LOGICS OF ROLL PASS DESIGN FOR HOT ROLLING MILLS
Adelaide, December 2015
Foreword
An ultimate goal in engineering design is to apply scientific knowledge in order to enable the sustainable manufacture of a product. In manufacturing systems such as hot rolling mills we are concerned with fabricating so called long products. Whichever design method is used, its validation takes place over several campaigns of semi-industrial and full-scale-production rolling. This usually takes several months, and often more than a year, during which period a number of features of the chosen roll pass design (RPD) will be modified.
This handbook is laying out the logical steps recommended when undertaking an RPD project. These recommendations are based on many years of author’s industrial experience as an RPD specialist in several rolling mills worldwide. Moreover, this experience is enriched by academic studies and research, leading to a comprehension of significant aspects that are of crucial importance for developing a satisfactory roll pass design.
The major advantage of this publication is drawn from its internet based hyperlinks. This approach allows for using the contents by following the reader’s needs, rather than authors line of thoughts. While the core of this handbook follows the logics of the principal steps in RPD, the incorporated links allow to the user to get straightforward to the points of immediate interests.
This handbook is delivered in 27 modules, via the Internet. You can purchase Module 1 by contacting sead.spuzic@unisa.edu.au.
Dr Sead Spuzic Adelaide, 7th December 2016
Preamble
A rolled product has to be designed to conform to a specified quality level. While there are quite extensive treatises discussing the concept of quality available elsewhere, we shall focus on the interdependence of quality components such as “usability”, “producibility”, “reliability” and “sustainability”. These four aspects will be contemplated in the framework of the roll pass design, (RPD) an engineering discipline that is among the most critical factors in manufacturing by plastic forming in hot rolling mills.
This publication is concerned with plastic forming of metallics by rolling at the elevated temperatures. The products are defined by standard specifications such as ISO, or ASTM, or by means of industrial contracts. The RPD constraints are defined by the competitive levels of productivity and sustainability.
Underlying knowledge
Plastic forming of steel at elevated temperatures by passing it between rotating rolls ("rolling") is today among the most important industrial processes; this is partly because of a relatively immense volume of material worked by this technique of shaping. Of the world's steel production nearly 90% was worked by rolling.
Key tools in this process are the rolls themselves. Structural mill rolls have to withstand severe conditions of temperature and extremes of load. In addition to the obvious need for resistance to breakage, there is the continuing component of roll wear that is critical to the economics of fabrication, and the geometrical tolerances of the rolled products.
The tool development is an activity as old as the human history and is, indeed, of enormous economic importance. From the earliest days of metal working (some 500 years ago), rolls have been used as plain (flat) or as grooved (calibre) rolls. Apart from categorisation based on product type, mill configuration, roll materials, etc, this subdivision into two classes remains unchanged.
Grooved rolls were introduced to improve the control of plastic deformation of rolled steel and their great flexibility for a variety of products has been proven especially in plastic forming of sections. The main disadvantage of calibre rolling, supplementary to complications in production and maintenance, is the higher degradation of the key tools when compared with plain rolls. This is associated with the non-uniform wear experienced, and also with the increased amount of radial machining required to regenerate calibre geometry during subsequent roll redressing. In an attempt to maintain simplicity in roll geometry, the complexity of rolling mills has been increased over the years, encouraging the development and application of various types of the universal mill stands and other complex constructions.
The key to understanding roll pass design (RPD) is to be found in the deformation zone. Significant knowledge, concerning the deformation zone in plastic forming of rectangular sections between flat rolls, has been accumulated as a natural progression of the learning from simple to complex phenomena. On the other hand, the development of calibre rolls has continued rapidly, often however by means of empirical progression.
Variety of RPD methods and techniques rely on iterative calculations. These stages proceed along initial, intermediate and finishing pass sequences by predicting deformation of rolled solids. Analyses range starting from bulk cross-section via large analytical portions called “web” and “flange” to the minute constituents such as finite elements. Although the RPD analyses based on these approaches are nowadays empowered by data processing facilities, the resulting solutions are approximations only that often are too far from a satisfactory level of optimization. As a consequence, costly trials are required by virtue of semi-industrial rolling runs.
However, new avenues based on human-computer interaction and experience-based design, as well as on data mining (knowledge extraction) open the opportunities for improved predictions in, and orienting of, RPD projects and trials.
The interaction and experience-based design is associated with the aspects of system interfaces that define and present its behavior over time, with a focus on using knowledge validated by experience. In this approach the designers solve problems by relying on records accumulated in rolling mill RPD databases as well as on theoretically anticipating metal flow and resulting shapes as they might be in the newly considered processes. For this, however, there is a need to develop intelligent way of translating the existing RPD records into a structured database - a matrix that can be analysed to extract useful RPD knowledge.
