloom (420mm x 530mm), to be rolled into round 270~320mm and square 200~300mm, but number of passes to be minimal due to temperature concern; (3) Smallest roll diameter (new/discard) required due to space and bearing restrictions, and so bite condition hard to meet; (4) Smallest barrel length required due to limited crane capacity; (5) Both round and square passes involved, so minimal number of grooves hard to achieve; (6) Hard steel to be rolled, with strength 30% higher than AISI 1080; (7) Some steel with 30% higher spread than average, and so the minimal number of passes hard to reach; (8) Crack to be avoided since some steel has low formability. In addition, number of passes in grooves should be balanced to achieve maximum roll life. Satisfied design was achieved with all conditions met, and corresponding roll force/torque checkup also passed.

Further design/development examples are such as former GST 19?Bar Mill, with 8-stand for 28 sizes from two sizes of billet. The first 4 stands are Diamond-Square and the last stands are tied Round-Oval sequence. Tension had to be used in some passes to achieve high reduction per pass.

Metal Pass Auto-Form and Free-Form roll pass design suites was used in the trial-and-error designs. The AutoForm suite allows any mill engineer to perform roll pass design by simply filling in mill operation parameters. No advanced knowledge on roll pass is required. The FreeForm suite gives roll pass designers full freedom in designing groove and pass parameters and specify spread behavior of metal. High-quality spread and forward slip models are provided as default. These powerful packages also incorporate tension correction for spread and forward slip into the metal deformation prediction. They can be used not only to design new passes, but also to study and improve the existing ones. Particular attention is paid to the special requirements in design of high-speed finish blocks.

The validity of the roll pass design programs mainly depends on the prediction accuracy of the rolling process models integrated into the programs. Each model considers influences of steel grade, speed, and temperature, etc. on metal deformation. Those models are developed based on large amount of testing results and field data the author collected in the past 20 years, including a 15-year testing results in a 4-stand continuous high-speed mill (up to 70m/s) from Germany, and a 5-year testing results and great number of field data from USA and other countries. Example of a single field data source in rolling block is the one from several months of onsite collection in former ASW No-Twist mill (Cleveland, USA).

Keywords: hard-to-design roll pass, roll pass software, stainless steel, interstand tension

More details, click here.

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